Volumetric Shrinkage Result
Volumetric shrinkage result shows the distribution of the percentage change in the part volume as the part is cooled from high temperature and high pressure to ambient temperature and ambient pressure at the end of filling. The calculation of volumetric shrinkage is based on the PVT relationship of the plastic material.
A positive value represents volume shrinkage while a negative value represents volume expansion. A high positive value represents high volume shrinkage, which may cause sink mark or void. Under optimal conditions, uniform volumetric shrinkage is desired. It is important to have more uniformity than a low magnitude of volumetric shrinkage.
The following are the reasons for occurrence of non-uniform volumetric shrinkage:
• Non-uniform pressure distribution
• Non-uniform temperature distribution
Non-uniform volumetric shrinkage can cause the following problems:
• Warpage after the part is ejected.
• Thermally induced residual stress, if the stress could not be transformed into deformation.