Prediction of the inter-track bonding during the dual-laser powder bed fusion

Multiple laser beams are often used in powder bed fusion to improve productivity by melting more material per unit of time than a single laser. However, improper fusional bonding between the neighboring tracks created by different lasers can affect the integrity of tracks and degrade the mechanical properties of the printed parts. Here, we apply experiments, an analytical model, and data analysis to investigate the influence of process parameters and alloy properties on the inter-track bonding for the dual-laser powder bed fusion process using stainless steel 316 and Ti6Al4V alloys. The inter-track bonding between two neighbor-deposited tracks is characterized and classified as merged or separated. We develop an inter-track bonding index, I_b, as the ratio of the mean value of the two melt pools' widths to the hatch spacing between two lasers. When I_b is greater than 1.2, it suggests that two tracks are merged. Otherwise, the two tracks are separated. This index can predict the inter-track bonding, merged or separated, with 95.5 % accuracy using two hundred independent experimental data. In addition, the Ti6Al4V alloy is more likely to get properly merged tracks compared to stainless steel 316 under the same process condition. Multiple inter-track bonding process maps are generated under various process conditions for two alloys. Both the inter-track bonding index and process maps provide easy-to-calculate and easy-to-apply methods to optimize process conditions and enhance the bonding between two neighbor-deposited tracks and the mechanical properties of the printed parts for dual-laser powder bed fusion.