The thermoplastics injection molding process is the most common method used to process thermoplastics, due to its ability to fabricate parts with a range of design variances, from simple shapes to high precision parts of geometric complexity. Thermoplastics, also referred to as thermosoftening plastics, differ than other plastic materials due to their ability to become liquid when heated and to freeze into a glassy, solid state when cooled sufficiently.
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Thermoplastic polymers differ from thermosetting polymers as because thermoplastics can be remelted and remolded. As a result, thermoplastics are the most common type of plastic used in injection molding processes. The thermoplastic materials that are most often processed using this process are acrylonitrile butadiene styrene (ABS), polyamides (such as nylon), polycarbonate, fluoropolymers, polysulfones and polyacrylates. Common applications of thermoplastic injection molding include caps, fasteners, plugs, connectors, inserts, tubing and containers. A wide range of industries that utilize thermoplastic injection molding includes electronics, plumbing, medical, automotive, aerospace, manufacturing and telecommunications.
Thermoplastics injection molding utilizes three main types of injection molding machines. The first type is a hydraulic oil injection molding machine that uses the force of hydraulic fluids to move the mold through the machine. Next in popularity is the toggle plastic molding machine. Toggle machines use mechanical links to advance the mold in the machine. Hybrid hydraulic/toggle machines are beginning to emerge in the injection molded plastics industry. Hybrid machines are used to eliminate some of the problems of other injection plastic molding machines, such as slow processing rates of parts and rapid wear and tear of machines. No matter the differences in the machine, the process itself remains the same and begins by heating the barrel of the machine. Next, thermoplastic pellets or granules are fed into a hopper where a screw pushes them to the heated barrel. In the barrel, the pellets or granules are heated to the melting point. The molten thermoplastic material is then injected into the cavity of a split die chamber/mold, which is then clamped shut. The thermoplastic resin cools as water or other fluids circulate through the cooling system of the mold, extracting the heat. The molded thermoplastic part is held in the mold under high pressure until the part solidifies. The thermoplastic part is finally ejected from the plastic mold, and the process begins again.