A study of the cutting modes in the grooving of tungsten carbide

In this paper, the cutting modes for grooving a tungsten carbide work material are investigated and presented. The grooving tests were carried out on an inclined workpiece surface using a solid CBN tool on a CNC lathe. The experimental results indicated that there was a transition from a ductile mode cutting to a brittle mode cutting in the grooving of tungsten carbide workpiece material as the depth of cut was increased from zero to a critical value. Ductile mode cutting is identified by the machined workpiece surface texture and the material removal ratio f _ab -ratio of the average of the volume of material removed to the volume of the machined groove. Scanning electron microscopy (SEM) observations on the machined workpiece surfaces indicated that there are three cutting modes in the grooving of tungsten carbide as the depth of cut increased: a ductile mode, a semi-brittle mode and a brittle mode. The ductile cutting mode depends on the stress in the cutting region, i.e., whether or not the shear stress in the chip formation region is greater than the critical shear stress for the chip formation (τ _slip >τ _c ), and whether or not the fracture toughness of the work material is larger than the stress intensity factor (K ₁<K _c ). When (τ _slip <τ _c ) and (K₁>K _c ), crack propagation dominates, the chip formation and the cutting mode are brittle.