Revealing particle-scale powder spreading dynamics in powder-bed-based additive manufacturing process by high-speed x-ray imaging

Luis I Escano,Wes Everhart,Niranjan D Parab,Qilin Guo,Lianyi Chen,Tao Sun,Kamel Fezzaa,Lianghua Xiong,Cang Zhao

doi:10.1038/s41598-018-33376-0

Abstract

Powder spreading is a key step in the powder-bed-based additive manufacturing process, which determines the quality of the powder bed and, consequently, affects the quality of the manufactured part. However, powder spreading behavior under additive manufacturing condition is still not clear, largely because of the lack of particle-scale experimental study. Here, we studied particle-scale powder dynamics during the powder spreading process by using in-situ high-speed high-energy x-ray imaging. Evolution of the repose angle, slope surface speed, slope surface roughness, and the dynamics of powder clusters at the powder front were revealed and quantified. Interactions of the individual metal powders, with boundaries (substrate and container wall), were characterized, and coefficients of friction between the powders and boundaries were calculated. The effects of particle size on powder flow dynamics were revealed. The particle-scale powder spreading dynamics, reported here, are important for a thorough understanding of powder spreading behavior in the powder-bed-based additive manufacturing process, and are critical to the development and validation of models that can more accurately predict powder spreading behavior.

Highlights

In the powder-bed-based additive manufacturing process, powders are spread in a thin layer and selectively melted/sintered by a heat source or selectively joined together by a liquid binding agent to form a part[1,2,3]
discrete element method (DEM) results showed that defects in the powder bed can lead to defects in the final manufactured parts[22,23]
With this newly developed experimental approach, we revealed the evolution of the repose angle, the slope surface flow speed, and slope surface roughness during the powder spreading process

Summary

Introduction

In the powder-bed-based additive manufacturing process, powders are spread in a thin layer and selectively melted/sintered by a heat source or selectively joined together by a liquid binding agent to form a part[1,2,3]. The powder flow environment in avalanche testing instruments and rheometers is very different from the conditions in additive manufacturing. Treating the powder as a continuous non-dense material that is subjected to shearing stresses, similar to the ones found during the spreading process, provided an insight into the external forces that affect the powder. With this assumption, the influence of layer thickness, roller geometry, and initial powder properties on the compacted powders’ relative density were studied[13,14]. Individual elements) that interacted with the environment as well, predictions of powder segregation and powder bed surface roughness require study at the particle scale. DEM results showed that defects (voids, surface roughness, thickness non-uniformity) in the powder bed can lead to defects (surface roughness and porosity) in the final manufactured parts[22,23]

Methods

Results

Conclusion