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

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Polymer injection molding

The Polymer Injection Molding machine is no longer available as an open access tool at DTU Nanolab. The machine has been moved to DTU Construct.

Description of machine

Injection molding machine in the basement under the cleanroom

The injection molder at DTU Nanolab was an Engel Victory Tech 80/45 which is a hydraulic machine with single motor. The machine was also equipped with a robot which could pick up finished samples and place them on a conveyor belt. See the table below for key capabilities of this machine. The user manual, user APV, technical information and contact information can be found in LabManager:

Equipment performance

The polymer injection molding machine previously installed at DTU Nanolab was a hydraulic system with the following capabilities:

Parameter		Value
General	Tools	Flat disc, Disc with Luer connectors, Microscope slide
	Clamping force	Up to 450 kN
Processing temperatures	Mold temperature	~15°C to 140°C
	Heating cylinder	Absolute max: 350°C
Molding parameters	Injection speed	Up to 53 cm3/s
	Injection pressure	Up to 2200 bar
	Process types	Constant or variable mold temperature

Polymers

At DTU Nanolab the following polymers were used routinely:

• Topas 5013L-10
  
• Topas 8007S-04
  
• PP
  
• PMMA
  

Process parameters and optimization

There are no standard injection molding processes because it varies significantly how users prefer to optimize their process and how they prioritize parameters such as polymer type, replication fidelity, dimensional accuracy, optical properties, residual stress and cycle time. However, browsing through the Process Log it's usually not a problem to find a program made for the polymer and tool at hand which can be used as a starting point.

The injection moulding cycle consists of the steps outlined below. Click on each step to get a description of the most important process parameters for each step:

1. Mold heating setup
   
2. Closing mold
   
3. Injection
   
4. Switch-over type
   
5. After (holding) pressure
   
6. Cooling
   
7. Dosing (plastizising)
   
8. Demolding
   
9. Ejection
   
10. Robot sample pickup
    
11. Nozzle settings
12. Process overview

Injection

Injection parameters are very important in injection molding optimization. The injection speed will of course determine how long time it takes to fill the cavity. It also has a large influence on the rheology of the polymer melt. Generally, viscosity of polymer melt will decrease with increasing injection speed (an effect known as shear thinning). The injection speed also influences how structures are filled, and to what extent the air inside the cavity has time to escape as polymer is injected. It therefore often takes some optimization to achieve all desired sample properties. Injection speed settings are adjusted in the 'Inject' screen:

• The injection velocity can be adjusted in several ways. One can tap the '=' sign to enter a constant velocity or alternatively use the up/down arrows to move the curve up and down. For more complicated injection speed profiles it is also possible to tap the curve to enter the graphical curve editor where the number and position of individual data points can be edited. This makes it possible to make custom injection speed profiles.
• The 'Specific injection pressure limit' is an upper safety limit that can be set to protect the mold and/or shim (e.g. if using shims that are soft and thus prone to deformation). Note that this setting does not in any way set the injection pressure. It is only an upper safety limit that will not be exceeded.
• The 'Minimum injection time' is usually set around 0-0,05 sec and 'Max. injection time' around 5-8 times the actual injection time. The actual injection time can be seen in the blueish/gray filed just over the max injection time setpoint (in this case it says 0.00 sec because no sample has been produced yet). Actual injection times are usually around 0,2 to 2 seconds so the 'Max. injection time' can typically be set to 1,0 - 15 seconds.