INFLUENCE OF PARAMETERS OF THE CALIBRATION PROCESS ON BENDING STIFFNESS OF STEEL ROD. PART 1. DETERMINATION OF RESIDUAL STRESSES IN THE CALIBRATED ROD

Calibrated metal is presented as an effective form of blanks for a number of metal technologies. Greater its use in industry is prevented by residual stresses formed during cold deformation. So, the main problem at manufacture from the calibrated metal of low-rigid details like shaft, is existence in material of the considerable level and a nonuniform distribution of residual stresses, the appearance of which is large due to technological reasons. 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 calibration process on residual stress state, on the basis of which the main parameters of the calibration process that affect the formation of technological residual stresses are revealed. Influence of extent of the relative cobbing, corner of a working cone and length of the calibrating zone of the working tool on the size and the nature of distribution of axial, tangential and radial residual stresses were determined. It was established, for example, that the stretching tangential stresses have the largest value at degree of the relative cobbing of 23  %, working angle of drawing die of 18° and calibration speeds of 2.5  mm/sec under the worst conditions of lubricant. The ambiguous dependence of components of residual stresses on process parameters should be noted. So, at the increase in extent of the relative cobbing, the tangential residual stresses increase and axial ones decrease. With increase in cobbing from 5 to 34  % tangential residual stresses increase by 2.5  times, and axial ones decrease by 13  %. It was established also that on axial tension the greater influence is exerted by an angle of working drawing die, and on tangential – extent of the relative cogging. In the range of angles of working drawing die from 80 to 240  character of residual stresses on the section of a bar does not change. With increase in length of the calibrating zone of the drawing die the values of components of residual stresses tensor significantly decrease. Increase in length of the calibrating zone is an effective remedy for decrease in residual stresses in the calibrated bars. Depth of distribution of compressive residual stresses is not a stationary value and depends on the calibration modes.

calibrated metal, residual stresses, calibration parameters, cobbing, angle of working cone, length of calibrating zone

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