Plastic Injection Moulding - A Detailed Overview

The history of injection moulding dates back to around 19th century. Ever since the invention of the injection, moulding machines have undergone several modifications to attain the form widely used today. Initially, the injection moulding methods were based on the die casting technology where immense pressure was applied to obtain the desired shapes. The plastic injection manufacturing became widely popular after the Reciprocating Screw moulding machine acquired the patent rights in 1956.

Raw Materials

There are several kinds of raw materials used for the manufacturing of the plastic injections. However, the thermosetting plastic, elastomers and thermoplastic polymers (resins) are widely used in the production process due the presence of greater viscosity in these materials.

Equipment

The Plastic injection moulding machines have basic component parts such as material hopper, heating unit, plunger etc. These machine parts are used to build pressure and keep the moulds in proper order to give the perfect shape once the molten material is poured inside it. They are also called presses, working in accordance with the tonnage ratings. Tonnage is the capability of the machine to exert clamping force during the manufacturing process to keep the moulds in closed position. The tonnage may range between 5 tons to more than 9000 tons depending upon the rigidity of the raw materials and the projected area of the moulding parts.

Plastic Injection Moulding Process

Melting Polymers: There is a broad and cylindrical melting unit in the injection-moulding machine, where the polymer is converted into liquid under high temperature and pressure. The polymer is filled in an auger, which has an opening at the bottom. The auger is introduced into the melting unit using a hydraulic motor. A valve system at the bottom of the cylinder restricts the passage of the liquid into moulds.

Pouring the Liquid Material into the Moulds

Once the heating process is over, the auger is pushed further to pour the liquid polymer in to the moulds to give the requisite shape to the injections. The moulds are compressed under huge pressure to keep them intact and in proper position. During this process, the liquid is poured twice or more to ensure there are no air spaces left.

Cooling

 After the moulding, the entire mould is introduced to cooling for compact solidification of the plastic injections, which consumes the major time-period during the entire manufacturing process. The cooling is done by passing air or water over the heated moulds or introducing cold water through small holes on the mould surface.

De-moulding

Once the cooling process is over, the compact plastic injections are ready for removal from the moulds. The clamp on the mould is unlocked to open the mould and derive the injection. The entire process is completed and the mould is now ready for the next unit manufacturing.

Plastic injections are affordable compared to other forms of injection. The cost of production mainly depends on the type of machineries. In the long run, this is a lucrative business. The plastic injection moulds are widely used in the manufacture of a number of other plastic products.

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Injection Moulding - Guidelines and Advantages

Injection Moulding - What is this?

Injection moulding is one of the most popular ways to create plastic products. For example, you are having a manufacturing company and you need to manufacture a large amount of plastic products in a short time period, also those products should be in same size. Then you could use plastic injection moulding to manufacture your products faster than ever before. The best thing about it is that it is cost effective and this moulding also requires little supervision from staff. Injection moulding machine works in a few stages. In the first stage, the given plastic is melted and then that melted plastic is inserted into a mould machine. That mould machine is then squeezed together to create a shape for your plastic product. The second stage is cooling stage. Here, the moulding machine will cool all your formed plastic products.

Nowadays many people are using this type of moulding to make their product faster and also the injection moulding is more accurate. All the parts in the moulding machine are computerized that means all your work will run like clockwork and the outcome will be more accurate. Handmade plastic products can be a nightmare and sometimes will go wrong. Injection moulding products are always better than our handmade plastic products. Nowadays most of the car manufacturing companies use this injection moulding a lot. For example, the lid of your car's radiator will be manufactured using this technology. There are millions of cars made every year all over the world and therefore this sort of process is required to make sure accuracy and speed.

Some Design Guidelines for plastic injection moulding:

Now we are going to see 5 more design techniques for injection moulding.
1# You should avoid small holes when you are designing a perfect product. Because these small holes are too intricate to mould, these small holes also lead to tool breakage.
2# If you want any hole in your product, through-holes are best.
3# sometimes there will be a variance in surface consistency or angle. This variance is totally depending on the type of material used. Sometimes this variance is little consequence for some products. But if your moulding design requires an exact surface or angle then you should be careful when designing that product.
4# You should use the uniform screw sizes, because they will make your manufactured product much more accessible to many people.
5# Each additional component in your manufactured product will increase the risk of anything going wrong. So always you should make your product more and more simple. Then only it will be easy to handle.

