Research On Formation Mechanism Of Chip And Surface Integrity In Hard Cutting Hardened Steel

Hard turning is also known as "turning instead of grinding". It refers to that the turning of hardened steel is taken as the final process of finish machining. In general, rough machining in hardened steel workpiece is performed before quenching and then grinding machining is conducted after quenching. But the grinding cost higher and the efficiency lower than cutting. Along with the development of high hard tool materials and related technology, PCBN cutting tools, ceramic tools or new hard alloy cutting tool is used to lathe or turning machining center of hardened steel turning and machining quality can also reach the level of fine grinding. The finite element software Advantedge FEM and method of micro-topography detection is used to simulate the turning of the typical hardened steel H13 and Cr12 MoV in the hard state turning. The formation mechanism of chip forming mechanism of hard turning and its surface integrity are studied systematically. It provided theoretical support for cutting parameters optimizing and the life of cutter extending and the quality of the die steel surface optimizing.In this paper, ceramic cutting tools?Si₃N₄? are used in cutting simulation. The influence of chip morphology, cutting force and cutting temperature under different cutting parameters are studied. Based on the analysis of strain, strain rates, maximum shear stress and cutting force, the formation mechanism of chip in hard turning is studied. The cutting parameters and conditions of forming serrated chips are defined. By means of the maximum thickness of the chip and the height parameters of the saw teeth chip, the degree of the chip serrated is quantitatively characterized, and the formation mechanism of serrated chip is clarified. The influence of cutting parameters on the degree of cutting to saw teeth are obtained. The forming process of the chip of hard turning is analyzed through the finite element simulation. Based on the analysis of strain rate images of the cutting process, the deformation process of the chip is studied. Simulation of residual stress on hard turning surface is studied. The distribution of residual stress on the surface of H13 steel and Cr12 MoV steel and the size of stress are compared. The influence of different cutting speed, feed rate and cutting depth of residual stress are obtained. The feed rate is the biggest influence on the chip shape, and the cutting speed is the second. The biggest influence on the residual stress is the material itself, the effect of feed rate of the residual stress is the biggest. The generation of serrated chip is due to the plastic instability of the material.The finite element simulation results are verified by the hard turning experiment, and the reliability of the finite element simulation is provided. The metallographic observation of the chips which obtained by experiment is carried out. The micro-morphology of chip morphology in hard turning is observed. The micro mechanism of chip formation in hard turning is analyzed. The surface integrity of the machined surface is studied. The surface roughness value and surface hardness are measured. The surface microscopic morphology is observed. The influence of the cutting speed, feed rate and depth on surface integrity is analyzed.