جستجوی مقالات مرتبط با کلیدواژه « Electrical Discharge Machining » در نشریات گروه « مکانیک »

Metal matrix composites have attracted a lot of attention for application in the aerospace, defense, and automotive industries. Machining these materials with traditional machining methods is very difficult due to the presence of abrasive particles. Electrical Discharge Machining (EDM) is one of the most widely used advanced machining methods and seems to be a good method for machining metal matrix composites. Tool wear occurs during the process and cannot be reduced to zero, but it can be reduced as much as possible. In this research, the effect of discharge peak current, pulse on time, and pulse off time on the workpiece made of AZ91 magnesium alloy, reinforced with 5% of powdered silicon carbide particles has been investigated. The effect of these parameters on the wear rate of copper electrode is studied. The tests of this process have been modeled using the response surface methodology. 17 experiments have been done to reach the results. Discharge peak current, pulse on time, the interaction effect of discharge peak current and pulse on time, and the interaction effect of pulse off time and discharge peak current are effective factors on electrode wear rate. The lowest electrode wear rate is on the 300 microseconds pulse on time, 11.69 amp discharge peak current, and pulse off time of 20 microseconds.

Metal matrix composites (MMCs) have higher modulus of elasticity, toughness and ductility than base metal and are widely used in many different industries. These materials have excellent properties such as light weight, high resistance to weight ratio, high specific hardness, high thermal conductivity and good abrasion resistance. Due to the high hardness, machining of these materials by conventional machining processes is very difficult. Electrical discharge machining (EDM) is an advanced machining process can be used to machining metal matrix composite. Experiments related to the present study were modeled using Design Of Experiments (DOE) and Response Surface Methodology (RSM) and the effect of parameters of discharge current intensity, pulse on time and pulse off time in the machining process of electric discharge machining of AZ91 alloy metal matrix composite Magnesium reinforced with 5% silicon carbide powdered particles has been studied and optimized on the material removal rate and surface roughness of the workpiece. The discharge peak current is the only factor affecting the material removal rate and the highest material removal rate can be achieved at pulse on time 300 µs, discharge peak current 17.5 A and pulse off time 40 µs as much as 542 mg/min. the parameters of pulse on time, discharge peak current and Interaction effect of pulse on time and discharge peak current are the factors affecting the surface roughness of the workpiece. The minimum surface roughness of the work piece is 9.55 µm in the pulse on time 100 µs and discharge peak current 5 A.

Electrical discharge machining is a non-traditional machining process, which is widely used for machining high-strength metals and alloys with low machinability. Due to the thermoelectric nature of this process, the poor surface integrity of the parts produced by this method is one of its weaknesses. In this research, the electric discharge machining method has been used for the machining of Ti-6Al-4V alloy using carbon nanotubes added to the dielectric. In this study, input variables include discharge current intensity, pulse duration, and dielectric; the effect of their changes on the shape of the output pulses, material removal rate, tool wear ratio, surface rouhness and heat affected layer has been investigated. The results show that the addition of carbon nanotubes to the dielectric reduces the harmful pulses and increases the effective pulses in machining, reduces the matrial removal rate and decrease the tool wear rate. The presence of carbon nano tubes significantly improves the surface quality and reduces the heat-affected layer.

Smoothness of the machined surface is an important feature in machining. Fractal geometry is a creative and practical branch of modern mathematics. One of the most important features of fractal fractal geometry is the fractal dimension. The purpose of this study is to investigate the effect of current intensity on the surface hardness and roughness of steel workpiece in the process of electric discharge using fractal analysis. For this purpose, parts of alloy steel AISI316 L were machined by Spark. Then, the samples were imaged microscopically to evaluate the quality of the machined surfaces by scanning electron microscopy (SEM). The results of experiments and fractal analysis showed that with 10 times increase in current intensity, average surface roughness increased about twice and surface hardness decreases 0.8 times.Also, increasing current intensities increased the standard and amplitude of surface signal while, the frequency of changes is decreased. This indicates that the level and height of the surface are increased and points of higher altitude and depth are created at the surface which means that the surface has become rougher. As a result, increasing the surface roughness and reducing the surface hardness of the workpiece has increased the fractal dimension of machining surfaces.

