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Stress

Edit: ABIS Mold Technology Co.,Ltd Date: Aug 17, 2017

The main enemy of any injection molded plastic part is stress. When a plastic resin (which contains long strains of molecules) is melted in preparation for molding, the molecular bonds are temporarily broken due to the heat and shear force of the extruder, allowing the molecules to flow into the mold. Using pressure, the resin is forced into the mold filling in every feature, crack and crevice of the mold. As the molecules are pushed through each feature, they are forced to bend, turn and distort to form the shape of the part. Turning hard or sharp corners exerts more stress on the molecule than taking gentle turns with generous radii. Abrupt transitions from one feature to another are also difficult for the molecules to fill and form to.

As the material cools and the molecular bonds re-link the resin into its rigid form, these stresses are in effect locked into the part. Part stresses can cause warpage, sink marks, cracking, premature failure and other problems.

While some stresses in an injection molded part are to be expected, you should design your parts with as much consideration for stress reduction as possible. Some ways to do this are by adding smooth transitions between features and using rounds and fillets in possible high stress areas.


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