LOADING REGIME OPTIMIZATION FOR HIGH-SPEED IMPACT EXTRUSION OF BIMETALLIC FLAT-STEP ROD PRODUCTS

Abstract

The work presents a physicomechanical model developed for calculating the force action on the punch with high-speed impact extrusion of bimetallic stepped rod products under conditions of plane deformation. In order to obtain the result, the process of impact loading of the workpiece is divided into two stages – acceleration and braking. At the acceleration stage, a linear dependence on the graph P n (h n ) “force on the punch – the deformation line” is adopted. For the braking stage, a procedure is given for calculating the force acting on the punch with the plastic flow of the bimetallic workpiece in a stepped narrowing cavity with three deformation centers. Based on the method of upper evaluation for the case of plastic flow at the final stage of the process, an equation is derived for calculating the force acting on the punch through deformation centers. By solving the problem in a quasistatic formulation (the action of dynamic tensions on the surfaces of velocity discontinuity and inertia forces does not affect the type and shape of the velocity and acceleration hodographs constructed), starting from the condition of the minimum power of plastic shaping, the dependences for calculating the optimum angles of the matrix cavity α опт , β опт , γ опт depending on the stretching λ and the coefficient of friction μ were determined. The use of a matrix with the optimum taper angles will allow us to realize the process of high-speed impact extrusion with minimum load acting on the punch. On the basis of the developed model, an equation for calculating the minimum upper force P n,min acting on the punch under high-speed impact plastic flow of metals through the deformation centers was obtained within the framework of the adopted assumptions. The equation presents the rheological characteristics of the deformed main part of the workpiece (k, ρ), technological parameters (λ 1 , λ 2 , λ 3 , V), contact friction coefficients μ for different parts of the surface of the matrix cavity, the impacting masses of the punch and the workpiece. The developed model for calculating the optimal power regime and equation can be used in engineering practice to develop a technology for high-speed impact extrusion of flat-step bimetallic products for various purposes.