Ultrasonic Assisted Electrical Discharge Machining Research Articles

Investigation of processing characteristics of PCD in ultrasonic-assisted graphene powder mixed EDM

Polycrystalline diamond is widely used in many fields including ultra-precise machining, optical material and semiconductor electronic devices due to its excellent physical properties. However, traditional mechanical processing methods of polycrystalline diamond leads to severe tool wear, low efficiency and high costs. Although electrical discharge machining can overcome some limitations, it usually exhibits a low material removal rate and poor surface quality. This study aims to explore the effect of graphene powder and ultrasonic vibration on polycrystalline diamond by electrical discharge machining. It was found that the synergistic effect of graphene powder and ultrasonic vibration can achieve a good surface quality. The results show that ultrasonic-assisted powder mixed electrical discharge machining can obtain the smallest surface roughness (1.98 μm) at low parameter and the biggest material removal rate (0.773 mg/min) at high parameter compared with ultrasonic assisted electrical discharge machining and powder mixed electrical discharge machining. In addition, after ultrasonic-assisted powder mixed electrical discharge machining, the minimum value (0.807) of ID/IG is obtained. For polycrystalline diamond, this study also proposes a removal mechanism that diamond converts into graphite and is peeled under tensile stress.

Surface integrity of Ti-6Al-4V alloy in hybrid electrical discharge machining processes

Titanium alloy is one of the difficult-to-machine materials. The final conditions of the machined surface of this alloy are influenced by electro-discharge machining. High temperatures and thermal cycles in machining operation induce undesirable alterations in the surface quality of Ti-6Al-4V. One of the ways to improve the negative effects of electrical discharge machining is to use hybrid methods. There is no comprehensive research on the effect of hybrid electrical discharge machining process on the surface integrity of the Ti-6Al-4V alloy. In this paper, hybrid electrical discharge machining techniques including ultrasonic-assisted electrical discharge machining, powder-mixed dielectric electrical discharge machining using Al2O3 nanopowders and powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining, were used for processing of this alloy. The hybrid electrical discharge machining processes were evaluated by basic specifications of surface integrity including surface cracks, heat affected area, residual stress, and corrosion resistance. It was found that in powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining process, developed microcracks were very low and this process developed a thinner heat-altered layer, compared to traditional electrical discharge machining process, which produced a thicker heat-altered layer. The findings also, demonstrated that ultrasonic waves have reduced residual stresses compared to other methods and its stress diagram was distinct in comparison with the other processes. The corrosion rate of samples machined by electrical discharge machining process was higher than other hybrid processes; in powder-mixed dielectric electrical discharge machining process, the machined samples had the highest corrosion resistance.

Experimental Study on Electro-Spark Additive/Subtractive Repair for Worn Cemented Carbide

Worn cemented carbide tool bits are often discarded because of the difficulty of their repair, resulting in a great deal of waste. Surface strengthening technology often extends the service life of worn tools. Electro-spark deposition (ESD) coating and matrix materials are metallurgically and closely bonded, and the approach has the characteristics of small heat input, a small heat-affected zone, and low repair cost, so it is suitable for strengthening the surface of cemented carbide tools. As the surface of cemented carbide tools is often not flat, which affects the uniformity of the deposited layer, the surface needs to be polished before ESD. Therefore, this paper proposed a method involving the electro-spark additive and subtractive repair of worn cemented carbide. Experiments involving the ultrasonic-assisted EDM grinding (UEDG) of cemented carbide were carried out. The effect of brass, 45 steel, and tungsten electrode materials on the removal rate, tool wear, and surface roughness were investigated. The results showed that the material removal rate of the tungsten electrode could reach 3.27 mm3/min, while the electrode loss was only 8.16%, and the average surface roughness was only 2.465 μm, which was better than the other two electrodes. Thus, the tungsten electrode exhibited a high material removal rate, low electrode loss, and good surface quality. The effects of the TiC, TiN, and TC4 electrodes on cemented carbide ESD were studied using optical 3D surface topography and other instruments, and the surface roughness, thickness, and hardness of the deposited layer were compared. The results showed that the surface roughness of the TC4 material reached 52.726 μm, which was better than that of the TiN and TiC materials. The thickness of the TiC deposition layer was 172.409 μm and the hardness value was 2231.9 HV; thus, the thickness and hardness of the TiC material’s sedimentary layer were better than those of the TiN and TC4 materials.

