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RESEARCH PRODUCT

COMPUTER AIDED ENGINEERING OF SOLID BONDING PHENOMENA

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description

Joining is a fundamental technological process in manufacturing used to create a single piece from two or more parts. Welding is still today one of the most popular joining techniques used in manufacturing allowing a permanent junction. Traditional welding processes are based on the melting of the materials to be joined. In this way, several defects may arise because of solidification problems, joints deformation due to elevated residual stress and metallurgical integrity of the joints (intermetallic, porosities, etc). As an example, some aluminum alloys present considerable problems the junction is carried out by traditional fusion welding methods. During the melting process, in fact, the liquid material can react with the surrounding atmosphere oxidizing and creating a weak joint. On the other hand, Solid Bonding based welding processes allow for defect free joints with low residual stress and low distortion. However, these processes are usually characterized by complex mechanics due to peculiar material flow. Hence, the engineering and optimization of solid bonding processes is difficult and requires a large number of time and cost consuming test trials. In this way, proper numerical models are essential tools permitting effective process design. The aim of this research was the computer aided engineering of two different manufacturing processes taking advantage of the same metallurgical phenomenon, namely solid boding. Linear Friction Welding (LFW), used to weld non-axisymmetric components and Accumulative Roll Bonding (ARB), used to increase the mechanical properties of sheet metals, were selected. Experiments, both of LFW and ARB, were run with the aim to study the effects of the process input parameters on the final product quality, to define proper process windows and to acquire the data needed for the numerical models set up and validation. In particular, as far as LFW is regarded, a dedicated experimental machine, able to produce LFWed joints with varying pressure, oscillation frequency and amplitude, was designed and built. Numerical models were set up, validated and used to design the process by studying the complex material behavior during the solid bonding of different aluminum alloys. In particular, as far as ARB is regarded, two different numerical models were considered, using an explicit and implicit approach, respectively, in order to study the process. An implicit approach was used for the LFW process, leading to the understanding of the main process variables influence on the field variables distribution and the occurrence of actual bonding. The simulation tools used in this work were DEFORM3D and ABAQUS CAE/6.9 (2D and 3D modes). The first prototype of the LFW machine was designed and developed during the first doctorate year. During the second doctorate year, the Accumulative Roll Bonding process was studied at the University of Erlangen-Nuremberg while, during the third year, the Linear Friction Welding process was analyzed at the University of Palermo.