Metrological characterization of stand-off distance measurement by off-axis camera in DED metal additive manufacturing

Laser-Based Direct Energy Deposition (DED-LB) is an additive manufacturing technique suited for repairing worn components or adding new features to existing parts. In DED-LB a high-power laser beam melts a metallic substrate, generating a melt pool. Four nozzles, coaxially symmetrical to the laser beam, eject metallic powder, adding raw material to the melt pool. Online measurements of the stand-off distance, from the nozzles to the melt pool, allow the reconstruction of the part’s geometry as the printing process is running, effectively using the laser as a probing system. We propose a metrological characterization of a stand-off measuring system based on an off-axis camera, looking at the melt pool from a perspective view. In the experimental campaign, we printed single tracks and thin wall parts and compared the local part height estimated from the stand-off with reference 3D scans, evaluating uncertainty. Part geometry monitoring based on stand-off in DED-LB opens the way to closed-loop printing strategies to correct geometrical anomalies.