The injection moulding is the most usable technology for manufacturing plastic products. A wide variety of details could be manufactured using this method, depending on their sizes, complexity and application.
Three elements are needed to carry out an injection moulding: injection moulding machine, granular plastic material and mould (die). Plastic material is melted in the injection moulding machine first, then is injected into the mould (die) where it is cooled and a detail is formed. We will try to explain all steps of this process in details in the next text:
There are many models of the injection moulding machines, depending on their configurations, applications and orientations. But all the machines have a zone for plastic preparation, zone of mould mounting, zone for closing and power unit (hydraulic station). There are machines on the market equipped with step motors, replacing hydraulic stations.
Zone for material preparation:
The material is prepared in this zone. The granular material is fed into a „hopper“ that is fixed to the reciprocating screw. Once the plastic is fed into the reciprocating screw it is heated by electric heaters to the required temperature for the specific material. Reciprocating screw is a cylinder with moveable screw. The whole cylinder is surrounded by heaters. The moveable screw injects and doses material by turning and reciprocating at the same time. The melted material is ready for injection. The screw moves forward by hydromotor or electric motor forcing the melted plastic through a nozzle into the mould cavity. It is called the injection moulding. After the whole dose is injected and the time, set by the operator, is up the screw begins turning and, in this way, the needed plastic is fed from the hopper to the front part of the screw. This process is called dosing.
Zone for mould mounting
Generally speaking this zone consists of two massive metal plates. One of them is fixed – always on the zone for plastic preparation. The other one is a movable plate. This plate opens and closes the mould. Between them the mould is mounted with the nozzle to the fixed part. Once the tool is mounted, the fixed and the movable parts are clamped to the corresponding plates. Due to the fixing ring the fixed plate is mounted so that its nozzle is on the same level as the screw nozzle.
Zone for mould closing
It is a part of the injection machine for closing and opening (cycle) of the mould. The movement is realized by hydraulic cylinder or movable mechanical units.
Hydraulic station supplies the pressure needed for normal operation of the injection moulding machine.
Mainly, the injection moulding machines are classified by their power – this is the power for tool closing. The bigger is the plastic detail, the bigger is the machine power.