Experiments And Simulation Of Friction Behavior In Micro Upsetting Of Pure Copper Without Lubricant

Although microforming technologies are very suited for the mass production of micro-scaled products,the industrial applications of microforming processes are still limited,because the so-called size effects.Among the size effects in micro-forming,which involve material flow,friction and scatter,friction plays an significant role.At present,size effect of friction with lubricant has been well researched.Open and closed lubricant pocket theory is developed to explain this phenomenon.However,size effect without lubricant is still absurd.The current used FEA software are based on traditional crystal plastic theories which can not be directly used in micro-forming.The Crystal Plastic Finite Element method is proposed to acquire more precise results by taking grain structure and orientation into consideration.Aiming at these issues,the scaled upsetting tests are carried out to investigate the scale phenomenon and to obtain the scale affected mechanical properties of pure copper billets.A constitutive model is developed based on grain boundary strengthening and surface layer effect.A method to introduce Wanheim/Bay friction model to current used FEA software is proposed.Multiple-factor experiments are carried out to investigate the friction factors and their relationship with specimen diameter,grain size,mold roughness and mold hardness.EBSD are used to investigate grain orientation and grain rotation of the copper billets.A multi-region FEA model is built based on Voronoi diagram and Abaqus/Python script.Finite element analyses are carried out using the preceding constitutive model and friction model.