Electrochemistry Encyclopedia

(http://electrochem.cwru.edu/encycl/)

ELECTROCHEMICAL MACHINING (ECM)

Joseph McGeough

Institute for Integrated Micro and Nano Systems

University of Edinburgh

Edinburgh, EH9 3JL, United Kingdom

(July, 2005)

Michael Faraday’s early metallurgic researches, from 1818 to 1824, anticipated the

developments which have led to widespread use today of alloy steels. Much effort has been

expended to improve their performance for their service as cutting tools in machining. The

aim has always been to yield higher rates of machining and to tackle recently developed

harder materials on the principle that the tool material must be harder than the workpiece

which is to be machined. Much progress has been made; however, in recent years some

alloys, which are exceedingly difficult to machine by the conventional methods, have been

produced to meet a demand for very high-strength, heat resistant materials. Moreover, these

new materials often have to take a complex shape. A search has had to be made for

alternative methods of machining since the evolution of suitable tooling has not kept pace

with these advances.

Electrochemical machining (ECM) has been developed initially to machine these hard to

machine alloys, although any metal can so be machined. ECM is an electrolytic process and

its basis is the phenomenon of electrolysis, whose laws were established by Faraday in 1833.

The first significant developments occurred in the 1950s, when ECM was investigated as a

method for shaping high strength alloys. As of the 1990s, ECM is employed in many ways,

for example, by automotive, offshore petroleum, and medical engineering industries, as well

as by aerospace firms, which are its principal user.

Metal removal is achieved by electrochemical dissolution of an anodically polarized

workpiece which is one part of an electrolytic cell in ECM. Hard metals can be shaped

electrolytically by using ECM and the rate of machining does not depend on their hardness.

The tool electrode used in the process does not wear, and therefore soft metals can be used as

tools to form shapes on harder workpieces, unlike conventional machining methods. The

process is used to smooth surfaces, drill holes, form complex shapes, and remove fatigue

cracks in steel structures. Its combination with other techniques yields fresh applications in

diverse industries. Recent advances lie in computer-aided tool design, and the use of pulsed

power, which has led to greater accuracy for ECM-produced components.

Theoretical background

Since electrolysis is the basis of ECM, it must be understood before going further through the

characteristics and other details of the process.

Electrolysis

Electrolysis is the name

given to the chemical

process which occurs, for

example, when an electric

current is passed between

two conductors dipped into

a liquid solution. A typical

example is that of two

copper wires connected to a

source of direct current and

immersed in a solution of

copper sulphate in water, as

shown in Figure 1. An

ammeter, placed in the

circuit, will register a flow

of current; from this

indication, the electric

circuit can be deduced to be

complete. A significant

conclusion that can be made from an experiment of this sort is that the copper sulphate

solution obviously has the property that it could conduct electricity. Such solution is termed

an electrolyte. The wires are called electrodes, the one with positive polarity being the anode,

and the one with negative polarity the cathode. The system of electrodes and electrolyte is

referred to as the electrolytic cell, whilst the chemical reactions which occur at the electrodes

are called the anodic or cathodic reactions or processes.

Fig. 1. Electrolysis of copper sulphate solution.

Electrolytes are different

from metallic conductors of

electricity in that the current

is carried not by electrons

but by atoms, or group of

atoms, which have either

lost or gained electrons, thus

acquiring either positive or

negative charges. Such

atoms are called ions. Ions

which carry positive charges

move through the electrolyte

in the direction of the

positive current, that is,

toward the cathode, and are

called cations. Similarly, the

negatively charged ions

travel toward the anode and

are called anions. The

movement of the ions is accompanied by the flow of electrons, in the opposite sense to the

positive current in the electrolyte, outside the cell, as shown also in Figure 2 and both

reactions are a consequence of the applied potential difference, that is, voltage, from the

electric source.

A cation reaching the cathode is neutralized, or discharged, by the negative electrons on the

cathode. Since the cation is usually the positively charged atom of a metal, the result of this

reaction is the deposition of metal atoms.

To maintain the cathodic reaction, electrons are required to pass around the external circuit.

These are obtained from the atoms of the metal anode, and these atoms thus become the

positively charged cations which pass into solution. In this case, the reaction is the reverse of

the cathodic reaction.

