Uneven Color or Discoloration: Uneven color on the surface of a plastic part may result from poor dispersion of pigments or fillers, or from discoloration of the plastic or pigments. If the entire plastic part shows uneven color, it is usually caused by poor thermal stability of the plastic. When the color is uneven at weld lines, it is related to the nature of the pigment.  Causes Solutions ...

Poor Demolding / Ejection Defects: Poor demolding occurs when the mold structure is unreasonable, manufacturing precision is insufficient, or overfilling makes it difficult to eject the part. It can also cause the part to be scratched, stretched, or deformed after ejection. 16.1 Causes 16.2 Solutions 16.1.1 Mold surface not smooth. 16.2.1 Polish the mold to meet surface finish requirements; reduce...

Cracks: Cracks occur when poor part design or inferior plastic material properties cause high internal stress, uneven cooling, poor demolding, or other defects. These stresses lead to cracks forming at stress concentration points or near the gate. Under overload or the influence of solvents, these cracks may propagate, resulting in part failure. No. Causes Solutions 15.1.1 Low material temperature...

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...

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...

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....

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...

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 ...

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, ...

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...