Defects in Injection-Molded Plastics

Defect		Definition	Common Causes
Flash		Excess plastic protruding at parting lines or edges of the part.	- Insufficient clamping pressure - Excessive injection pressure - Poor mold design (e.g., damaged or worn parting surfaces)
Vacuum Voids		Air pockets or bubbles trapped inside the molded part, weakening structural integrity.	- Gate location in thin section causing uneven cooling - Insufficient injection or holding pressure - High melt viscosity
Delamination		Surface layers peel or flake off; part disintegrates layer by layer.	- Contaminated plastic resin - Excessive moisture in the resin - Overuse of mold release agents
Short Shots		Incomplete filling of the mold cavity, resulting in missing sections of the part.	- Insufficient shot volume - Narrow or blocked flow channels - Low injection speed or pressure
Discoloration & Burnt Marks		Unexpected color variation or dark marks on the molded part.	- Excessive mold temperature - Low injection speed causing material degradation
Flow Lines		Wavy patterns or lines visible on the part surface following the plastic’s flow path.	- Inconsistent melt flow speed or direction - Variation in wall thickness - Suboptimal injection speed and pressure
Sink Marks		Depressions or dents on thicker areas of the part due to internal shrinkage.	- Inadequate or uneven cooling in thick sections - Insufficient packing/holding pressure - Improper part design (non-uniform wall thickness)

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