Study On Mechanical Properties Of Thick Cylinder Upsetting Under Real Contact Conditions

For the study on cylinder upsetting problems, the current research results of quantitative properties are more than that of qualitative properties, even though finite element numerical simulation technology is used as an analytical tool, but duo to the inaccuracy of the friction model in some forming process, it can not really get the conclusion with the quantitative nature.The most commonly used friction condition in the analysis of plastic forming technology is the coulomb friction condition and the constant friction condition. However, a large number of studies have shown that both the two friction conditions have a certain gap between the real surface and the contact characteristics.In this paper, the method of combination of experiment and numerical simulation is used to convert the quantitative description for the friction characteristics to the measurement of the contact surface velocity of the specimen, namely the velocity values of specimen contact surface points is measured by the experiment under the specific pressure speed, and translated into the corresponding velocity boundary conditions, using the commercial finite element software DEFO RM to calculate the stress, strain, displacement distribution characteristics and the regularity of variation in the interior of the upsetting body.Finite element calculation results show that when the height-to-diameter ratio is greater than 2.0, according to the size of the deformation degree, the cylinder inner can be divided into small deformation area and uniform deformation zone, and the small deformation zone is located near the contact surface of the tool and the workpiece.Studies have found that height-to-diameter ratio is relatively large, there will be a numerical smaller radial and tangential direction tensile stress; height-to-diameter ratio is small, the central part of the cylinder is in the triaxial compressive stress state, but it will appear tangential tensile stress which not allow to ignore in the vicinity of the outer surface, and the tensile stress increases with the increase of amount of reduction, that is the reason why the outer surface of forging have longitudinal crack when a large deformation upsetting is carried out.Using the method presented in this paper can not only get around on the demand of tribology which is still not perfect, but also can truly reflect the contact state of contact surface when upsetting, the mechanical properties(stress, strain distribution and its regularity of variation) of deformation internal that obtained is e xtremely true.