Distribution and evolution of thermal stress during multi-laser powder bed fusion of Ti-6Al-4 V alloy

The multi-laser powder bed fusion (MLPBF) has attracted more and more attention due to high productivity and large area. However, thus far the distribution and evolution of the thermal stress with different laser beams are rarely investigated. A block-by-block numerical model considering the laser scanning strategy and part-scale was developed to study the residual stress in MLPBF. As the laser beam number increased from 1 to 4, the residual stress at the top surface of the part decreased but the internal residual stress at the bottom center of the part significantly increased. The average and maximum stresses increased with the laser beam number, indicating that the cracks were more likely to occur with an increase of the laser beam number. The residual stress in the multi-laser overlap area was reduced, resulting in an important influence on the residual stress distribution. More frequent tension-compression stress transitions occurred during MLPBF, and the compressive stress along the deposition direction had a more important influence when the laser beam number increased. The simulated results agreed well with the experimental data. The results of the study provide a significant understanding of the residual stress and are helpful to the process optimization in MLPBF.