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Fine blanking produces parts with shear-cut edges that are smooth, perpendicular, and burr-free ??unlike conventional blanking which produces a rough fracture zone. Servo presses are increasingly used for fine blanking due to their precise force and position control.
## Fine Blanking vs Conventional Blanking
| Parameter | Conventional | Fine Blanking |
|-----------|-------------|---------------|
| Edge quality | 30-50% burnish | 100% burnish |
| Flatness | ?0.1mm | ?0.02mm |
| Burr height | 0.05-0.2mm | <0.01mm |
| Material utilization | Higher | Lower (V-ring area) |
| Press force | Blanking only | Blanking + blank holder + counter punch |
## Three-Force System
Fine blanking requires three simultaneous forces:
1. **Blanking force**: cuts the part (same as conventional blanking)
2. **V-ring (impingement ring) force**: clamps material around the cut line, preventing material flow
3. **Counter punch force**: supports the part from below during cutting
All three forces must be applied simultaneously and precisely. This is where servo press control is critical.
## Force Requirements
For a typical fine blanking operation on 4mm mild steel:
- Blanking force: 800-1200 kN
- V-ring force: 15-25% of blanking force (120-300 kN)
- Counter punch force: 5-10% of blanking force (40-120 kN)
## Servo Press Advantages for Fine Blanking
- **Programmable V-ring force**: adjust independently for different materials
- **Controlled blanking speed**: 5-15 mm/s for fine blanking (much slower than conventional)
- **Dwell at BDC**: 50-100ms improves edge quality
- **Data logging**: record force signature for every part (100% traceability)
## Setup Parameters
- Blanking speed: 8-12 mm/s (start slow, increase if edge quality acceptable)
- V-ring engagement: 0.5-1.0mm before blanking contact
- Counter punch pressure: set to prevent part deflection at BDC
- Clearance: 0.5% of material thickness (much tighter than conventional 10-15%)
mike_chen_eng
On fine blanking clearance: the 0.5% rule is a starting point. For stainless steel, we go down to 0.3% of thickness. For aluminum, 0.8-1.0% works better. The key is that clearance must be extremely consistent around the entire perimeter ??variation of more than 0.01mm causes rollover on one side.