Muhammad Pervej Jahan

Development, Modeling, and Experimental Investigation of Low Frequency Workpiece Vibration-Assisted Micro-EDM of Tungsten Carbide

This present study intends to investigate the feasibility of drilling deep microholes in difficult-to-cut tungsten carbide by means of low frequency workpiece vibration-assisted micro–electrodischarge machining (micro-EDM). A vibration device has been designed and developed in which the workpiece is subjected to vibration of up to a frequency of 1 kHz and an amplitude of 2.5 �m. An analytical approach is presented to explain the mechanism of workpiece vibration-assisted micro-EDM and how workpiece vibration improves the performance of micro-EDM drilling. The reasons for improving the overall flushing conditions are explained in terms of the behavior of debris in a vibrating workpiece, change in gap distance, and dielectric fluid pressure in the gap during vibration-assisted micro-EDM. In addition, the effects of vibration frequency, amplitude, and electrical parameters on the machining performance, as well as surface quality and accuracy of the microholes have been investigated. It has been found that the overall machining performance improves considerably with significant reduction of machining time, increase in MRR, and decrease in EWR. The improved flushing conditions, increased discharge ratio, and reduced percentage of ineffective pulses are found to be the contributing factors for improved performance of the vibration-assisted micro-EDM of tungsten carbide.

Study of Micro-EDM of Tungsten Carbide with Workpiece Vibration

Present study introduces low-frequency workpiece vibration during micro-EDM drilling of difficult-to-cut tungsten carbide with an objective to overcome the difficulty in flushing of debris and machining instability in deep-hole machining. The effects of vibration frequency, amplitude and electrical parameters on the machining performance, as well as surface quality and accuracy of the micro-holes have been investigated. It is found that the overall machining performance improves significantly with significant reduction of machining time, increase in material removal rate (MRR), and decrease in electrode wear ratio (EWR). The surface quality improves and the overcut and taper angle of the micro-holes reduces after applying the workpiece vibration in micro-EDM. The frequency and amplitude of 750 Hz and 1.5 μm were found to provide optimum performance.

A comparative study on the performance of sinking and milling micro-EDM for nanofinishing of tungsten carbide

Micro-electrical discharge machining (micro-EDM) is a flexible machining technique offering the possibility to produce freeform microstructures and micromoulds using hard-but-conductive materials like tungsten carbide (WC). It is desirable to obtain fine surface finish directly using micro-EDM when micromoulds and dies are machined, so that subsequent polishing can be avoided. This paper presents a comparative study between the performance of die-sinking and milling micro-EDM for the semi-finish and finish machining of WC. The comparison was conducted with respect to achieved material removal rate (MRR), relative electrode wear ratio (EWR), surface topography, average surface roughness (Ra) and peak-to-valley roughness (Rmax). It has been found that, micro-EDM milling is capable of generating smooth, shiny and defect-free surfaces with lower Ra and Rmax at comparatively higher MRR and lower EWR in the finish micro-EDM of WC. Moreover, the MRR in milling micro-EDM can further be increased at semi-finishing regime with the sacrifice of surface finish and EWR by increasing the electrode scanning speed. Comparing all the performance parameters, milling micro-EDM has been found to be the better option for semi-finishing and finishing of WC than die-sinking.

Migration of Materials during Finishing Micro-EDM of Tungsten Carbide

Present study aims to investigate the migration of materials onto the surface of workpiece and electrode during fine-finish die-sinking and milling micro-EDM of tungsten carbide using pure tungsten electrode. The effect of materials transfer on the machined surface characteristics is also presented. The machined surfaces have been examined under scanning electron microscope (SEM) and energy dispersive X-ray (EDX) in order to investigate the changes in chemical composition due to the migration of materials. It has been observed that materials from both workpiece and electrode transfer to each other depending on machining conditions and discharge energy. A significant amount of carbon migrates to both electrode and workpiece surface due to the decomposition of dielectric hydrocarbon during breakdown. The migration occurs more frequently at lower gap voltages during finish die-sinking micro-EDM due to low spark gap and stationary tool electrode. Milling micro-EDM suffers from lower amount of carbon migration and fewer surface defects which improve the overall surface finish and reduce surface roughness significantly.

Cutting Force Analysis of on-Machine Fabricated PCD Tool during Glass Micro-Grinding

Brittle and hard materials are problematic to mechanically micro machine due to damage resulting from material removal by brittle fracture, cutting force-induced tool deflection or breakage and tool wear. As a result, the forces arising from the cutting process are important parameter for material removal. This study was undertaken to investigate the effect of cutting conditions on cutting forces and the machined surface during the glass micro grinding using on-machine fabricated (Poly Crystalline Diamond) PCD tool. Experimental results showed that an increase in depth of cut and feed rate can result in increase of cutting forces and surface roughness as well. Among the forces in 3 axes, force along feed direction is found to be larger, which played a major role in material removal. Finally, it is observed that PCD tool exhibits promising behaviour to machine brittle material like BK-7 glass for producing micro molds and micro fluidic devices, since it has better wear resistance, experiences less cutting forces and generates smooth surfaces with Ra value of as low as 12.79 nm.