Vibratory drilling with digital adaptive control

Abstract

High standards and efficiency of deep hole drilling used for hard-to-machine metals and alloys could not be achieved if chips are not segmented in the cutting zone. Chip control could be achieved through transmission of harmonic vibrations to the drill in direction of its rotating axis. One way to maintain these vibrations is to replace a drill chuck with a special self-vibratory drilling head, which includes an elastic element that allows axial movement of the tool. The right stiffness value of an elastic element and appropriate machining conditions could lead to oscillation self-excitation of a drill due to the regenerative mechanism. It is advisable to support this mechanism with a control action defined within the feedback loop, which provides process quality necessary for chip control in the broad range of process parameters. This work analyzes adaptive control algorithm for vibratory drilling process dynamics where control action over an oscillating system is proportional to drill axial vibrational velocity, and a feedback gain is determined in the adaptation loop. Dynamics modeling of a closed-loop nonlinear system “elastic system-machining process-control system” is carried out for cases with or without control proving effectiveness of control algorithm. The model was used to analyze how control system analog-to-digital conversion parameters influence vibratory process quality. Requirements, which ensure control system achieves a control aim, were approximately stated for capacity and response limit for analog-to-digital conversion.

Method of Using the Correlation between the Surface Roughness of Metallic Materials and the Sound Generated during the Controlled Machining Process

“…Papers [22,26], proposed a vibrator be used to dampen parasitic vibrations, which is very difficult for implementation in industrial conditions. In the paper [27], a digital control system for the longitudinal spindle stiffness was considered, designed to dampen its parasitic vibrations, but it significantly complicates the machining process. The authors in the paper [28] proposed a sliding mode of adaptive control, demonstrating the complexity of adaptive control of the cutting process.…”