Investigation of the critical cutting edge radius based on material hardness

Abstract

This paper is aimed to investigate the influence of material hardness on the behaviour of cutting edge radius in tool-based micromachining process. The main governing process parameter considered for this study is relative tool sharpness (RTS) which is quantified as the ratio of undeformed chip thickness (a) to tool edge radius (r). The variation of RTS influences the chip formation behaviour with transition from concentrated shearing to ‘extrusion-like’ mechanism for achieving ‘grinding-like’ surface finishing by the extensive tool edge radius effect. As different materials have different characteristics and properties, the critical threshold RTS value (RTS _critical ) may vary with material hardness by significantly affecting the surface topography during ‘extrusion-like’ mechanism. In this study, material hardness is found to be an important mechanical property in orthogonal micro turning experiments conducted with a CBN tool for metal alloys. Best finishing (R _a ) values of workpiece surfaces were used to determine the material hardness effect on RTS _critical . Firstly, Aluminium and Magnesium alloys were used to construct a graphical trend for the relationship of material hardness and relative tool sharpness. Secondly, a random material was selected to predict the RTS value from the graphical trend based on material hardness. Thirdly, micro turning experiments were conducted to validate the predicted result. Finally, the graphical trend was updated to get the relationship of material hardness and critical relative tool sharpness (RTS _critical ) with the three experimental materials which are most widely used in micromachining industries.