Basically a sheet metal part is a formed part by drawings and bends. There are two kinds of bend: linear and not linear.
In both cases the unfolding process is based on neutral fibre, and it can be set by user for linear unfolding or fixed (0.5 of thickness) for the blank/flange unfolding.
Actually, in case of no-linear bend unfolding, we must use the flange unfolding functions based on (FTI) engine. In case of linear bends, is possible to apply in the same time: linear flange and flange unfolding, but the advice is to prefer linear flange, because is based on analytic algorithm and thus more precise.
The linear unfolding algorithm is used on: