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Injection molding process and application cases

Compression injection molding: (injection compression molding) is an advanced form of traditional injection molding.
Advantages: It can increase the flow length ratio of injection molded parts; use smaller clamping force and injection molding pressure; reduce material internal stress; and improve processing productivity.
Injection compression molding is suitable for products made of various thermoplastic engineering plastics, such as large-sized curved parts, thin-walled, miniaturized parts, optical lenses, and parts with good impact resistance requirements.

As we all know, optical lenses require very high geometric precision, including accurate dimensions and small deformation. However, it is difficult for general injection molding to meet this requirement.

Vented Injection Molding: The purpose of the “venting” procedure is to give the volatile fission products produced during the polymerization-solidification process a chance to escape. If these gases cannot be discharged from the mold cavity, the result will be incomplete products or bubbles in the closure.


  1. When the injection volume reaches approximately 80%-95%, injection molding is paused;
  2. Open the mold approximately 0.1-0.2mm to allow volatile gases to escape;
  3. Close the mold twice and inject the remaining injection volume.

Product: Filter plate for filter press 1500×1500
Number of holes: 1 out of 1
Raw materials: PP +6% (flow index 0.2 high viscosity)
Injection molding machine: BU4000 with 6800T

Low pressure injection molding
The low-pressure injection molding process is a packaging process that uses very low injection pressure to inject hot-melt materials into the mold and solidify them quickly. It uses the excellent sealing and excellent physical and chemical properties of the hot-melt materials to achieve insulation, temperature resistance, impact resistance, Vibration reduction, moisture-proof, waterproof, dust-proof, chemical corrosion resistance and other functions play a good role in protecting electronic components.

The picture shows the mold design of low pressure injection molding

The sensitivity of leather, wood, fiber fabrics, and PVC/TPO/PUR decorative films requires lower injection pressure.

Car pedal sensor 
The picture shows the car pedal sensor. The picture below shows the component before and after injection molding.

Gas-assisted injection molding: (Gas-assisted injection molding)

GAIM process:
Injection molding stage (part) – inflation stage (N2) – gas pressure holding stage (cooling air pressure remains unchanged) – pressure reduction stage – demoulding stage

GAIM device consists of:
Gas pressure generator, gas control unit, gas injection device, gas recovery device

  1. Water-assisted injection molding
    Water-assisted injection molding technology is an advanced injection molding process that after injecting part of the melt into the mold cavity, high-pressure water is injected into the melt through equipment to finally shape the workpiece.
    Due to the incompressibility of water, the front end of the water forms a solid interface, squeezing the inner wall of the product into a cavity, and the front end of the water also plays a role in rapid cooling. Therefore, water assistance has many advantages that gas assistance cannot match. Research and applications have shown that water assistance can produce thinner and more uniform cavity walls, and the inner wall surface of the flow channel is very smooth. Especially for thick-walled workpieces, the cooling time of water-assisted cooling can be significantly reduced compared with gas-assisted cooling.

The basic process of high-gloss injection molding is to use high-temperature and high-pressure water vapor to rapidly heat the mold surface before injection molding, so that the surface temperature of the mold cavity reaches above the glass transition temperature (Tg) of the resin plastic, and then the plasticized The plastic melt is injected into the closed mold cavity. During the injection stage, the mold temperature is kept constant by high-temperature and high-pressure water vapor. When the injection is completed, the air supply is stopped, and the water vapor in the pipe is blown away by the air pressure of the air pipe. Then cooling water is introduced to cool the mold. The temperature drops rapidly until it cools down and the mold is opened to take out the product.

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