Hole Electrical Discharge Machining Research Articles

In Situ Observation of Bubbles and the Effect of Ultrasonic Vibration on Bubble Behavior in EDM.

Accumulation and concentration of debris in deep hole electrical discharge machining (EDM) significantly hinder its machining efficiency and accuracy. It is believed that the movement of bubbles associated with the discharge gap flow field play a pivotal role in debris removal and influence the discharge conditions. Ultrasonic vibration (USV) of the electrode is thought to be an effective method for improving EDM-generated bubbles and debris exclusion. In this study, we first elucidated the behavior of bubbles during EDM of holes with varying aspect ratios. Subsequently, USV was introduced to EDM. The behavior of dielectric fluid flow under the influence of ultrasonic vibration was analyzed using computational fluid dynamics (CFD), which revealed time-varying changes in discharge gap flow pressure and velocity. The velocity of the dielectric flow field near the electrode's side face was found to reach a maximum of approximately 15.2 m/s, greatly facilitating debris removal. High-speed camera observations revealed that bubbles were dispersed within the side gap, with most of them adhering to the electrode's wall. Furthermore, the bubbles exhibited a tendency to continuously break up and coalesce near the hole's outlet before escaping in the USV-assisted EDM. These observed characteristics of bubble behavior under the influence of USV are expected to significantly enhance debris removal and promote efficient dielectric exchange.

Modeling of EDM Process Flushing Mechanism.

The study was performed to determine the optimum flushing condition for electrical discharge machining (EDM) of functional material titanium VT6 obtained by plasma cladding with a thermal cycle. Copper is used as an electrode tool (ET) to machine functional materials. The optimum flushing flows are analyzed theoretically by using ANSYS CFX 20.1 software which is also validated by an experimental study. It was observed that while machining the functional materials to adepth of 10 mm or more, the turbulence fluid flow dominates when nozzle angles are 45° and 75°, consequently drastically affecting the quality of flushing and the performance of the EDM. For the highest machining performance, the nozzles should be at an angle of 15° relative to the tool axis. The optimum flushing at deep hole EDM process minimizes the occurrence of debris deposition on tool electrodes, thus facilitating stable machining of functional materials. The adequacy of the obtained models was confirmed experimentally. It has been established that EDM of a hole with a depth of 15 mm, an intense accumulation of sludge, is observed in the processing zone. There arebuild-ups exceeding 3 mm in cross-section after EDM. This build-up leads to a short circuit and a reduction in surface quality and productivity. It has been proven that not correct flushing leads to intensive wear of the tool and a change in its geometric shape and, accordingly, to a decrease in the quality of EDM.

Development of Microrobot for Fabricating Curved Holes by Means of Electrical Discharge Machining

One of aims in our laboratory is to develop a curved hole electrical discharge machining (EDM) system by means of a microrobot. Three units constitutes the microrobot, i.e., autonomous EDM unit, machining direction steering unit, and in-pipe self-mobile unit. These units have been developed separately in our previous studies. These respective studies have developed the autonomous EDM unit which employs shape memory alloy (SMA) as its actuator and the machining direction steering unit which consists of a helical compression spring and wires whose respective posture and feeds are controlled by linear actuators. So, this study has developed the device combining these two units which makes the device fabricate a curved hole. The experiment result shows that the developed device has the ability to fabricate a curved hole.

Minimum-variance self-tuning regulator in EDM drilling processes for ultra-high-aspect-ratio small holes

High speed small hole electrical discharge machining (EDM) drilling processes can easily become unstable, due to changing flushing conditions, inappropriate preset electrical parameters, and machining debris residues. Although there are already successful attempts in controlling EDM processes, cost-effective adaptive control of high speed small hole EDM drilling has not been reported. Process stability can contribute to the improvement of machining efficiency and surface finish. To maintain a higher process stability, a minimum-variance self-tuning regulator (MVSTR) is designed based on an auto-regressive moving average exogenous (ARMAX) model. To determine specifications of the system, the time and frequency responses are analyzed, and the validation is executed for the offline system model. A series of high aspect ratio holes drilling experiments with different electrode diameters of 0.3 mm, 1.0 mm, and 3.0 mm show that, with the use of the MVSTR control scheme, a higher machining efficiency and a lower tool wear can be achieved as compared with the original controller. Microscopic pictures of drilled holes and electrodes show better surface quality.

