⬜ Stress Whitening
Causes, Solutions & Prevention in Thermoforming
White/hazy patches from molecular orientation and micro-voiding. Common in HIPS, PP, ABS.
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⚠️Root Causes by Category
⚙️ Process
- Sheet too cold — cold stretching
- Rapid mold closure — sudden strain
🔲 Mold / Tooling
- Sharp features cause localized over-stretching
🧪 Sheet / Material
- Material prone: HIPS, PP, ABS
📐 Design
- Localized high draw ratio areas
✅Solutions & Corrective Actions
Step 1
- Increase sheet temperature for molecular relaxation
Step 2
- Slow down vacuum rate
Step 3
- Use plug assist to reduce localized strain
Step 4
- Consider higher-impact material (HIPS → ABS)
🛠️Step-by-Step Troubleshooting
1
Step 1
Increase sheet temperature for molecular relaxation
2
Step 2
Slow down vacuum rate
3
Step 3
Use plug assist to reduce localized strain
4
Step 4
Consider higher-impact material (HIPS → ABS)
❓Frequently Asked Questions
What causes stress whitening?
Sheet too cold — cold stretching; Rapid mold closure — sudden strain; Sharp features cause localized over-stretching
How to fix stress whitening?
Increase sheet temperature for molecular relaxation
How to prevent stress whitening?
Prevention requires systematic process control: verify sheet temperature, maintain mold vents, ensure proper material drying, and document optimal parameters.
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