Numerical analysis of the effect of the spatial and temporal scanning strategies on the residual stress in the multi-laser powder bed fusion of Ti-6Al-4V

Multi-laser powder bed fusion (PBF-MLB) is an advanced additive manufacturing (AM) technology, which can effectively improve the forming size and efficiency of components by increasing the number of lasers. However, the high residual stress generated by the repeated melting and solidification of the material in the overlap region under the action of multi-laser adversely affects formability during the PBF-MLB process. In this respect, this manuscript presents a stress control method based on the spatial and temporal differences in scanning strategies between dual-laser in PBF-MLB. A three-dimensional finite element model based on the sequentially coupled thermal-structural method was established to forecast the influence of these scanning strategies on the thermal history and residual stress distribution in both overlap and isolated regions. Meanwhile, the effective absorptivity of Ti-6Al-4 V alloy powder was measured using a self-made calorimeter. The laser absorptivity of Ti-6Al-4 V alloy powder was found to be 42.8 % when P=170 W and V=600 mm/s, which was used in the simulation. The simulation results show that with the use of spatial difference scanning strategies (SDSC), the residual stress in the overlap region was greatly reduced by avoiding multiple synchronous remelting of the dual-laser. Meanwhile, after implementing temporal difference scanning strategies (TDSC) and spatial-temporal difference scanning strategies (S-TDSC), a lower temperature gradient was achieved compared to dual-laser synchronous scanning because only a single laser performs the processing. Therefore, the residual stress in the overlap region was significantly alleviated. Furthermore, the residual stress in the overlap region was lower with S-TDSC than with TDSC due to the more continuous thermal cycle created by the laser. In the inward symmetric scanning mode, the residual stress in the overlap region was reduced by 9.8 % through using the SDSC compared to the basic scanning strategy.