The injection moulding is a process for manufacturing a product by injecting molten material into a mould. The material of the mould is mostly metal.
In this process the material is injected into a heated barrel and mixed and then injected into a mould. After injected into a mould the material is cool down and gets it strength. The mould is mainly made with metals like aluminum or steel.
The first injection moulding machine was patented in 1872 by an American inventor John Wesley Hyatt and his brother Isaiah. The design is basic and much simpler than current machines.
The machine uses a hypodermic needle, use plunger to inject plastic into a heated cylinder to the mould. It is used to made products like buttons, combs and collar stays.
The growth of injection moulding products gets hike after American inventor James Watson Hendry invent the screw injection moulding machine. With this technique, the materials can be mixed to get the desired product before an injection. Today all the modern day machine uses screw injection.
How PLASTIC Moulding Works
The moulds are closes. After that, the heated plastic material is injected into mould. When the melted material is entered into mould the air flows through vents in injection pins.
After the mould is filled the mould is left for some time to be cool and the time is fixed for hardening the material. This time depends on the resin is used and the thickness of the product. Every mould has internal cooling lines where water flows continuously to maintain the constant temperature.
In the cooling process, when the resin cools down the screw barrel retracts the material from the hopper. The next step is the mould is open and ejects the ready product. There is a large tub or bin to collect the ready product.
Material Use In Moulding Process
Now which material we can use? The most of materials are polymers generally known as resin and also thermoplastics, some of the thermosets and some elastomers. After 1995 the total numbers of injection moulding materials are increased at 750 per year. There are more than 18000 materials are available.
The materials are generally alloys and are a mixture of materials. It is depending on the product designer that which material they choose. Mostly the materials are choosing on the basis of strength, costs and other properties like when the material bent, heat deflection and water absorption.
The common examples of thermosetting plastics are epoxy and phenolic and the thermoplastic is nylon, polyethylene and polystyrene.
Machine For Moulding
The machine for injection moulding contains a material hopper, a screw-type plunger and a heating unit.
Use of Mould in Moulding Process
There is also used a mould commonly known as die is used to make plastic products. There are various materials are used to make a mould. The manufacturing cost of a mould is very high and steel moulds are more costly. The materials used for making mould are hardened steel, pre-hardened steel, aluminum and beryllium-copper alloy.