Vision-based control for track geometry optimization of complex AM motion profiles by on-line laser power modulation

Abstract

In the metal additive manufacturing technique known as Direct Metal Deposition, parts are manufactured by blowing metal powder particles into a laser beam moved according to a predefined path. The trajectories the laser source follows usually include several changes of direction, in which local increase of energy density occurs due to both high curvature and deceleration/acceleration ramps the machine axis motion has to perform. This increase results in the typical presence of local over-deposition.Deposition tracks with uniform profiles are relevant especially when parts are composed by a significant number of layers and/or when short zig-zag tracks are preferred to longer linear tracks to avoid risks for thermal and mechanical distortion in large parts. The real-time measurement of an appropriate indicator for anomalous growth phenomena allow to dynamically correct for higher weld seam and finally part quality.This work presents a closed-loop control system able to adjust on-line the power of the laser beam according to the feedback provided by the analysis of meltpool images. The images are acquired by means of a camera mounted coaxially into the optical chain of the deposition head, which records images at 100 fps while the deposition is running. The benefits of the proposed approach are demonstrated experimentally by comparing the resulting over-deposition on sample test geometries with respect to the over-deposition obtained on a reference commercial open-loop laser deposition system.