Quantitative understanding of cutting forces under hard turning conditions is important for thermal modeling, tool life estimation, chatter prediction, and tool condition monitoring purposes. Although significant research has been documented on the modeling of forces in the turning operation in general, turning of hardened materials involves several distinctive process conditions, including negative tool rake angle, large tool nose radius, and rapid tool wear. These process conditions warrant specific treatment in the analysis of cutting forces. This paper first addresses these issues by formulating an oblique chip formation force model through the extension of a two-dimensional (2D) mechanistic force model while considering the effect of tool geometry complexities. The coefficients of the mechanistic force model are estimated by applying a genetic algorithm in overcoming the lack of explicit normal equations. Then the forces occurring due to flank wear are modeled by extending a 2D worn tool force modeling approach into a three-dimensional analysis to accommodate the effect of low feed rate, small depth of cut, and relatively large tool nose radius in hard turning. The total cutting forces are the linear summation of forces due to chip formation and forces due to flank wear. The model-predicted forces match well with experimental results in the turning of hardened 52100 bearing steel under practical cutting conditions (low feed rate, small depth of cut, and gentle cutting speed) using cubic boron nitride (CBN) tools under the progressive tool flank wear conditions.
Cutting forces in hard turning comprising tool flank wear and its implication for the friction between tool and workpiece