W.S. Lau

Un-conventional machining of composite materials

Abstract Using un-conventional machining techniques in shaping advanced composites materials has generated a lot of interest. The fact is that, machining operations such as cutting and drilling, are difficult to preform on these materials with conventional tools and techniques because of their peculiar properties including anisotropy, low thermal conductivity and the abrasive nature of the reinforcing phases. Among the many un-conventional processing techniques laser and electrical discharge machining (EDM) have been proved to be effective tools in shaping some of these materials. This paper not only provides a systematic analysis on the machining efficiency that can be obtained by laser and EDM and the maximum depth-of-cut that can be generated by laser, the important issue of machining defects is also addressed. It is hoped that this study will be helpful to the further understanding of the machining mechanisms of Nd:YAG laser, excimer laser and electrical discharge method and thereby to improve the techniques in the processing of composite materials.

Study on the electro-discharge machining of a hot pressed aluminum oxide based ceramic

Abstract In this paper, the machinability of ceramics is studied according to their physical properties. Research results show that EDM is suitable for conductive ceramics. The mechanism of electro-discharge machining ceramics is investigated. The effects on material removal rate, surface roughness, and diameter of discharge points by various parameters are measured and discussed.

A study of ultrasonic-aided wire electrical discharge machining

Abstract An investigation has been made into the combined technology of ultrasonic and wire electrical discharge machining (W-EDM), in which the design of the vibrating device is described. The theory to describe the vibration modes of the wire under the action of ultrasonic has been established. Experimental results show that wire vibration induced by ultrasonic action has a significant effect on the overall performance of the W-EDM process. It was found that there exists an optimum relationship between the vibration amplitude of the wire and the discharge energy, by which the highest cutting rate and the best machined surface quality can be obtained. In addition, ultrasonic vibration reduced the residual tensile stress of the machined surface.

Spark erosion with ultrasonic frequency

Abstract In this paper, spark erosion with ultrasonic frequency is proposed, using a D.C. power supply instead of the usual pulse power supply, the pulse discharge being produced by the relative motion between the tool and the workpiece. The tool vibrates sinusoidally with ultrasonic frequency and enables the melted materials to be ejected strongly, and the eroded materials to be flushed away easily from the gap. This machining method can easily perform cutting, drilling, engraving, and the combined technology of UM and EDM.

Investigation of the surface integrity of laser-cut ceramic

Abstract This paper intends to address the effects of laser machining on ceramic surfaces by evaluating the surface integrity of machined ceramics in terms of surface morphology, and flexural strength and its variances, under various machining conditions, a Weibull modulus ‘m’ being introduced to measure the degreee of variation in strength. Experimental results show that the damage to the ceramic, and the flexural strength and its Weibull modulus, are determined by the parameters of the laser beam. In general, the thermally-affected layer and cracks in this layer of laser-cut ceramic surfaces are critical, and need to be modified properly.

Study on the machining mechanism of WEDM with ultrasonic vibration of the wire

Abstract WEDM assisted by ultrasonic vibration of the wire has a better machining result than that of wire cut alone. In order to study its machining mechanism, the methods of experiment as well as simulation have been used to verify some hypotheses and interpretation. By means of experiments employing single pulse discharge it has been established that the high frequency vibration of the wire electrode is able to bring about multiple channel discharges so that better surface quality and a high cutting rate can be obtained simultaneously. The simulation of the dynamic characteristics of the wire electrode under the action of continuous discharge forces shows that ultrasonic vibration facilitates the shift of the discharge points and improves their distribution. A set of statistical experiments has been designed to analyzed the utilization of the pulse. It is revealed that with ultrasonic vibration there is a greater utilization of energy, which is a critical factor in securing an increase in the cutting rate.

Machining of Engineering Ceramics by Ultrasonic Vibration Assisted EDM Method

Abstract Ultrasonic vibration assisted EDM was performed by using an ultrasonic machine tool with a d.c. power supply, with its positive and negative poles connected to the workpiece and the tool electrode, respectively. The pulse discharge is produced by the relative motion between the tool electrode and the workpiece. In the working process of this combined technology, ultrasonic machining and EDM are complementary techniques. Experimental results show that the material removal rate is a little more than just the sum of ultrasonic machining and EDM, while surface roughness is about the same as that for ultrasonic machining.

Excimer laser surface modification of engineering ceramics for adhesive bonding

Abstract The surfaces of two engineering ceramics, LT35 (TiC + Al2O3) and Si3N4 were irradiated with a high power KrF Excimer laser. The effect of laser pulse frequency, energy intensity and number of pulses upon the surface morphologies and roughness were examined. Conical structures on the treated surfaces were observed after the laser treatment. The ablation depths were found to be dependent upon the type of ceramics and laser processing parameters. The treated surfaces were adhesion bonded using a toughened epoxy resin adhesive. Significant improvement in adhesion shear strength of the bonded specimen with laser-treated surfaces were achieved as compared with those specimen with surfaces in the as-received, SiC-paper-abraded and sand-blasted conditions.

Analysis of Ultrasonic-Aided Laser Drilling Using Finite Element Method

Abstract Previously, a novel Ultrasonic-Aided Laser (UAL) drilling technique has been developed to raise the performance of traditional laser drilling method, as well as to improve the overall quality of the “machined” hole. In this connection, a theoretical model using Finite element method (FEM) has now been developed to determine the shape of UAL drilled holes and the thickness of the re-cast layer. In addition, the temperature profile of the hole during UAL processing can be established and from which the size of the re-cast layer can be determined. Experimental results show good agreement with the theoretical predictions

High temperature deformation behavior of Al 2124-SiCp composite

Abstract The high temperature deformation of 2124/SiC p (17 vol.%) Composite material was investigated over the temperature range from 698 K to 823 K. It was shown that the 2124/SiC p composite did not behave superplastically at strain rates of from 10 −4 to 10 −1 s −1 . The strain rate sensitivity was found to be about 0.17, which was apparently below that (0.5) of a superplastic material. The activation energy for high temperature deformation was much greater than that of superplastic aluminum alloys. Numerous cavities on the fracture surfaces of the composite were observed by SEM. The high-temperature deformation of the composite was compared with superplastic behavior of 8090/SiC p composite, and the reasons for the 2124/SiC p composite not showing superplastic properties were explained according to superplastic deformation mechanism and the composite itself.