Shop Solutions
Smart Honing Delivers Tight Pump Tolerances
“W
e don’t believe it!” That’s how experienced machin- ists reacted to their fi rst encounter with a ma- chine tool that had produced nine bores per part with only 0.000020" (0.5 µm) variation, all day long, with essentially no operator attention on its fi rst run of production parts. That’s 2.21 Cpk
process capability for a game-changing
smart honing technology at Waltz Brothers Inc. (Wheeling, IL), a precision grinding and machining operation where fl ight-critical aerospace hydraulic pumps are produced by the hundreds every year.
Company president Larry Waltz knows it’s hard to hit this tolerance window honing one bore per part, as the shop had been doing with a standard machine. With nine opportunities to make a micron-sized mistake on an expensive workpiece, it takes great skill and many time-consuming machine/measure iterations to make these parts on a standard machine.
“The new SV-1015 honing system not only produces per- fect bores, it also records its fi nal air gaging measurements to track with each serialized part,” said Waltz. “When I showed this new machine to a customer for whom we’d been making these parts, they were so impressed they wanted us to commit to a blanket order for all their parts for the next fi ve years,” Waltz said. “In that instant, we validated our painstaking deci- sion to adopt this technology.”
Rotors of hydraulic piston pumps have nine circumferential piston bores from 0.1875 to 1.5" (4.8-38.1-mm) diameter that are honed to a tolerance range of 0.000060" (0.001524 mm) at Waltz Brothers Inc. (Wheeling, IL) using Sunnen’s SV- 1015 smart honing system. The piston bores are not through holes, but have small kidney-shaped slots cut through the bottom. Some designs call for heat treating, use of bronze bore liners, or bronze plating on the bottom of the part, its running face.
“We’re a second-generation grinding business started by my father and uncles in 1939. Our focus is close-tolerance preci- sion parts requiring many operations that typically conclude with grinding, honing, or lapping, so we added chip cutting to better control the processes upstream from grinding,” said Waltz. One specialty at this 60-person company is manufactur- ing parts that go into aerospace hydraulic actuation systems. “Piston pumps are a good niche for us,” Waltz said. “These are the most critical parts we make. There’s great variation in mate- rials, design details, process fl ow and assembly requirements, but the parts do have fundamental similarities.” The heart of the pump, called a cylinder block or ro-
tor, starts as a turned blank up to 8" (203-mm) diameter. Then, nine circumferential piston bores from 0.1875 to 1.5" (4.8–38.1-mm) diameter are roughed-in on a machining center, and the part may be heat treated. The piston bores are not through holes, but have small kidney-shaped slots cut
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ManufacturingEngineeringMedia.com | December 2013
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