Influence of parameters of adaptive control system on vibratory drilling efficiency

Abstract

One of the necessary conditions of ensuring the quality of deep hole drilling during manufacturing pieces from hard-to-machine metals is chip control. It can be ensured by applying harmonic oscillations to a drill bit in the direction of rotation axis. One possible way of maintaining such vibrations is to use a vibratory drilling head which contains an elastic element. This element allows axial displacements of the tool. If stiffness of the elastic element and the machining parameters are chosen correctly, self-actuating of axial vibrations of a drill bit in compliance with regenerative effect may occur. It is advisable to add control response, which is determined in the feedback loop, to this mechanism because of the significant damping in the cutting zone. The control response maintains the required process characteristics to ensure chip control. The algorithm of vibratory drilling dynamics adaptive control has been examined in this paper. The additional impact, which is proportional to axial speed of the drill bit, is supposed to be made on the vibration system according to this algorithm. The feedback gain is determined in the adaptation loop comparing the current value of peak-to-peak displacement and its target value. The dynamics modeling of closed loop non-linear system “elastic system-machining process-control system” has been carried out. The graphs of vibratory drilling integral characteristics plotted against processing characteristics and vibratory head parameters have been presented in this paper. These graphs are based on the multivariant modeling. The influence of the adaptation algorithm parameters on the quality of vibratory processing has been also studied.