The effect of magnesium content on drilling of Al-Mg-Ti alloy by hole electrical discharge machining process

This study presents an experimental investigation of small hole electrical discharge machining of Al-Mg-Ti alloys. A series of drilling operations were carried out for exploring the effect of magnesium content. Holes of 2 mm diameter and 15 mm depth were drilled using tubular single-hole rotary brass electrodes. The rates of material removal and electrode wear, surface roughness, overcut, average recast layer thickness, taper height and angle were studied for Al-Mg-Ti alloys contain 2%, 4%, 6%, 8%, 10%, 12%, and 14% Mg. The results show that the material removal rate is increasing with increasing Mg content while the rate of electrode wear is almost unchanged. Due to decreasing the melting temperature of the Al-Mg-Ti alloy with increasing Mg content, more metal melts and vaporizes during electrical discharge machining drilling. Therefore, more overcut and taper, thicker white layer, and rougher surfaces were measured for higher Mg content.

Sliding-mode controller and algorithm for improving servo control of discharge gap in precise fast hole EDM

Fast hole electrical discharge machining (EDM) is widely used in drilling circular holes with sub-millimeter diameters on metal alloy materials. As a kind of non-contact machining process, the discharge gap between tool electrode and workpiece significantly affects the machining efficiency. Ordinarily, this process can achieve high machining efficiency based on large discharge energy and high pressure inner flush. However, in case of demanding high shape precision and surface quality, such as film cooling holes, the discharge energy needs to be reduced. Thus the electrode wear ratio is increased and the removal of machining debris becomes more difficult. Consequently, the control of discharge gap gets hard and then the machining efficiency is significantly decreased. In this research, a nonlinear velocity controller based on sliding mode control (SMC) method is proposed to improve servo control of discharge gap in precise fast hole EDM. The dynamic model of fast hole EDM is firstly established to provide the physical basis for the controller design. Then a sliding mode algorithm is designed based on Lyapunov stability theory to improve the anti-interference of the control system, and the dynamic characteristics are analyzed through simulations based on the state equation and control algorithm. Furthermore, the performance of the proposed method is discussed by comparing the tool electrode movement, gap average voltage and utilization ratio of pulses measured in experiments. The experimental results showed that the proposed method can increase machining efficiency by 38.1%.

Multi Objective Optimization during Small Hole Electrical Discharge Machining (EDM) of Ti-6Al-4V using TOPSIS

Abstract The current study deals with electric discharge machining (EDM) of Ti-6Al-4V using brass tube electrode. The goal is to perform multi-objective optimization on the effect of process parameters namely current, capacitance, on-time and off-time to determine the response characteristics such as material removal rate, tool wear rate and overcut. The experiments layout was planned using RSM-CCD. The multi-objective optimization method, the “Technique for Order of Preference by Similarity to Ideal Solution” is pertained in the current study. The results authenticate that using a TOPSIS, the MRR of 3.6996 mm3/sec, TWR of 0.0625 mm/sec and OC of 0.33 mm have been achieved.

Dielectric flushing optimization of fast hole EDM drilling based on debris status analysis

Fast hole electrical discharge machining (EDM) drilling can machine holes of Φ0.1–3 mm with a rotating tube electrode passed through by high-pressure dielectric. It is widely believed that the machined debris can be washed away quickly under the high pressure of dielectric flushing to achieve the high processing efficiency. However, in our experiments, it was found that the machining efficiency in the final stage of drilling the holes decreases obviously. In this paper, by analyzing the machining process and simulating the debris status, a problem is discovered that there is debris accumulation into the machining gap without dielectric flow. To solve this problem, we propose the combined flushing with tube-inner dielectric under high pressure and tube-outer dielectric with high velocity. In the final stage (breakthrough-hole stage), the external flushing can update the dielectric in the machining gap. The multi-factors’ effect including the inner-flushing pressure, the external flushing velocity and angle, and the combined flushing on the EDM drilling process is researched by flow field simulations and machining experiments while considering different hole depths. The processing efficiency in the breakthrough-hole stage is significantly improved by ~ 89% because the debris concentration can be reduced by ~ 94% owing to the external flushing.

