Speed Wire Electrical Discharge Machining Research Articles

Experimental study on forming consistent accuracy and tool electrode wear involved in fabricating array microelectrodes and array micro holes using electrical discharge machining

Despite the non-contact nature of electrical discharge machining (EDM) process makes it become one of most promising methods to fabricate array micro structures, the low consistent accuracy, serious tool wear and low prepared efficiency has hindered the development and applications of EDM technology in fabricating array micro structures. To fill this gap, the mixture feeding model was firstly introduced to fabricate array microelectrodes by low speed wire electrical discharge machining (LS- WEDM) to balance the contradiction between consistent accuracy and prepared efficiency. Firstly, the contrast experiments of preparing array microelectrodes with various feeding models were conducted, and results indicated that the processing efficiency of square array microelectrodes obtained by mixture model was increased by 36.4% compared to constant velocity model. Besides, the consistent accuracy, corner radius and taper accuracy of square array micro holes were investigated in detail. The effects of lifting model and lifting speed on surface roughness parameters of inner wall of square array micro holes were disclosed. Moreover, the transverse and longitudinal tool electrode wear of square array microelectrodes were qualitatively measured and analyzed, and the mechanism for tool electrode loss involved in preparation of array micro holes in Ni-base single crystal superalloy was revealed. The research results are of great significance for improving the prepared accuracy of array microelectrodes and promoting engineering application of EDM technology in preparing array micro structures.

Micro-nano manufacturing of Ti6Al4V antibacterial surface

Ti6Al4V is often used in the manufacture of biomedical equipment due to its excellent properties such as light weight, high strength and good corrosion resistance in the physiological environment. Therefore, it is very important to form a non-toxic antibacterial surface on Ti6Al4V material. In this paper, a micro-nano manufacturing method of Ti6Al4V antibacterial surface was studied. In this process, the surface was firstly cut by low speed wire electrical discharge machine, and then the cut surface was hydrothermal treated. The antibacterial surface prepared by this process had the characteristics of non-toxic, stable structure, and would not cause bacteria to develop drug resistance. The preparation process is simple, friendly to the environment, and can realize mass production. The influence of different cutting times on the antibacterial surface morphology in the low speed wire electrical discharge machining was studied. The micron-grade surface obtained after three cutting times was of good quality, less molten material and high wear resistance. The influence of two etching agents mixed with different molar ratios on the micro-nano structure of antibacterial surface during hydrothermal treatment was analyzed. When the molar ratio of A and B solution was 14:1, the surface structure of the best size was obtained, and the wear resistance of the micro-nano structure surface was improved compared with the polished surface. The antimicrobial test results show that the surface of the prepared workpiece had obvious antimicrobial properties compared with the surface of the polished part after cultured for 24 h. The bacteriostatic rate of Escherichia coli was 49.55%. Based on the above, the research results of this paper have positive significance for the development of micro-nano antibacterial surface.

An investigation on discharge servo parameters and machining servo mode optimization of MS-WEDM

Increasing the machining efficiency of middle speed wire electrical discharge machining (MS-WEDM) is usually through optimizing process parameters, but the discharge servo parameters of the servo controller can also be optimized to achieve the same purpose. This paper develops a multi-mode servo controller for MS-WEDM to investigate discharge servo parameters. Firstly, the structure and control principle of the servo controller are introduced, and the core functions are described in detail. Secondly, it introduces the discharge servo parameters that can be optimized: gap state threshold and feedback period. At the same time, the platform specifications and parameters for optimization experiments are introduced. Thirdly, the experimental scheme and result analysis of parameter optimization are described, and the optimized parameters are obtained. Finally, different machining experiments are carried out for the multi-mode of the servo controller to investigate the effectiveness and practicability of the different machining servo modes. In the parameter optimization and machining experiments, the recording function of the servo controller was used to draw the speed curve, and the servo response effects of different servo modes were obtained.

