Analysis of electromagnetic force in wire-EDM

doi:10.1016/j.precisioneng.2008.07.004

Precision Engineering

Volume 33, Issue 3, July 2009, Pages 255-262

https://doi.org/10.1016/j.precisioneng.2008.07.004 Get rights and content

Abstract

This paper clarifies the mechanism of how electromagnetic force applied to the wire electrode in wire electrical discharge machining (wire-EDM) is generated. This electromagnetic force is caused not only by DC component but also by AC components of the discharge current supplied to the wire. We therefore developed and used a two-dimensional finite element method (FEM) program to analyze the electromagnetic field taking into account electromagnetic induction. Assuming that trapezoidal pulse current is supplied to the wire, distributions of the current density and magnetic flux density were analyzed and changes in the electromagnetic force applied to the wire were calculated. Wire movement when the electromagnetic force alone was applied to the wire was also calculated. The calculated wire movement agreed with the measured wire movement when pulse current actually used in WEDM was supplied to the wire, clarifying the mechanism of electromagnetic force generation.

Introduction

In wire-EDM (WEDM), four kinds of forces are applied to the wire electrode [1], [2]: discharge reaction force caused by rapid expansion of a dielectric fluid bubble at the discharge spot during discharge duration, electrostatic force when open voltage is applied between the wire and workpiece during ignition delay time, electromagnetic force caused by discharge current flowing through the wire, arc column, and workpiece during discharge duration, and hydrodynamic force generated by the flow of dielectric fluid. These forces cause vibration and deflection of the wire electrode, thereby lowering machining accuracy, speed, and stability [2], [3]. On the other hand, Obara et al. [4], Han et al. [5], and Tomura et al. [6] developed programs for WEDM simulation. The simulation is based on the repetition of the following routine; calculation of wire vibration considering the forces applied to the wire, determination of the discharge location considering the gap width between the wire and workpiece, and removal of workpiece at the discharge location. Correct values therefore need to be obtained for these forces applied to the wire for accurate simulation.

Obara et al. [7] and Yamada et al. [8], [9] obtained the discharge reaction force from solutions of inverse problems in which wire vibrations calculated using assumed values of the force were compared with measured ones. Han et al. [5] obtained the discharge reaction force in the same way from a solution of an inverse problem in which machined workpiece shapes simulated were compared with measured ones. Obara et al. [10] measured the change in the resultant force involving all the forces: discharge reaction force, electromagnetic force, and electrostatic force with various discharge frequencies. They then obtained the electrostatic force by extrapolating the resultant force to the limit of zero discharge frequency, because both the discharge reaction force and electromagnetic force are zero when discharge frequency is zero. Yamada et al. [8] analyzed the wire displacement caused by the electrostatic force when an open voltage was applied between the end of a thin plate and wire, and found that the analyzed results agreed with experiment. Han et al. [5] determined the relative permittivity in the gap where both dielectric liquid and bubbles exist during consecutive discharge using the inverse problem method and obtained the relation between the gap width and electrostatic force in actual working gaps. As for the influence of hydrodynamic force, Obara [11] analyzed the flow-field in a groove cut by WEDM and quantified the influence of the flow-field on the limit of wire breakage and machining speed.

Regarding electromagnetic force, Panschow [1] reported that the electromagnetic force caused by a consecutive pulse discharge current can be obtained by summation of the contributions from DC component and AC components in the Fourier transformation of the discharge current waveform. Electromagnetic force generated by DC component is attractive and Panschow calculated electromagnetic force using the principle of mirror image for workpiece materials with high permeability like mild steel. He obtained the electromagnetic forces generated by AC components from experiments measuring the wire deflection when a current with known frequency and amplitude was supplied to the wire. Since the wire was short-circuited with the workpiece, the electromagnetic force was measured independently without the influence of the discharge reaction force or electrostatic force. Thus, he found that when the workpiece was mild steel, the force was attractive with low frequency, but it changed to repulsive with increasing frequency. When the workpiece was brass, the force was always repulsive and increased with increasing frequency. Obara et al. [10] also found experimentally that the electromagnetic force is small and repulsive when workpiece is a paramagnetic material like copper, but it is attractive when workpiece is ferromagnetic like steel. Tomura and Kunieda [12] measured the wire movement caused only by the electromagnetic force. They also calculated the electromagnetic force by two-dimensional finite element method (FEM) analysis of electromagnetic field not taking into consideration electromagnetic induction, and analyzed the wire movement caused by the electromagnetic force calculated. They found that when permeability of workpiece was small like copper, the electromagnetic force due to DC component was negligible compared with the electromagnetic force generated by AC components. When permeability was large like steel, the electromagnetic force generated by DC component was dominant. However, there have been no reports on the calculation of the electromagnetic force taking into account electromagnetic induction due to AC components. Hence, in this research, a two-dimensional FEM analysis program taking into account electromagnetic induction was developed to clarify the mechanism of electromagnetic force in WEDM.

