Principle of Injection Molding
Injection molding is a widely used manufacturing process for producing plastic parts in large volumes. Its core principle is melting plastic material, injecting it into a closed mold cavity under high pressure, then cooling and solidifying the material to replicate the mold’s shape.
Key Working Principles
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Plasticization (Melting)
Plastic pellets are fed into a heated barrel of an injection machine. As the pellets move forward (driven by a rotating screw), they are gradually melted by the barrel’s heat and shear friction, forming a homogeneous molten plastic.
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Injection (Filling the Mold)
The molten plastic is pushed by the screw (or plunger) into a precision-designed mold cavity at high pressure (typically 50–200 MPa) and speed. This ensures the melt fills every detail of the mold (e.g., complex shapes, fine textures).
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Packing & Holding
After the mold cavity is filled, the machine maintains pressure (the "holding pressure") for a short time. This compensates for the shrinkage of the plastic as it cools, ensuring the final part matches the mold’s dimensions precisely.
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Cooling & Solidification
The molten plastic in the mold is cooled (via cooling channels in the mold) until it solidifies into a rigid part. The cooling time depends on the plastic’s thickness and thermal properties.
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Ejection
Once the part is fully solidified, the mold opens, and ejector pins (or other mechanisms) push the finished part out of the mold cavity.
In short, injection molding transforms solid plastic pellets into custom-shaped parts by melting → shaping (via mold) → solidifying—enabling high-precision, mass production of complex plastic components.
![mold]( "mold")
