As demand for vehicle transmissions and other systems requiring quieter, more compact and lighter gear mechanisms increases, gear manufacturers seek to continually boost productivity while lowering costs.

To enable manufacturers to quickly, accurately and completely produce those gears in a single machine, Mitsubishi Heavy Industries Ltd., Tokyo, developed a technology to permit machining of diverse gear types, such as internally and externally toothed ones. By applying two different multiple-threaded grinding wheels, the technology enables mass production of complex gears, including internal ring gears and some external gears, such as stepped gears and pinion gears with shafts.

Courtesy of Mitsubishi Heavy Industries

On the ZI20A grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpi…" title="Powers a grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpi…" aria-label="Glossary: grinding machine">grinding machine from Mitsubishi Heavy Industries, an hourglass-shaped, multiple-threaded grinding wheel can produce external gears, whereas a barrel-shaped, multiple-threaded wheel can create internal ring gears.

The machine tool builder reported that it developed the technology to significantly expand the applications for its ZI20A grinding machine, introduced in 2009 to make internal ring gears. To produce external gears on the grinder, MHI adopted an hourglass-shaped, multiple-threaded wheel, where the diameter gradually decreases from both ends toward the center. For example, stepped gears, which have gears of different diameters layered in a staircase pattern, and pinion gear and shaft assemblies can be machined in the ZI20A because the technology prevents interference between wheels and workpieces.

When grinding internal ring gears, which are generally used as planetary gears, the machine applies a barrel-shaped, multiple-threaded wheel, where the diameter expands toward the center. Similar to external gear grinding, the technology prevents wheel/workpiece interference.

Conventional methods for finish grinding internal ring gears, external stepped gears and gears with shafts after heat treating require grinding individual tooth grooves with a small-diameter, disc-shaped wheel to prevent interference—a procedure not suitable for mass production, according to MHI. In contrast, the ZI20A can now grind multiple teeth simultaneously.

For more information, contact the Gear Technology Center of Mitsubishi Heavy Industries Inc., Machine Tool Div., Wixom, Mich., at (248) 669-6136 or visit www.mitsubishigearcenter.com.