How to create a mold for casting.?

Question

I need to make a key chain by casting. Does anyone knows the steps?

Answer 1

I don't think it's a good idea to make a key chain by casting. If you use not too thick wire it's pretty easy to make the chain from that. If you cast it you need a separate sprue and vent for each link, it's going to be tedious.
What also matters is the material which you want to use, resin, hot metal, chocolate? Is there some reason why you can't just buy one, they are cheap...
Easiest might be if you have a mold with one link laying flat, then the next exactly sideways, then you could use a 2 part mold. Make very sure the individual links do not touch, otherwise they are going to fuse and not move. Don't forget the proper feeds for material and air vents.
If you never done any mold before start with something easier and get a book about it out of a library. It's a lengthy subject.

Answer 2

Model the thing in soft clay, working on it until the detail is right. Paint the model with many layers of latex mold material which goes on as a liquid, fills the details and dries to an amber rubber. A fan helps dry it. 8-15 layers. Before removing, put a ring around it (paper or tape) and pour a backing of plaster to hold the shape of the soft rubber. Remove the plaster, remove the rubber. Let both dry for a day or more. Put the rubber negative into the plaster. Now it depends on the result you want. If you want to pour molten metal, then melt wax into the rubber mold, take out the hardened wax and make a lost wax investment. If you want a resin (clear or colored plastic) then you will need resin separation compound to paint the mold, resin, catalyst, and color.