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RICCARDO PELACCIA

Ricercatore t.d. art. 24 c. 3 lett. A
Dipartimento di Scienze e Metodi dell'Ingegneria

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Pubblicazioni

2024 - Ablation rate assessment of GHz femtosecond laser in burst mode through fast numerical simulation [Relazione in Atti di Convegno]
Mazzonetto, Manuel; Pelaccia, Riccardo; Greborio, Alessandro; Conzatti, Riccardo; Siciliani, Vincenzina; Oubellaouch, Keltoum; Ricucci, Antonia; Orazi, Leonardo
abstract

In this work, the use of an innovative, compact femtosecond laser operating in the GHz regime for laser ablation and microtexturing is investigated and discussed. The processing performances of burst mode for pulses shot in the GHz regime are numerically simulated. The proposed ablation model is based on the two-temperature model and considers, in a simplified way, the effect of plasma. The numerical results are compared in terms of ablation depth with experimental investigations on stainless steels. The numerical outputs allow an understanding of the influence of different process parameters and support the selection of the operating window where GHz laser became competitive with traditional ultrashort laser sources in the MHz regime.

2024 - Adaptive Optics to enhance LIPSS surface texturing [Relazione in Atti di Convegno]
Siciliani, Vincenzina; Zaniboni, Giulia; Pelaccia, Riccardo; Mazzonetto, Manuel; Bonora, Stefano; Orazi, Leonardo
abstract

2024 - Adaptive optics solution to improve laser-induced periodic surface structuring (LIPSS) [Relazione in Atti di Convegno]
Siciliani, Vincenzina; Zaniboni, Giulia; Pelaccia, Riccardo; Mazzonetto, Manuel; Oubellaouch, Keltoum; Bonora, Stefano; Orazi, Leonardo
abstract

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 - Experimental investigation and numerical prediction of the peripheral coarse grain (PCG) evolution during the extrusion of different AA6082 aluminum alloy profiles [Articolo su rivista]
Negozio, Marco; Segatori, Antonio; Pelaccia, Riccardo; Reggiani, Barbara; Donati, Lorenzo
abstract

2024 - Numerical, experimental, and analytical investigation of the skin contamination evolution in the extrusion of different industrial profiles [Articolo su rivista]
Negozio, Marco; Pelaccia, Riccardo
abstract

In the context of aluminum alloy extrusion, the presence of the skin contamination defect imposes the scrap of the contaminated profile length due to its lower mechanical properties. For understanding the evolution of the defect, comprehensive analyses, either experimental investigations or reliance on predictive techniques, are mandatory. Recently, numerical methods have gained interest in predicting the development of skin contamination, although their level of accuracy remains uncertain. This research focuses on a detailed experimental and numerical analysis of three different AA6XXX industrial extruded profiles. The aim is to compare the evolution of the skin contamination experimentally observed with the outcomes of the simulation using the commercial finite element code Qform Extrusion UK. The main findings of the analysis confirmed the potentiality and the accuracy of the numerical tools, also evidencing the current limitations of the empirical and analytical industrial practices.

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 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 - Experimental analysis and modeling of the recrystallization behaviour of a AA6060 extruded profile [Relazione in Atti di Convegno]
Negozio, M.; Donati, L.; Pelaccia, R.; Reggiani, B.; Di Donato, S.
abstract

The microstructure of Al-Mg-Si alloys is gaining nowadays an increasing industrial interest because it influences the strength, crash, corrosion and esthetic properties of the extruded profiles. In order to investigate and predict the recrystallization behaviour in the extrusion of 6XXX aluminum alloys, experimental and numerical activities are still needed. In this work, the extrusion of an industrial-scale AA6060 aluminum alloy hollow profile was carried out. An innovative recrystallization model was developed and optimized by comparing the microstructural data experimentally acquired with the outputs of the simulation performed using the Finite Element commercial code Qform Extrusion. A good correlation between numerical prediction and experimental data was found, thus proving the reliability of the proposed AA6060 recrystallization model.

