Papers by Author: Kah Chuan Shaw

Abstract: So far, the industrial application of ultrasonic vibration assistance has been successful in continuous machining process such as turning process where ultrasonic vibration velocity is much higher than cutting velocity. Recently, vibration assistance has been experimentally investigated to the intermittent milling process mainly for feed and cross- feed directions. This paper focuses on the effect of ultrasonic vibration assistance in spindle axial direction for improvement of machined surface. With the designed ultrasonic vibration assisted milling process with 39.7 kHz and a few micro-meter amplitudes, workpiece vibrates along spindle axial direction while different RPMs and feed rates are applied. The axial directional vibration assistance acts as additional cutting motion which further reduces the leftover surface error. Experimental results validate that surface roughness can be improved from 20 % to 65 % for the tested conditions. Apparently chatter marks of the milling process are reduced with the help of the axial ultrasonic vibration assistance.

Abstract: In this study, a computer numerical control (CNC) programming software platform for ultra precision machining of optical surfaces was developed based on an MS Windows application framework and openGL. Using cylindrical coordinates, the tool path can be generated based on the polar angle, radius and a linear coordinate of the Z-axis, as well as cutting tool nose radius compensation. A 3D simulation based on tool path generation was developed for machining verification, which largely reduces the oscillation of the machine during the ultra precision machining process. Ultra precision machining of an optical lens array was carried out on a 5-axis ultra precision machining centre using a single crystalline diamond cutter. The experimental results indicated that the oscillation effect can be largely reduced using the cutting tool path using a super steady machining strategy. This software platform is designed as a framework, where the capability and functions can be expanded by adding in more freeform surface packages.

Abstract: There are increasing demands for polymer based microfluidic devices as polymer devices can be mass produced using the injection molding process for disposable analytical applications. However, fabrication of precision injection molds with micro features down to tens of micro meters is a challenging task. The most efficient manufacturing method for this type of high precision micro mold is the tool-based micro machining. In this paper, studies have been conducted to develop metal injection mould manufacturing technologies for polymer microfluidic device fabrication. An injection mould with a micro feature of 29m wall thickness, 20m height and 9.8mm length has been successfully achieved on brass with very precise dimensional accuracy and surface quality for molding process of polymer microfluidic devices. Polymer microfluidic chips with micro channels of 30m width have been successfully produced using the machined metal injection mould.

Abstract: One-directional ultrasonic vibration assisted milling system is designed and its performance is investigated in terms of machined surface quality under 135,000 rpm. The ultrasonic vibration generator excites the workpiece with a frequency around 40 kHz and amplitude of a few micro meters. The milling tool’s cutting speed is controlled by an air-bearing spindle system. Both feed-directional and cross-feed directional ultrasonic vibration assistance are considered in order to understand the mechanism of ultrasonic vibration assistance for surface roughness generation. A comparison is done on a milled surface which is generated with and without ultrasonic vibration assistance. The experimental results show that ultrasonic vibration assistance can improve the machined surface quality which depended on the cutting edge radius and the feed per tooth.

Abstract: A study was carried out to investigate effects of crystallographic structure on the machining performance with polycrystalline oxygen free copper (OFC) using a single crystalline diamond (SCD) micro-tool. The SCD micro-tool used in this study fabricated with a focused ion beam (FIB) has a cutting length of around 30 µm on the primary clearance face. It was found that a change in crystallographic orientation resulted in a variation in machining force, chip thickness and shear angle, leading to a change in machined surface integrity. When a micro-size tool traverses within a grain at a machining direction aligned with a particular crystallographic orientation, the work material in front of the machining tool is found to be severely deformed. If the orientation changes to a less favorable orientation, this may lead to a much reduced shear angle, a thicker chip, striation at the chip back, higher machining forces and a degraded machined surface. This study contributes to the understanding of the physics of micro scale mechanical machining (micro-machining).