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

Coin blanking on servo press - high speed setup tips

joe_stampworks

We do coin blanking at high speed on our servo press. Took a while to get the setup right. Here's what works for us.

**Why Coins Require Special Setup
**
Coin blanking (cutting coin blanks from strip) requires:
- Very tight dimensional tolerance: +/-0.01mm on diameter
- Burr-free edges (burrs cause problems in coin striking)
- High SPM: 300-600 SPM for production efficiency
- Consistent material flow to prevent edge cracking

**Material
**
Coins are typically blanked from:
- Cupronickel (75% Cu, 25% Ni) — most common
- Brass (70% Cu, 30% Zn)
- Stainless steel (some modern coins)
- Bimetallic (two-material coins require special tooling)

**Die Setup
**
**Die clearance:** 4-6% of material thickness per side for coin blanking. Tighter than general blanking to minimize burr.

**Punch material:** Carbide (K10 or K20 grade) for long life at high SPM. HSS punches wear too quickly above 300 SPM.

**Stripper:** Spring-loaded with controlled force. Too much stripper force causes material distortion.

**Press Motion Profile**

For 400 SPM coin blanking:
- Approach: 600mm/s
- Contact: 200mm/s at 5mm above material
- Blanking: 150mm/s through material
- Return: 800mm/s

The fast return is critical for high SPM — most of the cycle time is in the return stroke.

**Quality Control
**
- 100% vision inspection for diameter and edge quality
- Weight check every 1000 blanks (weight variation indicates thickness variation)
- Die wear monitoring: check burr height every 50,000 strokes

toolndye_dave

Coin blanking dies are some of the most demanding I've built. The punch-to-die clearance is typically 3-5% of material thickness —half of what you'd use for normal blanking. The servo press's BDC repeatability is essential because any variation in penetration depth shows up as a burr height variation on the coin edge.

lisaQ_metrology

We supply blanks to a mint. The dimensional tolerance is ?0.01mm on diameter and the burr height limit is 0.02mm. We run SPC on every 100th blank and our CPK stays above 2.0 on the press. On our old mechanical press, CPK was 1.1-1.3 and we were sorting 5% of production. The servo press eliminated the sorting operation entirely.

mchen_servo

We ran coin blanks for a couple years on a Komatsu H2W. The thing nobody mentions about high-speed coin blanking is strip tension control. At 400+ SPM the strip accelerator needs to be perfectly synced to the press crank angle or you get micro-shifts in blank position. We ended up using the press encoder to trigger the feed directly instead of relying on the feed controller timing.

Clearance-wise we run 3% on copper alloy and 4% on nickel-plated steel. But the real trick is regrind interval. We track burr height with a profilometer every 2 hours and regrind at 0.015mm. Most shops wait until 0.02-0.025mm and by then the edge quality has already drifted. Shorter regrind cycles cost more in tooling downtime but the scrap reduction more than pays for it.

One more thing: die temperature matters more than people think. After 30 minutes of continuous running at 500 SPM the die heats up 15-20C from friction alone. That thermal expansion changes your clearance by a few microns. We added thermocouple monitoring and adjust BDC by 0.005mm when die temp exceeds 45C.

raj_pm

At 400+ SPM you start running into press frame dynamics that don't matter at normal speeds. The frame deflection per stroke is the same but the rate of deflection change is much higher, which means the die sees dynamic loads on top of the static forming load. On our 200T running coin blanks at 450 SPM, we measured 15-20% higher peak force than the same operation at 200 SPM. Make sure your tonnage budget accounts for that.

The other high-speed issue: lubrication. At 400 SPM the strip is moving fast enough that conventional roller-applied lube doesn't coat evenly. We switched to spray application with a mist system and it made a noticeable difference in burr consistency. The lube also needs to be lighter viscosity than what you'd use at normal speeds — we went from a 40cSt stamping oil to a 15cSt.

On die clearance — we run 3% for copper alloys and 4% for nickel-silver. Tighter than that and the punch wear accelerates dramatically at high speed because of the heat buildup. We sharpen every 200K strokes which sounds aggressive but the blanks stay within spec the whole run.