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Elena BASSOLI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - A methodology to reduce the computational effort in 3D-CFD simulations of plate-fin heat exchangers [Articolo su rivista]
Torri, Federico; Berni, Fabio; Giacalone, Mauro; Mantovani, Sara; Defanti, Silvio; Colombini, Giulia; Bassoli, Elena; Merulla, Andrea; Fontanesi, Stefano
abstract

The analysis of a plate-fin heat exchanger performance requires the evaluation of key parameters such as heat transfer and pressure drop. In this regard, computational Fluid Dynamics (CFD) can be proficiently adopted, at the design stage, to predict the performance of plate-fin heat exchangers. However, these last are often characterized by a complex geometry, such as in the case of plate exchangers with turbulators, leading to a huge computational effort, which often exceeds the available resources. In this study, a numerical methodology for the simulation of plate heat exchangers is proposed, to bypass the limits imposed by the computational cost. The methodology relies on the simulation of a minimal portion of the exchanger (two plates, one per fluid) characterized by periodic boundary conditions (that mimic the presence of several layers). The total heat exchanged is obtained simply multiplying the calculated heat transfer by the number of plate couples composing the device. Moreover, the two plates allow to calibrate porous media which are adopted to rebuild (in a simplified version) the two fluid circuits of the whole exchanger and obtain the overall pressure drop across the device for both the hot and cold fluids. The proposed approach is validated against experimental data of an oil cooler for automotive application, that is a plate-fin heat exchanger characterized by the presence of turbulators. The numerical outcomes are compared to the experiments in terms of pressure drop and heat transfer for a wide range of volumetric flow rates. Particular attention is devoted to the mesh sensitivity and the adopted computational grid minimizes the number of cells (and, thus, the computational cost), without compromising the accuracy. Moreover, the Reynolds-Stress-Transport turbulence model is accurately selected among the most diffused ones, in order to properly match the test bench data. The proposed methodology allows to reduce of nearly one order of magnitude the total number of cells required for the simulation of the heat exchanger performance. The heat transfer is predicted with high accuracy, i.e. error is always lower than 4%. As for the pressure loss, the deviation compared to the experiments increases up to nearly 15% (for one of the simulated conditions) but it is considered still acceptable.

2024 - Life cycle assessment of lattice structures: Balancing mass saving and productivity [Articolo su rivista]
Colombini, Giulia; Rosa, Roberto; Ferrari, Anna Maria; Defanti, Silvio; Bassoli, Elena
abstract

Additive Manufacturing has revolutionized manufacturing processes, offering design flexibility and advances in various applications. The integration of lattice structures into lightweight designs has attracted attention due to their ability to optimize properties such as stiffness, strength and energy absorption. This paper explores the trade-off between mass reduction and productivity while evaluating the environmental sustainability of lattice structures manufactured with Laser-based powder bed fusion for metals Using Life Cycle Assessment, two design variants for an automotive component are compared: a topologically optimized version with a solid bulk section, and a second design with lattice structures for additional weight reduction. Experimental measurements and a detailed analysis of the laser strategy were performed to build the Life Cycle Assessment inventory. The integration of lattice structures allowed a weight reduction of 6 %, but resulted in a significant decrease in productivity and a higher environmental impact. Surprisingly, lattice geometries, often perceived as green solutions, can have negative sustainability implications due to longer manufacturing times and impact of auxiliary equipment. Successful implementation of environmentally sustainable designs requires a balance between mass reduction and productivity while addressing potential environmental consequences.

2023 - On the Technological Feasibility of additively manufactured self-supporting AlSi10Mg lattice structures [Articolo su rivista]
Bassoli, Elena; Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Defanti, Silvio
abstract

The capability to design and manufacture metal lattice structures is today one of the most promising targets of Powder Bed Fusion technologies. Not only additively manufactured lattices offer great lightweighting possibilities, but they open the way to tailored and graded mechanical response. To best capitalize on this opportunity, research effort is first needed to assess the feasibility of reticular structures and to quantify the expected deviations from the nominal geometry, as a function of the cell topology and dimensions. Notwithstanding the inherent suitability of additive processes to complex shapes, this paper proposes a more exact definition of the technological boundaries for body-centred cubic lattices, showing to what extent specific dimensional ratios, as well as a self-supporting cell structure, can be favourable to minimize thedeviation from the nominal reticulum in terms of dimensions, density and presence of defects.

2022 - Additive manufacturing process and product obtainable through the process [Brevetto]
Galati, Manuela; Bassoli, Elena; Gatto, Andrea; Iuliano, Luca
abstract

An additive manufacturing process for manufacturing a solid body (2) designed to be delimited by a predefined outer surface includes selecting at least one volume portion (6) of the solid body (2), preparing a three-dimensional model of the solid body (2) by means of a computer, in which the selected volume portion (6) is modelled independently of the rest of the solid body (2), supplying the model in a suitable data interface format to the processing unit of an additive manufacturing machine, and operating the additive manufacturing machine for producing the solid body (2) according to the model, thus obtaining the predefined outer surface.

2022 - Effective Mechanical Properties of AlSi7Mg Additively Manufactured Cubic Lattice Structures [Articolo su rivista]
Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Bassoli, Elena; Defanti, Silvio
abstract

Lattice structures, whose manufacturing has been enabled by additive technologies, are gaining growing popularity in all the fields where lightweighting is imperative. Since the complexity of the lattice geometries stretches the technological boundaries even of additive processes, the manufactured structures can be significantly different from the nominal ones, in terms of expected dimensions but also of defects. Therefore, the successful use of lattices needs the combined optimization of their design, structural modeling, build orientation, and setup. The article reports the results of quasi-static compression tests performed on BCCxyz lattices manufactured in a AlSi7Mg alloy using additive manufacturing. The results are compared with numerical simulations using two different approaches. The findings show the influence of the relative density on stiffness, strength, and on the energy absorption properties of the lattice. The correlation with the technological feasibility points out credible improvements in the choice of a unit cell with fewer manufacturing issues, lower density, and possibly equal mechanical properties.

2021 - Design for additive manufacturing and for machining in the automotive field [Articolo su rivista]
Bassoli, E.; Defanti, S.; Tognoli, E.; Vincenzi, N.; Esposti, L. D.
abstract

High cost, unpredictable defects and out-of-tolerance rejections in final parts are preventing the complete deployment of Laser-based Powder Bed Fusion (LPBF) on an industrial scale. Repeatability, speed and right-first-time manufacturing require synergistic design approaches. In addition, post-build finishing operations of LPBF parts are the object of increasing attention to avoid the risk of bottlenecks in the machining step. An aluminum component for automotive application was redesigned through topology optimization and Design for Additive Manufacturing. Simulation of the build process allowed to choose the orientation and the support location for potential lowest deformation and residual stresses. Design for Finishing was adopted in order to facilitate the machining operations after additive construction. The optical dimensional check proved a good correspondence with the tolerances predicted by process simulation and confirmed part acceptability. A cost and time comparison versus CNC alone attested to the convenience of LPBF unless single parts had to be produced.

2021 - Repeatability of the fatigue performance of additively manufactured A357.0 under different thermal treatment conditions [Articolo su rivista]
Defanti, S.; Bassoli, E.
abstract

A357.0 parts were produced by laser-based powder bed fusion. An in-situ annealing strategy was applied by pre-heating the build platform, in order to relieve residual stresses and reduce anisotropic effects upon processing. The mean value and standard deviation for the fatigue strength at the given life time of 1 × 107 cycles were determined according to the staircase method, before and after T6 heat treatment. Samples parallel to the build platform and parallel to the growth direction were analysed separately and compared. The fatigue behaviour was substantially insensitive to post-processing heat treatment, since fracture initiation was governed by sub-surface lack-of-fusion defects that remained unchanged in the T6 conditions. The heat treatment caused an increase in porosity, yet without significant detriment to the fatigue resistance. The build orientation was not found to affect the average value of the fatigue strength, but it caused variations of the repeatability.

2021 - Synergy between topology optimization and additive manufacturing in the automotive field [Articolo su rivista]
Mantovani, Sara; Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Croce, Alessandro; Sola, Antonella; Bassoli, Elena
abstract

This article purposes on developing and on re-interpreting the numerical results of a topology optimization for a structural component built via additive manufacturing. A critical appraisal of the optimization results is presented by modeling the feasible component with a holistic approach that merges structural and manufacturing requirements. The procedure is expected to provide a design guideline for similar applications of practical relevance, toward an increase of the right-first-time parts that is required to bring additive manufacturing to its full competitiveness. Topology optimization of a steering upright for a Formula SAE racing car was performed by targeting weight minimization while complying with severe structural constraints, like global and local stiffness performance. Cornering, bumping and braking vehicle conditions were considered. The optimization constraints were evaluated via finite element analysis on a reference component, where the loading conditions were retrieved from telemetry data. The reference part was manufactured by computer numerical control machining from a solid aluminum block. Spurred by the interpretation of the topology optimization predictions, a new upright geometry was designed and validated by calculating its stress field and the possible occurrence of Euler buckling. The new upright was 9% lighter than the reference component. The new geometry was analyzed according to Design for Additive Manufacturing principles to choose the orientation on the build platform and the supports’ location and geometry. The part was successfully manufactured and proved consistent with the application.

2020 - Development of a reliable method for contamination detection in raw metal powders for additive manufacturing [Relazione in Atti di Convegno]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Denti, L.; Bondioli, F.; Barucca, G.
abstract

The evolution of additive manufacturing draws a growing attention to the quality of the raw materials involved. During Powder Bed Fusion (PBF), impurities can be trapped by the melting action of the laser or electron beam followed by a rapid solidification, resulting in discontinuities of the sintered products where failure is likely to start. To increase the quality of the sintered parts, it is mandatory to minimize the presence of impurities in the final product and therefore the risk of failure under service. This result can be achieved by improving the quality of the raw metal powders, which plays a key role in the overall process. In this study, intentionally contaminated AM metal powders were characterized by coupling scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques with a statistical treatment of the data, obtaining a reliable method for powder impurities detection.

2020 - Environmental sustainability of orthopedic devices produced with powder bed fusion [Articolo su rivista]
Cappucci, G. M.; Pini, M.; Neri, P.; Marassi, M.; Bassoli, E.; Ferrari, A. M.
abstract

Additive manufacturing consists in melting metallic powders to produce objects from 3D data, layer upon layer. Its industrial applications range from automotive, biomedical (e.g., prosthetic implants for dentistry and orthopedics), aeronautics and others. This study uses life cycle assessment to evaluate the possible improvement in environmental performance of laser-based powder bed fusion additive manufacturing systems on prosthetic device production. Environmental impacts due to manufacturing, use, and end of life of the designed solution were assessed. In addition, two powder production technologies, gas atomization (GA) and plasma atomization (PA), were compared in order to establish the most sustainable one. Production via traditional subtractive technologies and the additive manufacturing production were also compared. 3D building was found to have a significant environmental advantage compared to the traditional technology. The powder production process considerably influences on a damage point of view the additive manufacturing process; however, its impact can be mitigated if GA powders are employed.

2020 - Laser Powder Bed Fusion: Tailoring the microstructure of alloys for biomedical applications [Relazione in Atti di Convegno]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Denti, L.; Rutkowski, B.; Barucca, G.
abstract

Additive manufacturing (AM) is particularly attractive for biomedical applications, where complex geometries and a high degree of individualization are required. Laser powder bed fusion (LPBF) is an AM technology exploiting the action of a solid-state laser to locally melt a metal powder according to a computer aided design (CAD) model. In the present study, the EOS Cobalt Chrome SP2 (Co-Cr-Mo-W) and Ti64 (Ti6Al4V) powders were sintered by the system equipped with a Yb fiber laser. During LPBF, the Co-Cr-Mo-W metal powder undergoes total melting followed by rapid cooling, giving rise to athermal martensitic phase transformation from the high-temperature ? (fcc) phase to the low-temperature ? (hcp) phase. This produces an intricate network of thin ?-lamellae inside the ? phase matrix. After the firing cycle this structure is maintained, and a massive presence of coarse precipitates is also observed. Owing to the rapid cooling taking place during LPBF, in Ti6Al4V sintered samples only the acicular martensitic a' phase is present. The firing cycle induces the ß phase formation at the a plate boundaries and this microstructure leads to reduced values of strength, with respect to those of the as-sintered samples. The highlighted behaviors show that by tuning the post-production heat treatments it is possible to tailor the microstructure and the mechanical properties.

2019 - Cross-contamination quantification in powders for additive manufacturing: A study on Ti-6Al-4V and maraging steel [Articolo su rivista]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Defanti, S.; Barucca, G.
abstract

Metal additive manufacturing is now taking the lead over traditional manufacturing techniques in applications such as aerospace and biomedicine, which are characterized by low production volumes and high levels of customization. While fulfilling these requirements is the strength of metal additive manufacturing, respecting the tight tolerances typical of the mentioned applications is a harder task to accomplish. Powder bed fusion (PBF) is a class of additive manufacturing in which layers of metal powder are fused on top of each other by a high-energy beam (laser or electron beam) according to a computer-aided design (CAD) model. The quality of raw powders for PBF affects the mechanical properties of additively manufactured parts strongly, and therefore it is crucial to avoid the presence of any source of contamination, particularly cross-contamination. In this study, the identification and quantification of cross-contamination in powders of Ti-6Al-4V and maraging steel was performed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. Experimental results showed an overall good reliability of the developed method, opening the way for applications in machine learning environments.

2019 - Effect of Three Different Finishing Processes on the Surface Morphology and Fatigue Life of A357.0 Parts Produced by Laser‐Based Powder Bed Fusion [Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Sola, Antonella; Tognoli, Emanuele; Comin, Andrea; Porro, Juan Antonio; Cordovilla, Francisco; Angulo, Ignacio; Ocaña, Jose Luis
abstract

A357.0 parts are processed by laser-based powder bed fusion and surface finished via plastic media blasting, ceramic sand blasting, and laser shock processing. The morphological analysis proves that plastic media blasting causes the most effective peak removal, the most efficient decrease in valley depth, and the greatest reduction in surface roughness. All the surface finishing processes enhance the fatigue life, however ceramic sand blasting bring about the greatest increase in the value of σmax for an infinite fatigue life limit of 2106 cycles. The experimental results suggest therefore that the infinite fatigue life value is more sensitive to the residual stress state engendered by ceramic sand blasting than to the reduction in surface roughness. Breakthrough cracks start at the interface between crushed or modified surface particles and the underlying macro-surface. However, at a distance of a few hundred microns from the crack initiation point, the fracture surface morphology become cellular for all the specimens.

2019 - Enhancing the quality of metal powder feedstock for laser PBF through cross-contamination removal [Relazione in Atti di Convegno]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Denti, L.; Gheorghiu, B.; Barucca, G.
abstract

The presence of impurities in metal powder feedstock for laser powder bed fusion (L-PBF) can strongly affect the mechanical properties of the sintered part. As a matter of fact, the contamination particles trapped in the uniform metal matrix of the raw material, act as a discontinuity and, therefore, as a site for fatigue crack nucleation and growth, leading to a dramatic reduction of the expected fatigue life. While cross-contamination detection is a key parameter to establish the quality level of the metal powder feedstock, its removal is crucial to ensure that the sintered parts will fulfil the service requirements. In this study, metal powder feedstock for laser PBF were intentionally contaminated, submitted to a removal process based on their magnetic properties, through suitably developed equipment. The contaminated and processed powders were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques.

