In situ powder height measurement as process signature for quality control in electron beam powder bed fusion

Abstract

Quality assurance is one of the most important challenges in powder bed fusion. Binding faults are triggered by locally too thick powder layers and consequently insufficient connection to the layers below. Therefore, the knowledge of the local powder height could be one essential aspect in future quality assurance routes. In this work, multi-detector electron optical imaging based build surface topography measurements of the melted surface and the subsequently applied powder layer are combined to determine the local powder height in situ. The local powder height is measured during the build of a complex part, purely from experimentally measured data. Differences to theoretical continuum-based considerations are rationalized and the role of the process-cycle induced temperature evolution on recorded build surface topographies after melting and powder application revealed. The widths of height histograms, originating from segmented part and powder areas, are identified as key elements to assess the quality of the applied powder layer and the melted surfaces. The developed measurement principle and derived process signatures can serve as basis for future quality assurance routines in series production environments.