The electrolyte in its bulk must be electrically neutral; that is, there must be equal numbers of

opposite charges within it, and thus there must be equal amounts of reaction at both

electrodes. Therefore, in the electrolysis of copper sulphate solution with copper electrodes,

the overall cell reaction is simply the transfer of copper metal from the anode to the cathode.

When the wires are weighted at the end of the experiment, the anodic wire will be found to

have lost weight, whilst the cathodic wire will have increased in weight by an amount equal

to that lost by the other wire. Some examples of the reactions occurring in these processes are

shown in the Appendix.

These results are embodied in Faraday’s two laws of electrolysis:

1. The amount of any substance dissolved or deposited is directly proportional to the

amount of electricity which has flowed.

2. The amounts of different substances deposited or dissolved by the same quantity of

electricity are proportional to their chemical equivalent weights.

Fig. 2. Electrolytic dissolution of iron.

A popular application of electrolysis is the electroplating process in which metal coatings are

deposited upon the surface of a cathodically polarized metal. An example of an anodic

dissolution operation is electropolishing. Here, the item which is to be polished is made the

anode in an electrolytic cell. Irregularities on its surface are dissolved preferentially so that,

on their removal, the surface becomes flat and polished.

ECM is similar to electropolishing in that it also is an anodic dissolution process. But the

rates of metal removal offered by the polishing process are considerably less than those

needed in metal machining practice.

Some observations relevant to ECM can be made:

Since the anode metal dissolves electrochemically, its rate of dissolution depends only

upon the atomic weight and the ionic charge, the current which is passed, and the time

for which the current passes. The dissolution rate is not influenced by the hardness or

other characteristics of the metal.

Since only hydrogen gas is evolved at the cathode, the shape that electrode remains

unaltered during the electrolysis. This feature is perhaps the most relevant in the use

of ECM as a metal shaping process.

Characteristics of ECM

In ECM, electrolytes serve as conductors of electricity and Ohm’s law also applies to this

type of conductor. The resistance of electrolytes may amount to hundreds of ohms.

Accumulation within the small machining gap of the metallic and gaseous products of the

electrolysis is undesirable. If growth were left uncontrolled, eventually a short circuit would

occur between the two electrodes. To avoid this crisis, the electrolyte is pumped through the

interelectrode gap so that the products of the electrolysis are carried away. The forced

movement of the electrolyte is also essential in diminishing the effects both of electrical

heating of the electrolyte, resulting from the passage of current and hydrogen gas, which

respectively increase and decrease the effective conductivity.

Working principles Electrochemical

machining is

founded on the

principles

outlined. As

shown in Figure

3, the workpiece

and tool are the

anode and

cathode,

respectively, of

an electrolytic

cell, and a

constant potential

difference,

usually at about

10 V, is applied

across them. A

suitable

electrolyte, for

example,

aqueous sodium

chloride (table

salt) solution, is

chosen so that

the cathode

shape remains

unchanged during electrolysis. The electrolyte is also pumped at a rate 3 to 30 meter/second,

through the gap between the electrodes to remove the products of machining and to diminish

unwanted effects, such as those that arise with cathodic gas generation and electrical heating.

The rate at which metal is then removed from the anode is approximately in inverse

proportion to the distance between the electrodes. As machining proceeds, and with the

simultaneous movement of the cathode at a typical rate, for example, 0.02 millimeter/second

toward the anode, the gap width along the electrode length will gradually tend to a steady-

state value. Under these conditions, a shape, roughly complementary to that of the cathode,

will be reproduced on the anode. A typical gap width then should be about 0.4 millimeter.

Being understood the characteristics and working principles of ECM, its advantages should

be stated in short before going further through machining processes:

• the rate of metal machining does not depend on the hardness of the material,

• complicated shapes can be machined on hard metals,

• there is no tool wear.

The schematic of an industrial “electrochemical machine” is shown in Figure 4, and an actual

example of a cathode tool and anode workpiece are shown in Figure 5.

Fig. 3. Working principles of ECM.

Fig. 4. Industrial electrochemical machine.

Fig. 5. Example of cathode tool (above) and

anode workpiece (below).

