Application of TOPSIS to Taguchi method for multi-characteristic optimization of electrical discharge machining with titanium powder mixed into dielectric fluid

Mixing powder into dielectric fluid in electrical discharge machining (PMEDM) is a very interesting technological solution in current research. This method has the highest efficiency in simultaneously improving the productivity and quality of a machined surface. In this study, material removal rate (MRR), surface roughness (SR), and the micro-hardness of a machined surface (HV) in electrical discharge machining of die steels in dielectric fluid with mixed powder were optimized simultaneously using the Taguchi–TOPSIS method. The process parameters used in the study included workpiece materials (SKD61, SKD11, SKT4), electrode materials (copper, graphite), electrode polarity, pulse-on time, pulse-off time, current, and titanium powder concentration. Some interaction pairs among the process parameters were also used to evaluate the effect on the optimal results. The results showed that MRR and HV increased and SR decreased when Ti powder was mixed into the dielectric fluid in EDM. Factors such as powder concentration, electrode material, electrode polarity, and pulse-off time were found to be significant in the optimal indicator (C*) and the S/N ratio of C*. Powder concentration was also found to be the most significant factor; its contribution to C* was 50.90%, and S/N ratio of C* was 51.46%. The interactions of the powder concentration and certain process parameters for C* were found to be largest. The optimum quality characteristics were MRR?=?38.79 mm³/min, SR?=?2.71 μm, and HV?=?771 HV. The optimal parameters were verified by experiment, and its accuracy was good (max error ≈13.38%). The finished machined surface under optimum conditions was also analyzed. The machined surface quality under optimum conditions was good. In addition, the results of the study showed the TOPSIS limitations of TOPSIS in a multi-criteria optimization problem.     

Optimal parameter settings for rough and finish machining of die steels in powder-mixed EDM

The present study was undertaken to identify the appropriate parameter settings for rough and finish machined surface for EN31, H11, and high carbon high chromium (HCHCr) die steel materials in a powder-mixed electric discharge machining process. The effect of seven different process variables along with some of their interactions was evaluated using a dummy-treated experimental design and analysis of variance. Material removal rate (MRR), tool wear rate, and surface finish were measured after each trial and analyzed. The parameter settings for rough and finished machining operations were obtained. EN31 exhibited maximum MRR as compared to the other two materials at similar process settings. Copper (Cu) electrode with aluminum suspended in the dielectric maximized the MRR. Suspending powder in the dielectric resulted in surface modification. Graphite powder showed a lower MRR but improved the surface finish. HCHCr require higher current and pulse on settings for initiating a machining cut and works best in combination with tungsten–Cu electrode and graphite powder for improved finish. The MRR for H11 is lower than EN31 but significantly higher than HCHCr under same process conditions.     

A hybrid Taguchi-artificial neural network approach to predict surface roughness during electric discharge machining of titanium alloys

In the present study, electric discharge machining process was used for machining of titanium alloys. Eight process parameters were varied during the process. Experimental results showed that current and pulse-on-time significantly affected the performance characteristics. Artificial neural network coupled with Taguchi approach was applied for optimization and prediction of surface roughness. The experimental results and the predicted results showed good agreement. SEM was used to investigate the surface integrity. Analysis for migration of different chemical elements and formation of compounds on the surface was performed using EDS and XRD pattern. The results showed that high discharge energy caused surface defects such as cracks, craters, thick recast layer, micro pores, pin holes, residual stresses and debris. Also, migration of chemical elements both from electrode and dielectric media were observed during EDS analysis. Presence of carbon was seen on the machined surface. XRD results showed formation of titanium carbide compound which precipitated on the machined surface.     

Influence of machining parameters on surface roughness in finish cut of WEDM

Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.     

Influence of dielectric and machining parameters on the process performance for electric discharge milling of SiC ceramic

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD).     

Investigating surface properties of OHNS die steel after electrical discharge machining with manganese powder mixed in the dielectric

Although electrical discharge machining is essentially a material removal process, efforts have been made in the recent past to use it as a surface treatment method. An additive powder in the dielectric medium affects the sparking action and helps in improving the surface properties. It may melt at the high temperature of the plasma channel and alloy with the machined surface under appropriate machining conditions. Breakdown of the hydrocarbon dielectric contributes carbon to the plasma channel. In this paper, changes in surface properties of oil-hardening non-shrinkable die steel after machining with manganese powder suspended in kerosene dielectric medium have been investigated. Results show improvement in microhardness by 73%, and no microcracks on the machined surface. X-ray diffraction analysis of the machined surfaces reveals the transfer of manganese and carbon from the plasma channel in the form of manganese carbide. Quantitative analysis of chemical composition by optical emission spectrometer confirms significant increase in the percentages of manganese and carbon.     

