In-situ laser beam melting investigation with multi-wavelength digital holography

Abstract

Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process to produce small and medium-sized structures. Due to the complex physical phenomena involved in the lasermaterial interaction, instabilities in the melt pool morphology affect the final quality of the structure and remain difficult to predict by simulation. Several monitoring approaches, based on the radiation of the melt process or on a secondary illumination source, have been developed to measure its length, width and height. Nevertheless, the final morphology of the part is influenced by the volumetric forces as well as by the capillary forces applied to the melt. Thus, the shape of the melt surface is of primary interest to control the stability of the melt. Due to its intrinsic heterogeneity, its motion on the powder bed and its own dynamics, the measurement of the melt pool surface shape requires a full-field "one-shot" acquisition with a short exposure time of a few microseconds. In this paper, we propose multi-wavelength digital holography for the in-situ investigation of the melt pool.