Honing tech lifts aerospace business

END USER: Waltz Brothers Inc., (847) 520-1122, www.waltzbros.com.
CHALLENGE: Produce flight-critical hydraulic pumps more rapidly and precisely.
SOLUTION: A multifeed honing system.
SOLUTION PROVIDER: Sunnen Products Co., (800) 325-3670, www.sunnen.com.

When Waltz Brothers Inc. needed to create flight-critical hydraulic pumps, it initially relied on standard horizontal honing equipment, which depends heavily on operator skill. The operator needed to hone one bore, clean the part, air gage it at three different levels and then at 90°—bottom, middle and top—to check for issues, such as tapering that may need to be feathered out. If one bore is incorrectly honed, it can result in a scrapped part.

But when the Wheeling, Ill., machine shop switched to the SV-1015 vertical CNC honing machine from St. Louis-based Sunnen Products Co., the nine-bore components were consistently produced with only 0.000020″ (0.5µm) variation—a quarter of the allowable tolerance.

Courtesy of Sunnen Products

The piston bores of the pump body are not through-holes, but have kidney-shaped slots cut through the bottom.

This accuracy is largely the result of Sunnen’s “smart” tooling technology, which combines controlled-force tool-feed capabilities with its existing controlled-rate feed system, according to Sunnen. This and other automation capabilities, such as robotic part indexing and in-process air gaging, have allowed Waltz Brothers to increase accuracy while decreasing cycle times.

“Our focus is close-tolerance, precision parts requiring many operations that typically conclude with grinding, honing or lapping,” President Larry Waltz said. “If a part is machined between centers, most shops will not be too concerned about variation in the centers, which will affect how consistently the part locates in a grinding fixture. But we want to control these factors, which include straightness, hardness and stock allowance.”

The rotors of Waltz’s piston pumps begin as a turned blank up to 8″ (203.2mm) in diameter. Then, nine circumferential piston bores from 0.1875″ to 1.5″ (4.8mm to 38.1mm) in diameter, depending on rotor diameter, are roughed on a machining center. The bores are not through-holes, but have kidney-shaped slots cut through the bottom. Some designs require heat treating, bronze bore liners or bronze plating on the bottom of the part. Liners may be cast in or produced on the shop’s screw machines, then anchored into retaining grooves with a ballizing process or swaging.