Compression molding is a highly adaptable and widely used method for molding various materials, offering numerous benefits in terms of offering flexibility in design, production efficiency, cost savings and material properties. This process involves the use of heat and pressure to shape and cure the molding material into the desired form. Compression molding is ideal for molding complex, high-strength and advanced thermoplastic components.

The compression molding process starts with the choice of molding material. Typically, thermoset materials are used in a cured stage, which are usually in the form of:

• Granules
• Putty-like masses
• Preform 

These materials will cure and harden when subjected to heat and pressure, resulting in a strong and durable final product.

What are the steps to compression molding components?

To begin the compression molding process, the mold is preheated to a suitable temperature based upon the material being molded. The preheating step ensures that the molding material can flow easily and uniformly within the mold, ensuring the full distribution of the material and minimizing any defects or inconsistencies in the final component.

Once the mold is heated, the preheated material is placed into the mold. The mold is then closed with a top force or plug member, which applies pressure to force the material into contact with all areas of the mold. This pressure ensures that the material takes the shape of the mold and fills any and all of the details or features of the mold.

Along with compression, heat is applied to the mold to initiate the curing process of the thermoset resin. The combination of heat and pressure accelerates the chemical reaction within the resin, causing the material into a process caused crosslinking which makes the parts tougher, less flexible and resistant to softening when heated. The duration of the heating and curing process varies depending on the specific resin and desired properties of the final product.

What are the benefits of compression molding?

Compression molding is known for its ability to mold large and fairly complex parts. The high-pressure nature of the process allows for the production of parts with excellent surface finish and dimensional accuracy. Also, the absence of shear forces during the molding process reduces the formation of what are called knit lines, which are visible lines that occur when the resin flow fronts meet and join together. This results in stronger and more structurally sound molded parts compared to other molding methods such as injection molding.

Another advantage of compression molding is the reduced degradation of fibers in composite materials. Fiber reinforcements, such as fiberglass, play a crucial role in enhancing the strength and stiffness of the molded parts. During compression molding, the fibers are subjected to less shear stress compared to injection molding, preserving their length and alignment more effectively. This leads to improved mechanical properties in the final product.

Furthermore, compression molding is compatible with a wide range of materials, including advanced composite thermoplastics. These materials can be in the form of unidirectional tapes, woven fabrics, randomly orientated fiber mat, or chopped strand. The ability to mold such materials opens up opportunities for creating lightweight, high-performance components for various industries.

In the case of thermoset transfer and compression molding, the advantages extend to the use of high-temperature thermoset materials. These materials exhibit superior dimensional stability compared to thermoplastics, meaning their shrinkage remains consistent throughout processing and under different environmental conditions. This stability is particularly valuable when molding parts with varying wall thicknesses, as it minimizes the risk of warping or distortion.

Moreover, high-temperature thermoset materials offer excellent heat resistance and can withstand extreme operating conditions. They are ideal for applications where thermal stability is crucial, such as in automotive under-the-hood components, aerospace structures, and electrical insulation parts.

Compression molding is a highly effective and versatile molding method with many advantages. Its ability to mold large, complex parts with minimal knit lines and fiber-length degradation makes it a preferred choice for industries requiring high-strength fiberglass reinforcements and advanced composite thermoplastics. The process enables precise control over dimensional stability, producing accurate and reliable parts. With the added benefits of compatibility with high-temperature thermoset materials, compression molding proves to be a valuable technique for a wide range of applications across various sectors.