It is the most common manufacturing technique employed in the making of the plastic objects we use each day, ranging from automotive dashboards to bottle caps and children’s toys.
The process of plastic injection molding is used for mass production and prototyping because of its ability to yield high runs at close tolerances. Injection molding is commonly used in the consumer, food service, medical, plumbing, computer and automotive industries, as almost any plastic object can be made from a plastic injection mold. Plastic molding has many advantages including: fast turnaround times, low labor costs and the ability to make complex plastic products.
Waste produced during the molding process is minimal because material is injected into a precisely cut mould. There may be a joining line where the two halves of the mold cavity meet, but the amount wasted is negligible and can be removed during finishing. Any other plastic material waste can easily be recycled for use in further production runs.
Another advantage of plastic injection molding is the wide variety of materials available for use in the manufacturing process. Material choice is usually dependent on the intended use and function of the product. Most molded plastic products are made from thermoplastics, which become more pliable when heated and rigid when cooled. Thermosets and elastomers, like rubber, are also used in the injection molding process.
The basic machinery used in the process of plastic injection molding consists of a hopper – where the plastic pellets are placed prior to being heated. The plastic material is then fed into a heating unit where it is heated and mixed until molten, at which point dyes or other chemical agents can be added to change the final appearance and feel of the product. The two halves of the injection mold are clamped together under pressure and then the molten plastic is injected into the mold – an inverse of the desired shape of the part being made.
The plastic is then left for a short time to cool and harden before the two halves are separated and the plastic part is ejected out of the mold using ejector pins or rods. Plastic injection molding is a highly beneficial manufacturing choice, yet a disadvantage to be considered is the initial expense of the plastic injection mold that will need to be designed and engineered. However, the many advantages outweigh this expense for many manufacturers.