Kashifuji Works Ltd. developed the KGH300 about 50 years ago based on an idea from late professor Masato Ainoura of the National Institute of Technology, Kurume College. The KGH300 used an externally threaded grinding wheel to hone gear teeth.
The first machine was sold in 1972 and in 1979, it received the Japan Society of Mechanical Engineers Award. The KGH300 was immediately successful after its release as an easy and economical way to polish tooth surfaces and remove dents. However, as the popularity of gear grinding machines increased, the demand for externally toothed grinding wheel gear honing machines themselves decreased, and the last Kashifuji gear honer, KGH220, was sold in 1992.
As the development of gear grinding and internally toothed gear honing technologies progressed, they became the mainstay of automotive gear production. Kashifuji aimed to further improve tooth surface finish. Since 2005, it has been researching a centerless gear lapping method with the National Institute of Technology, Sasebo College. However, because the company has had difficulty in reducing costs due to the structure of holding the workpiece with three lapping gears, it developed a new machine, the KGH250, which has a single grinding wheel axis and a structure similar to that of a vertical hobbing machine.
The KGH250 is a gear flank finisher machine that rotates the “threaded grinding wheel” with the workpiece to improve the roughness of the tooth surface in addition to removing dents. The machine structure is simple. The workpiece axis has no driving force. It is only equipped with a brake that generates a moderate braking force at the contact point between the grinding wheel and the workpiece. Consequently, it is not possible to control/modify the tooth shape or tooth trace like a gear grinding machine. The brake is an electromagnetic brake that allows for fine adjustment. Servo axes are used for all axes. The manual alignment of the workpiece and the grinding wheel has also been automated. There is no particular restriction on the grinding wheel to be used, and it can be selected according to the purpose. The machine structure is designed to reduce processing time.
In the recent trend toward electric vehicles, in addition to improving fuel efficiency by improving meshing efficiency, there are also growing demands for higher strength and quieter operation. Tooth surface roughness is now required to be greater than that achieved by gear grinding or internal gear honing. When improving the tooth surface roughness of gears that have been ground or internal gear honed, it is best to change the tooth profile and tooth trace shape as little as possible while improving the surface roughness. Also, there are some cases where higher-order gear noise was reduced by improving tooth surface roughness.
Although 50 years have passed since the development of the original model, the KGH250 has been completely reexamined and improved and was developed with the aim to produce “highly efficient mirror finish on tooth surfaces” in addition to “low-cost tooth surface finishing and dent removal.”