Research on the machining characteristics of vertical ultrasonic vibration assisted WEDM-LS

ABSTRACT In this paper, a novel composite process technology – Low Speed Wire Electrical Discharge Machining (WEDM-LS) with Vertical Ultrasonic Vibration (VUV) assisted is put forward to improve the performance of traditional WEDM-LS. First, a fluid-solid coupling model of interelectrode flow field and workpiece is established. The simulation result reveals that under the assistance of Vertical Ultrasonic Vibration of workpiece, the velocity of deionized water near the wall of discharge craters is much higher than traditional WEDM-LS or WEDM-LS with the assistance of wire ultrasonic vibration (Wire USV). Therefore, Vertical Ultrasonic Vibration is helpful to the removal of residual debris from the craters. Second, the multiphase flow model of debris, deionized water, and bubbles between electrodes was constituted, and it shows that workpiece vibration frequency is positively correlated with the movement intensity of bubbles and debris, which promotes debris removal throughout the whole processing area. Finally, based on the Taguchi method, the experiments of traditional WEDM-LS, Wire USV assisted WEDM-LS and VUV assisted WEDM-LS were conducted. The workpiece was selected as TiNi-01 shape memory alloy (SMA). The experimental results reveal that under the large electrical machining parameters, Vertical Ultrasonic Vibration assisted WEDM-LS can achieve excellent machining efficiency and quality.

Machining of cylindrical parts by wire electrical discharge grinding using thin plate guide

In order to meet the processing requirements of precise cylindrical parts on hard and difficult-to-machine materials, this paper introduces wire electrical discharge grinding (WEDG) using thin plate wire guide for cylindrical parts machining. The spindle system and the wire transport system to realize this processing method was added to a low speed wire electrical discharge machining (LS-WEDM) machine tool. In order to realize the online measurement of the machining accuracy of the cylindrical parts, an online measurement system of two-degree-of-freedom based on laser displacement sensor was built. The reasons for the incomplete removal of the machined surface were analyzed. Through the application of a new tool setting strategy and reasonable selection of processing parameters, the phenomenon of incomplete processing can be avoided. The experimental research on the effects of part rotational speed, wire feed rate, wire running speed and wire tension on roundness, surface roughness Sa, and surface morphology were carried out. Finally, example of the cylindrical parts is given to verify the machining accuracy.

Fabrication of Micro Ultrasonic Powder Molding Polypropylene Part with Hydrophobic Patterned Surface.

Constructing regular micro-structures with certain geometric characteristics on the surface of the polymer part can obtain some specific functions. Micro ultrasonic powder molding (micro-UPM) is an efficient processing technique for the fabrication of well-filled micro-structured Polypropylene (PP) parts. The micro-structure array on the surface of the core insert was obtained by low speed wire electrical discharge machining (WEDM-LS). PP polymer surfaces with micro-structured patterns were successfully replicated from the core insert surface after micro-UPM. By studying the detailed topography characterizations of micro-structured PP parts, the effects of processing parameters (ultrasonic energy, welding pressure and holding time) on the micro-structured filling show that when PP polymer was formed under the conditions of 1000 J, 115 kPa and 8 s during micro-UPM, well-filled micro-structured parts can be obtained. Besides, without low surface energy coating modification, the water contact angles (WCAs) of micro-structured PP parts increased from 85.3° to 146.8°, indicating that the wettability of the surface can be changed by replicating the micro-structure on PP parts after micro-UPM.

