Three-dimensional thermal-mechanical analysis of retractable pin tool friction stir welding process

Abstract

The retractable pin tool friction stir welding (RPT-FSW) is a technology for eliminating the exit hole at the end of the weld via in-process pin retraction. During RPT-FSW, the influence of the pin-retraction-induced continuous changing tool/workpiece interface on thermal-mechanical processes, such as the heat generation, temperature, and material flow, is critical knowledge for the process development and optimization. In this study, three-dimensional thermal-mechanical analysis based on computational fluid dynamics (CFD) is applied to investigate the RPT-FSW process. Technically, the dynamic mesh approach is utilized to allow dynamic geometric model for implementing the continuous change of the tool/workpiece interface. The thermal-mechanical condition during the RPT-FSW in the vicinity of the welding tool is investigated and compared with the conventional FSW. It is shown that the volume of the deforming material (with low viscosity) decreases significantly because of the reduction of the total area of the tool/workpiece interface immersed in the workpiece due to the pin retraction. Generally, in spite of the shrinkage of deforming zone volume, the thermal-mechanical condition during RPT-FSW inside the deforming zone is quite similar to the conventional FSW. Comparing to the conventional FSW, the decrease in average deformation temperature during the RPT-FSW is about 10 °C due to the reduction in heat generation. The pin retraction causes slight fluctuation in the average strain rate in the deforming zone. Finally, the numerical simulation data is supported by the experimental measurements regarding the temperature history and deformation zone geometry.