Do you know how we get many of the complicated plastic things that make our lives safer, more sterile and much more convenient? Many of them are formed by a process known as plastic injection moulding.
According to a recent article on Plastipedia, available at http://www.bpf.co.uk/plastipedia/processes/injection_moulding.aspx, this is a manufacturing method that has been in use since the 19 century. Since then, the process has been refined to make it better structured and to enable manufacturers to use different types of plastics that have different qualities.
Commonly used materials:
1) Acrylonitrile-Butadiene-Styrene ABS
2) Nylon PA
3) Polycarbonate PC
4) Olypropylene PP
4) Polystyrene GPPS
Key steps in the injection moulding process:
Clamping. An injection-moulding machine consists of three basic parts; the mould plus the clamping and injection units. The clamping unit is what holds the mould under pressure during the injection and cooling. It holds the two halves of the injection mould together.
Injection. Chuck Tuck in his article on Technology Student, http://www.technologystudent.com, argues that during the injection stage, plastic material, typically in the form of pellets, are loaded into a hopper on top of the injection unit. The pellets feed into the cylinder where they are heated until they reach molten form (think of how a hot glue gun works here). Within the heating cylinder there is a motorized screw that mixes the molten pellets and forces them to the end of the cylinder. Once enough material has accumulated in front of the screw, the injection process starts. The molten plastic is inserted into the mould through a sprue, while the pressure and speed are controlled by the screw.
Dwelling. The dwelling period consists of a pause in the injection process. The molten plastic has been injected into the mould and the pressure is applied to make sure all of the mould cavities are filled.
Cooling. The plastic is allowed to cool to its solid form within the mould.
Mould Opening. The clamping unit is opened, which separates the two halves of the mould.
Ejection. An ejecting rod and plate eject the finished piece from the mould. The un-used sprues and runners can be recycled for use again in future moulds.
This complicated process requires highly skilled engineers and technicians to create great products. Tool Craft are one of the leading plastic injection moulding companies in the UK and will modify and adapt this process to suit any requirement. Their website has full details of their services, http://www.toolcraft.co.uk/.
Typical Products Produced
1) Automotive Plastics (auto parts, aircraft parts, and tires).
2) Packaging Plastics (boxes, egg cartons, plastic cutlery, protective packaging for electronic goods and toys).
3) Industrial Consumer Plastics (plastic toys, furniture)
1)High production rates
3)Repeatability within tolerances
4)Can process a wide range of materials
5)Relatively low labour
6)Little to no finishing of parts
7)Minimum scrap losses
1) High set up costs (moulds etc)
2) Complicated process
3) Can only be used for large quantities due to costs
In summary, there are more than 30,000 unique products that can be moulded using injection process. The major advantage of plastic injection moulding is that products with complex geometry can be made which is not possible in any other processes. And it is clear, as long as there is a need for plastic components of complex shapes and sizes, the business of manufacturing plastics will continue to grow.