Experimental study on fabricating ball micro end mill with spiral blades by low speed wire electrical discharge machining

This study is focused on developing and fabricating ball micro end mills with spiral blades by using low speed wire electrical discharge machining (LS-WEDM). Firstly, the new type ball micro end mill is designed and the mathematical model of wire movement trajectory is established for optimizing machining parameters and realizing visual prediction. Then, the diameter, spiral width, and the length consistent accuracy of ball micro end mills fabricated by LS-WEDM is investigated in detail, and more importantly, the three-spiral blades ball micro end mill with the diameter of about 278 μm and the length of 1860 μm is firstly and efficiently manufactured by LS-WEDM. Besides, the micro machining performance and tool wear of LS-WEDM fabricated ball micro end mill are evaluated by conducting micro milling experiments on nickel-based single-crystal superalloy DD5 material, and experimental results revealed that the main tool wear of the new type ball micro end mill is friction wear and adhesion wear rather than diffusion wear. Furthermore, the surface roughness of machined surface can be reduced to 183 nm, which indicates that the ball micro end mills with spiral blades fabricated by LS-WEDM are significantly potential to achieve high-quality machining for complex micro structures on hard material.

Mechanism analysis and durability evaluation of anti-icing property of superhydrophobic surface

In this study, numerical and experimental investigations were performed to analyse the anti-icing mechanism of superhydrophobic surface (SHS) and to evaluate the durability of anti-icing property of artificial SHS respectively. Firstly, by coupling the Level set-Volume of Fluid (CLSVOF) and solidification-melting model, a three-dimensional Computational Fluid Dynamics (CFD) model was proposed to track the morphological changes of droplets, as well to simulate the phase transition process. Then, the freezing process of single droplet on different wettability surfaces was simulated and compared. Results showed that the nucleation position inside the droplet was located at the center of the contact region between the droplet and cold surface. Meanwhile, the temperature change, thermal equilibrium state and solid–liquid interface in droplet during freezing were studied systematically. Furthermore, the freezing delay function of SHS was measured qualitatively and quantitatively by using the solidification/melting cloud and the variations in solid volume fraction, respectively, and the action mechanism on anti-icing properties of contact angle (CA) was revealed by the stable shape of droplet. On the basis of simulation, inspired by the clover leaf bionic concept, we obtained SHSs with anti-icing properties by double-discharge machining of high speed wire electrical discharge machining (HS-WEDM) and evaluated its durability through experiments. Results showed that the anti-icing properties of such surface had mechanical durability and long-term durability.

Machining Characteristics of USV-MF Complex Assisted WEDM-LS Based on Multi-physical Coupling

Ultrasonic vibration (USV) and magnetic field (MF) complex assisted techniques are combined with low speed wire electrical discharge machining (USV-MF complex assisted WEDM-LS) to improve the machining performance of conventional WEDM-LS. Firstly, the simulation results of multi-physical coupling simulation model show that under the influence of ultrasonic vibration, the working fluid fluidity is greatly enhanced and its temperature is significantly decreased. Then, a three-phase flow model of bubble, working fluid and debris in the machining area is established to investigate the effects of ultrasonic vibration on bubble and debris, and the process of bubble rupture is simulated. The simulation results show that with the increase of ultrasonic frequency, the movement of bubble and debris becomes fiercer and fiercer, when ultrasonic frequency is 30 kHz and ultrasonic amplitude is 10 μm, the bubble is collapsed. Finally, comparison of the experimental results of conventional WEDM-LS, USV assisted WEDM-LS, MF assisted WEDM-LS and USV-MF complex assisted WEDM-LS in machining TiNi-01 shape memory alloy reveals that the ratio of normal discharge and the material removal rate are both increased, the workpiece surface roughness value is decreased and the workpiece surface quality is improved in the process of USV-MF complex assisted WEDM-LS.

