Numerical prediction of various defects and their formation mechanism during friction stir welding using coupled Eulerian-Lagrangian technique

Abstract

Defective weld significantly hampers the quality of the weld and selection of optimum process parameter which produces defect-free weld is an experimental tedious task. A robust numerical model capable of predicting various types of defects is required to save cost and time. In the current work, a numerical model is developed based on coupled Eulerian-Lagrangian method and the concept of Volume of Fluid is incorporated to predict defects. It is the first attempt to numerically predict and analyze various types of defects such as tunnel, void, cavity, and root defects associated with friction stir welding. Defect formation is studied by varying tool rotation speed from 600 to 1500 rpm, welding speed from 30 to 180 mm/min, and tilt angle from 0 to 3°. The tilt angle of zero degree resulted in tunnel defect and one degree resulted in void and cavity. Tilt angle of two degree produced a defect-free weld. Also, parameters with a three-degree tilt angle yielded defective welds. The defect formation mechanism is correlated with temperature history, material flow, and axial force. A process parameter window is developed indicating the defective and non-defective weld conditions.