昆虫型マイクロロボットによる曲がり穴放電加工システムの開発

昆虫型マイクロロボットによる曲がり穴放電加工システムの開発

Study on the Gap Flow Simulation in EDM Small Hole Machining with Ti Alloy

In electrical discharge machining (EDM) process, the debris removed from electrode material strongly affects the machining efficiency and accuracy, especially for the deep small hole machining process. In case of Ti alloy, the debris movement and removal process in gap flow between electrodes for small hole EDM process is studied in this paper. Based on the solid-liquid two-phase flow equation, the mathematical model on the gap flow field with flushing and self-adaptive disturbation is developed. In our 3D simulation process, the count of debris increases with number of EDM discharge cycles, and the disturbation generated by the movement of self-adaptive tool in the gap flow is considered. The methods of smoothing and remeshing are also applied in the modeling process to enable a movable tool. Under different depth, flushing velocity, and tool diameter, the distribution of velocity field, pressure field of gap flow, and debris movement are analyzed. The statistical study of debris distribution under different machining conditions is also carried out. Finally, a series of experiments are conducted on a self-made machine to verify the 3D simulation model. The experiment results show the burn mark at hole bottom and the tapered wall, which corresponds well with the simulating conclusion.

Optimization and predictive modeling using S/N, RSM, RA and ANNs for micro-electrical discharge drilling of AISI 304 stainless steel

In present work, micro-deep holes on AISI 304 stainless steel were drilled via electrical discharge machining (EDM) method. In the first phase of this work, the effect of test parameters on the drilling performance and the profile of drilled holes were investigated experimentally. Test parameters including discharge current, dielectric spray pressure and electrode tool rotational speed were taken and then the machining rate (MR), electrode wear rate (EWR), average over-cut (AOC) and taper angle (TA) were measured in order to assess the drillability of EDM. After experimental study, an analysis of variance was performed to identify the effect of the importance of test parameters on experiment outputs. In the second phase of this study, optimum process parameters were determined using signal-to-noise analysis and response surface methodology (RSM) for mono-optimization and multi-response optimization, respectively. In the last phase, regression analysis and artificial neural network (ANN) models for predicting the MRR, EWR, AOC and TA. As a result of experimental analysis, discharge current was the most important parameter for micro-drilling with EDM. It was found out that this parameter influenced positively MR, while it has negatively an effect on EWR, AOC and TA. Mathematical model based on ANNs exhibited a successful performance for predication of outputs. Optimum process parameters which were discharge current of 10.18 A, dielectric liquid pressure of 58.78 bar and electrode tool rotational speed of 100 rpm for multi-objective optimization were determined through RSM with desirability function analysis in micro-deep hole EDM drilling of AISI 304 stainless steel.

The Simulation Research of Tool Wear in Small Hole EDM Machining on Titanium Alloy

This article has carried on the simulation research of tool wear in electrical discharge machining (EDM) small holes on titanium alloy with the finite element method. Aiming at electrode material removal process in EDM, a 3D thermodynamics model of single pulse discharge material removal is established with Ansys software. By simulating the Gaussian distribution of heat flux and thermal convection loads of discharge channel, the same type of surface heat source is exerted on both positive and negative electrodes with different distribution coefficients and different material characteristics, to analyze the surface temperature field in the region of tool and workpiece processing area, and respectively obtain the heat distribution law along the radius and depth directions of copper and titanium alloy electrodes, in the condition of small hole positive polarity EDM machining on TC4 with copper as the tool electrode. Using the birth and death element method, the volumes of material removal on both electrodes are calculated to analyze the tool wear. The experiments of small hole EDM machining on TC4 are carried out, and the results of simulation and experiment are compared. It is shown that the simulation model can not only accurately predict the relative wear of both electrodes, the simulation results of material removal volumes on both electrodes are also almost accurate.

Effects of the condition of the tubular electrode on hole size and shape in micro deep hole electrical discharge machining

An attempt has been made to find out the effects of the electrode condition on the micro drilled deep holes with electrical discharge machining process. With optimised machining parameters for copper electrode–brass work material combination, experiments were carried out with different electrode conditions viz. straight, tilted and bent electrodes. The objective was to find out the signatures of these electrode conditions on the size and shape of the hole obtained from the experimental results. Based on the results a geometrical model is constructed and presented.

