Tool Forces and Tool-Chip Friction in Orthogonal Machining

Abstract

An examination of previous work on metal cutting reveals that the normal characteristics of sliding friction do not hold for the friction between chip and tool. Several explanations for the variation in coefficient of friction have been proposed; however, none is entirely-consistent with experimental evidence. In the present work an analysis of the physical variables in metal cutting is presented. This allows the force acting on the tool rake face to be separated from the force acting in the region of the tool nose. Experimental results obtained when cutting an aluminium alloy are presented; in obtaining these, the tool forces were measured with a strain-gauge type dynamometer. The results show that two mechanisms of friction exist on the chip-tool interface: (1) Over part of the contact area between chip and tool ‘sliding’ friction occurs in which the coefficient of friction is constant; (2) Over the remainder of contact, ‘sticking’ friction occurs in which the frictional stress remains constant and independent of normal pressure. This model of combined sticking and sliding friction is verified by examination of the contact conditions at the chip-tool interface after the cutting action has been abruptly stopped; a theoretical analysis based on this model shows good agreement with the experimental results.