Papers by Author: Francesco Gagliardi

Abstract: The production of prostheses is still not completely optimized, especially for those districts where both functional and aesthetic requirements have to be combined with the urgency of intervention. The prostheses manufactured by machining using CAD/CAM techniques represent the conventional way to obtain a “custom-made” part. However, the above-mentioned solutions are penalized by the too long manufacturing time. This limit can be overcome by using an innovative metal-forming process, i.e. the Incremental Sheet Forming (ISF), which also allows to obtain complex patient-specific geometries even if characterized by a lower precision compared to the conventional process. In this paper, alternative approaches to manufacture a skull prosthesis (i.e. conventional milling and ISF) are compared from technological and economical points of view.

Abstract: Nowadays manufacturing technologies have to be evaluated not only for the technical features they can provide to products, but also considering the environmental perspective as well. As long as the technological feasibility of a given process is guaranteed, processes minimizing resources and energy consumption have to be selected for manufacturing. With respect to this topic, the research studies in the domain of metal processing technologies predominantly focus on conventional material removal processes as milling and turning. Despite some exceptions, many other non-machining technologies, such as metal forming processes, are still not well documented in terms of their energy and resource efficiency, and related environmental impact. In this paper, an environmental challenge between two traditional technologies is developed: the environmental performances of a partial hot extrusion process and of a turning processes are quantified and compared. A Life Cycle Assessment (LCA) approach is implemented to properly analyze the considered processes. The material production step and the manufacturing phase to obtain a simple axy-symmetric aluminum component is considered for the Life Cycle Inventory (LCI) data collection step. Besides, the material and consumables usage and the consumed electrical power are measured in order to quantify the energy consumption of the manufacturing phase. Further, the environmental impacts related to the manufacturing of the extrusion dies and of the turning process are included in the analysis. The paper presents an early step of a wider research project aiming at identifying the greenest technologies as functions of given product features.

Abstract: Porthole die extrusion of lightweight alloys is used for the production of profiles, which may have complex cross section geometries. The mechanical properties of these profiles are deeply affected by the seam welds, which are generated in hollow profiles along the whole length. The seam welds result from the rejoining of the material streams in the welding chamber of the porthole die. The joining phase and hence the seam weld quality are strongly influenced by the temperature and the pressure conditions in the welding chamber. Those process conditions can be adjusted by a proper die design. In this work, the focus lies on the feeder section of the extrusion die, which consists of a set of bridges, whose shapes influence the material entry in the welding chamber. A numerical study was carried out to investigate different bridge shapes with regard to the pressure inside the welding chamber and the punch load. Subsequently, the volume of the bridge was fixed to isolate and better investigate the influence of the shape. It was observed that bridge designs leading to higher flow distortion cause higher pressure decrement along the welding plane and, consequently, degradation of the welding conditions.

Abstract: It is well known that Incremental Sheet Forming has two main drawbacks, i.e. accuracy and slowness. The former has been studied and partially solved by several researchers while the latter did not receive convincing answers. Thus, the idea of several research groups is that the process applicability is suggested only for rapid manufacturing or small batch production. The lack of knowledge is certainly caused by the available machines, like milling or Amino, which are typically used for incremental forming operations. In the present research the attention was focalized on the above limit: an experimental campaign was performed in order to evaluate the process feasibility at very high speed. To do that a lathe machine has been used instead of the conventional milling one, increasing the process speed up to two order of magnitude. An aluminum alloy, widely used in the mechanical fields, has been chosen as sample material and an experimental investigation has been aimed at determining the influence of tool speed on the material behavior.

Abstract: Flexible sheet metal forming processes represent a big challenge, which involved a number of researchers all over the world in the last decades. Among these, Incremental Sheet Forming (ISF) process is one of the most investigated and promising due to its simplicity, cheapness and applicability. Furthermore, the possibility to increase the process velocity makes the ISF more suitable than in the past; as a consequence, its application potential is surely increased. It was already highlighted that high speed significantly raises the process temperature, improving the workability of Titanium alloys. In this process configuration, no further heating source is strictly required because the temperature increase is generated due to the plastic deformation and the friction conditions at the interface between the punch and the sheet. While the process feasibility has been already investigated, a lack of knowledge in the literature is present focusing on the analysis of the process impact on the material properties. Accordingly, an experimental campaign on Ti6Al4V sheets has been performed, considering a punch speed two orders of magnitude higher than the conventionally used one. The obtained surfaces have been compared to sheets worked by traditional velocity in order to accurately analyze the impact of high speed. Furthermore, microstructural analyses have been carried out confirming the high speed suitability. All the details are reported in the manuscript