In this study, the effect of using of aluminum oxide and silicon oxide nanoparticles simultaneously into dielectric has been investigated in the process of electrical discharge machining of titanium alloy Ti-6Al-4V. After analyzing the parameters affecting the process of the electrical discharge machining using nanoparticles, intensity of the current, concentration, pulse on time, and particle composition were considered as input parameters. The effect of each parameters has been investigated on three levels; the material removal rate (MRR), the tool wear rate (TWR) and the surface roughness (SR) of the work piece. With respect to the development of the industry in the use of environmentally friendly dielectrics, deionized water was used as the dielectric fluid. Also, Design Expert software has been employed for the design of the experiments, analysis of the results and optimization of the parameters. The results showed that the best surface morphology is obtained by machining with the addition of nanoparticles in the relative composition of 50%. In this percentage of the composition, the surface roughness has the least value of the crack and the recast layer. In addition, the maximum value of the MRR and minimum value of TWR can be achieved in 12A of current intensity, 100µs of pulse on time and 75% of relative composition.

Despite the unique usage of electrical discharge machining process at machining in small dimensions, machining complex shapes and machining of high-strength parts such as ceramics and heat treated steels, which can’t be machined by traditional machining methods, low machined surface integrity achieved by electrical discharge machining process is one of the most important limitations of this process. In this investigation the machined surface integrity will be improved by applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance of electrical discharge machining process, simultaneously. So several experiments were designed and performed based on full factorial method by selecting pulse current and pulse duration as the most important input parameters, in order to study the effects of pulse current and duration on surface integrity of workpiec machined by this hybrid process and to investigate the effects of tools ultrasonic vibrations and external magnetic field on machined surface roughness and integrity of machined surface. According the results, machined surfaces roughness is increased by applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance of electrical discharge machining process, simultaneously, while the SEM pictures of machined surfaces showed that the, amount of created surface cracks, blowholes, globules and beads of debris are decreased and integrity of machined surfaces by EDM process is improved by applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance, simultaneously.

Electrical Discharge Machining (EDM) is one of the most important nontraditional manufacturing processes in machining of precise and complex parts made of hard materials. Improvement of its machining operation, due to the application of this method in advanced industries is important. One of the effective methods to improve the efficiency of electrical discharge machining is the addition of powder to the dielectric fluid and usage of ultrasonic Vibrations of electrode. In this paper three Nano-powders, TiO2, Al2O3 and ZnO and ultrasonic vibrations were investigated, and the effects of input parameters including powder type and concentration, pulse-on time and the current on the material removal rate, surface roughness, and tool wear rate were investigated. Based on the results, this method has no significant effect on the tool wear rate but Average material removal rate can be increased up to 30%, So that the mean surface roughness and tool wear rates remain constant. Addition of the ZnO Nono-powder to the dielectric fluid caused the most material removal
rate and surface roughness. Addition of the Al2O3 Nono-powder to the dielectric fluid caused the least surface roughness. In addition, the most material removal rate was obtained at powder concentration equal to 3 g/lit

Titanium aluminide intermetallic compounds are a small group of materials that can be used at high temperature structures where the specific strength (strength to density ratio) and specific stiffness (elastic modulus to density ratio) are very important. In this study, some output characteristics of electrical discharge machining (EDM) process; including material removal rate (MRR), surface roughness and topography are investigated for this material. The DOE method of full factorial is used for planning the machining tests that two main input parameters of pulse current and pulse on time are changed in five and four different levels, respectively and other input machining parameters are kept constant during tests. The results show that in lower currents (3 and 6 A), despite the increase in pulse time, there is no significant change in MRR and the MRR for these two currents is negligible, indicating that finishing process of titanium aluminide is difficult and time consuming, but there is no such situation in more currents (12, 24 and 64 A) and the roughing process of this material is optimally carried out. For the currents above the 24 A, the gradient of MRR increase, is decreased because of arc appearance. In the states of higher electrical currents, the lengths of cracks on the machined surface are increased and the widths of cracks are growing. While arc is occurred for the higher electrical discharge energy, the surface roughness and topography are intensively different from the other current and pulse on time conditions.

Electrical discharge machining process is one of the most Applicable methods in Non-traditional machining for Machining chip in Conduct electricity Piece that reaching to the Pieces that have good quality and high rate of machining chip is very important. Due to the rapid and widespread use of alloy DIN1.2080 in different industry such as Molding, lathe tools, reamer, broaching, cutting guillotine, etc. Reaching to optimum condition of machining is very important. Therefore the main aim in this article is to consider the effect of input parameter such voltage, Current strength, on-time pulse and off-time pulse on the machining chip rate and optimizing this in the electrical discharge machining for alloy DIN1.2080. So to reach better result after doing some experiments to predict and optimize the rate of removing chip, neural network method and genetic algorithm are used. Then optimizing input parameters to maximize the rate of removing chip are performed. In this condition, by decreasing time, the product cost is decreased. Optimum parameters in this experiment in this condition are obtained under Current strength 20 ampere, 160 volt, on-time pulse 100 micro second and off-time pulse 12 micro second that is obtained 0.063 cm3/min as rate of machining chip. After doing experiment, surveying the level of error and its accuracy are evaluated. According to the obtained error value that is about 5.18%, used method is evaluated for genetic algorithm.