Wire Electrochemical Trimming of Wire-EDMed Surface for the Manufacture of Turbine Slots

Turbine slots are categorized as crucial structures in aero engine and have strict demands on surface integrity concerning fatigue strength. In the last decade, low speed wire electrical discharge machining (LS-Wire EDM) with multiple cuttings has been proposed as a method to replace the well-established broaching process, which needs expensive assets investment and lacks flexibility to new designs. However, recast layers and heat-affected zones still remain in doubt from industries. Wire electrochemical machining (Wire ECM) has similar kinematic flexibility with Wire EDM, but possess exclusive advantages like being free of tool wear and recast layers. Unfortunately the state of art of Wire ECM could not afford efficient precision machining of macro structures with a thickness over tens of millimeters.This work proposes an integrated process combining high speed wire electrical discharge machining (HS-Wire EDM) and wire electrochemical trimming (Wire ET) for the manufacture of turbine slots. Here, HS-Wire EDM takes on the low-cost efficient pre-slotting while a single cutting of Wire ET plays the roles of roughing, semi-finishing and finishing. Experimental results indicate that the electrode trimming rate have a significant influence on material removal rate. Under the process conditions as a pulsed voltage of 40% in duty ratio, 16 V in amplitude and 20 kHz in frequency, a trimming depth of 10 μm and an electrode trimming rate of 7.2 mm/min, the material removal depth is 30 μm and recast layers overlapped on WEDM surface could be entirely removed. Finally, a 20 mm-thick fir-tree slot in Inconel 718 free of recast layers was machined in the proposed integrated process. The average machining efficiency is 64 mm2/min and the profile allowance could reach -0.010 to +0.010 mm.

The Electrical Gap Model of High Speed Wire Electrical Discharge Machining with Power-electronic-based Pulse Power Supply

Considering the not well-insulated dielectric fluid in High-Speed Wire-Electrical-Discharge-Machining (HSWEDM), the equivalent electrical model of the discharge gap of HSWEDM in open circuit, normal discharge and short circuit is established and simulated. A prototype of no-resistance power-electronic-based buck-type pulse power supply is tested on a commercial HSWEDM machine. The experimental verification shows that the proposed electrical model can predict the gap conditions in real machining, and assist the discharge current and discharge energy control.

Geometrical Analysis of Wire Electrochemical Machining for the Manufacture of Turbine Disc Slots

The advantages of sinking electrochemical machining (ECM), e.g. best surface integrity, are always faced with the cost-intensive initial effort for the component specific design of a machining device and its tool geometry. However, this disadvantage does not apply to wire ECM where no task-specific tool design is required for cutting 2.5-dimensional geometries like fir tree slots in turbine discs. An industrial application is still being hindered by insufficient flushing concepts. However, a previous study showed that the flushing approach of High Speed Wire Electrical Discharge Machining (HSWEDM) is also successfully transferable to wire ECM. Workpiece heights up to 40 mm could be machined with a cutting rate of Vw = 20 mm2/min. Nevertheless, these investigations were only performed with straight cuts, radii were not examined. Therefore, in this paper the geometrical accuracy of the wire ECM process is analyzed using the example of two different turbomachinery disc slot geometries with 20 mm and 40 mm heights by a coordinate measuring machine.

Micro milling characteristics of LS-WEDM fabricated helical and corrugated micro end mill

Micro milling offers a high potential for fabricating three-dimensional micro structure, such as micro grooves, micro channels and micro dimples. However, the fabrication of solid micro end mills with hard materials and complex structures poses many challenges. In this study, a new method based on low speed wire electrical discharge machining (LS-WEDM) is presented to prepare solid helical micro end mills. The machining process of helical micro end mill is kinematically modeled and simulated, which can realize visual predictability and provide theoretical basis for parameters selection. Experimental results indicated that corrugated micro end mill with about 269.8 μm in diameter and 1850.2 μm in length, and three helical blades micro end mill with 123.8 μm in diameter and 800 μm in length, six spirals and varied helical angle micro end mills can be flexibly prepared. Furthermore, the use of these micro end mills in hard material of DD5 single crystal nickel-based superalloy substrates is described to demonstrate their potential. Thus, the technique proposed in this study is significantly contribute to the fabrication of complex solid micro end mills with helical blades.

