Process monitoring and inspection in metal additive manufacturing: powder bed inspection with angle selective illumination

The homogeneity of the metal powder bed within the selective laser melting process is essential to realize the promising possibilities of metal additive manufacturing and to create dense and stable parts. We will show, how angle selective illumination can be integrated in 3D-Printers to detect anomalies and defects in the powder bed. Amongst others, the most important issues are: missing powder, elevated melted structures, recoater defects, particle drag. For the detection of defects, a locally correlative height map of the powder bed is used. The generation of this height map has its origins in computational phase imaging microscopy.