The influence of material properties and process parameters on the spreading process in additive manufacturing

TL;DR

This study uses simulations to analyze how material properties and process parameters affect powder layer quality in laser powder bed fusion, revealing key influences of particle shape, surface roughness, cohesion, and spreading tool design.

Contribution

It provides new insights into the effects of particle shape, surface roughness, and cohesion on powder spreadability, and compares different spreading tools in additive manufacturing.

Findings

Irregular particles and rough surfaces generally worsen spreadability.

Higher cohesion can either improve or impair layer quality depending on conditions.

Counter-clockwise roller improves powder layer quality over blade spreading.

Abstract

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) technology. To achieve high product quality, the powder is best spread as a uniform, dense layer. The challenge for LPBF manufacturers is to develop a spreading process that can produce a consistent layer quality for the many powders used, which show considerable differences in spreadability. Therefore, we investigate the influence of material properties, process parameters and the type of spreading tool on the layer quality. The discrete particle method is used to simulate the spreading process and to define metrics to evaluate the powder layer characteristics. We found that particle shape and surface roughness in terms of rolling resistance and interparticle sliding friction as well as particle cohesion all have a major (sometimes surprising) influence on the powder layer quality: more irregular shaped particles, rougher particle surfaces and/or higher interfacial cohesion usually, but not always, lead to worse spreadability. Our findings illustrate that there is a trade-off between material properties and process parameters. Increasing the spreading speed decreases layer quality for non- and weakly cohesive powders, but improves it for strongly cohesive ones. Using a counter-clockwise rotating roller as a spreading tool improves the powder layer quality compared to spreading with a blade. Finally, for both geometries, a unique correlation between the quality criteria uniformity and mass fraction is reported and some of the findings are related to size-segregation during spreading.