Abstract:
The use of high-powered lasers in laser powder bed fusion (LPBF) presents an opportunity to improve productivity without significantly increasing equipment costs. Instead of using a multi-beam system, a single laser equipped with a larger beam spot size can increase the melting volume, thus allowing the melting of a large area of powder to reduce the scanning time, which in turn increases the build rate. However, random porosity, poor surface quality, high residual stresses, and inconsistent mechanical properties are some of the challenges in LPBF, and this can be made worse by the increased intensity at the processing zone when the laser power is increased without increasing the beam spot size. The purpose of this study was to investigate the manufacturability of Ti-6Al-4V alloy using high laser powers at an enlarged beam spot size and shorter interaction times to improve productivity. This study has demonstrated the feasibility of improving productivity by using high laser power and shorter interaction time to gain a high build rate. It was shown that almost fully dense test coupons could be manufactured at a build rate of 18 mm3/s, exhibiting low top surface roughness and residual stress below the yield strength, while the microstructure exhibited coarser priorbeta grains in the as-built condition. The vertical surface roughness of the parts manufactured using high-power was found to be higher due to the presence of partially melted powder particles attached to the surface. Surface finishing by centrifugal barrel finishing was investigated to improve the surface quality, and it was shown that the surface roughness could be reduced by 90%, with some small cavities remaining on the surface. The application of HIPing improved tensile properties and fatigue strength. However, the presence of localized near-surface and interlayer defects drastically affected the fatigue strength. These defects are believed to be related to powder delivery and contouring deficiencies. The key contributions in this study further enrich the scientific knowledge regarding LPBF process development and improvement of build rate and highlight some of the challenges that may arise, especially for researchers and machine developers wishing to improve the build rates of their machines by using high powers from a single laser source.
