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Leonardo ORAZI

Professore Ordinario
Dipartimento di Scienze e Metodi dell'Ingegneria


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Pubblicazioni

2024 - Assessment of fiber orientation models predictability by comparison with X-ray µCT data in injection-molded short glass fiber-reinforced polyamide [Articolo su rivista]
Oubellaouch, Keltoum; Pelaccia, Riccardo; Bonato, Nicolò; Bettoni, Nicola; Carmignato, Simone; Orazi, Leonardo; Donati, Lorenzo; Reggiani, Barbara
abstract

The distribution of fibers in injection molded thermoplastic-reinforced parts is known to significantly affect both the final mechanical properties and the appearance of defects related to undesired shrinkages and warpages. Even if the numerical modelling of the process is in the state-of-the-art, the selection criteria of the model for the fiber orientation predictability and the influence of the models’ parameters are not yet clearly understood. The complexity of the matter increases further considering that, inside the same injection molded part, the fiber orientation distribution could differ from one region to another depending on the local melt shear-flow type. In this context, the aim of this study is to investigate the orientation of fibers in regions of non-simple shear flow in an injection molded short glass fiber reinforced part. X-ray micro-computed tomography is used to experimentally investigate fiber distribution and orientation. Furthermore, a number of numerical simulations of the injection molding process are performed in Moldflow® by varying the mesh type (2D/3D), the selected predictive model and the models’ coefficients. The main findings indicates that, in regions with non-simple shear flow, a 2D mesh fails to capture accurate fiber orientation. A 3D mesh is essential for reliable predictions. MRD-specific parameters from the literature reduce prediction error by 37.5% compared to Moldflow's default MRD parameters. Regarding the RSC model, both Wang’s optimal retarding rate parameter and AMI's default retarding rate parameter result in similar 5% prediction errors. However, employing a literature-suggested interaction coefficient raises the prediction error to 26%.


2024 - Surface Functionalization of Metallic Biomaterials: Present Trend and Future Perspectives [Capitolo/Saggio]
Rotella, G.; Basile, V.; Carlone, P.; Col, J. D.; Filice, L.; Orazi, L.; Romoli, L.; Rubino, F.; Saffioti, M. R.
abstract


2023 - Adaptive Optics for Laser Beam Shaping [Relazione in Atti di Convegno]
Siciliani, V.; Orazi, L.; Pelaccia, R.; Mazzonetto, M.; Oubellaouch, K.; Reggiani, B.
abstract


2023 - Advanced simulation of nitrogen cooling in extrusion of light alloys [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Pelaccia, Riccardo; Rinaldi, Gabriele; Reggiani, Barbara; Orazi, Leonardo
abstract

Extrusion of light alloys is considered one of the most relevant processes in high-volume manufacturing. Production rate shall be kept as high as possible; however, the process bears limitations due to the operating conditions and mechanisms, which yield a large amount of heat generated by deformation energy and friction forces. Profile temperature likely reaches values close to 580 – 590 °C and the resulting thermal stress may reduce the tool life and lead to cracks and defects in the profile. Therefore, cooling of the zones where the higher temperatures occur is instrumental. Nitrogen has been recently brought at the forefront as a coolant, thanks to its low boiling point at atmospheric pressure. However, the design of cooling channels mostly relies on models that include either the liquid or the gas phase. The present work is focused on assessing the homogenous-flow approach as a method representative of the involved physics, also not being as computationally demanding as those simulating both phases. A Finite Element model was developed in a multiphysics environment, encompassing both the extrusion process and the nitrogen flow. The latter consisted of a homogeneous flow requiring dedicated formulation of thermophysical properties. Transient analyses were carried out with different models and the results were validated against an experimental dataset that stemmed from AA6063 billets extruded at variable speed in a reduced-scale industrial line. The ability to predict temperature measured at a location close to the billet was evaluated. The results from homogeneous flow modeling appear the most accurate, whereas modeling only the liquid phase leads to an overestimation of the cooling effect, as opposed to the underestimation associated with including the sole gas phase. Running time also proved as short as industry typically requires.


2023 - Development of an automatic procedure to texture cutting tools with a complex geometry [Relazione in Atti di Convegno]
Mazzonetto, Manuel; Siciliani, Vincenzina; Orazi, Leonardo; Pelaccia, Riccardo; Oubellaouch, Keltoum; Reggiani, Barbara
abstract


2023 - Effects of anisotropic and isotropic LIPSS on polymer filling flow and wettability of micro injection molded parts [Articolo su rivista]
Gnilitskyi, I.; Alnusirat, W.; Sorgato, M.; Orazi, L.; Lucchetta, G.
abstract

In micro injection molding, the specific cavity surface texture and roughness directly influence the polymer flow and the heat transfer between polymer melt and mold. In this work, two different types of laser-induced periodic surface structures, linear and hexagonal, were generated, and their impact on the flow length in micro injection molding was evaluated. A complete investigation of the surface treatment effect on the polymer flow was carried out, comparing the performance of an untreated cavity surface with surfaces modified by LIPSS. The phenomenon was examined by localizing the weld lines created by the polymer flowing in two parallel channels having different surface treatments. Several cavity inserts were treated by varying the LIPSS process parameters to generate surfaces with different micro-and nanostructures directions and periodicity. Furthermore, the paper addresses the hydro-phobicity achieved on the micro molded surfaces replicated from mold inserts with different LIPSS-based surface topography. Mold surfaces with linear and hexagonal LIPSS and the respective molded parts were analyzed by optical profilometry and scanning electron microscopy to characterize the cavity surfaces replication and localize the weld lines on the micro injection molded parts.


2023 - Effects of Ti6Al4V mechanical and thermal surface modification on the adhesion of a chitosan-bioactive glass coating [Articolo su rivista]
Sanguedolce, M; Rotella, G; Curcio, F; Pelaccia, R; Siciliani, V; Cassano, R; Orazi, L; Filice, L
abstract

Biomedical implants interact with human tissues introducing significant perturbation into the body. Implant surfaces can be then functionalized enabling better biocompatibility. At the same time, the additional use of a coating provides further functions such as corrosion protection, osteointegration, and drug delivery. In this context, a composite made of chitosan and bioactive glass nanoparticles has been used for coating Ti6Al4V alloy samples processed beforehand using different processes, i.e., polishing, milling, grit blasting, and electrical discharge machining. Experiments have been carried out to correlate substrate surface conditions and coating effectiveness in terms of scratch resistance with the final aim to obtain suitable guidelines to improve substrate-coating performances.


2023 - Estimation of Analyte's Vertical Positions above the Surface of Nanocapacitor Array Biosensors [Relazione in Atti di Convegno]
Goldoni, Daniele; Ongaro, Claudio; Orazi, Leonardo; Rovati, Luigi; Selmi, Luca
abstract


2023 - Surface micro – texturing of tapping tools with complex geometry [Relazione in Atti di Convegno]
Mazzonetto, Manuel; Siciliani, Vincenzina; Pelaccia, Riccardo; Orazi, Leonardo
abstract


2023 - Ultrafast laser texturing to improve wettability of polyimide (Kapton) films [Articolo su rivista]
Orazi, L.; Pelaccia, R.; Siciliani, V.; Oubellaouch, K.; Mazzonetto, M.; Reggiani, B.
abstract


2023 - UV picosecond laser processing for microfluidic applications [Relazione in Atti di Convegno]
Siciliani, Vincenzina; Betti, Alice; Ongaro, Claudio; Orazi, Leonardo; Zardin, Barbara; Reggiani, Barbara
abstract


2023 - Wetting Characteristics of Laser-Ablated Hierarchical Textures Replicated by Micro Injection Molding [Articolo su rivista]
Gao, P; Mackay, I; Gruber, A; Krantz, J; Piccolo, L; Lucchetta, G; Pelaccia, R; Orazi, L; Masato, D
abstract

Texturing can be used to functionalize the surface of plastic parts and, in particular, to modify the interaction with fluids. Wetting functionalization can be used for microfluidics, medical devices, scaffolds, and more. In this research, hierarchical textures were generated on steel mold inserts using femtosecond laser ablation to transfer on plastic parts surface via injection molding. Different textures were designed to study the effects of various hierarchical geometries on the wetting behavior. The textures are designed to create wetting functionalization while avoiding high aspect ratio features, which are complex to replicate and difficult to manufacture at scale. Nano-scale ripples were generated over the micro-scale texture by creating laser-induced periodic surface structures. The textured molds were then replicated by micro-injection molding using polypropylene and poly(methyl methacrylate). The static wetting behavior was investigated on steel inserts and molded parts and compared to the theoretical values obtained from the Cassie-Baxter and Wenzel models. The experimental results showed correlations between texture design, injection molding replication, and wetting properties. The wetting behavior on the polypropylene parts followed the Cassie-Baxter model, while for PMMA, a composite wetting state of Cassie-Baxter and Wenzel was observed.


2022 - A novel algorithm for a continuous and fast 3D projection of points on triangulated surfaces for CAM/CAD/CAE applications [Articolo su rivista]
Orazi, L.; Reggiani, B.
abstract

In the present work, a novel algorithm for the continuous projection of point triangles belonging to a triangle mesh is presented. The algorithm uses the normals defined at the vertices of the triangle to perform the projection. The direction of projection is not chosen a priori but depends on the point to be projected: the proposed algorithm, named Fast Continuous Projection method (FCP) lets the projection direction vary continuously on the mesh. Moreover, the direction is coherent with the original surface that is approximated with the triangle mesh. An optimized version of the algorithm is also presented: this uses pre-evaluated matrices to reduce the calculation time. This algorithm can be effectively used when a large set of points has to be projected on a coarse mesh as, for example, to generate the scanning vectors for laser engraving/milling.


2022 - An Alternative Solution for Microfluidic Chip Fabrication [Relazione in Atti di Convegno]
Ongaro, C.; Betti, A.; Zardin, B.; Siciliani, V.; Orazi, L.; Bertacchini, J.; Borghi, M.
abstract


2022 - Selectively Tunable Luminescence of Perovskite Nanocrystals Embedded in Polymer Matrix Allows Direct Laser Patterning [Articolo su rivista]
Martin, C.; Prudnikau, A.; Orazi, L.; Gaponik, N.; Lesnyak, V.
abstract

Cesium lead halide perovskite nanocrystals (NCs) have gained enormous attention as promising light-emitting and light-converting materials. Most of their applications require embedding NCs in various matrices, which is a challenging task due to their low stability, especially in the case of red-emitting CsPbI3 NCs. In this work, a new approach is proposed allowing the formation of red-emitting perovskite NCs by anion exchange induced directly inside a solid polymer matrix using green-emitting CsPbBr3 NCs as templates and iodododecane as an iodine source. Moreover, a simple and efficient route to photo-assisted termination of the anion exchange reaction in the polymer composite after reaching desired optical properties is demonstrated. The findings allow the authors to pattern a thin composite film with an ultrashort UV laser resulting in a selective generation of green- and red-emitting features with a 15 µm resolution.


2022 - Surface Characterization Of Ultra-Short Laser Textured Titanium For Biomedical Application [Relazione in Atti di Convegno]
Sanguedolce, Michela; Rotella, Giovanna; Siciliani, Vincenzina; Pelaccia, Riccardo; Orazi, Leonardo; Filice, Luigino
abstract


2022 - Tailoring surface properties, biocompatibility and corrosion behavior of stainless steel by laser induced periodic surface treatment towards developing biomimetic stents [Articolo su rivista]
Saqib, M.; Beshchasna, N.; Pelaccia, R.; Roshchupkin, A.; Yanko, I.; Husak, Y.; Kyrylenko, S.; Reggiani, B.; Cuniberti, G.; Pogorielov, M.; Opitz, J.; Orazi, L.
abstract

Laser-Induced Periodic Surface Structures (LIPSS) holds great potential for regenerative biomedicine. Creating highly precise LIPSS enables to generate biomimetic implant surfaces with improved properties. The present study focuses on the fabrication and investigation of laser-treated stainless steel samples with applied linear LIPSS patterns with grooves made by means of a picosecond laser system using wavelengths of 1064 nm and 532 nm. To investigate properties of the laser-treated surfaces and to understand the basics of cell-surface interactions between the LIPSS and human Umbilical Cord Mesenchymal Stem Cells (UCMSC), flat stainless steel samples with various applied nanopatterns were used. Such LIPSSs demonstrated higher surface roughness, good biocompatibility, lower wettability and higher corrosion resistance compared to the untreated (polished) spec-imens. The surface roughness of laser-treated samples was in microscale that enabled adhesion and migration of endothelial cells, thus increasing the likelihood for endothelialisation. This thereby could reduce the chances for the development of Late Stent Thrombosis (LST) and In-Stent Restenosis (ISR). Furthermore, laser textured surfaces demonstrated an environment supportive for cell attachment, proliferation and alignment with the nanogroves. Therefore, application of the biomimetic nanopatterns could help to overcome frequent post-surgery complications after the stent implantation.


2022 - Ultrafast laser micromanufacturing of microfluidic devices [Relazione in Atti di Convegno]
Orazi, Leonardo; Siciliani, Vincenzina; Pelaccia, Riccardo; Oubellaouch, Keltoum; Reggiani, Barbara
abstract


2021 - Correction to: Point Inversion for triparametric NURBS (International Journal on Interactive Design and Manufacturing (IJIDeM, (2020), 10.1007/s12008-020-00719-z) [Articolo su rivista]
Orazi, L.; Reggiani, B.
abstract

Authors would like to correct the error in article title. Word “for” in the title has been inadvertently changed to “ior”. Correct version of article title updated here. The original article has been corrected.


