How Does Injection Molding Work?

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Injection molding is a method of manufacturing parts from plastic. Plastic pellets are placed in a large hopper, which feeds the pellets into a heated chamber. The chamber melts the pellets and injects the liquefied plastic into a variety of molds, where the plastic cools and hardens into the appropriate shape. Once the big plastic injection has cooled, the piece is removed from the mold. Excess plastic is scraped away and recycled, and the finished piece is polished and cleaned. Injection molding takes place in large machines, and the necessary molds are purchased from specialty toolmakers, who build the molds from steel or aluminum.
The first step in the injection molding process is to feed plastic pellets into the hopper, which then feeds the pellets into the barrel. The barrel is heated and contains a reciprocating screw or a ram injector. A reciprocating screw is typically found in machines that produce smaller parts. The reciprocating screw crushes the pellets, making it easier for the plastic to be liquefied.