Numerical simulation of wire arc additive manufacturing

The automotive industry is constantly looking for new technologies to be applied in order to improve the qualities and performances both of the components produced and of the whole production chain. Among these, the Wire Arc Additive Manufacturing (WAAM) is earning increasing interest in the last few years. It belongs to the so-called additive manufacturing (AM) processes, in which the part is fabricated by the addition of material, rather than subtraction of it. The AM processes constitute an innovative method to produce components, consequently, a huge amount of research has been focused on them in the last two decades. Among the different variants, the WAAM process is meant for the fabrication of metal components and is based on conventional welding technologies. Taking into consideration that, several applications of it have been studied for numerous industrial sectors, and, in the last period, even the automotive field is approaching this technology. In particular, the stiffener parts have always represented a fundamental element in the design of structural components, used to reinforce the overall structure. In this context, the conventional manufacturing processes currently applied to fabricate the stiffener elements could be replaced by the implementation of the AM, with clear advantages deriving from an increase in the performance and a reduction in weight and parts, with a consequent drop in costs and wastes. Despite the possible benefits gained from the application of the additive process, however, the knowledge and studies regarding the application of stiffener elements by WAAM onto automotive components are exiguous. In addition, a large number of physical tests should have been performed for each type of component to satisfy the stringent requirements stated in the assembly and crash tests. Considering that, a virtual instrument able to simulate all the processes composing the whole manufacturing chain, going from the stamping to the assembly and, eventually, the final crash test simulation, would represent an effective resource, with the purpose of conducting a predictive analysis. Being the last cited virtual instrument an appealing solution for the automotive industry, it is currently the object of various projects and studies, nevertheless, its intrinsic complexity has led to its decomposition into several parts, one of which has been designed in this thesis work. It has consisted of the development of a finite element (FE) tool designed for the simulation of the stiffeners fabrication on car-body parts, deposited with the WAAM process. Two finite element software are at the basis of the virtual tool: Altair HyperMesh and SYSWELD, respectively specialized in the pre-processing modeling and in the welding processes simulation. During the study, the potentialities of the developed FE tool, among which stands out the possibility to impose various configurations without the need to have a number of physical prototypes and experiments, has been explored in two industrial applications, through the analysis of the FEA outcomes in terms of thermal distribution, microstructural evolutions, residual stresses and distortions, that altogether represent a major concern when the performances and qualities of parts fabricated with WAAM are investigated.