Plastic injection molding requires three primary components – an injection molding machine, a mold, and raw plastic material. Molds for plastic injection consist of high strength aluminum and steel components that have been machined to operate in two halves. The mold halves come together inside the molding machine to form your custom plastic part.
The machine injects molten plastic into the mold, where it solidifies to become the final product. The injection molding process is actually a complex process with many variables of speed, time, temperatures and pressures. The complete process cycle for making each custom part can range from no more than a few seconds to several minutes. Below we offer you a very brief explanation of four steps of the molding process.
Before the plastic is injected into the mold, the machine closes the two halves of the injection mold with tremendous forces which prevent the mold from opening during the plastic injection step of the process.
Raw plastic, generally in the form of small pellets, is fed into the injection molding machine at the feed zone area of a reciprocating screw. The plastic material heats up by temperature and compression as the screw conveys the plastic pellets through heated zones of the machine barrel. The amount of melted plastic that is conveyed to the front of the screw is a strictly controlled dosage because that will be the amount of plastic which will become the final part after injection. Once the proper dosage of melted plastic reaches the front of the screw and the mold is fully clamped, the machine injects it into the mold, pushing it into the endpoints of the mold cavity under high pressures.
As soon as the molten plastic contacts the internal mold surfaces, it begins to cool. The cooling process solidifies the shape and rigidity of the newly molded plastic part. The cooling time requirements for every plastic molded part depends on the thermodynamic properties of the plastic, the wall thickness of the part, and the dimensional requirements for the finished part.
After the part is cooled inside the mold and the screw has prepared a new shot of plastic for the next part, the machine will unclamp and open the plastic injection mold. The machine is equipped with mechanical provisions that work with mechanical features designed within the plastic injection mold to eject the part. The custom molded part is pushed out of the mold during this stage and once the new part is fully ejected, the mold is ready for use on the next part.
Many plastic molded parts are fully completed after they are ejected from the mold and simply fall into their final carton to be shipped in, and other plastic part designs require post operations after they are injection molded. Every custom injection molding project is different!
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