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Injection Molding Process

Rajib Singha

Injection molding is one of the most important and common manufacturing processes employed in many industries. Know what it comprises here.
Have you ever wondered about how are the parts of thermostatic and thermosetting plastic materials are fabricated or produced? The manufacturing process which is used for the fabrication of plastic parts, is the simple definition of injection molding process, which came into existence in the 1930s.
Through this technique, a wide variety of products have been manufactured with different shapes and sizes, having varying complexity and application.
The basic components which are used in this process consist of an injection molding machine, raw plastic material and a mold. The steps which take place in this process include clamping, injection, cooling and ejection. Each of these steps have been described in brief here.


The clamping unit closes the two halves of the mold. This is done before the material is injected into the mold. Both the halves are attached to the injection molding machine. Out of the two halves, one is allowed to slide. When the material is being injected, the mold must be securely closed. This is done by the clamping unit that is powered hydraulically.


The next step is injection, wherein, the raw plastic material is fed into the molding machine. Here, the material is melted with the application of heat and pressure. Once melted, the plastic makes its way into the mold and it is kept in place with the pressure built by the clamping unit.
The flow of the molten plastic into the mold is a bit complex and changing process. This makes it difficult to derive an exact injection time.


Here, the molten plastic gradually starts cooling as it starts making contact with the interior surfaces of the mold. The cooling will transform the raw plastic into the desired part. In order to make up any amount of shrinkage of the part, additional material is allowed to flow into the mold.
The mold can be released or unclosed, only post the cooling time has expired. This time is determined by the thermodynamic properties which the plastic hold and the maximum wall thickness of the part that has formed.


This deals with the ejection system which is used to eject the cooled part from the mold. This system lies at the rear half of the mold. During the cooling period, the part shrinks and tend to attach to the mold. So, in order to eject the part out of the mold, external force must be applied.
In order to make the ejection process easier, a mold release agent can be sprayed onto the surface of the mold cavity. This can be done before the injection process is started.
The injection molding process is related to what is known as an injection blow molding process, as the later is part injection and part blow molding. It is usually used in the production of plastic bottles, jugs, jars and other hollow articles.
Plastic housings which are used in household appliances, consumer electronics, power tools, buckets, small plastic toys, etc. are among the myriad of products produced with the help of the injection molding process.