2023 - Investigation of the skin contamination predictability by means of QForm UK extrusion code [Relazione in Atti di Convegno]
Kniazkin, I.; Pelaccia, R.; Negozio, M.; Di Donato, S.; Donati, L.; Reggiani, B.; Biba, N.; Rezvykh, R.; Kulakov, I.
abstract

The paper presents an innovative approach implemented in QForm UK Extrusion FEM software to analyse one of the core defects encountered in profile extrusion known as billet skin defect. The validation of the algorithm has been performed based on a number of experimental case studies taken from the literature [1,2]. Additionally, the sensitivity of the accuracy of the results to the variation in initial parameters has been analysed for both types of profile shapes: solid and hollow. Based on this, practical recommendations have been formalised for the successful industrial use of the presented algorithm.

2023 - Investigation on the topological optimization of cooling channels for extrusion dies [Relazione in Atti di Convegno]
Pelaccia, R.; Reggiani, B.; Negozio, M.; Di Donato, S.; Donati, L.
abstract

During the extrusion process, high temperatures are generated, due to friction and deformation works, potentially leading to profile and die defects. Among the suggested solutions aimed at controlling the thermal field of the process, the most accredited one involves the manufacturing of cooling channels at the mating face between the die and a third plate. Despite the proven efficiency of well-designed channels, the main drawback lies in the managing of the many variables involved that strongly affect the cooling efficiency and balancing. In this frame, aim of the work is to investigate the applicability of the topological optimization tool, proposed by COMSOL Multiphysics software, for the design of cooling channels in extrusion dies. To validate the tool, an industrial case study has been selected and results compared between not optimized and optimized cooling solutions.

2023 - Numerical investigation of the surface recrystallization during the extrusion of a AA6082 aluminum alloy under different process conditions [Articolo su rivista]
Negozio, M.; Pelaccia, R.; Donati, L.; Reggiani, B.
abstract

2023 - Simulation of the microstructure evolution during the extrusion of two industrial-scale AA6063 profiles [Articolo su rivista]
Negozio, M.; Pelaccia, R.; Donati, L.; Reggiani, B.
abstract

The microstructure of lightweight alloys is of a primary interest for manufacturing companies since it affects mechanical strength, crash, corrosion and esthetic properties. Numerical and experimental research activities are needed to investigate the relation between manufacturing process parameters and grain structure evolution in order to control the properties of the final component. In this context, aim of this work is the experimental investigation of the evolution of the microstructure in two different industrial-scale AA6063 aluminum alloy extruded profiles. Furthermore, a novel modeling of the AA6063 recrystallization behaviour is developed and implemented within the commercial FEM code Qform UK Extrusion®. The results of the numerical evaluations are then compared to the experimental data in order to assess the accuracy of the model. A good correlation between numerical predictions and experimental data is found for both profiles, thus proving the reliability of the proposed AA6063 recrystallization model.

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 - Three sustainable polypropylene surface treatments for the compatibility optimization of PP fibers and cement matrix in fiber-reinforced concrete [Articolo su rivista]
Malchiodi, B.; Pelaccia, R.; Pozzi, P.; Siligardi, C.
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 - 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 Homogeneous Flow Model for nitrogen cooling in the aluminum-alloy extrusion process [Articolo su rivista]
Pelaccia, Riccardo; Santangelo, Paolo Emilio
abstract

Extrusion of aluminum alloys has become extensively employed as a process to manufacture a variety of products. However, heat generated by the high deformation energy and the high friction forces imposed during the process may cause defects in the extrudate, as well as reduce tool life. So, effective die cooling is key in achieving high product quality and production rate. Nitrogen has recently been identified as a promising coolant; however, current modeling does not take the presence of two phases into account, only including either the liquid or the gas phase within cooling channels, which often results in poorly designed cooling systems. The present research was aimed at exploring the homogenous flow approach as a simple, yet representative method to account for the liquid and the gas phase, as they both occur during the cooling subprocess. Ten AA6060 billets were extruded in an industrial production line, varying nitrogen flow rate and monitoring temperature trend at various locations of interest. A Finite Element model was then developed in a multiphysics environment, into which the simulation of both the extrusion process and the nitrogen flow were integrated, with the latter being represented as a homogeneous flow. Validation was performed against the experimental dataset through steady-state and transient analysis. This work proved the homogeneous-flow approach remarkably successful in capturing the involved physics and assessing the provided cooling effect quantitatively.

