Metal additive manufacturing is a rapidly expanding area owing to its capacity to fabricate parts of intricate geometries with customized features for a wide range of applications. However, these parts generally exhibit inadequate and poor surface quality in the as-built configuration. The surface imperfections and defects ranging from staircase effect due to the layer by layer nature of the deposition techniques, partially fused feedstock material, balling effects, spatters, or inadequate fusion lead to a notably irregular surface morphology. This high surface roughness can significantly deteriorate the performance of the additive manufactured parts imposing a substantial limit on their prospective applications; for instance, fatigue performance, wear and scratch resistance, dimensional accuracy, and aesthetical aspects can be highly affected by these surface defects. A great effort has been lately dedicated to developing post-treatments for improving the surface quality of additively manufactured metallic parts. In this paper, various treatments applied to as-built samples fabricated using different additive manufacturing technologies are introduced and discussed. The advances in this area are highlighted, and the results obtained from different categories of post-treatments are compared and reviewed. Challenges and opportunities to gain more control on the surface roughness of additively manufactured metallic parts through the application of these post-treatments are addressed.

Surface post-treatments for metal additive manufacturing: Progress, challenges, and opportunities

Abstract This study presents an experimental investigation to improve Selective Laser Melting (SLM) regarding aspects such as surface roughness, density, precision and micro machining capability by employing secondary processes such as Selective Laser Erosion (SLE) and laser re-melting. SLM is a layered additive manufacturing technique for the direct fabrication of functional parts by fusing together metal powder particles. Laser re-melting, applied after each layer or only on the top surfaces, is used to improve the roughness and density while SLE, a subtractive process, is combined with SLM to improve the precision and micro machining capability.

Manufacturing by Combining Selective Laser Melting and Selective Laser Erosion / Laser Re-melting (Productie door het combineren van selectief laser smelten en selectief laser eroderen / laser hersmelten)

Metal additive manufacturing: Technology, metallurgy and modelling

Improved fatigue strength of additively manufactured Ti6Al4V by surface post processing

Laser polishing of additive manufactured CoCr alloy components with complex surface geometry

https://pure.hw.ac.uk/ws/files/14101010/1_s2.0_S1875389216301286_main.pdf

Enhancing Surface Finish of Additively Manufactured Titanium and Cobalt Chrome Elements Using Laser Based Finishing

Laser polishing (LP) is an emerging technique with the potential to be used for post-build, or in-situ, precision smoothing of rough, fatigue-initiation prone, surfaces of additive manufactured (AM) components. LP uses a laser to re-melt a thin surface layer and smooths the surface by exploiting surface tension effects in the melt pool. However, rapid re-solidification of the melted surface layer and the associated substrate thermal exposure can significantly modify the subsurface material. This study has used an electron beam melted (EBM) Ti6Al4V component, representing the worst case scenario in terms of roughness for a powder bed process, as an example to investigate these issues and evaluate the capability of the LP technique for improving the surface quality of AM parts. Experiments have shown that the surface roughness can be reduced to below Sa = 0.51 μm, which is comparable to a CNC machined surface, and high stress concentrating defects inherited from the AM process were removed by LP. However, the re-melted layer underwent a change in texture, grain structure, and a martensitic transformation, which was subsequently tempered in-situ by repeated beam rastering and resulted in a small increase in sub-surface hardness. In addition, a high level of near-surface tensile residual stresses was generated by the process, although they could be relaxed to near zero by a standard stress relief heat treatment.

https://www.research.manchester.ac.uk/portal/files/64386713/Final_Manuscript_for_Pure.pdf

Aldara Pan Cabo

Papers

Enhancing Surface Finish of Additively Manufactured Titanium and Cobalt Chrome Elements Using Laser Based Finishing

Material interactions in laser polishing powder bed additive manufactured Ti6Al4V components