Abstract
The paper presents an original contribution to the prediction of surface topography produced by precision hard turning operations using CBN cutting tools and the variable feed rate of 0.025–0.075 mm/rev. The differences between theoretical and real surface roughness parameters Rz and Sz are quantified in terms of springback effect, additional smoothing of irregularities and side flow effect. The primary experimental study includes measurements of 2D and 3D surface roughness parameters using contact profilometer. Correspondingly, cutting forces were measured using a piezoelectric dynamometer, and based on this data, specific corresponding values of ploughing energy and friction coefficient were determined. It was found that the measured value of maximum height of the surface Sz differs from the theoretical value mainly due to elastic recovery of the machined surface and the smoothing effect at the lower feeds and the elastic recovery and the side flow effect at the higher feeds employed. An empirical model for the prediction of the Sz value in function of the feed rate is derived. The prediction accuracy can be improved by advanced numerical modelling of surface generation mechanisms and associated distortions.
Highlights
Hard machining has been established as a leading machining technology for various machine components made of highstrength steels with surface finish comparable to grinding effects [1]
The main advantage of this study is that several factors such as ploughing action of the cutting edge, elastic recovery, smoothing effect of the increased irregularities and unremoved material on the surface were considered comprehensively in precision hard turning (PHT) with variable feed of 0.025–0.075(0.1) mm/rev using chamfered CBN tools
They include such effects as elastic recovery caused by intensive ploughing action of the cutting edge, smoothing effect of the irregularities in subsequent revolutions and plastic side flow due to the lateral flow of the thermally softened material
Summary
Hard machining has been established as a leading machining technology for various machine components made of highstrength steels with surface finish comparable to grinding effects [1]. It is evident to incorporate the specific influence of the mechanics of the chip formation and the tool wear in the formation of the machined surface and subsurface layer It was revealed [4] that in ultraprecision hard turning, the generation of surface roughness is limited by such factors as tool cutting edge defects, cutting vibration and elastic and plastic deformation of the workpiece material. The main advantage of this study is that several factors such as ploughing action of the cutting edge, elastic recovery, smoothing effect of the increased irregularities and unremoved material on the surface were considered comprehensively in precision hard turning (PHT) with variable feed of 0.025–0.075(0.1) mm/rev using chamfered CBN tools.
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