how to cut 3D model in pieces like a preparation for die casting and molding

I'm creating some models, and I would like them to be cut into pieces ( a little bit like the Warhammer figurines) in order to prepare a mold for plastic injection. 

I don't find a clear way to do that on the internet, and wanted to ask if you have some directions where you can point me to. 

I guess I need to manually cut my objects into pieces, and then

using some kind of software to 'calculate' based on a collection of meshes where the mold runners and gates must be. 

Do you know of any software I can use for that? Or does blender have addons for that?

thank you!