abstract: In this research, a new cutting edge wear estimator for micro-endmilling is developed and the reliabillity of the estimator is evaluated. The main concept of this estimator is the minimum chip thickness effect. This estimator predicts the cutting edge radius by detecting the drop in the chip production rate as the cutting edge of a micro- endmill slips over the workpiece when the minimum chip thickness becomes larger than the uncut chip thickness, thus transitioning from the shearing to the ploughing dominant regime. The chip production rate is investigated through simulation and experiment. The simulation and the experiment show that the chip production rate decreases when the minimum chip thickness becomes larger than the uncut chip thickness. Also, the reliability of this estimator is evaluated. The probability of correct estimation of the cutting edge radius is more than 80%. This cutting edge wear estimator could be applied to an online tool wear estimation system. Then, a large number of cutting edge wear data could be obtained. From the data, a cutting edge wear model could be developed in terms of the machine control parameters so that the optimum control parameters could be applied to increase the tool life and the machining quality as well by minimizing the cutting edge wear rate. In addition, in order to find the stable condition of the machining, the stabillity lobe of the system is created by measuring the dynamic parameters. This process is needed prior to the cutting edge wear estimation since the chatter would affect the cutting edge wear and the chip production rate. In this research, a new experimental set-up for measuring the dynamic parameters is developed by using a high speed camera with microscope lens and a loadcell. The loadcell is used to measure the stiffness of the tool-holder assembly of the machine and the high speed camera is used to measure the natural frequency and the damping ratio. From the measured data, a stability lobe is created. Even though this new method needs further research, it could be more cost-effective than the conventional methods in the future. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2019

Nowadays technology development places increasing demands on miniature and micro components and products, and micro-milling is one of the most flexible machining processes in manufacturing 3D structures and complex structured surfaces. A thorough and scientific understanding on fundamentals of the micro-milling process is essential for applying it in an industrial scale. Therefore, in-depth scientific understanding of the micro-cutting mechanics is critical, particularly on size effect, minimum chip thickness, chip formation, tool wear and cutting temperature, etc. so as to fulfil the gap between fundamentals and industrial scale applications. Therefore, three key fundamental research topics are determined for this research, and a comprehensive study on those topics is conducted by means of modeling, simulation, experiments. The topics include chip formation process in micro-milling, novel cutting force modeling in multiscale and study on the tool wear and process monitoring. The investigation into chip formation process in micro-milling consists of three stages; the micro-cutting process is firstly simulated by means of FEA with a primary focus on finding the minimum chip thickness for different tool/material pair and explaining the size effect; the simulation results are then validated by conducting micro-cutting experiment on the ultra-precision lathe. Experiments are carried out on aluminium 6082-T6 with both natural diamond and tungsten carbide tool. By knowing the minimum chip thickness for different tool/material pair, the chip formation process is investigated by performing comparative study by using the diamond and tungsten carbide micro-milling tools. As the minimum chip thickness for diamond micro-milling tool is smaller than that for tungsten carbide tool compared to nominal chip thickness, MCT is ignored in diamond micro-milling. Thus the comparative study is conducted by utilizing both tools with perfectly sharpened cutting edge and tools with the rounded cutting edge in micro-milling. The chips are inspected and associated with cutting force variations in the micro-milling process. The findings are further consolidated by comparing with research results by other researchers. The cutting force modeling is developed in three different aspects, e.g. cutting force on the unit length or area and cutting force on the unit volume in order to better understand the micro-cutting mechanics in aspects of size effect, tool wear mechanism and the cutting energy consumption. The mathematical modeling firstly starts with a novel instantaneous chip thickness algorithm, in which the instantaneous chip thickness is computed by taking account of the change of tool geometry brought about by the tool runout; then the collected cutting forces are utilized to calibrate the model coefficients. For accurate measurement on cutting forces, the Kalman Filter technique is employed to compensate the distortion of the measured cutting force. Model calibration is implemented using least-square method. The proposed cutting force model is then applied in micro-milling to represent the conditions of tool wear and the cutting energy consumption. Further study on the surface generation simulation is based on force model and its comparison with the machined surface is also performed. Cutting experiments using the new tungsten carbide tool are carried out and the tool wear is monitored offline at different machining stages. The dominant tool wear types are characterised. Tool wear is investigated by mainly analysing cutting force at different tool wear status. Frequency analysis by Fourier Transform and Wavelet Transform are carried out on the force signals, and features closely related to the tool wear status are identified and extracted. The potential of applying these features to monitoring the tool wear process is then discussed. Experimental studies to machine the structured surface and nano-metric level surface roughness are presented, the machining efficiency, dimensional accuracy and tool-path strategies are optimised so as to achieve the desired outcomes. Moreover, investigation on cutting temperature in micro-cutting is also studied to some extent by means of simulation; the influence of cutting edge radius on cutting temperature is particularly investigated. Investigation on above aspects provides systematic exploration into the micro-milling process and can contribute substantially to future micro-milling applications.