If the mold opening involves relief, you need three-dimensional digital sculpture software and then reverse engineering.
Here I recommend a software combination for you: UG+3DCoat+Geomagic Wrap.
UG can be used for modeling, parting and NC machining.
3DCoat can make three-dimensional relief.
Geomagic Wrap can reverse the relief into a surface and import it into UG for parting.
I use these three softwares in the bed below!