admin
Springback is the primary quality challenge in automotive bracket stamping, especially with HSS and UHSS materials. Servo press motion control offers several techniques to minimize springback without secondary operations.
## Why Springback Occurs
When metal is bent or formed, the elastic portion of the strain recovers when forming force is removed. For DP590 steel, springback angle is typically 2-5?. For DP980, it can reach 8-12?.
## Servo Press Techniques for Springback Control
### 1. Dwell at BDC (Most Effective)
Hold the slide at BDC for 50-200ms after forming. This allows stress relaxation in the material, reducing springback by 30-60%.
Parameter setting: BDC dwell time in motion profile
- DP590: 50-100ms dwell
- DP780: 100-150ms dwell
- DP980: 150-200ms dwell
### 2. Overbend Compensation
Program the slide to go 0.5-2mm below nominal BDC, then return. The material springs back to the target angle.
Requires iterative tuning: start with 0.5mm overbend, measure springback, adjust.
### 3. Pressure Dwell (for Coining Operations)
For coining operations, increase forming pressure at BDC by reducing slide speed to near-zero in the last 1-2mm. This increases contact stress and reduces springback.
## Motion Profile Example for DP780 Bracket
```
TDC (0mm) ??50mm above material: 300mm/s
50mm ??5mm above material: 150mm/s
5mm above ??BDC: 80mm/s
BDC dwell: 120ms
BDC ??50mm above: 200mm/s
50mm above ??TDC: 400mm/s
```
## Measuring Springback
Use a CMM or optical comparator to measure the formed angle immediately after forming and 24 hours later (some materials continue to relax). The difference is the springback angle to compensate for.