Powders by design for additive manufacture through multi-scale simulations

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The selective laser melting process is a promising large-scale additive manufacturing (or 3D printing) technique that allows for rapid production of prototypes, and lately for weight-sensitive/multi-functional parts at small volumes, with almost arbitrary complexity. The process builds the final parts layer-upon-layer by going through three main stages during each cycle: (1) deposition of a layer of fine powder (with a typical grain size of approximately 0.03 mm) on a fabrication surface to form a thin bed of powder, which is only marginally thicker than the average grain size; (2) a laser beam then melts the powder bed at specific locations, based on a 3D computer model of the final product; (3) the powder grains then fuse at those locations after cooling and solidifying to produce a layer of the final product.In general, the selective laser melting process and additive manufacturing provide several advantages compared to conventional manufacturing techniques, such as greater design freedom, mass customisation and personalisation of products, production of complex geometries to improve performance and reduce labour costs, decreased wastage of precious materials, and new business models and supply chains. However, several challenges also exist. For example, a lack of understanding of the impact of powder grain shape on the underlying physical processes has forced the industry to require the majority of individual powder grains to be spherical. Such a stringent requirement increases the cost of powder (raw material), which consequently increases the production cost and hinders the development of new processes and the introduction of new materials. To address this issue, high-quality research software for process simulation is required to complement experiments and to enable new scientific discoveries and innovations. The present research programme addresses this technological need by providing a novel computational package capable of modelling various complex physical phenomena underlying the selective laser melting process. To achieve this, high-performance computing will be used to track the motion of individual grains in the system, their interaction with a laser beam, and their phase changes. This computational package will then be used to uncover the complex impact of powder grain shapes on the absorption and scattering of a laser beam within the bed and the following rapid melting process. Furthermore, it is hypothesised that elongated or satellite-spherical particles with small inclusions on their surfaces (grain shapes which are commonly present in powders and are generally considered undesirable) can, in fact, improve the process if their number densities are carefully selected. This hypothesis will be tested here for the first time, which can greatly reduce the cost of raw materials for selective laser melting, which results in wider adoption of this enabling technology.