Processing parameters influence on dynamics of vibratory drilling with adaptive control

Abstract

Chip segmentation is one of necessary conditions of ensuring the deep hole drilling quality when processing hard-to-machine metals. It may be achieved through making drill bit harmonic oscillations in axial direction. Possible way to maintain such vibrations is to replace the standard drilling head with special vibratory head which includes elastic element giving the instrument a possibility to move in axial direction. Self-excitation of drill regenerative oscillations is possible if elastic element stiffness and processing parameters are chosen properly. It is advisable to complement this way of excitation by control action which is determined in feedback circuit and sustains required vibration process characteristics in wide range of processing parameters. In present paper the adaptive control algorithm of vibratory drilling process dynamics is proposed. Control action on oscillation system is proportional to drill vibrational velocity, the feedback gain is determined in adaptation circuit basing on comparison of actual peakto- peak vibrational displacement and its target value. Simulation of closedloop nonlinear system «elastic system – machining process – control system» dynamics has been performed for different values of processing parameters for cases with or without control. The simulation revealed efficiency of suggested algorithm in wide range of processing parameters. Joined influence of processing parameters and target peak-to-peak displacement values on chip breakage conditions is studied. Recommendations for choice of processing parameters and control parameters values are developed. Influence of control action magnitude limit on control system possibilities to achieve control target is analyzed.