激光微涂敷层的电火花后处理及其加工性能

分析、测量了不同加工条件下的材料去除率、相对电极损耗和电火花加工表面粗糙度,并研究了表面微裂纹和微硬度分布。实验结果表明,不同的材料具有类似的电火花加工性能,材料去除率随脉冲电流的增加而增加,峰值电流比脉冲宽度对表面粗糙度的影响更显著。研究结果对于选择合适参数进行电火花后处理具有重要意义。     

Study on the nano-powder-mixed sinking and milling micro-EDM of WC-Co

Present study investigates the feasibility of improving surface characteristics in the micro-electric discharge machining (EDM) of cemented tungsten carbide (WC?CCo), a widely used die and mould material, using graphite nano-powder-mixed dielectric. In this context, a comparative analysis has been carried out on the performance of powder-mixed sinking and milling micro-EDM with view of obtaining smooth and defect-free surfaces. The surface characteristics of the machined carbide were studied in terms of surface topography, crater characteristics, average surface roughness (R _a) and peak-to-valley roughness (R _max). The effect of graphite powder concentration on the spark gap, material removal rate (MRR) and electrode wear ratio (EWR) were also discussed for both die-sinking and milling micro-EDM of WC?CCo. It has been observed that the presence of semi-conductive graphite nano-powders in the dielectric can significantly improve the surface finish, enhance the MRR and reduce the EWR. Both the surface topography and crater distribution were improved due to the increased spark gap and uniform discharging in powder-mixed micro-EDM. The added nano-powder can lower the breakdown strength and facilitate the ignition process thus improving the MRR. However, for a fixed powder material and particle size, all the performance parameters were found to vary significantly with powder concentration. Among the two processes, powder-mixed milling micro-EDM was found to provide smoother and defect-free surface compared to sinking micro-EDM. The lowest value of R _a (38?nm) and R _max (0.17???m) was achieved in powder-mixed milling micro-EDM at optimum concentration of 0.2?g/L and electrical setting of 60?V and stray capacitance.     

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

The 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.     

Assessment of PM-EDM cycle factors influence on machining responses and surface properties of biomaterials: A comprehensive review

Powder mixed-electro discharge machining (PM-EDM) is recently evolving machining technique which can simultaneously remove and modify the machined surface through thermo-electrical process. It is a modified form of EDM in which the conductive powder elements are added in the dielectric liquid to enhance machined surface characteristics and machining responses. The commonly used biomaterials such as 316L stainless steel, Ti-based alloy, Ni–Ti, Mg alloy, and Co–Mo–Cr alloy have excellent mechanical characteristics while the biofunction of these materials are not in satisfactory level. Due to higher hardness, brittleness, and heat resistant natures of the biomaterials, it is very challenging to machine them with conventional machining. Both the system efficiency and modified surface properties depend on the associated electrical and non-electrical factors of PM-EDM cycle. This review focuses on the influence of process factors such as current, pulse duration, tool-polarity, duty cycle, potential voltage, types of liquid, and added powder concentration on performance outputs including material removal and tool wear rate, coating thickness, coarseness, microhardness, coating adhesion bonding, biocompatibility, and resistant to corrosion. This study also discusses influence of various powders on machining and modified surface characteristics of biomaterials. The future research scopes and challenges of PM-EDM process are included in this study thoroughly.     

Characteristic investigation of pipe cutting technology based on electro-discharge machining

Pipe cutting technology plays an important role in the process of offshore platforms decommissioning, as many devices such as tubing, drill pipe, and casing need to be decommissioned. In this study, a novel cutting pipe technology based on electro-discharge machining (EDM) is proposed, and a cutting pipe mechanism is developed to cut the pipes for decommissioning offshore platforms. The machining principles and characteristics of the technique are described. The effects of machining parameters, including tool polarity, dielectric fluid, electrode material and width, pulse on-time, pulse off-time, peak voltage, and electrode rotation speed to machining performance, are investigated. The material removal rate (MRR) of the machined casing and tool electrode wear ratio (EWR) is obtained based on the calculation of the percentage of mass loss per machining time. The experimental results show that a better cutting performance can be obtained with negative tool polarity at the conditions of dielectric fluid of emulsion, pulse on-time of 500 μs, pulse off-time of 200 μs, peak voltage of 70 V, copper electrode width of 28 mm, and electrode rotation speed of 250 rpm is a better choice. Additionally, the cutting slots surface has been investigated by the means of SEM. The cutting slots machined by the rotary EDM are clean and smooth.     

