Compression Molding Precision by Davies

Compression molding is an ideal method for molding plastic and composite parts because it offers the following benefits over traditional injection molding.

Video demonstrating Davies Molding's compression molding process in action

Benefits of compression molding:

  • Choice of different types of molding material such as Phenolic, Melamine, Epoxy and more
  • Parts that are exceptionally strong
  • Parts that are heat resistant
  • Parts that maintain their shape even under harsh conditions
  • Minimal excess material in production

Compression molding involves the use of both heat and pressure to shape and cure material into a desired form. This process is ideal for forming complex parts and components that require high strength and can withstand harsh environments. While many companies offer injection molding, few molding companies have the expertise needed to excel at compression molding.

The way the molding material behaves is quite unique and typically the parts being produced are complex. Because of that, it takes a high level of precision to form them properly. The molding material goes through an irreversible chemical reaction that if not done correctly can result in incomplete curing, part instability, or structural failure. Now, let's review the process.

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What is the Compression Molding Process?

The first step in the compression molding process is selecting the material that best fits the project. Typically, thermoset materials are used in one of the following forms:

  • Granules
  • Putty-like masses
  • Preforms
Compression Molding Diagram

Diagram of the compression molding process

When these materials are subjected to heat and pressure, they cure and harden into a strong, durable final product.

After selecting the material the molding process begins by preheating the mold to a temperature appropriate for the specific material being used.

Preheating the mold ensures that the molding material flows smoothly and evenly within the cavity. This step is critical in minimizing defects and achieving consistency in the finished part.

Once the mold reaches the desired temperature, the preheated material is placed inside. The mold is then closed using a top plate or plug, which applies pressure to force the material into all areas of the mold cavity. This pressure helps the material fully conform to the shape and detail of the mold.

Heat is applied in combination with pressure to initiate the curing of the thermoset resin. This triggers a chemical reaction known as crosslinking, which strengthens the material, reduces flexibility, and improves heat resistance. The heating and curing time will vary depending on the resin type and the performance requirements of the final product.

What Are the Benefits of Compression Molding?

This type of molding is ideal for producing large, complex parts with excellent surface finish and dimensional accuracy. Compression Molding Material Pucks One key advantage is the absence of shear forces during molding, which reduces the formation of knit lines—visible marks that occur when resin flows meet and rejoin. Minimizing knit lines results in stronger, more structurally sound parts compared to other methods like injection molding.

Another benefit is the preservation of fiber integrity in composite materials. Reinforcements like fiberglass significantly improve the strength and stiffness of molded parts. Since compression molding applies less shear stress than injection molding, fiber length and alignment are better preserved, resulting in superior product performance.

What Materials are Available for Compression Molding Parts?

A wide range of materials can be used including thermosets and other plastic or composite materials. These materials may come in forms such as:

Davies’ ability to mold these materials enables the production of lightweight, high-performance components for a wide range of industries.

In thermoset molding, high-temperature thermoset materials offer unique advantages. These materials maintain their shape with minimal shrinkage, even under extreme conditions. This dimensional stability is particularly beneficial for parts with varying wall thicknesses, as it minimizes warping or distortion.

Additionally, thermoset materials provide excellent heat resistance, making them ideal for applications that demand structural integrity in harsh environments. Thermoset parts are ideal for industries such as automotive under-the-hood components, aerospace structures, and electrical insulation.

Compression molding is also a top choice for producing large, intricate parts with minimal knit lines and reduced fiber degradation. It’s especially well-suited for industries requiring high strength and heat resistance. The process allows greater control over part formation, resulting in more accurate and reliable components.

While several molding techniques are available, compression molding remains the preferred method for creating strong, durable, and complex parts across a variety of applications.

Compression vs. Injection Molding – What’s the Difference?

Compression molding and injection molding are used quite often for shaping plastic parts, but they work in different ways. With compression molding, a pre-measured amount of material is placed into a heated mold, then the mold is closed and subjected to high pressure until the part takes shape. It’s a great method for larger, thicker, or simpler parts especially when thermoset materials, like phenolic or melamine are required.

Injection molding, in comparison, is a typically an automated process suited for high-volume production of complex and detailed parts. For this method, plastic, typically a thermoplastic material, is melted and injected into a closed mold under high pressure. After cooling and solidifying, the mold opens and ejects the finished part. This process is typically faster and repeatable, however the parts lack the benefits of compression molded parts as referenced above.

Choose between the two comes down to the part’s size, material, and production volume.

Additional Molding Options

    Questions and Answers about Compression Molding

    1What is compression molding, and how does it differ from other molding techniques?
    Compression molding is a manufacturing process that involves the use of heat and pressure to shape and form materials. It differs from other molding techniques such as injection molding due to its unique approach of using preheated material placed in a mold cavity, followed by compression to create the desired shape.
    2Which materials are commonly used in compression molding, and what are their advantages for specific applications?
    Compression molding typically uses thermosetting polymers, such as phenolic and melamine, along with composite materials. The key benefits of using these materials includes having tolerance to extreme heat, durability, and the parts maintain their shape even under harsh conditions. These materials are widely used in applications such as automotive parts, electrical components, and even aerospace applications due to these benefits.
    3Can compression molding be used for creating parts with complex designs?
    Yes, compression molding can produce parts with complex designs based upon the way compression molding works. The material is heated prior to entering the mold, this allows the material to flow better into the detail crevices in the mold when a consistent pressure is applied.
    4What are some common applications of compression molding in everyday products?
    Compression molding offers a versatile, high-quality, and cost-effective way to produce custom parts making it a popular choice in many industries. Compression molded parts can be found in kitchen utensils, electrical outlets, and components of automobiles.
    5What is the compression molding process?
    Compression molding involves the use of both heat and pressure to shape and cure material into a desired shape. It is a fairly straightforward method where a material is pressed between two heated molds, and once it cools down, it turns into a shaped part. It usually involves a rather large press and heated molds. This type of molding is ideal for complex, high-strength components.
    6What factors should I consider when selecting a compression molding partner?

    Experience and Expertise: Look for a company with a long history in compression molding. Compression molding takes a deep level of expertise to ensure quality and reliability.

    Material Versatility: Ensure the molder works with a wide range of materials to meet a wide range of applications.

    Domestic Manufacturing: A U.S.-based manufacturer can help you avoid international tariffs, reduce lead times, and streamline logistics.​

    Quality Assurance: Make sure the compression molding company holds a Certifications like ISO 9001, demonstrating a commitment to quality and continuous improvement.​

    Design and Engineering Support: Partners offering in-house design assistance can help optimize your product performance.​

    Production Capacity: Assess their ability to scale production to meet your volume requirements without compromising on quality.

    7Does Compression Molding require specialized skill?
    Yes. The material goes through an irreversible chemical reaction during the process, and if it’s not done correctly, you can end up with parts that don’t cure fully, lose their shape, or fail altogether. Once a part is formed there is no fixing it.