Selective Laser Melting technology (SLM) is a thermal process, and control of thermal effects is of great importance since enhanced productivity of modern SLM equipment can be achieved by increased laser power. To provide acceptable physical resolution of image recording, the TEM00 lasers are applied, for example fiber lasers which power reaches today several kW. However, the Gaussian intensity distribution of single-mode powerful lasers brings some problems in SLM: inhomogeneous intensity in focused spot results in non-uniform temperature profile and subsequent irregularities of melting process, unwished evaporation or sparking; another issue relates to optics – dynamic gradient heating of optical components and subsequent induce of waist shift and wave aberrations resulting in variation of size and intensity distribution of focused spot in working plane. The thermally induced effects are especially important for protective windows which are inevitably contaminated by fine powder inducing higher heating. Solution suggested to provide uniform temperature in working spot is beam shaping optics made from high purity fused silica and creating optimum for uniform melting flat-top or doughnut profiles. To stabilize the size and intensity of working spot it is suggested to apply athermalized protective windows from optical material self-compensating geometrical and refractive thermal effects. Detailed measurements of beam properties and measurements of real manufactured parts confirmed correctness of suggested approach, its possibility to stabilize drastically the SLM process. The paper presents description of optics applied; measurements of process parameters and analysis of properties of manufactured parts are presented as well.
Alexander Laskin, Dietrich Faidel, and Vadim Laskin, "Optics to control thermal effects in selective laser melting," Proc. SPIE 10523, Laser 3D Manufacturing V, 1052319 (Presented at SPIE LASE: February 01, 2018; Published: 26 February 2018); https://doi.org/10.1117/12.2289683.
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