Evaluation of laser polishing as post-processing of Inconel 625 produced by Directed Energy Deposition

As one of the Additive Manufacturing (AM) technologies, Directed Energy Deposition (DED) inherited common concerns from the AM concept, such as the layer discretization process, which brings about the staircase effect, and the complex thermal reheating cycles that occur due to the scanning strategies. In this regard, diversification in slicing strategies and the application of post-processing techniques arises as a feasible way to reduce defects and the usual poor surface finishing of DED parts. This study combines the non-planar slicing strategy as toolpath for laser polishing (LP) in DED parts, evaluating the influence of such post-processing for surface finishing, geometry and hardness of the Inconel 625 truncated pyramid built by DED. This geometry was built by using planar slicing and zigzag scanning strategy in BeAM M250 DED equipment. The non-planar coordinates of the LP were applied at an offset in the external profile of the pyramid with support of an open-source software Slic3R. The workpieces were built with laser power of 500 W delivered at the 800 μm spot diameter with scanning rate at 2000 mm/min and powder flow of 7.5 g/min. Laser polishing was performed considering three levels of energy density (9.38, 11.25 and 14.06 J/mm2) and the number of iterations (once, 3 and 5 times). Both, deposition and LP, were performed with local Argon gas shielding. Among the results, LP has shown to be a feasible post-processing technique to L-DED parts, which can improve surface finishing and shape, maintaining hardness. The energy spent LP causes the remelting of satellite particles and shown to be not enough to rearrange the microstructure. The non-planar slicing applied, as toolpath to the LP, comprises a new possibility allowing DED parts to have better results towards surface finishing with a clean and quick method of post-processing. This has shown to be beneficial to the efficiency of the post-processing stage by leading to a greater assertiveness of the process, less post-processing time and no waste of material.