Negative Inversion of complex geometry with non linear surfaces..........

I have a problem with handling mold tools in Solid works to get cavity from mold. The part has complex geometry with 2000 faces. Trying to get negative inversion of the part. The top surface of the part is non linear. Is there any other feature in solid works to get inversion of part with complex geometry having non linear surface?

SolidworksPlastics And Mold Design