The injection molding process may seem easy on the surface; however, it can be more complicated than it looks. Although the mold has been designed and the plastic injection machine is functioning well, if the process is not closely monitored and controlled, it may affect the outcome of the finished product.
Having an in-depth understanding of the injection molding process will help manufacturers know the best plastic components to use to produce quality plastic parts.
Step 1: Selecting The Right Thermoplastic And Mold
Before the actual process begins, manufacturers must be sure of how the thermoplastic and mold interact together. Not all plastics are applicable in every mold design. Depending on the requirements, mold tools can be designed to create several or complex parts. These molds are often made from solid materials like steel or aluminum. Hence, choosing suitable thermoplastic is imperative so there will not be any reaction with the mold. Each thermoplastic has unique properties, and their properties will determine where and how to use them. Once the thermoplastic and mold are tested and declared compatible, the molding process can begin.
Step 2: Feeding And Melting The Thermoplastic
Plastic injection machines can be powered by hydraulics or electricity, although electric-powered injection molding machines save more energy costs. The basic plastic injection machine consists of a feeder, a barrel(with a large injection screw attached), and a mold tool. The process begins by feeding raw pellets of the chosen thermoplastics into the hopper. Then the pellets are fed into the barrel of the machine. The heat from the barrel gradually melts the thermoplastic into a molten state. Maintaining the right temperature will ensure the plastic can be injected seamlessly and the final part is formed correctly.
Step 3: Injecting The Plastic Into The Mold
After the molten plastic gets to the end of the barrel, the gate closes, and the screw moves back. This gathers a set amount of plastic and prepares the pressure to insert it into a mold. The mold closes and is held under high pressure, called clamp pressure. This particular process should be closely monitored so that no plastic is allowed to escape during the injection.
Step 4: Holding And Cooling Time
After the plastic is injected into the mold, it is held under clamp pressure for some time. The holding time could be seconds short or minutes long, depending on the thermoplastic used. The holding time ensured that the plastic took the entire form and shape of the mold so that it could come out correctly.
After the holding phase, the screw releases pressure and cools the plastic in the mold. The cooling time can also be from a few seconds to a few minutes. The cooling time helps the product set correctly in the mold before it’s removed from the mold.
Step 5: Ejection And Finishing Processes
After the holding and cooling time, the part is ejected from the mold. After ejection, the part is dropped into a compartment at the end of the machine. Sometimes, the products or items can only be final when they go through the last finishing process, like polishing, dying, and removing excess plastics. Once these processes are complete, the products will be ready, packed, and sent out for distribution.