If i understand u r quariy; I think in sheet metal u will never come accross such a situation, or r y telling of a joint of two sheet metal parts welded together.If so it will be an assemly not a sheet metal part. can u explain u r problem more clearly.
I think I know what eugend is trying to achieve. If you create a panel with the rip diagonally across the corner (as tops of certain filing cabinets and lockers) you could create a point with three folds intersecting. However, I am currently trying to model the same without sucess.