Injection Molding Defects And Solutions

Injection Molding Defects and Solutions -- Black Spots 2025-10-17

Black Spots / Black Streaks: These defects occur when the plastic decomposes or contains volatile substances, air, or other gases that carbonize under high pressure. The carbonized particles are carried by the molten resin into the mold cavity, appearing on the surface of the molded part as black spots, black streaks, or burnt-like marks along the surface. 14.1 Causes 14.2 Solutions 14.1.1 Plastic...

Injection Molding Defects and Solutions -- Wrinkles 2025-10-17

Wrinkles / Halo at Gate: When molten resin enters the mold cavity, it suddenly cools near the gate, increasing in viscosity and slowing its flow. Subsequent resin with lower viscosity and higher flow rate quickly fills the cavity. The difference in viscosity between the first-cooled and later-flowing resin causes visible marks where they meet near the gate. 13.1 Causes 13.2 Solutions 13.1.1 Low mo...

Injection Molding Defects and Solutions -- S-shaped Flow Marks 2025-10-17

S-shaped Flow Marks (Snake Marks / Jetting): This defect occurs when the molten resin injected from the gate into the mold cavity solidifies on the surface of the molded part in a serpentine, snake-like pattern. 12.1 Causes 12.2 Solutions 12.1.1 Improper gate location, e.g., a direct gate allows molten resin to enter the cavity in a snake-like pattern and solidify quickly without resistance. 12.2....

Injection Molding Defects and Solutions -- Surface Flow Marks 2025-10-17

Surface Flow Marks (Flow Lines / Flow Ripples): This defect appears as streaked patterns radiating from the gate on the surface of the molded part. It occurs when the molten resin does not flow smoothly along the cavity surface but moves in a semi-wavy manner. During flow, stagnant zones form, and the resin that initially enters the cavity cools too quickly, creating a boundary with the subsequent...

Injection Molding Defects and Solutions -- Bending 2025-10-17

Bending: For narrow and long parts, one end deforms upward or downward, forming a shape similar to a bow. 10.1 Causes 10.2 Solutions 10.1.1 Poor part structure or low processability. 10.2.1 Modify the part structure. 10.1.2 Improper gate location. 10.2.2 Place the gate at one end of the part, not in the middle, or reshape the part after demolding. 10.1.3 Improper mold temperature (moving or fixed ...

Injection Molding Defects and Solutions -- Warping and Twisting Deformation 2025-10-17

Warping and Twisting Deformation: During molding, various internal stresses cause uneven shrinkage in different directions of the part. Poor demolding, insufficient cooling, or other factors can lead to abnormal shapes, uneven warping, or uneven wall thickness around holes. If the deformation occurs along edges in a parallel direction, it is called warping; if it occurs along diagonal directions, ...

Injection Molding Defects and Solutions -- Bubbles 2025-10-17

Bubbles: Bubbles and voids are cavities formed inside molded products. There are two types of bubbles: one occurs when the product cools and shrinks — as the surface hardens, the thicker areas inside form hollow voids known as vacuum bubbles; the other type occurs when moisture, volatile substances, or air trapped in the resin enter the cavity with the melt during molding and become enclosed insid...

Injection Molding Defects and Solutions -- Dimensional Instability 2025-10-17

Dimensional Instability: This occurs when the molded part exhibits inconsistent shrinkage due to poor mold manufacturing accuracy, unstable injection molding process conditions, or improper post-processing of the product. 7.1 Causes 7.2 Solutions 7.1.1 Unstable electrical or hydraulic system of the machine. 7.2.1 Check for faults in electrical components or hydraulic systems; regularly clean elect...

Injection Molding Defects and Solutions -- Weld Line 2025-10-17

Weld Line: When two or more streams of molten resin meet and the temperature drops during flow, the resin at the junction fails to fully fuse or bond. This results in a fine line formed along the surface or inside the molded part at the point of convergence. 6.1 Causes 6.2 Solutions 6.1.1 Low nozzle temperature or low mold temperature. 6.2.1 Increase melt and mold temperatures to improve resin flo...

Injection Molding Defects and Solutions -- Delamination or Peeling 2025-10-17

Delamination or Peeling: This defect occurs when foreign materials are mixed into the raw material, the mold temperature is too low, or the material compatibility is poor. Excessive shear stress during melt flow along the mold surface causes the material to separate into thin layers, resulting in peeling or delamination. 5.1 Causes 5.2 Solutions 5.1.1 Material not properly dried. 5.2.1 Dry the mat...

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