One of the most widely used plastic molding manufacturing techniques is compression molding. It is a process that is similar to injection molding, but a more economical and seamless option for fabricating plastic.

In compression molding, the preheated plastic material, which is referred to as charge, is placed in a heated open mold cavity and is compressed under pressure to create the part or product.

Compression molding presents a set of advantages over other manufacturing processes. It is an ideal process to produce parts with complex designs and larger sizes. It is also capable of producing parts using composite materials.

It may be an old application, yet it is very efficient. This manufacturing process has plenty of applications ranging from aircraft bodies and vehicle bumpers to smaller everyday products like buttons and shoe soles. Let us take an in-depth look at compression molding and its applications.

What is Compression Molding?

Compression molding is a manufacturing technique that uses heat and pressure to create the final shape of the product. This method is suitable for silicone rubber, thermosetting, and thermo-softening plastics like composite materials.

It employs a heated cavity and vertical press mechanism that makes it easy to make and maintain the necessary tooling. Aside from this advantage, the compression molding machines are simple and offer low-cost tooling for prototyping and small volume production.

There is also less material waste compared to injection molding because there are no runners, gates, and sprues required to form the part. This technique also produces beautifully crafted and functioning parts and products with a superior surface finish. It is the go-to technique for large flat and curved components.

This molding technique can outdo other manufacturing processes when the composite materials are given additional properties like corrosive resistance, stiffness, durability, and other special properties.

The most common materials used in composite molding is a mixture of thermoset and other materials called sheet molding compound (SMC) or bulk molding (BMC) in producing large and complex high-quality mechanical properties.

Like any other manufacturing technique, compression molding is not perfect. It also comes with a few drawbacks. For one, it takes longer to complete the process, and can be difficult to produce highly complex and intricate parts. The finished part can also come out with excess material known as flash. This has to be trimmed or cut off during finishing.

How Does Compression Molding Work

The compression molding process starts with the preparation of the raw material. These are resins that come in the form of powder, pellets, or pre-forms. The plastic or composite material is preheated and placed in the mold cavity made from steel or aluminum.

The matching half top of the molds is closed with a hydraulic press. Using vertical compression, the pressure forces the plasticized charge to uniformly fill the mold, which creates a homogenous structure of the part.

During the process, the mold is kept closed while the high temperature cures the charge material to take the final shape and composition. When the curing process is complete, the upper mold is lifted and the final product is removed.

Common Applications of Compression Molding

Compression-molded parts and products are a constant in our daily lives. You might not realize it yet but these are widely utilized in the automotive and aerospace industry, in consumer electronics and kitchenware, in the medical industry, and in many other applications where the benefits of compression molding are needed.

Aerospace: The ability of compression molding to create products from composites is valuable to the aerospace industry. In aerospace the strength-to-weight ratio is important. There are several materials like carbon fiber reinforced plastics (CFRP) and fiberglass reinforced plastics (GFRP) that can be molded into parts of the aircraft like the wings, blades, and aircraft engine casings.

Automotive: Like in the aerospace industry, compression molding is also valuable for the automotive industry because of the weight factor. It impacts the fuel efficiency of vehicles. Composites like CFRP and GFRP are the same materials made into several parts of the vehicles like bumpers and spoilers as well as door panels, dashboards, and seat backs. It is also used in making electrical and mechanical parts. Rubber is also a material for compression molding form sealants, vibration control, and O-rings.

Medical: Many of the products used in the medical industry are made from silicon rubber. These are made through compression molding. Some of them include orthopedic surgical implants, diaphragms, vibration inhibitors, lip seals of cylinders, silicone masks of CPAP equipment, and parts and components of other medical equipment.

Electronics: Compression-molded parts are used in electronic products. It is used in creating several types of casings for mobile devices like tablets and smartphones and in the fabrication of many electronic parts of electronic devices.

Other Industries: Compression molding is also used in agriculture, oil and gas, and others in producing key parts of their systems and pieces of machinery. For example, compression-molded parts are used as chain guards, distributors, and wear plates in agriculture. In oil and gas, compression-molded parts are found in seals, bearings and bushing, and other electrical and structural components.

Conclusion

As you can see, compression molding is a widely used manufacturing method across all industries. Owing to its strong ability to produce parts with high tensile strength and stiffness, and other extreme properties. It is a go-to manufacturing technique from high to low volume production as well as rapid prototyping.