Hobbing with sintered carbide hobs

Abstract

1. I N T R O D U C T I O N CYLINDRICAL gears of steel are generally cut with hobs of high speed steel. To meet the increasing demands for raising productivity as well as for cutting harder gear materials, the development of hobs with sintered carbide blades has been urged. This kind of hobs, however, has not come into practical use yet for steel gears except with those of fine modules because of technical and economic difficulties. From the technical point of view, chipping, which occasionally occurs at the cutting edges results in the distrust of users on the sintered carbide hobs. It is considered that the occurrence of chipping is due not merely to the inherent brittleness of carbides, but largely to the improper selection of carbide grade as well as cutting conditions. In USSR investigations have been made with sintered carbide hobs, in which only finishing of hardened gears has been done [1]. The purpose of this paper is to find out the optimum cutting conditions at which the sintered carbide hob can satisfactorily be used in rough cutting of steel gears. First of all, optimum carbide grade and cutting conditions were experimentally sought for the work pieces of a carbon steel by hobbing with the fly-tools on a gear hobbing machine. Then built-up types of sintered carbide hobs were tested by cutting solid gear blanks of plain carbon steel on another gear hobbing machine. The test results suggest that the sintered carbide hob makes it possible to raise productivity by increasing the cutting speed, about 200 m/min, and feedrate, 2 .0-2-5 mm/w-rev.