How to solve the problem of plastic parts sticking to the mold during injection molding?

Mold sticking means plastic parts stick on cavity, core, ejector pin or slider after cooling and cannot drop off normally. It mainly comes from 4 reasons below with corresponding fixes.

Mold problems (main cause, over 80% cases)

1.Rough mold surface, carbon deposit & dirt: plastic sinks into tiny marks and sticks.

→ Polish mold regularly and clean dirt before & after production.

2.Poor ejection system: uneven ejector pins, broken/rusty pins or tight sliders lead to unbalanced ejection.

→ Add more pins at thick plastic areas; replace bad pins and adjust slider clearance.

3.Poor air vent: no enough air escape creates vacuum suction to hold parts tight.

→ Widen vents, clean waste in vents; add vacuum exhaust for deep cavity molds.

4.Insufficient draft angle or sharp burrs/undercuts hook products.

→ Increase draft angle, remove burrs and optimize sharp corners.

Improper injection parameters (adjust machine only, no mold change needed)

1.Too high barrel or mold temperature makes soft sticky parts and carbon residue.

→ Lower temperature and ensure full cooling before opening mold.

2.Too high injection / packing pressure over-fills product and makes tight fitting.

→ Reduce pressure, speed and packing time; control proper shot size.

3. Short cooling time: parts stay soft and stick easily.

→ Extend cooling time especially for thick-wall items.

Raw material issues

1. High-viscosity material like ABS/PP/TPU or poor recycled material sticks easily.

→ Use prime material; apply proper release agent for sticky plastic.

2. Moisture inside pellets increases stickiness.

→ Dry raw material strictly before molding.

3. Too much / too little release agent causes sticking or dirt buildup.

→ Spray release agent evenly and moderately.

Bad product structure (need redesign for permanent solution)

Deep cavity, thin wall, dense ribs & unnecessary small undercuts bring big demolding resistance.

→ Simplify thin ribs; remove useless undercuts or use lifter/slider for required undercuts; reserve proper draft angle.

Final conclusion

Sticking is usually caused by multiple factors together: mold status, machine setting, material and product design.

Regular mold maintenance, standard parameter setup and good raw material control can greatly reduce sticking failure.

If you have any further questions about injection molds, feel free to consult us. We are ready to solve your problems and offer professional solutions.