If you see short shots (incomplete fill): increase injection pressure by 10-15% or increase injection speed. If you see flash (material escaping at parting line): reduce injection pressure by 5-10% or verify clamp force is adequate for the projected part area. The goal is the lowest pressure that consistently produces complete, flash-free parts.
Injection pressure troubleshooting decision tree:
| Symptom | Likely Cause | First Action | Second Action |
|---|---|---|---|
| Short shot — incomplete fill at end of cavity | Pressure too low | Increase pressure by 10% | If persists: increase material temperature 5°C |
| Short shot — at thin wall section | Material freezing before fill complete | Increase injection speed | Increase mold temperature 5-10°C |
| Flash at parting line | Pressure too high for clamp force | Reduce pressure by 5-10% | Verify projected part area × pressure < clamp force |
| Flash at gate | Gate erosion — gate too large | Reduce pressure; check gate condition | Repair or replace gate insert |
| Flash intermittent | Clamp force varying | Check hydraulic system | Check mold parallel alignment |
| Part Type | Typical Injection Pressure (MPa) | Notes |
|---|---|---|
| Simple shape, uniform wall | 80-120 | Low-end of range |
| Moderate complexity, thin walls | 100-150 | Standard production range |
| Complex, thin walls (<0.5 mm) | 140-200 | High-pressure — check mold strength |
| Micro-MIM (<0.3 mm walls) | 180-250 | Specialized high-pressure machine needed |
Pressure is not an independent parameter — it interacts with temperature, speed, and material viscosity. A change in any of these affects the pressure required:
- Increasing material temperature by 5°C reduces viscosity → reduces required pressure by 5-10%
- Increasing injection speed → increases pressure at the gate (more shear thinning, but also more flow resistance)
- Higher MFI feedstock → lower pressure required for same fill rate