The research on the parameter thresholds of titanium alloy laser welding

The CO₂ laser welding and YAG laser welding were conducted to investigate the effects of welding parameters on weld shape for 2.5mm thick TA15 titanium alloy in this paper. The results show that the welds present three typical shapes varying with parameters, i.e. semi-spherical weld, nail-head weld and glass-hour weld. The relationship between weld shape and parameters reveals that the mode of laser welding depends not only on laser energy density as usual, but also on heat input. When these two parameters exceed the threshold for penetration laser welding, the nail-head weld or glass-hour weld occur. It is found that the back width to surface width ratio (R_w) can be used to describe the feature of the weld shape and to evaluate the stability of full penetration laser welding for titanium alloy sheet. Based on the experiment, the R_w should be larger than 0.4 in order to get stable full penetration laser welding for 2.5mm thick TA15 titanium alloy. Considering this required R_w and requirements for perfect weld quality, the optimization window of laser power and welding speed can be obtained under the condition of constant defocus distance. The laser energy density and heat input threshold curve for stable full penetration laser welding can be similarly mapped according to the experimental data. With the threshold curve, laser energy density, heat input, laser power and welding speed can be properly selected for 2.5mm thick titanium alloy.