Injection Molding Process Parameters: Complete Optimization Guide
Key Parameters Overview
The five key parameter groups are: temperature, pressure, speed, time, and cooling. Getting these right is the difference between a profitable production run and costly rejects.
Temperature Settings
| Material | Melt Temp (°C) | Mold Temp (°C) | Drying |
|---|---|---|---|
| ABS | 200-260 | 50-80 | 80°C / 2-4h |
| PP | 200-280 | 20-60 | Not usually |
| PC | 280-320 | 80-120 | 120°C / 3-6h |
| Nylon 6 | 230-290 | 70-120 | 80°C / 4-6h |
| POM | 180-230 | 60-100 | 80°C / 2h |
| PMMA | 210-250 | 50-80 | 80°C / 4h |
| HDPE | 180-280 | 20-60 | Not usually |
Pressure Settings
Injection Pressure
Typically 500-2000 bar. Guidelines by wall thickness:
- Thin-wall (<1mm): 1,200-2,000 bar
- Medium (1-3mm): 800-1,500 bar
- Thick (>3mm): 500-1,000 bar
Holding Pressure
Typically 50-70% of injection pressure. Applied after cavity is 95-99% full.
Back Pressure
Applied during screw recovery. Typical range: 50-200 bar.
Injection Speed Profile
- Slow start (5-20% speed): Avoid jetting at gate
- Fast middle (40-80%): Fills cavity quickly
- Slow end (10-30%): Prevents flash
- Pack phase: Switch at 95-99% fill
Cooling Time
Cooling is 50-80% of total cycle. Simplified rule: 2-3 seconds per mm of wall thickness for most thermoplastics.
Optimization Sequence
- Set temperatures first (melt and mold per material spec)
- Set injection pressure at 80% of machine max
- Adjust injection speed for short shot analysis (97-99% fill)
- Set hold pressure at 50-70% of injection pressure
- Set hold time to 2x gate freeze time
- Adjust cooling time until part ejects without distortion