Numerical Simulation Of Roll Micro Cross Wedge Rolling Process Based On Multi Crystal Plasticity Model

Electronic,medical,machinery and other fields is becoming increasingly demand for the micro shaft parts.However,the current processing methods of micro shaft parts can not meet the requirements of large quantities,high efficiency and high precision.The plastic forming technology of cross wedge rolling is applied to the field of micro forming to machine the micro shaft parts as its unique advantages of high efficiency,environment friendly and high material utilization.However,the traditional model and theory of cross wedge rolling can not reflect the influence of micro size of workpiece on the forming process.Therefore,in order to simulate the roll cross wedge rolling technology,it is necessary to simulate the process of micro shaft forming by using the appropriate micro geometric model and polycrystal plasticity model.And the simulation parameters should be optimized in the final.First of all,aiming at the problem that the size and quantity of the grains will have a significant impact on the plastic forming of the workpiece under the micro scale,which contains only ten to tens of grains,a smooth model and a rough model based on voronoi principle has been established in this study.There are some similarities between the mesoscopic structure of the three-dimensional voronoi polyhedron and the real polycrystalline material,the grain boundaries of the smooth model coincide with the voronoi polyhedron,and the rough model is gained by the way of discreting the voronoi graph,which is similar to the voronoi graph.And then,in order to analyze the deformation characteristics of multi crystal plasticity after establishing micro geometric model of crystal structure,Two kinds of multi crystal plasticity models are established by giving different plastic deformation characteristics of different grains in the micro axis.By comparing with the bilinear kinematic hardening model and empirical model,the latter can reflect the deformation of micro forming more accurately.The initial orientation of grain material has a great influence on the forming quality of micro shaft,which can be obtained by electron backscatter diffraction and set into the material model of micro shaft.Finally,the finite element analysis model of the micro shaft has been established by combining the smooth / rough voronoi geometric model and the empirical model.After the simulation and analysis of the roll cross wedge rolling,it is found that the latter is more accurate and less expensive by comparing the advantages and disadvantages of these two kinds of finite element models.And the number of micro grid and grain refinement of cross wedge rolling simulation has a great impact on the accuracy of simulation,it is concluded that the rough model with a grid size of 0.03 mm and 82 grains can be used to describe the complex deformation of crystal grains accurately.Friction coefficient determines the product forming in cross wedge rolling and it has been found that the geometric precision of workpiece forming is better in the case of friction coefficient of 0.8 in the study,which provides a reference for the actual production and processing.