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

Hot stamping vs cold stamping on servo for structural parts

wayne_mfg

We do both hot and cold stamping for structural auto parts. Thinking about which operations to move to the press. Here's what I've figured out so far.

**Hot Stamping
**
Heats boron steel to 900-950C, forms and quenches in water-cooled die. Result: 1500-2000 MPa.

Press requirements:
- Forming speed: 50-150mm/s
- Dwell at BDC: 5-15 seconds for quenching
- Cycle time: 10-20 seconds

**Cold Stamping of UHSS
**
980-1500 MPa UHSS, no heating required.

Press requirements:
- 2-3x tonnage vs mild steel
- Forming speed: 30-80mm/s
- Dwell at BDC: 100-300ms

**Which to Choose?
**
Hot stamping: higher strength (1500-2000 MPa), better formability, less springback.

Cold stamping: no furnace ($2-5M saved), faster cycle (3-5s vs 10-20s), lower energy.

B-pillars/door beams: hot stamping. Bumper reinforcements at 980 MPa: cold stamping increasingly preferred.

yuki_rd

This is my area. For B-pillars above 1500 MPa, hot stamping is still the only viable option —you can't cold form 22MnB5 after quenching. But for 980-1180 MPa parts, cold stamping on a servo press is increasingly competitive. Our latest work shows that servo press cold forming of 1180 MPa DP steel can achieve 90% of the properties of hot stamped 22MnB5, at 1/3 the cost per part.

sarahJ_mfg

We run both processes. Hot stamping line cost us $4.5M. Servo press cold stamping line for similar parts: $1.2M. The hot stamping line makes sense for ultra-high volume (500K+ parts/year) but for lower volumes, cold stamping on servo press wins on economics every time.

anna_plc

I have run both on servo presses and the decision is simpler than most people make it. If your part needs above 1200 MPa final strength and has deep draws or complex geometry, hot stamp it. Everything else, try cold forming on servo first.

The servo press advantage for cold stamping high-strength steel is the programmable speed profile. We form 980 MPa DP steel at 15mm/s through the draw section then speed up to 80mm/s for the return. On a mechanical press you cannot slow down for the critical forming zone without killing your cycle time. The servo lets you have both.

Springback is the real challenge with cold forming AHSS. We compensate in the die design (overbend by 3-5 degrees depending on grade) and use a 200ms dwell at BDC to stress-relieve. That dwell alone cuts springback variation by 40% compared to no dwell. Hot stamping avoids springback entirely because you quench in the die, but you pay for it with cycle time (8-12 seconds vs 2-3 seconds cold).

Cost comparison from our shop: hot stamped B-pillar $4.80/part, cold formed 980 DP alternative $1.90/part. The cold part is 15% heavier but for non-crash-critical structural parts that trade-off works.

mike_blanking

Done both for B-pillar and door ring work and I'd push back gently on the framing of the question. "Hot vs cold on servo" usually gets debated as if servo is the variable. It isn't ??the press is the easy part. The hard part is the line around it.

For 22MnB5 hot stamping you need:

A furnace that holds austenitizing temp (900-950?C) with line speed matched to your SPM. Drop a blank below ~830?C at the die and you don't get a full martensitic transformation; you get inconsistent hardness across the part and the warranty engineer calls you.

Transfer time under 8 seconds blank-out-to-die-close, including any centering. Robotic transfer with insulated grippers or a gravity drop chute, not human hands. Cycle time on hot work is fundamentally transfer-limited, not press-limited.

Water-cooled dies with proper flow balance. Quench rate above 27?C/sec is what gives you the 1500 MPa final strength. We had a die that ran 1450 MPa for six months because one cooling channel had a 30% flow restriction nobody caught ??the press tonnage looked perfectly normal the whole time.

For cold stamping high-strength (DP980, MS1300) on the same servo you want:

Longer BDC dwell (200-400ms typical) for springback control, which mechanical presses can't really do. This is where servo earns its money on cold work.

Die material upgrade ??Vanadis 4 Extra or similar PM steel. Conventional D2 will galling-fail in 50K hits on DP980.

Nitrogen springs sized for the higher stripping forces. Blanking-grade gas pressure, not coining pressure.

Our shop runs both on the same servo line by changing the front-end (furnace in or out) and the cooling water plumbing. The press itself doesn't change much. People who think hot stamping is "just stamp it hot" lose money for two years before figuring this out.