Influence of the particle size distribution on surface quality and mechanical properties in AM steel parts

Purpose - A recent study confirmed that the particle size distribution of a metallic powder material has a major influence on the density of a part produced by selective laser melting (SLM). Although it is possible to get high density values with different powder types, the processing parameters have to be adjusted accordingly, affecting the process productivity. However, the particle size distribution does not only affect the density but also the surface quality and the mechanical properties of the parts. The purpose of this paper is to investigate the effect of three different powder granulations on the resulting part density, surface quality and mechanical properties of the materials produced. Design/methodology/approach - The scan surface quality and mechanical properties of three different particle size distributions and two layer thicknesses of 30 and 45 mu m were compared. The scan velocities for the different powder types have been adjusted in order to guarantee a part density >= 99.5 per cent. Findings - By using an optimised powder material, a low surface roughness can be obtained. A subsequent blasting process can further improve the surface roughness for all powder materials used in this study, although this does not change the ranking of the powders with respect to the resulting surface quality. Furthermore, optimised powder granulations lead generally to improved mechanical properties. Practical implications - The results of this study indicate that the particle size distribution influences the quality of AM metallic parts, produced by SLM. Therefore, it is recommended that any standardisation initiative like ASTM F42 should develop guidelines for powder materials for AM processes. Furthermore, during production, the granulation changes due to spatters. Appropriate quality systems have to be developed. Originality/value - The paper clearly shows that the particle size distribution plays an important role regarding density, surface quality and resulting mechanical properties.