2021 - Design and Fabrication of a Pillar-based Piezoelectric Microphone exploiting 3D-Printing Technology [Articolo su rivista]
Ricci, Y.; Sorrentino, A.; La Torraca, P.; Cattani, L.; Cotogno, M.; Cantarella, G.; Orazi, L.; Castagnetti, D.; Lugli, P.; Larcher, L.
abstract

This letter presents a 3-D-printed piezoelectric microphone with enhanced voltage sensitivity. The sensitivity is improved by a combination of a single-pillar mechanical design and a specific polyvinylidene fluoride (PVDF)-film electrode patterning. The moving part of the mechanical structure and the chassis are 3D-printed as a single unit and trimmed by laser cutting, allowing for a simple fabrication of the device. The measured sensitivity of 1 mV/Pa (±6 dB) in the bandwidth 500–2500 Hz agrees with simulations, showing an improvement over similar pillar-based piezoelectric sensor solutions. The sensitivity performance is shown to be comparable to existing microphones with different technologies. The microphone is also characterized by excellent linearity within the measurable range. 3D-printing technique can thus be adopted for the manufacturing of low cost and highly customizable microphone sensors.


2021 - Experimental investigation on a novel approach for laser surface hardening modelling [Articolo su rivista]
Orazi, L.; Rota, A.; Reggiani, B.
abstract

Laser surface hardening is rapidly growing in industrial applications due to its high flexibility, accuracy, cleanness and energy efficiency. However, the experimental process optimization can be a tricky task due to the number of involved parameters, thus suggesting for alternative approaches such as reliable numerical simulations. Conventional laser hardening models compute the achieved hardness on the basis of microstructure predictions due to carbon diffusion during the process heat thermal cycle. Nevertheless, this approach is very time consuming and not allows to simulate real complex products during laser treatments. To overcome this limitation, a novel simplified approach for laser surface hardening modelling is presented and discussed. The basic assumption consists in neglecting the austenite homogenization due to the short time and the insufficient carbon diffusion during the heating phase of the process. In the present work, this assumption is experimentally verified through nano-hardness measurements on C45 carbon steel samples both laser and oven treated by means of atomic force microscopy (AFM) technique.


2021 - Ultrafast laser manufacturing: from physics to industrial applications [Articolo su rivista]
Orazi, L.; Romoli, L.; Schmidt, M.; Li, L.
abstract

Modern ultrafast lasers are enabling better operative performances in micro and nano-fabrications of materials, benefited from their ease of use, robustness, and reliability. The purpose of this paper is to bridge the gap between the knowledge of ultrafast optics and the modern industrial applications. The paper introduces main phenomena in ultrafast laser-matter interactions by reviewing relevant theoretical models and simulation techniques. The operation of ultrafast lasers is based on nonlinear optics phenomena, fully described only in the framework of quantum-mechanics. Current trends in the development of modern ultrafast system are given. It also presents a review of the latest advances in ultrafast laser-based manufacturing processes, some of the most interesting industrial applications, and a discussion on future trends and challenges.


2021 - Water Soluble CdTe Quantum Dots and their Laser Reverse Patterning in Polyvinyl Alcohol Films [Abstract in Atti di Convegno]
Antolini, F.; Orazi, L.
abstract

The CdTe quantum dots of different size are obtained in water and are dispersed within a polyvinyl alcohol polymer. The nanocomposite is then irradiated with different UV laser to test the reverse laser patterning conditions.


2020 - Fast LIPSS based texturing process of dental implants with complex geometries [Articolo su rivista]
Orazi, L.; Pelaccia, R.; Mishchenko, O.; Reggiani, B.; Pogorielov, M.
abstract

In the present work, the generation of Laser Induced Periodic Surface Structures (LIPSS) by using femtosecond laser source is investigated in the surface texturing of Ti grade 5 dental implants. The proposed procedure permits a fast treatment of dental implants characterized by complex shape through the combined and synchronous use of a galvo scanner and of workpiece movements. The obtained surface micro- and nanostructures are characterized from a morphological point of view while in-vitro essays are performed to evaluate cellular proliferation. The results indicate the effectiveness of the LIPSS as method to increase cell viability and the efficiency of the proposed procedure to treat complex geometries as dental implants.


2020 - Generation and Characterization of Laser Induced Periodic Surface Structures on Plastic Injection Molds [Articolo su rivista]
Orazi, L.; Sorgato, M.; Piccolo, L.; Masato, D.; Lucchetta, G.
abstract

In injection molding, high pressure is required to fill the mold, due to the high viscosity of thermoplastic polymers, the reduced thickness of the cavity and the low mold temperature. In this work, we investigate the functionalization of mold cavities for Injection Molding by means of Laser-Induced Periodic Surface Structures (LIPSS) generated on the ground surface of AISI 420 stainless steel through a picosecond laser. The LIPSS formation is examined with reference to the process parameters, highlighting how they affect the generated pattern. The improvements of the functionalized mold surface on the Injection Molding process are experimentally characterized and discussed. In particular, the slipping of molten PET was investigated as a function of nano-structuring orientation and injection velocity. The results demonstrate that LIPSS parallel to flow induce strong wall slip of the polymer melt, allowing a maximum reduction of the injection pressure of 10%.


2020 - Innovative method for rapid development of shoes and footwear [Articolo su rivista]
Orazi, Leonardo; Reggiani, Barbara
abstract

In the present work, a novel set of software tools for the rapid development of shoes and footwear is presented aimed at strongly reducing the design time and then the time-to-market of the products. These tools are mainly based on an implementation of Constrained Free Form Deformation techniques and on the use of modern surface scanning methods. The proposed approach allows, in many cases, to avoid the mathematical surface reconstruction and to quickly generate the complex geometries that CAM systems will process in order to generate the tool paths for mold manufacturing.


2020 - Modeling and analysis of the visualized gas-assisted laser cutting flow from both conical and supersonic nozzles [Articolo su rivista]
Darwish, Mohamed.; Mrna, Libor; Orazi, Leonardo; Reggiani, Barbara
abstract

A coaxial high-pressure gas jet is normally used to assist and enhance laser cutting quality and capability. However, the gas nozzles are mostly of conical type causing the deterioration of the dynamic characteristics of the exit jet. In this research, the effect of both nozzle type and nozzle dimensions on the uniformity and behavior of the exit jet has been investigated. A total of three different supersonic nozzles have been designed in accordance to gas dynamics theory and manufactured using wire electrical discharge machining (WEDM). The exit jet patterns from these supersonic nozzles and a reference conical nozzle have been numerically modeled and compared with the experimental observations made through Schlieren visualization. The experimental results are found to match and hence validate the simulations. It is concluded that the exit jet from the supersonic nozzle is marked by uniformity, better dynamic characteristics, and longer effective exit jet length compared with conical nozzle.


2020 - Numerical analysis of the gas-assisted laser cutting flow from various supersonic nozzles [Articolo su rivista]
Darwish, M.; Orazi, L.; Reggiani, B.
abstract

In the present paper, the exit jet patterns from four different supersonic nozzles have been numerically simulated using OpenFOAM® Computational Fluid Dynamics (CFD) toolbox. The desired-design operating condition, for each of these nozzles, has been calculated using quasi 1-D gas dynamics theory. Mach number and pressure distributions are presented for each nozzle to illustrate the effect of both the nozzle geometry and the operating conditions on the behaviour of the exit jet. Then, the predicted numerical results have been validated by comparison with the experimental measurements reported in previous literature. As main outcomes, the simulations results are quantitatively in high agreement with the reported experimental observations. The correlations between jet flow stability and divergence angle are discussed and the effect of Mach number and exit diameter on the jet divergence are presented.


2020 - Numerical modeling and Schlieren visualization of the gas-assisted laser cutting under various operating stagnation pressures [Articolo su rivista]
Darwish, Mohamed; Mrňa, Libor; Orazi, Leonardo; Reggiani, Barbara
abstract

The uniformity of the exit jet pattern in high pressure gas-assisted laser cutting represents the main feature in order to achieve high cutting quality and capability. Therefore, the effect of both inlet stagnation pressure and nozzle geometry on the behavior of the exit jet has been investigated in this research. Quasi 1-D gas dynamics theory has been used to calculate the exact-design operating conditions for three different supersonic nozzles that were fabricated by means of Wire Electrical Discharge Machining. The jet flow through these nozzles has been numerically modeled and experimentally checked, using Schlieren visualization, under exact-design, over-expansion and under-expansion operating conditions coming to a good numerical-experimental agreement in terms of flow structure. As main result, the exit jet was found to preserve its uniform distribution with parallel boundaries and low divergence under the exact-design operating condition, differently to what observed for the others two conditions, especially for nozzle with small divergence angle.


2020 - Point Inversion for triparametric NURBS [Articolo su rivista]
Orazi, L.; Reggiani, B.
abstract

In this paper a Point Inversion algorithm for NURBS volumes is presented. This algorithm is an extension to 3D of the classic Newton–Raphson iteration, thus implying the calculation of the NURBS volume partial derivatives. Explicit formulas for the derivatives are deduced and reported, in turn requiring the evaluation of the corresponding derivatives of the rational basis functions. Also these derivatives are inferred and shown together with some examples of applications. The method, applicable to any free-form shape NURBS volume is moreover compared with Fast Mapping, a novel approach presented here that, once applied to simple NURBS boxes give performance 20–50 times higher.


2020 - Preform Mold Component [Brevetto]
Sorgato, Marco; Lucchetta, Giovanni; Orazi, Leonardo; Masato, Davide; Bessegato, Federico; Cavalet, Andrea; Zoppas, Matteo
abstract

A component of a mold for molding preforms made of thermoplastic material, comprising at least a first part (10) and at least a second part (20) adapted to mold part of the outer surface of a preform, wherein, when the first part (10) and the second part (20) are assembled to each other, at least a first surface (11) of the first part (10) and at least a second surface (21) of the second part (20) face each other and are spaced apart from each other, thus delimiting a passageway for gases or vapors to leave the mold; and wherein at least one of said first surface (11) and said second surface (21) comprises laser-induced periodic surface structures (LIPSSs).


2020 - Preform Mold Component [Altro]
Sorgato, Marco; Lucchetta, Giovanni; Orazi, Leonardo; Masato, Davide; Bessegato, Federico; Cavalet, Andrea; Zoppas, Matteo
abstract

A component of a mold for molding preforms made of thermoplastic material, comprising at least a first part (10) and at least a second part (20) adapted to mold part of the outer surface of a preform, wherein, when the first part (10) and the second part (20) are assembled to each other, at least a first surface (11) of the first part (10) and at least a second surface (21) of the second part (20) face each other and are spaced apart from each other, thus delimiting a passageway for gases or vapors to leave the mold; and wherein at least one of said first surface (11) and said second surface (21) comprises laser-induced periodic surface structures (LIPSSs)


2020 - Surface micro and nanostructuring of three-dimensional components of micro medical devices [Relazione in Atti di Convegno]
Biondani, Francesco; Benassi, Lorenzo; Bissacco, Giuliano; Orazi, Leonardo; Tang, Peter T.
abstract

Surface structuring of medical implants has been shown to reduce the rejection rate of medical devices inserted inside living tissue. Several studies have shown that by texturing the surface of medical implants at micro/nanoscale it is possible to foster cell adhesion. The surface texturing of medical devices poses many challenges in terms of cost and time when the nano texturing process is performed directly on the part surface. A viable solution for mass production of polymer based surface enhanced medical devices is achieved via injection molding. However, nano structuring of micro injection molding molds, requires techniques enabling processing of complex surfaces, small curvature radii and with high aspect ratios. Furthermore the accessibility of all surfaces to be structured and the processing time are the main concerns and limiting factors on the selection of the structures dimensions and geometries. In this work, two different process chains are analyzed for the nano structuring of a bone micro plug. The first method relies on a chemical deposition process in order to produce a semi random structure on the entire mold surface of the medical component. The characteristic size of the structures is controlled by acting on the deposition parameters. The second process, relies on laser structuring of the mold components by producing Laser-Induced Periodic Surface Structures (LIPSS).The two process chains are compared and an evaluation of the applicability in different production scenarios presented, with specific focus on surface accessibility, nano structures uniformity and applicability to surfaces with complex geometry


2019 - Cell and tissue response to nanotextured Ti6Al4V and Zr implants using high-speed femtosecond laser-induced periodic surface structures [Articolo su rivista]
Gnilitskyi, I.; Pogorielov, M.; Viter, R.; Ferraria, A. M.; Carapeto, A. P.; Oleshko, O.; Orazi, L.; Mishchenko, O.
abstract

In this paper, the effect of femtosecond laser nanotexturing of surfaces of Ti6Al4V and Zr implants on their biological compatibility is presented and discussed. Highly regular and homogeneous nanostructures with sub-micrometer period were imprinted on implant surfaces. Surfaces were morphologically and chemically investigated by SEM and XPS. HDFa cell lines were used for toxicity and cell viability tests, and subcutaneous implantation was applied to characterize tissue response. HDFa proliferation and in vivo experiments evidenced the strong influence of the surface topography compared to the effect of the surface elemental composition (metal or alloy). The effect of protein adsorption from blood plasma on cell proliferation is also discussed.


2019 - Effects of Surface Treatments on the Fatigue Response of High Strength Fasteners [Relazione in Atti di Convegno]
Reggiani, Barbara; Olmi, Giorgio; Orazi, Leonardo; Tomesani, Luca; Fini, Stefano; Barozzi, Lorenzo; Pelaccia, Riccardo; Bandini, Michele
abstract

The aim of the present work was the assessment of the impact of deep-rolling and shot-peening performed in the underhead and in the unthreaded shank of two high strength screws (36 NiCrMo and 42 CrMoV) for fatigue life enhancement. The experimental campaign consisted of six combinations, including the non-treated state. The aforementioned treatments were evaluated alone or with shot-peening performed after deep-rolling in the underhead fillet of the screws. Deep rolling was carried out at the optimal rolling force, whereas two shot diameters were considered for shot-peening (Z100 and UFS70). The results have been evaluated in terms of fatigue limits and factor effects have been assessed by marginal mean plots.


