The Material Density Function is the result of a calculation in which the contraction of the casting, and resulting flow of liquid feed metal, is taken into account during solidification. Areas that have metal removed due to feeding liquid metal to other areas of the casting will show up as having lower Material Density numbers. In this way, potential shrinkage can be predicted.
The Material Density Function is a number that can vary from 0 to 1. It is a measure of how much of the metal remains at each point in the model. A value of 0 means that the metal has been completely drained from that part of the casting; a value of 1 indicates completely sound metal. The Material Density Function therefore should be interpreted as follows:
Value = 0 0% Metal 100% Porosity
Value = 0.90 90% Metal 10% Porosity
Value = 0.99 99% Metal 1% Porosity
Value = 1.0 100% Metal 0% Porosity
In general, we have found that values in the range of .995-.990 and below are areas of detectable shrinkage porosity in castings.
The Material Density Function is a measure of macroporosity and is MOST useful in ferrous castings. In non-ferrous alloys, especially aluminum, it can be used to predict gross macroporosity, but structural microporosity due to poor or stagnant solidification can best be predicted by other criteria such as Niyama or the FCC Custom Criterion.
Indications show areas of likely shrinkage porosity in the casting.