Electrochemical machining

Machine components

Industrial electrochemical machines work on the principles outlined. Particular attention has

to be paid to the stability of the electrochemical machine tool frame, and to the machining

table which should also be stable and firm. The electrolyte has to be filtered carefully to

remove the products of machining and often has to be heated in its reservoir to a fixed

temperature, for instance 30oC (86

oF), before entering the machining apparatus. This

procedure is used to provide constant operating conditions. During machining the electrolyte

heats up from the passage of current. Precautions must be taken to avoid a high electrolyte

temperature which can cause changes in the electrolyte specific conductivity and subsequent

undesirable effects on machining accuracy.

Rates of machining

The rates at which metals can be electrochemically machined is in proportion to the current

passed through the electrolyte and the elapsed time for that operation, and is in inverse

proportion to the electrochemical equivalent of the anode-metal which corresponds to the

atomic weight of the dissolving ions over the ionic charge times the Faraday’s constant. See

the Appendix for more details.

Many factors other than current influence the rate of machining. These involve electrolyte

type, rate of electrolyte flow, and some other process conditions. For example current

efficiency decreases when current density is increased for a certain metal, for example, for

nickel.

If the ECM of titanium is attempted in sodium chloride electrolyte, usually very low (10–

20%) current efficiencies are obtained. When this solution is replaced by some mixture of

fluoride-based electrolytes, to achieve greater efficiencies (>60%), a higher voltage is used.

If the rates of the flow are kept too low, the current efficiency of even the most easily

electrochemically machined metal is reduced. Insufficient flow does not allow the products of

machining to be so readily flushed from the machining gap. When complex shapes have to be

produced the design of tooling incorporating the right kind of flow ports becomes a

considerable problem.

Surface finish

Type of electrolytes used in the process affects the quality of surface finish obtained in ECM.

Depending on the material, some electrolytes leave an etched finish. This finish results from

the nonspecular reflection of light from crystal faces electrochemically dissolved at different

rates. Sodium chloride electrolyte tends to produce an etched, matte finish with steels and

nickel alloys.

The production of an electrochemically-polished surface is usually associated with the

random removal of atoms from the anode workpiece, whose surface has become covered with

an oxide film. This is governed by the metal-electrolyte combination used. Nonetheless, the

mechanisms controlling high-current density electropolishing in ECM are still not completely

understood. For example, with nickel-based alloys, the formation of a nickel oxide film

seems to be a prerequisite for obtaining a polished surface; a finish of this quality, of 0.2 µm,

has been claimed for Nimonic (a nickel alloy) machined in saturated sodium chloride

solution. Surface finishes as fine as 0.1 µm have been reported when nickel-chromium steels

are machined in sodium chlorate solution. The formation of an oxide film on the metal

surface is considered the key to these conditions of polishing.

Sometimes the formation of oxide film on the metal surface hinders efficient ECM and leads

to poor surface finish. For example, the ECM of titanium is rendered difficult in chloride and

nitrate electrolytes because the oxide film formed is so passive. Even when higher voltages

about 50 V are applied to break the oxide film, its disruption is so non-uniform that deep

grain boundary attack of the metal surface can occur.

Occasionally, metals that have undergone ECM have a pitted surface while the remaining

area is polished or matte. Pitting normally stems from gas evolution at the anode; the gas

bubbles rupture the oxide film.

Process variables also affect surface finish. For example, as the current density is raised the

finish generally becomes smoother on the workpiece surface. A similar effect is achieved

when the electrolyte velocity is increased. In tests with nickel machined in hydrochloric acid

solution the surface finish has been noted to improve from an etched to a polished appearance

when the current density is increased from about 8 to 19 A/square centimeter with constant

flow velocity.

Accuracy and dimensional control

Electrolyte selection plays an important role in ECM. Sodium chloride, for example, yields

much less accurate components than sodium nitrate. The latter electrolyte has far better

dimensional control owing to its current efficiency - current density characteristics. Using

sodium nitrate electrolyte, the current efficiency is greatest at the highest current densities. In

hole drilling these high current densities occur between the leading edge of the drilling tool

and the workpiece. In the side gap there is no direct movement between the tool and

workpiece surface, so the gap widens and the current densities are lower. The current

efficiencies are consequently lower in the side gap and much less metal than predicted from

Faraday’s law is removed. Thus the overcut in the side gap is reduced with this type of

electrolyte. If another electrolyte such as sodium chloride solution was used instead, then the

overcut could be much greater. Using sodium chloride solutions, its current efficiency

remains steady at almost 100% for a wide range of current densities. Thus, even in the side

gap, metal removal proceeds at a rate which is mainly determined by current density, in

accordance with Faraday’s law. A wider overcut then ensues.

