Study On Friction Modeling And Calculation Of Size Parameters For Micro/meso Volume Forming Under Liquid Lubricant Condition

With the progress of science and technology,more and more industries rely on metal micro/meso forming technology.Micro/meso forming processes have many advantages,such as high production efficiency,excellent mechanical properties of parts,etc.But size effect is the unavoidable problem of micro/meso forming technology,which restricts the application of micro-forming in various fields.Friction is one of the most important factors which effects on the plastic forming processes.The researches show that the influence of friction on micro/meso forming is much greater than that on the macro forming and the law of influence also changes due to the size effect.Since the traditional friction models without considering the size effect,they can not be used in the micro/meso forming processes directly.Therefore,it is of great practical significance to quantify the size effect of friction and establish a friction model suitable for micro/meso forming processes to promote its application.However,how to introduce the size factor to quantify the size effect and how to determine the size parameters according to forming conditions are still the difficulties in friction modeling and size effect research of micro/meso forming.In this paper,the friction modeling of micro/meso bulk forming under liquid lubricant condition and how to calculate the size parameters in the model are systematically studied.The effects of sample size,grain size,surface roughness and lubricant conditions on friction behavior during micro/meso bulk forming were analyzed by micro copper cylindrical upsetting experiments.On the basis ofWanheim/Bay friction model,a friction model of micro/meso bulk forming under liquid lubricant condition was established by introducing the width t of the outer contact surface as a size parameter combined with the open-close lubricant pockets model.The Coulomb friction form of this friction model is deduced theoretically,and its input in the existing commercial finite element software is realized.Through finite element numerical simulation,the calibration curves of friction factor and size parameter in the model are obtained,which are compared with the data of micro copper cylindrical upsetting experiments.Hence,the friction factor and the width of outer contact surface under different experimental conditions are determined.The influence of sample size and roughness on the scale parameters was analyzed.Finally,the relationship between the surface roughness Ra and the width t of outer contact surface was fitted.The research results in this paper have important theoretical and practical significance for the numerical simulation and the application of micro/meso bulk forming processes.