Numerical analysis of the effect of welding positions on formation quality during laser welding of TC4 titanium alloy parts in aerospace industry

A large number of titanium alloy components have huge volume with a 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 (VU), vertical down (VD), and flat, with different welding parameters by using 3 mm-thick titanium alloy plates experimentally and numerically. The VU position showed a high tendency of bigger keyholes and resulted in 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 VD 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.