Seminar Series

Multiphysics Modelling of Bobbin Friction Stir Welding Process

Speaker

Abbas TAMADON, PhD student

Institute

Department of Mechanical Engineering, UC

Time & Place

Mon, 13 Jun 2016 10:00:00 NZST in Erskine Bldg, Room 101

All are welcome

Abstract

BACKGROUND- Bobbin Friction Stir Welding (BFSW) is a new class of solid-phase joining techniques, whereby a symmetrical rotating system (consisting of two shoulders, one on each side of the workpiece connected by the tool pin) ploughs through the interface of the two plates, and mixes the materials into a fully penetrated bonding by heat and stirring.

RESEARCH QUESTION- Due to severe dynamic plastic deformation and failure of the material flows during the process, existence of a continuous void line as the defect in weld region is one of the challenges of the work. There is no solid theory about variables of process and method of control to achieve the optimum parameters. Therefore, a transition from trial and error to a science based approach is highly necessary.

APPROACH- While the metallurgy of friction stir welding is well known, the process parameters have received less attention, and this is where the current project focuses. The aim of this research is to present a Multiphysics model for BFSW to optimize the variables of the process with specific tool features by consideration of their interaction on each other. This model should find a way for characterizing weld defects and also explain the microstructure trajectory during the process and how flow models can modify them.

FINDINGS- Experimental works were conducted on analogue modelling of BFSW process to understanding the variables of process, internal flow features and work on a theory for flow failure and predicting weld defects. The modelled weld structures by analogue methodology can elucidate the relationships between flow features and defects near to real circumstances of the BFSW welds. The entry zone of weld line is interesting in our research as the origin of spray defect and tunnel void. These defects can result other defects in the weld region, caused by loss of material and discontinuity in weld.

IMPLICATIONS- After a better understanding of weld parameters using analogue model, we have more approached to the main objective of this research. We discuss some computational models based on FEM and CFD, to adopt a problem solving method similar to analysis of thermomechanical metal forming processes. Also, ability of commercial modeling software (ANSYS, COMSOL, ABAQUS, etc.) in implementation of a multiphysics model for BFSW process will be discussed.

Originality: Due to the complex content of BFSW process and interaction of variables, up to now the study of BFSW process and tool development has been mostly empirical. On the other hand, there are some difficulties about control of process parameters for bobbin-tool FSW to avoid tool failure and weld defects. This analogue model method has the potential to make a significant contribution to understanding the transport regimes and lead to a better understanding of the causes of weld defects.