Numerical investigation on keyhole stability and weld pool dynamics during quasi-continuous laser beam welding of Ti6Al4V plate using constant and modulated high-frequency pulsed heat input

For numerical investigation of the quasi-continuous laser beam welding (Q-CLBW) process, the existing research usually considered a constant welding heat input, which to some degree loses accuracy in representing the welding dynamics. This paper developed a validated CFD model for the simulation of Q-CLBW of Ti6Al4V alloy based on a near-reality heat source model. The coupled transient temperature, velocity, and phase fields were solved under a high-frequency pulsed laser power (HF-PLP) at 5000 Hz as well as a constant laser power (CLP) which has been conventionally employed. Comparative analysis was carried out with respect to keyhole stability, melt flow pattern, and weld pool dimensions resulting from different heat sources and different heat input values with laser peak power of 2800 similar to 3800 W and welding velocity of 0.02 similar to 0.04 m/s. Results indicate that the time-dependent laser input yields less stabilized dynamics featured with middle-depth keyhole collapse, chaotic melt flow, and periodic vapor eruption, and such characteristics are difficult to be observed with CLP. The maximum temperature, pressure, and velocity magnitude of molten metal present remarkable oscillations in relation to welding time. With decreasing heat input in HF-PLP welding cases, the keyhole geometry tends to collapse in the tip segment while the melt flow becomes regular. Furthermore, the employment of the HF-PLP condition also enhances the accuracy in predicting the cross-sectional seam profile in terms of width and depth. Pulsed laser input should be taken into full consideration in the numerical simulation of the Q-CLBW process.