Surface topography of the cylindrical gear tooth flanks after machining

The paper presents an analysis of three-dimensional surface topography of side and side out in tooth space flanks of cylindrical gear machined after hobbing and chiselling by Fellows method. The parameters and functions of surface topography as well as spectral analysis were used. Primary surface topography after extraction of involute tooth profile was analysed. It was found that contour maps of areal power spectral density and autocorrelation functions were very useful for the analysis of teeth flank surface topography. The angular plot of areal power spectral density function assures proper description of surface, background and defects directionalities. Surface texture parameter SPtr and isotropy index Spiso are useful for quantitative surface topography analysis. Good distribution functions of amplitudes and summit curvatures isolate surface roughness height and shape. It was proved using a kinematical-geometric digital model of machining simulation in 3D system, universal generalised model and experimental investigations that the roughness height and roughness spacing were smaller for the tooth point surface than for the root surface after hobbing and Fellows chiselling. Roughness height of tooth profile after machining by one-coil cutter with great axial feed and by modular gear-sharper cutter is smaller than roughness height of tooth line. Inverse dependencies take place after hobbing by three-coil cutter with small axial feed. It was also found that flank teeth surface topography, primary profile along teeth height and teeth line along its width were quasi-periodic. In all the analysed cases, teeth flank surfaces going to the machining have higher roughness height than surfaces going out from the machining. It was probably caused by direction of chips runout; chips damage surface going into the machining. The flank tooth surfaces of a gear made by hobbing and Fellows-chiselling method are anisotropic and strongly oriented along the helix. The orientation of the flank surfaces after hobbing is considerably lower than after Fellows chiselling.