Please use this identifier to cite or link to this item: http://theses.ncl.ac.uk/jspui/handle/10443/5254
Title: Investigation into vibration assisted micro milling: theory, modelling and applications
Authors: Zheng, Lu
Issue Date: 2020
Publisher: Newcastle University
Abstract: Precision micro components are increasingly in demand for various engineering industries, such as biomedical engineering, MEMS, electro-optics, aerospace and communications. The proposed requirements of these components are not only in high accuracy, but also in good surface performance, such as drag reduction, wear resistance and noise reduction, which has become one of the main bottlenecks in the development of these industries. However, processing these difficult-to-machine materials efficiently and economically is always a challenging task, which stimulates the development and subsequent application of vibration assisted machining (VAM) over the past few decades. Vibration assisted machining employs additional external energy sources to generate high frequency vibration in the conventional machining process, changing the machining (cutting) mechanism, thus reducing cutting force and cutting heat and improving machining quality. The current awareness on VAM technology is incomplete and effective implementation of the VAM process depends on a wide range of technical issues, including vibration device design and setup, process parameters optimization and performance evaluation. In this research, a 2D non-resonant vibration assisted system is developed and evaluated. Cutting mechanism and relevant applications, such as functional surface generation and microfluidic chips manufacturing is studies through both experimental and finite element analysis (FEA) method. A new two-dimensional piezoelectric actuator driven vibration stage is proposed and prototyped. A double parallel four-bar linkage structure with double layer flexible hinges is designed to guide the motion and reduce the displacement coupling effect between the two directions. The compliance modelling and dynamic analysis are carried out based on the matrix method and lagrangian principle, and the results are verified by finite element analysis. A closed loop control system is developed and proposed based on LabVIEW program consisting of data acquisition (DAQ) devices and capacitive sensors. Machining experiments have been carried out to evaluate the performance of the vibration stage and the results show a good agreement with the tool tip trajectory simulation results, which demonstrates the feasibility and effectiveness of the vibration stage for vibration assisted micro milling. The textured surface generation mechanism is investigated through both modelling and experimental methods. A surface generation model based on homogenous matrices transformation is proposed by considering micro cutter geometry and kinematics of vibration assisted milling. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted micro milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. A new contact model, which considers both liquid infiltration effects and air trapped in the microstructure, is proposed for predicting the wettability of the fish scales surface texture. The following surface textures are used for T-shaped and Y-shaped microchannels manufacturing to achieve liquid one-way flow and micro mixer applications, respectively. The liquid flow experiments have been carried out and the results indicate that liquid flow can be controlled effectively in the proposed microchannels at proper inlet flow rates. Burr formation and tool wear suppression mechanisms are studied by using both finite element simulation and experiment methods. A finite element model of vibration assisted micro milling using ABAQUS is developed based on the Johnson-Cook material and damage models. The tool-workpiece separation conditions are studied by considering the tool tip trajectories. The machining experiments are carried out on Ti-6Al-4V with coated micro milling tool (fine-grain tungsten carbides substrate with ZrO2-BaCrO4 (ZB) coating) under different vibration frequencies (high, medium and low) and cutting states (tool-workpiece separation or nonseparation). The results show that tool wear can be reduced effectively in vibration assisted micro milling due to different wear suppression mechanisms. The relationship between tool wear and cutting performance is studied, and the results indicate that besides tool wear reduction, better surface finish, lower burrs and smaller chips can also be obtained as vibration assistance is added.
Description: PhD Thesis
URI: http://hdl.handle.net/10443/5254
Appears in Collections:School of Engineering

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