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What is injection molding?

Injection molding is a manufacturing process commonly used to make items ranging from plastic jewelry and toys to automotive body parts, mobile phone cases, water bottles and containers. Basically, many of the plastic parts we use in our daily lives are injection molded. This is a process of quickly creating a large number of identical plastic parts. The flexibility of shape and size achievable through the use of injection molding has been expanding the range of plastic designs and, thanks to design freedom and light weight, allows for a large number of alternatives to traditional materials.

How does it work?
The injection molding machine consists of three main components - the feed hopper, the screw and the heating barrel. The plastic pellets for the parts are fed through a hopper into a heated bucket. The plastic placed in the hopper is typically in powder or pellet form, although some resins (such as silicone rubber) may be liquid and may not require heating. The material is then melted by the friction of a reciprocating screw accompanying the heating belt. The molten plastic is then injected into the cavity through the nozzle - which seems easy, but injection molding is actually a very complicated process. In the mold cavity, the material cools and solidifies into a cavity structure. When the part is hardened, the movable platen of the mounting mold is opened and the part is ejected using the ejector pin.
The size of the injection molding machine can range from a clamping force of 5 tons to more than 6000. The higher the tonnage, the bigger the machine. In fact, injection molding machines are classified based on tonnage, or more specifically clamping force or pressure.
For instance, a machine capable of providing 110 tons of clamping pressure is rated at 110 tons. This pressure ensures that the mold remains closed during the injection process. Too small or too much pressure can lead to part quality problems and flashing, with extra material surfaces on the edges of the part. The viscosity of the plastic used is also affected by the pressure. MFI or melt flow index is a measure of the melt of a thermoplastic polymer that is easy to flow.
The larger the MFI, the higher the required tonnage. For example, suppose you have a 4-cavity mold, each part is a 5" x 5" x 0.2" square. First, you must calculate the projected area of the part. Using this mold, calculate 5" x 5" = 25 square inches ×4 cavities = 100 square inches of projected area. The estimated area calculation is required because it is the main variable affecting the clamping tonnage. If we use 10 MFI polypropylene, we usually use a projection of at least 2.5 tons per square inch. Therefore, for this mold, a 100 square inch projected area requires an injection molding machine with a size of at least 250 tons.
Another factor in determining the correct machine size is the injection size and mold size.
The main function of the clamping unit is to close and open the mold and to eject the part. The two most common fixtures are toggle clamps and hydraulic clamps. The switching jig is moved by the hydraulic cylinder. These clamps use mechanical connections to create greater force than hydraulic cylinders of the same size that are directly connected.
There are more foundations and foundations for the science and technology of injection molding, which we can introduce in a later blog post. However, it is worth mentioning that although the basic principles of injection molding remain the same, the more technology we introduce in existing fixtures and injection molding processes, the more complex it is in developing molds or building injection molding machines.

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