Numerical analysis of effect of welding positions on formation quality during laser welding of titanium alloys

Abstract

A large number of titanium alloy components have huge volume with complicated curved surface in aerospace industry hence it is necessary to develop an all-position welding process. Laser welding is regarded as a high quality method to join those components flexibly and efficiently. However, titanium alloys are very sensitive to laser processing parameters, and the formation quality can be a severe problem under different welding positions. In this work, the tendency of porosity and burn through holes was evaluated under different welding positions: vertical up, vertical down and flat, with different welding parameters by using 3mm-thick titanium alloy plates experimentally and numerically. Vertical up position showed high tendency of bigger keyholes, and resulted to the formation of burn through holes, which was not a problem for other positions with the same parameters. Low heat input was beneficial to eliminate burn through holes. The vertical down position increased frequency of keyhole collapse, and led to higher porosity compared with other positions. Welding with higher laser power at higher speed could reduce this kind of porosity. Numerical simulation results well exhibited the change of the keyhole size and the molten pool flow behavior, which is a powerful tool to understand the formation mechanism of different weld defects, and help to find the optimized processing parameters to eliminate the relative defects for different weld positions.