Mohammad Yeakub Ali

Experimental Study of Conventional Wire Electrical Discharge Machining for Microfabrication

This article discusses the investigation and optimization of the process parameters of conventional wire electrical discharge machining (WEDM) of a copper substrate for microfabrication. The effect of discharge current, pulse-on time, and gap voltage on surface finish were studied. The average surface roughness (R a ) and peak-to-valley height (R t ) were measured with a surface profiler. The surface roughness increased with higher discharge current and gap voltage. With the increase of pulse-on time, the surface roughness decreased. Statistical models were established to predict the surface roughness R a and R t in terms of discharge current, pulse-on time, and gap voltage. Using the optimized parameters, miniaturized spur gears, and plate-shaped hot embossing microtools were fabricated where an average surface roughness of about 1 µ m and dimensional accuracy of 1–2% were achieved.

Effect of Conventional EDM Parameters on the Micromachined Surface Roughness and Fabrication of a Hot Embossing Master Microtool

This article discusses the effect of conventional electrical discharge machining (EDM) parameters for generating micrometer and submicrometer leveled surface roughness. Fabrication of submillimeter-sized microstructure to use as a master microtool for replication of polymer microcomponents is also presented. Beryllium copper mold alloy was machined using very low values of three input parameters: discharge current, pulse-on time, and pulse-off time. The input parameters and measured surface roughness were analyzed, and statistical models were developed. The analysis showed that surface roughness increased with the increase of discharge current and pulse-on time. These models were applied to lower values of input parameters to achieve high surface finish. A hot embossing replication master with microchannel structure was produced using the optimized machining parameters with an average surface roughness of 0.60 µm. The replication master was tested with a prototype micro hot embossing machine where it faithfully duplicated its microstructures.

Influence of electrical discharge machining process parameters on surface micro-hardness of titanium alloy:

The resistance of a material to an indentation on microscopic scale is an indication of its micro-hardness. To a lubrication engineer, micro-hardness is synonymous with surface wear resistance of a material. In this study, an attempt was made to enhance the surface micro-hardness of titanium alloy (Ti-6Al-4V) through modification of electrical discharge machining process parameters. These parameters are the electrode, the dielectric fluid and the electrical variables of the machine. Cu–TaC composite electrode produced through powder metallurgy method was used during the electrical discharge machining with different urea concentrations in distilled water as dielectric fluid. The electrical variables used were the peak current, the pulse duration and the duty factor. Electrical discharge machining was also conducted with copper (Cu) powder metallurgy electrode with distilled water dielectric fluid for comparison. The results showed that the micro-hardness of the electrical discharge machined surfaces with Cu–TaC electrode/urea dielectric fluid was generally higher than that of those with Cu electrode/distilled water dielectric fluid. The highest micro-hardness of 1795 Hv was attained with 10 g/L of urea concentration.

Development of Microreplication Process - Micromolding

Abstract A microreplication process, micromolding, was developed to replicate three-dimensional microcomponents. It included modifying a conventional molding machine, developing a thermal control unit to control the mold temperature, and developing a vacuum unit to evacuate the microcavity before filling it with plastic melt. Focused ion beam sputtering, a maskless patterning of material, was used to fabricate a microcavity that was then used as a mold insert. Feasibility of the micromolding process was investigated by simulation, and results were verified with the replication of polymer microcomponents (e.g., microgear, gear-train). Commercial simulation software was used to reveal possible issues in micromolding by integrating the microcomponent with a larger base. The simulations predict the filling time, pressure distribution, volumetric shrinkage, stress distribution, etc., of the microcomponent.

SURFACE ROUGHNESS OF SPUTTERED SILICON. II. MODEL VERIFICATION

Experimental verification of the mathematical surface roughness model for sputtered silicon was performed. The beam shape and its significant level of intensity were determined first by measuring the topography of craters sputtered by focused ion beam (FIB). Then the beam function was generated for various combinations of beam parameters. The material function was developed both by theoretical and experimental analysis. These two functions were then used in the model to calculate the theoretical surface roughness. Microsurface analysis was formed by FIB sputtering of a (100) silicon wafer. The surface roughness at the bottom of the sputtered features was then measured using an atomic force microscope. The theoretical surface roughness was found to be within ±1 and ±5 nm of the measured surface roughness with the measurement uncertainty (standard deviation) of about ±0.36 and ±0.85 nm for R a and R t, respectively.