Shaping

Most metal-shaping operations in ECM utilize the same inherent feature of the process

whereby one electrode, generally the cathode tool, is driven toward the other at a constant

rate when a fixed voltage is applied between them. Under these conditions, the gap width

between the tool and the workpiece becomes constant. The rate of forward movement

between the tool and the workpiece becomes constant. The rate of forward movement of the

tool is matched by the rate of recession of the workpiece surface resulting from

electrochemical dissolution.

Three practical cases are of interest in considering some equations derived for the variation of

the interelectrode gap width:

1. When there is no tool movement, the gap width increases indefinitely with the square

root of machining time. This condition is often used in deburring by ECM when

surface irregularities are removed from components in a few seconds, without the

need for mechanical movement of the electrode.

2. When the tool is moved mechanically at a fixed rate toward the workpiece, the gap

width tends to a steady value. This inherent feature of ECM, whereby an equilibrium

gap width is obtained, is used widely in ECM for reproducing the shape of the

cathode tool on the workpiece.

3. Under short-circuit conditions the gap width goes to zero. If some process conditions,

such as too small equilibrium gap width caused by a too high movement of the tool

toward the workpiece, occur, contact between the two electrodes ensues. This causes

a short circuit between the electrodes and hence premature termination of machining.

The equilibrium gap is applied widely in the shaping process. Studies of ECM shaping are

usually concerned with three distinct problems:

1. The design of the cathode tool shape needed to produce a required profile geometry of

the anode workpiece.

2. For a given cathode tool shape, prediction of the resultant anode workpiece geometry,

for example, hole drilling by ECM.

3. Specification of the shape of the anode workpiece, as machining proceeds. This is

most readily predicted for the smoothing of surfaces, although for actual shaping of

components by ECM, estimates of the machining times as the shape develops provide

useful information about the process.

Applications

Smoothing of rough surfaces

Deburring, or smoothing, of

surfaces (Figure 6), is the

simplest and a common use

of ECM. A plane-faced

cathode tool is placed

opposite a workpiece that

has an irregular surface. The

current densities at the peaks

of the surface irregularities

are higher than those in the

valleys. The former are,

therefore, removed

preferentially and the

workpiece becomes smooth,

admittedly at the expense of

stock metal (which is still

machined from the valleys

of the irregularities, even

though at a lower rate).

Electrochemical smoothing

is the only type of ECM in

which the final anode shape

may match precisely that of

the cathode tool.

Electrochemical deburring is a fast process; typical times for smoothing the surfaces of

manufactured components are 5 to 30 seconds. Owing to its speed and simplicity of

operation, electrochemical deburring can be performed with a fixed, stationary cathode tool.

The process is used in many industries.

Fig. 6. Smoothing of rough surfaces.

Hole drilling Hole drilling is

another principal

way of using

ECM (Figure 7).

The cathode-tool

is usually made

in the form of a

tubular electrode.

Electrolyte is

pumped down

the central bore

of the tool,

across the main

machining gap,

and out between

the sidegap that

forms between

the wall of the

tool and the hole.

Reversal of the

electrolyte flow

can often

produce

considerable

improvement in

machining accuracy.

The main machining action is carried out in the gap formed between the leading edge of the

drill tool and the base of the hole in the workpiece. ECM also proceeds laterally between the

side walls of the tool and component, where the current density is lower than at the leading

edge of the advancing tool. Since the lateral gap width becomes progressively larger than that

at the leading edge, the side-ECM rate is lower. The overall effect of the side-ECM is to

increase the diameter of the hole produced. The distance between the side wall of the

workpiece and the central axis of the cathode tool is larger than the external radius of the

cathode. This difference is known as the "overcut". The amount of overcut can be reduced by

several methods. A common procedure involves the insulation of the external walls of the

tool (Figure 7), which inhibits side-current flow. Another practice lies in the choice of an

electrolyte such as sodium nitrate, which has the greatest current efficiency at the highest

current densities. In hole drilling these high current densities occur between the leading edge

of the drill and the base of the workpiece. If another electrolyte such as sodium chloride were

used the overcut could be much greater. The current efficiency for sodium chloride remains

steady at almost 100% for a wide range of current densities. Thus, even in the side gap, metal

removal proceeds at a rate that is mainly determined by the current density, in accordance

with Faraday's law.

