1. Introduction
Various industrial applications of electrochemical machining
have been developed for many years since the patent
of Gussef, such as electrochemical drilling, electrochemical
grinding (ECG), electrochemical deburring, and electropolishing
(EP) [1]. The electrochemical honing of cylindrical
holes improves dimensional accuracy and relieves surface
layer stress [2]. Acharya et al. [3] compared ECM with
traditional machining. They concluded the investment cost
of ECM is higher, while greater profit and higher quality
can be obtained when operated at optimal conditions [3].
Bannard [4] correlates the current efficiency with current
density and flow rate of electrolyte. The maximum efficiency
varies with the type of electrolyte. Using an electrolyte of
NaCl, metal is removed at 100% current efficiency, and the
current efficiency is nearly independent of the current density
over the anode surface. Using electrolytes NaNO3 and
NaClO3, current efficiency decreases with decreasing cur-
∗ Corresponding author. Fax: +886-3-5722840.
E-mail address: hocheng@pme.nthu.edu.tw (H. Hocheng).
rent density, and good dimensional control can be achieved
[5]. Laboda used aqueous NaNO3 as an electrolyte to replace
conventional salt water in order to increase the degree
of precision. Due to the risk of fire, NaClO3 was replaced
by NaNO3 as electrolyte [6]. Pulsed mode machining is one
of the most efficient methods of electrochemical machining
of metals, several investigations aimed at improving the
parts accuracy and the localization of anodic dissolution [7].
Noto et al. put forward the study of electrode gaps. This suggested
the control of workpiece geometry in electrochemical
machining [8]. Datta and Landolt showed that the gap
width between electrode and workpiece directly influences
the current condition and the dregs discharge of the electrolyte
[9]. Rajurkar obtained the minimum gap width based
on Ohm’s law, Faraday’s law, and the equation of conservation
of energy, beyond which the electrolyte will boil in
electrochemical machining. An on-line monitoring system
was proposed by Rajurkar [10]. Bejar and Gutierrez [11]
changed the machining gap width as well as the concentration
of electrolyte to investigate the influence upon current
efficiency. They found that current efficiency is raised with
the increase of current density and electrolytic concentration
[11]. Overcut increases with voltage as a result of the