A new processing concept as a visionary approach towards net-shaped DED-LB/M coatings

Abstract

Powder-based laser metal deposition (DED-LB/M) is often used to create coatings for rotationally symmetrical components. By creating a melting zone on a substrate with a laser beam and adding metal powder through a powder nozzle, a metallurgical bond results, and thus a robust coating is created. One of the parameters influencing the surface quality is the track overlap. When aiming for an optimized surface without post-processing expense, a high track overlap (around 50-60%) is needed to achieve less waviness for the coating. This leads to an extended processing time during the production of the coatings. In order to reduce the processing time, a low track overlap (around 10-20%) is needed, again leading to high waviness and an expanded post-processing time. In this paper, a new approach towards net-shaped DED-LB/M coatings is presented, leading to a significant reduction in the post-processing extent for various applications. The combination of supporting tracks, generated with a minimal spot size of 0.9 mm, and filling track, generated with a maximum spot size of 2.8 mm using stainless-steel (316L), is analyzed. In a first step, a parameter development for defect-free supporting tracks and filling tracks is performed by variating the laser power and powder mass flow. Using these parameters, the realization of a layer with reduced waviness is analyzed. Hereby, the track offset of both track types is set to 100%, leading to 0% overlap. Results show that the filling track parameter must be adapted to the height of the supporting tracks. A second parameter variation (laser power and powder mass flow) for the filling tracks is performed leading to a coating with reduced waviness. The manufactured layers with supporting tracks are showing a minimized waviness compared to standard layers that are generated without supporting tracks.