A novel slip rate model for determining the interfacial contact state in friction stir welding

Abstract

Slip rate is a key parameter that represents the interfacial contact state between the tool and the workpiece, and it determines the heat generated during friction stir welding (FSW). However, it is difficult to experimentally measure this interfacial field, and the actual contact state is quite unclear. Therefore, an advanced slip rate model is needed to determine the contact state and to accurately elucidate the heat generation mechanism in FSW. In this paper, a novel model is proposed to directly calculate the slip rate based on welding parameters; this model is established by conducting parametric inversion on the slip rate through finite element analysis. The results show that the slip rate increases with increasing welding speed and decreases with increasing rotational speed. Furthermore, the slip rate model reveals the impacts of the welding parameters on the interfacial contact state. When n/v is greater than 4.6, the dominant mode of heat generation is sticking friction in FSW. Conversely, the major mode of heat generation is sliding friction. A finite element model is used to investigate the thermal process and the distribution characteristics of the temperature field during FSW of 2219 aluminum alloy. The temperature field in the weld zone presents a ''bowl-shaped'' distribution, with the temperature at the top being higher than that at the bottom. Moreover, the temperature peak occurs at half the radius of the shoulder. The above results provide an important reference for understanding the heat generation mechanism and temperature history during FSW of aluminum alloys.

Keywords

• Friction stir welding
• Slip rate
• Interfacial contact state
• Parametric inversion
• Finite element model