2022 - Advancements in extrusion and drawing: a review of the contributes by the ESAFORM community [Articolo su rivista]
Donati, L.; Reggiani, B.; Pelaccia, R.; Negozio, M.; Di Donato, S.
abstract

The present review paper would celebrate the 25 years anniversary of the ESAFORM association by summarizing the studies performed by the delegates of the ESAFORM conference series within mini-symposium “Extrusion and Drawing” and of the papers published in the International Journal of Material Forming in the same fields. The 160 analyzed papers have been divided in four main categories corresponding to the paper main chapters (Hot Metal Extrusion, Cold Metal Extrusion, Polymer Extrusion and Drawing) then further divided in sub-chapters in order to group them in more specific research subjects. The aim of this review paper is then to provide to the reader a complete overview of the investigated topics and of the research trends over the years within the ESAFORM associate researchers.

2022 - Assessment of the Optimization Strategy for Nitrogen Cooling Channel Design in Extrusion Dies [Relazione in Atti di Convegno]
Pelaccia, Riccardo; Negozio, Marco; Reggiani, Barbara; Donati, Lorenzo
abstract

2022 - Extrusion of Light and Ultralight Alloys with Liquid Nitrogen Conformal Cooled Dies: Process Analysis and Simulation [Articolo su rivista]
Pelaccia, Riccardo; Negozio, Marco; Donati, Lorenzo; Reggiani, Barbara; Tomesani, Luca
abstract

The die cooling by means of liquid nitrogen is a widely adopted industrial practice used to increase theproduction rate in the hot extrusion process of light alloys. The development of a reliable numerical modelable to simulate the cooling channel efficiency has become of primary interest for the extrusion sector inorder to avoid ineffective die cooling and time-consuming trials and errors. In this work, H13 die insertswith a helicoidally conformal channel were designed and printed by means of the SLM additive technology.Billets of AA6063 aluminum and ZM21 magnesium alloys were extruded at different process speeds undermonitored conditions to verify the insert resistance and the cooling effectiveness. A 3D finite element modelof the extrusion process coupled with a 1D model of the cooling channel was generated within the COMSOLsimulation environment. The experimental outputs were also used to validate the numerical predictions ofthe developed simulations. The FEM results showed a good matching with the loads and temperaturesobtained in the experimental trials. Moreover, the endurance of the AM tool validated the prediction of thestress field, thus proving the reliability of the numerical model for the application in the extrusion of lightalloys sector.

2022 - FEM Analysis of the Skin Contamination Behavior in the Extrusion of a AA6082 Profile [Relazione in Atti di Convegno]
Negozio, Marco; Pelaccia, Riccardo; Donati, Lorenzo; Reggiani, Barbara
abstract

2022 - Liquid nitrogen in the industrial practice of hot aluminium extrusion: experimental and numerical investigation [Articolo su rivista]
Pelaccia, R.; Reggiani, B.; Negozio, M.; Donati, L.
abstract

Nowadays, the liquid nitrogen cooling in aluminium extrusion is a widely adopted industrial practice to increase the process productivity as well as to improve the extruded profile surface quality by reducing the profile exit temperatures. The cooling channels are commonly designed on the basis of die maker experience only, usually obtaining modest performances in terms of cooling efficiency. Trial-and-error approach is time and cost consuming, thus providing a relevant industrial interest in the development of reliable numerical simulations able to foresee and optimize the nitrogen cooling effect during the die design stage. In this work, an extensive experimental campaign was performed during the extrusion process of an AA6060 industrial hollow profile, in different conditions of nitrogen flow rate and ram speed. The monitored data (die and profile temperatures and extrusion load) were compared with the outputs of a fast and efficient numerical model proposed by the authors, and developed in the COMSOL Multiphysics code, able to compute not only the effect of nitrogen liquid flow but also the gaseous condition. The results of the simulations showed a good agreement with experimental data, and evidenced how far the experimental cooling channel design from an optimized condition was.

