Specific Process Knowledge/Back-end processing/Polymer Injection Molder/MoldTemp
Mold temperature setup
Injection moulding processes can be divided into two different types:
- Constant mould temperature processes
- Variable mould temperature (Variotherm) processes
1. Constant mould temperature processes
In this type of process the mould remains at the same temperature during the entire injection moulding cycle. The temperature should not exceed the glass transition temperature of the polymer being used. Otherwise the polymer will never get cold enough to solidify to a degree where it can be demoulded without being deformed/damaged. How close one can get to the glass transition temperature depends on several factors like e.g. polymer type, cooling time and whether the polymer has a tendency to stick to the shim (especially an issue when replicating high aspect ratio structures). With Topas 5013L-10 (which has a Tg around 135°C) one can often go up to 100°C and for samples that are easy to demold even higher (110-120°C). For polymers with very low Tg (such as e.g. flexible polyurethanes) one often has to run as cold as possible. With the mould heeting switched completely off and mould cooling water fully open, the lowest achievable mould temperature is around 15°C.
| Parameter | Benefits | Drawbacks |
|---|---|---|
| Low mould temperature | Very fast cycle times due to short cooling times | Problems with replication of small features because polymer solidifies prior to complete filling |
| High mould temperature | Reasonably short cycle times, improved replication | Problems with demoulding |
For constant mould temperature processes it is a good idea to manually close the mould cooling water valves e and g (see Chapter 4.11 in the manual).