Electrical discharge machining of dental implants in ultrasonic stimulated dielectric

In dental industry electrical discharge machining (EDM) is used for the production of high-precision dental prostheses made of hard non-precious alloys (CrCoMo). This paper presents the strategy and technology of EDM with ultrasonic stimulated dielectric of cavities for swivel latches. A EDM machining basin stimulated with plate oscillators is used to analyze the influence of cavitation effects on the machining process. In order to increase the efficiency of the ultrasonic-assisted EDM process, the fundamental relationships between the stimulation of the dielectric and its influence on the tool electrode wear ϑ, the removal rate Vw and the arith. surface roughness Ra are investigated experimentally. The results show a correlation between the temperature development in the dielectric as well as the ultrasonic frequency used in the EDM process.

INVESTIGATION OF DEBRIS PARTICLES DISTRIBUTION IN ELECTRICAL DISCHARGE MACHINING OF MICRO-HOLES ARRAY

Micro-holes array and micro-electrodes array are widely used in biomedical industry, aerospace industry and micro-electromechanical systems. The machining of micro-holes array is a difficult problem for traditional machining technology. Currently electrical discharge machining technology (EDM) is an alternative machining technology for the fabricating of micro-holes array in high strength and hardness of metal material because of it is free from mechanical force. However, distribution and concentration of debris particles in the discharge gap easily leads to the intensive distribution of discharge positions, which significantly influences machining performance of EDM of micro-holes array. In this study, a three-dimensional flow field simulation model of ultrasonic assisted EDM of micro-holes array is proposed by FLUENT software. The effect of ultrasonic vibration and the depth-to-diameter ratio on debris particles distribution in ultrasonic assisted EDM of micro-holes array will be investigated by numerical simulation. It is shown that reducing the depth-diameter ratio and increasing the ultrasonic amplitude and frequency are beneficial to enhance the exhaustion of debris particles out of the discharge gap and decrease the concentration of debris particles in the discharge gap. In addition, machining experiments are carried out.

Comparative evaluation of powder-mixed and ultrasonic-assisted rough die-sinking electrical discharge machining based on pulse characteristics

Electrical discharge machining is used in the machining of complicated shapes in hardened molds and dies. In rough die-sinking stage, attempts are made to enhance material removal rate with a consequential reduction in cycle time. Powder mix and ultrasonic assistance are employed in the electrical discharge machining process to create gap conditions favoring material removal. In the present work, experiments are carried out on hardened D3 die steel using full-factorial design based on three levels of voltage, current and pulse on time. The gap phenomena in graphite powder-mixed and ultrasonic-assisted rough electrical discharge machining are studied using a detailed analysis of pulse shapes and their characteristic trains. Two new parameters, namely, energy expended over a second ( E) and performance factor ( PF) denoting the ratio of energy associated with sparks to total discharge energy, bring out gap conditions effectively. In comparison with the conventional electrical discharge machining for the selected condition, it is seen that the graphite powder mixed in the dielectric enhances the material removal rate by 20.8% with E of 215 J and PF of 0.227, while these values are 179.8 J and 0.076 for ultrasonic-assisted electrical discharge machining with marginal reduction of 3.9%. Cross-sectional images of workpieces also reveal the influence of electrical discharge machining conditions on the machined surface. The proposed approach can be extended to different powder mix and ultrasonic conditions to identify condition favoring higher material removal.

Pulse Efficiency and Gap Status of Rotary Ultrasonic Assisted Electrical Discharge Machining and EDM Milling

This study proposed an ultrasonic assisted (UA-EDM) and rotary ultrasonic assisted EDM (RU-EDM) spindle with ultrasonic transducer for die sinking EDM and EDM milling processes. The research includes investigation of the ultrasonic amplitude effects, spindle revolution speed, peak current, feed-rate control of EDM on the removal rate and tool wear rate for machining of SKD 61 steel. The significant factors that affect the removal efficiency and the tool wear are further verified. Especially, the fundamental studies of the gap status including gas bubble morphology and movement, debris expelling efficiency and waveform of voltage and current pulses are also investigated through experiments with a transparent observation window. Experiment results reveal that RU-EDM is superior to conventional EDM in removal rate in both sinking and milling EDM, but with the cost of a larger tool wear rate. Explanation from gap status and characteristics of the EDM pulse trains with and without rotary ultrasonic waves are compared.

