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moldmakingtechnology.com 25 "Engineers designing a part usually begin with mechanical and other physical characteristics and then select their mate- rial based on these requirements. For me, it seemed logical to start with the mechanical and chemical properties that are required to create high-performance parts and molds and formulate the material to meet these requirements," Zollo says. It was then that he began to focus on developing mate- rials for finely extruded parts. He went back to the lab and worked with a few of his previously developed materials and discovered that some of the compounds worked well for 3D printing. These high-performance composite formulations caught the attention of an automotive manufacturer that was looking to make some soft tooling. At the time, there were no quality injection mold materials available for use on open-source FDM technology. The result of Zollo's R&D; was a carbon nanotube reinforced, high-performance composite filament for printed plastic composite molds, which he says could advance the state-of-the-art when it comes to material in injection and compression molding. To qualify for this demanding application, the mate- rial must meet certain requirements: It must print at very low-layer heights (0.1 millimeter or lower). It must support injection of common molding plastics, possess mechani- cal strength under high temperature and pressure, flex under high pressure to align to metal holding plates and alignment pins, and flex to a 100-percent seal between mold halves under pressure. It must withstand sanding, pol- ishing, drilling, tapping and threading; have low surface energy, offer a relatively high rate of thermal transfer, adhere strongly to the print bed to ensure a precision print within desired dimensions, and exhibit very strong layer-to-layer bonding. Finally, the material must be chemically nonreactive to the thermoplastic being molded. "The right composite material can handle a lot of stress, but more importantly it is resilient, which is important to the molding process. It also possesses low surface energy (like Teflon), which means the injected material comes in and just glides over the surface. The carbon nanotubes act as micro bearings that make the surface tough and slick, creating a heat barrier while the material is being injected," Zollo says. The carbon nanotubes are also excellent heat conductors within the mold that help overcome the relatively low rate of heat transfer exhibited by most plastics. Zollo explains that the proper design may include a variety of cooling channel configurations that produce good heat flow to preserve the integrity of the mold. Cooling channels can be printed as close as 2 to 3 millimeters from the cavity surface, creating a relatively short distance for cavity heat to travel. "This combination of higher heat transfer rates and con- formal cooling channels improves cycle time over third- party thermoset plastic molds. When designed and properly printed, there is basically no melting of the cavity surface, not even at the gates. The key is getting the heat out when it needs to get out," Zollo explains. Zollo's company has teamed up with an experienced plastics molding company that has customers with short- run requirements to experiment with material science for 3D-printed molds. This technical collaboration led to his ability to create commercial-grade molded tools that have successfully run in production environments. "We are for- tunate to have technical staff with experience and training in both disciplines and collaborative third parties who are helping us improve our techniques. This enables us to get the most out of the design to improve the precision, strength and finish of printed molds, as good as or better than what can be produced using more expensive industrial grade printers," Zollo says. Printer Problems and Potential Then there is the printer and the high cost of operating industrial-grade 3D printing systems for short-run injection molds. Options can cost anywhere from $100,000 to roughly $600,000. About 18 months ago, Zollo tested printing preci- sion molds and parts on a range of open-source printers. He was not satisfied with the precision, reliability and quality of any third-party printers. "Imprecisions are built into the typical systems that must be fixed, but companies just don't have the money or exper- tise to fix these machine issues," he says. So, he and CTO Ron Aldrich set out to develop and produce a proprietary high-precision desktop printer, which is his primary mold printing system. "The printer is just the delivery system of the actual (real) product: the printed plastic part," Zollo says. His approach was to develop and optimize a printer for the material being used, which is inverse to the current industry thinking. According to Zollo, his way is far more successful for print- ing high-performance parts. He believes that to accommo- date a range of materials, the printer must be designed to be adaptable. The delivery system should adapt to the material selected, not the other way around. "Our high-precision 3D printer looks like a conventional FDM printer, but there are several important unique fea- tures, that are not obvious, which enable printing a precision mold," Zollo says. Unlike most conventional printers that "It seemed logical to start with the mechanical and chemical properties that are required to create high-performance parts and molds and formulate the material to meet these requirements."