Hole Electrical Discharge Machining Using a High-Response and Multi-DOF Controlled Maglev Actuator (Effects of Direction, Amplitude and Frequency of Electrode Motion on Hole Machining Speed)

This paper describes hole electrical discharge machining (EDM) using a cylindrical electrode driven by a high response and multi degrees of freedom (DOF) controlled magnetically-levitated (maglev) actuator. To avoid abnormal electrical discharge and achieve high speed hole EDM, several combinations of electrode motions such as high speed and high precision axial positioning to keep a gap voltage, jump motion, orbital motion and high frequency axial vibration of electrode (dither) for facilitating debris ejection were tested. Experimental results showed that the combination of the high speed positioning, jump and orbital motions of the electrode was effective for improving the speed of hole EDM. Finally, frequencies and diameters of the orbital motions were surveyed in order to improve the machining speed.

Improving the Speed of Small Deep Hole Electrical Discharge Machining by Combining Rotation of the Electrode with a Rapid-Response

In this paper, we report on the co-operative control of a 5-DOF controlled magnetically-levitated (maglev) local actuator (MLA) combined with a conventional electrical discharge machine, which we developed as a means to increasing the electrical discharge machining (EDM) speed for small deep holes. The MLA enables the electrode to be rotated as well as to be rapidly positioned. Compared to conventional EDM without electrode rotation, the machining speeds in machining φ0.5×4mm and φ1×4mm through holes were increased by 125% and 337%, respectively, using the EDM machine combined with the MLA without electrode rotation ; while with electrode rotation, the co-operatively controlled combination increased the machining speed by a maximum of 343% in machining φ0.5×4mm through holes at 800rpm and 433% in machining φ1×4mm through holes at 600rpm.

Development of CAD/CAM System for Cross Section's Changing Hole Electrical Discharge Machining --- Formulation of Post Processor ---

This study deals with the development of a new CAD/CAM system for fabricating holes whose cross sections change variously. The cross sections of machined holes are generally constant. The limitations in the shapes of holes that can be machined make obstacles in the design stage of industrial products. A new device that utilizes electrical discharge machining has been developed that can create holes with various cross sections to solve this problem. However, it has been impossible to put the device into practical use since there has been no software that has enabled the designed shapes to be easily machined. Therefore, we aimed at developing a new CAD/CAM system for machining the beforehand designed holes with changing cross sections by using the device. As the first step in developing the CAD/CAM system, the post processor in the CAM system is formulated in this paper.

断面変化穴放電加工用CAD/CAMシステムの開発 : 2次元形状用ポストプロセッサの構築(<小特集>生産加工・工作機械の規範2008)

断面変化穴放電加工用CAD/CAMシステムの開発 : 2次元形状用ポストプロセッサの構築(<小特集>生産加工・工作機械の規範2008)

A11 Development of CAD/CAM System for Cross Section's Changing Hole Electrical Discharge Machining : Formulation of Post Processor(Digital design and digital manufacturing (CAD/CAM))

This study deals with the development of a new CAD/CAM system for fabricating the holes whose cross sections are changing variously. A cross section of a machined hole is generally constant. To solve the problem, a new device had developed which could create cross section's changing holes by means of electrical discharge machining. However, it was impossible to put the device into practical use, since the software to machine complicated shape did not exist. Accordingly, the study aims at development of the new CAD/CAM system for the machining using the device. As a first step, in this paper, the post processor of the CAD/CAM system is formulated.

3506 曲がり穴放電加工のための弾性波測定を用いた電極位置検出に関する基礎研究(S62,63 砥粒・特殊加工,S62,63 砥粒加工/レーザ・電気・化学加工)

This study deals with the feasibility of a position detection method of the electrode being used in curved hole electrical discharge machining (EDM) by means of elastic wave measurement. To establish a curved hole ma-chining method, the devices have been developed, which can machine curved holes. At present, the authors have developed the 3-dimensional long curved hole EDM system which consists of an in-pipe movable mechanism, a machining direction determining device and an die-sinking electrical discharge machine. The system has the ability to fabricate long and various curved holes like an earthworm does. In machining a curved hole by using the system, the electrode position cannot be known because whole electrode is inside a workpiece. This means that it is impossible to monitor the position of the electrode under machining and to feed back the electrode position to the system so that a designed curved hole is made. To solve the problems, a electrode position detecting device is developed, which can pinpoint electrical discharge positions by measuring elastic wave generated by EDM by means of acoustic emission (AE) sensors. From the results of the basic experiments, it is found that the device has the ability of electrode position detection.

Micro Hole Electrical Discharge Machining on Insulating Ceramics with Pipe Electrode

Micro Hole Electrical Discharge Machining on Insulating Ceramics with Pipe Electrode