Micromoulding with liquid silicone rubber: What to ask your vendor
Krissy Dempsey, medical moulding market manager and Angie Alt, marketing coordinator, both from manufacturer, Saint Gobain explain what to discuss with your vendor when creating a part that will be micromoulded utilising Liquid Silicone Rubber (LSR).
Market research company, BIS Research, estimates the global minimally invasive surgical systems market is estimated to grow at a Compound Annual Growth Rate (CAGR) of 10.9% to over $40.52 billion by 20251. As with the minimally invasive surgical market, the general trend in medical devices (for markets such as ophthalmic, drug delivery, vascular access and intravenous therapy) is a smaller footprint, lower cost, and disposable - when possible. In order to keep up with these trends, the supply chain must adapt in order to be able to provide components that are designed to be micro-sized yet still maintain the integrity of the design, the high-quality requirements and meet the volume expectations of the Original Equipment Manufacturer (OEM).
The evolution of micromoulding a variety of materials from metals to plastics to thermosets, such as silicone, are all spurring new design changes and updates to meet the expectations of OEMs and patients for smaller devices. With LSR, parts can be made as stand-alone parts or overmoulded to a variety of substrates for sealing, soft-touch, and other functions.
Silicone is very inert and is a good choice for fluid path components. Depending on the application, there are a variety of grades you can choose from. However, it is important to think if the application of the silicone part will be static or dynamic. Other critical factors to consider are if the silicone needs to return to shape, if it is sealing and if it needs to be medical grade (class VI) or if an implant grade is required. Micromoulding vendors should be able to help you determine the appropriate grade based on physical properties, application requirements and certifications.
In addition to material expertise, OEMs will want to find component suppliers that can deliver high precision, shot-to-shot repeatability, and achieve very tight tolerance targets on your complex medical device components. Silicone can be a very difficult material to work with so working with a vendor that is well versed in the processing of this material will be key.
Silicone has the ability to flash at <0.0001” or <0.003mm making mould design and precise mould-build key factors to a successful micromoulding project. The tool design and manufacturing equipment used (press) will need to allow for the ability to control a very small shot size. From Saint-Gobain’s experience, parts can be moulded as small as 0.001g with a hole size as small as 0.003.” These micro-parts can contain complex part geometries, undercuts, threads and blind shutoffs. By working with a vendor on the design you can ensure the component functions as intended and is able to be manufactured in such a way that will meet the dimensional, tolerance and volume requirements for the life of the device.
Some other challenges to keep in mind and discuss with your vendor include being able to develop a reliable and reproducible measurement technique, particularly when cross-sections are required. Silicone is not rigid and therefore using non-contact measurement equipment is recommended and a thorough gage repeatability and reproducibility study. Part handling is another factor which is important to discuss with your vendor. As the parts are so small, they are often difficult to handle manually, and so automation, when volume supports it, is a suitable option. There are specialised techniques which exist and can help with automation. Additionally, silicone attracts debris and holds on to it so it would be a good idea to ensure that the vendor is using a certified cleanroom that meets your expectations.
Micro-overmoulding of silicone to substrates such as stainless steel, polycarbonate, nylon or PolyEther Ether Ketone (PEEK) provides a range of design possibilities. However, adding the substrate to the moulding process does add a layer of complexity for your vendor. If you work closely with your vendor to allow for design tweaks early on in the design process this will allow for manufacturability and save both of you time in the long run.