Did you know that a very large variety of plastic products is made by a process known as injection molding? These items include washers, valves, knobs, pulleys, power tools, bottle caps, gears, toys, keyboards,computer monitors, car panels, furniture and many more. Injection molding is an economical, efficient way of manufacturing plastic items on a mass scale. The size and specifications of each machine varies with the product to be manufactured.
The credit of inventing this process goes to John Wesley Hyatt. He created billiards balls during 1868 by just injecting celluloid in a mold. Subsequently, he made an injection molding machine by incorporating a plunger. In 1946, one more inventor, named James Hendry, modified Hyatt’s design to fashion an injection molding machine having a screw.
The present industry producing plastic goods employs both, the plunger type and the screw type machines. The chief difference between the two is the manner in which plastic gets transferred to a given mold. Screw type injection molding machines are more popular because of the convenience they offer.
The process of molding employs plastic resins in a granular or pallet form. The selection of plastic to be used varies with the type of item to be produced, its end use, and the overall budget. There are numerous kinds of plastics available, but not all are safe for human use. Plastics that are often used in case of injection molding are polystyrene, polypropylene, polycarbonate, polyamide, polyethylene, polyvinyl chloride, acrylic, Teflon®, and Delrin®.
Being non-degradable, plastics can’t be treated as environment-friendly. However, the process of injection molding helps reducing waste, as it allows us to reuse the same plastic repeatedly.
Granules or pallets of plastic are fed to the hopper of the machine. The hopper is a big container having an opening through which plastic is moved to a heating cylinder, where pallets are heated to a temperature that melts the plastic.
The plunger or screw then forces the melted plastic to pass via a nozzle into the mold, which is the opposite of the component to be produced. A mold may have one or more cavities for the simultaneous production of many components. Long-lasting costly steel may be used for making molds. Molds made from beryllium-alloy and aluminum are quite economical, but don’t last for long.
The selection of correct plastic and the metal for the mold is decided by the item to be produced, its desired durability and the overall cost. The normal practice for manufacturers is to employ not so expensive metal for making prototypes of molds, but long-lasting, accurately machined molds are employed for the mass production of items.
Molten plastic gets cooled in the mold and takes the shape of the mold when getting hardened. Later, the mold is thrown open to drive out the component. It may then be packed for shipping or subjected to additional operations. The entire process of molding is finished in a couple of minutes and is done automatically.
The process of injection molding enables manufacturers to produce thousands of items in a short span of time. Moreover, the labor cost is also low, and precision components can also be produced by this process. The only limitation of the process of injection molding using machines is that its initial cost and maintenance, which is rather high.