In addition to 3D printing, one of the primary methods of creating parts in small quantities is by silicone moulding and casting.
This is what a silicone mould looks like-
RTV Silicone is a liquid pourable 2 part silicone which becomes solid when a hardener is added to the silicone base. Once the two parts are mixed, they are poured over the master parts that need to be replicated.
After a few hours, the silicone hardens into a rubbery solid which can be cut and stretched to remove the master. It always comes back to it’s original shape.
Silicone needs to be ‘degassed’ which means removing any air bubbles stuck in the liquid silicone during mixing and pouring. The bubbles often result in parts that have an uneven surface.
Silicone is degassed using a vacuum chamber like ours where we attach a vacuum pump to a chamber and remove all the air bubbles from the liquid mould.
The next step is pouring the material that you would like to create the part out of. We typically use Polyurethane, Polyester, and Epoxy resins but a large number of materials can be used in this process (including wax and foam).
These resins usually come in two parts that need to be mixed together and then poured into the mould.
After pouring, in order to remove the bubbles in the resin, the resin and mould can either be degassed again, or it can be put into a pressure chamber, like the one we have, in which the air is highly pressurised. We use the same chamber with an air compressor instead of the vacuum pump in order to create a pressure pot. Without the pressure pot, the part would have bubbles throughout the surface of the part.
The pressurised air causes the bubbles in the resin to become extremely tiny (almost negligible) and once the resin cures and becomes a solid plastic, the bubbles are almost non-existent.
Depending on the quality of silicone and resin, a mould can produce between 20-100 casts. However, for this method to work, a master (original) is still required. This can either be 3D printed, or created manually out of wood or clay.
The advantage of this method over 3D printing multiple pieces is the repeatability is extremely high (the degree to which the dimensions are exactly the same as the original piece). The cost of each piece is also lower than a 3D printed piece because pouring resins are generally less expensive than filaments or resins made for 3D printers.
For large parts, the process of casting is also faster than 3D printing (where prints can take close to 1-2 days to print).
However, the plastic used in casting has different properties compared to 3D printed parts.
In order to place an order or know more about this process, email us at [email protected]
Moulding and Casting
