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What You Need to Know About Compression Molding Technique

by Nice Rapid | Jan 04,2021 | Compression Molding

There are plenty of manufacturing options available to produce a part. One of them is compression molding. This process is similar in principle to injection molding, but the difference is the application of heat and pressure. These two powerful combinations press the material into the mold. With the continuous application of pressure and heat, it hardens the material until it is set.

For those who are new to the process or you are looking into the possibility of using this method to manufacture your product, you should read this article first. It will explain how compression molding is done and what are its basic applications.

Compression molded foam

The Compression Molding Process

There is no other ideal method to use in creating rubber products of different volumes than compression molding.

Compression molding requires mold in two parts – the cavity, which is the female part, and the plunger that is its male counterpart. Another integral part of the process is to press in the form of the heated plate. The mold is attached to the upper and lower plate. These components should be aligned when assembled because it is the basis of the compression technique.

Since the position of the mold cavity and plunger relative to the upper and lower platen is critical, it should be thoroughly checked before starting the compression molding process. When using molding compounds, the cavity part of the mold is attached to the lower platen while the plunger is mounted on the upper platen.

If plastic impregnated material is used, the cavity part of the mold is attached to the upper platen while the plunger is attached to the lower platen. In both cases, you have to ensure that the two parts of the mold and the platens are perfectly matched and aligned.

Once the alignment is all set, the molding material is injected into the cavity part of the heated mold. It has to be weighed and preheated before injection. After the injection, the cavity part and the plunger are pressed together to create pressure. This action forces the material to fill all the parts of the cavity while displacing the entrapped air in the system. The product is ready after applying the right temperature, pressure, and time. It will cure the material completely.

After the molding process is completed, the flash or excess material is squeezed out of the mating surfaces. Additional finishing like filing and sanding can be applied to remove the flash.

Thermoset and Thermoplastic

There are two types of compression molding materials: thermoset and thermoplastic. With thermoset plastic, the temperature of the preheated material should not be lower than 300 F, the mold heat temperature within the range of 250 and 350 degrees, and the pressure between 1000psi to 2000psi.

For thermoplastics, the compression molding process is different. Instead of heating the mold, it is cooled at the end of the molding operation. After the plastics are hardened, it will not be able to flow after molding.


The compression molding processcan be as quick as three minutes or as slow as two hours. It will depend on the type of material and the size of the final product. In both types of materials, the curing and cooling process takes the majority of the time.

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