Low Speed Wire Electrical Discharge Research Articles

Enhancing low-speed WEDM machining capabilities on Nitronic-50 with a constant frequency ultrasonic hybrid method

Nitronic-50 stainless steel is a high-strength and corrosion-resistant austenitic premium steel. It requires improved surface characteristics due to its wide use in various applications like fasteners, marine hardware, hydroelectric-power turbines, pressure vessels, etc. This work focuses on machining hard-to-machine Nitronic-50 steel is unconventionally machined using constant frequency ultrasonic-aided low-speed wire electrical discharge machining (USV-LS-WEDM) to enhance its machined surface integrity. This method achieves effective results when cutting high-strength materials with intricate shapes. Material removal rate (MRR) and surface roughness (Ra) were measured by considering inputs such as servo voltage (SV), pulse off time ( Toff), pulse on time ( Ton) and current (I) with an ultrasonic-vibration range of 20,000 Hz. The appropriate selection and usage of LS-WEDM parameters is a challenging process and is done with parametric analysis. The MRR of Nitronic-50 was enhanced with an increase in Ton and I along with a reduction in Toff and SV. Surface roughness (Ra) decreased with a gradual reduction in Ton, I, and an increase in SV. The USV-WEDM was compared with a stand-alone WEDM indicating that the MRR for USV-WEDM was improved by 12% and the Ra was decreased by 9% due to effective distribution of spark discharges, which increased material erosion and redistribution of molten metal characteristics. Machining quality for hard-to-machine Nitronic-50 steel was certainly enhanced via hybrid ultrasonic vibration with the existing LS-WEDM.

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.

Test and Improvement of a Fuze MEMS Setback Arming Device Based on the EDM Process.

This paper introduces the working principle of a MEMS safety and arming (S&A) device for a fuze that is installed perpendicular to the axis of the projectile. Additionally, the application of low-speed wire electrical discharge machining (EDM) in the fabrication of the device is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, a problem that is solved by designing the auxiliary support beam, using multiple cuts, destress annealing and optimizing the processing parameters. The difficult problem of setback slider deformation in the principle prototype test is properly solved by establishing V-shaped grooves at both ends of the setback slider. The connection mode between the microspring and the frame is changed to a clearance fit connection. The improved setback arming device can guarantee service process safety and launch reliability. The maximum overload that can be withstood in service processing is 20,000 g, and the minimum overload for safety release during launch is 12,000 g. The results show that the EDM process can greatly reduce the machining cost while improving the machining precision and machining speed, which can compensate for the defects of the current manufacturing technology.

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.

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.

Ultrasonic injection molding of glass fiber reinforced polypropylene parts using tungsten carbide-cobalt mold core

A hybrid process combining ultrasonic injection molding and electrical discharge machining was proposed to realize the economic, high-precision, and environmental-friendliness production of glass fiber reinforced polypropylene microstructured parts. First, the prism array microstructures were processed on tungsten carbide-cobalt (WC-8 wt% Co) substrate by low-speed wire electrical discharge machining and used as the mold core. Then, the glass fiber reinforced polypropylene composite (GF/PP) was melted under ultrasonic vibration, and the surface microstructure of the mold core was replicated. The experimental results show that this method can efficiently and accurately manufacture microstructured parts, and the microstructure has a high replication rate up to 95.5%. By replicating the microstructure, the surface contact angle of GF/PP parts increased from 57.1° to 134.9°, and the wettability changed from hydrophilicity to hydrophobicity. The mechanical properties test results show that the GF/PP parts fabricated by ultrasonic injection molding had excellent mechanical properties, and the 30% GF/PP parts show the highest tensile strength of 56.9 MPa. This work provides a new option for fabricating fiber reinforced composite parts.

Study on surface characteristics in ultrasonic vibration-assisted WEDM-LS based on spatial vibration of electrode wire

