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Due to its electro-mechanical properties, commercially pure aluminium wires have attracted the interest of automotive industry representing a functional and efficient economic solution to reduce vehicle’s weight leading to the diminishing of energy consumption and emissions in today’s society. However, to consolidate its use in this sector and in new market realities, it is necessary to increase the flexibility of the aluminium conductor wires, consenting their installation in very small spaces and with high curvatures, avoiding any failure and electrical conductivity decrease. Thus, the evolution of microstructure and service performance needs to be investigated and controlled to improve the service safety. The present research shows a new approach to continuously manufacture efficient long wires with smaller diameters and fine grains at room temperature. It is studied the strengthening effects (yield and tensile strength, plasticity, hardness), the electrical conductivity, and the microstructural changes of commercial 1370 pure aluminium (99.7% Al) when traditional wire drawing process is combined with equal channel angular drawing (ECAD) technique. The results of this proposed procedure of deformation “drawing-ECAD-drawing” show an evident benefit, compared to the classic technology of production of aluminium wire, obtaining fine grain structure product with superior mechanical strength and not influenced electrical conductivity. The proposed manufacturing approach leads to fine wires enhancing the material mechanical properties by microstructural evolution (i.e. grain size reduction) avoiding the traditional post manufacturing thermal treatments requiring a high amount of energy and time and careful steps.

Porthole die extrusion has been more and more utilized to produce hollow complex cross-section profiles. The porthole die is characterized by complex shapes and various geometric variables have to be set properly for the process optimization. Numerical simulations combined with optimization methods are effective strategies, which can be used for a proper die design reducing the experience and “trial and error” sequences. In this study, 12 geometric variables of a standard porthole die, used to extrude profiles with circular section, were identified and varied on three levels. The entire solution space was investigated using a Taguchi method based on a special design of orthogonal array with the grey relational analysis. Firstly, the influences of the investigated geometric variables on three extrusion outputs, e.g., the required ram load, the maximum pressure inside the welding chamber, and the material flow homogeneity, were highlighted by ANOVA technique. Afterwards, the Grey relational analysis was introduced determining an optimal combination of the investigated parameters that optimize all the process outputs according to specific process needs.

Incremental sheet forming has been proposed as a flexible manufacturing technique to process thermoplastic resins characterized by a glassy state at room temperature. Specifically, poly(methyl methacrylate) (PMMA) sheets were formed. A controlled room was designed, and the sheets were heated, before starting the forming phase, to a temperature above the PMMA glass transition, but avoiding onset of internal stresses that may lead to significant material springback at elevated temperature. Therefore, the process parameters, such as forming temperature and punch speed rate, have to be kept in well-defined ranges to be able to optimize the forming process of thermoplastic components by ISF. Furthermore, different sheet thicknesses were formed. Indeed, this size affects the flexural strength of the processed polymer as confirmed by reported tests. Experiments were planned out for the aim to take into account various process variables, i.e. spindle speed, step depth, punch diameter and feed rate. A plan based on a design of experiments (DoE) method was applied for a robust analysis. Macroscale observations were carried out to evaluate the product soundness, highlighting influences of the monitored process variables, on the process temperature and on the accuracy error of the formed parts. Furthermore, microscopic analyses evidenced the integrity grade of the surface on the side in contact with the punch for various combinations of process parameters. The results proved the process feasibility also for thermoplastics, which need to be heated before their forming phase.

Hot single point incremental forming (SPIF) with induction heating and cryogenic cooling has been applied to form the Ti-6Al-4V sheets. The influence of both the forming temperature and the cooling rate after deformation, on microstructure evolution and microhardness of Ti-6Al-4V sheets, has been extensively studied. We propose the use and development of a new system of heating by induction. The system is composed of a medium–high frequency generator and a continuously water-cooled heating head, which is placed under the sheet and linked axially to the punch movement, heating the material locally by generating an eddy current within the material. Furthermore, a cooling system integrated with the movement of the forming punch allows us to apply a cryogenic fluid to the recently deformed sheet metal. Both localized heating and cooling systems are particularly suitable for such a process as SPIF, whose primary characteristic is the incremental forming of localized sheet zones. The meta-dynamic and static recrystallization processes have been suppressed in the sheet material, evident by the final microstructure and mechanical properties. Finally, a comparison between parts is made, both with and without cooling during hot SPIF.

Aluminium sheets (EN AW-1050) have been worked by a friction stir process to allow forming pins to be used as joining elements, in a clinching-type solution, for assembling multi-material components. Two lines of pins of diameter 4 mm and 6 mm, respectively, have been formed experimentally at various process conditions. A process control, using the force-trend distribution, has been pursued for a full comprehension of the forming steps. The strength of the pins has been tested aiming at understanding the influence of all the analysed process parameters thoroughly. Additionally, a numerical model has been developed and compared with the experimental evidence. This model has been employed to investigate the material flow during the pin formation. The results demonstrate the feasibility of this innovative method and highlight the significance of the main parameters that have to be set carefully for an optimised implementation of friction stir forming based joining technique. Graphical abstract

Cranial reconstructions are essential for restoring both function and aesthetics in patients with craniofacial deformities or traumatic injuries. Titanium prostheses have gained popularity due to their biocompatibility, strength, and corrosion resistance. The use of Superplastic Forming (SPF) and Single Point Incremental Forming (SPIF) techniques to create titanium prostheses, specifically designed for cranial reconstructions was investigated in an ovine model through microtomographic and histomorphometric analyses. The results obtained from the explanted specimens revealed significant variations in bone volume, trabecular thickness, spacing, and number across different regions of interest (VOIs or ROIs). Those regions next to the center of the cranial defect exhibited the most immature bone, characterized by higher porosity, decreased trabecular thickness, and wider trabecular spacing. Dynamic histomorphometry demonstrated differences in the mineralizing surface to bone surface ratio (MS/BS) and mineral apposition rate (MAR) depending on the timing of fluorochrome administration. A layer of connective tissue separated the prosthesis and the bone tissue. Overall, the study provided validation for the use of cranial prostheses made using SPF and SPIF techniques, offering insights into the processes of bone formation and remodeling in the implanted ovine model.

