Plastic Injection Molding

What is Compression Molding Process

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Compression molding​
Compression molding is a processing method that obtains the desired shape by pressing preheated raw materials into a closed mold cavity through external force, followed by curing or cooling. Its core steps include:
  1. Material Preheating: Heating sheet, granular or fibrous materials (such as phenolic resin, silicone rubber) to a softened state to shorten the molding cycle.
  2. Mold Pressurization: Using a hydraulic press or mechanical press (usually with a pressure of 10-50 MPa) to make the material fill the mold cavity and eliminate air bubbles.
  3. Curing and Shaping: Thermosetting materials undergo cross-linking reactions (curing time is about 1-15 minutes, temperature 120-200°C), while thermoplastic materials cool and harden.
This process is particularly suitable for high-filled materials (such as glass fiber reinforced plastics) and products with complex geometric shapes, such as automobile bumpers and electrical insulation components.

Process Flow and Key Parameters of Compression Molding

  1. Feeding Stage: Calculate the feeding amount according to the product volume. Excessive amount may lead to flash, while insufficient amount may cause material shortage. For example, producing a gear with a diameter of 30 cm requires accurate weighing with a tolerance of ±2% for resin powder.
  2. Pressing Stage: Pressure and time directly affect the product density. Taking carbon fiber composite materials as an example, it needs to be kept under 15 MPa pressure for 5 minutes to ensure uniform fiber distribution (data source: "Handbook of Composite Molding Technology").
  3. Post-Release Treatment: Some products need to trim flash or undergo secondary processing (such as drilling).

Advantages and Limitations of Compression Molding

  1. Advantages:
    • Low equipment cost (about 1/3 of that of injection molding machines), suitable for small-batch production.
    • Can process high-viscosity materials (such as BMC bulk molding compounds).
  2. Disadvantages:
    • Long cycle time (5-30 minutes per piece), less efficient than injection molding.
    • Complex structures may require split mold design, increasing mold difficulty.
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