Particle scale modelling of melt pool dynamics and pore formation in selective laser melting additive manufacturing

Selective laser melting is an advanced additive manufacturing technology to use laser beams to melt metal powder and fabricate parts layer by layer. To understand the involved multi-physics, a validated mathematical model is employed in this work to assess effect of material properties such as powder melting and solidification coefficients and mushy zone constant. The results show that large pores are produced by the gas bubble coalesce and elongated narrow pores are generated from the gas bubble compression by the melt pool flow at the low melting coefficient. Two freeze modes, the pasty freeze mode and full freeze mode, can be observed, depending on the magnitude of the solidification coefficient. The results indicate that a large solidification rate is preferred to avoid the pore defect and surface cavity. A low mushy zone constant provides a high velocity of molten liquid resulting in large pores and severe surface concave cavities.