Quantitative analysis of thin metal powder layers via transmission X-ray imaging and discrete element simulation: Roller-based spreading approaches

TL;DR

This study combines transmission X-ray imaging and discrete element simulations to analyze roller-based powder spreading in additive manufacturing, revealing how roller speed and rotation direction influence layer density and uniformity for different powders.

Contribution

It introduces a novel experimental setup with X-ray mapping and DEM simulations to understand and optimize roller-based powder spreading in additive manufacturing.

Findings

High roller speeds hinder dense, uniform layers in high-flowability powders.

Counter-rotation improves uniformity by reducing particle clustering.

Adjusting roller motion can mitigate cohesion effects in powder layers.

Abstract

A variety of tools can be used for spreading metal, ceramic, and polymer feedstocks in powder bed additive manufacturing methods. Rollers are often employed when spreading powders with limited flowability, as arises in powders comprising fine particle sizes or high surface energy materials. Here, we study roller-based powder spreading for powder bed AM using the unique combination of a purpose-built powder spreading testbed with a proven method for X-ray mapping of powder layer depth. We focus on the density and uniformity of nominally 100 micrometer thick layers of roller-spread Ti-6Al-4V and Al-10Si-Mg powders. Our results indicate that when rotation is too rapid, roller-applied shear force impedes the creation of dense and uniform layers from powders of high innate flowability, or where inertial forces driven by particle density dominate cohesive forces. Roller counter-rotation augments the uniformity of cohesive powder layers, primarily though reducing the influence of particle clusters in the flowing powder, which are otherwise shown to cause deep, trench-like streaks. Companion discrete element method (DEM) simulations further contextualize the experiments through isolation of the effects of cohesion on layer attributes. Results suggest that roller motion parameters could apply a strategic level of additional shear force to the flowing powder, thereby mitigating the clumping behavior characteristic of highly cohesive feedstocks while maintaining high layer uniformity.