A wide variety of products are manufactured using injection molding, which vary greatly in their size, complexity, and application. The injection molding process requires the use of an injection molding machine, raw plastic material, and a mold.
The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part. The steps in this process are described in greater detail in the next section.
Injection molding along with extrusion ranks as one of the prime processes for producing plastic articles. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods.
Injection Moulding Machine
A moulding machine, also known as an injection press, consists of two main parts: the injection unit and the clamping unit. Moulds can be fastened by injection machines in either a vertical or horizontal position, depending on the size or type of application required.
A choice of cold or hot runner systems can also be selected for carrying the plastic into the mould cavities. Again, this will depend on the product being manufactured.
There are various types of moulding machines classified by the various driving systems they use, including: hydraulic, mechanical, electric or hybrid machines.
Injection Mould Process
Although the manufacturing of plastic products using an injection mould may seem quite simple at first (the plastic material is injected into a mould, left to cool, then removed when ready) there are however more complex steps involved in order for this seemingly simple process to occur. The six main steps are as follows:
Clamping – the clamp unit consists of metal plates (or platen). The process begins with the mould being clamped together under pressure to accommodate the injection and cooling processes.
Injection – the molten thermoplastic material, which has been melted by pellet form in the barrel of the machine, is injected under pressure into the mould through either a screw or ramming device.
Dwelling – once the molten plastic is injected into the mould, more pressure is exerted to make sure all the mould’s cavities are filled, using hydraulic or mechanical pressure.
Cooling – the plastic is left to cool and solidify within the mould.
Opening – the movable platen is separated from the fixed platen to separate the mould.
Ejection – ejection is completed by the use of rods, a plate or an air blast to remove the plastic component completely from the mould.