Productivity optimization of laser powder bed fusion by hot isostatic pressing

Abstract

Laser Powder Bed Fusion is today used for the serial production of parts, e.g. in the medical and aerospace markets. One of the major limitations is the comparatively low build rate of the process, which leads to low productivity and high costs when compared to conventional processes. Current approaches such as the use of multi-laser systems help increasing the build rate but come at higher investment costs. Overall, the low productivity limits the number of business cases for Laser Powder Bed Fusion and hinders the market uptake in more cost-sensitive industries.This paper suggests a combined approach of Laser Powder Bed Fusion and subsequent Hot Isostatic Pressing as a method to improve productivity. Hot Isostatic Pressing is often used as a post-process to eliminate any remnant porosity. It is shown that the process, however, is able to densify specimens that come out of Laser Powder Bed Fusion with an as-build density as low as 95 %. This opens up a larger process window for the initial Laser Powder Bed Fusion step. Experimental investigations are presented using two commercial Laser Powder Bed Fusion systems with the widely used titanium alloy Ti-6Al-4V. Instead of optimizing the process for the highest possible density, the parameters were optimized to yield the highest possible speed while maintaining a density above 95 %. A scan speed increase of 67 % was achieved and the specimens were then successfully compacted to above 99.8 % density in the Hot Isostatic Processing step. The high-speed parameter set was then applied to a demonstrator build job, where it leads to an overall saving of 26 % of build time.This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.