The Injection Moulding Process: Cycles and Equipment for Toys, Bins, and Medical Containers

Injection moulding is a process that entails the high-pressure injection of polymer into a mould for shaping. The various steps in this process are brief, typically lasting from 2 seconds to 2 minutes. The injection moulding cycle consists of four key stages: clamping, injection, cooling, and ejection.

Clamping:

To initiate the injection process, both halves of the mould must be securely closed using a clamping unit attached to the injection moulding machine. Material is injected as the clamping unit presses the halves together, ensuring a tight seal during injection. Larger machines, with greater clamping power, may require more time to close and secure the mould.

Injection:

Plastic pellets are fed into the injection moulding machine via a hopper and are propelled towards the mould by the injection unit. The pellets are melted by the heat and pressure within the barrel. The quantity of material injected, known as the 'shot', is determined by the filling of the mould to 95%-99%. Calculating the exact injection time is challenging due to the dynamic nature of plastic flow. Injection time is estimated based on factors like injection pressure, power, and shot volume. Injection pressure typically ranges from 35-140 MPa and is controlled by the machine's hydraulic system.

Cooling:

During the cooling stage, the plastic within the mould begins to solidify upon contact with the mould's interior. As the plastic cools and hardens, it adopts the desired shape, potentially shrinking slightly during the process. The mould cannot be opened until the cooling period has concluded. Cooling time estimation depends on the part's wall thickness and the plastic's thermodynamic properties.

Ejection:

The final phase involves ejecting the part from the machine using an ejection system. When the mould opens, the part is pushed out, requiring force due to potential shrinkage and adhesion to the mould. After ejection, the mould can be closed again for another shot to commence the cycle anew.

Mould design plays a critical role in determining the quality of the final product. The mould's robustness, durability, shape, and size are crucial factors influenced by the type of mould used. Proper polymer flow within the mould, as well as efficient heat transfer for cooling, are essential design considerations.

This intricate process requires skilled oversight to ensure its success. At Automatic Plastics, we prioritize both productivity and safety. We strive to deliver high-quality plastic parts across diverse industries through injection moulding. For your injection moulding needs, reach out to APL for a detailed discussion about your requirements and to receive a competitive quote.