2019 - Investigation on the Inert Gas-Assisted Laser Cutting Performances and Quality Using Supersonic Nozzles [Articolo su rivista]
Orazi, Leonardo; Darwish, Mohamed; Reggiani, Barbara
abstract

In the present work, three different supersonic nozzles were designed and manufactured to operate at various stagnation pressures during laser cutting. Several cutting experiments were performed on stainless steel samples of various thicknesses (2, 4, 6 mm) using a fiber laser of 3 kW with a head adapted to fit with both the proposed supersonic nozzles and a commercial reference conical nozzle. The flow through these nozzles was numerically modeled and compared with the Schlieren visualization measurements. The mass flow rate, the Mach number, and the pressure distributions were selected in detail in order to analyze the dynamic characteristics of the exit jet and to comparatively assess the achieved cutting quality (roughness perpendicularity) and capability (maximum thickness, cutting speed). The numerical and the experimental results were found to be in high agreement in terms of the flow structure and mass flow rate. In addition, a significant reduction of the assistance gas consumption of up to 65% on average was achieved by using supersonic nozzles as opposed to conical ones, accompanied with the decrease of the operating pressure and the increase of the cutting speed.


2019 - Osteoblast Cell Response to LIPSS-Modified Ti-Implants [Relazione in Atti di Convegno]
Orazi, Leonardo; Pogorielov, Maksym; Deineka, Volodymyr; Husak, Evhenia; Korniienko, Viktoriia; Mishchenko, Oleg; Reggiani, Barbara
abstract

In the present work, the surface of Ti-6Al-7Nb samples was patterned with Laser Induced Periodic Surface Structures in order to improve biocompatibility, increase tissue ingrowth and decrease bacterial adhesion and inflammatory response for applications in dental and orthopedic implants. Polished and sandblasted disks 10 mm in diameter were treated generating LIPSS under two different sets of parameters. The surface morphology and chemistry were investigated both by secondary electrons imaging, EDS analysis and Atomic Force Microscopy. Primary rat osteoblast culture (passage 2) was used to assess cell toxicity and biocompatibility. Alamar Blue assay was used to access cell viability and proliferation on day 1, 3 and 7. The difference between cell adhesion on polished and sandblasted surface as well as between polished and LIPSS-modified surface are described and discussed.


2019 - Quantum Dots Synthesis Through Direct Laser Patterning: A Review [Articolo su rivista]
Antolini, Francesco; Orazi, Leonardo
abstract

In this brief review the advances on Direct Laser Patterning (DLP) for the synthesis of photo-luminescent semiconductor quantum dots (QDs) belonging to II-VI groups, especially in solid state using laser-assisted conversion are reported and commented. The chemistry of the precursor synthesis is illustrated because it is a crucial step for the development of the direct laser patterning of QDs. In particular, the analysis of cadmium (bis)thiolate and cadmium xanthates precursors after thermal and laser treatment is examined, with a special focus on the optical properties of the formed QDs. The second part of the review examines how the laser parameters such as the wavelength and pulse duration may regulate the properties of the patterned QDs. The DLP technique does not require complex laser systems or the use of dangerous chemical post treatments, so it can be introduced as a potential method for the patterning of pixels in quantum dot light emitting diodes (QD-LEDs) for display manufacturing.


2019 - Simulation and analysis of the jet flow patterns from supersonic nozzles of laser cutting using OpenFOAM [Articolo su rivista]
Darwish, Mohamed; Orazi, Leonardo; Angeli, Diego
abstract

The operating pressure of gas-assisted laser cutting and the resulting exit jet pattern is one of the most important process parameters in high-pressure laser cutting. Many studies have been done to illustrate the effect of this parameter on both laser cutting quality and laser cutting capability. However, most of these studies have been done using conical nozzles. In this paper, the exit jet from supersonic nozzle has been studied, analyzed, and simulated under three different operating conditions, namely desired design, under-expansion, and over-expansion to illustrate the effect of these operating conditions on the dynamic characteristics of the exit jet. Quasi 1-D gas dynamics theory has been used to calculate the desired design operating condition, and then an axisymmetric 2-D model has been created using the OpenFOAM Ⓡ Computational Fluid Dynamics (CFD) toolbox to simulate the gas-assisted laser cutting flow through the modeled supersonic nozzle. Finally, the proposed simulations have been validated by comparing the results with experimental observations reported in previous literature. The effect of the turbulent viscosity has been considered through the proposed model to better simulate real conditions. Moreover, the model has been optimized to be effectively used for engineering purposes. The simulation results are qualitatively consistent with the reported experimental measurements and they demonstrate that in the case of supersonic nozzles, the exit jet pattern is characterized by high uniformity, absence of Mach disks, and bounded shape for a long distance especially under the desired design operating conditions.


2019 - Solid state synthesis of CdS quantum dots through laser direct writing [Relazione in Atti di Convegno]
Antolini, F.; Orazi, L.
abstract

The synthesis of colloidal photo-luminescent semiconductor quantum dots (QDs), belonging to II-VI groups, even from single source precursors is presented. Since three decades their synthesis has been pursued implementing new and easier synthetic conditions that standardize their production. In this work is reported the production of luminescent of CdS QDs in a polymeric film induced by laser processing (www.miledi-h2020.eu/). A film of PMMA doped with two types of precursors (cadmium xanthates) is irradiated with an UV laser source with different energy doses. The structured film will then be observed with confocal fluorescent microscope. The interesting results shows that the two different xanthates display a different behavior under the laser source even if their absorption spectrum is similar. The second interesting result is that the effect of the laser is the production luminescent pattern only for certain fluences and that the same film treated with the temperature did not show any luminescence.


2019 - Tribological Properties of High-Speed Uniform Femtosecond Laser Patterning on Stainless Steel [Articolo su rivista]
Gnilitskyi, Iaroslav; Rota, Alberto; Gualtieri, Enrico; Valeri, Sergio; Orazi, Leonardo
abstract

In this work, an analysis of the tribological performance of laser-induced periodic surface structures (LIPSS) treated X5CrNi1810 stainless steel was conducted. The approach followed by authors was to generate LIPSS-patterned circular tracks, composed of radial straight grooves with uniform angular periodicity. This permitted to measure the tribological properties in a pin-on-flat configuration, keeping fixed the orientation between the grooves and the sliding direction. A Stribeck curve was measured, as well as the consequent wear. A deep analysis of the sub-surface conditions after LIPSS generation was moreover performed using Focused Ion Beam (FIB) cross-section.


2018 - Effect of different laser-induced periodic surface structures on polymer slip in PET injection moulding [Articolo su rivista]
Sorgato, M.; Masato, D.; Lucchetta, G.; Orazi, L.
abstract

In injection moulding, high pressure is required to fill the mould, due to the viscosity of thermoplastic polymers, the reduced thickness of the cavity and the low mould temperature. In this work, significant pressure reduction was achieved inducing the slip of the polymer melt over the mould surface by means of Laser-Induced Periodic Surface Structures (LIPSS). In particular, the slipping of molten PET was investigated as a function of nano-structuring orientation and injection velocity. The results demonstrate that LIPSS parallel to flow induce strong wall slip of the polymer melt, allowing a maximum reduction of the injection pressure of 23%. (C) 2018 CIRP. Published by Elsevier Ltd. All rights reserved.


2018 - Superhydrophilic properties driven by highly-regular laser-induced periodic structures on Si surface [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Rota, Alberto; Orazi, Leonardo
abstract

In this work an investigation about the effects of high-speed, highly-regular laser induced periodic surface structures (HR-LIPSS) on wetting properties of silicon surface are presented and discussed. In order to investigate the influence of chemistry on wetting properties of textured surfaces, treatments were performed both under air and N2 shielding gas. The morphology was investigated by Scanning Electron Microscope (SEM), the chemistry by energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy and the wetting properties by camera recording. The results demonstrate substantial effects of HR-LIPSS on wetting properties of silicon surface. The hydrophilic Si surface becomes superhydrophilic after femtosecond nanopatterning and the addition of N2 in laser treated zone essentially influences the chemistry of the surface, this permits to control the water flowing and makes HR-LIPSS more flexible, bringing up to a new level of control of wettability properties for several applications.


2018 - Ultrafast Laser Texturing on Si with Burst-mode Picosecond Laser Pulses [Relazione in Atti di Convegno]
Gnilitskyi, I.; Orazi, L.; White, T.; Gruzdev, V.
abstract

Picosecond laser-induced periodic surface structures (PLIPSS) have been fabricated on surface of Si in uniform and burst-mode regimes at a high speed. The effects of burst-mode respect to uniform one are examined in term of chemical, mechanical and morphological properties.


2018 - Ultrafast laser texturing on Si with burst-mode picosecond laser pulses [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Orazi, Leonardo; White, Tommi; Vitaly Gruzdev, And
abstract

Picosecond laser-induced periodic surface structures (PLIPSS) have been fabricated on surface of Si in uniform and burst-mode regimes at a high speed. The effects of burst-mode respect to uniform one are examined in term of chemical, mechanical and morphological properties.


2017 - Highly-regular laser-induced periodic surface structures: Experiment and atomistic modelling [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Shugaev, Maxim V.; Bulgakova, Nadezhda M.; Zhigilei, Leonid V.; Orazi, Leonardo
abstract

Surface nano- and microstructuring with additive and subtractive lithography techniques are commonly used in nanotechnology and photonics, while nanoimprint lithography and nanosphere lithography are used for creating periodic structures for plasmonics applications. Single step, maskless optical patterning techniques also exist, notably multi-beam interference based techniques and Laser Induced Periodic Surface Structures (LIPSS).


2017 - High-speed manufacturing of highly regular femtosecond laser-induced periodic surface structures: Physical origin of regularity [Articolo su rivista]
Gnilitskyi, Iaroslav; Derrien, Thibault J. Y; Levy, Yoann; Bulgakova, Nadezhda M.; Mocek, Tomã¡å; Orazi, Leonardo
abstract

Highly regular laser-induced periodic surface structures (HR-LIPSS) have been fabricated on surfaces of Mo, steel alloy and Ti at a record processing speed on large areas and with a record regularity in the obtained sub-wavelength structures. The physical mechanisms governing LIPSS regularity are identified and linked with the decay length (i.e. the mean free path) of the excited surface electromagnetic waves (SEWs). The dispersion of the LIPSS orientation angle well correlates with the SEWs decay length: the shorter this length, the more regular are the LIPSS. A material dependent criterion for obtaining HR-LIPSS is proposed for a large variety of metallic materials. It has been found that decreasing the spot size close to the SEW decay length is a key for covering several cm2 of material surface by HR-LIPSS in a few seconds. Theoretical predictions suggest that reducing the laser wavelength can provide the possibility of HR-LIPSS production on principally any metal. This new achievement in the unprecedented level of control over the laser-induced periodic structure formation makes this laser-writing technology to be flexible, robust and, hence, highly competitive for advanced industrial applications based on surface nanostructuring.


2017 - Innovative high-speed femtosecond laser nano-patterning for improved adhesive bonding of Ti6Al4V titanium alloy [Articolo su rivista]
Rotella, Giovanna; Orazi, Leonardo; Alfano, Marco; Candamano, Sebastiano; Gnilitskyi, Iaroslav
abstract

In this work the effect of femtosecond Yb fiber laser irradiation on Ti6Al4V titanium alloy is assessed. An extensive experimental campaign is carried out to survey surface properties through the use of SEM, AFM, EDS mapping and contact angle measurements. It is shown that the generation of uniform nanoscale laser induced periodic surface structures (LIPSS) allows to tailor surface properties and improves adhesive bonding with epoxy resin. The potential of the technique to improve the durability of the joints against accelerated aging is also evaluated.


2017 - Laser Nanopatterning for Wettability Applications [Articolo su rivista]
Orazi, Leonardo; Gnilitskyi, Iaroslav; Serro, Ana Paula
abstract

We report on periodic, homogeneous nanoripples fabricated on stainless steel (SS), copper (Cu), and aluminum (Al) substrates using an ytterbium pulsed femtosecond laser. These structures called laser induced periodic surface structures (LIPSS) are processed at a relatively high-speed and over large areas. This paper investigates the effect of LIPSS on a wettability behavior of SS, Cu, and Al surfaces. It is shown that nanoripples significantly influenced the wettability character of these metals turning them from hydrophilic to hydrophobic behavior.


2017 - Method and System of Ultrafast Laser Writing of Highly-Regular Periodic Structures [Altro]
Orazi, Leonardo; Gnilitskyi, Iaroslav; Thibault, Derrien; Bulgakova, Nadezhda; Mocek, Tomáš
abstract

A method, a product by the method and device of preparation of highly-regular periodic structure using a pulsed laser beam irradiating a spot on a surface of a substrate are disclosed. The method of direct formation of highly-regular periodic structure on a materials uses activation of Surface Electromagnetic Wave (SEW) interfering with the laser beam on the surface of the substrate in a manner which ensures high quality and regularity of the obtained pattern.(FR)La présente invention concerne un procédé, un produit obtenu par le procédé et un dispositif de préparation d'une structure périodique très régulière à l'aide d'un faisceau laser pulsé irradiant un point sur une surface d'un substrat. Le procédé de formation directe d'une structure périodique très régulière sur des matériaux utilise l'activation d'une onde électromagnétique de surface (SEW) interférant avec le faisceau laser sur la surface du substrat de manière à assurer une qualité et une régularité élevées du motif obtenu.


2017 - Method and System of Ultrafast Laser Writing of Highly-Regular Periodic Structures [Brevetto]
Orazi, Leonardo; Gnilitskyi, Iaroslav; Derrien, Thibault; Bulgakhova, Nadezhda; Mocek, Tomáš
abstract

A method, a product by the method and device of preparation of highly-regular periodic structure using a pulsed laser beam irradiating a spot on a surface of a substrate are disclosed. The method of direct formation of highly-regular periodic structure on a materials uses activation of Surface Electromagnetic Wave (SEW) interfering with the laser beam on the surface of the substrate in a manner which ensures high quality and regularity of the obtained pattern.


2017 - Multifunctional properties of high-speed highly uniform femtosecond laser patterning on stainless steel [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Rota, Alberto; Ctvrtlik, Radim; Serro, Ana Paula; Gualtieri, Enrico; Orazi, Leonardo
abstract

Highly-regular laser-induced periodic surface structures essentially change surface properties of treated surfaces. Here, effect of HR-LIPSS on optical, tribological, mechanical and wetting properties of stainless steel were systematically investigated.


