No 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.

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.

The dynamics of the gun drilling process is analyzed in this paper. The tool shank is modeled as long straight beam vibrating in transverse direction under action of cutting forces. Axial force component is expressed as proportional to cutting thickness, which is determined as nonlinear function of beam transverse deflection with time delay. Nonlinear equations of motion of the drilling shank are derived. The stability diagram of the system dynamics was determined. The bifurcation analysis of nonlinear differential delay equations by means of multiple scale method was performed. The obtained results were verified by numerical integration of nonlinear equations. The influence of cutting conditions on system stability and chatter amplitude was observed.

In this paper method of numerical computations using explicit scheme, implemented in LSDyna (Ansys) software complex, is introduced and verified. Obtained solution explains experimental fact mentioned by P. Ludwik, that cracking in cylindrical test specimen made of plastic material starts in the middle of the smallest cross-section of the specimen. Introduced method allows verifying law, obtained by N.N. Davidenkov during unique experimental research in which he studied logarithmic strain in specimen’s neck by pickling of cross-sections in this zone. Additionally it is possible to estimate amount of heat, generated during rupture of specimen, using obtained solution and law of conservation of energy. For this purpose tensile tests, in which thermal camera was used for temperature measuring, were conducted. It was shown, that all deformation energy apart from elastic and shape-forming energy in volume element, calculated in the moment before rupture is transformed to heat. Also tensile tests with various rate of loading were conducted for more detailed research of rupture process.