Study On The Burr Formation Mechanism And Sizes Prediction Theory In Cutting Metal Materials

Due to the deformation of workpiece material, the workpiece edge is often associated with burr or breakout after metal cutting. As a result, the presence of burr makes the contour of workpiece deviating from the ideal boundary, and impact the size precision and position precision of parts, thereby affecting the performance of workpiece. With the transformation and upgrading of national industrial structure,manufacturing industry is more and more emphasis on the development of high quality, high precision. So study on the metal burr/breakout formation is is very important. Combined with the theoretical analysis and finite element simulation, this paper systematically studied the metal cutting burr as following:(1) Based on two-dimensional metal orthogonal cutting theory, and combining with the existed burr formation mechanisms, by comparison of the burr foamation of ductile material Al6061-T4 and edge defects of brittle material, the finite element simulation is used to observe the burr formation process of several different material cutting. Through studying the burr formation of different materials, and combined with the temperature field, strain field, stress field analysis, the intiation and development of burr are analysed in detail. It is found that the edge defect consists of two fracture surfaces, namely, the first fracture surface of opening-mode crack and the second fracture surface of sliding-mode crack. The studies aim at using economic and efficient simulation method to obtain the burr formation process, and reveal the formation mechanism and provide valuable guidance for the optimization design of the cutting method and process parameters.(2) Based on the Johnson-Cook material constitutive model and the Cockroft-Latham fracture criterion, a thermal mechanical coupling model of the two-dimensional finite element orthogonal cutting is established by combining the Lagrange equation of large plastic deformation. The temperature field distribution and the maximum temperature of the workpiece and tool are obtained, and the tangential and normal cutting forces in the cutting process are obtained. The effects of cutting speed, edge geometry, rake angle and cutting depth on the burr geometry and size are analyzed in detail. It is found that the burr sizes is very sensitive to processing parameters, Smaller cutting depth and cutting tool radius can effectively reduce the burr sizes. In addition, increasing the cutting speed and rake angle can also restrainthe increase of burr sizes. The research provides the parts of Ti6Al4 V alloy materials reasonable proceessing selection and guidance, to small burr and burr free,controllable morphology edge to achieve high quality and high precision of surface integrity.(3) Based on Merchant cutting force model and Flamant-Boussinseq equation in plastic problem, a new theoretical prediction model of Poisson burr thickness and height is established by considering the coupling effect of thermal and mechanical load. The effects of cutting depth and tool rake angle on the Poisson burr sizes of cross section is analysed detailly, the influence of process parameters on the longitudinal cutting Poisson burr morphology is further discussed, the strain field distribution and the burr sizes of cross section under different process conditions are obtained. By comparison of the finite element simulation and theoretical analysis, the burr sizes distribution is obtained, in addition, the factors causing error are also analysed in detail. The results show that the sizes of Posson burr have a great sensitivity to material properties and processing parameters. In addition, due to the serrated chips and brittle frature of high strain rate, the Poisson burrs are not continuous along the longitudinal cutting direction. The research results provide theoretical basis for the ductile material parts design and process plan.