Formation mechanism of pore defects and surface ripples under different process parameters via laser powder bed fusion by numerical simulation and experimental verification

The formation mechanism of pore defects and surface ripples takes a crucial position in quality control during the laser powder bed fusion process. This paper explores the evolution of the melt pool in the LPBF process and elucidates the impact of flow state and temperature field distribution on the melt pool with different process parameters. Through computational fluid dynamics methodology, the study clarifies the formation mechanism of pore defects and surface ripples. The discrete element method was applied to simulate the powder bed using a set of processing parameters. The free surface of the melt pool was then calculated employing the volume of fluid method. It was found that surface ripples on the melt pool and irregular pore defects in the lap joints appeared due to the lack of fusion at a laser energy density of 32 J/mm³ under the pre-set conditions. As the laser scanning speed dropped to 600 mm/s, keyholes were generated inside the melt pool due to the recoil pressure. Similar phenomena of pore defects and surface ripples were observed in the experiments. The measured and simulated average widths of the molten track showed good agreement, with relative errors of less than 6%, confirming the accuracy of the simulated formation. Our work sheds new light on the quality control of LPBF fabricated parts for the future.