Plastic has become part and parcel of our lives. Plastic production is inexpensive and productions that are needed in mass can be processed easily and fast. Since we cannot do without plastics, it is necessary to understand the manufacturing process of plastics.
Injection Moulding, Design Process and Tooling
The process used to convert raw materials into usable plastics is called injection moulding. This process is used to manufacture products/parts from both thermoplastic and thermosetting plastic materials. These materials are melted, designed and cooled in order to be released for use. Injection moulding is commonly and widely used to manufacture a variety of parts, usually for the car industry.
Initially, the moulding machines used the pressure technology to give the needed end products. This graduated to pneumatic cylinders and then the hydraulic systems which also borrowed from the die cast technology. The modern machines use the injection barrel of a plunging helical screw because it is fast and efficient.
The injection process comprises four easy steps which are
- Clamping — At this stage, the mould is held securely by the hydraulically powered clamping unit which in turn pushes the mould and exerts force to keep it securely closed while being injected.
- Injection — The polymeric material which is available in powder form is transferred into the injection moulding machine by the injection unit for melting. Once it is molten, it is quickly injected into pressure packs under a certain temperature.
- Cooling — The molten material solidifies quickly after a pre-determined cooling time. As the plastic cools, it adopts the shape of the desired part. The cooling process is sometimes affected by shrinkage and this is corrected at the injection stage where additional material is allowed to flow into the mould.
- Ejection — This uses a particular mechanism to push the part out of the mould. Some force must be exerted since the part adheres to mould. A release agent may be sprayed on the surfaces of the mould to facilitate ejection.
The moulding design and tooling puts into consideration the part design. This includes the draft, wall thickness, radii and corners, ribs and bosses and the weld part lines. The draft describes the degree of a taper needed to allow the ejection of the moulded plastic. The ribs are necessary to add the structure strength of the part design. The bosses locate, mount and assemble the moulded parts. The radii help to avoid sharp corners and also help to strengthen the part.
The advantages of plastic injection moulding include the ability to keep up high production levels, high tolerance level in the products and lower labour cost since the bulk work is machine based. In addition, there is little waste and therefore the scrap costs are lower. The major disadvantage of plastic injection moulding is the acquisition of the equipment which is usually very expensive.
At Boddingtons, you are assured that you will be provided with an injection moulding device and a complete service necessary for your business growth.