Influence of dielectric fluids on surface properties of electrical discharge machined titanium alloy

Dielectric fluid is one of the major components of electrical discharge machining. In this article, the influence of two dielectric fluids on the surface properties of workpiece was investigated. Machining was conducted on the titanium alloy (Ti-6Al-4V) with the new Cu-TaC composite electrodes under the two dielectric fluids, which are the urea solution and distilled water. Cu-TaC electrodes were produced from copper and tantalum carbide powders by powder metallurgy method with 50/50% composition at compacting pressure of 24.115 MPa. The main objective is to compare the effect of these dielectric fluids on the electrical discharge machined surface properties—microhardness (Mh) and surface roughness (Ra). The machining variables used to investigate the Ra and Mh were peak current and pulse duration. The surface roughness was found to be generally higher in the specimens machined with urea solution dielectric fluid, the highest being 19.05 µm. For the specimens machined with distilled water dielectric fluid, the highest Ra is 14.45 µm. The highest microhardness improvement ratio attained by the specimens electrical discharge machined with urea dielectric fluid is about 48% higher than those machined with distilled water. It is concluded that distilled water dielectric fluid gave better surface roughness, while the urea dielectric fluid provides the machined surface with higher microhardness.

Form Characterization of Microhole Produced by Microelectrical Discharge Drilling

This article discusses the characterization of form of microholes produced by microelectrical discharge drilling (micro-EDD) on beryllium-copper alloy using tungsten carbide electrode of 300 µm diameter. Using a fixed set of micro-EDD parameters, microholes of different aspect ratio were drilled. The selected form characteristics diameter, roundness, and taper angle were investigated. The hole diameter and roundness were estimated by using scanning electron microscope (SEM) and graphical calculation. The microhole was sectioned to measure the depth and taper angle. The variations of these form characteristics were plotted against aspect ratio. This experimental study showed that diameter, roundness error, and taper angle of the microhole increase with the increase of aspect ratio almost at the same rate. The electrode wear ratio was not insignificant for low aspect ratio microhole. However, it increased sharply with the increase of aspect ratio.

Improving micro-hardness of stainless steel through powder-mixed electrical discharge machining

Powder-mixed electrical discharge machining (PMEDM) is the technique of using dielectric fluid mixed with various types of powders to improve the machined surface output. This process is fast gaining prominence in electrical discharge machining (EDM) industry. The objective of this investigation is to determine the ability of tantalum carbide (TaC) powder-mixed dielectric fluid to enhance the surface properties of stainless steel material during EDM. The properties investigated are the micro-hardness and corrosion characteristics of the EDMed surface. Machining was conducted with 25.0 g/L concentration of TaC powder in kerosene dielectric fluid. The machining variables used were the peak current, pulse on time and the pulse off time. The effects of these variables on the micro-hardness of the EDMed surface were determined. Corrosion tests were also conducted on the samples that exhibited higher hardness. Results showed that the EDMed surface was alloyed with elements from the TaC powder. The highest micro-hardness obtained with PMEDM is about 1,200 Hv. This is about 1.5 times that obtained without TaC powder in the dielectric fluid. The loss in weight during corrosion test was found to be 0.056 µg/min for the PMEDM which was much lower than the lowest value of 10.56 µg/min obtained for the EDM without powder dielectric fluid.

SURFACE ROUGHNESS OF SPUTTERED SILICON. I. SURFACE MODELING

A mathematical model for the calculation of surface roughness was developed for focused ion beam (FIB) sputtering. The surface roughness function is a combination of the beam function and the material function. The beam function includes ion type, ion acceleration energy, and beam parameters. Furthermore, the beam parameter incorporates ion flux, the ion beam intensity distribution profile, tailing and neighboring of the successive beams, dwell time, etc. The intensity distribution inside the ion beam is considered to be Gaussian. The cumulative intensity over the total milling area is calculated by the algebraic summation of individual beam intensity delivered to every pixel successively. The material function includes the inherent material properties related to the ion beam micromachining. If one knows the beam function and material function, surface roughness at the bottom of the sputtered features can be calculated using this model.

Powder Mixed Micro Electro Discharge Milling of Titanium Alloy: Investigation of Material Removal Rate

This paper presents effects of silicon carbide (SiC) powder in dielectric fluid of micro EDM on material removal rate (MRR). The aim is to identify the optimum level of SiC powder concentration and other micro EDM parameter for higher MRR. The work material was titanium alloy (Ti-6Al-4V) machined with tungsten carbide (WC) electrode by varying two machining parameters SiC powder concentrations and discharge energy. By using two factor four level factorial design of experiment, sixteen experiments were conducted. Data were analyzed by Design Expert® software. In this experimental investigation, maximum MRR of 7.3 µg/min was obtained for 24.75 g/l SiC powder concentration and 56.77 µJ discharge energy. The analysis of variance revealed that the SiC powder concentration in dielectric fluid on micro EDM has significant influence on MRR Ti-6Al-4V titanium alloy.