Specific Process Knowledge/Back-end processing/Polymer Injection Molder/MoldTemp

Mold temperature setup

Injection moulding processes can be divided into two different types:

1. Constant mould temperature processes
2. 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. For reproducible results it is also a good idea to make sure that you always run at the same temperature setpoint for the mould casing cooling water controllers (see Chapter 4.11 in the manual). A setpoint around 70°C for both sides works well in most cases. If the tool casing is allowed to heat up to 90°C or higher it will often result in problems because the internal parts of the mould will get stuck (especially the ejector pin system).

2. Variable mould temperature (Variotherm) processes

In this type of process, the mould changes temperature during the cycle. There are two principal ways to achieve this:

A: Switch off mould heating during the moulding cycle. This case is best suited for situations where a slow and well-controlled cooling is desirable. Since cooling happens quite slowly (heat dissipates out in the tool casing) this method is usually only of practical interest when the mould temperature only has to drop slightly (maybe up to ~10-20°C drop in temperature).

B: Switch off mould heating and enable mould cooling water during the moulding cycle. This is basically the same procedure as above except we also send cooling water through the mould. This allows for rapid cooling of the mold making it suitable for situation where large drops in temperature are desired (> 20°C temperature drop).

A: Variable mould temperature: Switch off heating without insert cooling

To set up the machine for this mode do the following:

• Set up the points in your cycle where you want the mould heaters to switch on and switch off (See Chapter 4.12 in the manual)
• Close valves e and g as described in Chapter 4.11
• Heat up the mould to the setpoint (you have to fulfull the condition set above to switch on the mould heating)

There are many possibilities for defining point where heating should activate (switch on) and deactivate (switch off). Selecting 'Ejector advance' as Activate point and 'Inject' or 'Holding pressure' usually works well. But there are many other options, including delays and defining the activate/deactivate points in the Process sequence.

B: Variable mould temperature: Switch off heating with insert cooling

To set up the machine for this mode do the following:

• Set up the points in your cycle where you want mould heaters to switch on and switch off (See Chapter 4.12 in the manual)
• Set up the points in your cycle where you want insert cooling valves to open and to close. Valves are set up for each half of the mould separately.
• Close the magnetic valves f and h by fulfilling the 'Activate' condition set above (you have to fulfill the condition set above to close the valves)
• Open valves e and g. Since magnetic valves f and h should be closed the propellers should NOT be spinning. The cooling water flow can be adjusted with valves b and c. For fastest possible cooling rate the valves should be fully open. If better control is preferred the flow can be reduced.
• Heat up the mould to the temperature setpoint (you have to fulfill the condition set above to switch on the mould heating)

The machine should now be ready for your process. Please remember that:

• Every time you open the gate at the mould (either the front gate or the back gate) mould heating will switch off and the insert cooling water valves (f + h) will open due to a safety interlock. To switch heating back on and close the cooling water vales, the 'Activate' conditions have to be fulfilled again.
• Avoid circulation of mould cooling water while the mould heating is switched on. The machine will give an error stating that the mould heating is defective. Mould heating should always be switched off before opening mould coolinger water valves.