Firms make inroads in 3D production of heat-cured silicone parts

German RepRap GmbH, a manufacturer of industrial 3D printers, has developed a platform for liquid silicone rubber that it claims makes it possible to 3D print heat-cured silicone parts using a high-performance LSR.

The company's next-generation printer — the model L320 — was designed to use a high-performance LSR from Dow Performance Silicones, called Silastic 3D 3335. The LSR prints colored parts, offers properties comparable to injection molded components and transfers easily to injection molding processes, according to RepRap.

Unlike thermoplastic materials, LSR is a thermoset that must be cured. The L320 printer precisely dispenses and cures Silastic 3D material, which "speaks to the ingenuity and quality" of the printer and specially formulated material, according to Tom Jenkins, executive director of business development for R.D. Abbott Co. Inc., North American distributor of Dow silicone rubber products.

"German RepRap's printer cures the rubber while it's producing parts with physical and dynamic properties that are comparable to an LSR molded part," Jenkins said. "The combination of the printer with the Dow 3D 3335 LSR is the only commercially available technology that heat cures the silicone rubber, the same curing method as used in the LSR manufacturing process."

Since the printer hit the market last July, RepRap has been working with R.D. Abbott and other companies to promote liquid additive manufacturing and how LAM can help businesses move from design to production more quickly, or make customized parts. Common applications include seals, gaskets, shoe midsoles and insoles. In addition, business partners said LAM and Silastic 3D LSR support greater design freedom for other products in the automotive, aerospace, marine, medical devices, defense, transportation and window manufacturing markets.

RepRap said its thermal crosslinking process reduces printing time while setting new standards. One of the updates is print head technology that allows precise metering and mixing ratios, and it can influence application direction or cross-linking at the molecular level.

Instead of filament, the L320 printer deposits liquid, which then is vulcanized into a solid object through exposure to a high-temperature halogen lamp, according to RepRap. The lamp passes over the bed between layers and releases energy to accelerate cross-linking at the molecular level, the company said.

With the L320 printer and 3335 LSR material, product designers can form complex shapes, honeycombs, lattices, flat bottoms and geometries with limited overhangs, according to Gifford Shearer, market manager of Dow Silicone Elastomers. The 3D prototypes resemble production-quality components, he added.

"Not only can this technology be used for fit and form analysis, but it can be used for functional product testing. So this truly is a game-changer when it comes to rapid prototyping," Shearer said.

Another partnership involving RepRap, Dow and Nexus Elastomer Systems is bringing new colors to LSR. Although it primarily is used for prototyping, 3D printing is entering a realm of production-scale manufacturing, putting a focus on development of innovative coloring processes.

Nexus engineered a new color dosing system and RepRap linked its 3D printer to it so product designers have the option of making silicone rubber parts in color when using Silastic 3335 LSR material.

Potential applications include colorful products for mobility and lighting, wearable devices, consumer electronics and custom footwear.

"The collaborative work to align the new Nexus dosing system with the German RepRap L320 3D printer enabled us to give designers the option of printing colored parts — as well as transparent parts — from this uniquely beneficial material," Hans Peter Wolf, Dow research and development manager, said in a statement.