Temperature Control of Injection Molding Moulds

In the injection molding mold, the molten plastic material flows into the mold in a fluid state to fill the cavity, and after the filling is completed, it is cooled and solidified, thereby being fixed into the shape of the molded product.

In this series of processes, the higher the cavity temperature, the better the fluidity in the fluid state, so that stable filling can be achieved at a lower pressure. On the other hand, during cooling and solidification, in order to shorten the molding cycle and improve economic efficiency, it is desirable to keep the cavity temperature as low as possible.

If a conventional mold structure is used, it is extremely difficult to control the surface temperature of such a cavity within a few seconds to tens of seconds.

In general, a compromise temperature range is selected between the above-mentioned contradictory cavity surface temperature controls, and temperature control is performed by water cooling or cartridge heaters.

In addition, regarding the temperature distribution on the surface of the cavity, minimizing the temperature difference distribution as much as possible helps to stabilize the shrinkage state and reduce differences in warpage, deformation, and surface gloss. In the case of crystalline resins, it is also effective to stabilize the size and distribution of crystal grains.

Regarding the temperature control of injection molding molds, heat transfer includes the following three forms.

1. Thermal conduction (the heat transfer that occurs within the material)

2. Convective (heat transfer from liquid to solid)

3. Radiation (heat transfer by electromagnetic radiation)

Heat transfer in actual injection molding molds is complex, making analysis difficult to easily complete. In the heat balance calculation, it is more practical to first confirm its directionality to some extent, and then use the experimental data and empirical rules to take local measures to achieve the quality goal of the molded product, or to use an approximation method to optimize the cycle time.

But no matter what method is used, how to properly manage the heat transfer in the mold of new plastic materials that will appear in the future is a universal and important topic. Whether to retain heat or release heat, it is becoming increasingly important to explore this concept in depth during the mold design phase.