Laser Polishing of Laser Powder Bed Fusion AlSi10Mg Parts—Influence of Initial Surface Roughness on Achievable Surface Quality

Markus Hofele,David K Harrison,Anjali K M De Silva,Harald Riegel,Jochen Schanz,Andre Roth

doi:10.4236/msa.2021.121002

Abstract

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing technique, which allows production of highly complex solid metal parts with good mechanical properties, compared to conventionally manufactured parts. Nevertheless, the layer-by-layer fabrication process also offers several disadvantages, including a relatively high surface roughness depending on the shape of the component, its position and orientation during the fabrication process. This paper deals with investigations on the surface roughness reduction capability, and residual surface structures by laser polishing of LPBF AlSi10Mg parts under varying initial surface roughness in order to investigate the influence of the surface behavior and initial surface roughness to the achievable surface quality by laser polishing. Hereto test specimens with varying fabrication orientations regarding to the built platform are printed and further polished. Thereby the initial arithmetic roughness varies between 19.2 μm and 8.0 μm. It could be shown that the achievable surface roughness by laser polishing with continuous and pulsed laser radiation is increasing with rising initial roughness, but the relative roughness reduction is almost constant in the range of 95% - 97.5%. The analyzation of the residual roughness structures shows, that the main roughness differences is found in the middle and long structure wavelength regime, which are directly depending on the initial surface structures of 3D printing.

Highlights

The powder-bed based selective laser melting (SLM) process is still in an ongoing investigation and development
It could be shown that the achievable surface roughness by laser polishing with continuous and pulsed laser radiation is increasing with rising initial roughness, but the relative roughness reduction is almost constant in the range of 95% - 97.5%
At 45 ̊ degree the arithmetic roughness on the overhanging backside of the sample is with Ra = 19 μm double as high compared to the front side of the part

Summary

Introduction

The powder-bed based selective laser melting (SLM) process is still in an ongoing investigation and development. The production of individual and complex parts with high mechanical properties and a wide range of applicable metals are essential advantages of the SLM-technology [1] [2]. This technology permits the production of parts directly from a CAD model. Because of the layer-by-layer process and the complex geometrical shapes, high surface roughness and contaminated surfaces result [5], which is undesirable for most applications, especially in the medical sector, the food industry or in clean rooms. The surface roughness depends on the energy density which is imposed by the Laser on the surface. By optimizing the linear energy density the surface roughness of vertical planes can be reduced by more than 70% [8]

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Results

Conclusion