Electrical Discharge Machining Surface Research Articles

The influence of shot peening on the fatigue response of Ti-6Al-4V surfaces subject to different machining processes

Machining processes are known to drastically impact the performance and lifetime of a component subjected to fatigue in service. Therefore, understanding the effect of manufacturing processes on surface integrity is vital to determine their suitability for any given application. As part of a wider study investigating multiple production operations, results are presented here which characterise the fatigue performance and failure mechanisms of Ti-6Al-4V specimens subject to conventional (end milling, surface grinding) and non-conventional machining processes (abrasive waterjet machining, wire electrical discharge machining, large area electron beam melting). Post process shot peening was then applied on each of the 5 different surfaces generated and the resulting fatigue response similarly evaluated. The abrasive waterjet machined specimens generally exhibited the longest fatigue life, particularly at higher applied stress (≥ 700 MPa) irrespective of surface condition. Despite the difference in process mechanisms, fatigue results for the milled and wire electrical discharge machined surfaces were comparable. Examination of the fatigue specimen fracture surfaces however, revealed that the locations of crack initiation were inconsistent for the different processes and conditions assessed. In general, post process shot peening increased the fatigue strength/life of all the evaluated specimens, regardless of the base machining operation.

Impact Analysis of Electrode Material on Electrical Discharge Grinding Polycrystalline Diamond Cutting Tools

The electrode material plays a very important role in the electrical discharge grinding (EDG), affects the electrical discharge machining efficiency and machining surface quality. Experiment testing and materials analysis as the primary method, affected layer thickness and workpiece surface roughness value as evaluation indexes. Polycrystalline diamond cutting tool samples were electrical discharge machined using copper electrodes and graphite electrodes respectively. After machining, the polycrystalline diamond cutting tool samples’ surfaces was analyzed by X-ray diffraction, Surfaces appearances were observed under the scanning electron microscope, and the surface roughness values were measured by the roughness measuring instrument. Polycrystalline diamond samples’ surface effect layer thickness values and surface roughness values, affected layer distribution structure was statically analyzed in typical EDG process conditions with different electrode materials. Test results demonstrate that the affected layer is inevitably presented on a polycrystalline diamond surface after electrical discharge grinding polycrystalline diamond. The principal cause of the affected layer is the diamond graphitization and the decomposition of binders. In the same EDG process parameters, the processing efficiency of the graphite electrode is clearly higher than that of the copper electrode; but the tool edge roughness value and affect layer thickness of the graphite electrode machining is greater than those of the copper electrode machining. This research provides an essential experimental basis for designing technics of precision and highly efficient electrical discharge grinding polycrystalline diamond cutting tools.

Effect of various surface preparation techniques on the delamination properties of vacuum infused Carbon fiber reinforced aluminum laminates (CARALL): Experimentation and numerical simulation

Carbon fiber reinforced aluminum laminates (CARALL) are one of the aluminum based Fiber metal laminates (FMLs) which, due to their high strength to weight ratio and good impact resistance are greatly replacing aluminum alloys in aircraft structures. In this research work, interlaminate shear strength of Vacuum assisted resin transfer molding (VARTM) manufactured CARALL has been investigated. Numerical simulation model incorporated with real time material data has been developed to predict the delamination behavior of CARALL laminates. Standard CARALL specimens with different surface morphologies were prepared by electric discharge machining, mechanical, chemical and electrochemical surface treatments. T-peel tests were carried out according to standard ASTM D1876-08 to find out inter laminate shear strength. FMLs made out of mechanically, chemically and electrochemically cleaned metal sheets depicted high interlaminate shear strength. SEM micrographs of failed surfaces verify the high adhesive strength of epoxy. Developed numerical simulation model accurately predicts the delamination behavior of CARALL as observed during experimentation.

