Pilot investigation of surface-tilt and gas amplification induced contrast during electronic imaging for potential in-situ electron beam melting monitoring

Abstract

Electron Beam Melting (EBM) is a powder bed fusion (metal additive manufacturing) technique employed by many industrial sectors. In-situ EBM monitoring for quality assurance purposes has been a popular research area, and the potential of electronic imaging has been investigated recently. The imaging conditions inside an EBM machine are different from that of a typical scanning electron microscope. These differences are thought to affect image quality, and investigations should be carried out to understand the potential challenges of carrying out electronic imaging inside an EBM machine. This study addresses two of these challenges: (1) surface-tilt image contrast due to large-area imaging, and (2) gas amplification of the feedback electron signal due to the presence of chamber gas. This knowledge gap was tackled by the following approach: (1) estimating both the feedback electron yield and gas amplification of electron signal during electronic imaging; (2) simulating the surface-tilt image contrast during large-area imaging; and (3) presenting an electronic imaging experiment conducted at room temperature to investigate the influence of surface-tilt and gas amplification on image contrast. Experimental results indicate that when conducting electronic imaging in a typical EBM machine, the total feedback electron yield is of the order of 20%; the surface-tilt image contrast is insignificant over the EBM machine processing area; and the influence of gas amplification creates observable, non-uniform signal variation when imaging was conducted over a plain stainless steel plate. This article serves as a pilot study, laying the scientific foundation for subsequent investigations into another challenge under real EBM condition, i.e. the influence of metallisation during melt-pool electronic imaging.