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 - Analysis and optimization of cooling channels performances for industrial extrusion dies [Relazione in Atti di Convegno]
Pelaccia, Riccardo; Negozio, Marco; Reggiani, Barbara; Donati, Lorenzo; Tomesani, Luca
abstract

Liquid nitrogen cooling is widely used in the extrusion industrial practice in order to increase the production rate, to reduce the die temperature and to avoid defects on the profile exit surfaces resulting from an excessive heating. However, the efficiency of the cooling is deeply affected by position and design of the liquid nitrogen channel so that numerical modelling is gaining an increasing industrial interest in relation to the possibility offered to optimize the channel design without expensive and time-consuming experimental trials. In this work, a numerical FE model developed within COMSOL Multiphysics® is proposed and validated against experimental trials performed in industrial environment. The model combines the 3D simulation of the extrusion process with a 1D model of the cooling channel thus allowing the testing of a number of different solutions at the die design stage. The global aim of this work is the assessment of the liquid nitrogen cooling efficiency in the extrusion of an industrial aluminum profile and the proof of the potentials offered by numerical models to get an optimized channel design in terms of cooling efficiency, die thermal balancing and reduction of liquid nitrogen consumption.

2021 - Finite Element Model Prediction of Charge Weld Behaviour in AA6082 and AA6063 Extruded Profiles [Articolo su rivista]
Negozio, M.; Pelaccia, R.; Donati, L.; Reggiani, B.; Pinter, T.; Tomesani, L.
abstract

Charge welds are unavoidable defects of the continuous extrusion process whose extension needs to be accurately predicted in order to avoid profile mechanical failures or to minimize unrequired scrap of material. The aim of this work was then to evaluate the accuracy of the charge welds FEM predictions and their applicability in the industrial field. Two different industrial cases involving A6082 and AA6063 aluminium alloys were analysed. The data of charge welds behaviours were experimentally collected, discussed and then innovatively compared to the predicted outcomes of FEM simulations performed using QForm Extrusion® software and of theoretical formulas reported in the literature. As main results, a very good numerical-experimental matching was found, with a peak discrepancy of 122 mm in terms of charge weld extent, while theoretical formulas returned a significant underestimation.

2020 - Efficiency of conformal cooling channels inserts for extrusion dies [Relazione in Atti di Convegno]
Pelaccia, R.; Negozio, M.; Donati, L.; Reggiani, B.; Tomesani, L.
abstract

During aluminum extrusion process, critical temperatures can be reached both in the profile and in the tooling set due to the high pre-heating temperatures and to the work spent in overcoming friction at the workpiece/tool interfaces and in deforming the billet that is converted into heat. By considering that especially the rising of temperature in the profile can represents a critical aspect of the process strongly limiting the maximum achievable extrusion speed, liquid nitrogen die cooling is becoming a consolidated industrial practice in order to increase the process productivity. If cooling channels are traditionally manufactured by subtractive technologies on a third plate (the backer), a more flexible and efficient solution is offered by the selective laser melting (SLM) technology. SLM allows the design of free-form channels with the opportunity to efficiently remove the heat as near as possible to the bearing zones where the highest temperatures are reached. In the present work, the design approach and the manufacturing parameters of an SLM printed H13 die insert for the extrusion of a 10 mm round bar are presented. In addition, the extrusion process is simulated by means of the COMSOL code accounting for the nitrogen cooling effect. Experimental extrusion trials have been furthermore performed with ZM21 magnesium and 6063 aluminum alloys to assess the potentiality of the conformal cooling channel design and to validate the developed numerical model. As main result, a good experimental numerical matching has been achieved with peak errors of 7.5% and 14% in terms of temperature and extrusion load respectively.

