Study On Dynamic Characteristic Of Cutting Process And Cutting Parameters Of High Speed Dry Turning Hardened Steel

As the hardened steel is a typical wearing resistant and difficult-to -machine material, the traditional manufacture order such as cutting-harden-grinding may be changed by using ceramic cutter to carry out high speed dry turning, and the weariness strength of workpiece and productivity are improved, and the consumed power is reduced. The change rule of the cutting process information such as cutting force, cutting temperature and chip is the basis of estimating high speed machining stability and improving productivity and the quality of machined surface. Study on dynamic characteristic of cutting process when high speed dry turning hardened steel with ceramic cutter can help to select the machine tool, the tooling geometry and cutting parameters, to avoid the vibrations, to optimize the structure of ceramic cutter and to monitor the high speed cutting process. So based on the experiments of high speed dry turning hardened steel (Cr12) with ceramic cutter made in China the author studies the dynamic characteristic of cutting process, then proposes a dynamic cutting force modeling and a surface micro-topographic modeling.A series of experiments of turning hardened steel (Cr12) are made with NC lathe and ceramic blade made in UNISCERA and University of Science & Technology Beijing.The results of experiments indicate that the radial force is the highest, followed by the tangential and axial forces. Cuttings forces increase almost linearly with depth of cut and feed rate. According to the theory of three-group steady cutting experiments, the dynamic force modeling is proposed. The tooling geometry such as side cutting edge angle and approach angle make an important effect on the force distribution in three directions, so the tooling geometry is the most important factor to the stability of the high speed cutting process. For the influence of cutting speed and hardness of workpiece on cutting force in high speed turning hardened steel is different from that in common cutting, the study on the change rule of cutting force is benefit to the ceramic blade manufacture, the cutting parameters selection and the monitoring of cutting process.Chip information shows that the hardness of workpiece is the most important factor for the chip form and cutting temperature, the second is nose radius and the last is cutting parameters such as cutting speed and feed rate. The Wavelet results of cutting forces signals show that there are inherence relations between chip shape and the cutting forces.By measuring the machined surface roughness and the two-dimensional surface micro-topography and analyzing the factors such as cutting parameters, tooling geometry and the relative vibrations between tooling and workpiece the conclusion is drawn that the most important factors to the quality of machined surface is the relative vibration between tooling and workpiece, followed by feed rate, nose radius and the material properties of workpiece. Based on the metal cutting theory and the machine tool kinematics, a new surface micro-topography modeling is proposed. Machining case studies and their simulation results show the modeling will be used to predict machined surface micro-topography.