UHSS is where I spend most of my time these days so I'll share what's been working and what hasn't.
The biggest forming challenge nobody warns you about with 980+ MPa steel: edge cracking on stretch flanges. You can have a perfect motion profile, perfect lube, perfect blank holder pressure, and still get cracks on the stretch flange if your blank edge quality is poor. We found that laser-cut blanks crack at 30% less strain than die-cut blanks on 1180 MPa DP steel. The heat-affected zone from the laser creates a brittle edge. Switched to mechanical blanking with a sharp trim die and our reject rate dropped from 8% to under 1%.
For the motion profile side of things, what works for us on 980-1180 MPa:
- Approach at 200-300mm/s (fast, no contact yet)
- Decelerate to 30-50mm/s about 5mm before material contact. The exact distance depends on your die — you need to know your first-contact point precisely.
- Through the draw: 20-40mm/s. Slower than you'd think. The material work-hardens as you form it, so the force ramps up steeply. Going too fast causes the force spike to exceed your tonnage capacity before the press can react.
- BDC dwell: 30-80ms depending on part geometry. This isn't for the material — it's for the die structure to stabilize and for any elastic deflection in the press frame to settle out.
- Return: full speed, 400+ mm/s. No reason to go slow here.
Temperature management: we preheat our UHSS dies to 40-50C before the first hit of the shift. Cold die + cold UHSS = first 10-15 parts are scrap because the material behaves differently at shop ambient vs steady-state die temperature. A $200 cartridge heater in each die half solved this completely.
One thing I disagree with in the conventional wisdom: people say servo press is mandatory for UHSS. It's strongly preferred, but I've seen shops running 780 MPa DP on well-set-up mechanical presses with acceptable results. Above 980 MPa though, yeah, you really need the servo's speed control through the forming zone.