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Design, control and cutting process for a three-degree-of-freedom ultrasonic vibration tool holder

University of British Columbia

Ultrasonic vibration-assisted cutting is a popular unconventional manufacturing process with lower cutting forces and less heat generation. Special tools are required to excite high-frequency vibrations at the tool tip during cutting; however, there is no ultrasonic vibration actuated tool holder for general-size milling or drilling tools reported in the literature. This thesis presents the design of a novel three-degree-of-freedom (3DOF) ultrasonic vibration tool holder with a sensorless control system. In addition to proposing a mechatronics design, this thesis presents the cutting dynamics and mechanics exhibited by the developed vibration tool holder. The 3DOF ultrasonic vibration tool holder is designed for milling and drilling operations. 3DOF vibrations are generated by the actuator consisting of three groups of piezoelectric rings actuating in the X-, Y-, and Z-directions at the natural frequencies of the structure. The vibrations excited in the XY produce an elliptical locus to assist milling process. The vibrations along Z-axis are used in drilling operations. A sensorless method is developed to track and control the frequency and amplitude of ultrasonic vibrations produced by the 3DOF vibration tool holder during machining. A dynamic model of the actuator is first established to obtain a transfer function between the supply voltage and driving current. An observer with Kalman filters in each actuator direction is designed to estimate the vibrations during cutting to closed-loop control the amplitude and track the resonance The dynamics of the ultrasonic elliptical vibration-assisted milling operations is analyzed to assess the system stability. The chip thickness is modeled by considering the rigid body motion of the tool, regenerative vibration and ultrasonic vibration. The loss of contact between the tool and workpiece at the ultrasonic vibration excitation frequency is considered in evaluating the directional factors. The stability of the system is solved using the semi-discrete time-domain method and verified experimentally. The effects of ultrasonic vibration assistance in cutting of Ti-6Al-4V are investigated. A plastic chip flow model is developed to predict the stress and temperature variations in the primary shear zone. Simulation results show that the temperature in vibration-assisted cutting is much lower than that for conventional cutting.

Text

2020-03-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73849

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/