  A multiscale numerical model based on nonequilibrium thermal effect for
melting of metal powder bed subjected to constant heat flux is developed. The
volume shrinkage due to density change is taken into account. The
nonequilibrium model is discretized by an implicit finite difference method and
solved numerically using an iterative tri-diagonal matrix algorithm. The
evolutions of powder bed surface temperature and various interfacial locations
as well as the melting temperature range during the melting process are
investigated. The results show that liquid region, upper and lower parts of
mushy zone are formed on the top of unsintered zone as the melting progresses.
The duration of the preheating stage shortens and the melting rate accelerates
as the initial porosity or initial temperature increases while particle size
has much less effect on the melting process. The parametric study shows the
melting temperature range of the powder bed widens with increasing initial
porosity, decreasing initial temperature or increasing particle size.
