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UBC Theses and Dissertations

Adaptive tuned mass damper boring tool Lappin, Derry William


Single point boring of highly slender workpieces with internal features requires vibration damped tooling to avoid unwanted chatter vibrations. The tuned mass damper (TMD) boring tool has made machining of these highly slender features possible by increasing the dynamic stiffness and therefore the chatter stability of the cantilevered tool. Chatter stability of these vibration damped tools is sensitive to how well the TMD has been tuned to the tool’s first bending mode, which varies between machine tools and mounting styles. This thesis presents a novel, automatically tunable TMD system for boring tools. The TMD mass is suspended in the frontal bore of the tool by adjustable springs in the form of compressible neoprene O-rings. The natural frequency of the TMD is adjusted automatically by a position control servo, which actuates a power screw and compresses the O-rings. The damping coefficient of the TMD is adjusted by identifying an oil of favorable viscosity. The TMD system requires the measurement of the boring tool’s Frequency Response Function (FRF) when it’s mounted on the machine tool. A computer-controlled electromagnetic force exciter has been developed. The impulse force delivered by the exciter is estimated from the measured magnetic field. Tool vibration response is measured from a standard non-contact capacitance probe or an accelerometer. With the tool mounted on the machine tool, automation software automatically tunes the TMD’s natural frequency in an iterative manner by commanding the position servo to compress the O-rings. At every iterative adjustment the tool’s FRF is measured using the computer controlled electromagnetic exciter. A search algorithm monitors the minimum real part of the tool’s FRF and adjusts O-ring compression until the negative real part is maximized, therefore maximizing chatter suppression. The proposed computer controlled, fully integrated excitation and tuning system has been built and experimentally validated in boring steel workpieces. It is shown that the system can increase stability relative to traditional slender boring tools by almost 100 times, and therefore provide increased capabilities and productivity.

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