Advantages injection moulding:

1# This injection moulding allows you to create more products within a short time period.
2# When manufacturing your product you may use fillers, these will increase product strength.
3# You can use more than one material.
4# Human work is reduced
5# Design flexibility
6# The outcome will be more accurate than handmade plastic products.

These are some design guidelines and advantages about injection moulding.

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The complete cycle of Plastic Injection Moulding Explained in Detail

Plastics are the cheapest raw materials available in the market. Plastic gets in to proper shape and size by the process of Injection Moulding. Plastic injection moulding is the process of manufacturing of plastic components. Plastic is an economical material which is used in various applications. Plastic Injection moulding is a process of forcing molten plastic by the application of pressure.

Plastic in the form of powder or liquid is fed through hopper into the barrel which is heated up to certain temperatures where it is mixed and then forced through a nozzle with the help of a plunger to the mould cavity where it hardens by cooling and sets to the configuration of the mould. The plunger is used to force the heated raw material through the nozzle. The plunger which is usually used is a ram or a screw-type. The mould is designed and made from steel or aluminium, and then precision machined forming the desired parts. Plastic Injection moulding is used to manufacture various parts, varying from small components to whole body of a vehicle. Manufacturing a mould is very expensive, so a mould is only used for mass productions. Moulding is the process of shaping a raw-material into the desired shape, by applying pressure. A mould is a hollow block which is filled with a liquid like plastic, glass or a rubber. Plastic injection moulding is one of the types of moulding which involves injecting a raw material into a pattern and applying certain factors like heat and pressure.

CYCLE OF INJECTION MOULDING

The sequence of events through which a raw material is converted into a finished part is known as the injection mould cycle. It includes the supply of granules being fed into a hopper to a heated chamber, where the granules are melted into the form of a liquid. Then a plunger is used to force the liquid through a nozzle to the mould. These processes are repeated again to form a cycle for mass production of products.

TYPES OF PLASTIC INJECTION MOULDING

The above described method is the conventional method of plastic injection moulding, although various other unconventional processes include co-injection moulding, fusible core injection method, injection-compression moulding, thin-wall moulding, powder injection moulding and many more.

With Plastic Injection moulding, a variety of plastic goods can be manufactured. Huge numbers of identical products can be manufactured with this process. A design engineer considers lot of parameters and venture specifications and designs accordingly. Manufacturing problems can be prevented right at the initial stage of design itself.

There are more than 30,000 unique products that can be moulded using plastic injection process. Its advantages include repeatable high tolerances, low labour cost, high production rates, easy to finish parts after moulding and the ability to use extensive range of materials. The major advantage of plastic injection moulding is that products with complex geometry can be made which is not possible in any other processes. As long as there is a need for plastic components of complex shapes and sizes, the business of manufacturing plastics will continue to grow.

How The Process of Plastic Injection Moulding Works

One of the most commonly used processes in the production of plastic items is the process most often referred to as ‘Injection Moulding’. There are several reasons as to why the process of plastic injection moulding is very popular, however one of the most common reasons given as to its popularity is the fact that as a means of goods production, the process can be used to produce enormous quantities of identically shaped plastic items of a variety of purposes. The goods produced by this process range from simple and disposable consumer goods to essential engineering components of high precision.

The Basic Process

In the most basic terms, the process of Plastic Injection Moulding involves the introduction of a certain material into the moulding machine (most typically via a ‘hopper’). The moulding machine is most commonly made up of a heated barrel (equipped with a reciprocating screw, usually driven by a hydraulic or an electric motor, which usually then feeds molten plastic into a temperature controlled split mould via a comprehensive network of gates and runners).

The polymer is melted by the reciprocating screw, which also then acts as a ram during the injection process. The shearing action of the rotating screw on the plastic assists in providing even more heat that can be utilised in this part of the process before the polymer is then injected into a mould which has been created in accordance to the required dimensions of the finished product desired by the client or customer. The pressure involved in the production process when the polymer is injected into the mould is extremely high, possibly even reaching 1000 atmospheres depending on the material being used in the process.

There are many companies and firms who specialise in producing important components and items made from plastic via the process of injection moulding. There is also a large number of companies which specialise in the production and supply of the moulds used in the injection moulding process.

The importance of the process of Plastic Injection Moulding is demonstrated by the fact that the service provided by the companies practising the process is in great demand by a considerable number of customers, including those in specialist industries such as aerospace and defence which require necessary specialist plastic goods and items produced by this process. The process is most commonly used in the production of the majority of thermoplastics such as polystyrene and nylon.