Papers by Author: Luigino Filice

Abstract: Nowadays manufacturing companies have to face conflicting issues continuously. Solving this type of problem means finding solutions that ensure a fair compromise between different objectives. In this work, a porthole die extrusion is considered as a specific case study. Usually, the main objective of this process is to find the combination of input parameters that allow the product quality to be maximized. However, product quality is not the only variable that companies have to take into account. In fact, it is also necessary to design the process in an efficient and sustainable way in order to reduce process cost and environmental impact. To this purpose, in this study the conflicting aims of product quality maximization and energy assumption minimization are considered and optimized. To pursue this aim an experimental investigation was executed, in order to build a preliminary database. The decision variables are the profile thickness and the process velocity. During the tests, the punch was measured in order to quantify the absorbed power along with the environmental impact of the process for changing conditions. In the same way, the mechanical properties of the extruded profile were measured by means of a tensile test, in order to assess the product quality. To solve this kind of problem the use of multi-objective optimization techniques is required in order to find the set of Pareto optimal solutions from which a single configuration will be selected according to specific business needs.

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: 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: 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 reports the results of an experimental study of the tool wear and cutting forces in turning of Inconel 718 with coated carbide inserts. Inconel 718 is a difficult-to-cut nickel-based super-alloy commonly used in aerospace industry. The effects of cutting speed, feed rate and cutting tool geometry on tool wear have been widely analyzed in literature. Turning operations on complex components such as aircraft engines casings require the insert replacement at the end of each geometric feature manufacturing, independently from the actual tool wear level. For this reason, it is important to preserve tool integrity mainly in the most critical phase of operation (i.e., when the tool engages the workpiece). In fact, if the tool is damaged in this stage the quality of the whole operation is compromised. The attention has been focused on engage cutting conditions because the phenomenon that appears in this critical step plays a wide influence on tool integrity and, consequently, on the quality of the operation. For this purpose a nickel-based super alloy ring-workpiece, (Inconel 718), has been machined in lubricated cutting conditions by using a CNC lathe with carbide coated tools. Two variables have been investigated in this study: the Depth Of Cut (DOC) and the approaching Engage angle (En). In the studied working conditions Speed (S), Feed-rate (F) and removed volume (Vrim) were kept constant. Both tool wear and cutting forces evolution during cutting have been analyzed.

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.

Abstract: The conventional tube extrusion process has been substituted by porthole die extrusion due to relevant advantages in terms of productivity and quality. However, the porthole die has a complex geometry to be effectively designed; consequently, several studies can be found out in the technical literature based on experimental and finite element analyses of the process. From this point of view, while the experimental investigations entail cost and time increasing, due to the die building complexity, finite element techniques present some drawbacks such as the difficulty to simulate material joining and the loss of accuracy due to the heavy mesh distortion and related remeshing. Therefore, the introduction of new numerical techniques for the analyses of this process could have positive effects. In this paper, the Natural Element Method (NEM) together to the alpha shapes and some extra numerical procedures are used in the simulation of tube extrusion, focusing the attention on the simulation of the welding line in a fully 3D analysis. The obtained results are compared with the finite element and experimental ones, measuring the accuracy of the proposed methodology.

Abstract: FEM implicit formulation shows specific limitations in processes such as cutting, where large deformation results in a heavy mesh distortion. Powerful rezoning-remeshing algorithms strongly reduce the effects of such a limitation but the computational times are significantly increased and additional errors are introduced. Nodal Integration is a recently introduced technique that allows finite element method to provide more reliable results when mesh becomes distorted in traditional FEMs. Furthermore, volumetric locking phenomenon seems to be avoided by using this integration technique instead of other methods, such as the coupled formulations. In this paper, a comparison between a “classical” FEM simulation and the Nodal Integration one is carried out taking into account a simple orthogonal cutting process.

Abstract: Flexible sheet metal forming processes represent one of the most relevant industrial issues of the scientific research. Incremental Sheet Forming is one of the most promising answers for many production scenarios. In particular, it becomes competitive when the production lot size decreases and the production variability increases. The process is basically set up on numerically controlled machines: a blank is clamped at its border and progressively deformed by a punch that moves according to a proper tool path program, reproducing the final part shape. Thus, the manufacturing time is directly dependent on the tool path length. Up to now, this aspect is one of the reasons why a systematic industrial application is not permitted. To overcome this drawback, an experimental investigation was planned in order to evaluate how the process is affected changing the cycle time. More in detail, an extended experimental investigation on the influence of process speed (i.e. tool rotation speed, tool feed) and other process parameters was executed taking into account a relatively simple 3D component. An accurate analysis of the obtained parts was performed, with particular attention to the thinning distribution that, of course, influences the material failure. Finally, the surface quality was also measured as an output variable.

Abstract: Aluminum (Al) and Magnesium (Mg) alloys are nowadays widely employed in order to produce lightweight automotive and aeronautical components and to gain fuel saving and reduced emissions. However, the joining of Al and Mg alloys poses well known technical problems and the application of conventional joining techniques, e.g. welding, may be ineffective. On the other hand, adhesive bonding may be considered as a candidate replacement of the traditional techniques and for this reason it has been recently proposed as an alternative technology for Al/Mg joints. In particular, it has been demonstrated that adhesive bonding, in conjunction with state-of-the-art surface treatments, can provide Al/Mg joint with enhanced strength. However, in order to evaluate the potential of adhesive bonding to outperform the conventional joining techniques a systematic comparative analysis is needed. Therefore, the aim of this work is to supplement the existing studies on Al/Mg bonding providing a comparative analysis between Al/Mg joints prepared using gas metal arc (MIG) welding, riveting and adhesive bonding. Probably, the use of adhesive bonding as complementary joining process will be the industrial answer to the hybrid joints performance needs.