How to make mold of this part??

Is this the kind of mold you want?

  1. Step 1:

    Create a Extrude Boss around your part. Make shore that the Merge Result is not checked.

  2. Step 2:

    Now you should have 2 Solid Bodies. Now use the Combined tool and subtract the part that you don't want as shone.

    Combined tool is located Insert, Features, Combine