Abstract: Extrusion processes can be utilized for production of parts characterized by complex shapes; furthermore, nowadays, the market needs are always more driving towards the manufacture of components with thinner thickness for weight and volume reduction. As a consequence, the process complexities are growing up but, nevertheless, quality and productivity have to be guaranteed by companies if they want to survive in an increasingly competitive society.In this work, a ductile criterion was utilized to highlight which variations due to thickness reduction can bring to superficial defects in extruded components. The study was carried out by using a suitable die geometry where thickness changes can be performed keeping constant the other geometrical variables. The die optimization was carried out by numerical simulations which were utilized for homogenizing the extruded velocity at the exit of the bearing zone. Different working conditions were numerically analyzed and geometrical die changes were performed to highlight their influences on the superficial integrity of the extruded parts.

Abstract: The material flow in porthole dies is of crucial importance with regard to the seam weld quality in aluminum extrusion. Thus, experimental as well as numerical investigations on the effect of die geometry on the material flow were conducted. The experimental tests were performed on a 10 MN laboratory extrusion press. During the experimental trials, the extrusion ratio was varied by means of exchangeable die plates. Since the modular die allows removal of the aluminum in the welding chamber as well as in the feeders after the process, the material flow could be inspected in detail. The experimental results were used to improve the accuracy of FEA simulations, which were also conducted by commercial software. An attempt was made to improve the result quality of Eulerian FEA model regarding the simulation of an extrusion process with a gas pocket in the welding chamber. The influence of the modeling approach on the predicted material flow and on the contact pressure was analyzed and finally linked to the seam weld quality.

Abstract: Incremental sheet metal forming (ISF) had a great interest in the scientific community, in the last years. A common opinion is that ISF has not to be considered as an alternative to conventional stamping but has to be regarded as a process able to work materials in a new way. Furthermore, ISF could be a suitable alternative to manufacture some “hard to work materials”. Among them, Titanium plays a relevant role. Today Titanium is usually worked by superplastic forming (SPF) or hot forming (HF) in case of simple shapes. However, both the processes are very slow and expensive. In a previous work the authors showed how it is possible to form Titanium alloys using ISF combined with a local heating. However, heating suggests also to analyze energy consumption. The process does not requires large forces but is really slow. Thus, the different heating sources can have a deep impact on the global energy performance. The paper is a first attempt to consider the process in a wider view, looking at the energy consumption as a primary issue. In particular, a comparison among different heating methods was carried out.

Abstract: This paper presents a study of the influence of cutting conditions on the finished surface obtained after an hard turning process, in particular a case study is presented where AISI 52100 bearing steel is machined under different cutting conditions. An analysis carried out using Surface Response Methodology has been developed in order to study the influence of the main cutting parameters such as cutting speed, feed rate and workpiece initial hardness on white (WL) and dark layer (DL) thickness. The whole experimental campaign has been performed using a chamfered PCBN tool inserts without any cutting fluid. Results show an evident influence of cutting speed and feed rate on both white and dark layer thickness while less relevant is the contribute given from the workpiece hardness on defining WL and DL depth. Finally, a model to find the optimal process conditions to minimize white and dark layer thickness is developed.

Abstract: Porthole die extrusion has been always more used for the production of hollow profiles. The process is characterized by a complex die whose design is important for the product soundness. The quality of the welding line and, consequently, the quality of the extruded parts strictly depends on the extrusion optimization; for this reason, the influences that, each process parameter has on the pressure along the welding plane, have to be correctly understood. Unfortunately, the complexity of the die geometry generates great research difficulties if different parameters are analyzed; furthermore, even 3D numerical investigations present relevant drawbacks due to the high computational time and the results quality. In this work, a simplified and flexible porthole die is proposed; the equipment was designed and manufactured rectifying a quarter of a traditional porthole die. Moreover, the extruded part has flat shape with welding line in the middle; by doing that, its quality can be simply analyzed through standard tensile tests. Different geometrical variables were investigated, i.e., the bridge shape and width and the bearing length; their interactions on the process dynamics and on the product quality were also discussed. The Analysis of Variance (ANOVA) technique was used to evaluate the obtained results.