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Friction drilling utilizes the heat generated from the friction between the tool and the thin workpiece to form a bush for fixtures such as screw threads in plastic deformation process. This process produces no chip, shortens the time required for hole-making and incurs less tool wear, thus lengthening the service life of the drill. In this study, tungsten carbide drills with and without coating were employed to make holes in AISI 304 stainless steel, which is known to have high ductility, low thermal conductivity and great hardness. TiAIN and AlCrN were coated onto the drill surface by physical vapor deposition (PVD). Performance of coated and uncoated cutting tools was examined for drillings made under different spindle speeds. Changes in relationship between drill surface temperature, tool wear and axial thrust force during machining were also explored. Experimental results reveal that lubricating effect of the coating and low thermal conductivity of AlCrN caused AlCrN-coated drill to produce the highest surface temperature but the lowest axial thrust force with the least tool wear. However, the difference in performance between coated and uncoated drills diminished with increase in number of holes drilled.

This study presents a spiral polishing method and a device for micro-finishing purposes. This novel finishing process has wider application than traditional processes. This offers both automation and flexibility in final machining operations for deburring, polishing, and removing recast layers, thereby producing compressive residual stresses even in difficult to reach areas. Applying of this method can obtain a fine polished surface by removing tiny fragments via a micro lapping generated by transmission of an abrasive medium through a screw rod. The effect of the removal of the tiny fragments can be achieved due to the function of micro lapping. The method is not dependent on the size of the work-piece's application area in order to carry out the ultra precise process. The application of this research can be extended to various products of precision ball-bearing lead screw. The proposed method produces products with greater precision and more efficiently than traditional processes, in terms of processing precisions and the surface quality of products. These parameters used in achieving maximum material removal rate (MRR) and the lowest surface roughness (SR) are abrasive particle size, abrasive concentration, gap, revolution speed and machining time.

In order to achieve a mirror-like workpiece surface by EDM, a micro-energy EDM or a manual lapping is normally used. However, both methods are time consuming and economically unattractive. To have better performance, a sinking EDM machine was first used in this research on SKD 61 for a micro-energy discharge process followed by the electrophoretic deposition (EPD) process to coat Al2O3 particles uniformly on a rotation electrode. The precision polishing process was then applied on the discharged workpiece with suitable parameters including the voltage, electrode rotating speed, pH value of electrolyte, and abrasive concentration. After the EDM process, the surface roughness and the recast layer thickness of a workpiece could also be reduced. The experimental data showed that when 0.3 μm of Al2O3 particles was used for the EPD polishing process, the initial roughness of a discharge surface could be improved from 0.52 μm Ra (6.50 μm Rt) to a mirror-like surface of 0.068 μm Ra (0.742 μm Rt). Also, the total working time could be reduced significantly to within the range of 5 to 10 min.

This research presents a novel process using micro electro-discharge machining (micro-EDM) combined with high-frequency dither grinding (HFDG) to improve the surface roughness of micro-holes. Micro-EDM is a well-established machining option for manufacturing geometrically complex small parts (diameter under 100 μm) of hard or super-tough materials. However, micro-EDM causes the recast layer formed on the machined surface to become covered with discharge craters and micro-cracks, resulting in poor surface quality. This affects the diameter of the micro-hole machined and undermines seriously the precision of the geometric shape. The proposed method that combines micro-EDM process with HFDG is applied to machining high-nickel alloy. As observed in SEM photographs and surface roughness measurement, HFDG method can reduce surface roughness from 2.12 to 0.85 μm Rmax with micro-cracks eliminated. Our results demonstrated that micro-holes fabricated by micro-EDM at peak current 500 mA followed by HFDG at 40 V can achieve precise shape and good surface quality after 6–8 min of lapping.

In this study, the feasibility of fabricating micro-holes in the high nickel alloy using micro-electro-discharge machining (micro-EDM) was investigated. The high nickel alloy is a material with high magnetic permeability. It can be used to shield MEMS prevent interference of the magnetic field. Micro-systems can be assembled and micro-wires can be connected through micro-holes that are drilled in the workpiece. In this way, the internal electronic system can communicate with external system without magnetic wave disturbance. However, since the high nickel alloy is tough and can easily cause cutting tool wear, it is difficult to fabricate micro-holes by the conventional machining methods. In this work, a two-stage cylindrical cutting tool of high hardness was first fashioned. The tool was precisely shaped with a first stage (i.e., tip) having a smaller diameter, and a helically grooved second stage with a larger diameter by the wire electro-discharge grinding (WEDG) process. The first stage of the tool electrode was then used to drill a micro-hole in a plate using micro-EDM process. To improve the roughness of micro-holes, the second stage with helical groove was used for in situ grind machining with SiC particles. Our experimental results show that by optimizing EDM machining parameters, i.e., discharge current of 500 mA, pulse duration of around 4 μs, etc., favorable diameter variation between the entrances and the exits (DVEE), good material removal rate (MRR) and good electrode wear rate (EWR) could be obtained. The addition of the in situ grind machining leads to precise contours, and the surface roughness of micro-holes is reduced to 0.85 μm Rmax, as revealed by SEM photographs.

