Injection Molding Bubbles? 5-Step Troubleshooting + Solutions

• Insufficient Drying: Hygroscopic resins such as PA, PC, and ABS will vaporize moisture at high temperatures to form honeycomb-like bubbles if moisture content exceeds standards (e.g., PA66 moisture content > 0.1%). Solution: Customize drying parameters by material properties – PA66 requires drying at 80-90℃ for 4-6 hours, PC at 120-130℃ for 4-8 hours. Use drying air with dew point ≤ -40℃ to avoid reabsorption.
• Material Contamination: Excessive regrind ratio (>30%), residual carbonized material, or additive decomposition releases gas. Solution: Regrind ratio ≤ 10% for precision parts. Test moisture content with an infrared moisture meter for each batch and verify drying effectiveness via the "burst test".

Step 2: Process Parameter Adjustment – Optimize Filling and Venting Rhythm

• Temperature Control: Excessively high melt temperature accelerates volatile release; low temperature reduces fluidity causing voids. Solution: Adjust melt temperature by material MFI (e.g., HDPE at 210-230℃). Increase mold temperature to 60-80℃ for thick-walled parts to extend venting time.
• Injection and Holding Pressure: High-speed injection triggers turbulent gas entrapment; insufficient holding pressure causes shrinkage bubbles. Solution: Adopt segmented injection (low speed for runners, medium speed for cavities). Set holding pressure to 60%-80% of injection pressure, with 3-5 seconds holding time per mm of wall thickness.
• Back Pressure and Screw Speed: Back pressure < 5MPa fails to expel gas; speed > 80rpm intensifies entrapment. Solution: Adjust back pressure to 5-10MPa and speed to 40-60rpm.

Step 3: Mold Structure Inspection – Unblock Critical Venting Paths

• Venting System: Lack of vents at parting lines or weld lines leads to >90% bubble rate in deep-cavity parts (e.g., phone casings). Solution: Add vents (0.03-0.05mm deep, 5-10mm wide) and use porous steel for hard-to-vent areas.
• Gates and Runners: Undersized or mispositioned gates trap air. Solution: Gate cross-section = 1.2-1.5x maximum part wall thickness. Avoid right-angle bends in runners; ratio of length to part projection ≤ 3:1.
• Cold Slug Wells: Absence of wells pushes gas-laden cold material into cavities. Solution: Add cold slug wells at runner bends.

Step 4: Equipment Condition Verification – Ensure Plasticizing and Sealing Performance

• Screw and Barrel: Gap > 0.3mm causes uneven plasticization. Solution: Clean barrels weekly with dedicated cleaners; repair/replace when worn excessively.
• Nozzle and Sealing: Clogged nozzles or leaking parting lines draw in air. Solution: Use self-locking nozzles; inspect slider/seal performance and replace damaged parts timely.

Step 5: Part Structure Optimization – Reduce Gas Retention Dead Zones

• Wall Thickness Uniformity: Ratio > 1.5:1 (max:min) causes bubbles in thick sections. Solution: Add 工艺 holes in thick areas and 0.5-1mm ribs to guide flow.
• Complex Structures: Multiple inserts/holes increase flow resistance. Solution: Add auxiliary gates at structural transitions to optimize filling paths.