Research On Friction Model Of Plastic Forming Based On Shear Rate

Friction in metal plastic forming in industrial production is one of the most complex ones,and it has a very important influence on the forming process or the forming quality,and it may even affect the success or failure of the forming process.The influencing factors of metal plastic forming friction are relatively complex,such as the type of metal,the state of the contact surface between the blank and the mold,the deformation speed,the deformation temperature,and the like.Due to the complex and highly nonlinear physics of friction,it is influenced by many factors.At present,the existing plastic forming friction model can not satisfy the constitutive relationship in the plastic state of the material,and thus cannot explain the irrationality of the frictional distribution law of the contact surface.In this paper,a new plastic friction model with the shear rate on the contact surface as a parameter is proposed based on the incremental theory in plastic mechanics.The idea and method for verifying the new friction model by combining test and numerical calculation are put forward.Calculate the boundary conditions by using the experimentally measured contact surface displacement(velocity)as a numerical value to calculate the corresponding nodal forces,and then obtain the relationship between shear rate and shear stress at each point on the contact surface,and quantify this relationship for this article.The proposed new friction model was verified.Different specifications of cylinder upsetting experiments were carried out to measure the radial displacement(velocity)of the contact surface of the cylinder under real contact conditions.This displacement is the real reaction of the friction effect at the contact surface.These test data are therefore provided for numerical calculations.True displacement(speed)boundary conditions.A verification numerical program for a new friction model was developed.This program takes rigid plastic FEM as the core and the corresponding experimental data as the velocity boundary conditions.It can be used to calculate the shear rate and friction shear stress at the contact surface.Through the experimentally measured data and the developed numerical calculation program,it was found that the shear rate and the shear stress on the contact surface are approximately linear.