Effects of hybrid electrical discharge machining processes on surface integrity and residual stresses of Ti-6Al-4V titanium alloy

The performance of the produced parts in the electrical discharge machining (EDM) is strongly influenced by the final quality of surface. High thermal gradients in EDM process develop considerable changes in surface integrity of machined samples such as changing the chemical composition of the surface, micro cracks appearance, recast layer, residual stresses, and reduction in fatigue life and corrosion resistance. Ultrasonic-assisted EDM (USEDM) and powder-mixed dielectric EDM (PMEDM) are two techniques in improving EDM efficiency. This paper was an attempt to investigate the effects of USEDM, PMEDM, and powder-mixed dielectric USEDM (PM-USEDM) processes on main characteristics of the surface integrity such as surface roughness, micro cracks, heat-altered metal zone, and residual stress. Scanning electron microscopy (SEM) micrographs were used to analysis micro cracks and heat-altered metal zone, and nanoindentation method was utilized to measure the amount of residual stress of discharged surface. The results indicated that PMEDM process improved surface roughness as well, induced micro cracks in PM-USEDM were very low, and heat-altered metal layer was very thick in traditional EDM comparing to PM-USEDM process which was thinner. The results of the present study also confirmed that the amount of residual stress of ultrasonic-assisted process was partially in lower level and had different profile compared with traditional EDM and PMEDM process.

Pulsed ultrasonic assisted electrical discharge machining for finishing operations

Electrical Discharge Machining (EDM) is a non-conventional machining process specially suitable for manufacturing hard-to-machine materials or geometrically complex parts. Many investigations have been presented combining EDM with ultrasonic (US) vibration of the electrode, but most of them have been intended to enhance the material removal rate of the process. In this paper US assisted EDM process has been used in order to improve the surface roughness in a finishing operation. For that purpose a copper rod tool electrode and a 1.2344 tempered alloy steel workpiece have been used. A pulsed US assisted EDM mode (PUEDM) has been developed and compared with the current EDM process and EDM assisted with continuous US vibration (UEDM). The results show that PUEDM process can improve the surface roughness and homogeneity of the machined surfaces in finishing EDM operations.

Flow Field Simulation and Experimental Investigation of Ultrasonic Vibration Assisted EDM Holes Array

Debris distribution in the bottom and side gap significantly affects machining performance of electrical discharge machining (EDM) of holes array. Therefore, the mechanisms of debris distribution and velocity field of flow field in the discharge gap between tool electrode and work piece during EDM process should be investigated. However, these mechanisms have not been fully understood because it is difficult to observe debris distribution process. In this paper, a two-dimensional model of flow field with liquid and debris phase for the bottom and side gap in ultrasonic assisted EDM of holes array was created by computational fluid dynamics. The debris distribution and velocity field of flow field in the bottom and side gap during an ultrasonic vibration cycle was investigated through the numerical simulation. The results show that holes in the center of the array are larger than those at the periphery, which is caused by difference of debris distribution. Machining experiments were conducted to verify the simulation results of debris distribution during EDM of holes array.

EDM Machinabilities of EC-PCD Using Ultrasonic Assisted EDM and Bipolar Pulse Current EDM

In order to achieve a high efficient and high quality EDM of PCD, the authors have developed a new PCD having superior electrical conductivity by using boron diamond as a source material. On the other hand they applied a method to give ultrasonic vibrations to the electrode, and have made it clear that even the standard PCD could be machined at the similar level of efficiency to the cases of EDMing die steels and cemented carbides. With a purpose to obtain a good surface roughness on the PCD at high efficiency, various EDM conditions and methods were compared in this paper. Firstly, influence of discharge duration time was examined, and it was found that a shorter pulse duration time as te=0.5μs showed high efficiency and smaller electrode wear rate. Secondary, influence of bipolar pulse current method was examined, and it was found that the method effected higher efficiency but rather large amount of electrode wear resulted. Thirdly, ultrasonic assisted EDM was conducted, and it was found that the method showed superior result regarding efficiency and wear rate on both standard PCD and EC-PCD. A combination use of ultrasonic assisted and bipolar pulse current EDM methods was also attempted in this research. On the contrary to the expectation, efficiency and electrode wear rate became worse in EDM of standard and EC-PCD in comparison with other methods tested before.

