What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Servo Press Die Cushion Setup: Force and Stroke Optimization

admin

The die cushion is a critical component in servo press deep drawing operations. Proper setup directly impacts part quality and tool life.

## Die Cushion Function

The die cushion provides controlled blank holder force during the drawing stroke. In servo presses, the cushion can be hydraulic, pneumatic, or servo-driven. Servo cushions offer the most flexibility — force and position can be programmed independently throughout the stroke.

## Force Setting

Blank holder force should be set to the minimum that prevents wrinkling. Too much force causes tearing; too little causes wrinkling. Start at 20-30% of blanking force and adjust based on part quality.

For servo cushions, program a **force ramp** — start at 80% of target force at initial contact, ramp to 100% as the draw progresses. This reduces shock loads and improves material flow.

## Stroke Setting

Cushion stroke must be greater than draw depth plus 10-15mm clearance. Set the cushion return speed to match the press slide return speed to avoid impact at the top of stroke.

## Pressure Pins

Distribute pressure pins evenly around the blank holder. Uneven pin distribution causes uneven blank holder force and part distortion. Use a pressure-sensitive film (Fujifilm Prescale) to verify even force distribution.

## Troubleshooting

- **Wrinkling in flange:** Increase blank holder force 10% at a time
- **Tearing at punch radius:** Decrease blank holder force, check lubrication
- **Uneven draw depth:** Check pressure pin heights (should be equal ±0.05mm)
- **Cushion bounce:** Reduce cushion return speed, check nitrogen pressure

dave_toolmaker

Die cushion pressure is the most tweaked parameter in my experience. For deep drawing stainless steel, I start at 30% of drawing force for blank holder and adjust in 5% increments. Too much and you get thinning at the punch radius. Too little and you get wrinkles. There's a sweet spot and it's different for every part.

yuki_rnd

The interaction between slide motion profile and die cushion force is often overlooked. Our FEA simulations show that a 50ms dwell at BDC with 10% reduced cushion force during the dwell produces better material flow than constant cushion force. The servo press makes this possible —you can't do it on a hydraulic.