Silicone mould vacuum casting is used for small production runs or to duplicate prototypes and models. When you want to make a silicone mould, we first need to make a master prototype through 3D printing, CNC milling or SLA laser printing, we can also use clay carving to create a master prototype. The silicon rubber mould is used to produce accurate duplicates of the original products, via vacuum casting.
The Maximum size is 1000mm×800mm×800mm, and the tolerance can be controlled to 100mm/±0.20mm.
First we need to produce a master prototype by 3D printing, CNC, SLA or clay mock up. The transparent and high gloss part needs to be polished perfectly to prevent any imperfections on the final mould.
A silicone mould exists always of two halves. Because the split (parting line) will always be visible and the part has less strength on this line, three things have to be taken into consideration, when defining where to split the mould:.
Generally, the injection point will be set at the invisible surface of the component. In this way, the injection point cannot be seen after the assembling of the whole model. This can be at the inside of a bottle lid, or at the bottom of a cup. For a simple construction or a symmetrical part, the injection point should be set in the centre of the part, so the liquid runs equally in the mould when casted, and the bubbles can be controlled easily.
Make a box of aluminum plates according to the dimension of the model. Then hang the model, which has been taped on the parting line, in the box. For some big silicone moulds we use steel bars to reinforce it, to prevent deformation of the part.
Calculate the needed weight of silicone and pour the silicone into a bucket. Then add the catalyst according to the specific ratio to the silicone, and pour the content of the bucket into the vacuum mix machine to mix the liquid silicone under vacuum. When the content had been mixed, pour the liquid silicone slowly into the box, place the box into the vacuum machine and vacuum it, this process is to suck the bubbles out of the silicone. When the vacuuming is finished, move the box into the oven and cure it with fewer than 40 centigrade degree. Normally, it takes about 7~8 hours to finish the curing.
Take the cured mould out, and use a knife to split the mould along with the tape connected to the part. One silicone mould can be used 10 times, but you will get the best duplications if you use the mould 3 to 5 times.