INVESTIGATING THE EFFECTS OF EDM PARAMETERS ON SURFACE INTEGRITY,MRR AND TWR IN MACHINING OF Ti–6Al–4V

Ti–6Al–4V is a kind of difficult-to-cut material with poor machinability by traditional machining methods, while electrical discharge machining (EDM) is suitable for machining titanium alloys. In this paper, three input machining parameters including pulse current, pulse on time and open circuit voltage were changed during EDM tests. To investigate the output characteristics; material removal rate (MRR), tool wear ratio (TWR) and different aspects of surface integrity for Ti–6Al–4V samples such as topography of machined surface, crack formation, white layer (recast layer) thickness and microhardness were considered as performance criteria. The variations of MRR and TWR versus input machining parameters were investigated by means of main and interaction effect plots and also verified by ANOVA results. The effect of pulse energy based on pulse on time and pulse current variations against recast layer thickness and microhardness was studied. The possibility of forming different chemical elements and compounds on the work surface after EDM process was investigated by EDS and XRD analyses. The experimental results revealed that general aspects of surface integrity for machined samples are mostly affected by pulse current and pulse on time. The approximate density of cracks, micro holes and pits on the work surface is intensively dependent on pulse energy variations. Although increase of pulse energy improves the material removal efficiency but leads to increase of average thickness and microhardness of recast layer.     

磁场电化学磁粒复合光整加工实验研究

开发出一种新的光整加工工艺－磁场电化学磁粒复合光整加工。研究了磁场环境下离子运动轨迹方程,分析了复合光整加工的原理并进行了相应的实验,由于洛仑兹力和电场力的综合作用,改变了离子运动轨迹,使被加工表面峰点电流密度更集中,磁场的搅拌作用,加快了电化学过程,使极间电流密度增大,蚀除速度加快,磁场电化学磁粒复合光整加工,与磁粒光整加工,电化学磁粒光整加工相比,提高了加工效率,改善了表面粗糙度。     

An access detection and machine cycle tracking system for machine safety

Abrasive water jet (AWJ) machining is characterized by its versatility, i.e., it can be applied to a wide variety of materials. Currently, one important application is for manufacturing gem artifacts, especially agate, which is the largest gemological material produced in the state of Rio Grande do Sul. However, one of the main obstacles to its popularization is the cost associated with the process, due to the high abrasive consumption required for a good quality surface finish. In this sense, this research paper presents a study of the influence of the main process parameters (traverse speed and abrasive mass flow rate) on the surface finish of agates machined by AWJ. The experimental procedure used three different traverse speeds, four abrasive mass flow rate in two different thicknesses of agate’s plates. Surface roughness and angle of striation marks were observed for different depths from the jet entrance surface. Results were analyzed using analysis of variance (ANOVA). Through the study, it was found that the machined surface finish varies according to the depth from the entrance surface of the abrasive jet. Also, it was concluded that the surface finish of the machined surface by AWJ (surface roughness and striation marks) of the agate’s plates machined by AWJ exhibits similar results for both thicknesses tested. ANOVA showed that the traverse speed is more significant than abrasive mass flow rate for the material studied with respect to the surface finish. Thus, for a small material thickness, it is possible to use high traverse speed and low abrasive mass flow rate which makes the process more economical.     

Tribological compatibility and improvement of machining productivity and surface integrity

Machining process productivity and machined part quality improvement is a considerable challenge for modern manufacturing. One way to accomplish this is through the application of PVD coatings on cutting tools. In this study the wear rate and wear behavior of end milling cutters with mono-layered TiAlCrN and nano-multilayered self-adaptive TiAlCrN/WN PVD coatings have been studied under high performance dry ball-nose end-milling conditions. The material being machined in this case is hardened H13 tool steel. The morphology of the worn surface of the cutting tool has been studied using SEM/EDX. The microstructure of the cross-section of the chips formed during cutting was analyzed as well. The surface integrity of the workpiece material was also evaluated. Surface roughness and microhardness distribution near the surface of the workpiece material was also investigated. The data presented shows that achieving a high degree of tribological compatibility within the cutting tool/workpiece system can have a big impact on tool life and surface integrity improvement during end milling of hardened tool steel.     

Advantages of carbon nanotubes in electrical discharge machining

Carbon nanotubes (CNTs) have a small specific gravity and a straight-pin shape, which allow them to continuously float and to uniformly disperse throughout the entire dielectric-filled cavity with little agglomeration during electrical discharge machining (EDM). In the past, powder mixtures of silicon, aluminum, and chrome have been used in the EDM process. However, there are concerns about flushing the controlled gap between the electrode and the workpiece because of their heavy specific gravity and their associated non-uniform dispersion in the dielectric. In this study, the effect of adding CNT powders to the dielectric on the surface integrity and the machining efficiency of the workpiece were investigated. CNTs can avoid the agglomeration problem. The CNTs were fabricated by chemical vapor deposition and added to the dielectric at a concentration of 0.4?g/l. The average surface roughness of 0.09?μm was achieved within 1.2?h, and the material defects of the recast layer and the micro-cracks were considerably reduced. The adopted processing parameters were a negative electrode polarity, a discharge current of 1?A, a pulse duration of 2?μs, an open-circuit voltage of 280?V, and gap voltage of 70?V. This technology improved the surface finish by 70% and the machining time by 66%. The achievement is attributed to the nanoscale characteristics of the CNTs in the dielectrics. The surface force became large and was able to balance the gravity body force of the CNTs. Consequently, the electric arcs were well dispersed and more uniform across the electrode gap, thus significantly enhancing the performance of the electrical discharge. It is expected that carbon nanotubes will be used in many EDM applications.     

