Balancing act

Core shift analysis

Core shift is generally defined as the movement of the core from its original position in the mold in response to plastic flow through the cavity during injection molding. Using Computer Aided Engineering (CAE) tools to simulate core shift can help correct this phenomenon.

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Parts molded with long, unsupported cores can experience core shift if the plastic flow around the core is unbalanced. This can lead to wall thickness variations, filling difficulties and fatigue failure in the core.

When the part in this example is  gated in  the center, the short side fills sooner than the long side, causing the core to flex, resulting in an uneven wall thickness. The addition of flow leaders, which are areas of increased wall thickness, can alter the filling pattern to balance the pressure acting on the unsupported core by the advancing flow  front. This can greatly reduce the amount of core shift and unintentional wall thickness variation while maintaining the same filling pressure.

As a leading supplier of polycarbonate resins and blends, Covestro works with customers to optimize part production through use of CAE core shift analysis. This analysis provides valuable guidance for adjustments that can be made to eliminate this issue.

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