Injection moulding cooling time calculator

The cooling time is calculated via a heat transfer equation based on the maximum thickness of the part, the thermal diffusivity of the polymer, the injection temperature, the target ejection temperature, and the mould temperature. The general formula takes the form t = (h²/π²α) × ln[4(Ti-Tm)/π(Te-Tm)].

The cooling time typically accounts for 70 to 80 per cent of the total plastic injection moulding cycle time. This phase therefore accounts for the vast majority of the cycle, making it the key area for optimisation in order to reduce unit costs. Reducing the cooling phase by 20 per cent can reduce unit costs by the same proportion.

To reduce cooling time, we can decrease the maximum part thickness, lower the mould temperature without deforming the part, optimise the cooling circuit with channels that conform to the geometry, or choose a polymer with high thermal diffusivity, such as PP rather than PC.

The key parameters are wall thickness with a quadratic effect, polymer thermal conductivity, initial injection temperature, mould temperature, target ejection temperature and cooling circuit efficiency. Thickness remains the dominant factor as time increases with its square.

Wall thickness influences cooling time quadratically: doubling the thickness quadruples cooling time. This stems from the physical laws of heat transfer by conduction. This is why design favours thin and uniform walls over a single concentrated excessive thickness.