In connection with my feature article on abrasive machining for the May issue, I spoke with Steve Kendjelic, senior applications engineer for Norton/Saint-Gobain Abrasives, Worcester, Mass., about power gear honing. The process is used for ultrafinishing generated gear teeth and is generally performed on a honing machine. The hones are rubbed against the profile generated on the gear tooth.

Gear honing and gear lapping are the last finishing operations of a gear-generation process. Kendjelic pointed out that the Big Three automakers perform power gear honing, as well as automotive transmission manufacturers.

Grinding the gears after heat treatment can impart grinding lines, which causes transmission noise. As a result, he said manufacturers are hard finishing with honing tools after hobbing and heat treating gears to eliminate the grinding process and impart a crosshatch pattern for oil retention in the hardened workpiece and reduce transmission noise.

Tools with a higher concentration of ceramic grain than in the past are now applied when power gear honing to reduce cycle time by increasing the feed per revolution, Kendjelic added. Previously, there was a 30 percent ceramic content and now it's up to 100 percent in some applications.

In addition, Kendjelic discussed generating grinding and said, "The grinding machine tool people want to have gears continued to be produced on their equipment but also take advantage of technology to go ahead and superfinish gears to compete with the power honing people." Suitable wheels include conventional grinding wheels, and electroplated and vitrified CBN wheels.

One change to become more competitive when generating grinding is switching from a large-diameter wheel, such as a 16" one, to a smaller-diameter one to grind at a higher peripheral speed, he explained. The width of the new wheel, however, increased. Then end users added a second wheel to do polishing. The goal is to improve the surface finishing without having to reclamp the part.