2020 - FEM validation of front end and back end defects evolution in AA6063 and AA6082 aluminum alloys profiles [Relazione in Atti di Convegno]
Negozio, M.; Pelaccia, R.; Donati, L.; Reggiani, B.; Tomesani, L.; Pinter, T.
abstract

The reduction of scraps related to back end defects (i.e. billet skin contamination) and front end defects (i.e. charge welds) is gaining nowadays an increasing industrial interest in order to obtain greater process efficiency. Today, extrusion industrial practice faces the issue by means of technician's experience, empirical rules or, in most critical profiles, through time consuming and expensive experimental analyses. On the other side, FEM simulation of extrusion dies is becoming a common support tool for the design of new critical dies. Stating this scenario, the possibility to include the prediction of front end and back end defects evolution as simulation output can then be easily obtained at almost comparable computational costs. In this paper the FEM code Altair HyperXtrude® is used for the simulation of 2 industrial cases made by AA6063 and AA6082 alloys following the transient moving boundaries approach. Experimentally, the profiles were extruded, sectioned, polished and etched with caustic soda in order to reveal and measure front and back end development in front of and behind the profile stop mark. The data obtained from experimental analyses are initially discussed referring to billet skin contamination and charge weld evolution, then compared to industrial experience, to theoretical and empirical methods available in literature and to FEM results in order to evaluate pros and cons of each evaluation method.

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.

2019 - A NOVEL 3D PRINTED COOLING INSERT FOR EXTRUSION DIES [Relazione in Atti di Convegno]
Valli, Giuseppe; Reggiani, Barbara; Todaro, Ivan; Pelaccia, Riccardo; Squatrito, Rosario; Pinter, Tommaso; Mainetti, Enea; Rami, Yoram; Donati, Lorenzo; Tomesani, Luca
abstract

An accurate control and monitor of the temperatures developed during the extrusion process is a key factor for the process success in order to produce sound profiles and extend the die life. To this aim, conformal channels can be used to achieve a targeted process cooling by means of liquid nitrogen and the additive manufacturing technologies offered the best solution for a free form design with almost no geometrical constraints. In this work, a multi die concept for hot aluminum extrusion process is proposed in which the insert with forming zones and cooling channels was manufactured by means of the slm technology while the external insert support by conventional methods. This solution allowed obtaining a free-form cooling channel with the aim to get an optimized and targeted cooling nearby the bearing zones, where the highest temperatures are reached. Inserts were slm printed and complex Finite Element simulations of the extrusion process with nitrogen cooling performed in order to predict the thermal field of the inserts.

2019 - A novel design concept of the extrusion dies [Relazione in Atti di Convegno]
Reggiani, Barbara; Donati, Lorenzo; Tomesani, Luca; Pelaccia, Riccardo
abstract

In aluminum extrusion, one of the main limit is the developed temperature field that limits the maximum achievable production rate. Liquid nitrogen cooled dies are frequently today used in industry but they remove heat far away from the bearings, where the most critical conditions are reached. The novel concept involves the use of the additive manufacturing technology (SLM) to grant a full cooling channel design freedom, including the possibility to be located nearby the bearings. The insert is fit in a steel-housing die conventionally manufactured in order to limit final die costs. A comprehensive numerical analysis has been performed with the aim to investigate the insert thermo-mechanical performances, including the nitrogen cooling effect. The achieved numerical results encouraged the experimental manufacturing and testing of the insert. Specifically, eight inserts have been produced by SLM technology and the optimal one was successfully tested in the extrusion of an aluminum alloy.

2019 - Advanced modeling of die cooling with liquid nitrogen [Relazione in Atti di Convegno]
Pelaccia, Riccardo; Reggiani, Barbara; Donati, Lorenzo; Tomesani, Luca
abstract

The profile temperature monitoring during aluminum extrusion is a an important information performed in order to avoid profile defects such as burn and crack, or an incorrect tempering, or to preserve the die life and to increase the process productivity. In the last decade die cooling systems through liquid nitrogen have been installed on several extrusion plants. However, a comprehensive and systematic assessment of the liquid nitrogen die cooling effect on process parameters is still missing in literature. In this context, aim of the present work is to develop an advanced numerical finite element model of the extrusion that accounts for liquid nitrogen cooling. The numerical model is then validated over ICEB 2011 Industrial Benchmark experimental trials, where the cooling efficiency in a multi-hollow industrial profile was evaluated. The results of the simulations have been compared to experimental investigation both in cooled and uncooled conditions. The assessment showed a good experimental-numerical agreement in terms of temperature map and extrusion load, thus suggesting the reliability of the novel modelling to support the process optimization.