2019 - Experimental Study on Forces and Surface Roughness in Peripheral Grinding of an Aluminum Alloy [Articolo su rivista]
Atzeni, E.; Calignano, F.; Salmi, A.; Bassoli, E.
abstract

Peripheral grinding of the aluminum alloy EN AB-AlSi9Cu3(Fe) using a vitrified silicon carbide grinding wheel was investigated in this article. The effect of grinding parameters, namely, grinding speed, feed and depth of cut, and grinding condition, up-grinding or down-grinding, on resulting forces, grinding energy, and surface roughness were analyzed. A 22 × 32 full factorial design of experiments was performed. The ground surface morphology showed evidence of rubbing and plowing effects, and ductile material removal was the main mechanism. Within the analyzed process window, the minimum value of surface roughness was 0.28 μm. The experimental evaluation highlighted that forces and grinding energy are directly dependent on chip thickness, and this relationship was further explored as a function of depth of cut and feed per grain. Conversely, an inverse dependence was observed in the case of surface roughness. Empirical relationships for a reliable prediction of the grinding force and the specific grinding energy were defined. On the contrary, the surface roughness could not be fully modelled by the variation of the kinematic factors considered, and only a rough estimation was obtained. The results may be used for a more conscious setup of the grinding process on aluminum alloys, especially in the automotive field, where these are key materials.

2019 - Experimental approach to measure the restraining force in deep drawing by means of a versatile draw bead simulator [Articolo su rivista]
Bassoli, E.; Sola, A.; Denti, L.; Gatto, A.
abstract

The extreme personalization of the sports car industry requires the development of reliable and affordable techniques for the in-house set-up and control of processing conditions in deep drawing of body-in-white parts. In order to cope with this urgent need, a handy draw bead simulator (DBS) is proposed to measure the restraining force exerted on a sheet metal by the draw bead during deep drawing. The apparatus can be integrated into a common tensile testing machine and the male-female parts of the DBS are variable to account for different geometries of the draw bead and for different thicknesses of the sheet metal. For validation, the DBS is operated to reproduce the effect of a draw bead working on an Al6014-T4 strip according to assigned industrial conditions. Tensile tests repeated on the metal strip after drawing open the way to quantify work hardening effects. The new DBS can be applied to measure the restraining force and investigate the specific role of the draw bead in deep drawing, but it may also be used to verify the predictivity of computational models, thus supporting the development of simulations for feasibility studies and tool design optimization.

2019 - Fatigue life and microstructure of additive manufactured Ti6Al4V after different finishing processes [Articolo su rivista]
Denti, L.; Bassoli, E.; Gatto, A.; Santecchia, E.; Mengucci, P.
abstract

Finishing methods of additive manufactured metal parts are becoming a key driver of industrial viability, increasingly with additive processes being challenged in demanding end-product applications. The same scenario stresses the requirements as to fatigue life of parts built by Additive Manufacturing (AsM). The paper addresses fatigue life of Ti6Al4V produced by Powder Bed Fusion in four finishing conditions: as-built, tool machined, after tumbling and after tumbling and subsequent shot-peening. Failure mechanisms at the micro-scale are observed in order to reinforce the mechanical results by identifying the role of different surface morphologies in crack initiation. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques and microanalysis (EDX) are used to investigate microstructural modifications generated by the different finishing methods. Results show that tumbling alone does not improve fatigue life against the as built condition, whereas tumbling and subsequent shot peening allow matching the fatigue endurance of tool machined specimens. The shot peening process causes surface amorphization and implantation of the peening media turning into subsurface inclusions. Based on the results, an optimized finishing process can be envisaged, consisting in prolonged tumbling up to the removal of a stock allowance at least equal to the powder size, before shot peening.

2019 - Laser powder bed fusion: Tailoring the microstructure of alloys for biomedical applications [Relazione in Atti di Convegno]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Denti, L.; Rutkowski, B.; Barucca, G.
abstract

Additive manufacturing (AM) is particularly attractive for biomedical applications, where complex geometries and a high degree of individualization are required. Laser powder bed fusion (LPBF) is an AM technology exploiting the action of a solid-state laser to locally melt a metal powder according to a computer aided design (CAD) model. In the present study, the EOS Cobalt Chrome SP2 (Co-Cr-Mo-W) and Ti64 (Ti6Al4V) powders were sintered by the system equipped with a Yb fiber laser. During LPBF, the Co-Cr-Mo-W metal powder undergoes total melting followed by rapid cooling, giving rise to athermal martensitic phase transformation from the high-temperature γ (fcc) phase to the low-temperature ε (hcp) phase. This produces an intricate network of thin ε-lamellae inside the γ phase matrix. After the firing cycle this structure is maintained, and a massive presence of coarse precipitates is also observed. Owing to the rapid cooling taking place during LPBF, in Ti6Al4V sintered samples only the acicular martensitic α' phase is present. The firing cycle induces the β phase formation at the α plate boundaries and this microstructure leads to reduced values of strength, with respect to those of the as-sintered samples. The highlighted behaviors show that by tuning the post-production heat treatments it is possible to tailor the microstructure and the mechanical properties.

2019 - Metastable Al–Si–Ni alloys for additive manufacturing: Structural stability and energy release during heating [Articolo su rivista]
Bedo, T.; Varga, B.; Cristea, D.; Nitoi, A.; Gatto, A.; Bassoli, E.; Bulai, G.; Velicu, I. -L.; Ghiuta, I.; Munteanu, S.; Pop, M. A.; Gabor, C.; Cosnita, M.; Parv, L.; Munteanu, D.
abstract

Rapid solidification with high cooling rates of metal alloys determines both the improvement of mechanical properties, due to the finishing of the structure, as well as obtaining metastable structures in the form of supersaturated or amorphous/nano solid solutions, which could potentially confer the material outstanding properties. It is of particular interest to use the energies released during the heating stage for these materials, due to the potentially lower input energy required to melt/fuse these materials. This phenomenon could add to the development and diversification of additive manufacturing technologies. The paper presents results concerning the structural development and phase transformation of metastable structures from Al–Si–Ni-based alloys, obtained by melt spinning and atomization techniques. It was observed that the structural transformations occurring during the heating process, starting from metastable structures, generate significant amounts of energy. This is of practical importance in the use of metallic powders in additive manufacturing technology, due to potentially reduced energy input.

2019 - Precipitates formation and evolution in a Co-based alloy produced by powder bed fusion [Articolo su rivista]
Santecchia, E.; Gatto, A.; Bassoli, E.; Denti, L.; Rutkowski, B.; Mengucci, P.; Barucca, Giulia
abstract

Metal additive manufacturing is strongly employed in aerospace and biomedical applications, whose high degree of customization and low production volumes are the main characteristics. Cobalt-based alloys have been widely used for dental prosthesis and can be produced via metal additive manufacturing, or rather powder bed fusion, in a more convenient way compared to traditional manufacturing techniques. In the present paper, a comprehensive study of the tight correlation between the microstructure and the static mechanical properties of Co-Cr-Mo-W samples produced by powder bed fusion, is reported. In particular, the formation of precipitates during the sintering process is observed, and the evolution of their size, shape and frequency due to post-processing and to a heat-treatment typical of dental applications, is exhaustively studied. By coupling different characterization techniques such as scanning transmission electron microscopy and small-angle neutron scattering, it was possible to correlate the ductility degradation of the samples with the formation and growth of coarse and elongated precipitates.

2019 - Solid-state phase transformations in thermally treated Ti-6Al-4V alloy fabricated via laser powder bed fusion [Articolo su rivista]
Mengucci, P.; Santecchia, E.; Gatto, A.; Bassoli, E.; Sola, A.; Sciancalepore, C.; Rutkowski, B.; Barucca, G.
abstract

Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained β in α' martensite of the as-produced (#AP) sample. The retained β was not detectable byXRDanalysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the α ↔ β transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained β phase plays a key role in the α' → β transformation kinetics.

2019 - Sustainability impact assessment of additive manufacturing productive processes [Relazione in Atti di Convegno]
Cappucci, GRAZIA MARIA; Pini, Martina; Neri, Paolo; Marassi, Marta; Bassoli, Elena; Ferrari, Anna Maria
abstract

2019 - Ti-Zr-Si-Nb nanocrystalline alloys and metallic glasses: Assessment on the structure, thermal stability, corrosion and mechanical properties [Articolo su rivista]
Gabor, C.; Cristea, D.; Velicu, I. -L.; Bedo, T.; Gatto, A.; Bassoli, E.; Varga, B.; Pop, M. A.; Geanta, V.; Stefanoiu, R.; Codescu, M. M.; Manta, E.; Patroi, D.; Florescu, M.; Munteanu, S. I.; Ghiuta, I.; Lupu, N.; Munteanu, D.
abstract

The development of novel Ti-based amorphous or β-phase nanostructured metallic materials could have significant benefits for implant applications, due to improved corrosion and mechanical characteristics (lower Young's modulus, better wear performance, improved fracture toughness) in comparison to the standardized α+β titanium alloys. Moreover, the devitrification phenomenon, occurring during heating, could contribute to lower input power during additive manufacturing technologies. Ti-based alloy ribbons were obtained by melt-spinning, considering the ultra-fast cooling rates this method can provide. The titanium alloys contain in various proportions Zr, Nb, and Si (Ti60Zr10Si15Nb15, Ti64Zr10Si15Nb11, Ti56Zr10Si15Nb19) in various proportions. These elements were chosen due to their reported biological safety, as in the case of Zr and Nb, and the metallic glass-forming ability and biocompatibility of Si. The morphology and chemical composition were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the structural features (crystallinity, phase attribution after devitrification (after heat treatment)) were assessed by X-ray diffraction. Some of the mechanical properties (hardness, Young's modulus) were assessed by instrumented indentation. The thermal stability and crystallization temperatures were measured by differential thermal analysis. High-intensity exothermal peaks were observed during heating of melt-spun ribbons. The corrosion behavior was assessed by electrocorrosion tests. The results show the potential of these alloys to be used as materials for biomedical applications.

2019 - Weight reduction by topology optimization of an engine subframe mount, designed for additive manufacturing production [Relazione in Atti di Convegno]
Merulla, A.; Gatto, A.; Bassoli, E.; Munteanu, S. I.; Gheorghiu, B.; Pop, M. A.; Bedo, T.; Munteanu, D.
abstract

Additive Manufacturing (AM) technologies are getting more and more strategic for different purposes in many industrial fields. Among the most outstanding are part prototyping, single part to small batch production, relatively reduced manufacturing times and investments costs, reduced material consumption, and innovative and efficient shapes. The considerable advantages these technologies offer, compared to subtractive ones, make additive manufacturing a potentially industry-leading process in almost all domains - from aeronautics to the medical industry. Under these circumstances, the inspiration given by topology optimization tools can lead to feasible industrial parts, with fewer constraints in comparison to traditional manufacturing processes. The paper presents the development and the results obtained using topology optimization and design for AM technology on an automotive part: an engine mount sub-frame component for a rear middle engine sports car. The final design enables a significant weight reduction.

2018 - A Study on the Use of XCT and FEA to Predict the Elastic Behavior of Additively Manufactured Parts of Cylindrical Geometry [Articolo su rivista]
Esposito, F.; Gatto, A.; Bassoli, E.; Denti, L.
abstract

Defining general criteria for the acceptability of defects within industrial components is often complicated, since the specific load conditions and the criticality of the given application should be considered individually. In order to minimize the risk of failure, high safety factors are commonly adopted during quality control. However this practice is likely to cause the rejection of components whose defects would be instead acceptable if a more sound knowledge of the component behaviour were achieved. Parts produced by additive manufacturing (AM) may suffer from various defects, including micro- or macro-holes, delamination and microstructural discontinuities. Such processes, which are specially suitable for one-off components, require robust and reliable inspection before a part is accepted or rejected, since the refusal of even a single part at the end of the production process represents a significant loss. For this reason, it would be very useful to simulate in a reliable way whether a certain defect is truly detrimental to the proper working of the part during operation or whether the component can still be used, despite the presence of a defect. To this purpose, the paper highlights the benefits of a synergistic interaction between Industrial X-ray computed tomography (XCT) and finite element analysis (FEA). Internal defects of additively manufactured parts can be identified in a non-destructive way by means of XCT. Then FEA can be performed on the XCT-based virtual model of the real component, rather than on the ideal CAD geometry. A proof of concept of this approach is proposed here for a reference construct produced in an Aluminium alloy by AM. Numerical results of the proposed combined XCT–FEA procedure are contrasted with experimental data from tensile tests. The findings sustain the reliability of the method and allow to assess its full provisional accuracy for parts of cylindrical geometry designed to operate in the elastic field. The paper moves a step beyond the present application limits of tomography as it is currently employed for AM parts and it evidences instead the possibility of extending the usage of tomography to acceptance testing and prediction of operative behaviour.

2018 - Assay of secondary anisotropy in additively manufactured alloys for dental applications [Articolo su rivista]
Bassoli, Elena; Denti, Lucia
abstract

Even though additive manufacturing (AM) techniques have been available since the late 1980s, their application in medicine is still striving to gain full acceptance. For the production of dental implants, the use of AM allows to save time and costs, but also to ensure closer dimensional tolerances and higher repeatability, as compared to traditional manual processes. Among the several AM solutions, Laser Powder Bed Fusion (L-PBF) is the most appropriate for the production of metal prostheses. The target of this paper was to investigate the mechanical and microstructural characteristics of Co-Cr-Mo and Ti-6Al-4V alloys processed by L-PBF, with a specific focus on secondary anisotropy that is usually disregarded in the literature. Tensile specimens were built in the EOSINT-M270 machine, along different orientations perpendicular to the growth direction. Density, hardness, and tensile properties were measured and the results combined with microstructural and fractographic examination. For both alloys, the results provided evidence of high strength and hardness, combined with outstanding elongation and full densification. Extremely fine microstructures were observed, sufficient to account for the good mechanical response. Statistical analysis of the mechanical properties allowed to attest the substantial absence of secondary anisotropy. The result was corroborated by the observations of the microstructures and of the failure modes. Overall, the two alloys proved to be high-performing, in very close agreement with the values reported in the datasheets, independently of the build orientation.

2018 - Development of laser-based powder bed fusion process parameters and scanning strategy for new metal alloy grades: A holistic method formulation [Articolo su rivista]
Bassoli, Elena; Sola, Antonella; Celesti, Mattia; Calcagnile, Sandro; Cavallini, Carlo
abstract

In spite of the fast growth of laser-based powder bed fusion (L-PBF) processes as a part of everyday industrial practice, achieving consistent production is hampered by the scarce repeatability of performance that is often encountered across different additive manufacturing (AM) machines. In addition, the development of novel feedstock materials, which is fundamental to the future growth of AM, is limited by the absence of established methodologies for their successful exploitation. This paper proposes a structured procedure with a complete test plan, which defines step-by-step the standardized actions that should be taken to optimize the processing parameters and scanning strategy in L-PBF of new alloy grades. The method is holistic, since it considers all the laser/material interactions in different local geometries of the build, and suggests, for each possible interaction, a specific geometry for test specimens, standard energy parameters to be analyzed through a design of experiment, and measurable key performance indicators. The proposed procedure therefore represents a sound and robust aid to the development of novel alloy grades for L-PBF and to the definition of the most appropriate processing conditions for them, independent of the specific AM machine applied.

2018 - Directed energy deposition of steel 316L: Effects of build orientation [Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Gatto, Andrea; Sewell, Neil Thomas; Johns, Daniel
abstract

Metal Additive Manufacturing for the production of end parts is today the major interest in the field of layer-by-layer fabrication. Even if Powder Bed Fusion is by far the most diffused technology, powder-fed systems retain a specific attractiveness, mainly because they enable an easier manufacture of multi-material parts or even of composition-graded ones. These systems, recently categorized by ASTM standards under the term Directed Energy Deposition (DED), still suffer from scarce knowledge of part characteristics and of process robustness and repeatability. Among DED processes, Laser Consolidation (LC) allows the production of net-shape metal parts with good metallurgical soundness, high strength and ductility. As regards the mechanical performance, the non-coaxial architecture of the LC head poses the question of a secondary anisotropy, within each layer, in addition to the primary one that is due to the layerwise construction. The paper addresses the mechanical response and the microstructure obtained by LC with AISI 316L. The direction dependence of part properties is specifically explored. Remarkably high ductility, combined with high hardness and strength, are obtained. The effect of the relative orientation between the LC head and the part is quantified and associated with the observed microstructure.

