Why Do Car Parts Mould Have Tiger Skin Patterns?

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Why Do Car Parts Mould Have Tiger Skin Patterns?

  According to statistics, 70% of injection molding defects are caused by unreasonable production conditions, structural design, and mold design. Tigerskin pattern is a common defect in injection molds of car parts mold manufacturers.

  The tiger skin pattern of the automobile injection mold refers to the arc-shaped stripes of the tiger skin pattern on the surface of the plastic part, and there are generally intervals between them. It is easy to appear on large-area plastic parts such as dashboards, bumpers, door panels, and internal parts with a long process.

  The reason for the formation of car parts mould manufacturer's tiger skin pattern: polymer material has viscoelasticity, and its volume shrinks under pressure. When the pressure is released, the volume will recover and expand. When the polymer melt is extruded through the die, the cross-sectional area of ​​the extrudate is larger than the cross-sectional area of ​​the die outlet, this phenomenon is called Doswell.

  In the injection molding of car parts mold manufacturers, when the plastic melt passes through a small gate, it will encounter a lot of resistance at the gate, which will cause the plastic to shrink greatly in the shunt pipe. Once through the gate, its volume will immediately expand, which will cause the expansion of the melt flow front, and the appearance of the plastic part will form a tiger skin line.

  Similarly, in the process of melt flow, the plastic parts are thinner, the cavity gap is small, the mold temperature is low, the flow fluctuation caused by the structure or process of the plastic parts is too large, and the injection speed is fast. This will lead to an increase in the resistance of the melt front, and the flow of the melt will be significantly slowed down or stagnated.

  At this time, the filled area has poor gloss and a narrow appearance. But at this time, the hot-melt keeps coming out of the gate, and the rubber system begins to absorb and store energy. When the energy accumulates to a certain level, it can break through the resistance of the front end of the molten rubber, and the melt begins to expand rapidly and jump forward. At this time, the newly filled area has a good gloss and a wide appearance.

  The more rubber elastomers in the plastic, the more likely this phenomenon will occur. Materials with poor toughness seldom have tiger-skin patterns. For example, in the molding process of reinforced materials, non-toughened nylon, polybutylene terephthalate, and other materials, tiger skin has few defects and contains ethylene propylene diene monomer (EPDM) and polyolefin elastomer (POE). ) ABS, HIPS, and PP materials such as rubber components are prone to tiger skin defects.