Development of an application-oriented tool life equation for dry gear finish hobbing

Abstract

Gear finish hobbing offers high potentials regarding economic and ecological aspects. Pre- and finish machining can be realized using only one machine and a complete dry process chain can be implemented as the hard finishing process by grinding is neglected. During the finishing cut, a small stock on the gear flanks is machined using high cutting velocities. The combination of high cutting velocities and small chip thicknesses leads to machining conditions in the finishing cut, which differ from those of regular gear hobbing and influence the tool wear behavior. As the finishing cut also determines the gear quality, a focus on tool life and achievable geometry is important.This paper deals with tool wear investigations for the finishing cut in dry gear finish hobbing. Different cutting substrates were investigated and evaluated with respect to the process productivity, tool life and wear behavior. For this purpose, empirical studies were conducted using the established fly-cutting analogy trial for gear hobbing. Based on the results of the wear investigations and theoretical considerations, a tool life equation for the application-oriented design of dry gear finish hobbing was derived. Cutting velocities from vc = 250 m/min up to vc = 2250 m/min were investigated under dry cutting conditions. The derived equation for tool life takes the allowable tool wear width VBmax into account, which allows a process design with respect to the required gear quality. As the productivity of gear finish hobbing is decisively determined by the selection of suitable tool and process parameters, material coefficients were implemented in the equation and determined for the investigated cutting substrates. The paper concludes with a verification of the derived tool life equation. The present work contributes to the identification of potentials and limits of gear finish hobbing. The results will serve manufacturing engineers as basis for their decisions for implementing this technology in series production.