2018 - Evaluation of environmental sustainability in additive manufacturing processes for orthopaedic devices production [Relazione in Atti di Convegno]
Cappucci, GRAZIA MARIA; Pini, Martina; Neri, Paolo; Marassi, Marta; Bassoli, Elena; Ferrari, Anna Maria
abstract

Sustainability impact assessment of additive manufacturing represents one of the work packages (WP5) of the European Union Horizon 2020 project “Driving up Reliability and Efficiency of Additive Manufacturing” (DREAM). Additive manufacturing is a versatile technology consisting in melting metallic powders to produce objects from 3D data, layer upon layer. Additive manufacturing applications in industry range from automotive, biomedical (e.g. prosthetic implants for dentistry and orthopedics), aeronautics and others. One of the main target of WP5 is to assess the environmental sustainability of DREAM products and processes, conducted with laser-based powder bed fusion additive manufacturing systems through Life Cycle Assessment (LCA) methodology. Environmental impacts on different impact and damage categories due to manufacturing, use and end of life of the designed solution have been assessed adopting IMPACT 2002+ method.

2018 - Experimental investigation and optimisation of laser direct part marking of Inconel 718 [Articolo su rivista]
Leone, C.; Bassoli, E.; Genna, S.; Gatto, A.
abstract

Many industries need product identification; laser marking is suitable to produce any kind of symbol, data matrix or bar code on parts. Consequently, the most important requirement for marking acceptance is, doubtless, the mark readability. The present study deals on the effect of process parameters on the laser marking of Inconel 718, with the aim to find a relation between the process parameters and mark characteristics in term of both mark geometry and readability. To this aim, laser markings, under different process conditions, were performed on Inconel 718 sheets, adopting a 30 W Q-switched Yb:YAG laser. The mark geometry was acquired by a 3D surface profiling system. Optical microscopy and SEM analysis were also performed on groove sections. In order to evaluate the readability of the marks, Weber contrast was calculated and adopted. The mark characteristics have been investigated by mean of statistical methodology (ANalysis of VAriance and Response Surface Method) and related to the process parameters. Furthermore, Master Response Optimisation methodology was adopted to individuate the optimal process conditions. It was found that mark geometry and the Weber contrast are mainly affected by the average power and the energy input per mark-length. Moreover, operative conditions allowing for maximum readability, yet without excessive increase in burr height, were also determined.

2018 - Fatigue behavior of as-built L-PBF A357.0 parts [Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Comin, Andrea; Sola, Antonella; Tognoli, Emanuele
abstract

Laser-based powder bed fusion (L-PBF) is nowadays the preeminent additive manufacturing (AM) technique to produce metal parts. Nonetheless, relatively few metal powders are currently available for industrial L-PBF, especially if aluminum-based feedstocks are involved. In order to fill the existing gap, A357.0 (also known as A357 or A13570) powders are here processed by L-PBF and, for the first time, the fatigue behavior is investigated in the as-built state to verify the net-shaping potentiality of AM. Both the low-cycle and high-cycle fatigue areas are analyzed to draw the complete Wohler diagram. The infinite lifetime limit is set to 2 × 106stress cycles and the staircase method is applied to calculate a mean fatigue strength of 60 MPa. This value is slightly lower but still comparable to the published data for AlSi10Mg parts manufactured by L-PBF, even if the A357.0 samples considered here have not received any post-processing treatment.

2018 - Investigation on the effectiveness of through-hole replicas of deep small holes [Articolo su rivista]
Bassoli, Elena; Denti, Lucia
abstract

When a micro-hole of high aspect-ratio is required, in addition to machining problems, special attention should be paid to controlling the quality of the manufactured products. Dimensional and surface metrology in the field of micromachining can be as critical as machining itself, therefore several new measurement methods have been developed. However, many of these methods suffer from application limits when used in the case of a deep hole. Replication can be a useful approach, which has well-proven validity in the time-consuming case of the sectioned hole. The method of through replicas, to be pulled out of the unsectioned hole, still needs verification. In the present paper, the surface roughness of deep small electrodischarge drilled holes is measured, and the effectiveness of the use of both open- and through-replicas is evaluated, versus direct measurements on the microdrilled surfaces. Through-hole replicas, by means of injection and extraction of a silicone, are proven reliable for reproducing the surface morphology of holes down to 0.8 mm diameter with an aspect ratio of 12.5. The findings show that the operative range of the considered techniques may be extended with respect to the previous cases mentioned in literature.

2018 - Molla elicoidale perfezionata [Brevetto]
Gatto, Andrea; Gatto, Francesco; Bassoli, Elena; Denti, Lucia
abstract

2018 - Repercussions of powder contamination on the fatigue life of additive manufactured maraging steel [Articolo su rivista]
Gatto, A.; Bassoli, E.; Denti, L.
abstract

A wide range of materials is suitable for processing by powder bed fusion (PBF) techniques. Among the latest formulations, maraging steel 18Ni-300, which is a martensite-hardenable alloy, is often used when both high fracture toughness and high strength are required, or if dimensional changes need to be minimised. In direct tooling, 18Ni-300 can be successfully employed in numerous applications, for example in the production of dies for injection moulding and for casting of aluminium alloys; moreover, it is particularly valuable for high-performance engineering parts. Even though bibliographic data are available on the effects that parameters, employed in PBF processes, have on the obtained density, roughness, hardness and microstructure of 18Ni-300, there is still a lack of knowledge on the fatigue life of PBF manufactured parts. This paper describes the fatigue behaviour of 18Ni-300 steel manufactured by PBF, as compared by forging. Relevant negative effects of the cross-contamination of the raw material are originally identified in this paper, which emphasizes the inadequacy of current acceptability protocols for PBF powders. In the absence of contamination, endurance achieved by PBF is found equal to that by forging and consistent with tooling requirements as set out by industrial partners, based on injection moulding process modelling.

2018 - The influence of powder particle and grain size on parts manufacturing by powder bed fusion [Relazione in Atti di Convegno]
Ghiuta, I.; Gatto, A.; Bassoli, E.; Munteanu, S. I.; Bedo, T.; Pop, M. A.; Gabor, C.; Covei, M.; Cosnita, M.; Cristea, D.; Varga, B.; Munteanu, D.
abstract

Nanostructured powder materials, or powders with increased amorphous ratio, can potentially lead to increased productivity during powder bed fusion, due to the hypothesis that nanostructured raw materials can be layer-sintered with lower specific energy, and consequently lower processing times when compared to commercial powders. Sintering of such materials can potentially be done faster, as compared to conventional powders. In addition, using nanostructured powders, or powders with high amorphous content, or even nanometric (nano-sized particles) powders, can result in higher density and hardness values of the sintered part, using the same process parameters. The main issue with nano-sized particles is their loss of flowability, which could be overcome by controlling the particle shape during manufacturing. This work presents our results concerning the manufacturing and characterization of titanium alloy powders, with potential use in additive manufacturing. The powders were manufactured using severe plastic deformation by mechanical milling from commercially available powders, with various rotation speeds, ball diameters, and milling periods, in order to obtain micrometric particles, but with nanometric or high amorphous content structures. The powders were further analyzed in terms of morphology, structure, and chemical composition.

2018 - Towards additive manufacturing of ramified scaffolds of the thyroid vascular system: A preliminary fractal analysis [Articolo su rivista]
Bassoli, E.; Denti, L.; Gatto, A.; Spaletta, G.; Sofroniou, M.; Parrilli, A.; Fini, M.; Giardino, Raffaele; SANDUZZI ZAMPARELLI, Alessandro; Zini, N.; Barbaro, F.; Bassi, E.; Mosca, S.; Dallatana, D.; Toni, R.
abstract

Fractal properties have been demonstrated in literature for several human vascular systems. In the frame of the investigation of additive manufacturing (AM) as a viable solution to prototype single arterial branches of human soft tissue organs, the paper provides a fractal analysis of the arterial tree of the human thyroid gland. The possibility that the thyroid arterial structure may be described as auto-similar is investigated, by studying injection-corrosion casts of the cadaveric gland. Vessel branching is analyzed by measuring branch diameters, ramification angles, and vessel lengths with the use of an optical microscope. Metrological results are made dimensionless by applying, as a scaling parameter, the caliber of major arteries. Data are then studied on a cumulative basis and processed to infer general rules for vessel branching. High resolution microtomography (mCT) is used to determine the spaces occupied by vascular branches and calculate their planar fractal dimension. Finally, the vascular tree has been simulated by a mixed, stochastic / deterministic algorithm based on diffusion limited aggregation (DLA), in which mean values of vascular variables are set as constraints. The purpose of this research is to understand if fractality can be reliably assumed for computational modeling of the organ anatomy, in order to be able to produce, by AM, more representative physical prototypes and scaffolds. The finding allow to affirm that the human thyroid arterial structure exhibits a degree of auto-similarity.

2017 - A spot on Powder Bed Fusion of Metals [Monografia/Trattato scientifico]
Bassoli, Elena
abstract

Additive technology is raising a huge interest in all industry sectors, due to its peculiarities compared to more traditional manufacturing processes. Some advantages typical to this technology include the possibility to generate ideally any shape (geometrical complexity) and to reduce the number of parts required to obtain a given shape (functional integration). In addition, there is no (or very little) waste of material since only what is actually needed is used. It is interesting to notice that the technology is spreading also to critical parts, like turbine blades for energy and aero applications: components having rather complex shapes with internal cooling channels that are very challenging from the manufacturing point of view. AM processes have been proven to ensure lower cost, wider range of metal alloys and higher mechanical strength over conventional solutions. Some drawbacks are still associated to AM: build rates are generally slower than with traditional manufacturing processes, furthermore the size of the object that can be built is limited by the printing devices currently available. The process itself is somehow critical: it involves the sequential layer wise deposition and selective melting of material, which causes complex heat transfer. High stress gradients, varying at different locations of the components, need to be dealt with. Residual stresses can lead to deformation or failure of the component during the process itself, or after the relief treatment, if build strategy and parameters are not optimized.Powder Bed Fusion is the current standard designation of Additive Manufacturing processes in which a metal powder is laid in a bed and turned into a solid section by means of a high-energy beam. The term groups several processes that share the same layout, to such an extent that mere variations of process parameters result in a shift from one to another. This review addresses standards, machine layouts, process parameters, anisotropy, materials and properties, microstructures and possible defects. The main fields of application are then treated, focusing on outstanding success examples, to end with a critical discussion of risks and opportunities and an overview of the trends in research.

2017 - DREAM: Driving up reliability and efficiency of additive manufacturing [Relazione in Atti di Convegno]
Sciancalepore, Corrado; Bondioli, Federica; Gatto, Andrea; Defanti, Silvio; Denti, Lucia; Bassoli, Elena
abstract

The DREAM project, financed by the EU Commission (H2020, Work program: FOF-13-2016: Photonics Laser-based production) is an end-user driven action which aligns the research and development of Additive Manufacturing (AM) technologies to the specific needs of its three industrial end users, Ferrari SpA, Adler Ortho France SARL, and RB Srl. The Action brings together experts in the field of AM technologies, powder and material characterization, component engineering, laser-matter interaction, to deliver an optimized approach that will be developed and demonstrated to the requirements of the end users. The first results of the project are here reported.

2017 - Effects of build orientation and element partitioning on microstructure and mechanical properties of biomedical Ti-6Al-4V alloy produced by laser sintering [Articolo su rivista]
Mengucci, P.; Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Fiori, F.; Girardin, E.; Bastianoni, P.; Rutkowski, B.; Czyrska Filemonowicz, A.; Barucca, G.
abstract

Direct Metal Laser Sintering (DMLS) technology was used to produce tensile and flexural samples based on the Ti-6Al-4V biomedical composition. Tensile samples were produced in three different orientations in order to investigate the effect of building direction on the mechanical behavior. On the other hand, flexural samples were submitted to thermal treatments to simulate the firing cycle commonly used to veneer metallic devices with ceramics in dental applications. Roughness and hardness measurements as well as tensile and flexural mechanical tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate sample microstructure. Results evidenced a difference in the mechanical response of tensile samples built in orthogonal directions. In terms of microstructure, samples not submitted to the firing cycle show a single phase acicular α’ (hcp) structure typical of metal parts subject to high cooling rates. After the firing cycle, samples show a reduction of hardness and strength due to the formation of laths of the β (bcc) phase at the boundaries of the primary formed α’ plates as well as to lattice parameters variation of the hcp phase. Element partitioning during the firing cycle gives rise to high concentration of V atoms (up to 20 wt%) at the plate boundaries where the β phase preferentially forms.

2017 - Fatigue life of electrodischarge drilled Inconel 718 [Articolo su rivista]
Bassoli, Elena
abstract

The machining of complex shapes in difficult-to-cut materials is hardly achieved by traditional metal cutting. Particularly small deep holes are often a cause for premature tool failure or even a technological frontier. Yet, the use of Nickel-based alloys is common in high-temperature and aerospace applications, where thin shapes and deep holes are often required. In these cases non-contact processes, such as electrodischarge (ED) drilling, may be the only viable manufacturing solution. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. The paper addresses the effect of ED drilled holes (0.8 mm diameter, aspect ratio 10) on the fatigue life of Inconel 718. Rotating bending fatigue tests are executed on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Extremal ED parameters are selected based on previous studies: conditions for best surface finish are contrasted with those for highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.

2017 - Reinforcement effectiveness on mechanical performances of composites obtained by powder bed fusion [Articolo su rivista]
Gatto, A.; Bassoli, E.; Denti, L.
abstract

New material formulations to be used in Additive Manufacturing machines are one of the major interests in this fast growing field. The possibility to tune functional and mechanical properties, by the addition of reinforcements to a polymeric matrix, is hindered by the low provisional capability of the additive manufactured composite. The inherent anisotropy of layer manufacturing combines with mechanisms of filler dispersion and of filler/matrix adhesion in a complex scenario. The paper entails a critical evaluation of mechanical properties measured for several polymeric composites produced by Powder Bed Fusion, in the perspective of provisional models commonly accepted for composite materials. The models are reviewed versus experimental and literature data. The provisional effectiveness is generally good, except for the case of nanometric or surface treated fillers, or of specific anisotropic microstructures obtained by layer manufacturing.

2016 - Bioartificial endocrine organs: At the cutting edge of translational research in endocrinology [Capitolo/Saggio]
Toni, R.; Bassi, E.; Barbaro, F.; Zini, N.; Zamparelli, A.; Alfieri, M.; Dallatana, D.; Mosca, S.; Della Casa, C.; Gnocchi, C.; Lippi, G.; Spaletta, G.; Bassoli, E.; Denti, L.; Gatto, A.; Ricci, F.; Tazzari, P. L.; Parrilli, A.; Fini, M.; Sandri, M.; Sprio, S.; Tampieri, A.
abstract

2016 - Biomedical Co-Cr-Mo Components Produced by Direct Metal Laser Sintering [Relazione in Atti di Convegno]
Girardin, E.; Barucca, G.; Mengucci, P.; Fiori, F.; Bassoli, E.; Gatto, A.; Iuliano, L.; Rutkowski, B.
abstract

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technique based on a laser power source that sinters powdered materials using a 3D CAD model. The mechanical components produced by this procedure typically show higher residual porosity and poorer mechanical properties than those obtained by traditional manufacturing techniques. In this study, samples were produced by DMLS starting from a Co-Cr-Mo powder (in the γ phase) with a composition suitable for biomedical applications. Samples were submitted to hardness measurements and structural characterization. The samples showed a hardness value remarkably higher that those commonly obtained for the same cast or wrought alloys. In fact, the HRC value measured for the samples is 47 HRC, while the usual range for CAST Co-Cr-Mo is from 25 to 35 HRC. The samples microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX) in order to clarify the origin of this unexpected result. The laser treatment induced a melting of the metallic Co-Cr-Mo powder, generating a phase transformation from the γ (fcc) to the e (hcp) phase. The rapid cooling of the melted powder produced the formation of e (hcp) nano-lamellae inside the γ (fcc) phase. The nano-lamellae formed an intricate network responsible for the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields, where a high degree of personalization is required.

