The process of forcing melted plastic in to a mold cavity is termed as Injection molding. After the plastic has cooled, the part can be ejected. This is useful when the parts are too complex or cost prohibitive to machine and with this process, many parts can be made at the same time, out of the same mold.

Possibilities of Injection molding

There are many injection-molded parts around us in the current day and age: the mouse and keyboard used to surf through for this information is made through plastic injection molding process. Some parts of the chair you are sitting on can be traced back to this process as well. Plastic handled screwdrivers are also made by injection molding wherein the metal part of the screwdriver was suspended in the mold as the plastic is forced in and after cooling, a complete screwdriver is ready.

Basics of Injection Molding

Making polymers is and shaping the plastic into useful objects is a fascinating and useful science, of which the most common method of shaping plastic resins is the process of injection molding. This is accomplished by large machines called injection-molding machines wherein resin is fed to the machine through the hopper. Colorants are mostly fed to the machine directly after the hopper and the resins enter the injection barrel by gravity though the feed throat. After entering into the barrel, the resin is heated to the appropriate melting temperature and injected into the mold by a reciprocating screw or a ram injector. The ram injector has to inject at least 20% of the total shot while a screw injector can inject as little as 5% of the total shot; thus, the screw injector is better suited for producing smaller parts.

Finer aspects of injection molding

The machine part that receives the plastic and shapes it appropriately is known as the mold. This is cooled constantly to a temperature that allows the resin to solidify and be cool to the touch. The mold plates are held together by hydraulic or mechanical force and this clamping force are defined as the injection pressure multiplied by the total cavity projected area. Molds are over designed depending on the resin to be used and each resin has a calculated shrinkage value associated with in.

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