Proto Labs Offers Fast-Turn Optical Silicone

Ann R. Thryft

March 16, 2015

3 Min Read
Proto Labs Offers Fast-Turn Optical Silicone

Fast-turn molder Proto Labs has added a new optical-grade liquid silicone rubber (LSR) service to its lineup. Although optical LSR molding has been done before, a big difference about this service is the fact that it's using Dow Corning's material and process.

Engineering-grade optical silicone has clear advantages over glass in many applications. It's highly transparent, extremely flexible, and is even beginning to replace glass for many uses. This is driven partly because of the huge number of LEDs being used as light sources in so many applications, since silicone holds up well to high heat environments, where glass or other plastics would break.

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But optical LSR molding technology has not been as successful as it could be. "The industry hasn't taken advantage of the potential of using silicone for optical applications," Jeff Schipper, Proto Labs' product manager for LSR, told Design News. Dow Corning's optical silicone technology is definitely the exception: they've done it correctly. "I was very impressed with how well and how easy it was to use their material to make optical quality parts," he said.

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The challenges of molding silicone, optical, or otherwise, are daunting, since much of the process works in reverse of regular molding, said Schipper. For instance, Part A and Part B materials have to be kept separate because they start to cure as soon as they're mixed. The solution is to use a meter mixing pump to supply them into the press so they can be accurately measured and mixed. "Then, the real challenge is that the material's consistency is like water when it goes into press, so you have to use a press that's made for running silicone," he said. The mixed material goes into the barrel, where it's cooled, instead of heated as in regular injection molding, to slow down catalyzation. Then it's injected into a heated mold.

Some of those characteristics are also benefits: silicone's low viscosity makes it flow more easy throughout a mold, so it can move more readily through thin areas and fill small voids, helpful for creating fine features and thin walls. Its flexibility lets engineers simplify designs by combining a lens with a seal, reducing seams in the assembly, bill of materials, assembly cost, and inventory control.

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Optical silicone transfers light very efficiently. Its capable of making lens-quality optics, such as simple magnifiers, Fresnel lenses, and homogenizer lenses, said Schipper. "One customer has told us that we get a 14% light improvement over acrylic. Light transmission with optical silicone is 94% versus 95% with glass, and only 88 to 90% with polycarbonate." Optical silicone is also being used for outdoor lighting that has LEDs as a light source, because of its resistance to heat and its flexibility that help prevent breakage.

Proto Labs is making low volumes of parts in optical LSR for prototyping, and higher production volumes of 5,000 or more. You can find out more about optical LSR and its applications here.

Ann R. Thryft is senior technical editor, materials & assembly, for Design News. She's been writing about manufacturing- and electronics-related technologies for 25 years, covering manufacturing materials & processes, alternative energy, machine vision, and all kinds of communications.

About the Author(s)

Ann R. Thryft

Ann R. Thryft has written about manufacturing- and electronics-related technologies for Design News, EE Times, Test & Measurement World, EDN, RTC Magazine, COTS Journal, Nikkei Electronics Asia, Computer Design, and Electronic Buyers' News (EBN). She's introduced readers to several emerging trends: industrial cybersecurity for operational technology, industrial-strength metals 3D printing, RFID, software-defined radio, early mobile phone architectures, open network server and switch/router architectures, and set-top box system design. At EBN Ann won two independently judged Editorial Excellence awards for Best Technology Feature. She holds a BA in Cultural Anthropology from Stanford University and a Certified Business Communicator certificate from the Business Marketing Association (formerly B/PAA).

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