Experimental investigation and numerical simulation of chip formation mechanisms in cutting rock-like materials

In this study, the effects of tool geometry such as rake angle, and cutting parameters such as depth of cut on the cutting forces were studied and correlated with the built-up edge during the material removal process of a rock-like workpiece. Cutting or scratch tests were performed on low and high strength simulated rock-like materials using a tungsten carbide tipped orthogonal drag tool with three different rake angles (0°, 10° and 20°) in a custom-made machining set-up incorporating a high-speed video camera. Force data were measured by a tri-axial dynamometer and a compatible data acquisition system, and specific cutting energy was calculated to assess the material removal performance. Experiments showed that a cutting tool with a 20° rake angle produced an efficient cut. The high-speed video at the cutting edge were analysed to comprehend the formation and growth of the built-up edge. Novel insight was gained by characterising the shape and was observed that the constantly evolving shape was unique to each rake angle used, this creates an apparent rake angle. By varying the rake angle and cutting parameter, the measured cutting force and thrust force showed that the material strength, cutting tool geometry and depth of cut played important roles in removing materials. Higher cutting efficiency was indicated by lower specific cutting energy at higher depth of cut for all cutting conditions. The formation of the crushed zone in relation to the cutting force revealed that the cutting force increased with the size of the crushed zone having two types of chip formation modes: shearing and fracturing. Numerical simulations were performed using a commercially available tool called ELFEN, a hybrid finite-discrete element software package. The simulations correlated well with experimental investigation. The simulations also showed the formation of crushed zone and crack growth as observed experimentally through the use of high-speed video and also shed light on the state of stress state at the cutting edge.