Injection molding is a manufacturing procedure for making plastic parts either by manually injecting melted material into a mold, or by using a suitable machine. Injection molding can be carried out with a variety of different materials mostly consisting of plastics, polystyrene, acrylics, thermoplastics, and most importantly thermoplastic and thermoforming polymers. The process is also known as extrusion molding and injection molding. In general the parts made by injection molding are round and are usually used in low volume production. Parts made by extrusion molding are normally larger in size and use plastic parts such as buttons, trim, screws and hinges.
Plastic parts produced in this way are known as flow lines. Flow lines indicate where in the mold parts have been successfully inserted or removed. When manufacturing parts with flow lines, these markings are very clear and easy to identify. In most cases the process leaves few if any irregularities on the mold, which makes them ideal for use in the final production. Incorrective moulds leave broad stripes of melted plastic on the surface of the product and can often create disastrous consequences, especially when the manufacturing faults are allowed to proceed unchecked.
Injection moulding tools include machines for manipulating the plastic parts in a way that allows them to fit together correctly. The basic machines for injection moulding include the following: Cylinder machine, Die cutting machine, Plastic sheet machine, Rollers, and Enlargement kit or feed pipe. Each machine will be designed for a particular type of injection moulding process, but most machines will be able to handle a wide range of processes.
As, well as machines, there are many accessories that can be used to speed up the process of injection moulding, some of these are: injection ports, injection pressure, valve systems, heaters, expansion ports, injection tables and cavities. An injection port is a port where liquid injection occurs. If it is used incorrectly this could lead to catastrophic damage or even inflections on the part surface. This kind of error could also be caused if the injection pressure is too high, the pressure is not evenly distributed across the cavity or the valve. If injection pressure is too low then the mould can overheat and melt the plastic.
Injection moulds are usually used to manufacture hollow components that are required for the manufacturing of parts. These parts are typically the result of a complex component being created for the first time or they may be part of an extremely complex model kit. Some moudings are made to have the desired shape before they are sent to injection moulding to keep the plastic material cool. The cool plastic material is then injected into the mould to form the desired object.
As a result of injection speed and pressure, the length of time the plastic material spends in the mould can differ. It can either be very short, such as when it is used in toy drives and car wheels and shafts, or very long, such as when it is used to create aircraft models. Depending on the process being used it is important that the mould is set up correctly so that the right amount of time is allowed for the material to cool before it solidifies. If this cooling time is too short or the mould is over-pressurized, there can be many undesirable effects, including premature cooling and the loss of plastic quality.
