92 research outputs found
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
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
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
Transmission electron microscopic observation of nanoindentations made on ductile-machined silicon wafers
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
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
What micro-mechanical testing can reveal about machining processes
For many years, the machining community has dedicated significant efforts to investigate the microscopic scale level phenomena during the material removal process. On one hand much research has been carried out in relation to workpiece surface integrity after machining and the methods for its study. On the other hand, many studies have been dedicated to replicate machining conditions at microscopic scales using high resolution setups. Although these two topics seem to be little related, there is an opportunity of the machining community to take the advantage of the advanced testing/investigation setups that enable these two strands of research to be performed at very high resolution and repeatability, thus giving new pathways for research in this field. Here we are flagging up to the community the research opportunities offered by micro-mechanical testing that can be performed using in-situ scanning electron microscopes (SEM) or other high-resolution imaging instruments. As such, this review paper discusses the recent research advances in using in-situ micro-mechanical testing for: (i) understanding the phenomena occurring in the workpiece (sub) surfaces after machining operation by performing very high resolution micro-mechanical testing (e.g. compression/bending of micro-pillars/beams) within particular zones of machined superficial layers; (ii) studying the material removal mechanisms at micrometric level using common indenters or dedicated edges to understand how the workpiece materials (e.g. groups/single grains) react to cutting conditions. Finally, we comment on possible future research topics using micro-mechanical testing in-situ in high resolution imaging instruments and how this could help to advance the understanding of machining processes
A Rapid Detection Method for Freshness of Frozen Crayfish Based on Near-Infrared Spectroscopy
To establish a model based on near-infrared (NIR) spectra for quickly detecting the freshness of frozen crayfish, NIR spectra of thawed crayfish (tail, meat, and mince) were collected, and data were pretreated by first derivative, multiple scattering correction, wavelet transform (WT), or standard normal transform. The original and pretreated spectral data were correlated to total volatile basic nitrogen (TVB-N) contents using partial least squares (PLS) or convolutional neural network (CNN), and different quantitative prediction models were established and compared. The best model was selected to investigate its accuracy and applicability. The results showed that pretreatment methods had a significant influence on the accuracy of the model, and the CNN model established after spectral preprocessing had a better ability to predict the TVB-N content of crayfish compared with the PLS model. The CNN model based on the WT pretreated spectra of crayfish meat had the highest prediction accuracy for the validation set with correlation coefficients of 0.97 and 0.96, and root mean square errors of 1.26 and 0.93 mg/100 g for the calibration set and validation set, respectively. Moreover, the accuracy, precision, and sensitivity of the NIR method were within reasonable limits, and it had good figures of merit. According to the requirements of fast operation, accurate results, and low damage in practice, the WT-CNN-crayfish meat model was determined as the optimal model for predicting the TVB-N content in frozen crayfish. These results suggested that the WT-CNN-crayfish meat model have a great potential for predicting the TVB-N content and rapidly evaluating the freshness of frozen crayfish
Surface Modification And Functionalization By Electrical Discharge Coating: A Comprehensive Review
Hard coatings are extensively required in industry for protecting mechanical/structural parts that withstand extremely high temperature, stress, chemical corrosion, and other hostile environments. Electrical discharge coating (EDC) is an emerging surface modification technology to produce such hard coatings by using electrical discharges to coat a layer of material on workpiece surface to modify and enhance the surface characteristics or create new surface functions. This paper presents a comprehensive overview of EDC technologies for various materials, and summarises the types and key parameters of EDC processes as well as the characteristics of resulting coatings. It provides a systematic summary of the fundamentals and key features of the EDC processes, as well as its applications and future trend
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