Sun. Feb 25th, 2024

Plastic injection molding is one of the most common methods for manufacturing plastic parts. The process uses a reciprocating screw or injection plunger to inject molten plastic into an enclosed mold, which is then cooled and ejected as the finished part. Plastic injection molding can be used to create a wide variety of products, including automotive, medical, and consumer goods. Injection molding can also be used to make prototypes, which are generally made from cheaper materials and have smaller volumes than production plastic parts.

Injection molding uses a variety of plastics, including thermoplastics and thermosets. Thermoplastics are able to be remelted and reshaped, making them more useful in the injection molding process than thermosets. Thermosetting polymers, on the other hand, are less flexible and cannot be reshaped after heating.

The injected plastic is often reinforced with other substances to increase its strength, stiffness, and impact resistance. These reinforcements are usually long fibers of glass, sisal, cotton, or other natural materials that are bound into the plastic resin. The amount of reinforcement material used in the final product is a function of its strength requirements and the desired appearance of the part.

To ensure the correct viscosity of the injected plastic and to prevent premature solidification, the injection process must be controlled. Injection pressure, which is applied by the injection screw or injection plunger, increases as the molded plastic is filled. When the cavity reaches 95% fill, the injection pressure is switched to packing pressure, which completes the mold filling and compensates for thermal shrinkage of the plastic. Excess melted plastic that does not enter the cavities is contained in channels machined into the injection mould, which are called sprues, runners, and gates.

Clamping pressure, which complements the injection pressure, is also important in ensuring that the molded parts come out correctly. Insufficient clamping pressure will result in leaking molten plastic or the formation of flashes, while excessive clamping pressure can damage the injection machine and cause defects in the molded parts.

After injection, the molded plastic is allowed to dwell inside the cavities for a time to allow cooling and for additional melt to flow in order to compensate for shrinkage of the plastic. After a suitable time, the mold is cooled and the plastic is ejected.

Many different industries use injection molded parts in their processes, and the type of part that is injected will determine what material and how it is used. For example, automobile companies will use injection molded products like door panels and engine components that require high stiffness and chemical resistance. These products are typically produced with glass-filled nylon or a blend of plastics that provide both mechanical and chemical resistance, such as PBT, PPE-PS, and polyether imide. Prototypes for these types of products are often created with commodity plastics, like polycarbonate or ABS acrylonitrile butadiene styrene (ABS). Aerospace companies will also use injection molded products like turbine housings and blades, pump gears, and valve seats that are made from engineering plastics, such as PEEK and PAI.

By Admin

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