Shrinkage compensation

Shrinkage compensation accounts for the shrinkage allowance that the mold maker includes, when making the mold.

For example:

If a part should be 100mm long and the mold maker expects it to shrink by 2%, (s)he will cut the actual cavity dimensions to be 102mm, and hope that after shrinkage the final part is 100mm long. The amount of shrinkage that actually happens depends on the amount of packing, how early the gate freezes, the temperature and the properties of the material (some materials will shrinkage more than others). So the guess of 2% shrinkage from the mold maker is just a guess based on experience.

If you have a CAD model of the part (100mm long) and you setup a Moldflow analysis, it could be that if you use a high packing pressure, the Moldflow analysis predicts a final part length of 98.3mm (deflection value of 1.7mm). Assume you know the mold maker applies a shrinkage factor of 2%. If you want to see how this impacts the part dimensions and compare this to the original design, use the Shrinkage Compensation feature in our deflection results.

• Specify an Isotropic Shrinkage Compensation of 2%, to scale the predicted length up by 2% (98.3 * 1.02 = 100.27mm). Now when you display the deflection results, you see a deflection value of 0.27mm (100.27mm - 100mm). Compared with the original part design, the part is within 0.27mm of the target dimension, which may be within tolerance.
• Use the Anisotropic shrinkage compensation if the mold maker scales up the part dimensions by different % values for different directions.
• If you don't know the shrinkage compensation factor, or you want to suggest what compensation factor should be used, use the Automatic Shrinkage compensation. Synergy looks at the deflection prediction from the warp analysis and suggests the scaling factors (shrinkage compensation) that give a part which matches the original design dimensions as closely as possible. Of course, shrinkage might be different in different regions of the part (e.g. near gate vs far from the gate), so it might be impossible to make the deflections zero everywhere, but the automatic option picks the uniform shrinkage compensation factor that reduces the deflection values as much as possible. Since the Automatic Shrinkage compensation relies on the warp result to decide what compensation factor to apply, it depends on all the inputs that influence the warp prediction (processing conditions, material data, shrinkage data (if available), solver type (3D or DD or Midplane, etc)).