2017 - Multifunctional properties of high-speed highly uniform femtosecond laser patterning on stainless steel [Relazione in Atti di Convegno]
Gnilitskyi, I.; Rota, A.; Ctvrtlik, R.; Serro, A. P.; Gualtieri, E.; Orazi, L.
abstract

Highly-regular laser-induced periodic surface structures essentially change surface properties of treated surfaces. Here, effect of HR-LIPSS on optical, tribological, mechanical and wetting properties of stainless steel were systematically investigated.


2016 - Cell and Tissue Response to Modified by Laser-induced Periodic Surface Structures Biocompatible Materials for Dental Implants [Relazione in Atti di Convegno]
Gnilitskyi, I.; Pogorielov, M.; Dobrota, D.; Viter, R.; Orazi, L.; Mischenko, O.
abstract

The use of femtosecond laser-induced periodic surface structures (LIPSS) for dental implants surface modification for improving cell adhesion and proliferation is reported. Results demonstrated higher response of cells on modified surface compared to untreated ones.


2016 - Cell and tissue response to modified by laser-induced periodic surface structures biocompatible materials for dental implants [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Pogorielov, Maksym; Dobrota, Dusan; Viter, Roman; Orazi, Leonardo; Mischenko, Oleg
abstract

The use of femtosecond laser-induced periodic surface structures (LIPSS) for dental implants surface modification for improving cell adhesion and proliferation is reported. Results demonstrated higher response of cells on modified surface compared to untreated ones.


2016 - Diffraction gratings prepared by HR-LIPSS for new surface plasmon-polariton photodetectors and Sensors [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Mamykin, Sergiy; Dusheyko, Mykhaylo; Borodinova, Tatiana; Maksimchuk, Nataliia; Orazi, Leonardo
abstract

New method based on HR-LIPSS for diffraction grating formation on preliminary fabricated p-n junction on Si substrate are suggested. This allows to produce surface plasmonpolariton photodetectors based on periodically corrugated thin metal plasmon-carrying films.


2016 - Formation and Application of highly-regular LIPSS on Surface of Silicon Crystals [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Orazi, Leonardo; Bulgakova, Nadezhda; Gruzdev, Vitaly
abstract

Femtosecond laser pulses of sub-MHz repetition rate induce highly regular periodic surface structures on silicon by combining electron emission and ultrafast heating. They are favorable for photovoltaic, optoelectronic, and biomedical applications.


2016 - Highly regular LIPSS on silicon decorated with gold nanoparticles for plasmonic applications [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Orazi, Leonardo; Borodinova, Tatiana; Dusheyko, Mykhaylo; Maksimchuk, Nataliya; Ivaschuk, Anatoliy; Yakymenko, Yuriy I.; Mamykin, Sergiy
abstract

Plasmonic properties of gold nanoparticles self-assembled on silicon surfaces are significantly enhanced by a periodic surface ripples induced by ultrashort laser pulses. The nanostructured surfaces open new perspectives for production of photonic and plasmonic-sensor elements.


2016 - Highly Regular Nanostructuring of Si Surface by Ultrashort Laser Pulses [Relazione in Atti di Convegno]
Gnilitskyi, I.; Orazi, L.; Bulgakova, N. M.; Gruzdev, V.
abstract

Sub-MHz repetition rate femtosecond laser pulses produce extremely regular periodic surface structures on silicon surface due to competition between ultrafast heating and electron-emission. They allow manufacturing of novel devices for solar, optoelectronic, and biomedical applications.


2016 - Highly regular nanostructuring of Si surface by ultrashort laser pulses [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Orazi, Leonardo; Bulgakova, Nadezhda M.; Gruzdev, Vitaly
abstract

Sub-MHz repetition rate femtosecond laser pulses produce extremely regular periodic surface structures on silicon surface due to competition between ultrafast heating and electron-emission. They allow manufacturing of novel devices for solar, optoelectronic, and biomedical applications.


2016 - Laser nanopatterning for wettability applications [Relazione in Atti di Convegno]
Orazi, L.; Gnilitskyi, I.; Paula Serro, A.
abstract

We report on periodic, homogenous nanoripples fabricated on stainless steel (SS), copper (Cu) and aluminium (Al) substrates using an ytterbium pulsed femtosecond laser. These structures called Laser Induced Periodic Surface Structures (LIPSS) are processed at a relatively high-speed allowing us to fabricate quasi regular nanoripples in a short time over large areas. This paper investigates the effect of LIPSS on wettability behavior of SS, Cu and Al surfaces. It is shown that nanoripples significantly influenced the wettability character of these metals turning them from hydrophilic to hydrophobic behavior. The most notable behavioral change is observed for SS and Al, where strong hydrophobicity is observed after the generation of LIPSS.


2016 - Mechanisms of high-regularity periodic structuring of silicon surface by sub-MHz repetition rate ultrashort laser pulses [Articolo su rivista]
Gnilitskyi, Iaroslav; Gruzdev, Vitaly; Bulgakova, Nadezhda M.; Mocek, Tomáš; Orazi, Leonardo
abstract

Silicon is one of the most abundant materials which is used in many areas of modern research and technology. A variety of those applications require surface nanopatterning with minimum structure defects. However, the high-quality nanostructuring of large areas of silicon surface at industrially acceptable speed is still a challenge. Here, we report a rapid formation of highly regular laser-induced periodic surface structures (HR-LIPSS) in the regime of strong ablation by infrared femtosecond laser pulses at sub-MHz repetition rate. Parameters of the laser-surface interactions and obtained experimental results suggest an important role of electrostatically assisted bond softening in initiating the HR-LIPSS formation.


2016 - Nano patterning of AISI 316L stainless steel with Nonlinear Laser Lithography: Sliding under dry and oil-lubricated conditions [Articolo su rivista]
Gnilitskyi, Iaroslav; Rotundo, Fabio; Martini, Carla; Pavlov, Ihor; Ilday, Serim; Vovk, Evgeny; Ilday, Fatih Ömer; Orazi, Leonardo
abstract

Femtosecond laser-based Nonlinear Laser Lithography (NLL) was applied to AISI 316L stainless steel, which requires surface modification to achieve satisfactory tribological behaviour. NLL advances over the well-known Laser Induced Periodic Surface Structures (LIPSS) in terms of uniformity and long-range order of high speeds, over large areas. A galvanometric scanner head was used for an high production rate. Dry and lubricated sliding tests, considering different orientations of the nanotexture showed that COF values after NLL treatment are significantly lower. In lubricated tests, COF values of NLL-treated surfaces are nearly half the values of untreated surfaces, whereas the difference further increases when measured in dry conditions, where the orientation of the surface texturing influences the results.


2016 - Self-assembling of Gold Nanoparticles on Si-based Laser Nanotextured 1D Surface for Plasmonic Application [Relazione in Atti di Convegno]
Gnilitskyi, I.; Dusheyko, M.; Borodinova, T.; Mamykin, S.; Maksimchuk, N.; Ivaschuk, A.; Yakymenko, Yu.; Orazi, L.
abstract

Excitation of surface plasmon resonances has been observed on laser-induced highly-regular 1D periodic Si surface covered with Au nanoparticles. The nanostructured surfaces open new perspectives for production of photonic and plasmonic sensor elements.


2016 - Self-assembling of gold nanoparticles on si-based laser nanotextured 1D surface for plasmonic application [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Dusheyko, M.; Borodinova, T.; Mamykin, S.; Maksimchuk, N.; Ivaschuk, A.; Yakymenko, Y. u.; Orazi, Leonardo
abstract

Excitation of surface plasmon resonances has been observed on laser-induced highly-regular 1D periodic Si surface covered with Au nanoparticles. The nanostructured surfaces open new perspectives for production of photonic and plasmonic sensor elements.


2015 - CNC paths optimization in laser texturing of free form surfaces [Relazione in Atti di Convegno]
Orazi, Leonardo; Montanari, F.; Campana, G.; Tomesani, L.; Cuccolini, G.
abstract

Laser Texturing and Laser Engraving of free form surfaces are interesting alternative to EDM and micro milling in the fabrication of moulds and dies. The material removal rate of this process is typically very low and the maximum working area is limited by the maximum travel range of the galvanometric scanning head and also by the maximum deflection of the scanner or the surface curvature. As a consequence, in order to manufacture large or free form surfaces, a set of placements of the scanning head respect to the work piece must be calculated and controlled by the CNC. The number of these placements can be quite high due the small amount of material removed in each of them and the non-operative time spent to move the scanning head can be relevant compared to the overall time. In this work a method based on the solution of the Traveling Salesman Problem is proposed with the aim to optimise the number of displacements of the scanning head and generally in order to reduce the number of movement of the numerically controlled axes. The method that takes into account both the architecture and the dynamic characteristics of a 5 axis CNC system was implemented in the CALM (Computer Aided Laser Manufacturing) software used to program the laser path for part texturing and applied in industrial cases.


2015 - Laser-patterning stainless steel with nonlinear laser lithography for enhanced tribological properties [Relazione in Atti di Convegno]
Gnilitskyi, Iaroslav; Pavlov, I.; Rotundo, F.; Orazi, Leonardo; Ilday, S.; Martini, C.; Ilday, F. Ö.
abstract

This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL).


2015 - Laser-patterning stainless steel with nonlinear laser lithography for enhanced tribological properties [Relazione in Atti di Convegno]
Gnilitskyi, I.; Pavlov, I.; Rotundo, F.; Orazi, L.; Ilday, S.; Martini, C.; Ilday, F. O.
abstract


2015 - Nonlinear laser lithography for enhanced tribological properties [Relazione in Atti di Convegno]
Gnilitskyi, I.; Pavlov, I.; Rotundo, F.; Orazi, L.; Martini, C.; Ilday, F. O.
abstract

This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL).


2015 - Nonlinear laser lithography to control surface properties of stainless steel [Articolo su rivista]
Orazi, Leonardo; Gnilitskyi, Iaroslav; Pavlov, I.; Serro, A. P.; Ilday, S.; Ilday, F. O.
abstract

In the present work a novel method to improve the surface properties of stainless steel is presented and discussed. The method, based on the use of a high repetition rate femtosecond Yb fibre laser, permits generation of highly reproducible, robust, uniform and periodic nanoscale structures over a large surface area. The technique is characterized by high productivity, which, in its most simple form, does not require special environmental conditioning. Surface morphology is scrutinized through SEM and AFM analyses and wettability behaviour is investigated by means of the sessile drop method using distilled–deionized water. It is shown that optimization of process parameters promotes anisotropic wetting behaviour of the material surface.


2015 - Ottimizzazione dei percorsi CNC per lavorazioni laser di superfici free form [Capitolo/Saggio]
Montanari, Federico; Cocconcelli, Marco; Orazi, Leonardo; Rubini, Riccardo
abstract

L’utilizzo della tecnologia Laser, in lavorazioni Laser Texturing ed Engraving, per la realizzazione di superfici free form è un’interessante alternativa alle lavorazioni EDM e di micro fresatura nella fabbricazione di stampi e matrici. Il tasso di rimozione del materiale di questo processo è tipicamente molto basso e la massima area di lavoro è limitata dal campo di spostamento massimo della testa di scansione galvanometrica ed anche dalla deformazione massima dello scanner o la curvatura della superficie. Di conseguenza, al fine di realizzare superfici free form o grandi, è necessario eseguire una serie di posizionamenti della testa laser rispetto al pezzo da lavorare, calcolati e controllati dal CNC. Il numero di questi posizionamenti può essere molto alto a causa della piccola quantità di materiale asportato in ciascuno di essi ed il tempo non operativo speso per spostare la testina di scansione può essere rilevante rispetto al tempo complessivo. In questo lavoro viene proposto un metodo basato sulla soluzione del problema del commesso viaggiatore, con lo scopo di ottimizzare il numero di spostamenti della testa di scansione e generalmente per ridurre il numero di movimenti degli assi a controllo numerico. Il metodo, che tenga conto sia l'architettura e le caratteristiche dinamiche del sistema CNC 5 assi, è stato implementato nel CALM software (Computer Aided Laser Manufacturing) utilizzato per programmare il percorso laser per parte texturing e applicata in casi industriali


2015 - Structure, phase composition and microhardness of vacuum-arc multilayered Ti/Al, Ti/Cu, Ti/Fe, Ti/Zr nano-structures with different periods [Articolo su rivista]
Demchishin, A. V.; Gnilitskyi, Iaroslav; Orazi, Leonardo; Ascari, A.
abstract

The microstructure, phase composition and microhardness of multilayered Ti/Al, Ti/Cu, Ti/Fe and Ti/Zr condensates produced on stainless steel substrates via vacuum-arc evaporation of pure metals were studied. The sublayer periods (Λ) were regulated in the range 80–850 nm by varying the vacuum discharge current and the duration of the successive depositions of metallic plasma onto the substrates while maintaining the total deposition time constant. The regularity of the obtained nanostructures was investigated by scanning and transmission electron microscopy while phase compositions were identified with X-ray diffraction (XRD) analysis in order to evidence the presence of interdiffusion and the amount of intermetallics. Condensates cross sections were mechanically characterized by means of microhardness tests. Measurements were correlated to the periods and to the presence of intermetallics.


2014 - Laser surface hardening of large cylindrical components utilizing ring spot geometry [Articolo su rivista]
Orazi, Leonardo; Liverani, Erica; Ascari, Alessandro; Fortunato, Alessandro; Tomesani, Luca
abstract

A new process, based on ring spot geometry, is presented for laser surface hardening of large cylindrical components. The proposed technique leads to a very hard, deep and uniform hardened layer along the entire work piece surface without introducing a tempered zone, making the process very attractive compared to conventional induction hardening that exhibits both low energy efficiency and poor flexibility. A complete physical model is presented for the process, together with a study of the influence of process parameters on the final outcome. The results of an extensive validation campaign, carried out on AISI 1040 specimens, are also reported.


