Abstract
In this paper, discrete element method simulations were used to study the spreading of an idealised, blade based, powder coating system representative of the spreading of spherical, mono-sized, non-cohesive titanium alloy (Ti6AlV4) particles in additive layer manufacturing applications. A vertical spreader blade was used to accelerate a powder heap across a horizontal surface, with a thin gap between the blade and the surface, resulting in the deposition of a thin powder layer. The results showed that it is inevitable to deposit a powder layer with a lower packing fraction than the initial powder heap due to three mechanisms: shear-induced dilation during the initiation of powder motion by the spreader; dilation and rearrangement due to powder motion through the gap; and the inertia of the particles in the deposited powder layer. It was shown that the process conditions control the contribution of these three mechanisms, and that the velocity profile in the shear layer in front of the gap is critical to the final deposited layer packing fraction. The higher the mean normalised velocity in the shear layer the lower the deposited layer packing fraction. The gap thickness and the spreader blade velocity affect the properties of the deposited layer; with the former increasing its packing fraction and the latter decreasing it. The analysis presented in this study could be adapted to powders of different materials, morphologies and surface properties.
Highlights
According to the American Society for Testing and Materials (ASTM), additive manufacturing (AM) is defined as the process of joining materials to make objects from three-dimensional model data [1], usually in a layer upon layer fashion
The main aim of this paper is to develop, using Discrete element method (DEM) simulations, a better understanding of the dynamics of metal powder spreading in powder bed fusion additive manufacturing
DEM simulations were used to study the mechanics of powder spreading in an idealised, blade based, AM system
Summary
According to the American Society for Testing and Materials (ASTM), additive manufacturing (AM) is defined as the process of joining materials to make objects from three-dimensional model data [1], usually in a layer upon layer fashion. Conventional subtractive manufacturing, on the other hand, removes material from a continuous billet. Often referred to as 3D printing, has been called a new industrial revolution [2] due to its intrinsic digital approach in manufacturing three-dimensional objects. Complex shapes can be created enabling the production of topology optimised components, which reduces the overall weight and material used and facilitates the manufacturing of shape-customised objects. As implied by its name, powder bed fusion additive manufacturing techniques, such as Electron Beam Melting (EBM) and Selective Laser Melting (SLM), use the raw material in the form of powder.
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