I am designing a machine for expanding reasonably large (up to 150mm x 150mm cross section, up to 900mm OD and down to 300mm ID) forged rings. Typical materials are titanium, stainless steels, nickel alloys and particularly 718 alloys. The process will (thankfully) be done at temperatures of around 800 degrees, so my worst case yield stress is around 600MPa. I am having problems calculating the force required to plastically deform these rings, so any help would be appreciated, along with any tips from anyone who has had experience with these machines.