2019 - Back.end and front-end scrap in direct extrusion: an estimation by means of finite element analysis [Relazione in Atti di Convegno]
Tommaso, Pinter; Ezio, Sicignano; Pelaccia, Riccardo; Reggiani, Barbara; Lorenzo, Donati
abstract

Finite elements analyses are offering to extrusions a big opportunity: to estimate accurately not only the charge weld extension but also the billet skin contamination. The present work examined the dynamics of the back-end and front-end defect in the direct extrusion of a solid profile through the use of FE analyses. Numerical results have been compared with industrial experiments with the aim to understand the effect of the selected boundary conditions on the accuracy of the predictions.

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 - SLM of extrusion dies with liquid nitrogen cooling [Abstract in Atti di Convegno]
Pelaccia, Riccardo; Reggiani, Barbara; Todaro, Ivan; Valli, Giuseppe; Donati, Lorenzo; Squatrito, Rosario; Fortunato, Alessandro; Tomesani, Luca
abstract

Temperature control during aluminium extrusion is a mandatory activity in order to produce defect-free profiles and to optimize process productivity. During the extrusion process, the profile exit temperature increases due to amount of work spent to overcome friction and to plastically deform the workpiece that is converted to heat. In addition, if the ram speed or the extrusion ratio increase, the temperature further raises leading to detrimental surface defects such as hot cracks. The main advantages of dissipate the excessive generated heat in the die and at the end of the forming zone are related to the possibility of increasing only slightly the extrusion force and to reduce the conduction path from the forming zone to the cooling source. In addition, it is possible to cool critical die areas directly by sizing and positioning cooling channels or cooling nozzles adequately to prevent hot cracking. However, the manufacturing of conformal cooling channels close to the main forming zone by means of conventional machining is a difficult task for profiles and dies with highly complex geometries. Thus, the use of additive manufacturing technologies is a promising approach to allow a conformal cooling. The major advantage of additive manufacturing processes against conventional subtractive methods is the geometrical freedom of the produced components and the manufacturing of conformal cooling channels. The chromium hot-work tool steels are the most widely selected materials for forging, die-casting and extrusion dies applications because of their high thermo-mechanical strength, fatigue strength, toughness and relative low cost. Nowadays, thanks to the selective laser melting (SLM) technology, it is possible to produce structures with 99% density, since the material is completely melted and later solidified without forming spherical voids [4]. Since, to date, the additive manufacturing processes are often accompanied with higher manufacturing time and costs than conventional subtractive methods, a new concept for a hybrid extrusion die is presented. In the present work, a multi-die is proposed in which the expensive AM part, the insert with conformal cooling channels, is integrated into a conventional machined steel housing. A profile produced with a short die lifetime and critical issues on thermal field has been identified and selected consisting in a round bar of 10mm diameter made by AA6060.

2018 - A novel SLM H13 cooling insert for extrusion dies: experimental and numerical investigations [Relazione in Atti di Convegno]
Pelaccia, Riccardo; Reggiani, Barbara; Donati, Lorenzo
abstract

The additive manufacturing technology (AM) is considered to be the forth-industrial revolution allowing to produce «near net» components almost without geometrical constraints. This made the process perfectly fits with the requirement of extrusion dies since usually a maximum of two dies are required and the lack of design constraints allows to easily produce inserts with variable internal cooling channels. In the present work, a multi-die is proposed in which the expensive AM part, the insert with conformal cooling channels, is integrated into a conventional machined steel housing. Two AM inserts have been manufactured with SLM technology with different cooling channels diameters. Complex Finite Element (FE) simulations of the extrusion process have been performed by means of different FE codes in order to properly predict the thermal field gradient, the die stresses under the process thermomechanical loads and the multistate fluid dynamics. Preliminary results of the experimental trials of the insert are also presented in the present work.