Comparative Study of White Layer Characteristics for Static and Rotating Workpiece during Electric Discharge Machining

EDMed (Electric Discharge Machined) surfaces are unique in their appearance and metallurgical characteristics, which depend on different parameter such as electric parameters, flushing method, and dielectric type. Conventionally, in static workpiece method the EDM (Electric Discharge Machining) is performed by submerging both of the tool and workpiece in dielectric liquid and side flushing is provided by impinging pressurized dielectric liquid into the gap. Another flushing method has been investigated in this study, in which, instead of side flushing the rotation motion is provided to the workpiece. Surface characteristics for both flushing methods are determined and compared in this study. The investigated surface characteristics are: surface roughness, crater size, surface morphology, white layer thickness and composition. These investigations are performed using optical and SEM (Scanning Electron Microscope). Statistical confidence limits are determined for scattered data of surface roughness. It is found that the white layer thickness and surface roughness are directly proportional to discharge current for both flushing methods. The comparison has shown that the side flushing of statics workpiece gives thicker white layer and lower surface finish as compared to the flushing caused by the rotation of workpiece.

Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

Wire-electrical discharge machinable alumina zirconia niobium carbide composites – Influence of NbC content

Alumina zirconia (ZTA) ceramics can be made electric discharge machinable by addition of a percolating network of an electrically conductive phase. In this study the influence of NbC content on the mechanical and electrical properties as well as the ED-machinability of ZTA-NbC ceramics containing 17 vol.% zirconia and 24–32 vol.% NbC were investigated. Samples were hot pressed from mixed and milled starting powders. Surface morphology and surface roughness of wire electrical discharge machined surfaces were studied by SEM and perthometry. Cutting speed was determined to benchmark the ED-machinability.Rising NbC contents progressively impede sinterability. Maximum strength, Young’s modulus and hardness were found at intermediate NbC contents. Conductivity evidently rises with NbC content, the cutting performance showed an adverse tendency. The surface quality of the materials was improved by increasing the content of conductive phase. Additional trimming operations can reduce the mean roughness of machined surfaces to 1μm.

A comparative study on the wear resistance of electrical discharge machined surfaces

ABSTRACTThe properties of the surface were affected by many factors such as the pulse parameters, tool electrode material, and dielectric liquid in electrical discharge machining. Austenitic, dual-phase, and ferritic steel work materials were electrical discharge machined using graphite and copper tool electrodes in hydrocarbon- based oil and water dielectric liquids. Then the surfaces were analyzed regarding sliding friction wear responses on a comparative basis. The results revealed that the surface wear responses are sensitive to the type of the tool electrode material when machining in water dielectric liquid. However, the use of hydrocarbon-based dielectric liquid substantiality suppresses the influence of tool electrode on surface wear response due to excessive carbon release from the cracked dielectric. The machined surface topographical features were also affected due to the used electrical parameters regarding crater size, globular attachments, and microcracks that led significant alterations in sliding friction response. Primarily, weakly bounded globular attachments on the machined surface were dislodged at the initial stages of the friction tests and led higher sliding distances to the steady friction conditions. Finally, the results were compared with the subsurface microstructural properties to comprehend the wear responses.

Surface characteristics of Ti-5Al-2.5Sn in electrical discharge machining using negative polarity of electrode

A large number of parameters significantly affect the performance of electrical discharge machining (EDM) which is a non-conventional technique. The choice of the EDM parameters depends on workpiece-electrode material combination. So, the selection of parameters becomes intricate. This manuscript presents the surface characteristics of the machined surface in EDM on Ti-5Al-2.5Sn titanium alloy. The surface roughness and the microstructure of the machined surface are explored for different EDM parameters and electrode materials. Experimentation was accomplished using negative polarity of copper, copper-tungsten and graphite electrode. In this study, peak current, pulse-on time, pulse-off time and servo-voltage are taken into consideration as process variables. The surface roughness is greatly influenced by peak current and pulse-on time among the selected electrical parameters. Among the three electrodes, the copper electrode produces the lowest surface roughness whilst graphite electrode gives the highest surface roughness. The surface characteristics (crater, crack and globule) are distorted on account of discharge energy. In context of fine surface characteristics, the copper can become as first choice electrode materials.

Surface finish characteristics of titanium alloy in a non conventional technique

A large number of parameters knowingly affect the performance of electrical discharge machining (EDM) which is a non-conventional process. The choice of parameters becomes intricate. In this view, this article presents the surface characteristics of the machined surface in EDM on titanium alloy, Ti-5Al-2.5Sn. Experimentation was carried out using negative polarity of copper (Cu), copper-tungsten (Cu-W) and graphite (Gr) electrode. Among the electrodes, the copper electrode produces the lowest surface roughness whilst graphite electrode gives the highest surface roughness. In respect of fine surface characteristics the copper can become as first choice electrode materials.