Micro electro-discharge machining (micro-EDM) is a critical technology to fabricate high aspect ratio 3D micro-components. However, the surfaces of micro-components manufactured by micro-EDM will exhibit micro-cracks to produce notch effects, and lead to stress concentrate and reduction of fatigue strength. This paper performs micro-bending tests to investigate the influence of various roughness and size on the bending fracture strength of micro WC-shafts manufactured by micro-EDM. The experimental results indicate that the surface roughness, axial surface area, volume, and length of the specimen will affect its bending fracture strength. For specimens with the same size, the mean bending fracture strength decreases as the surface roughness increases, and the bending fracture probability of the specimens also increases (roughness effect). For specimens with the same roughness, reducing the length or axial surface area will increase the mean bending fracture strength, and reduces the bending fracture probability (size effect).

Electrical discharge machining (EDM) process is widely used to process hard materials in the industry. Electrical discharge distribution effects can be achieved by the addition of Al powder in the dielectric. A fine surface roughness value of the workpiece is thus obtained. However, the electrostatic force among fine Al particles is found to agglomerate the Al powders in the dielectric. A surfactant can be adopted to separate the Al powder in the dielectric homogenously. A better surface even the mirror-like quality of the EDMed workpiece is thus desired. In the study, the effect of surfactant and Al powders added in the dielectric on the surface status of the workpiece after EDM is investigated. It is observed the best distribution effect is found when the concentrations of the Al powder and surfactant in the dielectric are 0.1 and 0.25 g/L, respectively. An optimal surface roughness (Ra) value of 0.172 μm is achieved under the following parameter—positive polarity, discharge current 0.3 A, pulse duration time 1.5 μs, open circuit potential 140 V, gap voltage 90 V and surfactant concentration 0.25 g/L. The surface roughness status of the workpiece has been improved up to 60% as compared to that EDMed under pure dielectric with high surface roughness Ra of 0.434 μm.

Alumina particle reinforced 6061 aluminum matrix composites (Al2O3p/6061Al) have excellent physical and chemical properties than those of a traditional metal; however, their poor machinability lead to worse surface quality and serious cutting tool wear. In this study, wire electrical discharge machining (WEDM) is adopted in machining Al2O3p/6061Al composite. In the experiments, machining parameters of pulse-on time were changed to explore their effects on machining performance, including the cutting speed, the width of slit and surface roughness. Moreover, the wire electrode is easily broken during the machining Al2O3p/6061Al composite, so this work comprehensively investigates into the locations of the broken wire and the reason of wire breaking. The experimental results indicate that the cutting speed (material removal rate), the surface roughness and the width of the slit of cutting test material significantly depend on volume fraction of reinforcement (Al2O3 particles). Furthermore, bands on the machined surface for cutting 20 vol.% Al2O3p/6061Al composite are easily formed, basically due to some embedded reinforcing Al2O3 particles on the surface of 6061 aluminum matrix, interrupt the machining process. Test results reveal that in machining Al2O3p/6061Al composites a very low wire tension, a high flushing rate and a high wire speed are required to prevent wire breakage; an appropriate servo voltage, a short pulse-on time, and a short pulse-off time, which are normally associated with a high cutting speed, have little effect on the surface roughness.

This study investigates the influence of the machining characteristics on pure titanium metals using an electrical discharge machining (EDM) with the addition of urea into distilled water. Additionally, the effects of urea addition on surface modification are also discussed. In the experiments, machining parameters such as the dielectric type, peak current and pulse duration were changed to explore their effects on machining performance, including the material removal rate, electrode wear rate and surface roughness. Moreover, the elemental distribution of nitrogen on the machined surface was qualitatively determined by EPMA to assess the effects on surface modification. Micro hardness and wear resistance tests were performed to evaluate the effects of the reinforced surface. Experimental results indicate that the nitrogen element decomposed from the dielectric that contained urea, migrated to the work piece, forming a TiN hard layer, resulting in good wear resistance of the machined surface after EDM.

