Electrochemical discharge machining of small diameter holes M. Coteaţă, L. Slătineanu, O. Dodun, C. Ciofu Technical University “Gh. Asachi” of Iaşi, D. Mangeron Blvd., 59A, 700050 Iaşi, Romania e-mail:
[email protected];
[email protected]; URL: www.tuiasi.ro
[email protected];
[email protected].
ABSTRACT: Electrochemical discharge machining (ECDM) is considered to be a hybrid machining method where material removal is based on two phenomena: electrochemical dissolution of the material and thermal erosion by electrical discharges that occur between the electrodes. Obtaining holes of small diameter in hard materials is a challenge also for this machining method. The paper contains some results obtained by trying to achieve small diameters holes by electrochemical discharge machining using an aqueous solution of sodium silicate as working liquid. Identifying an optimized system for mechanical and electrical equipment was one of the targets of this research. By assuring a relative motion between the electrodes, holes (diameter 1.27>0.36).
0,6 0,5 0,4 0,3 0,2 0,1 0 0,5
0,6
0,7
0,8
0,9
D, mm Fig. 2. Influence of electrode tool diameter on electrode tool axial wear
The experimental results confirmed the increase of the electrode tool wear confirmed the increase of the electrode tool wear as the electrode tool diameter decreases, and electric capacity, electric voltage between electrodes and work liquid density increase. The mathematical model represented by the relation (1) was used for elaborating the graphical representations included in figures 2, 3 and 6. When the voltage and the capacity, respectively the U=35 V
2 1,5 1 0,5 0
U=45 V
wl, mm
For each experiment the working time was of 6 minutes. The frequency of the contacts between the electrode tool and the workpiece was about 80 contacts per minute. All the workpieces and the electrode tools were weighted by using a digital balance. The length of each electrode tool was measured before and after the experiments, in order to obtain information on the electrode tool wear rate along the axial direction. All the electrode tools were polished in order to have a plane active surface.
U=45 V
0,0001
200
400
600
800
C, microfarads
Fig. 3. Influence of electric capacity on electrode tool axial wear
liquid density, were at the upper values, the electrode tool registered the maximum wear on the length, but also on the diameter. Many microcavities could be observed on the lateral side of the electrode tool examined with a digital microscope, as figure 4 shows (the initial diameter was 0.5 mm).
5. CONCLUSIONS
a
b Fig. 4. - Electrode tool: a) ET before machining; b) electrode tool wear after machining process at upper values of voltage, capacity and liquid density
In this working setup (by using of upper values for the other three independent variables) with an electrode tool 0.5 mm in diameter, during the same working time of 6 minutes, the workpiece was completely drilled on its thickness. An image of the obtained hole is presented in figure 5. The hole edge has small burrs, probably formed by
The paper proposes a new solution for drilling by ECDM, in the case of metallic workpieces. Some experimental researches emphasized the increase of the electrode tool wear as the electrode tool diameter decreases, and, as the electric capacity, the electric voltage between electrodes and work liquid density increase. The experimental results permitted to establish an empirical mathematical model, showing the influence of the voltage U, the capacity C, the electrode tool diameter D, and the work liquid density on the electrode tool wear, evaluated by the reduction of the tool length. Further researches will be focused on ECDM drilling of different metallic materials. As performance criteria, the material removal rate and the shape accuracy of the machined hole could be considered. Different machining procedures, based on the use of tubular electrode tool for ECDM process or electrical discharge machining process could be studied. ACKNOWLEDGEMENTS The research was made within the projects no. ID_625 and TD_212, financed by the National Council of Scientific Research in Higher Education (Romania).
Fig. 5. Hole obtained by ECDM in a cutting steel workpiece
the melted material during the electrical sparks. The working liquid density has an important influence on the process development and also on the electrode tool wear (as diagram from figure 6 shows).
wl , mm
D=0,5 mm
D=0,9 mm
REFERENCES 1.
2.
0,6
3.
0,4 0,2
4.
0 1
1,05 1,1 1,15 density, g/cmc
1,2
Fig. 6. Influence of the work liquid density on the electrode tool wear
5.
Amalnik, S. M., El-Hofy, H.A, McGeough, J.A. An intelligent knowledge- based system for wire-electroerosion dissolution in a concurrent engineering enviroment. Journal of Materials Processing Technology, 79, (1998), 155- 162. Kim, D.J., Ahn, Y., Lee, S.H., Kim, Y.K. Voltage pulse frequency and duty ratio effects in an electrochemical discharge microdrilling process of Pyrex glass. International Journal of Machine Tools & Manufacture, 46 (2006), 1064-1647. Kobayashi F. Electrochemical discharge drilling methode. Pantent JP9234629 (1997); Kozak, J., Rajurkar, K.P. Selected problems of Hybrid machining processes, part I- Electrochemical Discharge Machining (ECDM/ECAM). Advances in Manufacturing Science and Technology (Journal of Polish Academy of Sc., Quarterly), 24 - 2, (2000) 25-50. Mediliyegedara, T.K.K.R., De Silva, A.K.M., Harrison, D.K., McGeough, J.A. New developments in the process control of the hybrid electro-chemical discharge machining (ECDM) process. Journal of Materials Processing Technology, 167 (2005), 338–343.