2014 - Pulsed Laser Ablation of Lithium Ion Battery Electrodes [Relazione in Atti di Convegno]
Lutey, Adrian H. A.; Fortunato, Alessandro; Ascari, Alessandro; Carmignato, Simone; Orazi, Leonardo
abstract

Lithium ion battery electrodes have been exposed to 1064nm nanosecond pulsed laser irradiation with pulse energy in the range 8μJ - 1mJ and fluence in the range 3:2 -395J=cm2. Experiments have been executed at translational velocities of 100mm=s and 1m=s, allowing individual characterization of the graphite and lithium metal oxide coatings of the copper anode and aluminum cathode, respectively, as well as that of the complete multi-layer structures. A 3D optical profiler has been utilized to measure the incision depth of all samples and allow observation of the process quality. At high velocity, partial or complete removal of the upper coating layers was achieved with little or no impact on the underlying metallic layers. At low velocity, complete cuts were possible under certain conditions, with process efficiency found to be almost entirely governed by the response of the metallic layers. While the coating layers of each electrode exhibited different responses than the metallic layer, the influence of the latter was found to be dominant for cutting operations. Shorter pulses with fluence in the range 30-60J=cm2 were found to lead to optimum process outcomes with the employed laser source


2013 - A Comprehensive Model for Laser Hardening of Carbon Steels [Articolo su rivista]
Fortunato, Alessandro; Ascari, Alessandro; Liverani, Erica; Orazi, Leonardo; Cuccolini, Gabriele
abstract

This article illustrates the development of a complete and exhaustive mathematical model for the simulation of laser transformation hardening of hypo-eutectoid carbon steels. The authors propose an integrated approach aimed at taking into consideration all the phenomena involved in this manufacturing process, with particular attention to implementing easy mathematical models in order to optimize the trade-off between the accuracy of the predicted results and the computational times. The proposed models involve the calculation of the 3D thermal field occurring into the workpiece and predict the microstructural evolution of the target material exploiting an original approach based on the definition of thermodynamic thresholds, which can be considered as a physical constant of the material itself. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics, fast austenization of the steel, and tempering effect due to mutually interacting beam trajectories. The accuracy of the model is presented by means of hardness comparisons between hardness predictions and measurements in single and double paths surface treating of AISI 1040


2013 - A comprehensive model for laser hardening of carbon steels [Relazione in Atti di Convegno]
Fortunato, A.; Ascari, A.; Liverani, E.; Orazi, L.; Cuccolini, G.
abstract

This article illustrates the development of a complete and exhaustive mathematical model for the simulation of laser transformation hardening of hypo-eutectoid carbon steels. The authors propose an integrated approach aimed at taking into consideration all the the phenomena involved in this manufacturing process, with particular attention to implementing easy mathematical models in order to optimize the trade-off between the accuracy of the predicted results and the computational times. The proposed models involve the calculation of the 3D thermal field occurring into the workpiece and predict the microstructural evolution of the target material exploiting an original approach based on the definition of thermodynamic thresholds which can be considered as a physical constant of the material itself. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics, fast austenization of the steel and tempering effect due to mutually interacting beam trajectories. Copyright © 2013 by ASME.


2013 - An exhaustive model for the laser hardening of hypo eutectoid steelHigh-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications II [Relazione in Atti di Convegno]
Alessandro, Fortunato; Orazi, Leonardo; Cuccolini, Gabriele; Alessandro, Ascari
abstract

This article presents an exhaustive mathematical model for the simulation of hypo-eutectoid carbon steel transformations during laser hardening. The proposed model takes into consideration all the the phenomena involved in the process with particular attention to implementing easy mathematical formulas in order to optimize the trade-off between the accuracy of the predicted results and the computational times. The proposed model calculates the 3D thermal field occurring into the workpiece and predicts the microstructural evolution of the target material exploiting an original approach based on the definition of thermodynamic thresholds. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics,scanning strategy of the target and tempering effect due to mutually interacting beam trajectories.


2013 - Laser micro-welding of high carbon steels [Microsaldatura laser di acciai ad elevato tenore di carbonio] [Articolo su rivista]
Ascari, Alessandro; Fortunato, Alessandro; Orazi, Leonardo
abstract

High carbon steels are commonly used in modern mechanical industry due to their good mechanical properties and to their relatively low cost. Unfortunately, when dealing with welding processes, these materials must be set aside because of their very high crack susceptibility and more refined and expensive steels must be taken into consideration, such as HSLA, DP and TRIP ones, thanks to their lower carbon equivalent and similar, or even better, mechanical properties. In micro-scale components industry the use of high carbon steels is also very common, in particular in precision mechanics, watch and MEMS industry. Considering the very low thicknesses typical of these components and the intrinsic welding difficulty related to the material, several studies stressed on the possibility to exploit nanosecond pulsed lasers in welding this kind of steels. These sources, taking advantage from the short duration of the pulse and from a repetition rate as high as I MHz, allow a very accurate control of the heat input delivered to the material and pave new ways in micro-welding of medium and high carbon steels. The present paper deals with the exploitation of a 20 W nanosecond pulsed laser source in welding low thickness C70 (AISI1070) plain carbon steel. The process is studied by evaluating the influence of the main parameters on its feasibility. The activity pointed out that, by properly selecting the main parameters, it is possible to achieve sound and crack-free weld beads with a maximum penetration as high as 200 μm and a very small heat affected zone. The main interesting point concerning this specific welding process is related to the fact that, by simply selecting the proper process parameters, it is possible to achieve high productivity working cycles involving laser cutting, welding and marking on the same machine and exploiting the same workpiece positioning.


2013 - Laser shock peening and warm laser shock peening: process modeling and pulse shape influenceHigh-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications II [Relazione in Atti di Convegno]
Alessandro, Fortunato; Orazi, Leonardo; Cuccolini, Gabriele; Alessandro, Ascari
abstract

Laser shock peening is a well-known technology able to enhance the fatigue life of mechanical components by means of the introduction of residual stresses on their surface. These stresses are induced by means of the recoil pressure caused by the abrupt expansion, in a confining medium, of a laser-vaporized coating layer. If high power densities are used the recoil pressure can be high enough to induce compressive residual stresses on the target surface and to modify its mechanical properties. These mechanical properties can be predicted if the recoil pressure of the ablating layer is determined. In this paper the influence of the laser pulse shape on the recoil pressure is determined by means of a proper modeling of the whole process and the difference between "cold" and "warm" laser shock peening is pointed out.


2013 - 5 Axes computer aided laser milling [Articolo su rivista]
Cuccolini, Gabriele; Orazi, Leonardo; Fortunato, Alessandro
abstract

In this paper a 5 axes CAM procedure for the laser milling of free form surfaces has been developed and experimentally verified. The laser beam is deflected by a galvanometric scanning head and is directly moved on the working surface by the CNC controlled axes of a machine center. The procedure has been implemented in a software called CALM (computer aided laser manufacturing) able to generate the laser paths and the movements of the controlled axes reducing the defects on the workpiece. The approach is based on the sequential overlapping of the scanning passes on the working area. The different working areas in every laser displacement are obtained directly from the triangulation of the whole surface to machine.


2012 - Numerical evaluation of the reflectivity coefficient in laser surface hardening simulation [Articolo su rivista]
A., Fortunato; A., Ascari; Orazi, Leonardo; G., Campana; Cuccolini, Gabriele
abstract

This paper reports the results concerning the simulation of a laser surface hardening process of a cylindrical surface. In particular it focuses on the problems related to the definition of the physical parameter values necessary in order to achieve an accurate and reliable simulation. The strict dependency of laser process simulation results on the physical parameters describing the target material is, in fact, a well known matter, especially considering that the values of these parameters change during the process dependently on temperature and time. Moreover in laser surface hardening this problem is even more important because melting of the target material should be avoided, surface roughness plays an important role and, sometimes, the surface is coated with absorbent layers. These factors increase the complexity of the simulations and make the evaluation of the physical parameters more difficult and critical. The results presented in this paper are obtained on AISI420B steel, coated with graphite and treated with a direct diode laser. Considering the above mentioned conditions, a plausible temperature dependent reflectivity coefficient was evaluated and its robustness was investigated. This reflectivity coefficient can be used with a good approximation for the simulation of laser hardening treatments of many carbon steels.


2012 - Numerical simulation of nanosecond pulsed laser welding of eutectoid steel components [Articolo su rivista]
A., Fortunato; A., Ascari; Orazi, Leonardo; Cuccolini, Gabriele; G., Campana; G., Tani
abstract

This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel grades. These materials are difficult to weld due to their poor ductility. In particular, in closed seam welding, the laser beam starts and finishes in the same point thus increasing the risk of cracks. A numerical simulation of micro-welding of nearly eutectoid steels by nanosecond pulsed laser is carried out to evaluate the weld pool dimension and the heat-affected zone extension. Optimized welding parameters and strategy are determined by means of simulation and they are successfully applied in the welding of a 1.0%C shaft and a 0.7%C gear.


2012 - The influence of process parameters on porosity formation in hybrid LASER-GMA welding of AA6082 aluminum alloy [Articolo su rivista]
Ascari, A; Fortuanto, A.; Orazi, Leonardo; Campana, G.
abstract

This paper deals with an experimental campaign carried out on AA6082 8 mm thick plates in order to investigate the role of process parameters on porosity formation in hybrid LASER-GMA welding. Bead on plate weldments were obtained on the above mentioned aluminum alloy considering the variation of the following process parameters: GMAW current (120 and 180 A for short-arc mode, 90 and 130 A for pulsed-arc mode), arc transfer mode (short-arc and pulsed-arc) and mutual distance between arc and LASER sources (0, 3 and 6 mm). Porosities occurring in the fused zone were observed by means of X-ray inspection and measured exploiting an image analysis software. In order to understand the possible correlation between process parameters and porosity formation an analysis of variance statistical approach was exploited. The obtained results pointed out that GMAW current is significant on porosity formation, while the distance between the sources do not affect this aspect.


2011 - A New Computationally Efficient Model for Tempering in Multitrack Laser Hardening in Medium Carbon Steels [Articolo su rivista]
A., Fortunato; Orazi, Leonardo; G., Tani
abstract

The bottleneck in laser hardening principally occurs when large surfaces have to be treated because this process situation leads to multitrack laser scanning in order to treat all the component surfaces. Unfortunately, multitrack laser trajectories generate an unwanted tempering effect that depends on the overlapping of two close trajectories. To reduce the softening effects, a simulator capable to optimize the process parameters, such as laser power and speed and number and types of trajectories, could sensibly increase the applicability of the process. In this paper, an original model for the tempering is presented. By introducing a tempering time factor for the martensitic transformation, the hardness reduction can be predicted according to any laser process parameters, material, and geometry. Experimental comparisons will be presented to prove the accuracy of the model.


2011 - il trattamento termico superficiale mediante laser [Articolo su rivista]
A., Ascari; A., Fortunato; Orazi, Leonardo; G., Tani
abstract

Il trattamento di indurimento superficiale mediante laser di componenti meccanici è un sistema di lavorazione che negli ultimi anni ha incontrato un consenso industriale in continua crescita, grazie ad alcune caratteristiche peculiari che lo differenziano dai suoi diretti competitori. Alla base di questa tecnologia risiede la necessità di riscaldare la superficie del componente in modo selettivo, mantenendo il più possibile controllata la temperatura la quale, infatti, deve essere superiore ai valori critici che sono funzione del materiale e dello specifico trattamento da realizzare, ma inferiore al punto di fusione del materiale stesso al fine di non causare un inaccettabile deterioramento della superficie del pezzo.


2011 - Investigation on porosity formation in AA6082 hybrid laser-gmaw welding [Relazione in Atti di Convegno]
A., Ascari; A., Fortunato; Orazi, Leonardo; G., Campana; G., Tani
abstract

This paper refers to the results obtained in the investiga-tion on bubbles formation in hybrid Laser-GMAWwelding. Bead on plate weldings were obtained on 8 mm thick AA6082 plates and the process parameters investigated were: GMAW current, arc transfer mode and mutual distance between arc and laser sources. Bubbles were observed by means of X-ray inspection techniques and measured exploiting an image analysis software. Finally a correlation, based on analysis of variance, between process parameters and porosity formation is proposed.


2011 - Microlavorazioni di superfici complesse [Articolo su rivista]
Orazi, Leonardo; Cuccolini, Gabriele; Claudio, Mantega; Giovanni, Tani
abstract

Una delle più interessanti caratteristiche nell’uso delle sorgenti laser per le lavorazioni industriali è sicuramente l’insensibilità dello “strumento” dalle proprietà meccaniche del materiale in lavorazione. Questa caratteristica, unita alla possibilità di collimare il fascio su diametri di dimensioni centesimali e di controllarne lo spostamento con notevole precisione grazie ai moderni scanner, crea le premesse per rendere il processo di fresatura e micro-fresatura laser (Laser Milling) molto efficace nella fabbricazione di stampi, punzoni, conchiglie e in tutte quelle situazioni nelle quali geometrie complesse con particolari molto dettagliati devono essere ottenute su materiali “coriacei” alle tradizionali lavorazioni meccaniche per asportazione.


2011 - Warm Laser Shock Peening: New developments and process optimization [Articolo su rivista]
G., Tani; Orazi, Leonardo; A., Fortunato; A., Ascari; G., Campana
abstract

Laser Shock Peening is a well-known technology able to enhance the fatigue life of mechanical components. Surface residual stress is induced by means of the recoil pressure of an ablated coating in a confining medium interacting with a high power density laser.Warm Laser Shock Peening is obtained by laser peening a pre-warmed workpiece surface: combining the thermal effect of the pre-heated surface and the mechanical phenomenon of the recoil shock pressure, the dynamic aging of the surface microstructure is obtained. Precipitates surrounded by dense dislocation together with residual stress considerable increase the mechanical properties of the workpiece.


2010 - A new computationally efficient model for martensite to austenite transformation in multi-tracks laser hardening [Articolo su rivista]
Orazi, Leonardo; A., Fortunato; G., Campana; A., Ascari; Cuccolini, Gabriele; G., Tani
abstract

When large steel surfaces have to be hardened by means of a laser heat treatment a multi-track scanning strategy must be exploited in order to overcome the relatively small dimension of the beam spot. Multi-track scanning strategies imply a mutual interaction of adjacent passes, which leads to the tempering of the previously hardened material in dependence to the degree of overlapping of the adjacent trajectories. In this paper an original and computationally efficient modeling for large surfaces processing of hardenable steels by means of laser was developed. Experimental tests have been conducted on AISI 1070 carbon steel and the comparisons with the predicted results are showed.