Tribological properties of fish scale inspired underwater superoleophobic hierarchical structure in aqueous environment

Underwater superoleophobic surfaces are becoming increasingly important in regard to self-cleaning, anti-fouling, oil droplet transportation and water/oil separation. Although a great number of underwater superoleophobic surfaces have been demonstrated, their tribological properties remain impractical for the purposes of real-life applications. Herein, a two-step method of high speed wire electrical discharge machining and boiling water treatment was adopted to fabricate fish scale inspired underwater oil repellent hierarchical structure on an aluminum (Al) alloy 5083 surface. The hierarchical roughness and hydroxyl groups were obtained on the surface, and the surface exhibited the ability to prevent contact with organic fluids when submerged in water. Moreover, the tribological properties of underwater superoleophobic Al surfaces in aqueous environments were analyzed. The average friction coefficient of underwater superoleophobic surfaces was decreased compared with the polished Al surface. We believe that this research will contribute to the engineering application of underwater superoleophobic surfaces in the future.

Fabrication of biomimetic multi-scale surface of rice leaf and anisotropic superhydrophobic properties

With the continuous exploration of the special morphologies and properties of skin of some animals and plant leaf surfaces in the nature, new hydrophobic surfaces are developed through imitation of the observed surface effects. The aluminum alloy surface which is similar to multi-scale hierarchical structure surface of biomimetic rice leaf can be obtained by combining high speed wire electrical discharge machining (WEDM) method and electric brush-plating technique. The morphological feature was analyzed by scanning electron microscopy (SEM). The surface wettability of the sample was measured at ambient temperature using a contact angle measurement instrument and the SCA20 software by placing a 4 μ L pure distilled water droplet onto the surface of the sample. Three dimensional (3D) profile of the sample surface was obtained through confocal laser scanning microscopy (LSCM). The elemental composition was determined by X-ray diffraction (XRD) analysis in order to determine the phase composition on the sample surface. The regular submillimeter groove ridge structures were processed on the aluminum alloy surfaces by the method of high speed wire electrical discharge machining. And the hierarchical cauliflower-like structures which were consisted of micro-protrusions and submicro-grains were formed on the sample surfaces by electric brush-plating technique. The anisotropic functional surfaces and the superhydrophobic surfaces were achieved by the combination of the regular submillimeter groove ridge structures and hierarchical cauliflower-like structures. The research showed that the regular submillimeter groove ridge structures are similar to the surface morphology on rice leaf, and the hierarchical cauliflower-like structures are similar to the surface morphology on lotus leaf. The results showed that double scale (micro-submicro) microscopic structure obtained by electric brush-plating can play a key role on the hydrophobicity of the surface. The regular submillimeter groove ridge structure obtained by high speed wire electrical discharge machining further enlarged the hydrophobic properties of the direction of parallel groove. The sample surface showed excellent superhydrophobic properties, and the contact angle of the direction of parallel groove could reach up to 151°. The sample surface also showed different hydrophobic properties in the direction of the parallel groove and the direction ofthe vertical groove. Due to the existence of the edge structure make the two directions, and the two directions have different static wettability, which also led to the surface anisotropy. With the changing of electric brush-plating time, the trend of double and multi scale structure surface contact angle had large difference on the sample surface. The sample surface is fabricated without any chemical modification by combining high speed wire electrical discharge machining method with electric brush-plating technique. Although the application of the surface anisotropy and superhydrophobicity were not showed in other places, it is important for animals and plants in the nature. With the deepening of the study, this research will rise to certain guiding significance on the applications of combining the anisotropic functional materials with the superhydrophobic materials.

Erratum to: Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

In this study, the breakdown voltage behavior in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V (TC4) in the deionized water is investigated. Firstly, the electric field distortion caused by impurity particles including TC4 or brass metal and bubbles is investigated. And then the breakdown voltage model of TC4 machined by LS-WEDM is established and the experimental verification result indicates that the model predicting results conforms to the actual processing and could be well follow experimental results. Second, the influence of breakdown voltage on surface roughness and kerf width has been revealed, it can be found that the kerf width decreases, and the surface roughness increases as breakdown voltage increased. Besides, the voids become bigger and the surface cracks become deeper and wider with the breakdown voltage increased based on analysis of experiment results but for microcracks distributed on spherical or irregular attachments are not influenced by breakdown voltage due to their randomness. Meanwhile, the transparent bubbles of diameter of 400 nm can be observed near the droplet on the machined surface and its major composing element is oxygen. Finally, internal voids can be found in the joint of deterioration layer and the substrate which will make the combination of deterioration layer and the substrate not strong and easy to fall off.

