Fundamental Research on the Hobbing of Austempered Spheroidal Graphite Cast Iron : On the Most Suitable Clearance Angle of the Hob

Abstract

This paper discusses the hobbing of gears made of austempered spheroidal graphite cast iron, which has become an object of attention recently as a new material for gears. This iron has many advantages, such as the properties of a cast material and a high strength equivalent to that of steels, and is also an economical material. However, this cast iron is hobbed before heat treatment at present, for the hobbing of teeth of a hardened gear blank is considered to be very difficult. Yet, if the cutting of a hardened gear blank is possible, the cost will be lower because the gear can be used without performing a finishing operation on the tooth surface removing the distortion from heat treatment. In this study, a basic test was conducted using a TiN - coated fly-tool having the same form as one blade of a hob. Next, a hobbing test was conducted using a TiN-toated hob with a large clearance angle of 15°. As a result, the following conclusions were obtdined : ( 1 ) A groove length of only 3.75 meters can be achieved for the work by a (TiN- coated) fly-tool with a clearance angle of 12°. ( 2 )A (TiN- coated) hob with a clearance angle of 15°can apply to ADI. ( 3 ) The accuracy of the tooth profile and the tooth trace of a hobbed ADI gear correspond to the JIS 1 st and 4 th grades. respectively.