Thermoforming Defect Library
12 Defects · Root Causes · Solutions · Prevention
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Incomplete Forming / Poor Detail
The part does not fully conform to the mold. Corners rounded, features lack definition. Most common ...
Uneven Wall Thickness
Significant wall thickness variation. Sidewalls and corners thinner than rim/base. Inherent thermofo...
Cracks / Rupture
Sheet tears during or after forming. Occurs at mold contact, sharp transitions or demolding. Structu...
Air Bubbles / Blisters
Trapped air or moisture-induced bubbles on/in the part surface. Affects appearance and integrity....
Poor Corner Definition
Corners rounded instead of crisp. Common in deep-draw and multi-cavity tools....
Sidewall Thinning
Excessive thinning on vertical sidewalls. Reduces structural strength. Critical for load-bearing par...
Webbing / Surface Folds
Wrinkles, folds or webs of excess material. Common around corners and geometry transitions....
Sheet Sticking to Mold
Part sticks to mold, hard to remove. Causes delays and damage....
Sheet Rupture
Sheet tears at mold contact or during clamping. Production stopper....
Stress Whitening
White/hazy patches from molecular orientation and micro-voiding. Common in HIPS, PP, ABS....
Post-Forming Shrinkage
Dimensional reduction after cooling. Causes fit issues and tolerance violations....
Poor Surface Quality
Orange peel, scratches, haze, gloss loss on formed part. Indicates process/material issues....
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