How to Solve Trapped Gas Problems in Thick-Walled Injection Molded Parts
Optimize venting systems: add vent grooves (0.02–0.03mm deep) at melt flow ends, thick-wall intersections, and rib roots to release trapped air. Use vent pins or inserts at deep dead zones for targeted air evacuation. Adjust gate locations to direct melt flow away from thick-wall dead zones, ensuring uniform filling without air entrapment. Modify cooling circuits to reduce melt viscosity and improve flow, allowing air to escape more easily.
2. Process Parameter Adjustments
Minimize thickness variations and eliminate sudden transitions that create enclosed air pockets. Add draft angles to thick-wall sections to facilitate air movement toward vents. Integrate flow leaders or rib modifications to direct melt flow toward vents, preventing stagnation in dead zones. For extremely thick sections, consider hollow structures or material reductions to reduce the volume of trapped air.
4. Material and Pre-Processing Improvements
Dry hygroscopic materials thoroughly to eliminate moisture-related gas formation. Use low-viscosity grades or add lubricants to improve melt flow and air release. Avoid excessive use of additives that generate gas during molding, or switch to low-gas alternatives. Purge the barrel regularly to remove degraded material that causes gas buildup.
| Defect Phenomenon | Causes of Trapped Gas | Mold Optimization Measures | Process Adjustment Scheme |
| Surface Burning & Sink Mark | Poor venting at thick wall junction; rapid melt filling compresses air | Add 0.02~0.03mm vent grooves at melt terminal position | Reduce injection speed; properly increase mold temperature |
| Internal Bubble & Void | Moisture in raw material; enclosed dead zone inside thick wall | Adopt insert venting and vent pin structure | Strengthen material drying; raise back pressure |
| Weld Line & Weak Strength | Air accumulation at melt convergence position | Optimize gate position to change melt flow direction | Multi-stage slow injection; extend holding time |
| Deformation & Dimensional Deviation | Uneven gas escape leads to inconsistent cooling shrinkage | Optimize cooling circuit layout for uniform temperature | Stabilize injection pressure and cooling time |
5. Post-Mold Inspection and Validation