2010 - An automated procedure for material removal rate prediction in laser surface micromanufacturing [Articolo su rivista]
Orazi, Leonardo; Cuccolini, Gabriele; A., Fortunato; G., Tani
abstract

In this paper, a laser surface micromachining process planning system is presented. In this system, based on a regression model approach, the empirical coefficients, which provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. Numerical models generally present some limits due to the elevated calculation time requested to simulate the laser micromachining of industrial features, especially when transient solutions are considered, and, for this reason, to carry out a useful industrial tool for the evaluation of the material removal rate, the regression model represents the best solution. The presented statistical method, avoiding physical considerations, correlates the material removal rate with the process parameters in a very short calculation time. The automatic procedure for the generation of the coefficients of the regression polynomial permits to easily extend the regression model to any working material and system configuration allowing us to determine the best process parameters in a very short period of time. The results of this work have been patented.


2010 - An Efficient Model for Laser Surface Hardening of Hypo-Eutectoid Steels [Articolo su rivista]
Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele; G., Tani
abstract

This paper presents a model able to predict the austenization of hypo-eutectoid steels during very fast heat cycle such as laser hardening. Laser surface hardening is a process highly suitable for hypo-eutectoid carbon steels with carbon content below 0.6% or for low alloy steels where the critical cooling rate is reached by means of the thermal inertia of the bulk. As proposed by many authors, the severe heat cycle occurring in laser hardening leads to the pearlite to austenite microstructures transformation happening to a temperature much higher than the eutectoid temperature Ac1 and, afterwards, all the austenite predicted during the heating phase become martensite during quenching. Anyway, all these models usually generate a predicted hardness profile into the material depth with an on–off behavior or very complicated and time consumed software simulators. In this paper, a new austenization model for fast heating processes based on the austenite transformation time parameter Ip→a is proposed. By means of the Ip→a parameter it is possible to predict the typical hardness transition from the treated surface to the base material. At the same time, this new austenization model also reduces the calculation time. Ip→a was determined by experimental tests and it was postulated to be constant for low-medium carbon steels. Several experimental examples are proposed to validate the assumptions and to show the accuracy of the model.


2010 - Hybrid metal-plastic joining by means of laser [Articolo su rivista]
A., Fortunato; Cuccolini, Gabriele; A., Ascari; Orazi, Leonardo; G., Campana; G., Tani
abstract

The growing need of lightweight components determined a large exploitation of non metallic materials such as polymers, fibres and elastomers in the industrial production with a consequent request of specifically optimized manufacturing processes. The high optimization demands in terms of cost, weight and productivity of the modern markets determined a growing interest towards hybrid components in which two or more different materials coexist in order to achieve specifically optimized characteristics. According to these considerations the work proposed in this article is aimed at experimentally evaluate the feasibility of joining processes between metal and plastic components by means of the exploitation of a laser source. The metallic material involved in the experimental trials is AISI 304 stainless steel joined in an overlapping configuration with several different polymers: PA66, glass fibre reinforced PA66, carbon fibre reinforced PA66. The laser source involved in this activity was a 100 W CW diode source equipped with a three axis cell. In order to evaluate the results of the joining process a tensile test was carried out on the obtained specimens.


2009 - A New Computationally Efficient Method in Laser Hardening Modeling. [Relazione in Atti di Convegno]
Orazi, Leonardo; A., Fortunato; G., Tani; G., Campana; A., Ascari; Cuccolini, Gabriele
abstract

Laser hardening is a laser assisted process devoted to the surface hardening of the mechanical components. This process is highly suitable for medium carbon steels with carbon content comprised between 0.2 - 0.6% or for low alloy steels which are usually surface hardened during their manufacturing process. Laser hardening technology is gaining a great industrial interest in the last years in fact, the possibility of integrating the heating source directly on the production line, together with the absence of the quenching medium, meets the production needs of modern industries. Laser hardening optimization could be complex especially when tempering due to multiple passes effects must be considered. Many research studies have been proposed in the last years aimed at predicting the optimal laser process parameters such as beam power density, beam velocity and scanning strategies. Many Authors agree with the assumption that the whole austenite resulting from the heating is transformed into martensite during the quenching. This is a valid approximation for single pass but could be a rough hypothesis in multiple-passes when the cooling rate could be not so high. Moreover hysteresis phenomena, due to the severe heat cycle occurring in laser hardening, should be taken into account for pearlite to austenite and martensite to austenite transformations during heating and for martensite tempering during multiple passes. In this paper the crucial problems to be faced regarding laser surface hardening modeling are discussed with respect to current literature. In particular, partial austenitization of the pearlite is suggested as a solution of the hardness prediction of the profile depth. Then three transformation parameters are proposed in order to take into account the hysteresis phenomena in martensite and pearlite transformations into austenite and in martensite tempering. Finally several experimental examples are proposed in order to validate the mentioned assumptions.


2009 - A New Computationally Efficient Model for Tempering in Multi-Tracks Laser Hardening. [Relazione in Atti di Convegno]
A., Fortunato; Orazi, Leonardo; G., Tani
abstract

The bottleneck in laser hardening principally occurs when large surfaces have to be treated because this process situation leads to multi-tracks laser scanning in order to treat all the component surface. Unfortunately, multi-tracks laser trajectories generate an unwanted tempering effect that depends on the overlapping of two close trajectories. To reduce the softening effects, a simulator capable to optimize the process parameters such as laser power and speed, number and types of trajectories, could sensibly increase the applicability of the process. In this paper an original model for the tempering is presented. By introducing a tempering time factor for the martensitic transformation, the hardness reduction can be predicted according to any laser process parameters, material and geometry. Experimental comparisons will be presented to prove the accuracy of the model.


2009 - An automated procedure for laser milling of textures for mould manufacturing [Abstract in Atti di Convegno]
Cuccolini, Gabriele; Orazi, Leonardo; G., Tani; A., Vaccari
abstract

In this paper an algorithm for texture generation by means of laser milling process is presented. The aim of this work is to develop an original software that automatically generates texture on general surfaces (cylinder, sphere, plane, cone) particular useful in mould manufacturing (automotive, leather, plastic molding, automotive and packaging).The geometries representative of the textures were obtained from bitmap images on two levels (white and black) or with a continuously variable density. The algorithm digitalizes the bitmap of the base texture and project it on the acquired surface realizing many replicas of it in order to cover all the working area. The system subdivides the single features of the texture and makes a triangulation of it (each pixel two triangles). The depth inside the material depends on the color gradient of the bitmap. The algorithm subdivide the texture in singles optical working areas and inside these areas the scanning heads deflect the laser beam and remove the material layer by layer as in milling.


2009 - Automated characterization of the material removal rate in laser manufacturing of TiAI6V4 and inconel 718 [Relazione in Atti di Convegno]
Orazi, Leonardo; Cuccolini, Gabriele; G., Tani
abstract

In this paper a system for the automatic determination of the material removal rate during laser milling process is presented. ”Laser milling” can be defined as an engraving process with a strictly controlled penetration depth. In industrial applications, when a new material have to be machined or a change in the system set-up occur the user has to perform a time-consuming experimental campaign in order to determine the correlation between the material removal rate and the process parameters. In these cases the numerical models present some limits due to the elevated calculation time requested to simulate the laser milling of industrial features. In the proposed system, based on a regression model approach, the empirical coefficients, that provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. A description of the automated method and the results obtained in engraving TiAl6V4 and Inconel 718 superalloy with a fiber laser are presented. The system can be adapted to every combination of material/laser source.


2009 - La saldatura laser tra plastica e metallo [Articolo su rivista]
A., Fortunato; Orazi, Leonardo; A., Ascari; G., Campana; Cuccolini, Gabriele; G., Tani
abstract

La saldatura laser plastica-metallo è una tecnologia sicuramente nuova ed innovativa e che ha notevoli vantaggi nella realizzazione di giunti per sovrapposizione. I vantaggi possono essere molteplici visto che le caratteristiche meccaniche del giunto saldato laser sono maggiori rispetto a tecnologie consolidate come l’incollaggio, rispetto al quale non restrizioni di natura ambientale di smaltimento di vapori e/o rifiuti, la tecnologia affianca i collegamenti meccanici espandendo la flessibilità progettuale del giunto. Non in ultimo, i costi di impianto e di funzionamento sono limitati dalle potenze in gioco, molto basse, e dai rendimenti complessivi delle sorgenti laser decisamente elevati.


2009 - Laser ablation simulation for copper [Articolo su rivista]
Tani, G.; Fortunato, A.; Orazi, L.; Cuccolini, G.
abstract

In this paper, a laser milling simulator package is shown and discussed. The software system has been developed to simulate the micro-manufacturing process using solid state lasers with pulse width in the range of 10 100 ns. The system can simulate the effects of the laser beam on the workpiece, keeping into account the surface conditions, the evolution of the workpiece temperature field, the phase changes in the material and the plasma plume effects. Simplifications concerning fluidodynamic and energy dispersions of the plasma plume are proposed. In particular, two empirical tuning parameters are considered: the first one is a global dispersion factor that keeps in account the fraction of energy lost in the environment by the plume; the second one is a spreading factor that permits to model the irradiated energy of the laser beam hitting the workpiece. The direct and coupled effects of these two parameters are evaluated and discussed. Copyright © 2009, Inderscience Publishers.


2009 - Laser hardening of hypo-eutectoid steels: an effective and efficient model [Abstract in Atti di Convegno]
Orazi, Leonardo
abstract

In this work a reliable and simple model to predict the hardness behavior in the surface layer during laser heat treatment is presented, the main advantage introduced by the model is to predict the smooth transition of the hardness and to be computationally efficient.An analysis of the austenization models found in literature is presented and an original algorithm is presented, based on a diffusion controlled parameter I_pa with a threshold uniformly distributed in the material. The carbon diffusion on a relatively long path between grains is neglected to improve the efficiency and the threshold values for AISI 1045 and AISI 1067 were experimentally obtained.The accuracy of the model was proved by means of experimental comparisons obtained with different laser powers and scanning speeds.


2009 - Laser Hardening of Large Cylindrical Martensitic Stainless Steel Surfaces [Relazione in Atti di Convegno]
A., Fortunato; Orazi, Leonardo; G., Campana; A., Ascari; Cuccolini, Gabriele; G., Tani
abstract

This paper deals with laser surfaces hardening process of martensitic stainless steel. The heat machined components are cylindrical shaped with a thin thickness. The heat treated area is larger than the laser spot dimension and for this reason multi-tracks or virtual spot technique are needed in order to process the whole surface. The typical problems of such a hardening method, concerning quenching and tempering involved phenomena, are faced and scanning strategies optimization are considered.The process optimization has been carried out by using a Laser Hardening Simulator (LHS) developed by the Authors. LHS allows to simulate the laser-material interaction in order to calculate the heat cycle into the bulk material and then the resulting micro-structures after the heat treatments according to laser scanning trajectories.


2009 - LASER hardening of 3D complex parts: industrial applications and simulation results [Abstract in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; A., Ascari; Cuccolini, Gabriele
abstract

Laser surface hardening of mechanical steel components is a rapidly developing manufacturing technology which allows to deal with small, confined and complex surfaces. It allows, in fact, to accurately focus the hardening treatment only where it is needed, without affecting the surrounding base material. This prerogative differentiates laser hardening from any other surface treatment, such as flame or induction, and makes possible to save time and energy during the process. On the other hand, when large surfaces have to be treated, the relatively small laser spot makes necessary to optimize new process strategies aimed at dealing with the inevitable tempering effect occurring when overlapping laser beam trajectories take place.According to these considerations the article analyzes the possibility to deal with large cylindrical surfaces, by means of laser surface hardening, exploiting the "apparent spot" technique. This solution applies on axisymmetric components and implies the combination of a rotation of the part to be treated and of the linear motion of the laser beam. In order to study the optimal process parameters involved in this technique a simulation analysis was carried out by means of a proprietary simulation software developed by the research group and a subsequent experimental campaign made possible to validate the whole procedure.


2009 - Reverse Engineering for the geometrical characterization of root canals in dental implant [Abstract in Atti di Convegno]
Cuccolini, Gabriele; Orazi, Leonardo; G., Tani; L., Laurentini; P., Baldissara
abstract

In this work an automated procedure to calculate the volume and the shape of humans root canals in which fiber posts should be inserted is presented. The currently commercial pivots are substantially smaller than the canals and their shapes are currently empirically determinated. The root canals replicas were acquired by means of a conoscopic laser scanning device mounted on a 4 axis controlled CNC measurement system. In order to acquire and analyze the scanned geometries an original software was developed.An experimental campaign was conducted on a set of about 100 teeth of different types. The morphologies obtained were divided in five classes by means of multivariate statistical analysis (cluster analysis). This subdivision provides anatomical information for the commercial producer of fiber posts, this can lead to a more suitable standardization of shapes and sizes of the commercial posts. So the aim of this research is to find the best adapted shape between the post and the canal for each family of teeth and a less invasive dental chairs for the patient.


2008 - An automated procedure for the geometrical characterization of root canals [Relazione in Atti di Convegno]
Tani, Giovanni; Orazi, Leonardo; Cuccolini, Gabriele
abstract

In this work an original system for the geometrical characterization of root canals for dental implants was developed and tested. The aim of this work is to determine the shape and the size of the posts that best fit a statistical population of root canals with a defined maximum amount of removed tissue. The task is performed by an accurate acquisition of the shape of a statistically significant batches of root impressions: the geometry are then processed to obtain the post geometry. The acquisition is carried out using a conoscopic laser scanning device mounted on a 4 axis controlled CNC measurement system. The shape of the root canals were measured for each type of tooth, obtaining an average 3-D computer design of the canal profiles. Several comparisons between the acquired geometry and the representative forms of commercial posts are finally presented.Copyright © 2008 by ASME.


