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Injection Molding

  • The method of forming objects from granular or powdered plastics, most often of the thermoplastic type, in which the materials is fed from a hopper to a heated chamber in which it is softened, after which a ram or screw forces the material into a mold. Pressure is maintained until the mass has hardened sufficiently for removal from the mold.

  • Injection molding is the most widely used polymeric fabrication process. It evolved from metal die casting, however, unlike molten metals, polymer melts have a high viscosity and can not simply be poured into a mold. Instead a large force must be used to inject the polymer into the hollow mold cavity. More melt must also be packed into the mold during solidification to avoid shrinkage in the mold. Identical parts are produced through a cyclic process involving the melting of a pellet or powder resin followed by the injection of the polymer melt into the hollow mold cavity under high pressure.

  • Injection molding can be used to form a wide variety of products. Complexity is virtually unlimited, sizes may range from very small to very large, and excellent control of tolerances is also possible. Most polymers may be injection molded, including thermoplastics, fiber reinforces thermoplastics, thermosetting plastics, and elastomers. Structural injection molding is also possible in which a core and skin may be made of different polymers. Reaction injection molding and liquid injection molding, which differ in the manner of mixing ingredients, involve the injection of liquid polyurethane systems that polymerize within the mold.
  • A method of manufacture (typically involving wood heads and face inserts) in which the material (ABS, epoxy, graphite, etc.) comprising the head is heated to a liquid state and injected under pressure into a mold. When the material hardens, it takes the shape of the mold into which it was injected

  • A hot, molten polymer is injected into a cold mold. A screw apparatus can be used to inject the polymer into the mold. After the part cools and solidifies, the mold is opened and the part is ejected. No chemical reaction occurs during the molding process. This molding process is termed injection molding.
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