Francesco Gagliardi

Sheet Thinning Prediction in Single Point Incremental Forming

Incremental forming processes are characterized by a well known and particular feature: any deformation across the sheet plane determines sheet thinning, since the blank is fully clamped by means of a proper equipment. As a consequence, the availability of effective and reliable CAE tools capable to supply an accurate prediction of sheet thinning as a function of process parameters, represents a strong requirement for a wider practical application of incremental forming. The already available theoretical models (i.e. the sine law) do not provide, on the other hand, satisfactory results. Therefore in the paper a couple of numerical analysis strategies was applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.

Modeling Approach for the Determination of Material Flow and Welding Conditions in Porthole Die Extrusion with Gas Pocket Formation

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.

Heuristic techniques to optimize neural network architecture in manufacturing applications

Abstract Nowadays application of neural networks in the manufacturing field is widely assessed even if this type of problem is typically characterized by an insufficient availability of data for a robust network training. Satisfactory results can be found in the literature, in both forming and machining operations, regarding the use of a neural network as a predictive tool. Nevertheless, the research of the optimal network configuration is still based on trial-and-error approaches, rather than on the application of specific techniques . As a consequence, the best method to determine the optimal neural network configuration is still a lack of knowledge in the literature overview. According to that, a comparative analysis is proposed in this work. More in detail four different approaches have been used to increase the generalization abilities of a neural network. These methods are based, respectively, on the use of genetic algorithms, Taguchi, tabu search and decision trees. The parameters taken into account in this work are the training algorithm, the number of hidden layers, the number of neurons and the activation function of each hidden layer. These techniques have been firstly tested on three different datasets, generated through numerical simulations in the Deform2D environment, in an attempt to map the input–output relationship for an extrusion, a rolling and a shearing process. Subsequently, the same approach has been validated on a fourth dataset derived from the literature review for a complex industrial process to widely generalize and asses the proposed methodology in the whole manufacturing field. Four tests were carried out for each dataset modifying the original data with a random noise with zero mean and standard deviation of one, two and five per cent. The results show that the use of a suitable technique for determining the architecture of a neural network can generate a significant performance improvement compared to a trial-and-error approach.

Enhancing Incremental Sheet Forming Performance Using High Speed

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.

White and Dark Layer Analysis Using Response Surface Methodology

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.

Forming Approaches Comparison for High Customised Skull Manufacturing

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.

Bridge Design Influences on the Pressure Conditions in the Welding Chamber for Porthole Die Extrusion

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.

Design of an optimized procedure to predict opposite performances in porthole die extrusion

The main objective of advanced manufacturing control techniques is to provide efficient and accurate tools in order to control the set-up of machines and manufacturing systems. Recent developments and implementations of expert systems and neural networks support this aim. This research explores the combined use of neural networks and Taguchi’s method to enhance the performance of porthole die extrusion process; the energy saving and the quality of the welding line are two conflicting objectives of the process taken into account. The complexity of the analysis, due to the number of the involved variables, does not allow the representation of the specified outputs by means of a simple analytical approach. The implementation of a more accurate and sophisticated tool, such as the neural network, results more efficient and easier to be integrated into a simple “ready to use” procedure for predicting the investigated outputs. The main limit to wider implementation of neural networks is the huge computation resources (times and capacities) required to build the data set; a finite element approach was adopted to overcome the time and money wasting typical of experimental investigations. Satisfactory results in terms of prediction capability of the highlighted outputs were found. Finally, a simple and integrated interface was designed to make easier the application of the proposed procedure and to allow the generalization to other manufacturing processes.

Towards Energy Efficiency in Incremental Forming of Titanium

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.

Analysis of joint quality along welding plane

Porthole die extrusion is an always more important process for industrial applications. It is, however, characterized by a considerable complexity; in fact, different parameters have to be carefully set for improving the final part. A critical zone that strongly influences the goodness of the extruded component is the so called “welding plane”. It is the junction area where material flows converge inside the welding chamber. The variables that have to be controlled for improving the material characteristics in this zone are the effective stress, the pressure and the time that the material takes to cross the welding chamber. Moreover, material temperature is another fundamental issue that influences both the quality and the typology of the final joint. However, especially for complex parts, the material can follow diverse directions to get out from the die; this means that the deformation history can be different, thus influencing the quality of the final jont. In the study here proposed, the property of the welding plane was highlighted for an industrial component that was cut through a profile cross section carrying out both metallurgical and mechanical investigations. More in detail, specimens, derived from the extruded part, were mounted, polished and etched with Keller reagent and observed by a light microscopy. Then, macro and micro observation were developed highlighting the welding line position. Moreover, local values of the average grain size of the material were measured showing the microstructural evolutions undergone by the material due to the extrusion process. As far as mechanical tests are regarded, micro-hardness tests were executed nearby the welding line; in this way, correlations between material metallurgical evolutions and subsequent local mechanical performances were highlighted. Furthermore, a 3D numerical study was developed in order to point out the numerical ability to predict the welding line position for complex parts; finally, a welding criterion was used in order to locally validate the experimental observations. All these aspects are accurately analyzed and discussed in the paper.