Every manufacturing process alters the state of a surface, endowing it with new attributes that engineers use to enhance the performance of the finished products. When these surfaces come into contact with the human body, they exert specific influences depending on their condition affecting medical device biocompatibility. This study shows how a titanium alloy surface, characterized by standard measurement parameters such as roughness and contact angle, specifically influences the response of osteoblast-like cells in terms of proliferation and morphology. This relationship is quantified by comparing different machine learning techniques. More in detail, the impact of the milling process on Ti6Al4V substrates on the growth of the human osteosarcoma cell line MG63 has been investigated. By varying the technological parameters such as the cutting speed and depth and, consequently, the surface condition, the number of cells after a 72-h culture was measured to correlate cell proliferation with the process parameters. Ultimately, it is conceivable that with further research, surfaces could be designed to elicit varying cellular responses by appropriately combining manufacturing processes and their technological parameters.

Currently, the growing need for highly customized implants has become one of the key aspects to increase the life expectancy and reduce time and costs for prolonged hospitalizations due to premature failures of implanted prostheses. According to the literature, several technological solutions are considered suitable to achieve the necessary geometrical complexity, from the conventional subtractive approaches to the more innovative additive solutions. In the case of cranial prostheses, which must guarantee a very good fitting of the region surrounding the implant in order to minimize micromotions and reduce infections, the need of a product characterized by high geometrical complexity combined with both strength and limited weight, has pushed the research towards the adoption of manufacturing processes able to improve the product’s quality but being fast and flexible enough. The attention has been thus focused in this paper on sheet metal forming processes and, namely on the Single Point Incremental Forming (SPIF) and the Superplastic Forming (SPF). In particular, the complete procedure to design and produce titanium cranial prostheses for in vivo tests is described: starting from Digital Imaging and COmmunications in Medicine (DICOM) images of the ovine animal, the design was conducted and the production process simulated to evaluate the process parameters and the production set up. The forming characteristics of the prostheses were finally evaluated in terms of thickness distributions and part’s geometry. The effectiveness of the proposed methodology has been finally assessed through the implantation of the manufactured prostheses in sheep.

Welding processes are widely used technologies in the industrial context for creating permanent connections between mechanical components. This popularity is due to their versatility, which arises from the numerous available process variants and the multiple advantages they offer compared to other joining techniques. In the manufacturing context, where devices often operate in extreme conditions, the quality of welds becomes a critical factor in ensuring the safety and reliability of the manufactured products. Furthermore, a sound joint requires careful compliance with the increasingly stringent design specifications demanded by customers who require industry-standard conformity in order to achieve defect-free, robust, and durable welds. To address these needs and to define the optimal roadmap for the investigated process condition, an experimental investigation was conducted on the submerged arc welding process. The experimental trials involved butt joints of ASTM A516 Gr.70 carbon steel plates with different thicknesses in a flat position, utilizing a U-shaped chamfer and a multi-pass welding technique. For each weldment, the effects of the main process parameters on the qualitative characteristics of the manufactured products were evaluated from a metallurgical perspective. This evaluation included an in-depth metallographic analysis of the heat-affected zone of the carbon steel joint and involved both the measurement of the dimensions of these areas as well as the amount of ferrite and pearlite that resulted as the phases observed in the final microstructure of the steel joint following its solidification. Furthermore, the joint quality was assessed with regard to mechanical strength through hardness measurements. By analysing the experimental data, the paper provides a valuable contribution for increasing the productivity of the investigated welding process, while simultaneously meeting the specified industrial quality requirements for the products made of medium-thickness carbon steels.

Industrial needs are becoming always more complex due to an ever more demanding market and an increasingly fierce competition. Flexibility is, without shadow of doubt, a sought point of strength for improving the company market competitiveness. On this direction, incremental sheet forming (ISF) properly responds to the standing industrial needs. Dimensional accuracy and process slowness are the main drawbacks, which have to be addressed for the growing use of ISF in the industrial scenario. Furthermore, taking into account the current requirements related to the reduction of weights and volumes for fuel saving in the automotive field, lightweight alloys are the materials, which have been always more utilized for the manufacture of several parts. Here, their reduced workability at room temperature has to be taken into account. In this work, high speed incremental forming on lightweight alloys was investigated. The increment of the process velocity was proposed as a possible solution to mitigate the emphasized process limitations. Different ISF conditions were investigated by an experimental plan varying the punch velocity of two orders of magnitude; furthermore, the coil pitch was also analyzed. Finally, the plan was carried out on two different lightweight alloys, an aluminum alloy (AA5754) and a titanium alloy (Ti6Al4V), to highlight the impact the different material properties have on the temperature distribution during the process. A wide discussion on the obtained results is reported.