What causes cracking in plastic injection molded parts? -1

What causes cracking in plastic injection molded parts?

Cracking is a commonly seen defect in plastic injection molded products, of which the main causes are stress and deformation, mainly including residual stress, external stress and product deformation caused by external environment.

(I) Cracking caused by residue stress

The residual stress is mainly generated in the following three scenarios, i.e., overfilling, product ejection and metal inserts. The cracking generated in the case of overfilling can be solved from the following aspects:

(1) Since the direct gate is able to minimize pressure loss, if cracking is mainly generated around the direct gate, you can opt for the multi-point gate, the side gate or the tab gate.

(2) On condition that the resin material does not decompose or deteriorate, appropriately increasing the resin temperature is able to reduce melt viscosity and improve fluidity, while reducing the injection pressure, so as to lower the stress.

(3) Usually, stress easily occurs when mold temperature is low, so the temperature should be appropriately increased. However, when the injection speed is high enough, stress can also be reduced even though the mold temperature is relatively low.

(4) Stress will also occur when the injection and pressure holding time is too long. It would be better to reduce the time or perform pressure switch appropriately.

(To be continued...)