Numerical study of the dielectric liquid around an electrical discharge generated vapor bubble in ultrasonic assisted EDM

In electrical discharge machining due to the electrical current, very small bubbles are created in the dielectric fluid between the tool and the workpiece. Increase of the number of bubbles and their growth in size generate a single bubble. The bubble has an important role in electrical discharge machining. In this paper the effect of ultrasonic vibration of the tool and the velocity fields and pressure distribution in the dielectric fluid around the bubble in the process of electrical discharge machining are studied numerically. The boundary integral equation method is applied for the numerical solution of the problem. It is shown that ultrasonic vibration of the tool has great influence on the evolution of the bubble, fluid behavior and the efficiency of the machining in EDM. At the last stages of the collapse phase of the bubble, a liquid jet develops on the bubble which has different shapes. Due to the different cases, and a high pressure region appears just near the jet of the bubble. Also the fluid particles have the highest relative velocity just near the liquid jet of the bubble.

Effects of Simultaneous Ultrasonic Vibration of the Tool and the Workpiece in Ultrasonic Assisted EDM

In this paper, a new, proposed, ultrasonic assisted EDM is investigated. The problem is assumed to be axisymmetric. Results show that simultaneous ultrasonic vibration of the tool and the workpiece increases the lifetime of the bubble and its growth and collapse rates. Results also show that simultaneous ultrasonic vibration of the tool and the workpiece causes the vapor bubble to expand to a larger maximum volume. This, in turn, causes the pressure inside the vapor bubble to drop to a lower minimum volume, facilitates the ejection of the molten material from the crater, and enhances the material removal rate.

Fuzzy approach to select machining parameters in electrical discharge machining (EDM) and ultrasonic-assisted EDM processes

Condition monitoring of the machining process is very important in today's precision manufacturing, especially in the electrical discharge machining (EDM). This paper introduces a fuzzy-based algorithm for prediction of material removal rate (MRR), tool wear ratio (TWR), and surface roughness (Rz, Rk) in the EDM and ultrasonic-assisted EDM (US/EDM) processes. In this system, discharge current, pulse duration, and ultrasonic vibration of tool are the input variables and outputs are MRR, TWR, Rz, and Rk. The proposed fuzzy model in this study provides a more precise and easy selection of EDM and US/EDM input parameters, respectively for the required MRR, TWR, Rz, and Rk, which leads to better machining conditions and decreases the machining costs. The fuzzy modeling of EDM and US/EDM were able to predict the experimental results with accuracies more than 90%.

Numerical study on the splitting of a vapor bubble in the ultrasonic assisted EDM process with the curved tool and workpiece

Electrical discharge machining (EDM) is a powerful and modern method of machining. In the EDM process, a vapor bubble is generated between the tool and the workpiece in the dielectric liquid due to an electrical discharge. In this process dynamic behavior of the vapor bubble affects machining process. Vibration of the tool surface affects bubble behavior and consequently affects material removal rate (MRR). In this paper, dynamic behavior of the vapor bubble in an ultrasonic assisted EDM process after the appearance of the necking phenomenon is investigated. It is noteworthy that necking phenomenon occurs when the bubble takes the shape of an hour-glass. After the appearance of the necking phenomenon, the vapor bubble splits into two parts and two liquid jets are developed on the boundaries of the upper and lower parts of the vapor bubble. The liquid jet developed on the upper part of the bubble impinges to the tool and the liquid jet developed on the lower part of the bubble impinges to the workpiece. These liquid jets cause evacuation of debris from the gap between the tool and the workpiece and also cause erosion of the workpiece and the tool. Curved tool and workpiece affect the shape and the velocity of the liquid jets during splitting of the vapor bubble. In this paper dynamics of the vapor bubble after its splitting near the curved tool and workpiece is investigated in three cases. In the first case surfaces of the tool and the workpiece are flat, in the second case surfaces of the tool and the workpiece are convex and in the third case surfaces of the tool and workpiece are concave. Numerical results show that in the third case, the velocity of liquid jets which are developed on the boundaries of the upper and lower parts of the vapor bubble after its splitting have the highest magnitude and their shape are broader than the other cases.

