Last year I created some 3D models using Rhino. These were then 3D printed in wax and then cast in silver. After getting them back this year I used them to create some rubber moulds in order to produce multiples of the same piece. The rubber mould, if made correctly, will produce wax replicas of the original metal master. When the rubber mould has been created successfully, I can use the wax injector to fill the rubber cavity with molten wax. After a few minutes the wax will solidify inside taking the shape of the original piece, that is, if enough wax was injected, to gauge the pressure right it can take a few goes. When the wax replica comes out correctly I can then sprue it up and cast multiples in one go.
- The first step is to solder a brass sprue to an area on your cast piece, preferably a flat area so no detail of the original is obscured or damaged. If the piece is made of plastic or other material then it can be super-glued to the brass sprue (although, sometimes can drift from the piece). Add a brass ‘cone’ to the end of the sprue creating a channel for the wax to flow through later.
- The college supplies two different sizes of moulding plates. The smaller one can hold up to 6 layers of rubber, whereas the larger one can hold 8 layers for thicker pieces.
- I used the metal plate to trace on top of the rubber sheet enabling me to cut out 6 of the correct sized pieces of rubber. I would snip the corners off the rubber to create a snug fit into the rounded plate mould.
- I’d peel off the protective film off the rubber and place it face up in the plate, I’d then repeat this with the second layer. With the third layer, I’d cut out a small triangle-like shape to fit round the metal cone. I’d also cut out areas of this layer to fit around the object or cut pieces out of some rubber to fill any open areas in a design. As the rubber needs to melt and form into the shape of the piece inside, all gaps need to be filled as much as possible. Again, I’d place this layer peeled side up.
- The fourth layer would be placed peeled side down, with another triangle shape cut out to fit round the cone. The final two layers will also be placed face down.
- The rubber and mould is then covered by some metal sheet and placed into the heat press and closed tight. For the 6 layer mould I leave it in the press for approx. 50 minutes with the temperature at 275 Degrees Celcius. With the 8 layer mould I would leave it in the press for approx. 1 hour.
- After 50 minutes, using large tongs, carry the mould over to the sink and rinse under cold water until cool to touch.
- Remove the metal plates and pop the rubber moulds out of the frame and secure in a vice.
- Using a sharp scalpel, start slicing through the rubber from each side of the brass cone, keeping the cut down the centre until you get to the piece inside, taking care as the piece could still be hot inside the mould.
- Continue slicing down the sides of the piece until you can free the object. Then continue slicing through where the object had been, not completely cutting the rubber mould in two.
- Once the pieces from inside have been removed, create some slices through the rubber, creating vents for air to escape. It should look something like this:
- Test out the mould using the wax injector. After a few minutes check the piece inside has worked. This can take a few attempts purely from trying to gauge how much wax to be injecting.
- If you find lack of detail in the piece or bubbles it could need more vents sliced through the rubber before attempting again.