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2/14/2019

How and Why Injection Molding Shrinkage Occurs

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For injection molded parts, the underlying cause of warpage is deceptively simple: variations in shrinkage. However, these causes become more complex based on the variations of shrinkage rate, location and other factors.

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The underlying cause of warpage is deceptively simple: variations in shrinkage. Simply put, if a part shrinks perfectly uniformly in all directions, it becomes smaller but retains the correct shape. If, however, any element of the part shrinks at a different rate than any other element, the difference creates internal stresses. If these stresses exceed the part’s structural integrity, the part will warp when it is ejected from the mold.

In general, there are four shrinkage variations:

  1. Regional
  2. Through the Thickness
  3. Directional
  4. In-plane vs. Thickness

While it’s clear that varying shrinkage rates can cause warpage, it’s also important to understand why these differences occur in the first place…READ MORE.