The injection moulding process produces plastic parts that can also have complicated geometric shapes. The raw material, usually a thermoplastic material, is fed in granular form to an injection moulding machine through a funnel.
The plastic is fed into a heatable cylinder in which there is a screw that can be rotated. In this cylinder, the granular plastic is heated to approx. 120 °C, which puts it in a viscous state. The rotating screw transports a precisely dosed quantity of this viscous plastic mass under high pressure into a two-part tool.
This tool incorporates exactly the desired shape of the required plastic injection-moulded part. The mould can be opened and closed by machine and is closed during the actual injection process. The mould gives the enclosed plastic compound the shape that is intended for the later plastic injection-moulded part. When the injection moulded part has cooled down to the correct temperature, the mould is opened and the injection moulded part is ejected by means of an ejector.
Summary of the injection moulding process:
The mould is closed.
The injection unit moves into position.
the plastic is injected in plastic form.
to compensate the shrinkage, the injection unit provides the necessary holding pressure.
the injection unit moves back.
When the remaining cooling time is reached, the mould is opened by the clamping unit.
The finished plastic injection moulded part is ejected by the ejector system.
Definition of thermoplastics
The essential characteristic of a thermoplastic material is its macromolecular molecular structure. It consists of linear hydrocarbon compounds which are arranged in long molecule chains to form macromolecules. However, these molecular chains have either no or very weak spatial cross-linking to each other. Due to this special molecular structure, thermoplastics soften when heated and become solid again when cooled.
When heated, thermoplastics are very easy to shape, so they can be used to produce injection molded plastic parts in almost any desired geometry. Important and well-known thermoplastics include polyamide (PA), polyethylene (PE) and polyvinyl chloride (PVC).
Toolmaking as an elementary important component for plastic parts
A separate tool is required for each type of plastic injection-moulded part. One tool can only be used to produce injection moulded parts with the same geometric shape. Toolmaking therefore plays a decisive role in injection moulding. The production of the tool requires a lot of experience and highest precision. Despite the effort required to manufacture the mould, injection moulding of plastic parts is an economic process.
If the injection moulding machine is operated carefully, the mould has a long service life. In addition, the pure production time for a plastic injection-moulded part is very short. For the manufacturer, the cost-effectiveness of the injection moulded parts is achieved in particular through high quantities.
Plastic injection moulded parts can be found in many products and assemblies of everyday life. The automotive industry is inconceivable without injection moulded parts. Examples include impellers, control knobs and brackets.
But plastic injection moulded parts can also be found everywhere in the electrical engineering sector. Plugs and sockets of all kinds are usually made of injection moulded plastic parts. Every printed circuit board manufactured for electronic applications of all kinds also contains injection-moulded plastic parts.
Plastic injection moulded parts are also frequently used in medical and dental technology. Handles for medical instruments, adapter pieces for anaesthesia and scale tubes are just a few examples.