Solutions for Mold Cavity Sticking in Injection Molding
Cavity sticking is a common injection molding fault, which causes production interruption, product scrap and mold damage. It is solved by four steps: emergency treatment, root cause analysis, permanent resolution and long-term prevention.
Emergency Treatment: Safely Remove Stuck Material
Immediate Shutdown: Stop the injection molding machine, turn off heating, injection and mold clamping functions, lock the safety switch, and wear protective gear.
Stuck Material Removal: Uncured material: heat mold to material softening point, clean with copper/nylon tools (no hard tools to avoid scratching cavity); cured material: heat locally with hot air gun (150–200℃) or embrittle with dry ice, then gently remove.
Post-Cleaning Inspection: Wipe cavity with anhydrous ethanol, inspect for scratches, polish and repair if necessary, and restart production after confirmation.
Root Cause Analysis: Multi-Dimensional Diagnosis
Mold-Related Factors (Most Common)
Insufficient cavity polishing (Ra＞0.8μm), too small draft angle (＜1.5°), defective ejection mechanism (insufficient ejector pins, uneven force), poor cooling/venting system, negative pressure caused by poor venting, leading to sticking.
Process-Related Factors
Excessive barrel temperature (material degradation, increased adhesion), excessive injection pressure/speed (overfilling), prolonged holding pressure/time (material compaction), insufficient cooling time (material softening), improper release agent use (excessive/insufficient/wrong type).
Raw Material-Related Factors
Insufficient drying of hygroscopic materials (moisture causing increased adhesion), high recycled material proportion (＞30%, poor fluidity), poor material fluidity, material decomposition caused by impurities.
Permanent Resolution: Targeted Optimization
Mold Optimization (Key)
Surface Quality: Repolish cavity to Ra≤0.8μm (Ra≤0.2μm for mirror molds), remove burrs and oil stains, apply anti-sticking agent.
Draft Angle: Adjust to ≥1.5° (≥3° for deep-cavity/soft-material products), add release grooves for special structures.
Ejection Mechanism: Increase ejector pins, optimize position, uniform ejection force; air-assisted ejection for deep-cavity products, regularly maintain ejector pins.
Cooling/Venting: Unclog cooling channels, optimize layout, add cooling points; add vent grooves (0.02–0.03mm deep, 5–10mm wide) at last filling position.
Process Adjustment
Temperature: Lower barrel temperature by 10–20℃, nozzle temperature 5–10℃ lower than barrel front section.
Pressure/Speed: Reduce injection pressure by 10–15% and speed by 10–20%, adopt segmented injection to avoid overfilling.
Holding/Cooling: Shorten holding time by 10–30%, reduce holding pressure to 50–60% of injection pressure; extend cooling time by 10–30%.
Release Agent: Select matching type, spray uniformly and thinly, clean cavity regularly to remove residues.
Raw Material Control
Drying: Strictly dry hygroscopic materials (PA: 100–120℃ for 4–6h; PET: 130–150℃ for 3–4h), moisture content ≤0.05%.
Recycled Material: Proportion ≤20%, sieve to remove impurities, dry before use.
Material Selection: Replace with materials with good fluidity, add 0.5–1.0% release agent masterbatch if necessary, avoid unqualified raw materials.
Long-Term Prevention: Establish Maintenance Mechanism
Regular Mold Maintenance: Clean cavity, runner and gate before/after each batch; weekly inspection of cavity scratches, ejector pin wear, cooling/venting system blockage, repair in time.
Standardized Process Management: Formulate standard parameter documents, prohibit arbitrary adjustment; train operators to shut down and inspect immediately when abnormalities occur.
Strict Raw Material Management: Inspect raw material quality before use, store in dry and ventilated warehouse, regularly maintain drying equipment.
Maintenance Ledger: Record mold use status, sticking faults, causes and solutions, analyze regularly to optimize mold and process.
