How Plastic Injection Molding Works
Plastic injection molding seems like an intimidating industrial process that only makes sophisticated products, but in reality it’s a very commonplace manufacturing technique used to make everything from Lego bricks to plastic tableware. The process works by injecting molten plastic into a mold, where it is then cooled to a solid state. The most commonly used plastics for injection molding are thermoplastics, which are polymers that turn molten under heat and solidify under cool temperatures. You can mix these polymers with other materials (such as recycled material, colorants or glitter), additives and fillers to create specific properties for your product or part.
To get started with the plastic injection molding process, a designer or specialized engineer needs to design a custom mold for the end product. A mold maker then builds the mold using metals such as steel or aluminium and constructs it with a variety of precision parts. A high-quality plastic injection mold can take months to make and can cost several thousand dollars. Because of these costs, it’s important to choose the right plastic for your project.
Once a custom mold has been made, it is mounted into an injection molding machine where the molten plastic will be injected and cooled. The machine is usually equipped with mechanical provisions that work with mechanical features built into the plastic injection mold to eject the new part from the mold once it has fully cooled.
There are a wide variety of plastics that can be used in injection molding, including all thermoplastics and some thermosets. Some of the most popular include ABS, which is a rigid and lightweight plastic known for its resistance to chemicals and extreme temperatures; PE, which is a flexible, inexpensive and eco-friendly plastic that’s often used in medical supplies and equipment; and TPE, which blends plastic with rubber to create a material that has both the properties of each.
When a part has been molded, the injection machine will stop injecting plastic and change from speed control to pressure control. When the injection reaches a transfer position, which is normally based on a 95-98% full cavity, the packing pressure will be applied. This completes cavity filling and compensates for thermal shrinkage, which is relatively high in most thermoplastics.
The injection mold is then unclamped and opened. The molded part is then removed from the mould and the process begins again. Because there is little or no waste created during the plastic injection molding process, it can be very cost-effective for long runs of a single plastic product or a large number of identical products.
Injection molding is also very environmentally friendly, since any unused plastic can be re-melted and reinjected into the mold, making it new again. This practice helps to reduce the need for raw material production and cuts down on landfill waste. It is for these reasons that many manufacturers use this type of manufacturing to produce their products. Plastic injection molding is a high-precision process that allows for tight tolerances, so your product will be consistent and accurate on both long and repeat runs.