Additive Manufacturing

MAR 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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MARCH 2018 Additive Manufacturing 18 TAKING SHAPE to create high-performance parts and molds, and formulate the material to meet these requirements," Zollo explains. After com- ing to this realization, he began to focus on developing materials 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. The result of Zollo's R&D was a carbon nanotube reinforced, high- performance composite filament for plastic composite molds. This composite material can handle the required stress and is reslient in the molding process. "It also possesses low surface energy (like Teflon), which means the injected material comes in and just glides over the surface," Zollo says. "The carbon nanotubes act as micro bearings that make the surface tough and slick, creating a heat barrier while the material is being injected." The carbon nanotubes are also excellent heat conductors within the mold that help overcome the relatively low rate of heat trans- fer exhibited by most plastics. Cooling channels can also be printed as close as 2 to 3 mm from the cavity surface, creating a relatively short distance for cavity heat to travel. The 3D printer. When Zollo tested printing precision 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 expertise to fix these machine issues," he says. So, he and CTO Ron Aldrich set out to develop and produce a pro- prietary high-precision desktop printer. The approach was to develop and optimize a printer for the material, not the other way around. "Our high-precision 3D printer looks like a conventional FDM printer, but there are several important unique features, that are not obvious, which enable printing a pre- cision mold," Zollo says. These include 25-point measurement of the entire print bed before each print job to create a 3D profile of any deviation in flatness; an ARM Cortex processor-based controller board; and proprietary printer driver controls of the stepper motors. The STL file-slicing engine software has also been customized to deliver more consistent plastic flow for a denser, smoother finish. When Zollo originally tested printing molds in his lab, he was pleasantly surprised to learn that his printed molds could easily support 100+ cycles, depending on the design of the mold and the material being molded. While none of his clients have at- tempted to mold more than 125 cycles to date, inspection of the molds after this many cycles indicates no visible wear on the cavity, gates or sprues. Zollo sees no technical reason why molding parts in HDPE, ABS or PP would not hold up to 500+ cycles. He believes this compares quite favorably with molds produced on third-party printing systems. He is hearing from service providers that typical life expectancy of printed plastic molds ranges from 5 to 25 parts, depending on the plastic to be molded. Zollo does note that there are a few practical limitations. "So far, we have focused on designing and printing simple, two-part, one- and two-cavity injection molds. The largest outer dimension printed to date is approximately 6 by 6 by 4 inches. We are working on methods to print larger molds that exhibit the desired dimensional precision, and expect to expand the range of dimensions in the near future through improved printing process control," Zollo says. The proprietary Fabricatus high-precision desktop 3D printer has automatic print bed contour profiling. Spring-loaded pins measure the exact height of 25 points on the print bed. Courtesy of Avante Technology. A completed two-cavity plastic composite mold was 3D-printed on a proprietary Fabricatus high-precision desktop 3D printer using a carbon nanotube reinforced, high-performance composite filament. The upper half shows the surface finish prior to postprocessing and the lower half is partially sanded.

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