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What causes cracking in TPU plastic injection molded parts and how to fix it
July 30 , 2021

Cracks are a fatal defect of TPU products, it usually happens to be hairy cracks on the surface of the product. It easily happened in the sharp edges and corners. It is harmful for products usage when the invisible cracks occur in the injection parts,

The main reasons that cause cracks during production are as follows:
1 Difficult to demold
2 Overfilling
3 Mold temperature is too low
4 Defects in product structure

TPU for injection parts

TPU for injection parts

To avoid Cracking caused by poor demolding, the mold must have sufficient demolding inclination, the size and location of the thimble should be appropriate. When ejecting, the demolding resistance of each part of the finished product should be even

Cracking caused by excessive filling, it is because of the excessive injection pressure or excessive material measurement which causes excessive internal stress in the product and causes cracks during demolding. Plus, the amount of deformation of mold parts also increases, which makes it more difficult to demold and promotes cracks. In this case, the injection pressure should be reduced to prevent overfilling.

Cracking caused by excessive internal stress in the sprue, it is because of the easy brittle near the sprue. Due to the internal stress the part of direct sprue easily to brittle.

Causes and solutions of cracks in injection parts



Injection pressure is too high

Reduce injection pressure, injection time and injection speed


Reduce raw material filling

Temperature of melt barrel is too low

Increase the temperature of the melt barrel

Insufficient sufficient demolding inclination

Adjust demolding inclination

Improper ejection method

Repair mold

Caused by metal embedded parts

Adjust or modify the mold

Temperature of mold is too low

Increase temperature of mold

Sprue is too small or improper


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