Thursday, May 5, 2016

Making Molds

One of the processes involved with making castings, if you want to make more than one, is making molds. I use a liquid room temperature Vulcanizing urethane or silicone. I use a semi clear formula that allows me to see the part as I cut it out of the mold. Otherwise I'm cutting blindly into block of rubber.

The first step is making the mold frame here I'm cutting a strip of aluminum and bending it into this U shape. I'll make a box out of this with two pieces of plexiglass, put my wax or metal model inside, fixed to the bottom and then pour the rubber around it.
In the picture above, from left to right, you see the box sealed up and ready to pour next is one that is already been poured, in the middle is another one that is ready to pour, second from the right is a cured mold with the box removed and on the end, on the right, is one that's been poured and ready to de-mold
above  is a stack of molds ready to start cutting.
Here the molds have been cut open along the sides of the models to make a 2 part mold. The top of the pictures shows the original bronze casting that I used to make the mold, the mold after cutting with the original removed, and the wax that was shot into the mold to make the reproduction. As you can see from the waxes, there is still a lot of work to be done before the casting process can begin. The next step is to in case these waxes in a cylinder filled with a special high temperature plaster then the plaster is placed in the oven and heated to 1600 Degrees to burn out the wax. Then the molten metal is forced into that cavity by centrifugal force of the casting machine.