Analysis and Solutions for 15 Common Injection Molding Plastic Defects

Common Injection Molding Defects:

Insufficient Filling

Flash

Air Pockets

Warping

Silver Streaks

Surface Dullness

Weld Lines

Air Bubbles

Black Streaks and Burn Marks

Cracking

Ejection Overflow

Bending

Ejection Failure

Ejection Failure at the Gate

Material Overlapping Defects

Analysis and Solutions for Defects:

Insufficient Filling

The molded part’s volume is too large.

The runner or gate is too small.

Nozzle temperature is low.

Material temperature or injection pressure is low.

Fluid flow distance in the cavity is too long.

Mold temperature is low.

Injection speed is slow.

Insufficient material supply.

Poor ventilation.

Flash

Insufficient clamping force.

Poor mold design.

Impurities on mold surfaces.

Molded part’s projected area is too large.

Material temperature is too high.

Excessive material supply.

High injection pressure.

Air Pockets

Small runner or gate.

Large wall thickness variation in the molded part.

High material temperature.

Long flow distance from the gate.

Premature demolding.

Low injection pressure.

Short cooling time.

Insufficient holding pressure.

Warping

Poor material flow.

Low mold temperature.

Small sprue.

Silver Streaks

Moisture or volatile components.

Excessively high material temperature.

Low mold temperature.

Poor ventilation.

Poor design of molded part or mold.

Moisture or volatile components on the mold surface.

Contamination with impurities.

Improper screw operation.

Surface Dullness

Excessive lubricant or volatile components.

Excessive release agent.

Weld Lines

Material temperature.

Improper gate design.

Excessive volatile components or release agent in the material.

Rapid solidification of the material.

Poor design of the molded part.

Air Bubbles

Small runner or gate.

Low injection pressure.

Excessive moisture.

Poor molded part design.

Poor ventilation.

Black Streaks and Burn Marks

Material overheating.

Poor molding machine.

Poor mold design (small gate, poor ventilation).

Cracking

Excessive injection pressure.

Poor material flow.

Pushing pins in thick areas.

Poor ventilation.

Poor adjustment of holding pressure.

Large thermal stress.

Chemical corrosion.

Ejection Overflow

Improper gate design.

High injection speed.

Low material temperature.

Low mold temperature.

Bending

Insufficient cooling.

Ejection failure at the gate.

Uneven cooling.

Inappropriate injection pressure.

Improper gate position.

Core misalignment.

Uneven flow distance from the gate.

Ejection Failure

High injection pressure.

Poor mold temperature adjustment.

Poor mold design, inadequate ventilation.

Ejection Failure at the Gate

Poor mold installation.

Poor gate shape.

Material Overlapping Defects

Poor material feeding.

Excessive inclusion of crushed recycled materials.

Excessive external lubricant.

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