Ultrasonic assisted EDM: Effect of the workpiece vibration in the machining characteristics of FW4 Welded Metal

This paper presents the results of experimental studies carried out to conduct a comprehensive investigation on the influence of ultrasonic vibration of workpiece on the characteristics of Electrical Discharge Machining (EDM) process of FW4Welding Metal in comparison with the conventional EDM process. The studied process characteristics included the material removal rate (MRR), tool wear ratio (TWR), and surface roughness (R a and R max) of the workpiece after the EDM and ultrasonic assisted EDM (US-EDM) processes. The experiments performed under the designed full factorial procedure and the considered EDM input parameters included pulse on-time and pulse current. The experimental results show that in short pulse on-times, material removal rate in the USEDM process is approximately quadruple than that of the EDM process. On the contrary, in the long pulse on-times, ultrasonic vibration of workpiece leads to the reduction in the MRR. On the other hand, in short pulse on-times, the TWR in the US-EDM process is lower than that of in the EDM process, and this condition reverses with increase in the pulse on-time. Furthermore, the surface roughness of the workpiece machined by EDM process is slightly lower than that of applied to the US-EDM process.

Micro-Hardness and Machined Surface Damage Study for Continuous and Discontinuous Ultrasonic Vibration Assisted Electrical Discharge Machining

A versatile process of Electrical Discharge Machining (EDM) using continuous and discontinuous vibrations to workpiece has been developed. The effects of continuous and discontinuous vibration assisted EDM were explored using high Carbon high Chromium steel as work piece and Copper as tool electrode. In this work L18 orthogonal array based on Taguchi design is used to conduct a series of experiments and the experimental data statistically evaluated by analysis of variance (ANOVA). The main machining parameters such as type of vibration, amplitude of vibration, peak current, no-load voltage, pulse-on time and duty factor were chosen to determine the EDM machining characteristics such as micro-hardness and heat affected layer on the machined surface. The advantages of ultrasonic assisted EDM were confirmed from the analysis of micro-hardness and SEM photographs. The experimental results show that the discontinuous ultrasonic assisted EDM has higher micro-hardness with reduced Heat affected layer as compared...

Productivity of EDM Process Assisted by Ultrasonic Waves

Ultrasonic assisted electrical discharge machining (USEDM) is one of hybrid machining methods based on the EDM process. The effects of ultrasonic waves on EDM process were analyzed and the experimental investigation of productivity of steel induced by USEDM was reported. Results indicated that ultrasonic waves and cavitation played an important role in improving the flushing and machining efficiency during USEDM. And the material removal rate of EDM assisted by ultrasonic waves was improved greatly.

Numerical study on the effect of the frequency and amplitude of the tool on the material removal rate in ultrasonic-assisted electrical discharge machining

This paper investigates the effects on the rate of material removal of the frequency and amplitude of the ultrasonic vibration of the tool used in ultrasonic-assisted electrical discharge machining. It is shown that increases in the amplitude and frequency of the tool vibration increase the rate of pressure drop inside the bubble and consequently increase the rate of pressure drop on the surface of the workpiece. The latter facilitates the escape of the molten material from the crater and consequently increases the rate of material removal from the workpiece.

Comparative Study and Mathematical Modeling of Machining Parameters in Ultrasonic-Assisted EDM of AISI H13 Tool Steel by the Application of Workpiece Vibration

The correct selection of the machining parameters is one of the most significant issues to take into consideration in Ultrasonic-assisted Electrical Discharge Machining (US-EDM) and EDM processes. In the present work, a study has been made to develop and extract statistical models to show the relationship between important machining performance data (material removal rate (MRR), tool wear ratio (TWR) and surface roughness Ra) and the input machining parameters (pulse current, and pulse-on time) in the EDM and US-EDM of AISI H13. The models obtained were used to analyze the effects of input parameters on machining performance. In addition, a comparative study was carried out to investigate the effect of ultrasonic vibration of the workpiece on machining performance. The results show that Ultrasonic vibration of the workpiece can significantly reduce the inactive pulses and improves the stability of process. Also US-EDM is effective in attaining a high material removal rate (MRR) in finishing regime in comparison with conventional EDM. The results of Analysis of Variance (ANOVA) indicate that the proposed mathematical models can adequately explain the performance within the limits of the factors being studied.