DETERMINATION OF RESIDUAL STRESSES IN THE CALIBRATED ROD

Abstract

Calibrated metal is presented as an effective form of blanks for a number of metal technologies. Greater its use in industry prevent residual stresses formed during cold deformation. The aim of this study was to determine the main calibration parameters that influence the formation of residual stresses. The main components of the tensor of residual stresses in a calibrated rod were determined by the method of grinding and boring of one cylinder. The planning methodology of multivariate experiments was used to determine the effect of the main parameters of the calibration process on the residual stress state. For the account of simultaneous effect on the residual stresses of the relative compression, angle of the working cone of the die, calibration speed and lubrication quality the fractional four-factor experiment has been planned and implemented. These experiments have shown that the parameters of the calibration process significantly affect the residual stresses, which vary not only in magnitude but also in sign. Experimental results have shown that the range of angles of the die was from 8 to 24°, the tangential and axial residual stresses increase simultaneously: increase by 2.3 and 1.8 times. With the increase in the length of the gauge zones maximum axial residual tensile stresses are reduced by 52 % and tangential increased by 21 %. The influence of the main parameters of the calibration process on the size and nature of the distribution over the cross section of cylindrical rods of axial, radial and tangential residual stresses was determined. Changing the sign of the residual stress depends on the deformation parameters and occurs at a depth of (0,5 – 0,8)r/R. It was revealed that at the calibration mode that is used in the production the axial and tangential residual tensile stresses are formed in the peripheral layers of rods at cold forming, and in the central layers – the compressive stresses are formed. Radial residual stresses at the surface are zero, and in the rest of the body volume residual stresses are compressive.