Given its excellent biocompatibility, heat resistance, and durability, silicone is an extremely popular material for medical devices (including implantable ones). Injection molding is just one way parts can be manufactured out of silicone, and in this article, we’ll discuss a few key advances that have brought Silicone Injection Molding industry to the mature state it is in today.

In this post, we’ll focus on silicone liquid injection molding (LIM), which uses a liquid silicone rubber (LSR), a thermosetting elastomer, which is injected into a heated mold and vulcanizes (cures) into the shape of the desired part. Since the viscosity of LSR is low, it’s a natural fit for injection molding, as the LSR can quickly fill the mold without excessive pressure. In addition to sharing silicone’s intrinsic biocompatibility and wide temperature range, LSR features a wide gamut of available hardness: from 5 to 80 Shore A.

These are just a few of the technologies that have advanced LIM, and propelled it into applications all the way from cookware to implantable medical devices:

Cold Decks Produce Hot Results

A “cold deck” is a cooled (usually by circulating water) section of a LIM mold that prevents the silicone from curing until it reaches and fills the hot mold. Thus the LSR remains liquid, and no material is lost to a solid sprue and runner system. This is the idea behind “hot runners” for thermoplastic resins (which keep the resin inside the runner system hot so that the molten resin doesn’t solidify). Cold decks also reduce cycle time since there is no attached sprue and runner to remove from the part after curing. This helps eliminate what is often a manual step. For high volume production runs, the reduced material waste and shorter cycle times provided by the cold deck can more than pay for that higher initial investment.

Self-Sticking Silicone

In a previous article titled ‘Thermoplastic & Silicone Use for Medical Molded Components‘ we discussed the self-adhering property of some LSR formulations. Continued innovations by silicone material suppliers have resulted in a wider selection of these self-adhering silicones. By eliminating a time-consuming (and often hazardous) priming operation, these LSR formulations improve machine operator safety as well as reduce total cycle times. With the hardness range of these formulations increasing to anywhere from 5 to 70 Shore A, LSR is satisfying the growing demand for softer, self-adhering silicones that meet regulatory standards for biocompatibility, and thus can be used in medical devices.

Overmolding is Outperforming

Advances in overmolding have also played a key role. This includes the use of High temperature thermoplastic substrates (like PEEK and polysulfone). Since both of these polymers have exceptionally high melting temperatures, the molds can be run hotter, curing the silicone faster, reducing cycle time, minimizing price per part, and increasing annual part yield.

Precise Control Yields Production Consistency

Not all of the innovation is happening in materials. As with so many other industrial processes, precision control, advanced sensors, and automation have improved the consistency and quality of parts made by LIM. By combining servo-electric motors, valve timing, intra-cavity pressure monitoring and precise control over pressure, flow rate, & temperature, integrated automation has led to more consistent results for OEMs and their Contract Manufacturing partners.

Precise Control Yields Production Consistency

Lastly, simulation and the application of CAD and CAE to LIM tooling and process parameters have taken hold in the LIM industry, just as it has in thermoplastic injection molding. Simulation early on in tool design can determine thermal behaviors in steel molds before any expense is made into machining them, enabling quick and comprehensive design for manufacturing (DFM) review and optimization of elements like the heating system and mold cavity entry points. Simulation can catch design mistakes early in the process, saving OEMs time and money.

ProMed’s expertise in silicone injection molding can guide your team’s silicone medical device concept from initial design to product delivery, leveraging these and many other technical advances.

Silicone Injection Molding Advancements
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Silicone Injection Molding Advancements
Given its excellent biocompatibility, heat resistance, and durability, silicone is an extremely popular material for medical devices (including implantable ones).
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ProMed Molding
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