Molecular Dynamics Simulation of Pressure Generated inside Melting Area in EDM

Abstract:

Electrical discharge phenomena in EDM occur in a very short time period and in a very narrow space, thus making both observation and theoretical analysis extremely difficult. For this reason, the material removal mechanism in EDM has yet to be understood clearly. EDM is a thermal process. Thermal energy is generated by a pulse discharge between the workpiece and the tool electrode. It results in melting and evaporating followed by removal of both the workpiece and tool electrode, forming a discharge crater on both surfaces. In this paper, the hydrostatic pressure distribution in melting area was simulated by Molecular Dynamics (MD) methods. The analysis shows that after discharge is ignited, extremely high pressure is generated inside the melting area. The pressure distribution along the central axis of the melting area at different times indicates that during the discharge duration, the hydrostatic pressure quickly increases to a peak value along the depth direction of melting area and then reduced to 0 GPa in the unaffected area. It was also found that with the passage of time, the depth of the point where the pressure peaks increases with the formation of the discharge crater, accompanied by the decrease in the peak pressure. In addition, the ejected material atoms at different times during the removal process were also analyzed. It was found that the material ablation occurs mostly during the discharge duration.

• Periodical: Key Engineering Materials (Volume 625)
• Pages: 525-529
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.625.525
• Online since: August 2014
• Authors: Xiao Dong Yang*, Xiao Han, Masanori Kunieda
• Keywords: Electrical Discharge Machining (EDM), Molecular Dynamic (MD), Pressure, Removal Mechanism

References

[1] A.S. Zingerman: Regarding the Problem of the Volume of Molten Metal during Electrical Erosion, Soviet Phys., Solid State, 1, 2, 1959, pp.255-260.

[2] DiBitonto DD, Eubank PT, Patel MR, Barrufet MA: Theoretical Models of the Electrical Discharge Machining Process I. A Simple Cathode Erosion Model. J. Appl. Phys., 66 (9), 1989, pp: 4095-4103.

DOI: 10.1063/1.343994

[3] Shuvra Das, Mathias Klotz, F Klocke: EDM simulation: Finite element-based calculation of deformation, microstructure and residual stresses, Journal of Materials Processing Technology, Vol. 142, No. 2 , 2003, pp.434-451.

DOI: 10.1016/s0924-0136(03)00624-1

[4] F. Van Dijck: Physico-mathematical analysis of the electro discharge machining process, Dissertation of Katholieke Universiteit, Leuven, (1973).

[5] S. Shimada, N. Ikawa, G. Ohmori, H. Tanaka, J. Uchikoshi: Molecular dynamics analysis as compared with experimental results of micromachining, Annals of the CIRP, Vol. 41, 1992, p.117–120.

DOI: 10.1016/s0007-8506(07)61165-2

[6] E. Ohmura, I. Fukumoto: Study on thermal shock phenomena due to laser irradiation using molecular dynamics, Int J JSPE, Vol. 29, No. 2, 1985, p.148–50.

[7] S. Shimada, H. Tanaka, N. Mohri, H. Takezawa, Y. Ito, R. Tanabe: Molecular dynamics analysis of self-sharpening phenomenon of thin electrode in single discharge, Journal of Materials Processing Technology, Vol. 149, No. 1-3, 2004, p.358–362.

DOI: 10.1016/j.jmatprotec.2003.11.048

[8] Xiaodong Yang, Jianwen Guo, Xiaofei Chen: Molecular Dynamics Simulation of the Forming Process of Discharge Crater in Micro-EDM, Asian Symposium for Precision Engineering and Nanotechnology, (2009).

[9] Xiaodong Yang, Jianwen Guo, Xiaofei Chen, Masanori Kunieda: Molecular Dynamics Simulation of the Material Removal Mechanism in Micro-EDM, Precision Engineering, Vol. 35, No. 1, 2010, pp.51-57.

DOI: 10.1016/j.precisioneng.2010.09.005

[10] H. Takeuchi, M. Kunieda: Effects of Volume Fraction of Bubbles in Discharge Gap, Proc. of ISEM XV, 2007, pp.63-68.

[11] A. Kojima, W. Natsu, M. Kunieda: Spectroscopic Measurement of Arc Plasma Diameter in EDM, Annals of the CIRP, Vol. 57, 2008, pp.203-207.

DOI: 10.1016/j.cirp.2008.03.097

[12] W. Natsu, S. Ojima, T. Kobayashi, M. Kunieda: Temperature Distribution Measurement in EDM Arc Plasma Using Spectroscopy, JSME International Journal Series C, Vol. 47, No. 1, 2004, pp.384-390.

DOI: 10.1299/jsmec.47.384

[13] Mark E. Tuckerman: Statistical Mechanics: Theory and Molecular Simulation [M], Oxford university press, 2010, pp.229-233.

[14] Cynthia L. Kelchner, S. J. Plimpton, J. C. Hamilton: Dislocation nucleation and defect structure during surface indentation, Physical Review B, Vol. 58, 2010, pp.11085-11088.

DOI: 10.1103/physrevb.58.11085