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

Abstract

The formation mechanism of the pore defects and the surface ripples takes an crucial position in the quality control of laser powder bed fusion process. This paper developed the melt pool evolution in LPBF process, and revealed the effects of flow state and temperature field distribution of the melt pool with various process parameters, from which the formation mechanism of pore defects and surface ripples had been clarified by computational fluid dynamics methodology. The discrete element method was applied to reproduce the powder bed with a set of processing parameters. Then free surface of the melt pool was calculated employing the volume of fluid method. It was found that surface ripples of 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 generated inside the melt pool due to the recoil pressure. Similar phenomenon 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 the relative errors of less than 6%, which verified the accuracy of simulated formation. Our work shed new light on quality control of LPBF fabricated parts for future.

Physical Mechanism of Selective Healing of Nanopores in Condensed Matter under the Influence of Laser Irradiation and Plasma

“…The surface layer of a solid material always has a higher density of defects [ 24 , 25 ]. In the case of amorphous metals/alloys, the surface layer has high density pores (the density of an amorphous metal alloy is always lower due to the excess and structurally determined free volume) [ 26 ].…”