Injection Molding Defects’Causes & Countermeasures

The causes and countermeasures described below are aimed to solve the commonly seen  injection molding defects that might occur in ordinary circumstances. The examples are just based on my own personal work experience, so if there is anything inappropriate, you are welcome to correct me!

Short shots (incomplete filling)

(1) Short shots (incomplete filling): The molten plastic fails to fill up each and every corner in the entire molding space (the cavity).

(2) Causes and Countermeasures

short shot injection molding defects


(1) Flash: Extra plastic material in the shape of films or burrs, which appears on the parting surface, around the runner or in the insert crevice.

(2) Causes & Countermeasures (See the table below)

flash,burrs injection molding defects
*Note: Flash also tends to occur when the injection pressure/speed are too high, but molding time is too long and mold temperature is too low.

Silver streaks

(1) Silver streaks (silver lines): The radial silver white streaks on or around the product surface, which is formed along the plastic flow direction.

(2) Causes & Countermeasures (See the table below)

silver strike injection molding defects

Low product glossiness

(1) Low product glossiness means the surface glossiness of the product does not meet the quality standard – the surface is not dioptric.

(2) Causes & Countermeasures (See the table below

Low product glossiness injection molding defects


(1)Deformation includes diagonal twists and warpage along parallel edges.They are the irregular curves that occur in the plastic injection molding process.

(2)Causes & Countermeasures (See the table below)

Deformation injection molding defects

Ejecting marks

(1) Ejecting marks (AKA white marks): The white marks that occur in the ejector pin or other ejecting positions during mold release.

(2) Causes & Countermeasures (See the table below)

ejecting marks injection molding defects

Weld lines

(1) Weld lines: The thin lines that occur when 2 or more molten materials are fusing in the plastic injection molding process.

(2) Causes & Countermeasures (See the table below)

welding lines injection molding defects

Jetting marks

(1) Jetting marks: The streaks that the molten plastic produces around the gate.

(2) Causes and Countermeasures

jetting marks injection molding defects  

Discoloration (black marks)

(1) Discoloration (black marks): The black marks or other dark marks that appear on the product surface during the plastic injection molding process.

(2) Causes & Countermeasures (See the table below)

Discoloration (black marks) injection molding defects


(1) Bubbles: The residual voids sealed up in the product, which are caused by the evaporation of the moist contained in the molten plastic.

(2) Causes & Countermeasures (See the table below)

Bubbles injection molding defects

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