This paper experimentally investigated the effects of electrical discharge machining processes parameters on fatigue resistance of 16MnCr5 alloy steel. 16MnCr5 alloy steels have good wear resistance. For this purpose, pulse current and pulse time have been considered as variables in the process. The selected EDM parameters were pulsed current (8, 16 and 32A) and pulse time (25, 100 and 400µs). Tests were conducted in full factorial mode and the R. R. Moore fatigue test machine was used to determine the fatigue life of components. The results show that by increasing the spark current and pulse duration 16MnCr5 alloy steel fatigue life is reduced. Respectively, the greatest resistance to fatigue achieved at current of 8A and pulse time of 25 microseconds and lowest resistance to fatigue achieved at pulse current of 32A and pulse time of 400 microseconds. Resistance to fatigue crack depends on cracks density on the surface of the workpiece and heat-affected zone, where the density of cracks increase resistance to fatigue will be reduced. Also in the specimens that have low resistance to fatigue, fatigue cracks are initiated from multiple points of the cross-section. It seems the reason for this phenomenon is the high surface roughness in the samples. EDM machining with high energy sparks can decrease the fatigue strength of 16MnCr5 by as much as factors of 3-5.

Electrical discharge machining (EDM) is a modern machining method which in pace with industrial developments, various studies are aimed at improving this process's parameters including material removal rate. In previous researches, changes in machining tool’s properties and specifications have been investigated as the solution to improve the material removal rate. A novel and efficient process to change material microstructure and properties is equal channel angular pressing (ECAP) that is appropriate method to produce fine grains materials with high strength and adequate properties. In this study, the pure copper material was processed through 4 and 8 passes of ECAP and its effect as a toolfor EDM process, on material removal rate, with different discharge current and pulse ontime was examined. Microstructure of the specimens were analyzed after ECAP operation using electron back scatter diffraction method (EBSD), and the average diameter of grains for specimens were measured using this technique. The results of the experiments indicated that processing the copper tool with ECAP through 4 passes, increases the material removal rate up to 13.2 percent. Moreover, increasing the number of passes of ECAP from 4 to 8 improved the effectiveness of this process on increasing the material removal rate up to 5.5 percent.

One of the fundamental problems of Electrical Discharge Machining (EDM) process is tool electrode wear. In this study، ultra fine grains (UFG) structure of pure copper was used to improve performance and also increase the electrical wear resistance of tool electrode. Equal Channel Angular Pressing (ECAP) was used to reduce the crystal size of pure copper. Samples were processed through ECAP die up to 8 passes، and then used as electrode in EDM process. The effect of electrodes grain size، discharge current، and machining time on the metal removal of the work piece and electrical wear of the electrodes were investigated. In addition، the microstructure، and electrical conductivity of copper tool electrodes were examined. By applying the ECAP on pure copper a fine، approximately 50-200 nm grain size، microstructure was obtained after 8 passes. The results show that for finer crystalline structure of copper electrodes، electrical wear decreases but material removal rate is somehow constant.

In this study the interaction of material and ultrasonic vibration of workpiece at different pulse on times (Ti) and discharge currents (I) in the electrical discharge machining (EDM) has been studied. The materials of machined samples were AISI H13 tool steel and FW4 weld steel. The results show that ultrasonic vibration of workpiece, independent of workpiece material increase material removal rate (MRR) and reduce tool wear ratio (TWR) and surface roughness. Also the results indicate that the effect of ultrasonic vibration on the material removal rate increase of FW4weld steel is higher than AISI H13 tool steel, and the reduction of tool wear ratio of FW4 weld steel is more than AISI H13 tool steel.

Manufacturing of blades in air turbine motors according to complicated shape and critical working conditions needs a high technology. The root of blade under applied forces should have high surface quality and dimensional accuracy in comparison with the other blade components. In this study, the surface quality due to different types of available wire-cut machines for machining of compressor blade root has been investigated. To this end some samples has been machined by different wire-cut machines. Afterwards the different components of surface integrity (such as surface roughness, surface topography, hardness, thickness of affected surface layers, microcrackes and pits, residual stresses) has been studied. Finally, the machining of the root of compressor blade with this process has been discussed and concluded.