Cold electrode erosion model applied to the electrical discharge

1
Cold electrode erosion model applied to the
electrical discharge machining process
L. I. Sharakhovsky , A. Marotta, and A.M.
Essiptchouk
A simple erosion model for electrical discharge
machining (EDM) is proposed and compared to other
authors' cathode experimental data. From these
comparisons, the effective arc spot current
density and erosion enthalpy have been obtained.
The good agreement between the experimental
results and the theoretically calculated erosion
curve validates the model.
The Electric Discharge Machining - EDM is widely
applied for cutting and shaping solid materials,
including hard-to-work materials. This device
gives a controlled sequence of electric pulses.
In Electric Arc Heaters - EAH the arc spot may
move continuously or in steps, jumping from site
to site. The step-wise motion of the arc spot can
be realized more closely, in its purest form, in
a pulsed, motionless device, like in EDM. Here,
we extend a recently published phenomenological
model for the erosion of electrodes of EAHs to
the EDM pulsed mode of discharge. This article
shows that the step-wise model of arc spot motion
can be applied to explain some of the features of
EDM pulsed arcs. In 1 there was assumed a point
heat source model with infinite current density,
which is unrealist from the physical point of
view. In the present report, assuming a finite
cathode spot current density, a simple EDM
cathode erosion model is proposed and compared to
experimental results in 1.
Assumptions 1) volumetric Joule heating
negligible 2) one spark per pulse 3) average
thermal properties 4) arc spot heat flux density
q0 jU uniform over circular cathode spot area
of diameter d, where j - effective arc spot
current density and U - thermal volt-equivalent
5) electrode semi-infinite body 6) effect of the
preceding arcs neglected 7) duration of EDM
pulse ?r satisfies Fourier condition Fo
a?r/d2, where a is the thermal diffusivity of
the electrode material. Apply one-dimensional
heat diffusion equation with boundary condition
q0 Const 2. Obtain time ? ?0 for a given
point on the electrode surface under the spot to
reach the fusion temperature T(0,?0) Tf
Abstract
Abstract