INFLUENCE OF PARAMETERS OF THE CALIBRATION PROCESS ON BENDING STIFFNESS OF STEEL ROD

The calibrated metal is efficient material for manufacture of details on automatic machines and automatic transfer lines, and also for production of smooth lengthy shafts and axes. Such details are not technological as during the machining and operation they change a form in a type of a curvature. Deformation comes at action of centrifugal forces even from sole weight of details. New constructional materials allow to create rather strong details with the reduced transverse section, but a flexural rigidity of such details significantly decreases. It is very difficult to increase flexural rigidity of actual details. In practice, constructive solutions that are associated with material costs are usually used. In this work the possibility of increase in a flexural rigidity of the cylindrical calibrated bars is considered due to the formation of technological residual stresses. The problem of their use is that residual stresses always exist of two types – stretching and squeezing. If external stresses of stretching increase rigidity of details, then pressure loads reduce it. Therefore, the main task of the work was to find such nature of distribution of residual stresses which would provide increase in a flexural rigidity of the details made of calibrated metal. The geometrical model of a bar consisting of thin-walled tubes of 0.2 mm thick was accepted at model operation of residual stresses. Each tube was loaded with the stretching or squeezing tension which corresponded to value of the experimental definition. At model operation and calculation two schemes of loading were used at which in the surface layers either residual stresses of compression or stretching are formed. Experimental calculation methods established influence of key parameters of calibration on a flexural rigidity of metal. The possibility of increase in a flexural rigidity of the calibrated bars is revealed almost twice when cogging from 5 to 34 %. For 20 % it is possible to increase rigidity at increase in length of the calibrating zone of the tool. The influence of the angle of the working cone of the machine is insignificant (about 10%), and for increasing the rigidity the operating angle of the tool must be reduced.

calibrated metal, residual stresses, bending stiffness, relative compression, working cone angle, length of gauge area

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