You can create simple molds using the Cavity 
tool.
Creating a mold using the
Cavity tool requires the following items:
- Design parts - The parts that you want to mold.
- A mold base - The part that holds the cavity feature of the design part.
- An interim assembly - The assembly in which the cavity is created.
- Derived component parts - The parts that become the halves of the mold after you cut them.
You combine the design parts and mold base in the interim assembly. Then, you create a cavity feature in the context of the interim assembly. This relates the mold base to the design part in the event that the design part changes shape.
To create more complex molds, use the tools and techniques presented in Mold Design.