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Hardened gears that have been accurately finished can handle higher loads and run at higher speeds than cut gears. Gears may be smaller and lighter due to this accuracy and efficiency. They also run quieter and are widely used in industrial applications to reduce or eliminate noise. As ground gear applications grow, so does the need for good gear grinding equipment.
Over the last 50 years, one way to improve the accuracy of carburized and hardened gears has been to grind them after heat treat. Distortions due to the relatively high temperatures and quenching techniques associated with hardening make it necessary to improve the lead, involute, and spacing characteristics. This, in turn, makes the gear capable of carrying the high loads and running at the high pitch line velocities required by today's most demanding applications. Gears that must meet or exceed the accuracy requirements specified by AGMA Quality 10-11 or DIN Class 6-7 must be ground or hard-finished after heat treat.
Over the past three decades, few manufacturers have worked to develop a gear grinding machine that fits all needs. Although most of today's modern machine tools are quite good at grinding external spur and helical gears, very few machines can handle internal gears without major compromises. Today, one of the only ways to grind internal gears efficiently is the single index method with a dressable vitrified wheel or a bonded cubic boron nitride (CBN) plated wheel. A plated wheel is effective at maintaining its form, but its high price and dedication to a single part result in a high perishable cost. A vitrified dressable wheel offers greater flexibility and is less expensive, but is more susceptible to process variables that can lead to geometry errors.
The five main gear grinding methods available today are:
* Single index form grinders from companies including Kapp, National Broach, Okamoto, Klingelnberg, Gleason, and Mitsubishi.
* Single wheel generating: Hofler or Niles machines.
* Double wheel generating: Maag method.
* Form generating: Reishauer Type RZP.
* Continuous generating: Liebherr, Okamoto, Gleason, Reishauer machines.
Each method has advantages, and disadvantages, as well as preferred applications.
Single Index Form Grinders
There are probably more manufacturers of single index form grinding machines than any other type of gear grinder. The process is...