Section snippets

Mechanism of electromagnetic force generation

Fig. 1 shows the principle of electromagnetic force generated by DC component. It is assumed that a constant current flows through the brass wire along the wire axis toward the front as seen in Fig. 1. When the workpiece is copper, and the atmosphere is air or water, distribution of the magnetic flux density is axisymmetric and counterclockwise around the wire axis as shown in Fig. 1(a), because all the materials are paramagnetic and have significantly small permeability in the same order. The

Electromagnetic field analysis using FEM

In the previous report [12], electromagnetic force generated by DC component alone was calculated. In this study, we developed an unsteady electromagnetic field analysis program taking into consideration electromagnetic induction using FEM [13], [14]. This program can solve the following Poisson's equation considering electromagnetic induction in the two-dimensional field perpendicular to the wire axis. $\frac{\partial}{\partial x} (\frac{1}{μ} \frac{\partial A_{z}}{\partial x}) + \frac{\partial}{\partial y} (\frac{1}{μ} \frac{\partial A_{z}}{\partial y}) = - J_{0} + σ \frac{\partial A_{z}}{\partial t} + σ \frac{\partial ϕ}{\partial z} .$ Here μ is permeability, A_z is Z-component of

Wire movement caused by electromagnetic force

Wire movement resulting from the electromagnetic force generated by a consecutive pulse current actually used in WEDM was measured. The wire movement was also calculated using the electromagnetic force which was calculated in the same manner as in the previous section.

Conclusions

To clarify the mechanism of the electromagnetic force applied to the wire electrode in WEDM, we developed a 2D FEM program for electromagnetic field analysis taking into consideration electromagnetic induction. Assuming that a wire faces a flat surface of the workpiece and pulse current is supplied to the wire and workpiece in a series, we also analyzed distributions of current density and magnetic flux density, and successfully obtained the electromagnetic force applied to the wire due to the

References (14)

N. Kinoshita et al.
Study on wire-EDM: in-process measurement of mechanical behaviour of electrode-wire
Ann CIRP
(1984)
F. Han et al.
High precision simulation of WEDM using parametric programming
Ann CIRP
(2002)
Panschow R. Über die Kräfte und ihre Wirkungen beim electroerosiven Schneiden mit Drahtelektrode. Dissertation. T.U....
W.L. Dekeyser et al.
Geometrical accuracy of wire-EDM
H. Obara et al.
Simulation of wire EDM
S. Tomura et al.
Simulation of wire EDM under rough cutting conditions
H. Obara et al.
Single discharging force and single machining volume of wire EDM
Proceedings of the ISEM, vol. 11
(1995)

There are more references available in the full text version of this article.

Cited by (62)