The spatial vibration model of the electrode wire in ultrasonic vibration (USV)-assisted low-speed wire electrical discharge machining (WEDM-LS) under continuous discharges is proposed for analyzing its vibration state, and subsequently, a theoretical model of material removal from the TiNi-01 shape memory alloy workpiece is established by means of Gaussian heat source in single-pulse discharge process and the principle of the nearest-point discharge breakdown. Then, the topological matrix of the surface morphology is developed for investigating the surface characteristics and the distribution of discharge points by simulation. Finally, the experiment of photographing the discharge channel position is accomplished to validate the reliability and feasibility of the model. The results show that the discharge channels are more uniformly distributed in the hybrid process, which enhance effectively the success rate of the discharge pulses and decrease the surface roughness. In addition, a mathematical model to evaluate the uniformity of the discharge point distribution is employed as an evaluation index of the burn degree on the workpiece surface. The distribution uniformity coefficient obtained by the compound process is higher than that of the traditional WEDM-LS. This is consistent with the phenomenon of alleviated surface burn under the hybrid machining technology, and the average errors of the simulated and experimental values of the uniformity coefficient of traditional WEDM-LS and the hybrid process are 4.9% and 3.4%, respectively. The maximum errors of surface roughness between simulated value and experimental value about the WEDM-LS and hybrid process are 7.4% and 8.2%, respectively. It is demonstrated that the model can effectively and accurately predict the surface roughness and the surface burn of the workpiece.

Investigation on the kerf and surface formation in the magnetic field-assisted WEDM-LS based on successive discharges

Magnetic field-assisted low-speed wire electrical discharge machining (MF-assisted WEDM-LS) is an effective technique to improve the surface quality of the workpiece. This paper presents a successive removing model to predict kerf width and the surface topography of nickel–titanium (Nitinol) shape memory alloy in different parameters. Firstly, the motion of an electron was calculated in the magnetic field. It could be obtained that if the length of the discharge channel path was the same with the condition that in traditional WEDM-LS, the width of the discharge gap was decreased because of the deflection of the electron trajectory caused by the magnetic field. Then, a modified gauss heat source equation was derived by calculating the incident angle of the discharge channel. Based on the principle of conservation of energy, the shape of the crater in different parameters was emulated. Moreover, an electrothermal coupling model was established to investigate the surface formation in the successive discharges process. The simulation results show that the average value of the surface roughness of the workpiece in WEDM-LS with magnetic field assisted was decreased by 12.3% compared with that in traditional WEDM-LS. Eventually, experiments of kerf and surface quality were carried out respectively. The experimental results showed that the kerf decreased from 376.2 to 361.7 μm in the magnetic field intensity of 0.4 T. The surface topographies of the workpieces showed good agreement with the simulation results, and the average relative error of surface roughness between simulated results and experimental results is 8.7%.

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.

Experimental Investigation on Machinability of Aluminum Alloy during Dry Micro Cutting Process Using Helical Micro End Mills with Micro Textures.

Aluminum alloy material is widely used in the electronics, weapons, aviation and aerospace industries, due to its medium strength, good corrosion resistance, good toughness and excellent oxidation properties. With the trend of product miniaturization, micro cutting has become the mainstream technique for fabricating micro parts and components, so it is very meaningful and vital to work on removing the cutting fluid from the micro cutting process and make it totally sustainable and eco-friendly. In this work, an attempt has been made to fabricate micro textures onto the rear surface of helical micro end mills with diameters of less than 1 mm. Micro textures in the form of grooves were fabricated using a noncontact low speed wire electrical discharge turning technique. Dry micro cutting experiments were carried out on an aluminum alloy material using helical micro end mills with micro textures and the dry micro cutting surface quality and tool wear have been investigated. The influence of dry micro cutting parameters on the surface roughness parameters were also investigated. Experimental results showed that the Sa and Sq can be reduced to be about 1.56 μm and 2.08 μm, respectively. Contrasting results indicate that the implantation of micro textures does not deteriorate the dry micro cutting surface but improves the machined surface consistency of an aluminum alloy workpiece. The tool wear on helical micro end mills with micro textures involved in the dry micro cutting process of Al 6061 mainly include rear frictional wear, oxidation wear and diffusion wear.

An experimental study on fabricating microstructured surface by using LS-WEDM-prepared ball micro end mills

In recent years, there is an increasing demand for fabricating microstructures such as micro grooves, micro holes, micro dimples, and micro channels on various materials. Micro machining is an alternative method to manufacture microstructures due to its high efficiency and flexibility, and the micro end mill preparation is an essential step. In this study, the low-speed wire electrical discharge machining (LS-WEDM) is used to fabricate ball micro end mills with four cutting edges and radius of less than 200 μm, and the optimized parameters and multiple cutting strategies are adopted to improve machining surface quality and edge sharpness of ball micro end mills. Then, the micro dimples on soft and hard materials are formed by the designed and prepared ball micro end mills made of cemented carbide, respectively. The micro machining performance of ball micro end mills was evaluated by investigating the surface quality and microstructure of micro dimples, cutting force, and tool wear, and the influence of micro machining parameters on micro dimples is discussed in detail. Experimental results indicated that tool wear patterns mainly are adhesion friction and cutting edge damage, and the LS-WEDM-fabricated ball micro end mills with four cutting edges are potential to manufacture microstructures on hard and soft materials with acceptable surface quality and tool wear.

