Process parameter optimization for selective laser melting Ti-6Al-4V with high layer thickness

Increasing the layer thickness is an important method to increase the forming efficiency of selective laser melting (SLM) but affects the forming quality. In this work, a single track and cube sample with an 80 mu m layer thickness was fabricated by SLM, and then the relative density, hardness, defects, and forming efficiency were studied. It is found that the morphology of the single tracks changes significantly with the change of scanning speed. Fewer defects appear on the top surface and cross section with scanning speed below 850 mm/s. However, the defects increase significantly with further increasing scanning speed. Furthermore, the relative density of the Ti-6Al-4V can reach 99.89 % when the scanning speed is 800 mm/s. The Vickers hardness is highest when the scanning speed is 500 mm/s with the top surface of 402 HV and the side surface of 378 HV. An increase of scanning speed not only causes larger balling particles, but also results in making an appearance of micro-cracks. The increase in layer thickness leads to insufficient energy density, which affects the occurrence of lack of fusion concurrently. Element evaporation occurs at low scanning speeds, which can increase defects in the sample. The appropriate process parameters are the laser power of 300 W, the scanning speed of 800 mm/s, and hatch distance of 0.17 mm. At this time, the forming efficiency is as high as 8.96 mm3/s.