1. Short Shot (Incomplete Filling)
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Cause: Insufficient material, low injection pressure, inadequate venting, or poor flow due to thin walls.
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Solution:
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Increase injection pressure and speed.
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Raise material or mold temperature to improve flowability.
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Enlarge gate or runner system.
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Add or improve venting.
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Use material with better fluidity.
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2. Flash (Excess Material at Parting Line)
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Cause: Excessive injection pressure, poor clamping force, worn mold parting surfaces, or misalignment.
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Solution:
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Reduce injection pressure or holding pressure.
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Increase clamping force.
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Repair or align mold surfaces.
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Reduce melt temperature to minimize material leakage.
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3. Sink Marks
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Cause: Uneven cooling, thick wall sections, insufficient packing pressure/time.
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Solution:
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Increase packing pressure and extend packing time.
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Optimize cooling system for uniform cooling.
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Reduce wall thickness or redesign part geometry.
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Use materials with lower shrinkage.
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4. Warpage (Deformation or Bending)
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Cause: Uneven shrinkage due to improper cooling, part design, or fiber orientation.
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Solution:
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Balance cooling system.
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Optimize part design to ensure uniform wall thickness.
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Adjust mold temperature and packing pressure.
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Use fillers (like glass fiber) to control shrinkage.
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5. Burn Marks (Dark/Black Stains at End of Fill)
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Cause: Trapped air or gas overheats due to high injection speed/pressure.
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Solution:
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Improve mold venting.
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Reduce injection speed and pressure.
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Lower melt temperature.
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Enlarge gates or runners for smoother flow.
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6. Weld Lines (Visible Lines Where Flow Fronts Meet)
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Cause: Incomplete fusion of two flow fronts due to low temperature or low pressure.
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Solution:
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Raise melt and mold temperature.
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Increase injection speed and pressure.
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Optimize gate location to reduce multiple flow fronts.
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Use materials/additives that improve bonding strength.
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7. Bubbles or Voids
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Cause: Moisture in material, trapped air, or insufficient packing.
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Solution:
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Dry material thoroughly before molding.
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Increase packing pressure/time.
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Improve venting system.
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Reduce melt temperature if degradation occurs.
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8. Discoloration (Streaks, Yellowing, Black Specks)
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Cause: Overheating, degraded material, contamination, or leftover resin.
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Solution:
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Lower barrel temperature.
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Use proper purging methods.
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Ensure material is clean and dry.
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Clean the screw, barrel, and hot runner.
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9. Jetting (Snake-like Flow Marks)
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Cause: High injection speed with a small gate causes material to jet.
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Solution:
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Reduce injection speed.
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Increase melt and mold temperature.
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Modify gate design (larger or differently located gate).
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10. Delamination (Layer Peeling on Surface)
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Cause: Contamination, incompatible material mixing, or poor bonding.
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Solution:
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Use pure, compatible materials.
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Dry material properly.
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Increase melt temperature to enhance bonding.
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Avoid mixing regrind with virgin material in high proportion.
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