For companies seeking high-quality and cost-effective parts and devices for the medical sector, silicone injection molding is an ideal solution. Below are the basics of medical silicone injection molding including the process, materials, advantages, and how it differs from other silicone molding techniques.


Common Silicone Molding Methods

To better understand the basics of silicone injection molding it will be useful to understand how this process compares to other silicone molding techniques. Below are the most common methods used to manufacture silicone into a final product.

  • Compression Molding: silicone is compressed between two heated mold cavities to force the material to fill the desired mold shape.
  • Transfer Molding: silicone is pushed into the heated mold using a plunger, where it takes the shape of the cavity.
  • Extrusion: melted silicone is pushed out of a die to form the shape of the desired finished product.
  • Injection Molding: melted silicone is injected into a mold cavity to form the shape of the mold.

It is important to note that each of the primary molding techniques above may have variations of the basic process. For example, rotational molding is an extension of the techniques above where silicone is inserted into the mold at the desired temperature while the mold continuously rotates to form hollow parts with uniform wall thickness. Additionally, blow molding is another variation where heated silicone is blown into a mold along with air and as the silicone expands, it presses against the walls of the mold forming a thin-walled, hollow shape.


Materials Used in Medical Silicone Injection Molding

Silicone elastomers have long been a popular material for medical devices and components due to their durability, wide temperature range, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for medical implants!

Silicone elastomers are available in two commercial forms: Liquid Silicone Rubber (LSR) and High Consistency Rubber (HCR). LSR and HCR are both used to manufacture medical device products. For companies already using HCR to manufacture medical device components, it may make sense to continue using this elastomer especially since the initial capital equipment costs have already been made. For new product development, LSR is often the best choice given the lower capital costs and labor associated with processing this elastomer. However, the decision to use LSR or HCR should be made on a case-by-case basis and OEMs should consult their molding partner.


Silicone Injection Molding Process and Equipment

There are also variations within medical silicone injection molding, however, the main equipment and process are generally the same. Below are examples of injection molding equipment. The process begins when silicone is fed into a heated barrel. In the picture below, solid raw material is stored in a hopper and then fed into the barrel. In the case of LSR manufacturing, the two liquids LSR components are stored in separate containers and then fed simultaneously into the barrel.

Next, a screw is used to mix, heat, and transport the silicone toward to the mold. The melted material is then injected through a nozzle into the mold and travels via a gate and runner system into the mold cavity; the proper design of the gate and runner system is essential to ensuring the mold is filled properly. As the silicone enters the mold, excess air can be released via vents. The pressure and temperature of the mold are maintained to allow the silicone to conform to the desired shape and harden quickly. Once the part is adequately cooled, the mold opens and the part is ejected, sometimes with the help of ejector pins. The mold is then ready to receive the next charge of silicone. The injection molding process is a continuous operation with minimal downtime, resulting in high output rates.

Medical Silicone Injection Molding
Medical Silicone Injection Molding

(photo credit: Wikipedia)


Advantages of Medical Silicone Injection Molding

Silicone injection molding has several benefits compared to other molding processes, and below are some of its key advantages.

  • High Quality & Very Reproducible: Silicone injection molding produces products that are virtually identical from part to part which provides excellent brand consistency and part reliability during high volume runs – this is especially crucial for parts and devices used in the medical industry! High reproducibility also allows for production to be scaled up to very large volumes, resulting in low costs per unit after the upfront equipment set-up costs are paid.
  • Excellent Versatility: silicone injection molding is a good choice for a wide range of part sizes, materials, and colors. Additionally, injection molding allows for the use of multiple materials simultaneously, allowing for a high degree of customization.
  • Able to Produce Complex Parts: silicone injection molding is typically performed at high pressure which forces the silicone into small crevices in the mold (that other molding processes are unable to reach), enabling the production of intricate and complex parts.
  • Efficient Production: silicone injection molding is a very fast process that generates high-output production compared to other molding methods, making injection molding a more efficient and cost-effective solution.
  • Automation Reduces Cost: silicone injection molding is highly automated via the use of machines and robotics, requiring less oversight by operations personnel. Automation reduces labor costs which decreases the manufacturing costs per unit.
  • Low Waste Generation: silicone injection molding manufactures smooth products that have minimal finishing requirements after removal from the mold – resulting in less waste generation compared to other molding techniques. Oftentimes, injection molding waste is able to be reused, resulting in a more environmentally-friendly and lower cost process.


ProMed’s Medical Silicone Injection Molding Capabilities

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 your next medical molding project.