While at BIOMEDevice Boston last week, I attended a presentation on the show floor focused on micromolding of liquid silicone rubber. Presented by Jeff LeFan, applications engineer at Saint-Gobain Performance Plastics (Portage, WI), the talk centered on the various applications for and advantages of the specialized process in addition to extolling the benefits of silicone. As is the case with any discussion on micromolding, there was the common, yet important, cautionary refrain that micromolding is vastly different from 'macromolding' and requires specialized machinery, processes, and skills. However, LeFan also imparted some useful advice to the throngs of attendees in regards to partnering with micromolders.

In the presentation, LeFan highlighted several unique advantages of micromolding--other than miniaturization, of course--over conventional medical molding in terms of part design.  "In general for macromolding, you don't want sharp corners, and if you can avoid them, it's for the best," LeFan notes. "But if it's needed for a micromolded part, because they are so small and the shrink rates are so low, we can get a nice sharp corner out of a micromold if needed." The low shrink rates associated with micromolding also allow for wall-thickness variation, according to LeFan.  In contrast, a macrosize part should feature as little variation in wall thickness as possible.

While micromolding presents new opportunities in terms of design, it also comes with unique issues that medical device OEMs should be aware of when selecting a micromolder, LeFan says. As noted, micromolding requires specialized machinery. Specifically, he states, equipment should be capable of accommodating very high injection pressures of greater than 10,000 psi as well as high injection velocities in excess of 3 in./sec. Automated parts handling is also imperative when dealing with silicone micromolded parts, he adds. "If you're looking at a part with an overall size of maybe 0.080 in., static electricity becomes a huge problem. The product sticks to everything, including operators handling the parts, so we ideally want to automate the handling process as much as possible because the human interaction is only going to increase and exacerbate all of the other problems. In particular with silicone, it is very tacky."

Additional requirements for micromolded parts, according to LeFan, include automated counting, customized packaging, and specialized micro and nanomeasuring systems with high magnifications for inspecting the small parts. "The quality inspection methods between a supplier and a manufacturer need to be agreed upon well ahead of time," LeFan advises. "This should be done in all manufacturing. But it's highly important with microparts because the measuring techniques are slightly different and everybody needs to be in agreement because when you're talking differences of tens of thousandths of an inch, it will make a huge difference when you're down the road in full production." --Shana Leonard