2008 - Laser Ablation of Metals: A 3D Process Simulation for Industrial Applications [Articolo su rivista]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele
abstract

A model for laser milling simulation is presented in this paper. A numerical model able to predict the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of the velocity of the vapor/liquid front, and the physical state of the plasma plume were taken into account. The model is fully 3D and the simulations makes it possible to predict the ablated workpiece volume and the shape of the resulting craters for a single laser pulse or multiple pulses, or for any path of the laser spot. The numerical model was implemented in C++ and an overview of the code capacities is presented.


2008 - Optimization strategies of laser hardening of hypo-eutectoid steel [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; A., Ascari; Cuccolini, Gabriele
abstract

The interest towards LASER hardening of steels has been increasing since the last few years due to its undoubted advantages. The main drawback affecting this manufacturing technology is the tempering effect induced when multiple passes on the same surface must be carried out. In order to minimize the softening effect due to tempering and to speed up the process a numerical model for the simulation of the treatment is proposed. This model is able to detect the optimal LASER path trajectory according to the source parameters and the scanning velocity, and it is able to predict the resulting microstructures and the relating hardness. Some examples on an hypo-eutectoid steel are presented together with validation tests.


2008 - Prediction of hypo eutectoid steel softening due to tempering phenomena in laser surface hardening [Articolo su rivista]
G., Tani; Orazi, Leonardo; A., Fortunato
abstract

The paper presents a mathematical model for predicting material mechanical property variation, in laser hardening of hypo eutectoid steel, when the softening effects due to the overlapping trajectories are considered. This generally occurs during laser hardening of industrial parts, especially when wide areas have to be treated, due to the tempering phenomena. An original tempering model for the prediction of the hardness reduction is presented in this paper. The proposed model is integrated in a Laser Hardening simulation package, previously developed by the authors. Experimental activities are also presented to validate the model.


2008 - 3D modelling of LASER hardening and tempering of hypo-eutectoid steels [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; A., Ascari
abstract

In this paper a mathematical model solved by means of the finite differences method (FDM) for laser surface hardening of complex geometries is presented. The 3-D transient model constitutes a software package named Laser Hardening Simulator (LHS), which makes it possible to predict the extension of the treated area into the mechanical components and thus the hardened depth into the bulk material. The obtained microstructures and the resulting hardness with respect to the laser parameters and to the laser beam path strategy can be determined by considering the quenching and the tempering effects due to the overlapping trajectories. The initial workpiece microstructure is taken into account in the simulation by a digitized photomicrograph of the ferrite-pearlite distribution before the thermal cycle. In order to show the accuracy of the model, experimental trials were conducted on the keyway for spline machined on a hub made of C43. The domain discretization for the solution of the heat flux problem into the workpiece and for the diffusion of the carbon is carried out by means of a mesh generator strategy implemented into the code.


2008 - 3D modelling of LASER hardening and tempering of hypo-eutectoid steels [Articolo su rivista]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; A., Ascari
abstract

In this paper a mathematical model solved by means of the finite differences method (FDM) for laser surface hardening of complex geometries is presented. The 3-D transient model characterizes a software package named Laser Hardening Simulator (LHS), which makes it possible to predict the extension of the treated area into the mechanical components and thus the hardened depth into the bulk material. The obtained microstructures and the resulting hardness with respect to the laser parameters and to the laser beam path strategy can be determined by considering the quenching and the tempering effects due to the overlapping trajectories. The initial workpiece microstructure is taken into account in the simulation by a digitized photomicrograph of the ferrite-pearlite distribution before the thermal cycle. In order to show the accuracy of the model, experimental trials were conducted on the keyway for spline machined on a hub made of SAE 1043. The domain discretization for the solution of the heat flux problem into the workpiece and for the diffusion of the carbon is carried out by means of a mesh generator strategy implemented into the code.


2008 - 3D Transient Model for C02 laser hardening [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana
abstract

A 3D numerical model for the surface hardening process simulation carried out by means of a CO2 laser source is presented. The model is able to predict the extension of the treated area into the workpiece, the type of the resulting micro-structure and the optimal laser path strategy in order to minimize the micro-structural softening due to the tempering effect. The Fourier equation is solved using the Finite Difference Method (FDM) applied on a generical grid obtained by means of the domain discretization. The resulting time dependent temperature distribution into the workpiece is used for the evaluation of the induced heating cycle. By calculating the cooling velocity, the micro-structure transformation is determined together with the hardness in every point of the domain. The hardness reduction due to the tempering effect is also predictible. The computational times are small and the software is very suitable in industrial environment in the early stage of the process planning when several simulation runs must be performed. The modeling activity was developed by considering the class of the hypo-eutectoid steel. The experimental tests were realized on a C43 steel plate. The good agreement between the theoretical and experimental results is shown.


2007 - A numerical model for laser Ablation with Plasma [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; Cuccolini, Gabriele
abstract

In this paper a 3-D transient model for laser ablation modeling with plasma plume characterization is presented. The plasma plume was considered in local thermodynamical equilibrium (LTE) and the energy balance permits to evaluate the plume temperature, ion distribution and pressure under the assumption that the gas expansion, from the surface target, produces a sonic front. The plume energy balance is influenced by the energy lost for irradiation from the plume and by the quantity of laser beam energy reflected from the target surface. Then, the physical state of the plasma plume was evaluated by means of the energy balance into the plume which makes it possible to determine the plasma temperature, the plasma ionization and, subsequently, the optical thickness of the plasma. This model predicts the time dependent laser energy delivered to work-piece according to the process parameters and it represents a part of a laser milling simulator previously developed by the authors. A simplified model of the plume geometry is also performed.Numerical simulations have been conducted to quantify this influence on the plasma plume physical state. Several simulation runs are presented in order to show the LAS accuracy and facilities.


2007 - A numerical model for laser heat treatment of steels with microstructure evolution and the annealing effect [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; G., Campana; A., Fortunato; A., Ascari
abstract

The present paper deals with a software simulation system with the aim to completely model surface hardening treatment. The system is composed by two integrated physical-kinetic modules. The former is based on the Fourier equation, solved by means of the finite difference method (FDM) in the 3D transient regime and it is suitable to be adapted for each engineering material. The latter is based on the works proposed by Reti and Denis, which are based on a multi-phase transformation model solved by means of the finite difference method (FDM) in the 2D transient regime. The second module is suitable for each heat treatable steels and it is based on the knowledge of the TTT diagrams. It makes possible to predict the microstructure evolutions during the heat cycle and the final mechanical properties into the surface material due to the quenching effect. Each austenite transformation is, as known, time dependent and it is described by means of a set of coupled system of differential equations. The martensite transformation and all the intermediate quenching phases have been modelled and then can be predicted. Besides the tempering effects due to close passes of the laser spot onto the working surface have been taken into account and the ε-carbides precipitation and martensite tempering effect were modelled. The software simulation system was implemented in C++ programming environment by using the Object Oriented paradigm and graphic outputs was implemented by using OpenGL libraries. A mechanical component was laser heat treated, as requested by an industrial supplier, by adopting different solution in order to achieve the required hardened material area. The laser hardened component was then experimentally analyzed by means of micrographies and by hardness profiles measurements.


2007 - Constrained free form deformation as a tool for rapid manufacturing [Articolo su rivista]
Orazi, Leonardo
abstract

In this study an application of free form deformation for the editing of clouds of points or tessellated surfaces representing industrial parts is presented. The application is based on an efficient implementation of NURBS based free form deformation and the implementation of functions for imposing constraints to position, directions and curvatures of embedded objects. The developed functions permit the direct manipulation of triangulated surfaces eliminating the surface reconstruction stage, reducing the time requested in the reverse engineering process and, at the end, reducing the time to market. (C) 2006 Elsevier B.V. All rights reserved.


2007 - Geometrical inspection of designed and acquired surfaces [Articolo su rivista]
Orazi, Leonardo; G., Tani
abstract

In this study a series of procedures were implemented to compare acquired surfaces with the nominal data or to directly compare different scanned surfaces. In particular a morphological evaluation algorithm based on the extended Gaussian curvature (EGC) and a method to compare features based on aggregate normal orientation are presented. To perform the comparison between the features a simple procedure for segmentation was developed. The main characteristic of the two methods is a robust behavior referring to the scan orientation. The procedures were implemented as software modules in a graphic environment.


2007 - Laser Hardening Modelling: Comparison between Induction and Laser Hardening on a Mechanical Part [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; Cuccolini, Gabriele
abstract

In this paper a numerical model for simulation of hypo eutectoid steel laser hardening process is presented. The Finite Difference Method (FDM) was used to solve the heat transfer and the carbon diffusion equations for defined workpiece geometry. The model is able to predict the thermal cycle into the target material, the phase transformations and the resulting microstructures according to the laser process parameters, the workpiece dimensions and the physical properties of the workpiece. The effects of the overlapping laser beam tracks on the resulting microstructures can be also considered. Besides the original material microstructure is taken into account in the simulation process by means of a digitized photomicrograph in which the initial ferrite-pearlite distribution is acquired. Several experimental tests were then carried out on a torque limiter hub made of C43 UNI 7847 and laser hardened by means of CO2 laser or induction source. The comparisons were made between the geometry of the two different surface hardenings and the hardness profiles.


2007 - Laser hardening process simulation for mechanical parts [Relazione in Atti di Convegno]
Tani, G.; Orazi, L.; Fortunato, A.; Campana, G.; Cuccolini, G.
abstract

In this paper a numerical simulation of laser hardening process is presented. The Finite Difference Method (FDM) was used to solve the heat transfer and the carbon diffusion equations for a defined workpiece geometry. The model is able to predict the thermal cycle into the target material, the phase transformations and the resulting micro-structures according to the laser parameters, the workpiece dimensions and the physical properties of the workpiece. The effects of the overlapping tracks of the laser beam on the resulting micro-structures is also considered. The initial workpiece micro-structure is taken into account in the simulation by a digitized photomicrograph of the ferrite perlite distribution before the thermal cycle. Experimental tests were realized on a C43 plate and the good agreement between the theoretical and experimental results is shown.


2007 - Laser Hardening Simulation for 3D surfaces of medium carbon steel industrial parts [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; G., Campana; Cuccolini, Gabriele; A., Ascari
abstract

This paper refers to a 3-D transient model for laser surface hardening of mechanical components. The model makes it possible to predict the hardened depth into the bulk and the extension of the treated area together with the resulting microstructures with respect to the laser parameters and to the laser beam path strategy. The hardness reduction due to the tempering effects in the overlapping trajectories can be estimated. The solution of the heat flow problem into the bulk and the solution of the solute diffusion problem into the transforming phases are obtained by means of two independent meshes. The mesh generator was developed to manage complex geometry. The initial work-piece microstructure is taken into account in the simulation by a digitized photomicrograph of the ferrite-pearlite distribution before the thermal cycle. In order to validate the model, experimental trials were conducted on the keyway for spline machined on a hub made in C43. The model generates a part program in ISO base code to directly command the laser source and the controlled axes for the work-piece displacements.


2007 - Laser Milling Simulation System for Moulds Manufacturing [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele; G., Campana
abstract

This paper refers to the development of a numerical simulator for Laser Milling process useful for industrial applications able to predict the machining results when different materials are processed, different surface conditions are encountered and spatial and temporal distributions of the pulsed beam are set. The original software presented, developed by the authors, are well suited for simulating laser milling or laser micromachining operations with power density up to 1014 W/m2 and pulse duration in the order of nanoseconds.The temperature of the solid phase is evaluated by solving the Fourier equation by using the finite difference method (FDM). The recession velocity of the ablating surface is evaluated according to the Hertz-Knudsen equation assuming that the explosive effects are negligible. The plasma plume is considered in local thermodynamical equilibrium (LTE) and the energy balance permits to evaluate the plume temperature, ion distribution and pressure under the assumption that the gas expansion, from the surface target, produces a sonic front. The plume energy balance is influenced by the energy lost for irradiation from the plume and by the quantity of laser beam energy reflected from the target surface.Numerical simulations have been conducted to quantify this influence on the plasma plume physical state and, consequently, on the ablation process considering a Nd:YAG diode pumped source and three different target materials: Fe-C alloy, copper and aluminum.


2007 - Metallurgical Phases distribution detection through image analysis for simulation of laser hardening of carbon steels [Relazione in Atti di Convegno]
G., Tani; A., Ascari; Orazi, Leonardo
abstract

This paper deals with an original method for detecting the topological distribution of the ferrite and pearlite phases concerning a medium carbon hypo-eutectoid steel. Starting from a digital metallographic image a computation algorithm is applied to the pixel grid and a text array is generated reproducing the actual position of every phase into the bulk of the material. This result could be very useful to technological processes FEM simulators, where a good knowledge of the starting material is a required condition in order to obtain reliable and accurate results.


2007 - The influence of plasma plume in laser milling for mold manufacturing [Articolo su rivista]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele
abstract

The paper refers to the modeling of the plasma plume influence on the shape of the crater obtained by means of nanosecond pulsed laser milling. A transient model of the physical state of the plasma plume is developed according to the laser parameters. Two empirical coefficients are proposed in the model in order to evaluate the plasma plume self-emission energy lost towards the environment and the energy spread from the plasma towards the target surface. These two coefficients, directly correlated to the depth and to the width of the crater, can be experimentally determined, due to the difficulty of their analytical quantification, and they can be used for tuning a complete plasma plume software package for laser milling simulation named LAS (Laser Ablation Simulator) already developed by the authors. In this paper their influence on the crater shape will be proved by means of several simulation runs.


