TRANSIENT MELT POOL FORMATION IN LASER-POWDER BED FUSION PROCESS

Parts are built in a layer-by-layer fashion in the laser powder bed fusion process. Each layer of scan in the parts is defined by a scan strategy that consists of many small patches and scans. The scan length of those multiple scans is not always long enough to have reached a quasi-steady state of the melt pool. The length at which it achieves a steady state is different for different process parameters. The available literature related to the melt pool considers the melt pool has already achieved a steady state, which holds true to a large extent. However, there is always a transient state of melt pool with different characteristics compared to the quasi-steady state. The transient state of the melt pool is particularly significant, for small, features and thin walls. This paper explores the cross-section and width of the melt track in the transient state. Single-tracks are deposited on semi-cylindrical samples with 71-6Al-4V powder particles for three levels of power and speed combinations. The single tracks are built at a certain height from the base plate instead of on the build plate to include the effect of the powder particles. The experiment includes single tracks of four scan lengths i.e. 0.25, 0.5, 1 and 2 mm. Once the parts are built and removed from the build plate, White light interferometer is used to capture the melt track information and data processing is done in Matlab (TM). The results show that the transient length is directly proportional to the laser power and inversely proportional to the scan speed. The highest transient length value is obtained for the highest power of 195 W and lowest scan speed of 50 mm/s.