2016 - Effects of thermal treatments on microstructure and mechanical properties of a Co-Cr-Mo-W biomedical alloy produced by laser sintering [Articolo su rivista]
Mengucci, P; Barucca, G.; Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Fiori, F.; Girardin, E.; Bastianoni, P.; Rutkowski, B.; Czyrska Filemonowicz, A.
abstract

Direct Metal Laser Sintering (DMLS) technology based on a layer by layer production process was used to produce a Co-Cr-Mo-W alloy specifically developed for biomedical applications. The alloy mechanical response and microstructure were investigated in the as-sintered state and after post-production thermal treatments. Roughness and hardness measurements, and tensile and flexural tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate the microstructure in different conditions. Results showed an intricate network of ε-Co (hcp) lamellae in the γ-Co (fcc) matrix responsible of the high UTS and hardness values in the as-sintered state. Thermal treatments increase volume fraction of the ε-Co (hcp) martensite but slightly modify the average size of the lamellar structure. Nevertheless, thermal treatments are capable of producing a sensible increase in UTS and hardness and a strong reduction in ductility. These latter effects were mainly attributed to the massive precipitation of an hcp Co3(Mo,W)2Si phase and the contemporary formation of Si-rich inclusions.

2016 - Influence of electrode size and geometry in electro-discharge drilling of Inconel 718 [Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Gatto, Andrea; Iuliano, Luca
abstract

Electro-discharge machining (EDM) of thin deep features widens processing opportunities of difficult-to-cut materials, such as Ni-based alloys, towards attractive industrial applications. Conversely, the complex interaction between electrical, thermal, and chemical phenomena in EDM thwarts process modeling and prediction. As a matter of fact, recent experimental discoveries encourage setting forth a new theory of discharge ignition in the gap, based on the role of debris, which lays foundations for a recursive mathematical model showing a chaotic evolution. The paper reports on electro-discharge drilling of small deep holes in Inconel 718. Process performances are measured with varying electrode size and geometry, attesting a pivotal effect of gap pollution on productivity and on the onset of a secondary detrimental removal of material by intergranular corrosion. All findings support the emerging model for discharge ignition via debris bridges, and, most notably, debris chains are documented for the first time in the field of metals, second only to a previous case for a ceramic composite. On the whole, the paper provides conclusive validation of the role of debris in the ignition of discharges.

2015 - Energy harvesting smart floor for indoor people localization and tracking [Relazione in Atti di Convegno]
Gatto, Andrea; Bassoli, Elena; Contigiani, Marco; Frontoni, Emanuele; Mancini, Adriano; Zingaretti, Primo
abstract

The aim of this work is to describe an innovative smart floor based on a self powered system able to allow the localization and analysis of the movement of the users in a specific area. The solution presented involves the use of capacitive sensors on a polymeric support to be inserted between solid wood and a wooden part of a floating parquet. A detailed architecture and implementation of the smart floor is proposed together with an exhaustive test phase. In this paper we first describe the measurement system used to perform reliability and efficiency test of the system. Then the results are discussed and compared with the expected results and the performance of other solutions already known to the state of art. The proposed system is part of HDOMO, an Ambient Assisted Living (AAL) project aimed at developing smart solutions for active ageing.

2015 - Impact of additive manufacturing on engineering education – evidence from Italy [Articolo su rivista]
Minetola, Paolo; Iuliano, Luca; Bassoli, Elena; Gatto, Andrea
abstract

Purpose - The purpose of this paper is to evaluate how the direct access to additive manufacturing (AM) systems impacts on education of future mechanical engineers, within a Master's program at a top Italian University. Design/methodology/approach - A survey is specifically designed to assess the relevance of entry-level AM within the learning environment, as a tool for project development. The survey is distributed anonymously to three consecutive cohorts of students who attended the course of "computer-aided production (CAP)", within the Master of Science Degree in Mechanical Engineering at Politecnico di Torino. The course includes a practical project, consisting in the design of a polymeric product with multiple components and ending with the production of an assembled prototype. The working assembly is fabricated by the students themselves, who operate a fused deposition modelling (FDM) machine, finish the parts and evaluate assemblability and functionality. The post-course survey covers diverse aspects of the learning process, such as: motivation, knowledge acquisition, new abilities and team-working skills. Responses are analyzed to evaluate students' perception of the usefulness of additive technologies in learning product design and development. Among the projects, one representative case study is selected and discussed. Findings - Results of the research affirm a positive relationship of access to AM devices to perceived interest, motivation and ease of learning of mechanical engineering. Entry-level additive technologies offer a hands-on experience within academia, fostering the acquisition of technical knowledge. Research limitations/implications - The survey is distributed to more than 200 students to cover the full population of the CAP course over three academic years. The year the students participated in the CAP course is not tracked because the instructor was the same and there were no administrative differences. For this reason, the survey administration might be a limitation of the current study. In addition to this, no gender distinction is made because historically, the percentage of female students in Mechanical Engineering courses is about 10 per cent or lower. Although the answers to the survey are anonymous, only 37 per cent of the students gave a feedback. Thus, on the one hand, impact assessment is limited to a sample of about one-third of the complete population, but, on the other hand, the anonymity ensures randomization in the sample selection. Practical implications - Early exposure of forthcoming designers to AM tools can turn into a "think-additive" approach to product design, that is a groundbreaking conception of geometries and product functionalities, leading to the full exploitation of the possibilities offered by additive technologies. Social implications - Shared knowledge can act as a springboard for mass adoption of AM processes. Originality/value - The advantages of adopting AM technologies at different levels of education, for diverse educational purposes and disciplines, are well assessed in the literature. The innovative aspect of this paper is that the impact of AM is evaluated through a feedback coming directly from mechanical engineering students.

2015 - Multi-disciplinary approach in engineering education: learning with additive manufacturing and reverse engineering [Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Iuliano, Luca; Minetola, Paolo
abstract

Purpose - The purpose of this paper is to report an interdisciplinary, cooperative-learning project in a second-year course within the "Enzo Ferrari" Master of Science Degree in Mechanical Engineering. The work aims to raise awareness of the educational impact of additive manufacturing and reverse engineering. Design/methodology/approach - Students are asked to develop, concurrently, the design and the manufacturing solution for an eye-tracker head mount. A digital head model is reverse engineered from an anatomical mannequin and used as an ergonomic mock-up. The project includes prototype testing and cost analysis. The device is produced using additive manufacturing techniques for hands-on evaluation by the students. Findings - Results of the presented case study substantiate the authors' belief in the tremendous potential of interdisciplinary project-based learning, relying on innovative technologies to encourage collaboration, motivation and dynamism. Originality/value - The paper confirms a spreading conviction that the soon-to-be engineers will need new practice-oriented capabilities to cope with new competitive scenarios. Engineering education must adapt to the social, rather than industrial, revolution that is being brought about by additive fabrication.

2015 - On the chaotic nature of electro-discharge machining [Articolo su rivista]
Gatto, Andrea; Sofroniou, Mark; Spaletta, Giulia; Bassoli, Elena
abstract

The long-accepted thermoelectric model for electro-discharge machining is being brought into question. Several experimental facts prompt the proposal of a new theory based on the effect of gap pollution on the ignition of discharges. The first experimental proof comes from the recently reported observation of debris chains and clusters. In this view, each step of the process depends on the previous ones through a deterministic relation, even if the overall evolution is unpredictable. The paper establishes mathematical grounds for the abovementioned intuitions by setting up and solving a recursive equation for the machining energy employed at each discharge event. By means of numerical and algebraic tools, the above equation is studied and shows a chaotic evolution similar to that of the logistic map. Results reconcile the apparent paradox between deterministic nature and stochastic localization of the discharges and introduce a description of the chaotic dynamics of electro-discharge processes.

2015 - Structural characterization of biomedical Co-Cr-Mo components produced by direct metal laser sintering [Articolo su rivista]
Barucca, G.; Santecchia, E.; Majni, G.; Girardin, E.; Bassoli, Elena; Denti, Lucia; Gatto, Andrea; Iuliano, L.; Moskalewicz, T.; Mengucci, P.
abstract

Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co-Cr-Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin ε (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The ε-lamellae grown on the {111}γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

2015 - Surface and sub surface evaluation in coated-wire electrical discharge machining (WEDM) of INCONEL® alloy 718 [Relazione in Atti di Convegno]
Atzeni, E.; Bassoli, E.; Gatto, A.; Iuliano, L.; Minetola, P.; Salmi, A.
abstract

Wire Electncal Discharge Machining (WEDM) is one of the most versatile and useflil technological processes for cuttmg complex shapes made of conductive matenals such as those typical of aerospace applications. With the aim to optimize process parameters, this paper studies the surface and subsurface modifications of INCONEL® alloy 718 (UNS N077 18) machined by WEDM using a Zinc coated brass wire. Machining was perfomwd under roughing and finishing conditions by setting different values of discharge energy and wire feed rate. Surface roughness of the cut surfaces was measured as well as the micro-hardness profile on polished sections. WED-machined surfaces and their cross sections were also observed by Scannmg Electron Microscope (SEM) and analyzed by Energy Dispersive X-ray Spectroscopy (EDS) to evaluate possible vanations of the surface chemical composition. In this investigation, results are discussed as a ifinction of the feed rate and of the smgle pulse discharge energy, which is determined by duration, peak current and discharge voltage of the discharge pulse. The research demonstrates that the required surface roughness can be achieved by properly settmg the feed rate and the smgle pulse discharge energy on the WEDM machme. Expenmental results also show that under the re-melted layer thickness no significant white layer formation or thermal modification occur, indicatmg that the chosen set of operatmg parameters minimizes secondary and unwanted chemical reactions.

2015 - Tolerance analysis for cast vs machined dental implants [Relazione in Atti di Convegno]
Atzeni, E.; Bassoli, E.; Denti, L.; Gatto, A.; Iuliano, L.; Minetola, P.; Salmi, A.
abstract

The paper addresses the dimensional tolerance and assembly accuracy of prosthetic components obtained by different manufacturing processes. The success of single tooth implant replacements hangs on the stability of the hexagonal connection, but no standard control procedures are available for its evaluation. The research aims at proposing a new protocol for the dimensional assessment of implant-Abutment connections, based on non-contact measurement and statistical data processing. The procedure is applied to machined-And cast-on abutments, as well of the matching implants. Samples are measured using an optical measuring microscope and data are processed to obtain the international tolerance (IT) grade. The rotational misfit is then calculated using the apothems of the external and the internal hexagon. As to the results, all the components are classified between IT8 and IT9 and the maximum rotational misfit is around 4 for all the assemblies, inferior to the critical limits for the screw joint stability. An objective dimensional characterization of prosthetic components and assemblies is reported, which is the basis for their reliability in clinical applications. From a wider perspective, an original measuring protocol is proposed, independent of parts assembly and based on international tolerances.

2014 - A planar fractal analysis of the arterial tree of the human thyroid gland: implications for additive manufacturing of 3D ramified scaffolds. [Relazione in Atti di Convegno]
Bassoli, Elena; Denti, Lucia; Gatto, Andrea; G., Spaletta; M., Sofroniou; A., Parrilli; M., Fini; R., Giardino; A., Zamparelli; N., Zini; F., Barbaro; E., Bassi; S., Mosca; D., Dallatana; R., Toni
abstract

It is currently known that a number of human vascular systems have a fractal geometry. Since we have recently developed a technique to prototype single arterial branches of human soft tissue organs by additive layer manufacturing (AM), we have explored the possibility that auto-similarity in vessel branching represents a key variable for accurate computational modeling of the organ three-dimensional (3D) macro / microscopic anatomy, and its reproduction by inverse engineering. To this purpose, ramification features of the intralobar arteries of the human thyroid were studied using injection-corrosion casts of the cadaveric gland. Vessel diameters, ramification angles, and branch lengths were measured by light microscopic, computer-aided optical metrology. Distribution of morphological variables was considered on a cumulative basis, and special focus was given to the branching laws. To reduce the bias of vascular distortion due to the pressure of intravascular resin injection, measures were made dimensionless through the use of a scaling parameter set on the vascular caliber of major afferent arteries. In addition, using high resolution microtomography (mCT) equipped with CTAn software and the Otsu algorithm for segmentation, spaces occupied by vascular branches (referred to as Volume of Interest, VOI) were selected, and their planar fractal dimension calculated. Finally, a computational simulation of the vascular tree was achieved using a mixed, stochastic / deterministic algorithm based on diffusion limited aggregation (DLA), constrained by mean values of vascular variables. Ratios among decreasing cast calibers, ramification angles, and branch lengths, respectively, were found strictly interrelated, mCT-VOI depicted fractal dimensions, and DLA simulation led to a fractal-like organization consistent with real data morphometrics. In summary, thyroid arterial geometry reliably exhibited a degree of auto-similarity, suggesting that fractality is a key feature for computational modeling and eventual AM of 3D vascular networks of the human thyroid.

2014 - Additive manufacturing as a cost-effective way to produce metal parts [Relazione in Atti di Convegno]
Atzeni, E.; Iuliano, L.; Marchiandi, G.; Minetola, P.; Salmi, A.; Bassoli, E.; Denti, L.; Gatto, A.
abstract

Recent developments in additive manufacturing technologies for the production of metal parts make this processes very attractive to high technology industries. Especially the geometrical freedom allow to produce components optimized for their functionality, disregarding limitations imposed by the manufacturing process. However, production costs should be evaluated to assess the convenience of additive manufacturing (AM) with respect to traditional technologies. Thus in this paper a break-even analysis is described, comparing the Selective Laser Melting (SLM) additive process with High Pressure Die Casting (HPDC) and 5-axis machining. Costs models are discussed for each process and benefits of applying redesign for additive manufacturing are illustrated. An aeronautical component is selected as case study to estimate the production volume for which additive manufacturing is cost-effective. The study proves the economical convenience of additive manufacturing with respect to traditional technologies from prototypes to small batch production. © 2014 Taylor & Francis Group.

2014 - Electro-Discharge Drilling on DMLS parts in Co-Cr-Mo alloy [Relazione in Atti di Convegno]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; E., Atzeni; L., Iuliano; G., Marchiandi; P., Minetola; A., Salmi; F., Calignano
abstract

Cobalt-base alloys are generally used in applications that require wear, corrosion and heat resistance. In particular, Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy is adopted in the aerospace and medical field. These applications are characterized by low volumes and high personalization, so they could take advantage by the employment of additive technologies, such as Direct Metal Laser Sintering (DMLS). This technology still has limitations for the manufacture of small cavities, such as holes with diameters below 0.6mm and high aspect ratio, which require drilling of the additive manufactured part. Scope of this research is to investigate the effects of Electro-Dicharge Drilling (EDD) on surface and subsurface features of CoCrMo samples built by DMLS. High aspect ratio holes are produced with diameter of 0.6 mm and depth fifteen times higher. The attractiveness of ED machining for thin deep geometries stems from then absence of physical contact between tool and workpiece, which makes machining forces negligible and minimizes tool deformation. Micro features can be produced with a high accuracy irrespective of the material hardness and strength. Material Removal Rate (MRR), Electrode Wear (EW) and surface roughness are investigated versus the process parameters. Results are supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends.

2014 - On the Effect of Electrodischarge Drilling on the Fatigue Life of Inconel 718 [Relazione in Atti di Convegno]
Bassoli, Elena; Baldini, Andrea; Gatto, Andrea; Strozzi, Antonio; Denti, Lucia
abstract

Difficult-to cut-materials are associated with premature tool failure, most likely in the case of complex geometries and this shapes. However, Nickel-based alloys are commonly used in high-temperature and aerospace applications, where thin deep holes are often required. Then, the only viable manufacturing solution relies on non-contact processes, like electrodischarge (ED) drilling. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. Aim of the paper is to study the effect of holes (0.8 mm diameter, aspect ratio 10) produced by ED drilling on the fatigue life of Inconel 718. Rotating bending fatigue tests are carried out on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Based on previous studies, extremal ED parameters are selected, giving best surface finish versus highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.

