The random powder particles in additive manufacturing add complexity to the track formation compared to welding. In this paper, the track irregularity in electron beam selective melting of Ti–6Al–4V has been studied with validated high-fidelity multi-physics modelling for an enhancement in understanding the formation mechanisms. It reveals two main mechanisms in track irregularity, necking and fluctuation. It is the powder coalescence behaviour that leads to track fluctuation, and the mitigation of track fluctuation could be ascribed to the melt pool development process. In a multi-layer building process, the track irregularity could increase the possibility of voids generation and development across multilayer, which makes it crucial to explicitly consider the discrete particles for better prediction of build quality.
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