A micro slit die easily manufactured using a micro electrical discharge machining (MEDM) is proposed for micro heat sink fabrication. In the investigations described in this paper, processed concave and rectangular shaped copper foils were combined piece by piece to form an assembled electrode. This electrode was used to fabricate a micro slit die. This die included 15 micro fins in a small tungsten carbide plate. The micro heat sink was made by applying a pressing or scraping method when the micro slit die was used. The experiments showed that debris, produced by the MEDM, might cause a discharge concentration effect because of the narrow gaps between the workpiece and electrode. Parts of the micro fin were seriously melted during this process. Flushing dielectric could effectively remove the debris from the narrow gap, generating an appropriate discharge dispersing effect. However, the discharge effect was unstable when large flushing pressure was applied, thus reducing the machining precision. The micro fins were formed into a rectangular shape using kerosene as the MEDM dielectric. Using distilled water as the MEDM dielectric produced a higher material removal rate and serious assembled electrode wear. Therefore, the micro fins formed as triangle profiles. The micro heat sink was higher even when the pressing method was used. The heat sink deviated and was full of burrs on the fin edge when the scraping method was used.

In microhole machining of metal, micro electro-discharge machining (MEDM) is an effective method that can easily create a hole with a diameter under 100 μm. Due to the poor surface quality and shape of MEDM, a machining method that compounds MEDM and micro ultrasonic vibration lapping (MUVL) is proposed here to allow the production of high precision microholes with high aspect ratios. In our investigations, first, a circular or stepped circular microtool was made by the MEDM process, and the tool was used to create a microhole on a small piece of titanium plate in the same machining process. Finally, the abrasive particles driven by the same tool were utilized to grind this hole in the MUVL procedure, and a hole with a diameter about 100 μm can be obtained. Owing to the microtool and workpiece not taking apart from the clamping apparatus during different machining steps, the microhole was processed in the co-axial situation, so the precise shape and perfect surface can be obtained easily. For example, the diameter variation between the entrances and exits of the microholes could reach a value of about 5 μm when the workpiece had a thickness of 500 μm, if the circular microtools was used. Meanwhile, the roundness of the microholes clearly improved, regardless of whether circular or stepped tools were used. However, owing to the perfect grinding effect between the microholes and microtools, the stepped circular tools produced high quality surfaces more easily than the circular tools.

This paper presents a novel technique to improve the machined surface of Al–Zn–Mg aluminum alloy by a combined machining process of electrical discharge machining (EDM) with ultrasonic machining (USM). In these experiments, SiC particles were added into the dielectric fluid to produce a particle-reinforced mechanism and solid solution strengthened structure to form a modified layer on the machined surface in a short working time. The experimental investigation also discusses the influence of machining polarity on the modified layer of aluminum alloy. Furthermore, quantitative analysis of element content has been carried out by electron probe micro-analyzer (EPMA) to determine the thickness of the modified layer and the distribution of silicon and carbon in the cross-section of the machined zone. Moreover, micro-hardness tests and wear tests were also conducted to evaluate the effects of surface modification by the combined process. From the experimental results, it can be seen that the combined process of EDM with USM can achieve an 80 μm deep modified layer on the machined surface of aluminum alloy in 240 s, and that such layer can significantly improve the hardness and wear resistance of the machined surface.

This study investigates the influence of process parameters of electrical discharge machining (EDM) on machining performances with the addition of Al and Cr powder into kerosene. In addition, the effects of powder addition on surface fine-finish and modification are also discussed. The machining process parameters of this empirical investigation included peak current, pulse duration, as well as the type of powder added, its grain size, and mixing ratio. The machining performance, characterized by material removal rate (MRR), electrode wear rate (EWR) and surface roughness, was monitored as a function of process variables. Moreover, surface modifications were also explored thoroughly. The experimental results demonstrate that addition of Al and Cr powders into the dielectric enlarges the gap distance and divides discharge current, which promotes better EDM performance. Restated, adding a mixture of Al and Cr powders into dielectric yields the best results. Moreover, during EDM, the added powder migrates and penetrates the machined surface. Test results reveal that the corrosion resistance and surface hardness was improved by adding the proper powder into dielectric.

1. Electrical parameters, e.g. polarity, peak current, pulse duration, and powder supply voltage. 2. Non-electrical parameters, e.g. circumferential speed of electrode, reciprocating speed. The analysis of the Taguchi method reveals that, in general, the electrical group more significantly affects the machining characteristics than the non-electrical group. Also derived herein are semi-empirical equation that contain all of the machining characteristics. Experimental results are presented to illustrate the proposed approach.

