Plastic Injection Moulding – Explained


You will be well aware what moulding is. Moulding can be precisely defined as giving a particular shape to something in a molten or plastic state. Plastics are widely used today instead of conventional glass, wood and other materials because of its high durability. These plastics are molded into desired shapes using various techniques. The plastic injection moulding is one of the cost effective moulding techniques available today.

Little history about Plastic injection moulding

The injection moulding process is not a new concept. It came into existence by 1872. By the introduction of plastic injection moulding, the plastic industry saw multi-billion dollar earnings, with 32 % of all plastics, by weight processed by injection moulding. This has made the plastic injection moulding the best moulding method ever available.

The Principle of Plastic Injection Moulding

Thermoplastics and thermosetting plastics are the two materials that is involved in the plastic injection moulding process. Some of the polymers used in injection moulding are Epoxy and Phenolic that comes under thermosetting plastics, whereas the nylon and polyethylene comes under the thermoplastics. In this process the liquefied plastic is fed into a heated barrel where the plastic granules are mixed and forced to form a mold cavity. Once this is done, the molded cavity is cooled and then hardened. The plastic moulding machine consists of the reciprocate screws to mix the plastic granules, while the moveable pattern molds the plastic into desired shape which takes place in the clamping part of the machine. The engineer designs the mould, and then a mold is manufactured by the mold maker either in aluminum or iron to make a desired part in a precision machine. Injection moulding is widely used for manufacturing variety of components from small parts to the entire components for vehicles.


Plastic injection moulding is used to produce many parts like bottle caps, containers, plastic combs, home appliances and most other plastic products that we use today. Injection moulding is the only technique for producing many idle products in large volume and the most common method in part manufacturing. Low labor costs, materials can be used in wide range, scrap losses are minimal and high tolerances are repeatable are some of the advantages of the injection moulding techniques.

Usage of Polymers

According to BBC, in 1995 approximately 18,000 different materials were used in this process and the number was increasing at an average rate of 750 per year. Materials are chosen by the product designers, from alloys or from the previously developed blend material that has exactly the vast properties. For injection moulding, the materials selected are based on their strength and function required for the final part. Also, the material used has different parameters for moulding and that has to be taken in account. The injection moulding process can be of different types, namely Co-injection moulding, Fusible core injection moulding, Gas-assisted injection moulding, In-mold decoration and in mold lamination, Microinjection moulding, Multiple live-feed injection moulding and with some other types.

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