CNC grinders deliver precision, quality

Tooling & Production, Jun 1999

The precision required of transfer case parts is uncompromising. Dozens of parts must fit and function trouble-free for years. The demand is even tougher for Ford 4WD truck transmissions.

Borg Warner Automotive, Muncie, IN, has produced gears and transmissions since the beginning of the 20th Century. Today it is producing reduction gear sets for the larger range of Ford 4X4 trucks. Within each set are four pinion gears that must be ground flat on each end, with minimum runout to the bore and to a specific microfinish.

To keep up with production requirements and replace aging grinding capacity, Borg Warner decided to purchase an automatically loaded KOYO KVD 302 twin-spindle vertical CNC disc grinder, from Koyo Machinery USA Inc, Plymouth, MI. Since 1997, the decision has paid off in consistently high-quality production and improved uptime.

The process capability studies performed by Borg Warner before machine delivery showed that the Koyo disc grinder was capable of producing parts well within the transfer case builder's specifications. To assure the gears have specified size and microfinish, each is face ground, holding a 0.005" size tolerance, 30 microfinish max, and a 0.0012" runout face-to-bore-all at a Cpk exceeding the targeted 1.33.

In operation, the parts come from heat treat and are manually loaded on the incoming conveyor, which brings the parts into the first station for finishing one end of the pinion gear. The parts are automatically unloaded and transferred to the next station where they are automatically turned over and transferred for finishing the second end of the gear. More than 4500 gears are produced daily.

"It's all about quality and uptime, which translates into cost per piece," says Roy Markwell, process engineer.

The CBN grinding wheel, designed to break down during the grinding cycle and requiring no dressing, has lasted for more than a year, grinding flat ends while removing 0.3mm of material from the steel part. The tooling cost savings and reduction in toolchange downtime have been important, especially compared with