This work presents a revised EDM process by quantitatively and qualitatively measuring the process using different dielectric fluids. The revised EDM process is developed by modifying the discharging circuit to minimize the discharging current and introducing a new driven mechanism with horizontal rotating electrode. By applying a thin copper diskette electrode, titanium alloy is machined using micro-slit EDM with various dielectric fluids. The dielectric fluids used herein are kerosene, kerosene with aluminum powder, and kerosene with SiC powder. The effects of the various fluids used during the machining process are numerous. Such effects are more clearly accounted for by closely examining the material removal depth, the electrode wear rate, the slit expansion, the surface roughness, and the waveform of the discharging condition. The addition of both SiC and aluminum powder to the kerosene permit an extension of the gap between the electrode and the workpiece. The extended gap increases the debris removal rate and the material removal depth. Furthermore, a bridging effect is created by the added powder drifting within the kerosene and, in doing so, facilitates the dispersion of the discharge into several increments. Thus, several discharging trajectories are formed within a single input impulse and several discharging spots are created within a discharging impulse also. The effects due to the discrete discharging pulses are elucidated, these effects being the minimizing of the machined debris, which is easily removed, and the increasing of the material removal depth and surface roughness. However, the addition of the powder to the kerosene disturbs the adherence of carbon nuclides attached to the surface of the electrodes. By doing so, the electrode wear rate is increased, as also is the slit expansion.

To circumvent the high cost of micro electro-discharge machining (MEDM) with superfine wire, the authors modified a conventional electro-discharge machine (EDM) by fitting a rotating disk as the electrode (RDE). Locating the electrode below the workpiece in the modified RDE-EDM, the debris removal rate was greatly improved. Further, by an improved fixture design to stabilize electrode vibration during machining and by a revised circuit designation to reduce the discharge current, micro slit machining was made feasible in practical application. A 42 μm-wide micro slit with a depth of 1.02 mm was fabricated successfully on a Ti–6Al–4V workpiece by using 25 μm thickness copper as the material of the rotating disk electrode and kerosene as the dielectric fluid. The effects of polarity, discharge current, pulse duration and rotational speed on the material removal rate (MRR), the electrode wear rate (EWR), the expansion of slit, the surface profile and the recast layer of micro slit machining are reported and discussed.

This paper describes the characteristics of the micro-hole of carbide by electric discharge machining with a copper tool electrode. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. Therefore, the process works very efficiently, particularly in the machining of difficult-to-cut materials. This study takes advantage of these features to carry out the micro-hole machining of carbide with a copper tool electrode. To achieve minimal expansion of the machined micro-hole and minimal tool electrode wear rate to secure a high precision micro-hole in the carbide, the effects of changing the polarity, the tool electrode shape, and the rotational speed of the tool electrode are studied. The present experimental results show that positive polarity machining must be used. As for the rotational speed of the tool electrode, it is shown that a higher rotational speed electrode can minimize the expansion. In addition, it is demonstrated that the cross-sectional area of the tool electrode greatly affects the expansion and the tool electrode wear. Finally, removal of the debris discharge and reduction of expansion is shown to be improved remarkably by making a notch on the cylindrical cross-section.

In this study, we first applied the variation principle to derive a new finite element method (FEM) based on the theory of beam on elastic foundation using line element. The derived FEM was then applied to solve, for the first time, the pressure vessel problems with uniform thickness. Our FEM results, obtained even by using only one line element, agreed exactly with the available closed-form solution, confirming the validity and computing efficiency of our finite element formulation. Moreover, we have applied our new FEM to solve pressure vessel problems with non-uniform thickness where no exact analytical solution is known to exist. The distributions of discontinuity stress in the cylindrical part were obtained. We found that shear force and bending moment were indeed discontinuous at the geometrically discontinuous juncture, due to the bending rigidity and elastic constant change by the non-uniform thickness. Finally, the case of discontinuity stresses in a bimetallic joint was also studied. The locations of maximum shear force and bending moment were found to be affected by the bending rigidity of the material.

Based on linear micropolar thermoelasticity theory, a two-dimensional boundary element method (BEM) formulation is derived and the corresponding computer programs are developed to solve the problems of micropolar solid. The program is verified by computing the thermal stress in a hollow cylinder. In addition, the new BEM formulation is applied to solve, for the first time, the thermal stress of a square region with a circular hole. The effects of coupling number and characteristic length on the micropolar effects are derived, and the important new findings are summarized.