2013 - Bridges of debris in the edd process: going beyond the thermo-electrical model [Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Iuliano, L.
abstract

Electro-Discharge (ED) processes depend on the contemporaneous effect of many factors, which complicates process control/predictability and induced many authors in the last 60 years to work on explicative models. Studies split into two main approaches: theoretical and empirical. Theoretical works are based on the thermo-electrical theory and try to describe process phenomena by a physical model, with unavoidable assumptions and simplifications that cause a move away from veracity. On the contrary, experimentalists establish empirical models based on statistical analysis of results and optimization methods, but the findings are limited to domain-specific applications. In addition, numerous papers focus on single-spark analysis, failing in considering the interaction between successive discharges, or of transient phenomena as the presence of bubbles and debris in the gap. At present the scientific debate involves the ignition model, with two different points of view regarding the discharge-driving phenomenon: the debris bridge effect (pollutants in the dielectric drive the performances), and the dielectric strength effect (properties of the dielectric drive the performances). The paper addresses this dispute by investigating the debris formed during small-hole ED drilling of a 72 wt% Al2O3 - 28 wt% TiC composite. Particles are found to hollow out and pack within the gap, joining by necks. The first experimental evidence is given of the presence of chains and clusters of debris, towards a new model for electrodischarge processes that goes beyond the thermoelectric theory.

2013 - Investigation into the failure of Inconel exhaust collector produced by laser consolidation [Articolo su rivista]
Bassoli, Elena; Neil, Sewell; Denti, Lucia; Gatto, Andrea
abstract

Among layer manufacturing techniques, Laser Consolidation (LC) finds its ideal application in the production of thin-walled metal parts for industrial niches characterised by high innovation and product complexity. To fully exploit the technological potential, developments must be made to assess LC’s repeatability and reliability. Previous studies proved that high strength parts of fine microstructure are obtained if appropriate build strategies are used. The aim of this research is to analyse a racecar exhaust collector, built in Inconel by LC, relating the failure modes and microstructure to the construction plan. The exhaust collector component was built using a custom strategy and was run on a dynamometer before failing after approximately 1200 km. An investigation of the failure mechanism was carried out by a primary macroscopic analysis, aided by an X-ray control and dye penetrant test. Metallographic sections were then sampled from the critical areas to study the microstructure and relate it to the manufacturing process. Results proved that the distribution of primary microcracks associated with internal residual stresses caused by the build strategy and aggravated by differential shrinkage during the test thermocycles was responsible for ultimate failure. This issue was a result of build strategy and the non-coaxial laser head, therefore, alternative pathways could be developed capable of removing most, if not all, of the contributory factors. The analysed case suggests that LC build strategy selection is as critical to ensure low cycle fatigue resistance as component design and confirms that LC is effective in the production of advanced technological parts with high geometrical complexity given the correct build strategy.

2013 - Studies on electro discharge drilling of an Al2O3 –TiC composite [Articolo su rivista]
F., Calignano; Denti, Lucia; Bassoli, Elena; Gatto, Andrea; L., Iuliano
abstract

Ceramic matrix composites (CMCs) can be attractive for structural applications, but their machining by conventional methods is expensive and often critical. Complex geometries on advanced ceramics require contactless processes, such as electro discharge machining (EDM) or -drilling (EDD). These proved to be viable for CMCs with electrical resistivity below a critical value in the range of 1-3 Ωm. The condition is complied with by many CMCs: an example is alumina with titanium carbide. Material removal of ceramics by electrical discharges is a complex process involving different mechanisms, depending on the process setup. The paper describes an experimental study on EDD of 0.4 mm diameter holes with aspect ratio of 20 in Al2O3-TiC, using copper electrodes. Peak current (Ip), pulse-on time (ton) and pulse-off time (toff) are varied as independent variables. Four performance indicators are measured: material removal rate (MRR), electrode wear rate (EWrate), overcut (OC) and surface roughness (Ra, Sa). Empirical models are proposed to describe t the effect of process parameters on the output indicators. The analysis is supported by the observation of the surface and subsurface morphology, with the aim of investigating the material removal mechanisms and attaining a full comprehension of macroscopic results. It is found that removal mostly occurs by melting and evaporation and that surface morphology is determined by two phenomena ruled by pulse power. A process description is proposed, built around power as the ruling factor.

2012 - A combined Additive Layer Manufacturing / Indirect Replication method to prototype 3D vascular-like structures of soft tissue and endocrine organs [Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Gatto, Andrea; G., Spaletta; A., Paderno; N., Zini; A., Parrilli; R., Giardino; V., Strusi; D., Dallatana; S., Mastrogiacomo; A., Zamparelli; M., Iafisco; R., Toni
abstract

We describe an innovative methodology combining Additive Layer Manufacturing and indirect replication to reconstruct reticular-like, three-dimensional structures mimicking the vascular network of soft tissue and endocrine organs. Using a fractal-like algorithm capable of modeling the intraparenchymal vascular distribution of these viscera, single intraglandular branches of the human thyroid arteries were prototyped with synthetic resin, based on the algorithmic STL output and ALM techniques. Satisfactory dimensional accuracy was obtained for these models, which were used as masters to evaluate protocols for their indirect replication, through both single and double procedures. Additional studies were conducted using casts of the human kidney arteries, obtained by injection / corrosion of the isolated organ. Satisfactory 3D reproduction of the external morphology of the kidney vessels was achieved. We conclude that our approach has the potential to develop up to the reconstruction with biomaterials of an entire, intraparenchymal vascular tree of soft tissue and endocrine organs.

2012 - Bioengineering of the thyroid lobe: use of its stromal / vascular matrix as a scaffold for ex situ reconstruction [Abstract in Atti di Convegno]
Toni, R.; Strusi, V.; Zini, N.; Dallatana, D.; Mastrogiacomo, S.; Parrilli, A.; Giardino, R.; Lippi, G.; Spaletta, G.; Bassoli, Elena; Gatto, Andrea; Iafisco, M.; Sandri, M.; Tampieri, A.
abstract

Regenerative medicine of endocrine glands is one of the newest fields in biomedical research, and promises to become a primary strategy to treat a number of endocrine disorders. Using computational bioengineering we have recently suggested that the threedimensional (3D) geometry of the thyroid, stromal / vascular matrix may act as an epigenetic guidance for growth and differentiation of developing thyrocytes (1-3). To test this hypothesis, we have bioengineered ex situ (i.e. on the laboratory bench) a bioartificial rat thyroid lobe using its decellularized stromal/vascular matrix as a natural 3D scaffold, to be eventually recellularized with thyroid stem/precursor cells. Sprague-Dawley male rats (125- 225 g) were used as thyroid donors, and lobe matrixes were prepared using a N 2 freezing / Trypsin-EDTA / Triton-deoxycholate processing. Test matrixes were made electrondense, and analyzed by microTC (Skyscan 1172) to define their architecture. Primary thyroid cells were isolated after 72 h in primary monolayer culture, whereas presence of ABCG2-positive stem/precursor elements was determined using Western blotting. Following trypsinization, 250 - 450 x 103 cells were harvested and dropped onto the empty follicular cavities of the inner matrix of single lobe halves for homing . Cultures were kept in static conditions up to 14 days. The recellularized matrixes were either fixed in aldheydes and analyzed with light, transmission, and scanning electron microscopy, or denaturated and processed for ABCG2 immunoblotting (polyclonal rabbit anti-human 1:2000, Cell Signalling). Culture supernatants were collected every 48 h for assessment of FT3 and FT4 by immuno-chemiluminescence (Beckman-Coulter). Complete decellularization and maintenance of the 3D native architecture of the lobe matrix were achieved. Thyroid-derived cells including thyrocytes, epithelialmesenchymal elements, and stem/precursors were found to migrate inside matrix septa, selfassemble like follicule, and recellularize the decellularized native follicular spaces. Thyroid hormone secretion occurred for at least 7 days. These results show that the 3D matrix of the rat thyroid may guide both differentiated and stem-like elements to self-assemble into functional follicular units, up to the lobar recellularization. This raises the possibility that a bioartificial, immuno-tolerant thyroid gland be bioengineered ex situ using autologous stem cells, and eventually transplanted.

2012 - Electro-Discharge Drilling performance on parts produced by DMLS [Articolo su rivista]
Gatto, Andrea; L., Iuliano; F., Calignano; Bassoli, Elena
abstract

Cobalt-base alloys are generally adopted in applications that require wear-, corrosion- and heat resistance. In particular, Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy is currently being used in the aerospace and medical field. Both applications require product personalization and take advantage by parts manufacturing through additive technologies, such as Direct Metal Laser Sintering (DMLS). This technology still has limitations for the manufacture of small cavities, such as holes with diameters below 0.6mm, which require drilling of the additive manufactured part. This research aims at investigating the effects of Electro-Dicharge Drilling (EDD) on surface and subsurface features of CoCrMo samples built by DMLS. High aspect ratio holes are produced with diameter of 0.6 mm and depth fifteen times higher. Due to the absence of physical contact between tool and workpiece in EDD, machining forces are negligible and micro features can be produced with a high accuracy irrespective of the material hardness and strength. In this study, peak current, pulse-on-time and duty ratio are adopted as control factors using the Taguchi method. Material Removal Rate (MRR), Electrode Wear (EW) and surface roughness are measured as responses. Signal to noise ratios and ANOVA analysis lead to identify the significant process parameters, the levels that optimize each response and regression models for the performance criteria. From an overall evaluation of the responses an optimum process set-up can be determined which ensures high productivity and smooth surface finish, even if tool wear is medium-high. All the analysis is supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends.

2012 - Endocrine bioengineering: reconstruction of a bioartificial thyroid lobe using its three-dimensional (3D) stromal/vascular matrix as a scaffold. [Abstract in Atti di Convegno]
Strusi, V.; Zini, N.; Dallatana, D.; Mastrogiacomo, S.; Parrilli, A.; Giardino, R.; Lippi, G.; Spaletta, G.; Bassoli, Elena; Gatto, Andrea; Iafisco, M.; Sandri, M.; Tampieri, A.; Toni, R.
abstract

To test the feasibility of reconstructing ex situ an entire bioartificial thyroid gland suitable for transplantation we have bioengineered a rat thyroid lobe using its decellularized stromal / vascular matrix, eventually 3D recellularized with thyroid stem / precursor cells. Sprague-Dawley male rats (220–240 g) were used as thyroid donors, and lobe matrixes obtained by freezing / detergent / enzyme processing. Test matrixes were made electrondense and analyzed by microtomography (microTC). Primary thyroid cells and ABCG2-positive, thyroid stem/precursor elements were expanded and isolated either in primary monolayer or 3D matrigel cultures for 72 h, using low-glucose DMEM and high vs low serum media. Following trypsinization, 250–450.000 cells were harvested to coat the empty follicular and vascular cavities of the inner matrix surface, and grown up to 21 days in static conditions. The colonized matrixes were either fixed in aldheydes for processing by light (LM), transmission (TEM) and scanning electron (SEM) microscopy or denaturated to get total proteins, and run for ABCG2 westen blotting. Culture supernatants were collected every 48 h, and free thyroid hormone levels assessed with chemiluminescent immunoassays. Complete decellularization and maintenance of the 3D native architecture of the thyroid SVS were achieved. Thyroid-derived cell, including differentiated thyrocytes, elements showing epithelial-mesenchymal transitions, and stem/precursor cells were found both to heterotopically migrate inside matrix septa and to orthotopically aggregate, link and give rise to intracytoplasmic cavities, up to recellularize the decellularized follicular spaces. Thyroid hormone secretion occurred for at least 7 days. These results show that the natural 3D matrix of the rat thyroid acts as a scaffold to bioengineer ex situ a functional thyroid lobe with progenitor-like elements (Fig.), suggesting that a biocompatible construct can be realized for eventual transplantation replacement. Grants FIL09, PRIN082008ZCCJX4, FIRB2010RBAP10MLK7

2012 - Joining mechanisms and mechanical properties of PA composites obtained by Selective Laser Sintering [Articolo su rivista]
Bassoli, Elena; Gatto, Andrea; L., Iuliano
abstract

PURPOSEAdditive Manufacturing is today a viable industrial solution besides traditional processes. Techniques like Selective Laser Sintering address the issues of digital production and mass customization in a variety of materials. Composite parts can be obtained with specific functional and mechanical properties. Building orientation during Additive Manufacturing often causes anisotropy of parts’ properties that is still unspecified in technical information. The paper investigates the mechanical performances and failure mechanisms of an Aluminium-filled polyamide and of a new Alumina-polyamide composite produced by SLS, in comparison with unfilled PA.DESIGN/METHODOLOGY/APPROACHA specific focus is set on the evaluation of primary and secondary anisotropy in the case of metal or ceramic filler, as well as on the specific contribution of powder distribution modes and joining phenomena. Macroscopic mechanical tests and the observation of joining and failure micro-mechanisms are integrated.FINDINGSThe results prove the absence of relevant anisotropy amongst specimens that are produced with the axis parallel to the plane of powder deposition. Samples whose axis is parallel to the growth direction Z, instead, reveal a significantly different response with respect to other orientations.ORIGINALITY/VALUEAn original explanatory model is assumed and validated, based on an anisotropic distribution of the reinforcing particles during parts’ production, which determines the efficacy of the strengthening mechanisms during crack propagation.

2012 - PREPARAZIONE E CARATTERIZZAZIONE DI COMPOSITI POLI(BUTILENE TEREFTALATO)/GRAFENE DA POLIMERIZZAZIONE IN-SITU DEL MONOMERO CICLICO [Relazione in Atti di Convegno]
P., Fabbri; Bassoli, Elena; S., Bittolo Bon; L., Valentini
abstract

La viscosità “ultra bassa” degli oligomeri ciclici del butilene tereftalato è stata sfruttata per attivare la loro polimerizzazione per apertura d’anello in presenza di grafene, al fine di ottenere compositi omogenei poli(butilene tereftalato)/grafene (PBT/G) (0.5-1.0 %wt G). Gli studi morfologici dimostrano che il metodo consente facilmente di ottenere compositi in cui le lamelle di G sono altamente disperse nella matrice polimerica. I risultati della cromatografia GPC mostrano che, a parità di tempo di polimerizzazione, l’aumentare del contenuto di G causa l’ottenimento di pesi molecolari inferiori per il PBT. Le proprietà termiche dei campioni PBT/G, studiate mediante analisi calorimetrica differenziale a scansione e termogravimetria, mostrano che l’aumentare del contenuto di G non influenza significativamente la cristallizzazione del PBT, mentre la stabilità termica del polimero è fortemente aumentata dal G. Tutti i compositi PBT/G preparati sono elettricamente conduttivi; è stato anche dimostrato che un annealing termico dei compositi PBT/G condotto in presenza di campo elettrico induce un significativo aumento della loro conducibilità.

2012 - Preparation and characterization of poly (butylene terephthalate) / graphene composites by in-situ polymerization of cyclic butylene terephthalate [Articolo su rivista]
P., Fabbri; Bassoli, Elena; S., Bittolo Bon; L., Valentini
abstract

The ultra-low viscosity of cyclic butylene terephthalate oligomers has been exploited to perform their in-situ ring-opening polymerization in the presence of graphene, to obtain homogeneously dispersed poly(butylene terephthalate)/graphene (PBT/G) composites containing 0.5 to 1.0 %wt of graphene. The results of gel permeation chromatography show that increasing amounts of graphene causes a decrease in the average molecular weight of PBT if the time of polymerization is kept constant, and morphological investigations performed by electron microscopy and x-rays diffraction show that high levels of dispersion of the G sheets are easily obtained by this method of composites processing. Thermal properties of the composites were studied by differential scanning calorimetry and thermogravimetric analysis; results indicate that increasing amounts of G do not strongly influence the degree of crystallinity and the crystallization temperature of PBT, while its thermal stability is significantly increased by the presence of G. All the PBT/G composites demonstrated to be electrically conductive; we found that the electric field assisted thermal annealing of the PBT/G composites induces an increase in conductivity.

