Improving the quality of workpieces obtained by breaking by bending under static-dynamic loading on a press hammer
DOI:
https://doi.org/10.37142/2076-2151/2022-1(51)123Keywords:
workpiece, rolled metal, cold bending, static-dynamic loading, stiffness, quality, prime cost.Abstract
Karnaukh S. G. Improving the quality of workpieces obtained by breaking by bending under static-dynamic loading on a press hammer
Of all the methods for separating rolled workpieces into dimensional blanks used in modern blank production, the most productive and economical are the waste-free methods for separating workpieces: shear cutting and cold bending. The aim of the work is to improve the quality of workpieces by breaking rolled products by studying the separation process under static-dynamic loading on a press hammer. Combined static-dynamic loading during cold breaking by bending makes it possible to reduce the high-frequency vibrations of the «tool-sample-supports» system, eliminate the violation of the contact of the sample with the supports, and reduce the peak forces from the striker and supports. The presence of a static force at the moment of impact provides a certain initial level of tensile stresses in the stress concentrator zone, which increases the controllability of the crack. It is assumed that the destructive crack will always propagate in the area of tensile stresses, which improves the quality of the workpieces to be separated. A more tangible improvement in the quality of blanks will be manifested when separating samples of large cross sections. The reactive forces from the side of the supports from the action of the static force coincide with the direction of the inertial forces of the halves of the sample and additionally break the sample. In this case, with an increase in the length of the sample, the value of its separation from the supports in the initial phase of loading decreases, which has a positive effect on the quality of the resulting workpieces. The results of the experiments show that the value of the static force required to prevent the sample from being separated from the supports depends on the stiffness of the contact of the female with the intermediate punch and increases with the increase in the stiffness of the contact of the female with the intermediate punch. The value of the stiffness of the contact of the head hammer with the intermediate punch should be chosen optimal due to the special design of the punch. It has been experimentally established that the value of the preliminary static force must be at least 40% of the force at which the sample is destroyed. An analysis of the geometric accuracy of the workpieces made it possible to conclude that with an increase in the rate of deformation, the quality of the workpieces improves. But the highest quality of the separated workpieces is observed under static-dynamic loading. The results obtained can be used to improve the technology of the process of separating rolled workpieces into cut-to-length blanks by cold breaking by bending.
Key words: workpiece, rolled metal, cold bending, static-dynamic loading, stiffness, quality, prime cost.
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