A Guide To Plastic Compression Molding

Plastic compression molding plays a huge role in the plastics industry, yet it is often overlooked. Perhaps this is due to the fact that it is primarily used to produce large molded products, such as car hoods and fenders. This is rather specialized and requires large equipment and tooling, so many small and medium sized companies have not included it in their lines.

Another reason is that plastic compression molding is also specialized in the electrical connector industry. Most connectors are made of thermosetting plastic that is compression molded. Thermoplastic materials can also be compression molded, given the right application and custom material.

How Does It Work?

The material, or "charge", is placed in the open lower half of the mold (the cavity), which is heated. This material is usually preheated as well. The two halves of the mold are closed by hydraulic pressure and the material is forced to fill the shape of the mold. Once the material is set, or cured, the mold is opened and the ejector pin pushes the molded part out of the mold. The process is then repeated over and over again.

This is, of course, a very simplified description of the process. Numerous types of plastic, both thermoset and thermoplastic can be used. The advantage is that the parts are very strong and stable. In fact, many products were designed to replace metal, such as in a hood or spoiler on a car.

Some of the other advantages of compression molding are improved knit lines and less fiber-length degradation of the material. Other advantages include the ability to mold large, intricate parts in very high volumes, as in the automotive applications.

Electrical connectors that are compression molded are very stable and have exceptional strength and hardness. Unfortunately, they can also be brittle and prone to chipping.

How can plastic compression molding fit your needs? 

As a molder you are always on the lookout for profitable trends to strengthen your bottom line and help maintain some kind of steady workflow. By adding compression molding to your arsenal you can tap into various niche markets that lend themselves to this specialty. Over time you can discover that a multi-faceted approach can help you, provided you don't spread yourself too thin!

One company that has excelled in combining injection molding and compression molding is Longzu Plastic Molding Company, located in Taiwan. They are a high end mold builder and molder of many electrical components. They also do injection themoset molding.