Process of Injection MouldingInjection moulding is a popular manufacturing process and is the go-to choice for many industries to mass-produce everyday products. This article defines the process of injection moulding, providing detail as to how injection moulding works and why it is such a popular choice for so many businesses and industries. At Get it Made, Injection Moulding is just one of the services we offer. You can find out more about our range of CNC Machining services here.
What is Injection Moulding?Injection moulding is a very prominent manufacturing process, used to predominately manufacture high volume plastic parts. Injection moulding can be used to produce parts and products of various materials, however, most commonly, it’s used to produce thermoplastic polymers and thermosetting polymers.
What is injection moulding used for?Injection moulded parts can be found in most industries and in consumer plastic products. Common uses for injection moulding include:
- Medical equipment
- Electrical appliances
- Agricultural items
- Automotive parts
- Lighting components
- Telecoms equipment
How does injection moulding work?Once a part is designed, a metal mould is precision machined to create the desired part shape. This can have a single cavity for the molten plastic to fill or multiple cavities. This decision is largely based on the economics of the mould and volume of parts required. Increased cavities mean more parts can be produced per cycle. The chosen material is fed through a heated chamber. This melts the material before it enters the hollow mould. After the cavity is filled, the machine then exerts additional pressure to account for any expansion of the plastic upon cooling. The part often cools incredibly quickly and solidifies into the moulded shape. Once the part solidifies, it’s ejected from the mould through the use of ejector pins or via a manual process. The process of injection moulding itself is a relatively simple one. However, there are several complex steps to ensure that the final product is precise and of the required quality, finish and design. The exact type of machine used is dependant on the type of part being moulded, and the material being used. Larger parts, for example, will need machines that can exert a higher clamping force and more powerful injection pressure. Thermoplastics are usually the most preferred material because they have desirable qualities, such as:
- Recyclability, as they can be melted and moulded into a new product.
- Versatile properties with Polyethylene, Polypropylene and Polyvinyl Chloride.
- Protection from electrostatic discharge.
Injection Moulding Machine MouldsThe moulds can be fastened in either horizontal or vertical positions, with requirements depending on the size and type of application. There are various types of moulding machines and these are classified by the driving systems they use. These could be:
Injection moulding process step by step
ClampingThe two moulds must be securely closed by the clamping unit, with sufficient force applied to keep the mould securely closed while the material is injected. Metal plates are used to clamp the mould together.
InjectionMolten thermoplastic material is injected into the mould, with pressure & heat applied to heat the pellets in the barrel until they melt to liquid form.
DwellingOnce molten plastic is injected into the mould, more pressure is exerted. This is to ensure that every cavity in the mould is filled. This process uses hydraulic and mechanical pressure.
CoolingThe plastic is left to cool & solidify in the mould. This process is extremely quick, with the molten plastic cooling as soon as it comes into contact with the inner surfaces of the mould.
OpeningOnce cooled sufficiently, the moveable metal plates forming the mould are separated to reveal the final finished product.
EjectionThe final cooled product is ejected from the mould via the ejection system, which is attached to the rear half of the mould. It involves the use of rods and sometimes an air blast to remove the plastic component from the mould.
What are the advantages of injection moulding?Injection moulding is a preferred process due to the fact its:
- Cost-effective for high volume
- Part quality is easy to determine
- Quality assured