Flow Mark and Shear Stress

Flow marks are a phenomenon in which a pattern of the flow paths of the molten plastic remains on the surface of the molded product. Depending on the extension, these can become defects in the case of molded products in which their external appearance is an important aspect of quality, as in the case of household appliances, containers for cosmetics, etc.

Flow marks are caused because there is a difference in the extent that cooling occurs upon contact with the mold surface at the forward end of the plastic as the molten plastic flows into the mold cavity.

In this project i was examined and validated the flow mark phenomena into digital model. The digital model was using finite element method. You able to capture real defects on plastic part and counter measure it afterwards.

Left: High Shear Stress on Moldflow, Right: Prototype Product

So finite element could help even before prototype have made. Did not have to create any mold before the design of runner systems and plastic injection parameters are correct.

Those model were made on moldflow plastic injection software. With certain aspects the flow mark can be eliminated or vanished perfectly. We used shear stress as a results to capture the flow mark, then we use it again after some parameters were changed.

Enlarge the gate, increase mold temperature and slowing down ram speed during filling might help to cure this flow mark issue.

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