Investigation and characterization of a local remelting process for the improvement of surface properties resulting from extreme high-speed directed energy deposition

Extreme high-speed directed energy deposition (German acronym-EHLA) is a modified variant of the laser based directed energy deposition (DED-LB) and is being applied as an efficient coating process for rotational symmetric components. Recent advancements regarding available machine kinematics enable the utilization of the originally 2D rotational symmetric process for a 3D process so that EHLA technology can be used for additive manufacturing, repair, and free-form coating applications. Compared to conventional DED-LB, an EHLA coating process results in a lower surface roughness; however, a subtractive postprocessing is still required for most industrial applications. To minimize the extent of the surface postprocessing and to improve the resulting surface properties, the principle of a laser based remelting process is investigated and characterized in this work. In contrast to the conventional, scanner type laser polishing, the remelt process is conducted with the same machine which was also used for probe deposition. For this study, additively manufactured probes as well as coatings were deposited by using EHLA technology with 316L stainless steel. After the probe deposition, a remelt parameter study was conducted in which the process feed rate, beam power, beam diameter, and hatching parameter were variated. The resulting surface properties, Sa and Wa, were analyzed and evaluated by white light interferometry and compared to the as-built reference surfaces. As a result, the developed remelt parameters can reduce the Sa values of an additively manufactured EHLA wall by 94% and coating surface by 76%.