Clinical research involved in achieving osseointegration in implants with wire-type electric discharge machining surface

Clinical research involved in achieving osseointegration in implants with wire-type electric discharge machining surface

EDM machinability and surface roughness analysis of TiB2 using copper electrodes

Titanium diboride (TiB2) is a sintered ceramic material which has a high industrial interest due to its excellent mechanical properties, such as immense hardness, elastic modulus, and abrasion resistance. Unlike most ceramics, this material can be machined by using an electrical discharge machining (EDM) process because of its good thermal and electrical conductivity. In this present study the applicability of an EDM process for manufacturing titanium diboride is analysed. To do that, the influence of EDM parameters is studied on three of the most important technological characteristics in EDM: material removal rate (MRR), electrode wear (EW) and surface roughness (Ra). Results confirm that the most influential factor on MRR and Ra is the current intensity whereas in the case of EW, it is the pulse time. Additionally, the control of these parameters allows technological tables to be obtained in order to determine the optimum operating conditions. Such technological tables exist for the case of steels but they do not exist for TiB2, in which the optimal conditions are to be determined experimentally.

Experimental investigations on surface integrity issues of Inconel-690 during wire-cut electrical discharge machining process

Nickel-based alloys are finding a wide range of applications due to their superior properties of maintaining hardness at elevated temperatures, low thermal conductivity and resistance to corrosion. These materials are used in aircraft, power-generation turbines, rocket engines, automobiles, nuclear power and chemical processing plants. Machining of such alloys is difficult using conventional processes. Wire-cut electrical discharge machining is one of the advanced machining processes, which can cut any electrically conductive material irrespective of its hardness. One of the major disadvantages of this process is formation of recast layer as it affects the properties of the machined surfaces. In this study, experimental investigation has been carried out to study the effect of wire-cut electrical discharge machining process parameters on micro-hardness, surface roughness and recast layer while machining Inconel-690 material. Interestingly, hardness of the machined surface was found to be lower than that of the bulk material. The micro-hardness and recast layer thickness are inversely related to the variation of process parameters. Recast layer thickness, surface roughness and hardness of the wire-cut electrical discharge machined surfaces of Inconel-690 are found to be in the range of 10–50 µm, 0.276–3.253 µm and 122–171 HV, respectively, for different conditions. The research findings and the data generated for the first time on hardness and recast layer thickness for Inconel-690 will be useful to the industry.

English

English

Surface modification and machining of TiNi/TiNb-based alloys by electrical discharge machining

Ti50Ni50 and Ti50Ni49.5Mo0.5 shape memory alloys and Ti30Nb1Fe1Hf alloy with a low elastic modulus were prepared for biomedical implant applications. Effects of the composition of the TiNi/TiNb-based alloys and electrical discharge machining (EDM) parameters on the properties of the materials were investigated. The addition of Mo to TiNi or of Nb to Ti clearly reduced the material removal rate (MRR), electrode wear rate, surface roughness, and recast layer thickness, which was attributed to the increased melting temperature and thermal conductivity of the materials. The surface roughness (Ra) of the electrical discharge machined (EDMed) alloys obeyed the empirical equation Ra = β(Ip × τp)α. A higher discharge current Ip combined with an appropriate pulse duration τp can achieve the highest MRR and lowest thickness of the recast layer. However, under low current and a small pulse duration, the recast layer has a surface roughness of 1 μm, which is favorable for oral implants. In addition, the EDMed surface contains Ti and Nb oxides, which are well-known biocompatible materials.