Effects of cutting conditions on microhardness and microstructure in high-speed milling of H13 tool steel

In the present study, high-speed side milling experiments of H13 tool steel with coated carbide inserts were conducted under different cutting parameters. The microhardness and microstructure changes of the machined surface and subsurface were investigated. A finite element model, taking into account the actual milling process, was established based on the commercial FE package ABAQUS/Explicit. Instantaneous temperature distributions beneath the machined surface were analyzed under different cutting speeds and feed per tooth based on the model. It was found that the microhardness on the machined surface is much higher than that in the subsurface, which indicates that the surface materials experienced severe strain hardening induced by plastic deformation during the milling process. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. In addition, optical and scanning electron microscope (SEM) was used to characterize the microstructures of cross sections. Elongated grains due to material plastic deformation can be observed in the subsurface, and white and dark layers are not obvious under present milling conditions. The thickness of plastic deformation layer beneath the machined surface increases from 3 to 10 μm with the increase of cutting speed and feed per tooth. The corresponding results were found to be consistent and in good agreement with the depth of heat-affected zone in finite element analysis (FEA).     

Material removal rate and electrode wear ratio study on the powder mixed electrical discharge machining of cobalt-bonded tungsten carbide

In this article, a material removal rate (MRR) and electrode wear ratio (EWR) study on the powder mixed electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been carried out. This type of cemented tungsten carbide was widely used as moulding material of metal forming, forging, squeeze casting, and high pressure die casting. In the PMEDM process, the aluminum powder particle suspended in the dielectric fluid disperses and makes the discharging energy dispersion uniform; it displays multiple discharging effects within a single input pulse. This study was made only for the finishing stages and has been carried out taking into account the four processing parameters: discharge current, pulse on time, grain size, and concentration of aluminum powder particle for the machinability evaluation of MRR and EWR. The response surface methodology (RSM) has been used to plan and analyze the experiments. The experimental plan adopts the face-centered central composite design (CCD). This study highlights the development of mathematical models for investigating the influence of processing parameters on performance characteristics.     

PARAMETRIC INFLUENCE AND OPTIMIZATION OF WIRE EDM OF HOT DIE STEEL

Wire-cut Electro Discharge Machining (WEDM) is a special form of conventional EDM process in which the electrode is a continuously moving conductive wire. The present study aims at determining parametric influence and optimum process parameters of Wire-EDM using Taguchi's technique and a Genetic algorithm. The variation of the performance parameters with machining parameters was mathematically modeled by Regression analysis method. The objective functions are defined as Dimensional Error (DE), Surface Roughness (SR) and Volumetric Material Removal Rate (VMRR). Experiments were designed as per Taguchi's L₁₆ Orthogonal Array (OA) wherein Pulse-on duration, Current, Pulse-off duration, Bed-speed and Flushing rate have been considered as the important input parameters. The matrix experiments were conducted for the material Hot Die Steel (HDS) having the thickness of 40 mm. The Heat Affected Zone (HAZ) characteristics of the eroded materials were assessed by Scanning Electron Microscope (SEM) and the microhardness of the material was tested using Vickers microhardness tester. The results of the study reveal that among the machining parameters, it is preferable to go for smaller pulse-off duration for achieving overall good performance. Regarding pulse-on duration, higher values are recommended for error constrained machining with higher MRR and constrained/limited values for attaining good surface texture. Smaller current is suggested for better surface finish/texture control, medium range for error control and high value for MRR. Finally, the validation exercise was performed with the optimum levels of the process parameters. The results confirm the efficiency of the approach employed for optimization of process parameters in this study.     

Roughness and wear characteristics of spark-eroded surfaces

Measurements of surface roughness H_r.m.s were made on spark-eroded samples of tungsten carbide, high speed tool steel, high carbon steel and mild steel machined with graphite, copper and tungsten tools. The roughness increased with increasing pulse energy for particular work-tool combinations. The surface finish improved as the melting point of the work material increased for a particular tool material and as the work function of the tool material decreased for a particular work material.The surface roughness profile records were graphically analysed to obtain the average and maximum peak-to-valley height and the free polishing depth. The heterogeneity of the surface, expressed as the ratio of the range of microirregularities to its average value, was between 1.1 and 1.5. Reduction in pulse energy, which resulted in a better surface finish, correlated with reduction in the free polishing depth. The average diameter of the crater increased with increasing pulse energy.