Abstract
Additive Manufacturing (AM) using powder spreading requires uniform spreading. For narrow spreader gaps, as commonly used, transient jamming and segregation could adversely affect the uniformity of the spread layer. Here, we consider the dynamics of powder spreading by roller for a gas-atomised metal powder and analyse the effects of gap height and the rotational speed of roller on the evolving particle trajectory and spread layer uniformity by Discrete Element Method. It is shown that transient jamming in narrow gaps and size segregation in the spreading heap, the latter brought about by particle convection/circulation, adversely affect the uniformity of the spread layer. The segregation extent decreases with the increase of gap height or decrease of roller rotational speed. The conditions for uniform spreading are deduced from the simulations.
Highlights
Additive Manufacturing (AM) creates three-dimensional (3D) objects by stepwise layer-by-layer building approaches which are controlled by a digital model [1,2,3]
The extensive segregation in the spread layer at the gap height of δ/D = 1.5 is related to the occurrence of transient particle jamming in the narrow and confined region between the rough roller and base
The particle spreading process with a roller spreader has been analysed by DEM simulations, using realistic physical and mechanical properties of particles as measured for single particles in the previous work
Summary
Additive Manufacturing (AM) creates three-dimensional (3D) objects by stepwise layer-by-layer building approaches which are controlled by a digital model [1,2,3]. Herbold et al [25], Mindt et al [26], Zhang et al [27], Lee et al [28], Fouda and Bayly [29], and Desai and Higgs [31] identified the factors affecting the layer quality, such as the spreader velocity and layer thickness, where the particles in DEM simulations were considered to be of spherical shape without cohesion This approach is not representative of real powders used in AM. The effects of gap height and roller rotational speed on the particle flow and quality of spread layer are analysed This provides a step forward in our understanding of the particle convection/circulation in the heap and the consequent size segregation in the spread layer, which is a key factor affecting the production quality
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