The Volumetric shrinkage at ejection result shows the volumetric shrinkage for each area expressed as a percent of the original modeled volume.
Volumetric shrinkage at ejection is the decrease in local volume from the end of the cooling stage to when the part has cooled to the ambient reference temperature (the default value is 25°C/77°F).
Note: The packing phase includes both packing time and cooling (holding) time.
Using this result
For unambiguous interpretation of the Volumetric shrinkage at ejection result, deselect the Nodal averaged display option. Right-click the result name and select Properties, select the Optional Settings tab, and then deselect Nodal averaged.
This result can be used to detect sink marks on your model. High shrinkage values could indicate sink marks or voids inside the part.
Volumetric shrinkage should be uniform across the whole part to reduce warpage.
Note: For thermoplastic materials, volumetric shrinkage should be less than the observed maximum value for the material. You can find material shrinkage information in the Thermoplastic material database. Right-click the material in the Study Tasks pane and select Details. The Thermoplastics material dialog is displayed. Select the Shrinkage Properties tab. The observed maximum shrinkage values are in the Observed shrinkage section.
Volumetric shrinkage can be controlled by the use of packing profiles.
Things to look for
When viewing the Volumetric shrinkage at ejection result, watch for the following:
- Localized areas of high shrinkage can result in internal voids or sink marks when the part cools.
- Shrinkage values should be uniform throughout the part. This is important for good packing of the material, ensuring good structural and visual integrity of the part. Use a packing profile to make the shrinkage more uniform.
- Negative volumetric values indicate expansion rather than shrinkage. Avoid negative shrinkage on ribs because this can cause ejection problems.
- Check that values are in the expected range for the material, noting the following:
- Materials that shrink isotropically have a linear shrinkage that is approximately one third of the volumetric shrinkage.
For molded materials, the linear shrinkages in the thickness, flow, and transverse directions depend on the effects of relaxation and orientation.
- For shell-like geometries, the shrinkage in the thickness direction should be higher than the shrinkage in the plane of the part. Shrinkage in the thickness direction is likely to be greater than one third of the volumetric shrinkage, and in-plane shrinkage should be less than one third of the volumetric shrinkage. Many mold features act as constraints on in-plane shrinkage. When fiber-filled material are used, the orientation of the fibers in the plane of the part will limit shrinkage in this direction. Shrinkage in the thickness direction is relatively unconstrained.