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Dielectric Fluid Flow in Die -Sinking EDM Gap ○Serkan CETIN, Yoshiyuki UNO, Akira OKADA,

and Yoshifumi KAWAZOE

Okayama University, Department of Mechanical Engineering

1. IntroductionEjection of debris from the working gap in EDM is an important

phenomenon for stable and precise machining. Therefore, the

relationship between the flushing action of the electrode and the

behavior of the debris is of technical interest [1,2]. Recently with the

help of high-speed jump function of linear motor equipped ED

machines, the debris disposal has improved even for deep machining

for no-flush machining [3]. This paper deals with the dielectric fluid

flow in working gap during electrode jump for different jump rates

and heights.

2. Experimental Analysis

A dummy electrode-workpiece is fabricated to simulate the

real dielectric flow in working gap, where the dummy electrode

moves with the same real machining jump parameters. The

observation and flow visualization in the model gap are carried outby using PIV (Particle Image Velocimetry) technique (Fig.1). In

this technique, the images of glass powder particles (ø22µm) put

into the fluid are recorded with a high-speed camera (maximum

speed of 10,000 fps) and then interrogated with a PIV software

package to understand the flow characteristics of the dielectric fluid.

The analysis showed that, a side gap vortex is generated during the

descending period of the electrode jump ( Fig.2(a)(b), where side

gap=0.2mm, bottom gap=0.5mm, jump speed=15m/min, jump

time=0.3s). In real machining, this vortex is supposed to capture

some of the debris that is trying to flow out of the gap by the effect

of jump flushing. The captured debris will increase the debris

concentration at the side gap resulting in secondary discharges

between the workpiece and electrode. These secondary discharges

are considered to be the main cause to obtain concave side surfaces,

especially in deep machining.

3. Computational AnalysisThe electrode jump motion was modeled and the flow field in

gap was simulated using CFD (Computational Fluid Dynamics)

calculations. The 2-D flow in gap was modeled for electrode jump

heights of 2 and 10mm and jump time of 0.16s, with bottom and

side gaps of 0.1 and 0.2mm, respectively (Fig.3). The jump motion

was simplified to a sine wave  function since it was close to the real

 jump motion. The analysis was done by assuming that the kerosene

fluid flow in gap is laminar and unsteady for fluid density of 

760kg/m3 and dynamic viscosity of 1.881x10-6m2  /s. The CFD

calculations showed that for different electrode jump speeds and

heights, a side gap vortex is again generated during the descendingperiod of the electrode jump (Fig.4(a) for jump height=2mm, (b)  

for jump height=10mm). Since higher electrode jump pumps more

dielectric into the working gap, the debris concentration in gap is

lower for high electrode jump machining compared to low jump

machining [1]. This result when combined with the CFD results

may show the correlation why the concavity of the EDMed holes

becomes smaller with higher electrode jumps.

4. Reference

[1] S. Cetin et al.: Effect of Electrode Jump Height on DebrisAccumulation in EDM, Proc. of Autumn Meeting of JSPE, (2002)

506. [2] M. Akiyoshi et al.: Study of Sludge Behavior in Jump Movementof EDM, Annual Meeting of the Japan Society of Electrical

Machining Engineers, (2002) 97-98.[3] Y. Kaneko et al.: Performance of linear motor equippeddie-sinking EDM, International Journal of Electrical Machining,

No.5, (2000) 59-64.

Fig.1 Schematic illustration of PIV set up

Fig.2 Observation of vortex at side gap 

Fig.4 Dielectric fluid velocity pattern and vortex

simulated by CFD

(a) (b)

(a) (b)

Fig.3 Electrode jump model in CFD

2003年度精密工学会春季大会学術講演会講演論文集

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