Holes with diameters of 0.05 to 75 millimeter have been achieved with ECM. For holes of

0.5 to 1.0 millimeter diameter, depths of up to 110 millimeter have been produced. Drilling

by ECM is not restricted to round holes; the shape of the workpiece is determined by that of

Fig. 7. Electrochemical hole drilling.

the tool electrode.

Full-form shaping

Full-form shaping utilizes a constant gap across the entire workpiece and the tool is moved

mechanically at a fixed rate toward the workpiece in order to produce the type of shape used

for the production of compressor and turbine blades. In this procedure, current densities as

high as 100 A/square centimeter are used, and across the entire face of the workpiece, the

current density remains high.

Electrolyte flow plays an even more influential role in full-form shaping than in drilling and

smoothing of surfaces. The entire large cross-sectional area of the workpiece has to be

supplied by the electrolyte as it flows between electrodes. The larger areas of electrodes

involved mean that comparatively higher pumping pressures and volumetric flow rates are

needed.

Electrochemical grinding

The main feature of electrochemical grinding (ECG) is the use of a grinding wheel in which

an insulating abrasive, such as diamond particles, is set in a conducting material. This wheel

becomes the cathode tool. The nonconducting particles act as a spacer between the wheel and

workpiece, providing a constant interelectrode gap, through which electrolyte is flushed.

Accuracies achieved by ECG are usually about 0.125 millimeter. A drawback of ECG is the

loss of accuracy when inside corners are ground. Because of the electric field effects, radii

better than 0.25 – 0.375 millimeter can seldom be achieved.

A wide application of electrochemical grinding is the production of tungsten carbide cutting

tools. ECG is also useful in the grinding of fragile parts such as hypodermic needles.

Electrochemical arc machining

A process that relies on electrical discharges in electrolytes, thereby permitting metal erosion

as well as ECM in that medium, has been developed. Because this process relies on the onset

of arcs rather than sparks, it has been named electrochemical arc machining (ECAM). A

spark has been defined as a sudden transient and noisy discharge between two electrodes; an

arc is a stable thermionic phenomenon. Duration discharges of approximately 1 second to 1

millisecond are described as sparks, whereas for durations of about 0.1 second said

discharges can be considered arcs. Because in the ECAM process duration, energy, and time

of ignition of sparks are under control, it is valid to regard them as arcs.

An attraction of the ECAM technique is the very fast rates of metal removal attainable by the

combined effects of sparking and ECM. The ECAM technique can be applied in all the ways

discussed for ECM, thus surfaces can be smoothed and drilled. Turning is also possible, as is

wire machining.

One form of this process relies on a pulsed direct current, that is, full-wave rectified ac power

supply that is locked in phase with a vibrating tool head. The oscillation of the tool gives rise

to a set of conditions whereby ECM occurs over each wave cycle. The interelectrode gap

narrows as the tool vibrates over one cycle. During the same period the current rises until

sparking takes place by breakdown of the electrolyte and/or generation of electrolytic gas or

steam bubbles in the gap, the production of which aids the discharge process.

For drilling, the discharge action occurs at the leading edge of the tool, whereas ECM takes

place on the side walls between the tool and the workpiece. The combined spark erosion and

ECM action yields fast rates of metal removal. Because ECM is still possible, any

metallurgical damage to the components caused by the sparking action can be removed by a

short period of ECM after the main ECAM action. Currents of 250 A at 30 V are typically

used in the process.

Economic aspects

The industrial sectors utilizing ECM technology fall into five main categories: tool and die,

automotive, aerospace, power generation, and oil and gas industries. Leading the world’s

principle machine tool manufacturing nations in production and export of tools in the 1980s

were Japan followed by the former West Germany. The United States led in imports and

consumption; consumption was high for both Japan and W. Germany as well.

Unconventional machine tools including ECM are generally considered to account for only

1% of total production. Electrodischarge machining (EDM) holds the largest share, possibly

as much as 50% and ECM about 15% lagging behind laser processes which are 20%.

Manufacturing engineers wishing to use ECM processes in industry need to address the

challenge of proper tool design. The cost of design can be as much as 20% of the cost of an

electrochemical machine for complex components. Predictability of overcuts obtained for

specific applications and the particular electrolytes to be used for the alloy metals that have to

be machined must also be considered along with specific controls and limits on the ECM

equipment needed.

