Split part along Boundary Surface for mold

Hello all,

New guy here.  Been using SW for about 5 years, but new to surfacing and mold work.  I have a model of a fiberglass wing tip that I want to split into an upper and lower half for the purpose of making layup molds.  The model was drawn in Catia, then brought into SW as a surface, then thickness added to make it a solid.  I want to separate the wing tip into halves along the 3DSketch12.  After that, I want to make a tool that is offset from the outside (OML) of the part by .100" and add a flange around the perimeter.  See pdf for a section view of what I want to do.  Advice?  Before I added thickness to the surface model I had a Boundary Surface that followed the 3D sketch.  Now that I've added thickness I can't get the Boundary Surface to work. 

Thanks,

Stephan

SolidworksPlastics And Mold Design