Experimental analysis on autoresonant control of ultrasonically assisted drilling

The target of this paper is to employ autoresonant control technique to maintain the nonlinear oscillating mode at resonance (ultrasonic vibration at the tip of a drill bit at a desired level) during vibro-impact process. In order to achieve this, an autoresonant control system which intends to provide the possibility of self-tuning and self-adaptation mechanism for an ultrasonic vibrating system to maintain the resonant regime of oscillations automatically by means of positive feedback was developed and manufactured. The autoresonant control system was implemented through a 'controlled variable' transformation and amplification. Three feedback control strategies were employed depending on the attributes of the 'manipulated variables'. Mechanical feedback control uses the displacement signal at the end of an ultrasonic transducer. The other two control strategies are current feedback control and power feedback control. The current feedback control employs the current flowing through the piezoceramic rings as the 'controlled variable' while power feedback control takes into account both current and power of an ultrasonic vibrating system. In order to investigate the tool effect on the established autoresonant control system, two sizes of drill bits with diameters 3 mm and 6 mm were employed in combination with three autoresonant control strategies. These were executed in drilling aluminium alloys 1050 with hardness 45 HV with a fixed rotational speed combined with several feed rates. Controlled variables, responding variables, feed force reduction were monitored. Holes quality and surface finish examinations supplement the analysis of the efficiency of the control systems. (C) 2015 Elsevier Ltd. All rights reserved.