マイクロバブル混入加工液を用いた放電加工面の変化

マイクロバブル混入加工液を用いた放電加工面の変化

EDM machinability and surface roughness analysis of INCONEL 600 using graphite electrodes

Nowadays, graphite is one of the most popular electrode materials in electrical discharge machining (EDM) processes due to the high rate of removal material which reduces machining times. This reduction has a direct impact on the cost of manufacturing the parts. In this research, the influence of EDM parameters and graphite electrode in an INCONEL 600 alloy has been studied for both positive and negative polarity. To do so, the machining performances of the process are evaluated in terms of material removal rate (MRR), electrode wear (EW), and surface roughness (SR). Results confirm that the use of negative polarity leads to higher material removal rate whereas positive polarity is recommended when low values of EW and a good surface roughness are needed. Moreover, values of 22.2854 and 15.3602 mm3/min are achieved for negative and positive polarity, respectively. Furthermore, an attempt has been made to study the results obtained in economic terms for industrial purposes. To that end, both production costs and production time of the graphite electrode are compared with those obtained for copper electrodes. It will be shown that graphite electrodes and negative polarity are the most economical within the options considered.

Characteristics of Material Properties and Machining Surface in Electrical Discharge Machining of Ti2AlN and Ti2AlC Materials

Ti alloys are extensively used in high-technology application because of their strength, oxidation resistance at high temperature. However, Ti alloys tend to be classified very difficult to cut material. In this paper, The powder synthesis, spark plasma sintering (SPS), bulk material properties such as electrical conductivity and thermal conductivity are systematically examined on Ti2AlN and Ti2AlC materials having most light-weight and oxidation resistance among the MAX phases. The bulk samples mainly consisted of Ti2AlN and Ti2AlC materials with density close to theoretical value were synthesized by a SPS method. Machining characteristics such as machining time, surface quality are analyzed with measurement of voltage and current waveform according to machining condition of micro-electrical discharge machining with micro-channel shape.

Electrode wear protection mechanism in meso–micro-EDM

A carbonaceous layer builds up on the electrode surface in electrical discharge machining (EDM) when using low wear settings. Current paper investigates the carbonaceous layer and its formation during the erosion. It is found that a diamond like amorphous carbon layer embedded with the micro and nanosized metallic debris from the work-piece is deposited on the erosion front of the electrode. The microstructure of the layer depends on the parameters such as applied current and pulse duration. The diamond like carbon layer with sp3 bonds has lower thermal conductivity and higher hardness compared to the base graphite material, protecting it against the wear. A dense layer with larger porosity is formed when using 20A and stacked carbon layers with submicron porosity are formed during the erosion with 5A. A simple thermal model is proposed to simulate the pulse duration values at which the protective carbonaceous layer forms over the complete frontal surface of the micro-scale electrodes with projection area below 1mm2.

English

Enhanced productivity and workpiece surface quality after electrical discharge machining (EDM) is a concern of many researchers. In this study, the effect of powder concentrations on material removal rate (MRR), surface roughness (SR) and topography surface in powder mixed EDM (PMEDM) was investigated. The experimental studies were conducted keeping the various parameters like current, voltage and pulse time constant while using varying concentrations of titanium powder. Experimental research methods were employed to study performance characteristics in the machining of H13 steel using PMEDM with a graphite electrode. The results revealed that the concentration of titanium powder has a powerful influence on the MRR, SR and topography surface in PMEDM. Keys word: EDM; PMEDM; MRR; H13; titanium powder.

An experimental investigation on surface finish in die-sinking EDM of Ti-5Al-2.5Sn

Electrical discharge machining (EDM) is a non-conventional process for shaping hard metals and forming deep and complex-shaped holes by spark erosion in all kinds of electroconductive materials. The choice of the electrical parameters on the EDM process depends impressively on workpiece-electrode material combination. In this research, an effort has been made to study the surface finish characteristics of the machined surface in EDM on Ti-5Al-2.5Sn titanium alloy. The microstructure of the machined surface is investigated for discharge energy and electrode materials. The peak current, pulse-on time, pulse-off time, servo-voltage and electrode material (copper, copper–tungsten and graphite) are considered as process variables. The experimental work was performed based on an experiment design (central composite design). The surface roughness (SR) increases with peak current and pulse-on time and decreases with servo-voltage. Besides, the effect of the process parameters on surface roughness depends on electrode material. At low discharge energy, copper–tungsten electrode produces the finest surface structure whilst graphite delivers worst surface characteristics. Copper–tungsten with low discharge energy (low peak current and pulse-on time) can be used to obtain better surface finish.