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.

Study on workpiece surface forming mechanism by successive discharges during USV-MF complex–assisted WEDM-LS process

Ultrasonic vibration and magnetic field complex–assisted techniques have been used in low-speed wire electrical discharge machining (USV-MF complex–assisted WEDM-LS) to improve workpiece surface quality. In this paper, a novel approach, which is based on a three-dimensional successive discharge model, is proposed to investigate the interaction between the workpiece surface forming and the vibration of a wire electrode. The influence of USV-MF complex–assisted technique on workpiece surface forming and vibration of a wire electrode is considered by modifying the parameters in this model. During the simulation, the discharge location, which is determined by the minimum gap width in each step, makes it possible to calculate the vibration of a wire electrode in the successive discharge process. Workpiece surface topographies are obtained at the end of simulation, as well as the vibration responses of the wire electrode and the distribution of discharge locations. The simulation results show that the USV-MF complex–assisted technique can increase the vibration amplitude of the wire electrode by 1.12%. The surface roughness values decrease more than 10% and the distribution uniformity of discharge location increases in the USV-MF complex assisted WEDM-LS process. The simulation results are verified by experiments and simulation error of surface roughness value is less than 5% compared with the experimental results. The analysis shows that the servo feed speed increases more than 50% with surface quality unaltered in the USV-MF complex–assisted WEDM-LS process.

Fabrication of microplastic parts with a hydrophobic surface by micro ultrasonic powder moulding

Microstructures with hydrophobic surfaces have been widely used in industrial fields such as self-cleaning and drag reduction. With the aim of fabricating microplastic parts with a hydrophobic surface, the paper processed the mould insert with micro-groove arrays from 304 stainless-steel plate through low-speed wire electrical discharge machining (LS-WEDM). And the micro-groove arrays were designed to U shape with bottom radius of 70 μm and depth of 110 μm. Ultra-high molecular weight polyethylene (UHMWPE) powders were used as raw material to fabricate microplastic parts with hydrophobic surface structures by micro ultrasonic powder moulding (micro-UPM). The parameters of the micro-UPM process were obtained by the single-factor test method. Under the ultrasonic energy of 1200 J, welding pressure of 100 kPa and pressure holding time of 8 s, microplastic parts with well surface morphology (Ra =1.36 μm) and replication rate (97.76 %) were successfully fabricated. The surface contact angle of the microplastic part was 135.4°, which indicated well surface hydrophobicity.

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.

Optimization of a Fuze MEMS Setback Arming Device Based on the EDM Process

This paper introduces the working principle of a MEMS safety and arming (S&A) device and measures and tests a setback arming device. To solve the problem of large fabrication errors in the UV-LIGA process, a MEMS S&A fuze device fabricated by low-speed wire electrical discharge machining (EDM) is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, which is solved by setting the auxiliary support beam, using multiple cuts and destress annealing. The linewidth, thickness and elastic coefficient of the microspring fabricated using the EDM process are closer to the designed values than those fabricated using the UV-LIGA process under the same conditions. When comparing the MEMS S&A devices fabricated by the two processes, it is found that the EDM process has a the higher machining accuracy. In view of the plastic deformation of the upper end of the microspring, the structure of the microspring is optimized to incorporate a gradient linewidth, and the optimized setback arming device is tested. The results show that the device can ensure service process safety and launch reliability. The maximum overload that can be withstood in service processing is 17000 g, and the minimum overload for insurance release during launch is 1500 g.

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.

Design of superhydrophobic pillars with robustness

Superhydrophobic surfaces have huge applications in wetting fields. However, compared with natural biological surfaces, artificial superhydrophobic surfaces still show serious deficiencies in the theoretical design and durability. In this work, a robust superhydrophobic surface consisting of a regular array of square pillars with secondary structures on the sidewalls was prepared using low-speed wire electrical discharge machining. We developed the design criteria of regular arrays of square pillars for achieving superhydrophobicity based on interface characteristics and force balance. A series of samples were also prepared to validate the design criteria. The results indicate that the overlap part between the theoretical superhydrophobicity region before and after abrasion leads to stable superhydrophobicity. In addition, specific surfaces transform from the Wenzel state to the Cassie state after abrasion and the contact angle shows a large increase. The design criteria based on the research of predecessors are useful to design superhydrophobic surfaces with robustness.