2011 - Dimensional tolerances and assembly accuracy of dental implants and machined- versus cast-on abutments [Articolo su rivista]
Malaguti, Giuliano; Denti, Lucia; Bassoli, Elena; I., Franchi; Bortolini, Sergio; Gatto, Andrea
abstract

Background. The clinical application of prosthetic components obtained by different manufacturing processes lacks technological foundation: the dimensional tolerance of individual parts and their assembly accuracy are not known. The rotational misfit of the hexagonal connection is critical in single tooth implant restorations, but no standard control procedures are available for its evaluation.Purpose. The research aimed at proposing a new protocol for the dimensional assessment of implant-abutment connections, based on non-contact measurement and statistical data processing. The procedure was applied to machined- and cast-on abutments, as well of the matching implants.Materials and Methods. Three groups of 5 abutments each were studied: machined titanium abutments, premachined calcinable abutments before casting procedures and the same specimens after casting. A group of 5 corresponding implants was considered as well. Twice the apothem was measured on each hexagon through an optical measuring microscope. The data were processed to obtain the international tolerance (IT) grade. The rotational misfit was then calculated using the apothems of the external and the internal hexagon.Results. All the components were classified between IT8 and IT9 and the maximum rotational misfit was around 3-4° for all the assemblies, inferior to the critical limits for the screw joint stability.Conclusion. An original measuring protocol was developed, independent of parts assembly and based on international tolerances. An objective dimensional characterization of prosthetic components and assemblies has been achieved, which is the basis for their reliability in clinical applications.

2011 - Ex situ bioengineering of bioartificial endocrine glands: A new frontier in regenerative medicine of soft tissue organs [Articolo su rivista]
R., Toni; A., Tampieri; N., Zini; V., Strusi; M., Sandri; D., Dallatana; G., Spaletta; Bassoli, Elena; Gatto, Andrea; A., Ferrari; I., Martin
abstract

Ex situ bioengineering is one of the most promising perspectives in the field of regenerative medicineallowing for organ reconstruction outside the living body; i.e. on the laboratory bench. A number of hollowviscera of the cardiovascular, respiratory, genitourinary, and digestive systems have been successfullybioengineered ex situ, exploiting biocompatible scaffolds with a 3D morphology that recapitulates thatof the native organ (organomorphic scaffold). In contrast, bioengineering of entire soft tissue organsand, in particular endocrine glands still remains a substantial challenge. Primary reasons are that noorganomorphic scaffolding for endocrine viscera have as yet been entirely assembled using biocompatiblematerials, nor is there a bioreactor performance capable of supporting growth within the thicknessrange of the regenerating cell mass which has proven to be reliable enough to ensure formation of a completemacroscopic gland ex situ. Current technical options for reconstruction of endocrine viscera includeeither biocompatible 3D reticular scaffolds lacking any organomorphic geometry, or allogenic/xenogenicacellular 3D matrices derived from a gland similar to that to be bioengineered, eventually recellularizedby autologous/heterologous cells. In 2007, our group designed, using biocompatible material, anorganomorphic scaffold–bioreactor unit for bioengineering ex situ the human thyroid gland, chosen as amodel for its simple anatomical organization (repetitive follicular cavities). This unit reproduces both the3D native geometry of the human thyroid stromal/vascular scaffold, and the natural thyrocyte/vascularinterface. It is now under intense investigation as an experimental tool to test cellular 3D auto-assemblyof thyroid tissue and its related vascular system up to the ex situ generation of a 3D macroscopic thyroidgland. We believe that these studies will lay the groundwork for a new concept in regenerative medicineof soft tissue and endocrine organs; i.e. that the organomorphism of a biocompatible scaffold–bioreactorcomplex is essential to both the 3D organization of seeded stem cells/precursor cells and their phenotypicfate as glandular/parenchymal/vascular elements, eventually leading to a physiologically competent andimmuno-tolerant bioconstruct, macroscopically suitable for transplantation and clinical applications.

2011 - Grinding micro-mechanisms of a sintered friction material [Articolo su rivista]
E., Atzeni; Bassoli, Elena; L., Iuliano
abstract

New brake pad materials are inhomogeneous compounds with a variety of metallic and ceramic phases, whose interaction with the tool during the grinding operation is not fully understood. Yet, ground surface quality strongly influences the bedding-in phase. This research attempts to explain how grinding operation affects the pad surface. The purpose is pursued by adopting an investigation protocol merging macroscopic outcomes with the study of chip-removal mechanisms and of the ground surface morphology in the micro-scale. A multi-scale inspection procedure is proposed to assess the performances of a machining operation on complex materials, where the descriptive power of standard technological tests becomes inadequate.

2011 - High Speed Milling of tool steel dies for aluminium extrusion: surface roughness, dimensional tolerance and chip removal mechanisms [Articolo su rivista]
Bassoli, Elena; A., Salmi; P., Minetola
abstract

Die finishing has a fundamental importance to ensure a good quality of Aluminium extruded parts and involves important economic effects due to the vastness of metalworking industry and the relatively short tool life in this field. Maximum machining efficiency is thus crucial. The research addresses optimization of finishing performances on tool steel extrusion dies. Milling tests are carried out on semi-manufactured parts to ensure adherence to standard industrial technological chain, varying cutting parameters towards the field of high speed machining. Dimensional tolerance is determined on die lands. Land surface roughness is measured through a multiscale approach and modelled as a function of cutting speed and feed. The above methodology enables a correlation between macroscopic process outcomes and chip removal mechanisms in the microscale.

2011 - New approaches to prototype 3D vascular-like structures by additive layer manufacturing. [Relazione in Atti di Convegno]
Bassoli, Elena; Denti, Lucia; Gatto, Andrea; A., Paderno; G., Spaletta; N., Zini; V., Strusi; D., Dallatana; R., Toni
abstract

In this paper preliminary results are summarized on the use of a combined Additive Layer Manufacturing (ALM) and indirect replication methodology to reconstruct reticular-like, three-dimensional (3D) structures mimicking the 3D vascular network of the adult human thyroid gland. In a first step, we developed a fractal-like algorithm capable of modeling the native arterial distribution of the adult thyroid lobe, allowing for vascular growth within its geometrical domain. Although some arbitrary simplifications were adopted, yet the vascular density of the computational simulation showed good consistency with that of a native thyroid lobe. In a second step, single vascular branches were prototyped based on the STL output of the algorithm and ALM techniques, up to the achievement of a model having satisfactory geometrical/morphological accuracy. In a third step, the problem of reproducing the vascular geometry with a biocompatible polymer was ad-dressed, and different protocols of replication technology were evaluated. Limits and possible methodological solutions are discussed.

2011 - Performance Optimization in Machining of Aluminium Alloys for Moulds Production: HSM and EDM [Capitolo/Saggio]
Gatto, Andrea; Bassoli, Elena; L., Iuliano
abstract

Aluminium alloys offer many machining advantages such as excellent machinability and finish degree with high cutting speed, low cutting forces, outstanding tool life. Elevated thermal exchange and weight reduction compared to steels are additional characteristics that lead to increasing applications in the automotive and aerospace industry and in the field of mould production. Relatively recent Aluminium alloys derived by aeronautical uses offer very high strength and hardness: the gap with steels is thus reduced or even reversed in terms of specific properties. Two examples are Al 2219 and Al 7050. If the first examples of Aluminium moulds for plastic injection were limited to preproduction, the properties of these new alloys match the requirements of medium production volumes, which are also the main market demand.The research focuses on two distinct operations typical of the tooling phase: High Speed Milling (HSM) and Electro Discharge Machining (EDM). In both cases the machining performance is evaluated in specific tests through a multiscale approach: measurements of the macroscopic process outputs are merged with the investigation of mechanisms at a microscopic level. The methodology enhances optimization chances with respect to traditional practice.As to milling operation, several studies prove that Aluminium alloys allow the advantageous adoption of high cutting speed, ensuring time and cost savings together with excellent surface finish and low tool wear. Yet, the traditional laws between cutting parameters do not apply to the field of high-speed machining and the mechanisms of chip removal still need investigation. In order to appraise the machinability of Al 2219 and Al 7050 alloys, high speed milling tests using uncoated carbide tools are performed. The tests are carried out on Al 7075 as well, an alloy of common employment for preproduction moulds, to provide control data. Cutting speed ranges from 600 to 2200 m/min and feed per tooth between 0.075 and 0.18 mm/tooth. Correlations between cutting parameters and surface finish, tool wear and chip formation mechanisms are studied with the aid of SEM observation and EDX semi-quantitative analysis. The best surface finish is obtained for Al 7050 with high cutting speed and low feed. No tool wear is observed in the considered conditions. Microscope observation of tools and chip proves that surface finish is ruled by tool-chip adhesion and that alloys having almost the same chemical composition can provide substantially different results due to grain dimension and distribution.EDM is used for the machining of complex shapes and textures typical of plastic injection moulds. Aim of this research is to verify the EDMachinability of the Aluminum alloys previously studied with regard to HSM. Literature studies on the specific subject are very rare. EDM tests are planned and performed using electrolytic copper electrodes on Al 7050 and Al 2219, plus Al 7075 as a control. A benchmark is chosen whose geometry points out the typical problems of moulds machining and allows an easy and significant dimensional characterization, because of the presence of different geometrical features and relative orientations. Roughing, semifinishing and finishing cycles are conducted; then the effect of process parameters on dimensional tolerance, surface finish and electrode wear is studied. Moreover, the electrodes and the machined surfaces are observed through optical- and scanning electron microscope (OM, SEM) to verify the presence and composition of deposits on the electrodes surfaces, as well as the eroded surfaces morphology on the workpieces. No remarkable differences can be identified as to dimensional tolerances between the three alloys. A slight trend to give lower roughness values can be noticed for the alloy 7050. The results are coherent with the regular morphology observed on the machined surfaces of this alloy. The observation of the erosion mechanisms allows to affirm that, for th

2011 - Sintesi e proprietà di compositi poli(butilene tereftalato)/grafene preparati mediante polimerizzazione in situ del monomero ciclico [Relazione in Atti di Convegno]
P., Fabbri; L., Valentini; S., Bittolo Bon; Bassoli, Elena; Pilati, Francesco
abstract

Questo studio tratta della preparazione di compositi poli(butilene tereftalato)/grafene mediante polimerizzazione in-situ del monomero ciclico butilene tereftalato per apertura d’anello catalizzata da butil stagno cloruro diidrossido in presenza di grafene. Le caratterizzazioni condotte sui compositi di PBT contenenti 0.5%, 0.75% oppure 1.0% di grafene hanno mostrato in tutti i casi morfologie estremamente omogenee, bassa resistività superficiale, buon grado di esfoliazione del grafene e mantenimento di un elevato grado di cristallinità nella matrice polimerica.

2011 - Thermoplastic Resin Transfer Moulding in a rapid manufactured mould [Relazione in Atti di Convegno]
E., Atzeni; F., Calignano; L., Iuliano; P., Minetola; A., Salmi; Bassoli, Elena; Denti, Lucia; Gatto, Andrea
abstract

Resin Transfer Moulding (RTM) is a low-cost process for the production of composite parts with thermosetting resins. However, the economic convenience is lost in the case of large components, such as aeronautical panels, because of the high tooling cost. Step milling of a resin master for the electro-deposition of a nickel shell is proposed in this study as a valid alternative for the fabrication of a resin transfer mould. This solution allows overcoming the limitations regarding part size and cutting down tooling costs, but the expected dimensional accuracy needs to be assessed. On the field of materials, innovative thermoplastic resins are now available that can be used in the formof lowviscosity oligomers for optimal mould filling and fibre impregnation. Subsequent in situ polymerization provides high toughness composites. Cyclic Butylen Terephtalate (CBT), which polymerizes into PBT (Poly-Butylen Terephtalate), is studied in this work. The research focuses on two objectives: quantifying the dimensional accuracy of the technological chain and setting up the process of in situ polymerization.

2010 - DMLS DENTAL ALLOYS VS TRADITIONAL TECHNIQUE [Abstract in Rivista]
Bortolini, Sergio; Gatto, Andrea; Natali, Alfredo; Y., Ucar; G., Montin; Bassoli, Elena; Denti, Lucia; Consolo, Ugo; L., Iuliano; T., Akova
abstract

Additive Layer Manufacture (ALM) of dental prostheses allows the direct fabrication of parts from CAD data, replacing a human-sensible process with a faster reliable automatic one. Direct Metal Laser Sintering (DMLS) of Cr-Co alloys produces parts to be directly finished with ceramic and employed. PURPOSE: This study evaluated (1) the application of DMLS process for obtaining final dental prostheses in Co-Cr alloy, to compare mechanical characteristics of cast parts and layer-manufactured ones produced with different alloys and processes; and (2) the effect of porcelain firing cycles on mechanical properties. METHODS: This study was conducted on three classes of tensile specimens in five groups of six specimens: class 1 – 12 specimens built by DMLS (PM100T – Phenix System, France) with Co-Cr powder NOBIL 4000S (NOBIL METAL - Italy) divided in two groups (6 specimens were processed with ceramic heat treatment); class 2 – 12 specimens built by traditional lost-wax casting from Co-Cr bars for fixed prostheses V-CERAM MAGI LINE (SHERA - Germany) divided in two groups (6 specimens were processed with ceramic heat treatment); class 3 – 6 tensile specimens built by traditional lost-wax casting from Cr-Co bars for partial removable prostheses REMANIUM 800+ (Dentaurum - Germany). RESULTS: UTS of all sintered specimens (1174±165 MPa) was higher than of cast ones (503±45 MPa, 499±62 MPa, 712±51 MPa, respectively, for as cast Co-Cr, heat treated Co-Cr, and Remanium) where many porosities were found. UTS decreases after heat-treatment both for cats and DMLS parts. Yield strength was also highest for the laser sintered group (1148±161 MPa).No significant idfference was found for the elastic modulus of compared groups (P=0.398). CONCLUSIONS: DMLS of Co-Cr alloys produces excellent strength and absence of defects compared to traditional casting. This result is due to the fine microstructure obtained by DMLS (high thermal rate, heterogeneous nucleation).

2010 - Deep drilling of aluminium die-cast parts: surface roughness, dimensional tolerance and tool-chip interaction [Articolo su rivista]
Bassoli, Elena; L., Iuliano; A., Salmi
abstract

Many automotive applications require deep drilling on pressure die-cast parts in Aluminium alloys. Aim of the research was to understand if common cutting practices, usually determined on raw materials, can be successful on semi-manufactured parts as well, having an inhomogeneous microstructure. A specific investigation was carried out on deep drilling of a EN_AB-46000 cylinder block, varying technological parameters (cutting speed, feed, tool, lubrication). Dimensional tolerance and surface roughness were measured and statistically analyzed. The quantitative analysis of the process macroscopic performances was combined with an investigation of microstructural aspects of the material, their effects on chip formation and tool-chip interaction.

2010 - FRACTURE RESISTANCE ANALYSIS OF SINTERED AND CASTED COBAL/CROMIUM ALLOYS [Abstract in Rivista]
Natali, Alfredo; Bortolini, Sergio; G., Montin; Gatto, Andrea; L., Iuliano; Bassoli, Elena; Denti, Lucia; Y., Ucar; A., Tolga; Consolo, Ugo
abstract

THIS STUDY WANTS TO EVALUATE THE APPLICATION OF SLS PROCESS FOR OBTAINING FINAL DENTAL PROSTHESIS IN CR-CO ALLOY, DEVELOPING EXPERIMENTAL PLAN WITH THE PURPOSE TO MADE A COMPARATIVE ANALYSIS OF MECHANICAL CHARACTERISTICS BETWEEN CASTS PARTS AND SINTERED ONES PRODUCTED WITH DIFFERENT ALLOYS AND PROCESSES.

