Laser scan strategy for microtube building in PBF-LB/M (Heat input control based on actual laser scan speed)

Laser-based powder bed fusion of metals (PBF-LB/M) is one of the additive manufacturing (AM) techniques that enable the building of complex structures with high-precision. In particular, injection molds and die casting dies are products to which the advantages of PBF-LB/M are applied, such as improving the cooling performance by installing flexible cooling channels and suppressing the insufficient resin filling and the gas burning by incorporating the permeability through the porous structures. In this study, a new laser scan strategy is proposed to further improve the functionality of injection molds by building the microtubes concentrically. The timing of laser irradiation and the operation of galvanometer scanner were investigated, and the influence of microtube size on the actual laser scan speed and heat input was evaluated. In addition, the effect of correcting the amount of heat input on the accuracy of microtubes was also investigated. As results, the actual laser scan speed decreased as the number of control points on the scan path increased, and the decrease of actual laser scan speed caused the blockage of microtubes due to the increase of heat input. Furthermore, the heat input increased as the microtubes became smaller due to the acceleration and deceleration of the laser scan. Correcting the laser power according to the actual laser scan speed made it possible to form smaller microtubes. With a spot diameter of 0.2 mm and heat input corrected to 0.457 J/mm, the square microtube exhibited reduced blockage below 0.3 mm and formed 0.1 mm.