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New coating called 'as significant as intro of hard milling'

With the proper tooling, equipment and setup, hard milling 60-HRC D-2 tool steel is no sweat. Perspiration pours, however, when milling harder materials that are generally ground or sinker-EDMed.

U.S. Union Tool’s UDCB endmills have a diamond coating that enables the tools to cut hard materials, such as carbide, that typically are ground or sinker-EDMed. Video courtesy U.S. Union Tool.

That’s no longer the case with the introduction of diamond-coated UDCB ballnose endmills from U.S. Union Tool Inc., according to John Bradford, micromachining R&D team leader for Makino Micromachining, Auburn Hills, Mich. “From Makino’s perspective, we see this tooling development probably being as significant as the introduction of direct hard milling in the mid-1990s,” he said, noting that milling carbide with carbide tools previously achieved a 10 to 20 percent success rate.

At IMTS 2012, Mason, Ohio-based Makino milled carbide with a hardness of at least 93 HRA on its iQ300 micromachining center using a 1mm-dia. UDCB endmill designed for roughing and finishing. e cutting tool consistently experienced just 1.8?m of wear after a 38-minute cycle time, Bradford noted. He added that to sinker-EDM the carbide part would have consumed at least 4 hours, including programming electrode production, machining the electrodes and EDMing the part.

To cut multiple 2.200mm-deep features, the 2-flute tool ran at 30,000 rpm and a feed of 300mm/min., with a chip load of 10?m per flute per revolution.

The 2-flute endmills, developed by Union Tool Co., Tokyo, are available from 0.2mm to 6mm in diameter. e diamond coating has a consistent thickness of more than 10?m and is grown via hot-filament chemical vapor deposition under precisely controlled conditions, noted Jonathan Hay, senior vice president of sales and marketing at U.S. Union Tool, Anaheim, Calif. Compared to plasma CVD, hot-filament CVD provides a more homogenous coating on complex shapes, according to Hay.

He added that the coating’s hardness is about 100 GPa, or 9,000 HV. “It’s very close to a single-crystal diamond in terms of hardness.”

Because the cutting force when milling carbide is about three times greater than when milling 60-HRC D-2 tool steel, according to Hay, applying a UDCB endmill requires a rigid machine to minimize vibration and an inclined or helical approach to provide gradual cutter entry into the workpiece. During the show demo, Makino used a 1ş helical ramp and reduced the feed 90 percent for the lead-in.

“We found the helical feed to be more reliable because the cutting force is more even on the approach,” Hay said, noting the feed can remain constant throughout the cutting cycle. He added that an even cutting force helps prevent damage to the brittle workpiece, tool substrate and coating.

“Obviously, with three brittles, we need to get everything just right,” Hay said.

—Alan Richter

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