2010 - On the effects of build orientation in powder-fed Additive Layer Manufacture of steel 316L [Relazione in Atti di Convegno]
Bassoli, E.; Gatto, A.; Sewell, N. T.; Johns, D.
abstract

The major interest in the field of Additive Layer Manufacturing is at present the emancipation from prototyping towards industrial production. To this aim, a significant limitation is still the difficulty in predicting part characteristics and ensure robustness and repeatability. Laser Consolidation (LC) is a powder-fed process producing net-shape metal components with good metallurgical soundness, high strength and duc-tility. The specific LC head configuration is likely to cause direction dependant features varying not only along and perpendicular to the build direction, but also within each layer. Aim of the research is to investigate the mechanical properties and microstructure of AISI 316L parts built by LC, with a specific focus on the ef-fects of the direction of build, either axially aligned with the head or orthogonal to it. The results confirmed high hardness and strength and excellent ductility of LC parts. Anisotropy of mechanical response was quanti-fied and related to microstructure.

2009 - Additive Layer Manufacture of Tensile Tests Specimens in Stainless Steel 316L by Laser Consolidation [Relazione in Atti di Convegno]
Bassoli, Elena; N. T., Sewell
abstract

The major interest in the field of Additive Layer Manufacturing is at present the emancipation from prototyping towards industrial production. To this aim, a significant limitation is still the difficulty in predicting part characteristics and ensure robustness and repeatability. Laser Consolidation (LC) is a powder-fed process producing net-shape sheet-like metal components with good metallurgical soundness, high strength and ductility. The specific LC head configuration is likely to cause direction dependant features varying not only along and perpendicular to the build direction, but also within each layer. Aim of the research is to investigate the mechanical properties and microstructure of AISI 316L parts built by LC, with a specific focus on the effects of the direction of build, either axially aligned with the head or orthogonal to it. The results confirmed high hardness and strength and excellent ductility of LC parts. Anisotropy of mechanical response was quantified and related to microstructure.

2009 - CAST VERSUS LASER-SINTERED CR-CO ALLOYS: STUDY ON MECHANICAL CHARACTERISTICS [Abstract in Rivista]
Natali, Alfredo; Bassoli, Elena; Denti, Lucia; Berzaghi, Andrea; M., Franchi; Bortolini, Sergio; Consolo, Ugo
abstract

Objectives:Additive Layer Manufacture of dental prostheses allows the direct fabrication of parts from CAD data, replacing a human-sensible process with a faster reliable automatic one. Direct Metal Laser Sintering (DMLS) of Cr-Co alloys produces parts to be directly finished with ceramic and employed. Their clinical application requires a solid know-how on mechanical and functional characteristics, with respect to traditional cast parts.Methods:Tensile specimens were built (ASTM E8M) both by DMLS and traditional lost-wax casting, using the same Cr-Co alloy. An experimental plan was designed to evaluate the effect of all process phases. Standard parameters were used on EOSINT-M270 to fabricate the laser-sintered specimens. A group was left as-sintered (DMLS_L) and the others were heat-treated for stress-relief (DMLS). Wax parts were built by drop-on-demand, invested in ceramic and burnt away before casting (CAST). Then, two groups of specimens were subjected to the high temperature treatment used in ceramic covering without deposition (DMLS_H, CAST_H). On all specimens (6 for each of 5 groups) thickness was measured through a measuring microscope. Roughness was determined on Lm=4,8mm. Specimens were tensile tested obtaining UTS and percent elongation.Results:No significant dimensional variations were noticed among different processes. Sintered parts are on average rougher than cast ones (Ra~3.8vs2.6µm). UTS of all sintered specimens (~1400MPa) is almost double than of cast ones, where many porosities were found. Unlike cast parts, heat-treatment increases UTS for DMLS. Laser-sintered specimens are also much more fragile than cast ones (εb~5 vs 20%).Conclusion:DMLS of Cr-Co alloys produces excellent strength and absence of defects with respect to traditional casting. Low εb values are not critical, since deformation of the final prostheses is limited by the ceramic layer fragility. Slightly higher roughness of DMLS parts is likely to improve mechanical bonding with the ceramic layer or might be smoothed.

2009 - Comparative Mechanical Evaluation Of Three Y-TZP Formulations In Five Shades [Abstract in Rivista]
Berzaghi, Andrea; Denti, Lucia; Bassoli, Elena; A., Natali; M., Franchi; Bortolini, Sergio; Consolo, Ugo
abstract

Objectives: As integral structures in Y-TZP spread in dental practice, verifying the mechanical characteristics reported in literature and if they are affected by coloration becomes imperative. This study aims at determining flexural strength and hardness of three Y-TZP types in five different colours. Methods: Three commercial formulations of Y-TZP (A, B, C) were considered: as-received natural white and 4 different shades. Specimens were ASTM C1161, five for each typology (75 parts in 15 groups). Blocks of pre-sintered material were CAD/CAM dry machined, then some were coloured by dipping, before the last step of sintering (Tmax=1450°C). Three point flexural tests were performed to obtain flexural strength (S). After polishing Vickers hardness (HV1) was measured (ISO 14705). T-test for independent samples was carried out on the data, to evaluate the presence of significant differences (positive t-test) between the groups. Results: Mean S was between 500 and 800MPa, much lower than declared by the producers (1200 MPa). For B and C S tends to decrease with colour, but not significantly. For A S increases with colour and two cases present positive t-tests compared to natural white. There aren't significant differences between white specimens of the three companies. As to other shades, the t-test is positive between B and C for three colours over four and between A and B for one colour. HV1 results between 15.8 and 17GPa (in technical specifications HV=12.2 GPa). Colours significantly influence hardness, shifting towards higher values, for nearly all the studied comparisons. Conclusion: Material properties resulted greatly different from technical specifications. Flexural strength values suggest a careful design of frameworks connectors, especially in posterior prostheses. The studied materials resulted harder than expected, in particular when coloured. Colour proved to affect the performances in many cases, requiring esthetical and mechanical requirements to be merged

2009 - Direct Metal Rapid Casting: mechanical optimization and tolerance evaluation [Articolo su rivista]
Bassoli, Elena; E., Atzeni
abstract

Aim of the research was to optimize the mechanical performances of parts produced by the Z-Cast Direct Metal Casting process varying the thermal treatment parameters. Adopting the optimized settings, a specific dimensional evaluation was planned to calculate the International Tolerance (IT) grade ensured by the process.Cylindrical Z-Cast samples were manufactured and heat-treated varying time and temperature. The baked parts underwent compression tests and the rupture surfaces were observed using the S.E.M.. A regression analysis was performed on the results to optimize the baking process.For the dimensional assessment a specific benchmark was designed, built and treated. It was measured before and after baking using a CMM and the results were processed to obtain the IT grade.The results proved that in the heat treatment of Z-Cast parts time has a negligible effect on the compressive strength, whereas temperature can be optimized for best mechanical response. The IT grade was calculated for green and baked parts; separately in all three directions in space. Tolerance was proved to be fundamentally the same in every direction and independent on the heat treatment. The considered Rapid Casting process can be classified in IT15 grade.The paper suggests an original approach to improve knowledge of the Z-Cast process. The study of the building phenomena was combined with macroscopic measurements to develop a solid understanding of the expected performances, which is fundamental in order to support the industrial application of the technology.

2009 - Microwave Rapid Sintering of Nanostructured Stainless Steel Metal Powders [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Bassoli, Elena; Denti, Lucia; Gatto, Andrea
abstract

Nanostructured AISI430 stainless steel powders, obtained by high energy milling have been uniaxially pressed in order to obtain 8 mm diameter cylindrical compacts. Microwave sintering of the green compacts has been performed in a single mode microwave applicator, at 2.45 GHz. Maximum sintering temperature of each sample, monitored using a sapphire optical fibre, was varied in the 1000-1200°C range, with heating rates in the 20-30 K/s range, applying 1200 W of microwave forward power. Dense nanostructured samples, with less than 1% porosity were obtained, presenting small local variation of Cr content in proximity of the necking region. Rapid microwave sintering helps maintaining the nanostructure, despite a non homogenous densification due to the uneven electromagnetic field distribution in the single-mode applicator

2009 - “Microwave Rapid Sintering of Nanostructured Stainless Steel Metal Powders”,, Vol. 3, , Denmark, 2009, 143-148, ISBN [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Bassoli, Elena; Denti, Lucia; Gatto, Andrea
abstract

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2008 - Additive Layer Manufacture of Tensile Tests Specimens in Stainless Steel 316L by Laser Consolidation [Relazione in Atti di Convegno]
N. T., Sewell; Bassoli, Elena; Gatto, Andrea; K. E., Evans
abstract

Laser Consolidation (LC) is an Additive Layer Manufacturing (ALM) process which produces net-shape fully dense metal parts. LC uses a synchronised pulsed Nd:YAG laser and a powder delivery unit to build parts which exhibit excellent mechanical properties and impact resistance. These properties may be tailored at build time by modifying build parameters but the non-coaxial nature of the LC head assembly causes direction dependant features. This paper investigates the mechanical properties and microstructure of AISI 316l parts built by LC. Tensile test specimens were constructed in different orientations and underwent tensile testing and SEM observation. All the specimens exhibited high elongation at break and Ultimate Tensile Strength (UTS) but parts properties were significantly affected by build direction. Parts built by relative head movement along the plane of LC head assembly (X direction) were more ductile and stronger compared with parts constructed orthogonally. SEM analysis revealed a higher presence of voids in the latter. It was speculated that the voids were the major factor in the reduction in strength and ductility of the parts.

2008 - Additive Layer manufacture of Tensile test specimens in stainless steel 316l by Laser Consolidation [Articolo su rivista]
Sewell, N. T.; Bassoli, E.; Gatto, A.; Evans, K.
abstract

Laser Consolidation (LC) is an Additive Layer Manufacturing (ALM) process which produces net-shape fully dense metal parts. LC uses a synchronised pulsed Nd:YAG laser and a powder delivery unit to build parts which exhibit excellent mechanical properties and impact resistance. These properties may be tailored at build time by modifying build parameters but the non-coaxial nature of the LC head assembly causes direction dependant features. This paper investigates the mechanical properties and microstructure of AISI 316l parts built by LC. Tensile test specimens were constructed in different orientations and underwent tensile testing and SEM observation. All the specimens exhibited high elongation at break and Ultimate Tensile Strength (UTS) but parts properties were significantly affected by build direction. Parts built by relative head movement along the plane of LC head assembly (X direction) were more ductile and stronger compared with parts constructed orthogonally. SEM analysis revealed a higher presence of voids in the latter. It was speculated that the voids were the major factor in the reduction in strength and ductility of the parts.

2008 - Study of the EDM process effects on Aluminum alloys [Articolo su rivista]
L., Iuliano; M. G., Violante; Gatto, Andrea; Bassoli, Elena
abstract

Aluminum alloys offer many machining advantages such as excellent machinability and finish degree, elevated thermal exchange, reduction of weight. Till now aluminum moulds have been employed only for preproduction; with the new alloys Al 2219 and Al 7050, which have outstanding properties, we can think about medium productions of plastic components obtained by injection molding. Electro Discharge Machining is used for the machining of complex shapes typical of plastic injection moulds. In order to evaluate the machinability of these new alloys, some EDM tests have been planned. Comparison tests have also been done on Al 7075, an alloy of common employment for preproduction moulds, to have precise control data. The tests allowed understanding the correlations among process parameters, dimensional tolerances, surface finish and electrode wear. Moreover, the electrodes and the machined surfaces have been observed at the optical- and scanning electron microscope (OM, SEM) to understand the EDM mechanisms.

2007 - 3D Printing technique applied to Rapid Casting [Articolo su rivista]
Bassoli, Elena; Gatto, Andrea; L., Iuliano; M. G., Violante
abstract

Purpose To verify the feasibility and evaluate the dimensional accuracy of two Rapid Casting solutions based on 3D Printing technology: investment casting starting from 3D-printed starch patterns and the ZCast process for the production of cavities for light-alloys castings.Design/methodology/approach Starting from the identification and design of a benchmark, technological prototypes were produced with the two Rapid Casting processes. Measurements on a CMM machine allowed calculating the dimensional tolerances of the proposed technological chains. The predictive performances of CAE software were verified when applied to the ZCast process modelling.Findings The research proved that both the investigated Rapid Casting solutions are effective in obtaining cast technological prototypes in short times and with low costs, with dimensional tolerances that are completely consistent with metal casting processes.Practical implications The research assessed the feasibility and dimensional performances of two Rapid Casting solutions, providing data that are extremely useful for the industrial application of the considered technologies. Originality/value The paper deals with experimental work on innovative techniques on which data are still lacking in literature. In particular, an original contribution to the determination of dimensional tolerances and the investigation on the predictive performances of commercial CAE software is provided.

2007 - Direct Metal Rapid Casting: mechanical optimization and tolerance evaluation. [Relazione in Atti di Convegno]
Atzeni, E; Bassoli, Elena
abstract

The ZCast Direct Metal Casting process allows the direct fabrication of ceramic moulds and cores through Three Dimensional Printing. It ensures low costs and extremely short times for the production of cast metal prototypes, but the knowledge on the expected performances is still lacking. This paper describes a set of experiments done on Z-cast components, in order to evaluate the mechanical and dimensional performances and their dependence on the production parameters.Cylindrical samples have been manufactured and subjected to different posttreatments, varying process time and temperature. The baked parts, as well as some green ones for comparison, have undergone compression tests and the rupture surfaces have been observed using S.E.M.. The results proved that time has anegligible effect on the compressive strength, whereas temperature can be optimized for parts’ best mechanical response. For the evaluation of the dimensional performances, a specific benchmark has been designed, built and treated following the thermal cycle previously identified. Uniformly distributed measurements have been made on the benchmark before and after baking using a CMM. In the last part the paper evaluates the tolerance values and calculates the correct IT class location for the considered process.

2005 - Joining mechanisms and mechanical properties of PA-Al composites obtained by Selective Laser Sintering [Relazione in Atti di Convegno]
Bassoli, Elena
abstract

Innovative metal-polymer composites for Selective Laser Sintering (SLS) have been recently developed, characterized by high mechanical performances and high surface quality after finishing. An example is the polyamide-aluminium composite Alumide, suitable for functional prototypes as well as for Rapid Tooling and Rapid Manufacturing applications. The great advantages, in terms of reduced times and costs for the product launching, can be properly exploited only through a deep knowledge concerning the parts performances as a function of the construction process. The present research aimed at overcoming the trial-and-error approach diffused in industrial practice and filling a gap in existing literature. An accurate characterization has been carried out of PA-Al composite parts produced by SLS, investigating the effect of the manufacturing anisotropy on the mechanical performances, both in terms of additive construction and laser sintering strategy. The accurate observation of the joining and failure micromechanisms allowed accounting for the anisotropy of the macroscopic characteristics, developing an original model for the interpretation of the consolidation phenomena and mechanical behaviour.

2005 - New developments in steel formulations for Direct Laser Sintering: characterization and evaluation of joining mechanisms. [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; Iuliano, L.
abstract

Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions. Even so, the spread of these techniques is hardly supported by scientific knowledge about the micro-mechanisms ruling the macroscopic performances of the part. In the present research, parts produced by Direct Laser Sintering technique have been studied, using Direct Steel 20 and the innovative Direct Steel H20. The research aimed at investigating the sintering mechanisms and their influence on the failure modes and mechanical performances. Tensile specimens have been produced, with different orientations in regard to laser path, to study the effect of laser sintering strategy on the anisotropy of parts per-formances. The tensile tests results have been correlated to the SEM observation of the specimens rupture sur-faces. The results proved that no anisotropy can be noticed in the mechanical response for loads applied in the different directions within the plane of powder deposition.

