Compression injection molding

Compression injection molding

How Compression molding works

Compression molding is one of the oldest and simplest molding techniques, especially prevalent for thermosetting materials but also used for some thermoplastics. This process involves molding material (often in the form of pre-weighed pellets, granules, or sheets) by heating it and applying force.

1. Process:

A measured amount of molding compound (often a preheated preform) is placed in the open mold cavity.

The mold is closed, typically using a hydraulic press. The top half of the mold (the punch or ram) comes down onto the bottom half (the cavity).

With the application of heat (usually from the mold itself) and pressure, the material softens and flows to fill the mold cavity. The high pressure ensures the material completely fills the mold, conforms to its shape, and removes any trapped air or voids.

For thermosetting materials, a chemical reaction (cross-linking) occurs under the heat and pressure, which “sets” the material in its molded shape. Once set, the material will not melt again when reheated.

After a set period, allowing for curing and cooling, the mold is opened, and the part is removed. It might need further post-curing or finishing operations.

2. Advantages:

Compression molding is a straightforward process with relatively simple machinery.

There’s often less material waste in compression molding compared to other methods, as the exact amount needed is placed in the mold.

Silicone parts are flexible, resistant to compression set, and have excellent longevity.

The process can handle large and intricate parts with varying thicknesses.

While not as rapid as injection molding, compression molding can be cost-effective for medium production runs.

3. Challenges:

Compared to injection molding, compression molding generally has slower cycle times.

The process often requires more manual intervention than other automated molding processes, particularly in placing the material into the mold.

It’s best suited for thermosetting materials, although some thermoplastics can be compression molded.

3. Applications:

    Non-metallic parts, such as bumpers, fenders, and non-structural panels.

    Composite components

    Circuit breakers, switches, and other insulating parts.

    Bowls, trays, footwear soles, and more

    Orthopedic devices and certain prosthetics.

    4. Summary

    In conclusion, compression molding is a tried-and-true method for forming parts, especially from thermosetting materials. While it might not be as rapid or automated as some other processes, it remains valuable for specific applications and materials.

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