Abstract: Multi-cavity injection mold is used widely in practice, and filling balance is recognized as the most important problem in multi-cavity molding. Filling imbalance can also occur in a multi-cavity mold with a geometrically balanced runner. It may be due to the shear heat produced in melt flow, but it has not been proven by experimental results. Filling imbalance in a multi-cavity mold with a geometrically balanced runner is investigated by using the visualization glass-inserted injection mold and infrared thermometers, through visualizing the flow behavior of the melt in the runner and cavity and measuring the melt temperature near the cavity entrance simultaneously. The results show that the root cause of filling imbalance occurring in naturally balanced runner systems is due to that the symmetrical but no-uniform temperature distribution of the melt across primary runner section is lost when the flow splits at a branch, and the degree of filling imbalance not only depends on the melt temperature distribution inside the primary runner, but also depends on the frozen layer distribution in the secondary runner and the resin viscosity sensitivity to tempera-ture. It is a radical solution of avoiding filling imbalance in a multi-cavity mold with a geometrically balanced runner to im-prove or eliminate the asymmetry of the melt temperature distribution in flow plane.

Key words: Filling imbalance, Injection mold, Multi-cavity, Visualization