Compression Molding 101

From surgical instrument handles and catheters, to drug-eluting implants and stents, different jobs require different devices to be made – and different devices in turn, require different fabrication techniques. The following article on Compression Molding 101 provides an overview of the compression molding process as well as the advantages and disadvantages of this technique.

Compression molding is one of the most common closed-molding techniques and was initially developed to produce products for metal replacement applications, namely within the automotive sector for parts such as hoods and fenders. Use of this molding method has expanded significantly and it is now used to manufacture products for a wide-range of industries, including the healthcare sector.

The compression molding process starts with a thermoset elastomer, such as Liquid Silicone Rubber (LSR), that is often preheated and loaded into an open, heated mold cavity. Next, the mold halves are closed. Unlike injection molding and transfer molding where the molded material is forced into the cavity, compression molding forces the heated cavity onto the material and the silicone is forced into the shape of the mold. Heat and pressure are maintained within the cavity and the mold is held in place until the silicone has cured. It is important to note that the mold is heated, and the silicone is often preheated, to ensure the material is permanently cured during molding via a step called vulcanization. The molded part is cooled and removed from the mold, sometimes with the aid of an ejector pin, and the process is ready to begin again. Cycle times depend on the size and thickness of the molded parts, and how long the material needs to adequately cure. Click here for a simple graphic of compression molding equipment.

Compression molding yields high strength parts in a wide variety of sizes, and is ideal for efficient fabrication of consistent, quality parts. This process can be used for small, medium and high volume runs. Compression molding is known for excellent part-to-part repeatability.

There are several advantages to manufacturing products via compression molding. First, this method often involves tools that are less complex and less costly to construct, resulting in lower manufacturing costs compared to other molding techniques. Compression molding tooling can be fabricated of aluminum or other lower cost materials, further reducing tooling expenses. Second, compression molding is capable of fabricating large and even heavy products that other molding process may struggle to manufacture. Third, this technique generates less waste compared to other methods as there is no runner system or gates to trim off, which can be a huge cost savings when working with expensive compounds. Finally, there is little set-up time required for compression molding.

While there are many advantages of compression molding, there are also some key disadvantages. Compression molding cannot easily fabricate complex and intricate product designs. The flow of elastomer within the cavity is limited, making it difficult for material to get into the hard-to-reach spaces of complex parts. Additionally, this technique is not able to accommodate all product features. For example, compression molding is typically not able to utilize undercuts in the part design as this feature would make ejecting the cured product very difficult. Another disadvantage of compression molding is cycle time – in general, compression molding processes have higher cycle times than other techniques such as injection molding or transfer molding.

Compression molding is an excellent method but it is not the right choice for every project. This is why it is important to work with a trusted molding partner, like ProMed, who will guide you through the molding selection process to determine if compression molding, or another molding technique, is the best option for your specific project!

About ProMed

ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:

  • Automated Injection Molding
  • Multi-cavity tooling
  • Micro molds and micro molding
  • Servo-controlled de-molding capabilities
  • Insert molds, overmolds, and automation integration
  • Transfer molding
  • Compression molding

Contact ProMed today at 763-331-3800 to discuss how we can help with your next project!