Plastic injection moulding machines help to manufacture plastic products in the required shape and dimension. Most of the plastic products in automotive body parts, phone cases, toys, etc… are manufactured in bulk quantities using the injection moulding process. The common thermoplastics and thermosetting polymers used as raw materials in injection moulding are ABS, Polypropylene, PVC, Nylon, Polyetherimide (PEI), Polyoxymethylene (POM), and more. The commonly used ABS material offers excellent impact resistance, processability, and toughness. The dimensionally stable Polyoxymethylene(POM) thermoplastic used in mechanical automotive, gears, business machines, household appliances, bushings, etc., offers high stiffness and low friction. Polycarbonate is suitable for applications that require excellent thermal stability and strength. The thermoplastic Polyetherimide(PEI) are found in applications like aircraft interiors, cooking utensils, electronic parts, etc., that deals with high temperature. Likely, PVC and Nylon are polymers with features like insulation property, abrasion resistance, and mechanical properties.
The injection moulding machines can be classified into hydraulic, electric, and hybrid based on the type of drive system. Till the 1980s, injection moulding machines utilized hydraulics for operation and it offers exceptional clamping force and resistance to wear and tear. The next invention was the electric plastic injection moulding machine in 1984 and it was powered by digitally controlled high-speed servo motors. The hybrid injection moulding machines use a combination of both these technologies together.
The injection moulding machine consists of an injection unit and a clamping unit. The injection unit includes components like screw motor drive, heaters, thermocouple, ring plunger, reciprocating screw and barrel; and it melts the polymer resins and injects it into the mould. The clamping unit components are mould, clamping motor drive, and tie bars. The clamping unit places two parts of the mould together tightly for the melted polymer resigns to be injected.
If considering the process of injection moulding, the thermoplastic or thermosetting polymer in powder or granular form is selected according to the product specification and is fed into the heated barrel by a hopper. The frictional action of a reciprocating screw in heater bands will melt these raw materials and with a nozzle the melted plastic is injected into the mould cavity that is made with steel, aluminium, or other metals. The melted raw materials inside the mould cavity will cool and solidify to obtain the shape of the mould cavity.
Hydraulic Plastic Injection Moulding Machine Operation
Similar to every hydraulic system used, it is the pressure of the hydraulic fluid that makes injection moulding machine operation smooth and safe. The hydraulic pump is powered, the fluid inside the reservoir gets pressurized and are pumped towards other hydraulic components in the circuit. The relief valve will regulate the fluid pressure according to the system requirements.
In hydraulic plastic injection machine, hydraulics plays a key role in both the clamping unit and injection unit. The linear/rotary movement of the screw in the injection unit will melt the polymer resins stored in a hopper and injects melted particle through a nozzle into the mould cavity. This back and forth operation of this screw inside the heaters is controlled by a hydraulic cylinder. In the clamping unit, hydraulics cylinder is used for the opening/closing and clamping of mould tools. Also, the hydraulically-operated ejector will push the finished plastic product out of the mould.