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 for Coin and Medal Stamping: High-Pressure Forming Setup

admin

Coin and medal stamping is one of the most demanding servo press applications —extremely high forming pressures, tight dimensional tolerances, and complex surface detail requirements.

## Process Characteristics

- Material: brass (CuZn30), cupronickel, aluminum, silver
- Thickness: 1.5-3.5mm blanks
- Forming pressure: 600-1200 MPa (much higher than structural stamping)
- Surface finish requirement: mirror finish on die, Ra < 0.1?m
- Dimensional tolerance: ?0.01mm on diameter, ?0.005mm on thickness

## Press Selection

Coin stamping requires:
- **High rigidity**: frame deflection must be <0.01mm at full load
- **Precise BDC control**: ?0.005mm repeatability
- **High tonnage in small stroke**: typically 50-200 ton in 2-5mm forming stroke
- **Slow forming speed**: 1-10mm/s in forming zone

Knuckle-joint servo presses are preferred for coin stamping because they provide maximum mechanical advantage at BDC.

## Motion Profile for Coin Stamping

```
TDC —5mm above blank: 200mm/s (fast approach)
5mm above —1mm above: 20mm/s (slow approach)
1mm above —BDC: 3-8mm/s (forming speed)
BDC dwell: 200-500ms (critical for surface detail)
BDC —TDC: 150mm/s (return)
```

The BDC dwell is critical —it allows material to flow into die detail under sustained pressure.

## Die Requirements

- Die material: D2 or M2 tool steel, hardened to 60-62 HRC
- Die surface: polished to Ra < 0.05?m
- Die temperature: maintain at 20-25?C (temperature affects blank thickness)
- Die life: typically 500,000-2,000,000 strikes before re-polishing

## Quality Control

- Measure blank weight before stamping (weight variation = thickness variation)
- Check diameter and thickness every 1000 pieces
- Inspect surface under 10x magnification for flow lines or cold shuts

dave_toolmaker

Medal stamping is even more demanding than coin blanking because of the relief detail. The servo press dwell at BDC is essential —it allows the metal to flow into the fine details of the die engraving. Without dwell, you get incomplete fill on the highest relief areas. We typically use 200-500ms dwell depending on the detail depth.

lisa_quality

Surface finish on coins and medals is measured in Ra (roughness average). Target is typically Ra 0.1-0.2 micrometers. The servo press's vibration-free forming helps achieve this —any vibration during the coining stroke shows up as surface texture on the finished piece. We measure Ra on every 50th piece as part of our quality protocol.