The intelligent recoater: A new solution for in-situ monitoring of geometric and surface defects in powder bed fusion

Abstract

• Powder bed homogeneity, contaminations, and printed surface quality are crucial in powder bedbased AM processes to obtain a defect-free part. • Standard process monitoring equipment does not provide a sufficiently high resolution for detecting small-scale defects. • The optical scanner mounted on the recoater can provide high-resolution images (1200 dpi) of the last printed slice and the powder bed for the whole build platform, without affecting process time. • In-situ surface topography deviations and powder bed contaminations can be observed and studied with this new monitoring setup. Powder bed homogeneity, contaminations, and printed surface quality are crucial in powder bed-based AM processes to obtain a defect-free part, but the scale at which these defects are seen is not compatible with the resolution of current industrial image-based monitoring solutions. In this work, we explore the implementation of an optical scanner in an industrial laser powder bed fusion (L-PBF) machine to detect powder bed and part-related defects. The sensor is mounted ”parasitically” on the recoater and exploits its movement to scan across the build platform before and after powder deposition to obtain high-resolution images. The acquisition seamlessly integrates with the process, without delaying the production as the acquisition occurs in parallel with the new layer deposition. The system was used to monitor test builds as well as longer builds (1000+ layers) to prove its robustness to the challenging L-PBF chamber environment. The in-situ powder bed images of the new monitoring system were compared to the acquisitions of a standard external camera setup. The improved image quality and resolution of the new system were demonstrated on both large-scale ( > 1 mm) and small-scale features. The new system proved to be capable of capturing printed surface topography anomalies and powder bed contaminations ( < 100 µm), opening a whole new range of possibilities for detecting small-scale defects via in-situ monitoring.