PROTOTYPE SILICONE MOULDING PROCESS
By Hannaan Bhatti
Here at LUMA, we are often asked about the best way to prototype rubber components. Whilst this can be achieved with 3D printing, we've found that this is still a very expensive method, recently being quoted over £300 for a single component about the size of a large fruit pastel! This is prohibitively expensive for the vast majority of our clients, so we instead decided to try out injecting silicone into a 3D printed mould - effectively a low-pressure injection moulding process. Utilising the high surface finish of SLA 3D printing and plenty of trial and error, we have been able to create high-quality rubber parts for a fraction of the cost.
How do we create the mould?
1. Desired rubber component is modelled in CAD.
2. The mould tool is created next, using the component model to form the cavity.
3. The tool must be in two halves, taking into account where the 3D printing supports will be and how the rubber part will be removed once it has solidified.
4. A hole for injecting the liquid silicone is added to one half of the mould and air holes are placed on the other, allowing the cavity to completely fill with silicone.
5. Locating pins and holes are added to the mould tool. These ensure that the two halves line up correctly when injecting the silicone.
6. Finally, the CAD is sent to be printed!
Low cost - the liquid silicone is readily available with lots of different properties (heat resistant, high strength etc.).
High-quality - the smooth surface finish of the SLA 3D printed mould gives a great surface finish to your rubber parts.
No specialist tools - just some syringes and a few clamps are required.
Easily repeatable - create multiple parts from a single 3D printed mould.
Bubbles - At first these were quite problematic, but we have reduced this problem significantly and are constantly refining our process to eliminate them completely.
Hardening time - The silicone we use takes 24 hours to fully set and is, therefore, the main bottleneck for producing parts quickly.
Silicone mixture - The high viscosity of the silicone can be quite difficult to work with, especially when filling the syringe.