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Compression moulding is a process utilized to create stock shape materials that are both Thermoset and thermoplastic. It is done by placing a plastic material in the mold cavity that is produced by adding pressure and heat. The two factors combine to force the materials to form the product. Pressure and heat harden the material and then removed it from the mold.

Getting the Right Stiffness for Compression Moulding

The ratio between the metal part thicknesses to extensional modulus is being multiplied to the BMC or Bulk Molding Compound material modulus. This formula is very useful in achieving the right stiffness in compression molding.

If the part is added in bending, you can make the metal part thicker, but this is not that essential. The ribs are added to a compression-molded part to provide extra stiffness. There could be an additional weight on the material.

Rubber compression moulding

Rubber compression moulding

Tools Needed for Compression

One of the critical factors that are considered in choosing the tools for compression is the quality of the fiber. The matched-metal tooling is needed for compression since the long-fiber BMC, with high fiber content, needs high pressure up to 2000 psi to fill sophisticated features. Also, tolerances on the center and cavity halves of the tool should be well-controlled to trap the air that could escape. Because of these requirements, the total cost of tooling aside from the basic cost of lamination tooling is increased.

However, the cost is a bit lower as compared to the injection molding tool. The rule for sufficient tooling ROI is that it should be covered with 1000 production units. If the part is highly complex, this could be higher or lower if it is not. For instance, aluminum molds are priced lower than steel, but they are not suitable for production that requires higher volume. Multiple cavity tools are likewise helpful in reducing the mold costs since a higher amount of components can be created per mold cycle.

Steps on Compression Moulding using Thermoset Composites

Thermoset composites are the type of material that is usually used in compression molding. The steps involved in this process is quite easy.

A high potency, 2-part metallic tool is produced that matches the dimensions needed to develop the required component. The tool is then placed in a press at a very high temperature.

The needed composite is pre-formed into the tool shape. Pre-forming is a vital step that can improve the performance and outcome of the completed part.

The pre-formed component is then inserted into a very hot mold. Under very high pressure, the tool is then compressed. The pressure is usually from 800 psi to 2000 psi. It depends on how thick the part is and the material used.

Upon completion of the compression process, the component is then removed from the tool after releasing the pressure. Sometimes there is resin flash surrounding the edges of the part. You can remove the flash by cutting or trimming them.

Compression moulding is a simple process, but it requires the right material, tools, temperature, and amount of pressure.