Experimental research of console boring bars oscillations upon fine stepped holes boring
DOI:
https://doi.org/10.15276/opu.1.60.2020.01Keywords:
step boring bar, boring cutter, vibration amplitude, frequency, vibration resistance, technological dynamicsAbstract
Fine boring is a common way of finishing edge processing. Upon boring stepped hole, on practice it is necessary to design and produce special stepped console boring bars or multi-edged heads. In the experiments there were researched complicated dynamic interactions occurring in the technological system upon multi-edge boring with stepped boring bars. Regularities of forced oscillations ampli- tudes changes upon changes in flexible system parameters and cutting processes have been studied, namely upon changes in mass-geometrical properties of boring bars, stiffness and own frequencies, variation of lengths and diameters of steps. Out-of-roundness of cross sections and roughness values of processed surfaces within the terms of simultaneous and separate work of edges have been researched. The experiments were carried out on machines assembled on the basis of a finishing and boring machine equipped with a high precision spindle head with rotation speed stepless regulation and modern measuring equipment. Measurements were carried out using strain gauge methods as well as a vibration spectrum analyzer with a piezo sensor. Two and three-stage boring rods with different mass geometry parameters were used. Processing diagrams with rotating and non-rotating boring rods were studied. Relative position of edges and cutting depths were also varied during experiments that led to change of values of impact indexes. Complex dynamic interactions at thin boring by step boring bars at simultaneous operation of picks lead to non-monotonous change of amplitudes of forced vibrations, and vibration stability of boring process can either increase or decrease. The practical importance of the work allows to solve the field of application of stepped console boring bars by improving their design on the basis of not only static, but also dynamic calculations. Results of experimental researches are put into basis of theoretical modelling and development of dynamic calculation models. In addition, the results of complex experimental research in scien-tific terms develop technological dynamics as a part of engineering technology.
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