3 research outputs found
Investigation into vibration assisted micro milling: theory, modelling and applications
PhD ThesisPrecision 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
Cumulative index to NASA Tech Briefs, 1970-1975
Tech briefs of technology derived from the research and development activities of the National Aeronautics and Space Administration are presented. Abstracts and indexes of subject, personal author, originating center, and tech brief number for the 1970-1975 tech briefs are presented