Study on the surface integrity in ultrasonic vibration and magnetic field complex assisted low speed WEDM under different magnetic field coupling
2023, Journal of Manufacturing Processes
In this paper, a complex process of ultrasonic vibration (USV) and magnetic field (MF) complex assisted WEDM-LS is proposed, which provides a new method to solve the problems of low machining efficiency and poor machining surface integrity of traditional WEDM-LS. The self-generated MF of wire electrode is taken as the medium, and the influence mechanism of USV and additional MF on the intensity of self-generated MF is explored. Firstly, combined with the Galvanomagnetic effect and Biot-Safar Law, the mathematical models of self-generated MF under USV assisted WEDM-LS and USV-MF assisted WEDM-LS were deduced respectively. And then the MF coupling law between inter electrode was revealed; Secondly, the distribution of self-generated MF of wire electrode under different working conditions was simulated and analyzed. The results showed that compared with traditional WEDM-LS, the self-generated magnetic density under USV assisted WEDM-LS and USV-MF assisted WEDM-LS was increased by 12.1 % and 17.5 % respectively. As a result, the volume of single discharge crater was increased by 12.3 %; Finally, Taguchi orthogonal method was used to complete the USV-MF assisted WEDM-LS orthogonal experiment and the MF coupling verification experiment. The results showed that the Ra was reduced by 23.8 % and the MRR was increased by 25.1 % compared with the traditional working condition. The number of microcracks and micropores on the workpiece surface was significantly reduced, and the degree of workpiece surface burn was effectively reduced, which showed that the surface integrity of the workpiece had been greatly improved. The verification experiment results showed that compared with the opposite coupling of the self-generated MF and the additional MF, when the self-generated MF and the additional MF were coupled in the same direction, the Ra of the workpiece surface was reduced by 18.21 % and the feed speed was increased by 16.68 %. In addition, the removed particles were more evenly adsorbed on the surface of the wire electrode, which increased the normal discharge probability, indicating that the inter electrode MF coupling was the main effect model of ultrasonic vibration and MF recombination.
Measurement of discharge reaction force under different discharge conditions in WEDM using Hopkinson bar method
2023, Precision Engineering
Citation Excerpt :
Panschow [2] studied the electromagnetic force triggered by the discharge current flowing through the closed circuit formed by the wire and workpiece. Tomura et al. [3] obtained the electromagnetic force from both experiment and analysis and found that the electromagnetic force is ignorable when the discharge current is lower than 100 A. On the other hand, the jet flushing process is designed to effectively expel debris from the discharge gap. Okada et al. [4] simulated the deflection of the wire taking into account the fluid dynamic force caused by jet flushing and found that larger deflections were formed with shorter kerf width in roughing.
This paper reports the measurement of discharge reaction force with respect to the discharge bubble in wire electrical discharge machining (WEDM) using the horizontal Hopkinson bar method. Using an RC discharge pulse generator circuit which is of the single pulse control functionality, independent discharges are ignited in the gap between the wire electrode and end face of the Hopkinson bar while deionized water is continuously flushed. The reaction force acting on the Hopkinson bar from a single discharge was measured without the interference of subsequent discharges. The peak value of measured discharge reaction force reached several Newtons level in both finishing and roughing. The waveform patterns of discharge reaction force in WEDM were found to be significantly different from that in sinking EDM. The first peak of the force acting on the Hopkinson bar was found to be equivalent to the force acting on the wire electrode based on the observation of the interelectrode gap using a high-speed camera. Moreover, the influences of different discharge conditions on the force were investigated.
Simulation of Wire EDM Combined with Measurements of Discharge Locations and Wire Displacement
2022, Procedia CIRP
This paper describes a development of a wire electrical discharge machining simulation combined with the measurements of the wire displacement and discharge locations. The wire displacement was measured using an optical sensor to obtain the discharge reaction force and damping coefficient of the wire vibration which are variable during machining. The discharge locations were measured to obtain the points where the discharge reaction force is applied. Considering the discharge reaction force and electrostatic force acting on the wire electrode, the wire deflection and vibration were calculated to obtain the machined workpiece geometry to be compared with the experimental results. Most significant advantage of the simulation newly developed is that those parameters can be updated in real time during machining. With the help of the sensor fusion, the parameters were found to change with increasing the depth of cut and the cut geometries could be simulated with higher accuracy.
Novel method of multi-axis EDM machining of thin-walled Al-Mn parabolic reflector for aerospace applications
2022, Procedia CIRP
