The Runoff Surface Tool will help in creating the runoff surface of the surface body of a forming part.

Create 6 planar surfaces on X-, X+, Y-, Y+, Z- and Z+ directions of the selected part. Those planar surfaces will act as the boundary plane of the stock material when creating runoff surface.
Import
Copy the selected face and untrim all boundary.
Featured
Create a planar surface based on the selected surface and trim the planar surface with the boundary of the selected surface and the stock boundary planes.
Extended
Apply extend surface function to open boundary of the selected face and extend up to the stock boundary plane.
3 Edges Loft
Select 3 connected edges. A loft surface feature will be created between the first and the last selected edges, the second selected edge will act as the guide curve. The created loft surface will then be extended upto the stock boundary.
Untrim Open
Untrim all boundary of the selected face.
Check Gap
Highlight all vertexes/edges of the selected surface body to allow the user to visual check for any gaps between surfaces.