Fabrication of deep micro-holes in reaction-bonded SiC by ultrasonic cavitation assisted micro-EDM

Ultrasonic vibration was applied to dielectric fluid by a probe-type vibrator to assist micro electrical discharge machining of deep micro-holes in ceramic materials. Changes of machined hole depth, hole geometry, surface topography, machining stability and tool material deposition under various machining conditions were investigated. Results show that ultrasonic vibration not only induces stirring effect, but also causes cloud cavitation effect which is helpful for removing debris and preventing tool material deposition on machined surface. The machining characteristics are strongly affected by the vibration amplitude, and the best machining performance is obtained when carbon nanofibers are added into the vibrated dielectric fluid. As test pieces, micro-holes having 10 μm level diameters and high aspect ratios (420) were successfully fabricated on reaction-bonded silicon carbide in a few minutes. The hybrid EDM process combining ultrasonic cavitation and carbon nanofiber addition is demonstrated to be useful for fabricating microstructures on hard brittle ceramic materials

Carbon nanofiber assisted micro electro discharge machining of reaction-bonded silicon carbide

Carbon nanofiber assisted micro electro discharge machining was proposed and experiments were performed on reaction-bonded silicon carbide. The changes in electro discharging behavior, material removal rate, electrode wear ratio, electrode geometry, spark gap, surface finish, surface topography and surface damage with carbon nanofiber concentration were examined. It has been found that the addition of carbon nanofiber not only improves the electro discharge frequency, material removal rate, discharge gap, but also reduces the electrode wear and electrode tip concavity. Bidirectional material migrations between the electrode and the workpiece surface were detected, and the migration behavior was strongly suppressed by carbon nanofiber addition. Adhesion of carbon nanofibers to the workpiece surface occurs, which contributes to the improvement of electro discharge machinability. These findings provide possibility for high-efficiency precision manufacturing of microstructures on ultra-hard ceramic materials

Effect of Different Dielectric Fluids on Micro EDM of Low Conductivity Ceramic Material RB-SiC

The machining characteristics of reaction bonded silicon carbide (RB-SiC) in micro electrical discharge machining process were studied by using EDM oil, deionized water, and graphite fiber mixed EDM oil as the dielectric fluids. The process performances were measured in terms of material removal rate, surface roughness and surface topography. The effect of deionized water on SUS 304 also was tried and compared with that on RB-SiC. It was found that when graphite fiber mixed EDM oil was used, higher material removal rate, better surface finish and smoother surface topography were obtained compared to that pure EDM oil and deionized water on RB-SiC. Deionized water could produce better form accuracy, however, electrolytic corrosion occurred and small pits were formed around the machining area of RB-SiC. In contrast, electrolytic corrosion was insignificant for SUS 304

Experimental investigation on material migration phenomena in micro-EDM of reaction-bonded silicon carbide

Material migration between tool electrode and workpiece material in micro electrical discharge machining of reaction-bonded silicon carbide was experimentally investigated. The microstructural changes of workpiece and tungsten tool electrode were examined using scanning electron microscopy, cross sectional transmission electron microscopy and energy dispersive X-ray under various voltage, capacitance and carbon nanofibre concentration in the dielectric fluid. Results show that tungsten is deposited intensively inside the discharge-induced craters on the RB-SiC surface as amorphous structure forming micro particles, and on flat surface region as a thin interdiffusion layer of poly-crystalline structure. Deposition of carbon element on tool electrode was detected, indicating possible material migration to the tool electrode from workpiece material, carbon nanofibres and dielectric oil. Material deposition rate was found to be strongly affected by workpiece surface roughness, voltage and capacitance of the electrical discharge circuit. Carbon nanofibre addition in the dielectric at a suitable concentration significantly reduced the material deposition rate

Fabrication of Microstructures on RB-SiC by Ultrasonic Cavitation Assisted Micro-Electrical Discharge Machining

Ultrasonic cavitation assisted micro-electrical discharge machining was used to fabricate microstructures on reaction-bonded silicon carbide. To aid the removal of debris from the machining gap and to obtain a good surface finish, carbon nanofibers were added into the dielectric fluid. The suspension of carbon nanofibers in the dielectric fluid and the cavitation bubble effect induced by the vibration of the dielectric fluid proved to be effective in reducing the deposition of tool material on the workpiece surface. The tool material deposition rate was found to be significantly affected by the vibration amplitude and the distance between the oscillator and the workpiece. With a hemispherical electrode and inclined workpiece, high accuracy micro-dimples could be obtained within a short time. A nanometer-level surface finish was successfully obtained on a hard-brittle RB-SiCmoldmaterial

An Experimental Study to Enhance the Cutting Performance in Abrasive Waterjet Machining

An experimental study to enhance the cutting performance in abrasive waterjet (AWJ) machining is presented. The study uses the techniques of jet forward impact angles and multipass operations both individually and concurrently when cutting an alumina ceramic and a polymer matrix composite. A brief report on the effect of jet impact angle in single pass cutting is made first, which shows that the optimum jet impact angle for both the ceramics and polymer matrix composite is about 80o. It is found that the multipass cutting technique can increase the cutting capability and application domain of AWJ cutting. It can also improve the major cutting performance such as the depth of cut as compared to single pass cutting within the same total cutting time. The benefit of using multipass cutting operations is further enhanced when it is combined with a jet forward angle of 80o in cutting alumina ceramics