Abstract: The use of Additive Manufacturing (AM) is increasing at a fast rate in wide ranging industries, aerospace, medical technology, transport and energy. One of the manufacturing methods used in this field is based on powder processing, but its major bottleneck is associated with the quality of particle spread layer in the powder spreading process, as its underlying particle dynamics remains unknown, which is sensitive to the type of spreader and the cohesive interaction between particles. Here, the particle dynamics in the powder spreading process for a gas-atomised metal powder was explored by discrete element method (DEM), using the most realistic physical and mechanical properties of the particles. The velocity and trajectories of particle within the heap, and the quality of the particle spread layer, were compared in the blade and roller spreading processes. Their sensitivity to the cohesive interaction between particles were also explored. The results showed that compared to blade spreading, there were several velocity bands in cascading style and particle convection within the heap in the roller spreading process, due to the rotational motion of the roller spreader. Before the formation of particle spread layer in roller spreading, the particles needed to climb upward and slip downward along the edges of heap, resulting in longer trajectories of particles. With the increase of particle surface energy, the total particle volume of spread layer was reduced in both blade and roller spreading. Compared to blade spreading, the total particle volume of spread layer in the roller spreading was smaller and more sensitive to particle surface energy. This could be attributed to the formation mechanisms of particle spread layer, i.e. the ability of particles within the heap entering into the gap region between the rough base and spreader, and the drag effect of particles by the spreader in the gap region.

Key words: additive manufacturing, DEM, powder spreading, numerical simulation, metal powder, flowability

摘要： 增材制造技术在航空航天、医疗技术及运输和能源中的应用得到快速增长，其常用方式之一是基于粉末加工。该技术主要瓶颈之一往往与铺粉过程形成的粉层质量有关，颗粒动力学机制尚不清楚，且受铺粉装置的类型和颗粒的黏附性影响很大。本工作基于实验测量和表征的单个颗粒的真实物理和力学参数，采用离散元方法对增材制造常用气雾化金属粉末的铺粉过程进行了数值模拟分析，比较了刮刀和辊子两种铺粉装置中粉堆内颗粒速度和轨迹及最终铺粉层的质量，并分析了这些参数对颗粒黏附表面能的敏感程度。结果表明，相比于刮刀铺粉，在辊子铺粉过程中，由于辊子旋转运动的作用，粉堆内部存在多条拱形速度带和颗粒对流，且在形成铺粉层之前，颗粒需要经历爬坡上升和下坡滑落两个过程，运动轨迹更长。另外，两种铺粉装置中铺粉层颗粒总体积均随颗粒表面能的增加而降低，但与刮刀铺粉相比，辊子铺粉中铺粉层颗粒总体积小，且对颗粒表面能更加敏感。铺粉装置类型和颗粒黏附性对铺粉层质量的影响可以归因为铺粉层的形成机制，即颗粒从粉堆中进入铺粉间隙的难易程度及铺粉间隙中刮刀或辊子对颗粒的拖曳作用。

关键词: 增材制造, 离散元, 铺粉, 数值模拟, 金属粉末, 流动性