The production of high-precision parts and assemblies for aerospace applications requires not only mechanical but also physical and chemical methods of machining the workpieces to achieve required tight tolerances. Aerospace parts are often produced out of hard materials such as titanium or nickel alloys as well as soft materials such as aluminium alloys. In this paper, the improvement of the manufacturing process of thin-walled reflector for the narrow directional onboard antenna is investigated by applying multi-axis electroerosion machining. Due to advances in the technology of assembling waveguides, channels and flanges, it became necessary to change the material of the parabolic antenna reflector, which has excellent solderability, however, is poorly suited to stamping. Since stamping is no longer able to ensure precision in manufacturing, the edge of the reflector is machined using electrical discharge machining (EDM) which performance has low dependence on the material hardness. The mirror material is an aluminium-mangenese alloy of high corrosion resistance, high plasticity (relative elongation at break is 18%), high resistance to puncture loads and low weight. Cutting forces arising during the turning process can cause bending of the antenna mirror surface. The imperfection of the mirror creates uncorrelated areas which are parasitic radiating surfaces. These parasitic radiating surfaces reduce the efficiency of the antenna. A novel machining strategy using a wire EDM machine with an additional inbuilt two axes rotary table is used to replace mechanical cutting, as this machining no longer meets the high requirements for surface quality paired with geometrical tolerances. Measured Ra values of the machined edge machined by wire EDM are lower than 1.6 µm and the geometrical accuracy of the produced part is significantly improved, the standard deviations from the roundness of produced reflector surface are below 30 µm.
A review on magnetic field assisted electrical discharge machining
2021, Journal of Manufacturing Processes
Citation Excerpt :
The electromagnetic force generated by the magnetic field acts on the wire electrode. Tomura et al. [48] selected steel and copper as workpiece materials to analyze and distinguish the state of the electromagnetic force. Studies have revealed that the physical properties of materials, such as the permeability and conductivity, can substantially affect the electromagnetic force applied to wire electrodes.
Electrical discharge machining (EDM) is a thermophysical-based material removal process that has excellent ability for noncontact machining of brittle and hard materials with accurate 3-D complex shapes. Improvements in machining characteristics, including the material removal rate (MRR), surface integrity, electrode wear rate (EWR), energy consumption, and negative environmental impact, are significant for further developing the performance of the EDM process. Recently, magnetic field assisted method has shown great potential and superiority for enhancing the machining process and its performance due to the ease of contactless forces. In this paper, a review was conducted on the magnetic field-assisted electrical discharge machining process. This review first presented the principles and modeling of magnetic field-assisted electrical discharge machining (MF-EDM) and then analyzed the effect of magnetic fields on machining performance including the discharge status, MRR, EWR, and surface integrity. Parametric optimization and machining characteristics of typical difficult-to-cut materials in the MF-EDM process were further investigated. Finally, future research directions and trends were suggested for exploring new applications of magnetic field assisted technology in the electromachining process.
Transient thermo-physical finite element analysis of brass wire during electro-discharge machining of INCONEL material
2019, Materials Today: Proceedings
Citation Excerpt :
Finite difference schema was used to calculate temperature fields within the work piece which was generated by the superposition of multiple discharges. Tomura et al. [20] analyzed the electromagnetic field taking into account electromagnetic induction using a two-dimensional finite element method (FEM). Here introduce the paper, and put a nomenclature if necessary, in a box with the same font size as the rest of the paper.
Wire EDM is considered to be one of the most stimulating and varied machine tool developed for “difficult to machine” conducting materials and is quite extensively and productively used in industry owing to its effective merits. In EDM, the objective is to get enhanced Material Removal Rate (MRR) along with attaining better surface quality of machined component. In order to achieve this, it is always needed to have knowledge of the effects of the manufacturing parameters on the surface integrity, precision and productivity during Electro-Discharge machining of the components. Researchers used input parameters such as pulse on time, pulse off time, servo voltage, peak current and wire feed to optimize performance parameters of WEDM experimentally. Few have tried out Finite element analysis (FEA) of work piece and wire individually. This research attempt presents a study of investigations into the finite element simulations performed on Electro-Discharge machined components and wires both. Different FEM model conceded by different researchers, issues associated with performing such numerical studies and type of heat source utilised to simulate the EDM process using finite element method path are outlined in this research effort to predict the temperature distribution and Residual stresses. Experimental study is also conducted to predict the MRR and Tool wear rate (TER). The MRR is further compared with the simulated results. The percentage error of MRR obtained from simulated study comes out to be less than 7.9%. Optimised parameters are also found using parameters of experimental study and validated simulated model.

View all citing articles on Scopus

View full text

Analysis of electromagnetic force in wire-EDM

Abstract

Introduction

Section snippets

Mechanism of electromagnetic force generation

Electromagnetic field analysis using FEM

Wire movement caused by electromagnetic force

Conclusions

Ann CIRP

Ann CIRP

Geometrical accuracy of wire-EDM

Simulation of wire EDM

Simulation of wire EDM under rough cutting conditions

Single discharging force and single machining volume of wire EDM

Proceedings of the ISEM, vol. 11