Study of the Effect of Selective Laser Melting Process Parameters on Overhang Structures

In order to improve the ability of selective laser melting (SLM) to form unsupported overhang structures of titanium alloys, this paper carried out a study on the dimensional accuracy and surface quality of the overhang structures. In this study, the mechanism of the effect of different factor interactions on the accuracy of the overhang structure was evaluated by analysis of variance. The influence mechanism of SLM process parameters on the surface quality of the fabricated parts was investigated. The experiment results indicate that laser power, scanning speed, and powder thickness have a significant impact on the dimensional accuracy of overhang structures fabricated by SLM. The inability to replenish the powder in the overhang area and the differences in cooling rates of the melt pool at different locations are the main reasons causing the phenomena of the overhang angle of less than 90° and the lower convex of the overhanging undersurface. Increasing the designed overhang thickness (at least 3 mm) can effectively enhance the quality of the overhang upper surface. When the laser energy density was 75-85 J/mm3, the overhang upper surface obtained a better surface quality. The difference in surface roughness between the overhanging side surface and the non-overhanging side surface can be improved by using process parameters with a laser energy density in the range of 90-100 J/mm3. The optimal process parameters for forming unsupported overhang structures were determined in the experiment to be a laser power of 200 W, a scanning speed of 800 mm/s, and a powder thickness of 30 μm.