Wettability and Contact Time on a Biomimetic Superhydrophobic Surface.

Inspired by the array microstructure of natural superhydrophobic surfaces (lotus leaf and cicada wing), an array microstructure was successfully constructed by high speed wire electrical discharge machining (HS-WEDM) on the surfaces of a 7075 aluminum alloy without any chemical treatment. The artificial surfaces had a high apparent contact angle of 153° ± 1° with a contact angle hysteresis less than 5° and showed a good superhydrophobic property. Wettability, contact time, and the corresponding superhydrophobic mechanism of artificial superhydrophobic surface were investigated. The results indicated that the micro-scale array microstructure was an important factor for the superhydrophobic surface, while different array microstructures exhibited different effects on the wettability and contact time of the artificial superhydrophobic surface. The length (L), interval (S), and height (H) of the array microstructure are the main influential factors on the wettability and contact time. The order of importance of these factors is H > S > L for increasing the apparent contact angle and reducing the contact time. The method, using HS-WEDM to fabricate superhydrophobic surface, is simple, low-cost, and environmentally friendly and can easily control the wettability and contact time on the artificial surfaces by changing the array microstructure.

Fabrication and applications of two- and three-dimensional curved surfaces with robust underwater superoleophobic properties

In this work, a method for the fabrication of two- and three-dimensional curved surfaces with robust underwater superoleophobicity is reported for the first time on light alloys (including 5083 Al and TC4 Ti alloys) through the high speed wire electrical discharge machining (HS-WEDM). The surface morphology and compositions were characterized by scanning electron microscope and energy-dispersive X-ray spectrometer. The results showed that rough structures and a layer of oxidization were created on the light alloys by HS-WEDM cutting. The two- and three-dimensional structured curved surfaces after an ethanol immersion exhibited the extreme underwater superoleophobic property with the high oil contact angle and low oil sliding angle. More importantly, the underwater superoleophobic surfaces with the three-dimensional curved features could have many new applications. In order to use the potential functions, the durability of the fabricated samples was tested and the results showed that the samples still exhibited the underwater superoleophobic property after the underwater storage and physical mechanism tests. Additionally, this method is versatile, simple, environment-friendly, and cost-effective.

Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

Research on HS‐WEDM and chemical etching technology of superamphiphobic surfaces on Al substrates

Superamphiphobic (both superhydrophobic and superoleophobic) surfaces on Al substrates are fabricated by the high speed wire electrical discharge machining (HS-WEDM) and chemical etching technology. The surface morphology, chemical composition and wettability of the sample surfaces are investigated using scanning electron microscopy, energy dispersive X-ray diffraction system and optical contact angle (CA) measurements. The results show that, after the HS-WEDM and chemical etching, the micrometer-scale craters and nanometer-scale acicular structures are present on the sample surfaces. The obtained sample surfaces show superamphiphobicity after fluorination. The CAs of water, ethylene glycol and peanut oil are 155.9°, 153.1° and 151.7°, respectively. The sliding angles of water, ethylene glycol and peanut oil are 2°, 3.5° and 5°, respectively. The micro/nanometer-scale rough structures and the low surface energy are essential to fabricate superamphiphobic surfaces. Compared with the other methods, the main advantages of the HS-WEDM and chemical etching technology are simple, safe, highly effective and low cost. In addition, superamphiphobic Al surfaces have potential applications in fields such as self-cleaning, oil capture, oil transportation and anti-smudge.