Robustness analysis of imaging system for inspection of laser beam melting systems

Laser Beam Melting (LBM) is an additive manufacturing process, which enables the layer-based production of complex parts from metal powder, i.e. “3D printing” with metal. In previous publications, we presented a high-resolution imaging system for inspection of LBM processes, which uses a high-resolution camera to acquire images of each powder layer and laser exposure result. The external camera position necessitates perspective correction, which is based on calibration markers which are “drawn” onto the powder by the LBM system's laser in the first layer. As movements of the powder deposition mechanism cause vibrations, the orientation of the camera may be changed, which would invalidate the calibration results and lead to imprecise measurements or segmentations. To evaluate the effect of these disturbances, we placed calibrations markers in multiple layers and determined the position offset using template matching. We analyze the relative marker drift in three LBM processes and determine the spatial acquisition error. The maximum distance is 4.91 pixels (156.1 μm on the part), while most detected markers deviate by less than 1.5 pixels (46 μm). Compared to the pixel size of 20 μm to 32μm, these deviations are significant and require a repeated calibration in higher layers for valid high-resolution image-based measurements.