Causes and Solutions for Insufficient Material in Plastic Products

CAD Product Design
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1. Causes of Insufficient Material

  • Insufficient pressure in the injection molding machine or too short injection time.
  • Insufficient pressure inside the mold, meaning excessive pressure loss during the injection cycle.
  • Poor material flowability.
  • Poor air venting inside the mold cavity.
  • Imbalanced gates (in the case of multi-cavity molds).
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2. Related Knowledge

  • Insufficient material is generally determined by the shape of the mold and the flowability of the material. When it is caused by the molding conditions, the molding parameters should be adjusted to improve material flowability. This includes increasing the mold temperature, barrel temperature, injection speed, and injection pressure.
  • When the venting design of the cavity is inadequate, it becomes difficult for air to escape from the mold, leading not only to insufficient material in the product but also to defects like burn marks and weld lines.
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3. Solutions

  • Immediate: Increase the mold and barrel temperatures, raise the injection pressure, and add venting grooves (0.02–0.04 mm deep and 5–10 mm wide) on the parting surface.
  • Short-term: Enlarge the gate and flash (overflow edge). In cases with multiple cavities, if a specific cavity shows insufficient material, enlarge the gate for that cavity, adjust the flash configuration, add venting pins, and improve the mold’s surface finish.
  • Long-term: Avoid differences in product thickness during design. Add gates to areas where the product is thicker, understand the usage scenarios of the product, and if suitable, use materials with better flowability.
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4. Due to Material Differences
For resins like polycarbonate (PC), polyphenylene ether (PPO), and polyethylene terephthalate (commonly known as polyester resin, PETP), the material’s flowability significantly worsens when the mold temperature is not high. In such cases, it is necessary to heat the mold to above 80°C using a mold temperature controller.

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5. Reference Considerations
Material Flowability: The term “material flowability” generally refers to the weight of the material flowing into the injection port over a specified time at a given temperature and pressure. It indicates the material’s flow performance, such as its melt flow index.

Methods for Measuring Resin Flowability: The spiral flow (or vortex) mold can be used to determine the length of resin filling.

(1) The holding pressure time during injection does not correlate with the filling length if it exceeds a certain duration; however, if it is too short, it can lead to insufficient filling (insufficient material).

(2) The retention time of the same material in the barrel is unrelated.

(3) If the injection speed is too slow, filling becomes inadequate, although speeds above a certain threshold have minimal impact.

(4) Higher mold temperatures are preferable and have a minimal effect.

(5) If there is a slight excess in the screw’s plasticizing stroke, the filling length increases.

(6) Injection pressure generally exhibits a linear relationship with filling length.

(7) Within an appropriate range for material temperature during molding, there is generally a linear proportional relationship between temperature and filling length.

(8) The thickness of the cavity generally exhibits a linear proportional relationship with filling length.

Filling Maximum Length (L): The ratio of filling maximum length (L) to cavity thickness (T), denoted as L/T, serves as a standard for measuring the flowability of the molding material.

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  1. Filling Maximum Length (L): The ratio of filling maximum length (L) to cavity thickness (T), denoted as L/T, serves as a standard for measuring the flowability of the molding material.

Material L/T Ratio

Material T
PVC（hard） 150-100
PVC（soft） 240-160
PC 150-100
PA6 320-200
PS 200-220
PP 280-160
PE 280-200