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  • Writer's pictureKausarali Dalal

A layman's guide to Plastic Injection Moulding

Updated: Nov 21, 2020

Injection moulding is the oldest and most commonly used process for mass manufacturing of plastic parts across various industries like electrical, automotive, medical, packaging, homeware, kitchenware, toys and many more. Probably the device you are using currently to read this blog also has a plastic part which is produced through injection moulding and that's why through the blog I would like to shed some light over this process. The process has three main requirements:

  1. Plastic Raw Material

  2. Injection Moulding Machine

  3. Mould

By principle, injection moulding involves, heating the plastic to a molten stage, injecting that into the mould and letting it cool until the final product is formed. However in reality this process gets a lot more complicated due to the difference in properties of plastics. Plastics are of different types, and each one of them have certain characteristic properties. Among them PE (Polyethylene), ABS (Acrylonitrile butadiene styrene), PP (Polypropylene) are the most commonly found varieties. For injection molding, these materials are received in the form of plastic granules or pellets.

Plastic pellets/granules
Plastic pellets/granules

The granules are loaded into the hopper which is a part of the injection moulding machine. It holds the pellets and then transfers them into the barrel and screw assembly of the machine where it is further heated and brought to a molten state.

Injection moulding machine working
Injection moulding machine working

This barrel and screw assembly is covered by heaters that are responsible for heating the plastic uniformly and bringing it to a molten state. The screw brings the molten plastic forward into the injection chamber after which it is injected into the mold.

The mould is made according to the design specifications of the part one wishes to produce. In the injection moulding industry, moulds are also called as dies. The mould is fit onto the machine between the movable platen and stationary platen. Once the molten plastic is injected into the mould, the plastic cools taking the shape of the moulds cavity. The movable platen opens up after the cooling time is complete and the part is removed or automatically ejected. At the time when the plastic is cooling inside the mould, the process of converting the plastic granules to a molten state and bringing it into the injection chamber is repeated.

Mould used for injection molding
Mould used for injection molding

The quality of steel used, number of cavities required and complexity of part to be produced determine the mould cost. Building a mould for your product is only beneficial when high volumes are to be produced as that brings the per unit cost low. For product still at an introductory stage, options like 3D printing or Vacuum casting could be looked at.

eg. Suppose a part is to be produced and the quantity required is only 100 pieces. Let's estimate the price for building a mould would come upto $1000. In this case the per unit cost of the mould would come upto $10/ unit. However if this product would be produced through 3D printing, its price would be reduced by almost half as the mould cost would be eliminated. On the other hand if the quantity for the part would be 1000 pieces, the mould price would still remain $1000 but the cost per unit would be $1.

Another area which differentiates 3D printing from Injection moulding is time. Injection moulding is a much faster process of production. Suppose the part weighs 10 grams, producing this part through injection moulding will take a merely seconds but 3D printing would end up taking a couple of minutes.

 Injection Molding Machine
Injection Molding Machine

Lastly, Injection moulding machines.

These machines come in various sizes ranging from 5 tonnes to 4000 tonnes, Here unit 'tonnes' does not determine the machines weight but the clamping pressure which the machine can apply. In simple words, clamping pressure is the pressure needed to keep the mould closed when molten plastic is being injected into the mould. The size of the part to be produced, area of the mould and number of cavities are just a few factors which need to be taken into consideration before deciding which tonnage machine will be required. Within the industry the thumb rule for choosing the appropriate injection moulding machine is 2-5 ton of clamping pressure per sq. inch of the mould projected area. Smaller tonnage machines are recommended for producing small plastic parts or micro moulding, whereas larger machines can easily accommodate, larger molds or multi cavity molds.

Technology has made injection moulding a breezy process, Companies like Engel, Ferromatik Milacron, Boy and Toshiba who manufacture injection moulding machines, are constantly working towards innovating and upgrading their machines to best suit current technological requirements. What makes injection moulding complex is understanding the different types of plastics, their properties and suitability towards a specific end user application, manufacturing the mould and understanding how the material will flow through the mould.

Dalal Plastics Pvt Ltd offers a range of services to reduce such complexities for its customer. Our manufacturing plants located in Navi Mumbai, Hyderabad and Aurangabad makes it possible to deliver to customers located across India and other countries. 5 decades of experience in this industry has made us Turnkey manufacturers for handling all your project needs when it comes to injection moulding. Right from designing the mould for your product, developing it, procuring the necessary raw materials, production of the part and ultimately assembling it and delivering it to our customers. Our mould designers are also capable of 3D printing services before manufacturing the mould to help you at prototyping and further enhancing your new product developments.

We are the one stop solution to all your injection moulding needs.

Thank you for your time.

1 Comment

Feb 23, 2023

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