Partial Melting and Resolidification of Metal Powder in Selective Laser Sintering

Abstract

Partial melting and resolidification of single-component metal powders bed with a Gaussian laser beam is investigated numerically. Because laser processing of metal powder is a very rapid process, the temperature of the liquid layer and solid core of a partially molten particle may not at thermal equilibrium, that is, the temperature of the liquid part is higher while the temperature of the solid core is lower than the melting point. To use an equilibrium model to describe melting of single-component metal powder, the local temperature of regions with partially molten particles can be assumed to be within a range of temperature adjacent to the melting point, instead of at the melting point. In addition, the whole powder bed shrinks as the gas is driven out during the melting process. A temperature transforming model is employed to simulate the melting and resolidification process over a temperature range with the consideration of shrinkage. The convection driven by capillary and gravity forces in the melting liquid pool is formulated by using Darcy's law. Effects of laser beam intensity and scanning velocity on the shape and size of the heat affected zone and molten pool are analyzed.