Explanation Of Compression Molding Process; Advantages, Materials…

Compression molding is one of the most used plastic shaping processes that are generally applied to thermosetting polymers. There are various advantages and disadvantages of the compression molding process over plastic injection processes. In here;

  • General explanation of compression molding processes,
  • Materials used and parts produced in compression molding processes,
  • Advantages and disadvantages of compression molding processes.

Working Principle Of Compression Molding Process

In compression molding processes, thermosetting materials are shaped between two halves of mold that constitute the cavity of the produced product. A piece of plastic material is placed on the bottom half of the mold, and the upper half is presses on this plastic material.

Illustration of compression molding process.

The bottom half is generally preheated. And the piece of plastic material that is being placed inside the mold, is also heated with such systems. The piece of the initial charge of material can be in the form of pellets or semi-molten state. The heating of the initial plastic piece can be done with heated barrels which includes screw inside it, just like plastic injection molding, infrared heater, or convection ovens. Pre-heating of charge shorten the process cycle time.

Adjustment of required curing time for thermoplastic material is also a very important parameter. Curing of thermoset material takes place inside mold which is closed. Hydraulic systems are generally used to push or pull the two halves of mold in the compression molding process.

What Are The Types Of Compression Molding Machines?

A typical compression molding machine.

In general, the types of compression molding machines can be classified as automation is used or not. According to this aspect, there are three types of compression molding machines available.

  • Full Automatic Compression Molding Machines: These machines are fully automated in terms of the process cycle. All the process steps such as loading the charge, compression, and de-attaching the part from the mold are done by automatic systems.
  • Semi-Automatic Compression Molding Machines: In these types of compression molding machines, loading and de-attaching are generally done by the operator. Compression of mold halves done in specific time intervals.
  • Hand-held Compression Molding Machines: All the process cycle is done via operators. Loading of plastic charge, de-attaching it, etc.

What Types Of Materials Are Used And What Types Of Products Are Produced With Compression Molding Machine?

As we stated above, compression molding processes are generally used for the production of thermosetting polymer parts. Urea-formaldehyde, urethanes, epoxies, and phenolics are the most used types of thermosetting polymers in compression molding processes.

Electrical part and electrical plug coatings are the most important products that are produced with compression molding processes. Plates and pot handles are also produced with thermosetting polymers in compression molding machines.

What Are The Advantages And Disadvantages Of Compression Molding Process?

The most important advantage of the compression molding process is the simple parts are generally produced. So, the tooling required to obtain mold structures is also simple. Because of that, the use of compression molding processes is cheaper compared with other plastic shaping processes.

The produced scrap is nearly zero in compression molding machines, which means there are no waste materials produced from the production process. Waste means additional cost to complete the mechanism.

Because of the uniformity of parts and curing inside compression molds, lesser residual stresses occur inside produced parts.

The main disadvantage of the compression molding process is the long process cycle times compared with other processes. Curing of thermosetting leads these longer times for compression molding processes


In the plastic industry, the use of thermoplastic polymers is more common. So, the compression molding process is a special process to produce thermosetting parts, around other plastic shaping processes used.

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