Computer-controlled equipment and sensors are available for electrochemical machining

systems. However in the 1990s practical ECM systems are often favored because the amount

of control and/or monitoring of the process is far less than that which was required in the

1970s. Thus machines are used successfully in which electrical spark detection is eliminated

and machining products control, for example, pH monitoring, is nonexistent.

The present and future status of ECM

High-rate anodic electrochemical dissolution is a practical method of smoothing and shaping

hard metals by employment of simple aqueous electrolyte solutions without wear of the

cathodic tool. ECM can offer substantial advantages in a wide range of cavity-sinking and

shaped-hole production operations.

Control of the ECM process is improving all the time, with more sophisticated servo-systems,

and better insulating coatings. However there is still a need for basic information on electrode

phenomena at both high current densities and electrolyte flow-rates.

Tool design continues to be of paramount importance in any ECM operation. The use of

computer-aided design to predict cathode tool profiles will continue to advance.

Recently developments in ECM practice have dwelt on the replacement of constant dc by

pulsed currents (PECM). Significant improvements in surface quality have been claimed.

Much smaller electrode gaps may be obtained, for example, below 0.1 millimeter leading to

improved control of accuracy, for example to 0.02 to 0.10 millimeter, with dies, turbine

blades, and precision electronic components. The key to further advancement in PECM lies

in development of a low cost power supply. Successful development of technique will enable

on-line monitoring of the gap size, enabling closer process control.

Despite these attractions, PECM should be regarded as complementary to, and not a

substitute for, established ECM technology; the former is expensive and metal removal rates

can be lower than these of the latter.

The advent of new technology for controlling the ECM process and the development of new

and improved metal alloys, which are difficult to machine by conventional means, will assure

the future of electrochemical machining.

Appendix

Electrolysis

Reactions that occur during the electrolysis of copper sulphate (Figure 1) are as follows. The

anodic reaction is ionizing of copper:

Cu ==> Cu2+

(aq) + 2e-

While at the cathode the copper ions are discharged to form copper metal:

Cu2+

(aq) + 2e- ==> Cu

Reactions that occur during the electrolysis of iron (Figure 2) are as follows. The anodic

reaction is ionizing of iron:

Fe ==> Fe2+

(aq) + 2e-

At the cathode, the reaction is likely to be the generation of hydrogen gas and the production

of hydroxyl ions:

H2O + 2e- ==> H2 + 2OH

-

The net reaction is thus:

Fe + 2H2O ==> Fe(OH)2(s) + H2

The ferrous hydroxide may react to form ferric hydroxide:

4Fe(OH)2 + 2H2O + O2 ==> 4Fe(OH)3

Characteristics of ECM By use of Faraday’s laws, if “md” (kg) is the mass of metal dissolved, and because

“md = vd” where “v” (m3) is the corresponding volume and “d” (kg/m

3) the density of

the anode metal, the volumetric removal rate of anode metal (m3/second) is given by:

Where “a” (kg/mol) is the atomic weight of the anode metal, “I” (ampere) is the current

flowing, “z” is the ionic charge of the anode metal, and the Faraday constant “F” equals

96,487 coulombs/mol. If a machining operation has to be carried out on an iron workpiece at

a typical rate of 2.6 × 10-8

kg/C, for this removal rate to be achieved by ECM, the current in

the cell must be about 700 A, because “a/zF” = 29 × 10-8

and “d”= 7,860 kg/m3 for iron.

Rates of machining

By use of Faraday’s laws the rates at which metals can be electrochemically machined can be

calculated.

Where “md” (kg) is the mass of metal electrochemically machined by current “I” (ampere)

passed for a time “t” (second). The quantity “a/zF” is called the electrochemical equivalent of

the anode metal as mentioned before.

Table I shows the metal machining rates that can be obtained when a current of 1000 A is

used in ECM. Metal removal rates in terms of volumetric machining are often more useful

than mass removal rates, and both quantities are included. (It is assumed that the anodic

current efficiency is 100%, that is all the current is used to remove metal, which is not always

the case.)

