Meaning
Force imbalances across a molding core or insert can cause critical dimensional and structural faults during the mold filling stage. This condition occurs when a lateral pressure differential arises due to uneven melt flow on opposing sides of a core pin. The resulting force can deflect the core, leading to non-uniform wall thickness in the finished part.
To prevent this, tool designers use symmetrical gating to balance the flow. If the core deflects too far, it can damage the mold or cause part rejection due to thin walls.
Core Deflection
Melt front asymmetry generates unequal forces that push against tooling components during high-pressure injection. The lateral pressure differential can bend long, unsupported pins or cores in the cavity. This deflection shifts the cavity geometry and creates thin-wall sections that are prone to premature failure.
It also accelerates wear on the tool.
Flow Balancing
Gate location and runner sizing are the primary methods for ensuring that the plastic melt arrives at opposing sides of a feature at the same time. Reducing the lateral pressure differential requires a synchronized flow front that distributes the pressure symmetrically. Multi-gate systems must be carefully balanced to prevent one gate from dominating.
High melt temperature also helps by lowering the viscosity of the flowing polymer.
Tooling Modification
Reinforcing core pins or adding support pillars can help the tool withstand the flow forces. In some cases, the lateral pressure differential is managed by adjusting the injection speed to lower the peak filling pressure.
