Effect of laser beam drift at high scanning speed on relative density, thickness and roughness of thin-walled TC11 specimen by selective laser melting

Abstract

Due to the width of the laser melting pool and the sintering effect on the surrounding powder, the experimental size of the selective laser melting (SLM) specimen will be larger than the design size, which will greatly affect the dimensional accuracy and surface quality of thin-walled specimen. In order to obtain dimensionally accurate SLM thin-walled TC11 specimens, an orthogonal test was designed to investigate the effects of laser power, scanning speed and hatch space on the relative density, increase of wall thickness(IWT) and surface roughness of the specimens. Unlike the results of previous studies, of which results was that IWT and roughness decreased with increasing scanning speed, it was found that the IWT and roughness of the specimens decreased and then increased with increasing scanning speed due to the presence of laser beam drift at high scanning speed conditions. The laser beam drift increased with the scanning speed. When the scanning speed was ≤400 mm/s, drift of laser beam was almost 0 mm. At a scanning speed of 5000 mm/s, the laser beam drift was 1.51 mm in the x-direction and 1.28 mm in the y-direction. The drift of the laser beam caused an increase in the cross-sectional area of the specimen, which resulted in the same energy being distributed over a larger area, leading to a reduction in the relative density; at the same time, the drift of the laser beam caused the scan paths of the different layers to not coincide exactly, which increased the roughness of the specimen. At a laser power of 350 W and a scanning speed of 1000 mm/s, the increase in specimen cross-sectional area due to the melt pool width was 1.71 mm², which was greater than that induced by the laser beam drift of 1.70 mm². In this case, the melt pool width was the dominant factor affecting the specimen size. Therefore, in order to reduce the negative effect of laser drift on the density of the specimen, the scanning speed should be ≤1000 mm/s at a laser power of 350 W.