Using Liquid Injection Molding (LIM) for Medical Device Manufacturing

An important early step in Flexan’s method of creating successful components for our customers’ medical devices involves understanding how they will function within their end-use scenario. We work closely alongside our customers at every step throughout this process – from planning meetings through prototyping stages right up until when they launch their devices. Thus, we can determine if LIM is the best option, and how to ensure using this process goes as smoothly as possible. In this two-part blog series, we will look specifically at liquid injection molding as a product manufacturing tool.

If you would like to talk to one of our sales representatives now about your medical device or medical device component needs, contact us here.

Molding processes for medical device manufacturing come in a few varieties, including thermoplastic, micro molding, compression molding, transfer molding, and others. Choosing the right molding process is important to creating a successful and top-quality end product. Here are some common options:

Transfer Molding

With transfer molding, a hydraulic ram pushes rubber through runners and gates into specific cavities. The benefits of transfer molding are that it requires only a short setup time, plus it is very useful for both low-volume and high-volume production. Contract Manufacturing Organizations (CMOs) can also use the process for metal and plastic insert over-molding.

Compression Molding

Compression molding involves silicone being prepared outside of the molding process. Shot in place in each mold cavity, sealed with a top, then compressed to ensure all areas of the mold are touched. The compression molding process works well for larger geometric parts and over-molding applications.

Micro Molding

This is a form of LIM for components that require an injection volume under 6 grams. This is done for products requiring tight tolerances and stringent flash requirements. It is often used for parts in minimally invasive surgical tools, valves, and seals. Micro Molding is also chosen for micro sensory and microfluidic products due to its precise tooling.

Silicone to Metal Bonding/Insert Molding

Silicone rubber is bonded to a primered substrate via insert molding and over-molding. The challenge here is ensuring the insert maintains the correct position throughout the molding cycle. Pre-treatments of inserts are done to create maximum bond strength and durability.

Thermoplastic Injection Molding

Thermoplastic injection molding is a reversible molding process by which pellets of plastic are melted, forced into a mold to assume their final shape, and then quickly cooled to harden. This method is excellent for creating parts with superior surfaces and finishes. Precise, fully functional components and parts can be manufactured for both prototypes and full production runs.

Insert/Over-Molding

Thermoplastic material molded around an extrusion, metal insert, or other functional component that has been placed in a plastic injection mold. The benefit of using this technique is that it creates durable integrated components with lower assembly costs while maintaining quality.

Liquid Injection Molding (LIM)

Finally, we come to Liquid injection molding, or LIM, which uses silicone or Liquid Silicone Rubber (LSR) to make highly durable silicone parts capable of enduring extreme conditions. The liquid injection molding process injects the liquid silicone or rubber into a pre-made mold to form the device or component and then heat is applied to cure it and solidify the shape.

Liquid injection molding using Liquid Silicone Rubber provides medical device manufacturers with numerous benefits that make it one of the most popular solutions for the manufacture of rubber components. Here are some of the benefits:

• Durability: Liquid injection molding can last a long time, even in high and low temperatures, and it’s for this reason you often find LIM parts used in cars and airplanes, as well as the medical field. Since the silicone has fire retardant and heat resistant properties, liquid injection molding is unlikely to warp or melt like you find with plastic injection molded parts.
• Strength and Flexibility: Silicone LIM components are flexible yet strong, which means they can be stretched up to six times their length before snapping or breaking. This adds to the durability aspect, but also means it expands the number of potential uses across multiple industries.
• Superior Mechanical Properties: Silicone liquid injection molding works well with devices that have moving parts. It adds durability to complex components which need buffers and materials to keep parts working together without excess wear and tear.
• Biocompatibility: Silicone rubber is biocompatible, making it a safer and more hypoallergenic alternative than other materials used for medical devices.
• Accuracy: The silicone liquid injection molding process is highly accurate, and this means parts do what they are supposed to do.
• Automation and 24/7 Production: Once it is set up, liquid injection molding can be automated. This means the process can run pretty much 24/7 and doesn’t require much human intervention and monitoring.

As we’ve discussed, silicone liquid injection molding is an excellent option to use for many medical device applications, provided it is done correctly. One of the potential LIM risks is that the fabrication process needs to be handled precisely with exacting detail, especially when developing the mold. Mold tolerances must be tight and strict to prevent part flash from occurring.

LIM is a process best done with someone who has done it before and partnering with a contract manufacturer who has experience is very helpful. Using the expertise of the CMO can allow for development and manufacture of great medical devices and components using Liquid Injection Molding.

Flexan has extensive, successful experience in liquid injection molding to help create top-of-the-line medical devices that change people’s lives. Quality and engineering are part of our Flexacution method. The Flexacution model is a holistic way of looking at the manufacturing process that facilitates a proactive approach to identifying and resolving problems to bring much-needed, high quality medical devices to market quickly.

Our expertise includes silicone liquid injection molding, thermoplastic molding, micro molding, compression molding, and transfer molding. With ISO 13485 certification and a robust Quality Management System (QMS), we support bringing reliable medical device products to a global market.

Stay tuned for Part 2 of this blog, coming soon.

If your medical device company could benefit Flexan’s experience in bringing medical devices to market, contact our sales team today.