🔄 Post-Forming Shrinkage
Causes, Solutions & Prevention in Thermoforming
Dimensional reduction after cooling. Causes fit issues and tolerance violations.
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⚠️Root Causes by Category
⚙️ Process
- Demolded too early
- Insufficient cooling or mold too hot
🧪 Sheet / Material
- High-shrinkage material (PP, PE) not compensated
- Oriented sheet — frozen stresses relax
📐 Design
- Mold not oversized for shrinkage rate
✅Solutions & Corrective Actions
Step 1
- Increase cooling; target <Tg before demolding
Step 2
- Oversize mold by shrinkage factor (PP: 1.5–2.5%, ABS: 0.4–0.7%)
Step 3
- Use fans or water spray for uniform cooling
Step 4
- Anneal parts post-forming to relieve stress
🛠️Step-by-Step Troubleshooting
1
Step 1
Increase cooling; target <Tg before demolding
2
Step 2
Oversize mold by shrinkage factor (PP: 1.5–2.5%, ABS: 0.4–0.7%)
3
Step 3
Use fans or water spray for uniform cooling
4
Step 4
Anneal parts post-forming to relieve stress
❓Frequently Asked Questions
What causes post-forming shrinkage?
Demolded too early; Insufficient cooling or mold too hot; High-shrinkage material (PP, PE) not compensated
How to fix post-forming shrinkage?
Increase cooling; target <Tg before demolding
How to prevent post-forming shrinkage?
Prevention requires systematic process control: verify sheet temperature, maintain mold vents, ensure proper material drying, and document optimal parameters.
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