Thermal Cracks of Carbide Face Milling Cutter

Abstract

Under severe cutting conditions of carbide face-milling operation, cracks first come out almost perpendicularly to the cutting edge on both rake and relief surfaces of blades, and next, cracks parallel to the cutting edge appear according to circumstances. These cracks have negative effects to durability of cutter and especially when cutting fluids are applied, they occur remarkably and the cutter is damaged in an early stage. Situations and circumstances under which cracks occur have three characteristic features. (1) Cracks occur easily when the rate of cooling is better or cutting condition is severe, namely the effect of thermal stress whick depends on temperature difference of cutter surface is large. (2) Occurrence of cracks has size effect. (3) Cracks occur as a saturation curve. It is reported that probability Pv of which cracks occur by one thermal tensile stress σ_-T is given by the following equation and the features of crack occurence are explained qualitatively. [numerical formula] 2r_m : thickness of carbide tip, Ldsecc : size of chip contact area, σ₀ : strength const. of tip, K : const. depending on relative heat transfer coeff, m : material const.