3. Ductile Mode Cutting Characteristics

Ductile mode cutting characteristics and material removal mechanism of brittle material are discussed using tungsten carbide as an example work material in this chapter. Grooving and milling tests are designed and conducted to investigate their cutting modes. Experimental results indicate that there is a transition from ductile mode cutting to brittle mode cutting in grooving of tungsten carbide when depth of cut is increased from zero to a certain value. SEM observations on machined work surfaces show that there are three cutting modes in grooving of brittle material as depth of cut being increased: ductile mode cutting, semi-brittle mode cutting and brittle mode cutting. Cutting modes is identified and classified by machined surface texture and chip formation. In ductile mode cutting of tungsten carbide, thrust force F_t is much larger than cutting force F_c, which results in a large compressive stress in cutting zone. Large compressive stress and shear stress could shield the growth of pre-existing flaws in work material by suppressing its stress intensity factor K_I, such that K_I < K_C making work material is able to undertake a large cutting stress without fracturing to achieve ductile mode cutting. SEM and EDS examinations on cutting tools indicate that tool wear mainly occurs on flank face and tool wear mechanisms are dominated by diffusion, adhesion and abrasion in cutting of tungsten carbide.