Medical Silicone Molding
Medical Silicone Molding is a process of precision molding, either unrestricted silicone (implantable for over 29 days) or restricted silicone (limited to 29 day implants). During the molding process, the three variables that must be controlled are time, temperature, and pressure. The temperature must be high enough to minimize cure times, yet low enough to prevent material scorching. The selected pressure level must allow for complete mold filling while permitting the escape of air. The process must also be optimized to prevent voids and flash. The process produces diverse implant grade and disposable molded silicone parts. Long-term implantable silicone parts are used in medical devices (pacemakers, defibrillators, heart valves, etc.) designed for prolonged or extended service. Other silicone items are used in sealing systems, manifolds, connectors, stoppers and other devices.
Silicone elastomers are typically molded through three main methods:
- Liquid injection molding (LIM): LIM is the ideal medical silicone molding process when volume, speed and precision are critical. The ability to run with a lower injection pressure means less variation, tighter tolerances and consistent quality. LIM brings faster cycle rates and a more competitive piece price.
- Transfer molding/Compression Molding: Transfer Molding is a flexible production process when silicone gumstock is specified. Intricate shape, undercut and thin walls are possible with specially designed molds. Raw silicone is placed in a transfer pot on the vertical molding press and transferred through a runner system into the cavities. After the silicone is cured, the part undergoes a hand deflashing or cryogenic deflashing of the parting lines, depending on the critical nature of the part. Over molding of metal and plastic inserts are often achieved with transfer molding. The advantages of transfer molding are the accommodation of low and high volumes as well as the flexibility of short set up times. Compression molding places the silicone directly over the cavity and the closing action of the mold completes the cavity fill. Both processes require a two roll mill and either a peroxide or platinum catalyst to prepare the raw material for molding.
- Insert Molding: Devices often call for inserts encapsulated in silicone. We can overmold various substrates such as: Titanium alloys, Stainless steel alloys, Engineered plastics, and Ceramics
Additional applications include:
- Electrical stimulation
- Artificial joint implants
- Surgical reconstructive components
- Grafting / Suture points for implanted devices
- Injection ports
- Disposable silicone components
- Micro Molding
- Over Molded handles/surgical tools