What Everyone Must Know About Injection Moulding Steps


Injection moulding is a process in which a polymer is heated to above its melting point and then forced into a mold, where it shapes itself into a final part. The melted plastic is injected into the mold cavity and held under pressure by a screw. It then cools to a certain temperature and hardens in the mold before it is ejected.

Material Selection

Choosing the right material for your product requires an extensive knowledge of physical properties. These are influenced by the environment and application of your part. Injection moulded plastic parts often come in direct contact with harsh environments like aerospace, marine, and underwater applications. For these uses, you need materials that can withstand temperature changes, UV rays, chemical interaction, and radiation resistance.

In addition to hardness, plastics must also be flexible enough to bend without breaking. This means you need to select a material with the appropriate tensile strength and Izod impact resistance, which can be calculated using a standard test.

Mold Design

Injection moulding steps is a manufacturing process that uses solid thermoplastic resin pellets. They are melted and injected into a mold, then cooled to form a part. Designing a part for injection moulding is essential for ensuring its function and strength. It also helps to keep the total cost of a product to a minimum. Molders have a wide range of tools at their disposal, including CAD software and 3D machining systems. However, a designer must work closely with the molder to ensure the final part is optimized for production.

Mold Construction

Injection moulding is a process that involves creating a mold for the production of plastic parts. The design of the mold depends on the shape of the component and requires consideration of the parting line, runner and gate selection, and component ejection system. Injection molded parts are usually made from thermoplastics, including polypropylene (PP), polyethylene (PE), and polystyrene (PS). All of these materials are lightweight, heat resistant, chemical resistant, scratch resistant, strong and stiff, and can be custom colored or dyed.


Injection moulding is one of the most widely used methods for producing plastic parts, and it yields high-quality products with tight tolerances. However, injection moulding can be expensive and is largely dependent on the design of the part. Cost of tooling is a major driver, but it is also influenced by the number of cavities, additional details and surface finish. To minimize this impact, limit the number of cavities and avoid adding extra features such as undercuts.

Clamping – Once the mould is assembled, each half of the mold must be securely closed by the clamping unit. This is done with a hydraulically powered clamping motor that exerts enough force to keep the mold halves shut while the material is injected and then cooled.


Cooling is one of the most important steps in a plastic injection moulding process. It ensures a finished part that is free from warping, sink marks, and other defects. Thermoplastic resin doesn’t like to be molten for too long. It needs to be cooled quickly and at a uniform rate so it can return to a solid state. This is where the cooling line, or cooling channels, come in. If the engineer designs these correctly, they will help reduce part errors such as shrinking and warping.


When injection moulding steps, you want your plastic parts to easily eject from the mold. This helps reduce manufacturing delays and costs, as well as part defects. When your molded parts get stuck, it can cause damage to their components and lead to longer cycle times and tool wear. An experienced moldmaker knows how to design and implement an ejection strategy that meets your needs. During ejection, a pin extends into the mold cavity and pushes the part out of the mold. This can leave a mark on the part, which is called an ejector pin mark.

Final Thought

The injection moulding process involves injecting liquid plastic into a mold and cooling the part in between cycles. This process is repeated many times and can produce a large number of parts per hour. Injection moulding can be a good option for manufacturers with an appropriate budget. However, there are a few things to consider before going down this route.

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