Fundamental research on hobbing of austempered ductile iron gear - (Influence of graphite particle on machinability)

In this study, the influence of graphite particles (number of graphite particles) in austempered ductile iron (ADI) on tool wear and finished surface roughness was investigated, using TiN and (Al, Ti) N coated high-speed steel cutting tools in hobbing. The experiments were performed using a fly tool of the same geometry as that of one blade of a hob, at the cutting speed of 47 m/min in dry cutting. As a consequence, the following points were clarified: (1) ADI having an average number of 284 graphite particles per 1 mm(2) (the average diameter of 28.0 mum) showed a good machinability without causing tool failure. The tool life was improved when using the (Al, Ti) N coated tool, and the finished surface roughness R-y was 3.5 mum at the end of cutting. (2) It was suggested that the adhesion of deposited metal on the rake face influences the tool failure which occurred when cutting ADI. (3) The interrelation between the center wear and the surface roughness was recognized.