High Depth-to-Width Ratio Friction Stir Welding

For conventional friction stir welding (FSW), welding tool consists of shoulder and pin, in which the ratio of pin to shoulder is about 0.33. Zhang et al. (Metall Mater Trans A 42(10):3229–3239, 2011 [1]) showed that the shoulder was responsible for main part of heat generation. Larger shoulder diameter resulted in that higher heat input concentrated on the surface of joint, which broadened the width of the heat affected zone (HAZ) and reduced mechanical properties. The rotational pin is the main driven force of material flow around the tool. In order to obtain high-quality joint, decreasing shoulder diameter and optimizing pin geometrical structure are of vital importance. However, decreasing heat input by simply reducing the shoulder diameter easily results in the fracture of the pin and formation of defect. Obviously, it is not an acceptable choice to attempt massive possibilities one by one due to its potential risk of pin fracture. Thus, numerical methods were proposed to provide a better alternative to welding tool design, which saved time cost and improve the efficiency of the design process.