2007 - 3D Transient Simulation Model for Laser Micromilling Processes [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele
abstract

In this paper a laser milling simulator package is shown and discussed. The software system has been developed to simulate the micromanufacturing process using solid state lasers with pulse width in the range of 10–100 ns, but it can simulate every spatial and temporal distribution of the laser beam, so it is well suited to simulate both continuous and pulsed emission and every kind of laser spot distribution and trajectory. The system can simulate the effect of the laser beam on the workpiece, keeping into account the surface conditions, the evolution of the work-piece temperature field, the phase changes in the material and, at the end, the ablation rate. Particular attention has been focused in considering the influence of the plasma plume. Modeling and simulating the plasma plume creation and expansion is a very hard task, in the proposed package a simplified model is developed avoiding the fluid dynamic effects. In this work two empirical tuning parameters are considered: the first one is a global dispersion factor that keep in account the fraction of energy lost in the environment by the plume; the second one is a spreading factor that permits to model the irradiated energy of the laser beam hitting the workpiece and due to the plasma plume. The direct and coupled effects of these two parameters are evaluated and discussed.


2006 - Laser Ablation Modeling for CNC Machine Tool Application in Mould Manufacturing [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele
abstract

In this paper an original mathematical model of laser ablation is presented. Laser ablation optimisation is quite a complex activity due to the high number of parameters involved and nowadays the most common way to optimise the process, in industrial environments, is based on a “trial and error” activity.In order to reduce the set-up time, which can be very long when different materials and shapes have to be processed, a mathematical model is presented where the process parameters are related to the most important machining results such as ablated volume, temperature in work piece, resulting surface conditions, etc... The plasma plume effects on the machining operations are also considered. Comparisons between the theoretical and experimental results are also presented.


2006 - Process Planning in Laser Milling [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; Cuccolini, Gabriele; G., Campana
abstract

The present work defines a strategy to perform an automatic setup procedure for a laser milling manufacturing process. The manufacturing system is constituted by a milling CNC machine structure coupled with a DPSS Nd:YAG Laser source. This work shows the criteria developed to evaluate the influence of process parameters on material removal rate when processing mild steels and aluminium alloys. The method, based on a statistical approach, was performed by experiments executed using DOE techniques and developing a regression model validated by a ANOVA Analysis. It can be easily applied to other materials and it represents an useful tool to asses the right process parameters in roughing and in finishing operations. A basic manual approach is presented and the automatic procedure developed is in detail explained. The implemented Software System automatically generates a part program to laser milling a set of pockets, using different laser parameters, then permit to scan them by an optical sensor and to calculate the empirical coefficients to use in the regression model that provide the material removal rate.


2006 - 3-D Modeling of Laser Ablation of Metals in Mould Manufacturing [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo; A., Fortunato; Cuccolini, Gabriele
abstract

An original model for laser milling characterization is presented in this paper. A 3-D numerical model able to simulate the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of velocity of the vapour/liquid front and the physical state of the plasma plume were taken into account. The numerical model was implemented in C++ and an overview of the code capacities is presented.


2005 - Analysis and Monitoring of VARTM-SCRIMP Fabrication Process. [Relazione in Atti di Convegno]
G., Tani; L., Donati; Orazi, Leonardo
abstract

This study discusses the most used methods in manufacturing parts by means of VARTM (Vacuum Assisted Resin Transfer Molding) processes. In particular, attention is focused on the SCRIMP (Seaman Composite Resin Infusion Molding Process) process, widely used in naval, aeronautical and others military related productions.Many process parameters are involved using VARTM processes, particularly SCRIMP: material properties; composition of the mixture; reinforcing fibers; lamination sequence; infusion temperatures and humidity rate are a non-exhaustive list of the parameters influencing the final quality of the produced parts.A systematic study of the parameters and their mutual interaction effects was conducted by means of the structural analysis method. For the most significant ones an analysis of the monitoring systems available was performed. Some monitoring techniques were applied in the manufacturing of a Pershing 48 motorboat, with particular attention to the temperature evolution during resin injection. The parts produced were tested by means of DSC (Differential Scanning Calorimeter) analysis to evaluate the residual polymerization degree for different process configurations and a correlation with monitored data are presented


2005 - Shape evaluation procedure for free form surfaces [Relazione in Atti di Convegno]
Orazi, Leonardo; G., Tani
abstract

In this study a series of procedures were implemented to compare acquired surfaces with the nominal data or to directly compare different scanned surfaces. In particular a morphological evaluation algorithm based on the Extended Gaussian Curvature (EGC) and a method to compare features based on aggregate normal orientation are presented. To perform the comparing feature method a simple procedure for segmentation was developed. The main characteristic of the two methods is robust behavior referring to the scan orientation. The procedures were implemented as software modules in a graphic environment.


2004 - Experimental system to determine the start of fracture propagation during impact test [Abstract in Atti di Convegno]
A., Morri; Orazi, Leonardo; F., Tarterini
abstract

This work explains the sep-up of a fully automated method for the measurement of the fatigue threshold with an exponentially decreasing of the applied stress intensity factor.


2004 - Modifiche di Geometrie Acquisite mediante sistemi di Reverse Engineering. [Relazione in Atti di Convegno]
Orazi, Leonardo; G., Tani
abstract

I sistemi di scansione e di manipolazione dei dati geometrici hanno avuto, negli ultimi anni, un impressionante sviluppo e notevole diffusione, tuttavia il ciclo completo di Reverse Engineering, ovvero la trasformazione dell'oggetto fisico in un modello CAD di qualità, risulta tuttora un'operazione che richiede molte risorse umane di elevata competenza. Nel presente lavoro vengono esposti alcuni esempi di un approccio alla manipolazione dei dati acquisiti che evita la ricostruzione di superfici matematiche. La modellazione pertanto viene attuata direttamente sulle superfici poliedriche ottenute dalle nuvole di punti; garantendo comunque i necessari vincoli di continuità/tangenza curvatura rispetto alle superfici già esistenti all'interno del sistema CAD. Lo sviluppo di queste operazioni di deformazione vincolata da luogo alla realizzazione di un insieme di procedure per la manipolazione di oggetti ibridi, oggetti cioè, costituiti indifferentemente da curve e superfici parametriche e da geometrie ottenute da sistemi di scansione.


2003 - Application Of Reverse Engineering and Analysis Techniques for Surface Quality Control of Automotive Components [Abstract in Atti di Convegno]
Orazi, Leonardo; G., Tani
abstract

The aim of this work concern the analysis of the effectiveness of Reverse Engineering methods (scanning and processing data) for the purpose of evaluating and controlling the geometrical characteristics and surface quality of automotive body components. Evaluation of the surface characteristics of the part has been conducted utilizing reverse engineering instead of the traditional point-by-point measurement techniques. In particular, the study of the models focused on the behavior of the curvature, obtained on sections of the surfaces. The scatter present in data obtained from different scannings and other kinds of imprecision arising from the processing techniques employed create many problems in the assessment of surface quality. This study presents an original methodology for a benchmark test between different scanning methods, the benchmark is done by means of some aluminum alloy test plates with known, established surface features. By the acquisition of the test plates we could evaluate the different capability in revealing local curvature and other types of defects.


2003 - Application of Reverse Engineering techniques for surface quality control of automotive components [Relazione in Atti di Convegno]
Orazi, Leonardo; G., Tani
abstract

The aim of this work concern the analysis of the effectiveness of Reverse Engineering methods (scanning and processing data) for the purpose of evaluating and controlling the geometrical characteristics and surface quality of automotive body components. Evaluation of the surface characteristics of the part has been conducted utilizing reverse engineering instead of the traditional point-by-point measurement techniques. In particular, the study of the models focused on the behavior of the curvature, obtained on sections of the surfaces. The scatter present in data obtained from different scannings and other kinds of imprecision arising from the processing techniques employed create many problems in the assessment of surface quality. This study presents an original methodology for a benchmark test between different scanning methods, the benchmark is done by means of some aluminum alloy test plates with known, established surface features. By the acquisition of the test plates we could evaluate the different capability in revealing local curvature and other types of defects.


2002 - AA6082 Friction stir welded joints: propagation during impact test [Relazione in Atti di Convegno]
CAMMAROTA G., P; Morri, A; Orazi, Leonardo
abstract

AA6082 Friction stir welded joints: propagation during impact test


2002 - High strain rate superplasticity in aluminum matrix composites [Articolo su rivista]
L., Ceschini; A., Morri; Orazi, Leonardo
abstract

Recently, several studies have demonstrated that a variety of metallic materials, including aluminium-based composites, can exhibit superplasticity at relatively high strain rates (≥10-2s-1). High strain rate superplasticity (HSRS) is very attractive for commercial applications, mainly for materials difficult to shape or machine with conventional techniques, such as metal matrix composites. In this work, the possibility of achieving HSRS in a recently developed composite with an AA6013 matrix reinforced with about 20 vol % of SiC particles (AA6013/20/SiCp) was studied. Uniaxial tensile tests were carried out at high strain rates (1 x 10-1s-1 and 1 x 10-2s-1) and in a temperature range between 520 and 590°C. A maximum elongation-to-failure of 370 per cent was obtained at 560°C with a strain rate of 1 x 10-1s-1. This temperature is very close to the temperature at which melting of the composite starts. Scanning electron microscopy (SEM) analyses of fracture surfaces in the optimum superplastic condition showed the presence of filaments, the formation of which generally related to the presence of a liquid phase at the grain boundaries and/or at the interfaces.


2002 - Metodologie per la misura ed il controllo di stampi con tecniche di Reverse Engineering [Relazione in Atti di Convegno]
G., Tani; Orazi, Leonardo
abstract

Il presente lavoro propone una procedura per il controllo geometrico-dimensionale di stampi e pezzi che, utilizzando strumentazioni non convenzionali per tali scopi, si basa sulla creazione di un modello software dell’oggetto da misurare mediante la acquisizione di dati geometrico dimensionali con tecniche di scansione. Tale procedura permette: da una parte di effettuare misure puntuali sul modello acquisito; dall’altra di confrontare il modello così ottenuto con un modello matematico precedentemente creato ed usato come riferimento; essa si presta pertanto ad essere applicata per ottenere controlli diversi dal momento che si possono confrontare progetto, stampo ed oggetto realizzato. Il lavoro ha consentito inoltre di mettere a confronto sistemi di scansione basati su diverse tecnologie così da poterne valutare la loro effettiva applicabilità nel controllo dimensionale e di forma di stampi e pezzi di piccola, media e grande dimensione. L’attività è stata svolta nell’ambito Programma di Ricerca Nazionale “Tecnologia di Resin Transfer Moulding (RTM) per Infusion per componenti in materiale composito di grandi dimensioni”


2002 - Superplastic behaviour of metal matrix composites [Articolo su rivista]
L., Ceschini; A., Morri; Orazi, Leonardo
abstract

Studi recenti hanno mostrato la possibilità di osservare superplasticità ad elevata velocità di deformazione ( > 10^-2 s^-1 ) in materiali compositi a matrice di alluminio, purché caratterizzati da dimensioni molto fini ( < 5 micron ) sia dei grani della matrice che delle particelle di rinforzo. In questo lavoro è stata valutata la possibilità di indurre un comportamento superplastico nel composito AA6013/20SiCp, ottenuto da metallurgia delle polveri e successivamente laminato a caldo.I risultati delle prove di di trazione consentono di ipotizzare un ruolo importante della fase liquida, come meccanismo di "accomodamento" dello scorrimento a bordo grano (GBS), nel corso della deformazione superplastica.


2000 - Experimental and theoretical approach for an estimation of ΔKth [Articolo su rivista]
Herold, H.; Streitenberger, M.; Zinke, M.; Orazi, Leonardo; Cammarota, G. P.
abstract

The existence of a fatigue threshold value may affect the design process when a damage-tolerant design is considered that uses non-destructive techniques for evaluating the shape and dimensions of the defects inside materials. Obviously it should be possible to estimate the stress field surrounding these defects and this is not generally a problem with modern numerical methods.Many factors are involved in determining the growth rate of a fatigue crack. Some of these are highly significant and it is possible to obtain the coefficients of a correlation function. Some others are not well defined and the only effect is to expand the scatter of experimental data.Consider the sigmoidal curve we obtain when plotting the crack growth rate versus the applied DK_I . A very difficult parameter to measure but very useful for fatigue design is the DK_Ith value, because below this value a crack may be forming, hence, here DK_Ith is defined by the transition between a normal (e.g. 10-10 m/cycle) and a very low range of crack growth rate (<10-10 m/cycle).The DgrKIth value is very difficult to obtain by experimental methods because the growth rate is of the order or less than the atomic lattice span (3 × 10-10 m/cycle), but we can correlate the transition value with the cyclic crack tip plastic zone size and other structural parameters of metallic materials.The aim of this work is to offer a contribution about the parameters which influence DK_Ith in stainless steels and welded joints based on the crack tip plastic zone radius.


2000 - Fatigue threshold in aluminium alloys [Relazione in Atti di Convegno]
H., Herold; M., Streitenberger; M., Zinke; Orazi, Leonardo; A., Casagrande; G. P., Cammarota
abstract

The fatigue threshold of aluminum alloys has not been studied in detail in the near threshold region and the objective of the work reported here was to compare the behaviour of two traditional alloys (5754 and 6082) with two aluminium -lithium alloys (2091 and 8090) in the threshold stress intensity range.


1999 - Design of Experiments for Evaluating DKth in AISI 304 Stainless Steel [Articolo su rivista]
Orazi, Leonardo
abstract

This work concerns the application of Design Of Experiments (DOE) statistical techniques to obtain empirical correlation between DeltaK_th and microstructural parameters.The choice of developing a statistical model not based on physical principles is due to the difficulties encountered in the past applying these kind of models.After the development of an apparatus to automatically obtain the DeltaK_th, AISI 304 stainless steel was tested searching for correlation between fatigue threshold, grain size and load ratio.The author designed a 2^2 factorial experiment applying the Design Of Experiments to obtain a statistical bilinear model.


1997 - Influence of Testing Techniques and Micromechanical properties on DK Threshold [Articolo su rivista]
Orazi, Leonardo
abstract

A set of data were collected from literature about DK_th in order to correlate the fatigue thresholds with the material parameters. Data about yield strength and, from a microstructural point of view, about grain size were found. It is difficult to compare data token from different sources, this is due to the intrinsic scattering of high cycle fatigue test results and to the different testing methods adopted. The author tried to find a correlation using these data. A review of the most important methods to test the Fatigue Thresholds is also suggested.