Plastic injection molding is a cyclical manufacturing process that allows for cost efficient production of a mass number of identical parts made from either thermoplastic or thermoset materials. Depending on the material the major process steps are:
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Thermoplastic materials are commonly fed into the heated barrel of the machine in the form of pellets, where a screw conveys them forward creating shear heat to melt the material thoroughly. Once the desired amount of plastic has been plasticized it is injected into a mold under high pressure. As the material shrinks during cooling, a so called holding pressure is applied to counteract this volume contraction (shrinkage) for some time. After applying the holding pressure, the molded part further cools down to the demolding temperature, upon which, the mold opens and the part is either dropped out of the mold or removed by a robot. During the cooling time the injection unit of the machine melts the material for the next shot, which is injected once the mold is closed again. During injection the mold is held closed by the clamping unit of the machine applying a certain force to prevent the mold from being pushed open by the pressure/force created during filling the mold with plastic.