Abstract Scope |
Despite its slow rate, the tool wear during friction stir welding of aluminum alloys is an important factor in considering the tool life especially when the weld is very long. In this study, the worn depth of the Ni-based welding tool after a 120m long weld is experimentally measured and analyzed. It is found that the worn depth at tool surface distributes in a non-uniform manner. Significant worn occurs at the locations where the tool geometry changes sharply, and that the maximum worn depth is located in the middle of the probe. Experimentally-validated numerical simulation based on computational fluid dynamics (CFD) is conducted for predicting the in-process heat transfer and material flow in the vicinity of the welding tool. From the numerical simulation, the in-process thermomechanical state variables at the tool/workpiece interface, such as the temperature, the pressure and the slipping velocity, are quantitatively determined. The worn depth on the tool surface is discussed against the in-process thermomechanical state variables at the tool/workpiece interface. The non-uniform distribution of worn depth is mainly attributed to the pressure fluctuation at the locations where the tool geometry changes sharply and the temperature distribution. Finally, a new modified Archard wear equation is proposed by taking into consideration the temperature effect on material hardness, in which the wear rate is mathematically linked to the interfacial thermomechanical state variables between the welding tool and the workpiece, including the temperature, the pressure and the slipping velocity. The proposed equation is demonstrated to describe well the wear rate on the tool surface in the welding condition in this study. |