The role of laser operation mode on thermal and mechanical behavior in powder bed fusion: a numerical study

This numerical study investigates the influence of laser operation modes, continuous-wave (CW) and pulsed-wave (PW), on the thermal and mechanical behavior in powder bed fusion-laser beam/metal of Ti-6Al-4V (PBF-LB/M/Ti-6Al-4V). A finite element model was developed to simulate heat transfer and stress evolution, incorporating temperature-dependent material properties. The study compares the melt pool dimensions, temperature gradients, and residual stress development under both CW and PW laser modes. The findings reveal that the PW laser mode induces rapid temperature fluctuations (1300-2100 K) and sharper thermal gradients compared to the stable heat input of the CW laser (similar to 2600 K), leading to oscillations in melt pool size and a fluctuating residual stress pattern along the scanning path. PW mode generated approximately 1100 MPa of longitudinal residual stress, about 50% higher than the 740 MPa which observed in CW mode. Furthermore, the study explores the effect of PW process parameters such as duty cycle, frequency, and pulse width on thermal gradients and residual stress. Increasing the duty cycle from 50 to 100% led to a 25% reduction in peak residual stress, with the behavior approaching to CW-PBF-LB at higher duty cycles. While variations in frequency and pulse width (at a constant duty cycle) influenced the temperature profile, they did not significantly alter the overall residual stress magnitude.