​ ​ ​Seminar on A mechanical model in Wire + Arc Additive Manufacturing Process

Material properties are dependent upon the microstructural characteristics of the part. Developing an accurate and sufficient representation of the microstructure obtained in metal Additive Manufacturing (AM) is critical to precisely estimate material properties. Since the material properties for AM parts are an important function of the welding processing parameters, a fundamental understanding of how AM components behave in load-bearing applications depends on understanding the evolution of thermal cycles and residual stresses during component fabrication. In this work, a finite element thermo- plasticity procedure in wire + arc AM process was developed in a three-dimensional domain using the Finite Element (FE) code ABAQUS. The proposed research aims to establish a methodology for characterizing direct energy deposited metals by linking processing variables to the resulting microstructure and subsequent material properties. The effect of multi-layer deposition on the prediction and validation of local plastic strains and thermally induced stresses was investigated. It was found that the thermal (residual) stresses increase with either the increase of weld speed or the increase of the heat distribution parameter. On the other hand, local plastic strains increase with the increase of welding speed, but not necessarily with the increase of the heat distribution parameter. Similarly, the level of thermal stresses and local plastic strains is lower in each new sucessive AM layer. As a new layer is deposited over a previously heated one, the relief of thermal stresses and plastic strains occurs by preheating; the more preheated the previous layer, the less the level of thermal stresses and plastic strains in the succesive deposited layer. Furthermore, the lowest level of stresses and strains observed in the last deposited AM layer shows that the relief occurs also by expansion because the top unrestrained weldment surface is free to expand. Numerically predicted thermal stresses at different welding layers are presented for further experimental comparison. A firm foundation for thermo-mechanical modelling in wire + arc additive manufacturing process is established.

Dr. Bonifaz graduated Cum Laude with a B.S. degree in Mechanical Engineering from Escuela Superior Politecnica de Chimborazo in Ecuador, with a M.S. in Metallurgy from the University of Illinois at Chicago and with a Ph.D. degree in Materials Engineering from the University of Navarra in Spain. He was a recipient of several Fellowship Awards from international organizations such as: Korean Government, United Nations, Fulbright, OAS- Organization of American States, AECI-MUTIS, and the Open University, UK. He was a Visiting Professor in the Mechanical and Mechanics Engineering Department at Lehigh University, a Research Associate in the Mechanical Engineering Department at the University of Manitoba-Canada, a Post Doctoral Fellow in the Mechanical Engineering Department at the University of South Carolina, USA, and a Visiting Scholar, in the Civil and Materials Engineering Department at the University of Illinois at Chicago, USA. His research activities cover areas of Welding Metallurgy, Solidification, Additive Manufacturing, Strain Gradient Plasticity based on the micromechanics of dislocations, and high-temperature materials processing. Dr. Bonifaz has been with the University San Francisco de Quito (USFQ), Ecuador, since 2004. He is currently a full time mechanical engineering Professor and his research interests are focused on the analysis and understanding of micromechanics problems with the aid of the finite element method.