The identification of an accurate simulation approach to predict the effect of operational parameters on the particle size distribution (PSD) of powders produced by an industrial close-coupled gas atomiser

• A comparison of models to simulate gas atomisation secondary break-up is presented.
• The validated model combines CFD and a discrete particle model with KHRT break-up.
• The model has been used to predict the effect of parameters on atomised powder PSD.
• Results indicate potential for a predictive model used to optimise powder production.

Powder metallurgy (PM) refers to a range of engineering techniques whereby net shape or near-net shape bodies are produced through the aggregation of a powder substrate. Specifically, the emergence of Additive Layer Manufacturing (ALM) is an exciting development in this field. However, the quality of any product produced by ALM is highly dependent upon the quality of the powder used. Gas atomisation is a specialised processing route in the PM field for the production of fine, spherical powders directly from a molten metal melt. The close-coupled gas atomisation process involves a melt stream being impacted by high velocity, under-expanded gas jets which initiate its break-up in two distinct phases; the second critical in determining the final particle size distribution (PSD) of the powder produced. However, fully understanding the mechanisms at work and exerting a high level of control over any produced powder is a challenge faced by the powder manufacturing industry; highlighted by the stringent requirements of the new ALM manufacturing technique.Utilising Ansys Fluent v14.5 computational fluid dynamics (CFD) software, a 3D axi-symmetric simulation has been developed of a close-coupled atomising gas jet nozzle configuration utilised by a powder manufacturer. Through the two-way coupling of the CFD with a Discrete Particle Model (DPM) using the Euler–Lagrange approach, an assessment has been made of the effect of process parameters on the final PSD of the metal powders produced. The most appropriate model for the simulation of the secondary break-up phase has been identified from the Kelvin–Helmholtz (KH), Kelvin–Helmholtz Rayleigh-Transport (KHRT) and Taylor Analogy Break-up (TAB) models. Subsequently, the validated simulation approach has been used for the qualitative assessment of the effect of altering the atomising nozzle geometry and process conditions on the average size of powders produced i.e. finer or coarser. It was also established that there is potential for the model to be used as a quantitative predictive tool of powder size; useful for quality control especially when manufacturing powder for use in ALM. However, further development and validation is required for confirmation of this function.

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