Parametric effects in the frictional interaction of a tool with a billet in the process of its treatment by pressure

Abstract

Purpose. Justification of the influence of pulsating dynamic loads in the surface layers of parts obtained by plastic deformation methods on the quality of finished products during cold rolling, knurling, running in, drawing and stamping. Research methodology. A schematization was adopted in which the workpiece or part is an anisotropic medium elastically bonded along the surface of the junction of external reinforced layers with the internal mass of the part. On the basis of the proposed physical model, conditions were found under which under the action of cyclic surface loads, violations of the integrity of the appearance of fracturing and waviness of external fibers in the process of strengthening the treatment of semi-finished products and parts are possible. Findings. The obtained data allows us to establish the frequency characteristics of the process of unstable parametric oscillations caused by nonlinear friction between the forming element and the workpiece (part), which lead to a deterioration in the quality of finished products. In addition, for the steady-state operating modes of machines for cold metal forming, the dependence of the amplitudes of deformation waves, as functions of the maximum pulsations of the “periodic” components of surface forces, was obtained, and measures were proposed to reduce vibroactivity in the area of tool interaction with the workpiece and machine parts for cold processing. Originality. It consists in formulating and solving the second dynamic problem for the surface layers of the workpiece at the interface of the processed layers and the workpiece array. Depending on the occurring periodic forces for the surface layers, the conditions of steady and unstable operation of the shaping tool and the whole machine for metal forming by pressure, as a whole, are determined. Practical value of the work lies in the fact that safe modes of operation of metal forming machines have been identified, conditions for improving the design of machines for cold metal forming have been created, under which the possibility of occurrence of parametric oscillations, as well as the reduction of vibratory activity of machines for cold metal forming in minimized whole. Keywords: running in, knurling, drawing, plastic deformation, roller, tool, workpiece, the amplitude of oscillations, load, excitation coefficient, steady amplitude, deformation wave.