2005 - Rapid Casting in the development of an automotive component: evaluation of dimensional performances [Working paper]
Gatto, Andrea; Bassoli, Elena; L., Iuliano; M. G., Violante
abstract

Rapid Prototyping techniques can guarantee great competitive advantages if applied to the production of tools and moulds for the realisation of technological prototypes or pre-series.In the field of metal casting, innovative low-cost techniques have extended Rapid Casting possibilities, based on the 3 dimensional printing technology making use of a ceramic material. Complex cavities can be obtained quickly directly from the CAD model, complete of cores and air vents, which are suitable for casting light alloys. The process performances in terms of dimensional accuracy and surface finish still have to be evaluated.The research regarded the development and production of a metal prototype by means of an innovative rapid casting technique, referred to an aluminium casing for the automotive field. Initially CAE tools were applied to model the casting process, achieving the concurrent product-process development. Then, a technological prototype was obtained by rapid casting, using the ZCast technique. The metal prototype was measured on a CMM machine to calculate the dimensional tolerances ensured by the proposed technological chain.

2005 - Rapid Casting in the development of an automotive component: evaluation of dimensional performances. [Relazione in Atti di Convegno]
Gatto, Andrea; Bassoli, Elena; Iuliano, L.; Violante, M. G.
abstract

Rapid Prototyping techniques can guarantee great competitive advantages if applied to the production of tools and moulds for the realisation of technological prototypes or pre-series.In the field of metal casting, innovative low-cost techniques have extended Rapid Casting possibilities, based on the 3 dimensional printing technology making use of a ceramic material. Complex cavities can be obtained quickly directly from the CAD model, complete of cores and air vents, which are suitable for casting light alloys. The process performances in terms of dimensional accuracy and surface finish still have to be evaluated.The research regarded the development and production of a metal prototype by means of an innovative rapid casting technique, referred to an aluminium casing for the automotive field. Initially CAE tools were applied to model the casting process, achieving the concurrent product-process development. Then, a technological prototype was obtained by rapid casting, using the ZCast technique. The metal prototype was measured on a CMM machine to calculate the dimensional tolerances ensured by the proposed technological chain.

2004 - An innovative procedure to update moulds CAD model with the real geometry using Reverse Engineering [Relazione in Atti di Convegno]
L., Iuliano; P., Minetola; Gatto, Andrea; Bassoli, Elena
abstract

Modern CAD/CAM techniques together with 5 axis high speed milling allow to reduce moulds manufacturing time and costs. Nevertheless, in order to use the moulds, operations of manual finishing and fitting are still always required. Such operations, performed manually by mould makers, modify milled surfaces of the moulds. Changes in the product's shape are sometimes decided after the mould has already been machined. In such cases, if it's possible, the mould maker modifies directly the mould. The final real geometry of the mould does not coincide with the one of the original CAD model. The aim of this paper is to define a procedure, based on Reverse Engineering methods, to reconstruct and to update the mathematical model of the mould after it has been polished and fit. The procedure was tested on a mould for the production of a camera body. A zone of the mould was manually polished and an aesthetical change, not included in the original CAD model, was introduced on it directly. The mould was digitized with an optical system based on structured light and the point clouds were treated with a software for the reconstruction of the surfaces. After updating the CAD model of the mould, a conceptual prototype of the camera shell was created to appraise on the final product the aesthetical change directly introduced on the mould.

2004 - Characterisation of Innovative Materials for Direct Laser Sintering. [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; Iuliano, L.; Atzeni, E.
abstract

Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions, where prototype parts and tools are produced directly from the CAD model. In particular, Selective Laser Sintering (SLS) of metal powders with liquid phase is frequently applied for the production of inserts for injection moulding of plastic parts.An experimental campaign has been planned to investigate the surface finish and mechanical performances of Direct Laser Sintering technique, with particular regard to the effect of the laser sintering strategy on the anisotropy of the final part. Tensile specimens of DirectMetal 20 and DirectSteel 20 materials have been produced, with different orientations in regard to laser path. Rupture surfaces after the tensile tests were observed at the SEM, in order to understand failure mechanisms, whereas the observation of polished sections helped investigating joining phenomena between the particles. The proposed experimental methodology allowed correlating the macroscopic performances to the micro-mechanisms ruling the process, proving that no considerable differences can be noticed between samples produced in the X and Y direction within the plane of powder deposition.

2004 - Design for manufacturing of an ergonomic joystick handgrip [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; L., Iuliano; Leali, Francesco
abstract

A Reverse Engineering- (RE) and Rapid Prototyping- (RP) based approach to the development of a joystick handgrip with ergonomic features has been elaborated. The integration of Time Compression Techniques and Computer Aided Tools lead to a time-saving procedure for the design of a product whose ergonomic quality directly descends from users’ sensations of comfort. The CAD model availability throughout the progressive steps of product development ensured all the potentialities of Concurrent Engineering, while Computer Aided Engineering (CAE) simulation on the definitive geometry allowed to close the Computer Integrated loop to the manufacturing process.

2004 - Direct Laser Sintering of Metal Parts: Characterisation and Evaluation of Joining Mechanisms. [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; Iuliano, L.; Atzeni, E.
abstract

The performances achieved by Rapid Prototyping techniques are progressively leading towards Rapid Manufacturing, that is the capability to produce end products, directly from the CAD model. Even so, the diffusion of these techniques is hardly supported by scientific knowledge about the micro-mechanisms ruling the macroscopic performances of the part. In the present research, mechanical performances of new materials produced by Direct Laser Sintering technique have been studied: a Polyamide and an innovative Polyamide-Aluminium composite (Alumide). Specimens were produced with different orientations in regard to powder deposition plane and laser path, to investigate how the manufacturing anisotropy affects the part performances.

2004 - Direct Laser Sintering of metal parts: characterisation and evaluation of joining mechanisms [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; L., Iuliano; E., Atzeni
abstract

Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions, where prototype parts and tools are produced directly from the CAD model [1- 8]. In particular, Selective Laser Sintering (SLS) of metal powders with liquid phase is frequently applied for the production of inserts for injection moulding of plastic parts.On the basis of the deep knowledge developed by the authors on the solid-state process [1-4], an experimental campaign has been planned to investigate the surface finish and mechanical performances of Direct Laser Sintering technique. In particular, the research objective was to evaluate the effect of the laser sintering strategy on the anisotropy of the final part. Tensile specimens of DirectMetal 20 and DirectSteel 20 materials have been produced, following the specifications of standard ASTM E8, with different orientations in regard to laser path. Rupture surfaces after the tensile tests were observed at the SEM, in order to understand failure mechanisms, whereas the observation of polished sections helped investigating joining phenomena between the particles. The proposed experimental methodology allowed correlating the macroscopic performances to the micro-mechanisms ruling the process, proving that no considerable differences can be noticed between samples produced in the X and Y direction within the plane of powder deposition.

2004 - Direct Laser Sintering of metal parts: characterisation and evaluation of joining mechanisms [Working paper]
Bassoli, Elena; Gatto, Andrea; L., Iuliano; E., Atzeni
abstract

Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions, where prototype parts and tools are produced directly from the CAD model [1- 8]. In particular, Selective Laser Sintering (SLS) of metal powders with liquid phase is frequently applied for the production of inserts for injection moulding of plastic parts.On the basis of the deep knowledge developed by the authors on the solid-state process [1-4], an experimental campaign has been planned to investigate the surface finish and mechanical performances of Direct Laser Sintering technique. In particular, the research objective was to evaluate the effect of the laser sintering strategy on the anisotropy of the final part. Tensile specimens of DirectMetal 20 and DirectSteel 20 materials have been produced, following the specifications of standard ASTM E8, with different orientations in regard to laser path. Rupture surfaces after the tensile tests were observed at the SEM, in order to understand failure mechanisms, whereas the observation of polished sections helped investigating joining phenomena between the particles. The proposed experimental methodology allowed correlating the macroscopic performances to the micro-mechanisms ruling the process, proving that no considerable differences can be noticed between samples produced in the X and Y direction within the plane of powder deposition.

2004 - Planning and manufacturing a mould for Resin Transfer Moulding [Relazione in Atti di Convegno]
Iuliano, L; VIOLANTE M., G; Bassoli, Elena; Gatto, Andrea
abstract

Resin transfer moulding (RTM) is a low pressure moulding process, where a resin, mixed to a catalyst, is injected into a closed die, which vacuum has been obtained, containing a reinforcing pre-formed fibre [1, 2]; this fibre can be glass, carbon, aramidic fibre or a mixture of them. The resin and the catalyst are injected by a pump into a mixing head and then into the closed mould. When the resin is solidified, the die is opened and the piece is extracted [3, 4].Our study deals with the planning and the manufacturing of a low-cost modular die to be used in the resin transfer moulding (RTM) and it analyzes the costs and benefits of the suggested innovative solution.

2004 - Plasma Transferred Arc deposition of powdered high performances alloys: process parameters optimisation as a function of alloy and geometrical configuration [Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; M., Fornari
abstract

The deposition of high wear- and corrosion-resistant alloys through Plasma Transferred Arc (PTA) is an easily automated process combining the possibility to obtain very thick coatings with high deposition speeds, low thermal distortion of the part and negligible dilution levels, thanks to a very high energy-concentration [S. Kalpakjian, S.R. Schmid, Manufacturing Engineering and Technology-4th edition, Addison-Wesley Publishing, 2001, p. 789-790, Scripta Materialia 37 (1997) 721, Applied Surface Science 201 (2002) 154, Surface and Coatings Technology 71 (1995) 196, Journal of Materials Processing Technology 128 (2002) 169, M. Bonacini, Plasma ad arco trasferito per riporti saldati con superleghe in polvere, Saldatura e taglio termico verso il 2000 IIS Meeting, October 3rd 1998, Milan-Italy, Wear 250 (2001) 611, Wear 249 (2002) 846, Composites Science and Technology 58 (1998) 299]. Literature studies regard mostly wear or high temperature behaviour of the deposited alloys and plasma hardening treatment without powder [Applied Surface Science 201 (2002) 154, Surface and Coatings Technology 71 (1995) 196, Journal of Materials Processing Technology 128 (2002) 169, M. Bonacini, Plasma ad arco trasferito per riporti saldati con superleghe in polvere, Saldatura e taglio termico verso il 2000 IIS Meeting, October 3rd 1998, Milan-Italy, Wear 250 (2001) 611, Surface and Coatings Technology 106 (1998) 156, Wear 249 (2002) 846, Surface and Coatings Technology 92 (1997) 157, Wear 181-183 (1995) 8 10, Wear 225-229 (1999) 1114], rather than an optimisation of process parameters, also in critical geometric configurations. An experimental campaign has been carried out on the deposition of two nickel- and a cobalt-base superalloys: Hastelloy 276, Inconel 625 and Stellite 6. Benchmarks of C-Mn steel have been chosen to test geometrical configurations that are critical for the application (corners and grooves). Specimen characterisation through liquid penetration inspection, optical- and scanning electron microscopy and microhardness tests proved that process parameters optimisation depends only on the geometrical configuration and not on the deposited alloy. This result suggests the importance of an accurate design of the reciprocal positioning and movement between the torch and the part to be coated, as a function of the deposition geometry.

2004 - Reverse engineering methodologies applied to complex virtual models development in the medical field [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Bassoli, Elena; Gatto, Andrea; Leali, Francesco; Pellicciari, Marcello
abstract

Negli ultimi anni si è assistito, nell’ambito della ricerca applicata, ad un progressivo processo di trasferimento delle pratiche e delle metodologie tipiche dell’ingegneria industriale in ambito medicale, ed alla costituzione di gruppi di lavoro eterogenei, formati sia da personale medico che tecnico-ingegneristico. In particolare, sembra essersi affermata la tendenza alla definizione di modelli ed ambienti virtuali, ad esempio, per la pianificazione pre-chirurgica degli interventi e per la comprensione delle problematiche ad essa inerenti, e sembra progressivamente essersi diffusa la consapevolezza che sfruttando l’elevato contenuto informativo delle rappresentazioni grafiche tridimensionali è possibile favorire il superamento delle normali barriere culturali e comunicative, soprattutto tra medici e pazienti o tra insegnanti e studenti e creare gruppi di lavoro in grado di comunicare più facilmente e, quindi di raggiungere risultati migliori in tempi ridotti. Il presente lavoro di ricerca, realizzato grazie alla forte sinergia tra il gruppo di Disegno e Metodi dell’Ingegneria Industriale e il gruppo di Tecnologia e Sistemi di Lavorazione del Dipartimento di Ingegneria Meccanica e Civile di Modena, riguarda la definizione di una procedura che, attraverso l’uso combinato di differenti tecnologie di reverse engineering e di strumenti software dedicati alla generazione ed alla modellazione delle superfici, consenta di ottenere un prototipo virtuale complesso di un oggetto fisico. Il benchmark adottato, fornito dal Dipartimento di Neuroscienze, Testa-Collo, Riabilitazione di Modena è costituito dall’arcata mascellare di un modello artigianale scomponibile, formato da una base in resina e legno e da 14 denti in resina completamente estraibili, che, inserito in un apposito articolatore insieme alla corrispondente arcata mandibolare, viene attualmente utilizzato per descrivere la normale occlusione in ambito didattico. Il metodo sviluppato, basato sull’uso di strumenti hardware e software di costo medio basso, ha consentito di definire una procedura rapida e facilmente implementabile anche da parte di personale non tecnico, facilitando l’accostamento alle potenzialità offerte dalle tecnologie assistite da calcolatore per la realizzazione di prototipi virtuali.

2003 - A time compression approach for styling design [Relazione in Atti di Convegno]
M., Germani; F., Mandorli; Gatto, Andrea; Bassoli, Elena; F., Piatto; N., Tulloch
abstract

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2003 - Microwave assisted sintering of SLS green metal parts [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Bassoli, Elena; Gatto, Andrea; L., Iuliano
abstract

Microwave assisted post-treatment of selective laser sintered green metal parts proved to be a new, fast and efficient way to densify complex-shaped elements, suitable for near-net-shape and net-shape manufacturing. Electromagnetic field modelling on pressed samples of RapidSteel 2.0 helped in choosing the proper experimental set up, using either single mode or overmoded microwave applicators operating at 2.45 GHz ISM frequency. LaserForm SLS green parts were exposed to high intensity microwave fields, using different lining configurations. Samples were characterized in terms of densification behaviour and microstructure: SEM observation of fracture and lapped surfaces allowed to analyse failure mechanisms and sintering degree.

2003 - Reverse Engineering approach for a joystick handgrip re-styling with ergonomic features [Relazione in Atti di Convegno]
Bassoli, Elena; Gatto, Andrea; L., Iuliano; G., Marchiandi
abstract

Ergonomics plays a more and more important role in product development, ensuring a better quality of life and work and also contributing to enrich the product image. If the importance of an ergonomic design is commonly recognized, no stated procedures for the development of an ergonomic product are still available. This is probably due to the fact that ergonomics is a qualitative subjective characteristic, that can’t be reduced to a list ofspecifications. In agreement with the opinion that a product can be defined ergonomic only in reference to a precise target of users and for a definite application [1], this paper regards aninnovative user-based procedure for the re-styling of a commercial handgrip. The proposed procedure, combining traditional modeling and Time Compression techniques, guarantees the time- and cost-saving development of a product ensuring comfort of use and minimizing pressure concentrations on the user’s hand [2] that can be defined ergonomic since it directly derives from users’ physical characteristics.

2003 - Selective Laser Sintering Of Metal Parts:Comparison Of Two Material Systems [Relazione in Atti di Convegno]
L., Iuliano; Gatto, Andrea; Bassoli, Elena; E., Azteni; M. G., Violante
abstract

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