Meaning
Dynamic temperature control processes that heat the mould cavity above the polymer’s glass transition temperature before injection and cool it before ejection enable the production of microstructured parts without surface defects. This process, known as variothermal moulding, prevents the melt from freezing prematurely as it fills thin channels or micro-grooves. It ensures that the plastic remains highly flowable to fully replicate the details of the mould insert.
Once the cavity is filled, high-speed cooling runs through the mould plates to solidify the part for ejection.
Heating Cycle
Thermal cycles are achieved by routing hot and cold media through the same mould temperature control channels. During the heating phase of variothermal moulding, pressurized water or steam heats the insert surface to maximize polymer flow. Following the injection phase, cold water flows through the channels to cool the polymer.
This rapid thermal shifting minimizes the total cycle time while maintaining replication quality.
Part Quality
Eliminating surface knit lines and reducing internal stress increases the mechanical and optical performance of the moulded component. Since the polymer melt does not freeze against a cold tool surface, it flows smoothly to join flow fronts without creating weak weld lines. The low thermal gradient during cooling also prevents the development of internal orientation stresses.
This is necessary for optical lenses where stress leads to birefringence.
Energy Cost
High energy consumption arises from the continuous heating and cooling of the massive steel mould plates. To mitigate this expense, moulders use insulated inserts to localize the thermal shifts to the cavity surface. This localized heating reduces energy waste and shortens the heating cycle.
