Injection molding is an essential industrial method. It is similar to die casting, but the raw materials are different. In die casting, we use extremely high temperatures to melt metals. This process is done by heating the raw materials and injecting them under pressure at a specific temperature into the mold cavity without changing their chemical composition. Still, injection molding is mainly used for glass, elastomers, and most commonly thermoplastic and thermoset polymers, but this technique is widely used to make thermoplastic materials.
Main parts of injection molding machine:
The main components of the injection molding machine are the hopper, the barrel, the injection piston/rotary screw plunger, the heating device (heater), the movable model, the injector, and the mold in the cavity.
Usually, injection molding machines work horizontally. The injection molding machine consists of a barrel (cylindrical tube). The hopper is located at one end of the bucket. A hydraulic cylinder or a rotating screw driven by an electric motor that provides force is located within the barrel. A heating element (heater) is attached to the barrel to melt the molding material from the hopper.
The mold cavity is attached to the other side of the barrel. The mold is located within the cavity, and a movable template is used throughout the manufacturing process. This can be selected as needed. Molds are generally made of copper, aluminum, and tool steel. The life cycle of different material molds is different.
Injection molding works like extrusion and, as the name suggests, works like an injection. The molding material/raw material is poured into the hopper through the feeding device. After that, the molding material descends into the cylinder (barrel) under the action of gravity, as shown in the figure. Peripheral heaters located on the barrel are used to melt the material. When the molding material in powder form enters the barrel from the hopper, it starts to melt. The hydraulic cylinder or rotating screw pushes the material forward into the mold by applying a certain pressure. Injects molten plastic material into a closed mold attached to the other side of the barrel; used in this split mold. The rotating screw continuously advances the molding material. A hydraulic system applies pressure. The injection pressure is generally 100-150 MPa. after injection;
After the whole process is completed, the manufactured parts are sufficiently cooled. Then open the mold and use some ejectors to remove the part without damage properly. After removing the part, the mold closes again. This process is speedy and repeats automatically. Parts of complex shapes can be easily manufactured here. Injection molding has a production capacity of 12-16,000 parts per cycle.
- Process parameters vary according to conditions and requirements.
- The weight of parts produced by this process is generally 100 to 500 grams.
- The cycle times to produce a single part typically range from 5 to 60 seconds, depending on the manufacturer.
- The heating temperature of the molding material is 150-350 degrees Celsius.
- The injection volume of the molding machine is 12,000 to 2.2×〖10〗^6 〖mm〗^3.
- The injection pressure is 100-150 MPa.
- The locking force is 0.1 to 8.0 MN.
- The main advantage of this process is that complex-shaped parts with small wall thicknesses (5-15 mm) can be easily formed and 2. removed from the mold without damage.
- Injection molded parts have good dimensional tolerances.
- The main advantage of this technique is that it produces very little waste compared to some other processes.
- Parts made by the injection molding process compete with those made by investment casting and complex machined parts.
- The process has high productivity compared to other techniques.
- The initial cost/setup cost of the process is very high due to the entire device’s design, testing, and tooling.
- Investment molding is usually limited to exotic materials such as thermoplastics or polymers.
- The cost of the mold is high; that is, the mold used is made by several processes, and the overall cost of testing a single mold is very high. For different parts, different types of molds are required.
Application Of Injection Molding Machine:
Injection molding is used to manufacture complex shaped parts of various sizes with low wall thickness.
Typical parts include cups, containers, toys, plumbing fittings, electrical components, telephone handsets, bottle caps, and auto parts.