Evaluation of Powder Spreading Effects on Powder Bed Quality

Abstract

This thesis explores the effect of powder spreading on the quality of the powder bed in electron beam powder bed fusion (EB-PBF) additive manufacturing for Ti-6Al-4V alloy. The motivation stems from the pivotal role of deposited layer thickness in the integrity of produced parts, productivity, geometric accuracy, and effective defect avoidance. A build in the Freemelt One system with in-situ electron optical imaging (ELO) in backscattered electron (BSE) detectors were conducted to image pre-and post-melting surface conditions. Data analysis involved STSA contrast correction, calculation of gradients through normalized differences, and global least squares integration towards surface reconstruction. Height map results indicate increasing levels of topographical irregularity with the number of layers, thickness gradient asymmetry resulting from recoater kinematics, and a reduction in average layer thickness from about 108 μm to 50 μm in 18 layers due to cumulative heat impact and solidification-induced sinking ending with consistent layer thickness. Thickness profiles of layers confirm spatial and time-dependent variations with implications for melt pool stability and quality of fusions. The results emphasize the imperative of even spreading of the powder for the attainment of the desired parts quality and indicate ELO to be an effective tool for in-process control.