Table I. Metal machining rates

Metal Atomic Ionic Density Removal rate

weight charge 10

3 kg/m

3 10

-3 kg/s 10

-6 m

3/s

Aluminum 26.97 3 2.67 0.093 0.035

Beryllium 9.0 2 1.85 0.047 0.025

Chromium 51.99 2 7.19 0.269 0.038

3

0.180 0.025

6

0.090 0.013

Cobalt 58.93 2 8.85 0.306 0.035

3

0.204 0.023

Niobium 92.91 3 9.57 0.321 0.034

(Columbium)

4

0.241 0.025

5

0.193 0.020

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Copper 63.57 1 8.96 0.660 0.074

2

0.329 0.037

Iron 55.85 2 7.86 0.289 0.037

3

0.193 0.025

Magnesium 24.31 2 1.74 0.126 0.072

Manganese 54.94 2 7.43 0.285 0.038

4

0.142 0.019

6

0.095 0.013

7

0.081 0.011

Molybdenum 95.94 3 10.22 0.331 0.032

4

0.248 0.024

6

0.166 0.016

Nickel 58.71 2 8.90 0.304 0.034

3

0.203 0.023

Silicon 28.09 4 2.33 0.073 0.031

Tin 118.69 2 7.30 0.615 0.084

4

0.307 0.042

Titanium 47.9 3 4.51 0.165 0.037

4

0.124 0.028

Tungsten 183.85 6 19.3 0.317 0.016

8

0.238 0.012

Uranium 238.03 4 19.1 0.618 0.032

6

0.412 0.022

Zinc 65.37 2 7.13 0.339 0.048

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Analysis of Electrochemical Arc Machining by Stochastic and Experimental Methods,

A. B. M. Khayry and J. A. McGeough, “Proceedings of the Royal Society of London”

Vol. A412, pp 403-429, 1987.

An Electrochemical Machining Method for Removal of Samples and Defective Zones

in Metal Pipes, Vessels and Structures, D. Clifton, J. W. Midgley, and J. A.

McGeough, “Proceedings of the Institution of Mechanical Engineers, Part B, Journal

of Engineering Manufacture” Vol 201, pp 229-231, 1987.

Surface Effects on Alloys Drilled by Electrochemical Arc Machining, A. DeSilva and

J. A. McGeough, “Proceedings of the Institution of Mechanical Engineers, Part B,

Journal of Engineering Manufacture” Vol. 200, pp 237-246, 1986.

Analysis of Taper Produced on Side Zone During ECD, V. K. Jain and V. N. Nanda,

“Precision Engineering, Journal of the American Society for Precision Engineering”

Vol. 8, No. 1, pp 27-33, 1986.

Electrochemical Wirecutting, S. R. Ghabrail and C. F. Noble, in “Proceedings of the

24th

International Machine Tool Design and Research Conference” pp 323-328, B. J.

Davies (editor), Macmillan, Manchester, UK 1984.

Drilling Without Drills, G. Bellows and J. D. Kohls, “American Machinist” pp 178-

183, 1982.

Deburring-2: Electrochemical Machining, D. Graham, “The Production Engineering”

Vol. 61, No. 6, pp 27-30, 1982.

Comparative Studies of ECM, EDM and ECAM, I. M. Crichton, J. A. McGeough, W.

Munro, and C. White, “Precision Engineering” Vol. 3, pp 155-160, 1981.

Aspects of Drilling by Electrochemical Arc Machining, T. Drake and J. A.

McGeough, in “Proceedings of the 21th

Machine and Tool Design and Research

Conference” pp 362-369, J. M. Alexander (editor), Macmillan, New York, 1981.

Basic Study of ECDM-II, M. Kubota, Y. Tamura, H. Takahahi, and T. Sugaya,

“Journal Association Electro-Machining” Vol. 13, No. 26, pp 42-57, 1980.

Basic Study of ECDM-I, M. Kubota, Y. Tamura, J. Omori, and Y. Hirano, “Journal

Association Electro-Machining” Vol. 12, No. 23, pp 24-33, 1978.

Newcomers for Production, G. Bellows, in “Non-Traditional Machining Guide 26” pp

28-29, Metcut Research Associates Inc., Cincinnati, Ohio, 1976.

Electrochemical machining, J. Kaczmarek, in “Principles of Machining by Cutting,

Abrasion and Erosion” pp 487-513, Peregrinus, Stevenage UK, 1976.

Principles of Electrochemical Machining, J. A. McGeough, Chapman and Hall,

London, 1974.