Technical report on Electroc

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Production Engineering Department, Jadavpur University
1. Introduction
Electrochemical micromachining (EMM) has emerged as a versatile process for
machining and surface structuring of metallic materials for biomedical and
microsystems applications. From a fundamental point of view EMM presents
many similarities with electrochemical machining (ECM) and electro polishing
(EP) provided one takes into account the scale dependence of phenomena.
Surface Structuring is the process of manipulating the material surface in such
a way so that the tribological properties of the surface get enhanced. Tribology is
the science and engineering of interacting surfaces in relative motion. It includes
the study and applications of the principles of lubrication, friction and wear. We
all know that tribology studies the ways to maintain the surface characteristics of a
material at its best conditions so that the production process reaches its highest
efficiency. As for example, making the surface better introduced to lubricating
fluids so that the lubricants assume the correct positions to the correct extents.
And the application of EMM process in surface structuring has opened a new
direction and a scope of thought for the scientists. In this paper we’ll discuss scale
dependent surface structuring phenomenon. Scale resolved electrochemical
surface structuring of titanium leads to well-defined topographies on the
micrometer and nanometer scales, which are of interest for biomedical
applications.
In this report we shall concentrate our discussion to surface structuring of
Titanium.

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1. i. Surface Structuring Present Status
Surface Structuring is the process of manipulating the material surface in such
a way so that the tribological properties of the surface get enhanced Currently in
the field of manufacturing science, surface structuring is opening new windows
for higher study and research. The various advantages and disadvantages of this
surface structuring process are must know for further study purposes.
Advantages:
i. This helps in developing the surface properties of the material.
ii. Frictional wear can be reduced up to great extent.
iii. The surface can be manipulated in such a way so that lubricants get their
full functionality properly.
iv. Ensure an excellent surface finish to the final product for precision
manufacturing processes.
Disadvantages:
i. The initial cost of the instruments is a bit high.
ii. This process needs high level of expertise and hence only professional
people are eligible to operate and perform it.
iii. If the process isn’t fully correct, then negative results may appear which
means the surface quality can go down further.
Every coin on this earth has two flip sides. So as similar to all other processes,
this surface structuring process has also some disadvantageous sides. But despite
all of them, for higher precision and perfection in the field of manufacturing, it has
been necessary to research more and more on this science.

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1. ii. An Overview Of ECM
Electrochemical machining (ECM) is a method of removing metal by
an electrochemical process. It is normally used for mass production and is used for
working extremely hard materials or materials that are difficult to machine using
conventional methods. Its use is limited to electrically conductive materials. ECM
can cut small or odd-shaped angles, intricate contours or cavities in hard and
exotic metals such as titanium aluminides, Inconel, Waspaloy and high nickel,
cobalt, and rhenium alloys. Both external and internal geometries can be
machined using this process.
ECM is often characterized as "reverse electroplating", in that it removes
material instead of adding it. It is similar in concept to electrical discharge
machining (EDM) in that a high current is passed between an electrode and the
part, through an electrolytic material removal process having a negatively charged
electrode (cathode), a conductive fluid (electrolyte), and a conductive work piece
(anode); however, in ECM there is no tool wear. The ECM cutting tool is guided
along the desired path close to the work but without touching the piece. Unlike
EDM, however, no sparks are created. High metal removal rates are possible with
ECM, with no thermal or mechanical stresses being transferred to the part, and
mirror surface finishes can be achieved.
In the ECM process, a cathode (tool) is advanced into an anode (work piece).
The pressurized electrolyte is injected at a set temperature to the area being cut.
The feed rate is the same as the rate of "liquefication" of the material. The gap
between the tool and the work piece varies within 80–800 micrometers (0.003–
0.030 in.) As electrons cross the gap, material from the work piece is dissolved, as
the tool forms the desired shape in the work piece. The electrolytic fluid carries
away the metal hydroxide formed in the process.
As far back as 1929, an experimental ECM process was developed by W.
Gussef, although it was 1959 before a commercial process was established by the
Anocut Engineering Company. B.R. and J.I. Lazarenko are also credited with
proposing the use of electrolysis for metal removal.
Much research was done in the 1960s and 1970s, particularly in the gas turbine
industry. The rise of EDM in the same period slowed ECM research in the west,
although work continued behind the Iron Curtain. The original problems of poor
dimensional accuracy and environmentally polluting waste have largely been
overcome, although the process remains a niche technique.

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The ECM process is most widely used to produce complicated shapes such
as turbine blades with good surface finish in difficult to machine materials. It is
also widely and effectively used as a deburring process.
In deburring, ECM removes metal projections left from the machining process,
and so dulls sharp edges. This process is fast and often more convenient than the
conventional methods of deburring by hand or nontraditional machining
processes.
Advantages and Pitfalls:
Because the tool does not contact the work piece, there is no need to use
expensive alloys or tempering procedures to make the tool tougher than the work
piece. As a result, the tools can be made from any cheap and easily machined,
cast, or engraved electrically conductive substance. Along with this, there is less
tool wear in ECM, and less heat and no stress are produced in processing that
could damage the part. Fewer passes are typically needed, and the tool can be
repeatedly used. Also this method works even on very hard and brittle work
pieces.
The saline (or acidic) electrolyte poses the risk of corrosion to tool, work piece
and equipment. Only electrically conductive materials can be machined. High
Specific Energy consumption.
Applications:
Some of the very basic applications of ECM include:
• Die-sinking operations
• Drilling jet engine turbine blades
• Multiple hole drilling
• Machining steam turbine blades within close limits
• Jet engines
• Micro Machining (EMM)

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1. iii. An Overview Of EMM
This objects to removal of material of very small dimensions. This ranges from
several microns to millimeters. It has a promising future for production of
miniaturized parts and components.
Several difficulties have been noted while machining of miniature parts and
components with the help of conventional machining processes. Also the huge
requirement of precision manufacturing process has led to the wide application of
electrochemical machining process or EMM.
When electrochemical machining process (ECM) is applied to micro
machining range i.e. 1 micron to 999 micron, for manufacturing of ultra-precision
shapes then this is termed as electrochemical micro machining or EMM process.
Several fundamental observations in this EMM process are that- a very small
inter electrode gap is used. Rate of dissolution or material removal rate depends
upon atomic weight of the material (a), valance (v) of ions produced, machining
current (I), and the time (t) for which the current passes. Though the shape of
electrodes remain unaltered like ECM. Material removed can be calculated as
MRR= Iaη/Fvρ
Where η= metal dissolution efficiency, ρ= density of material and F=
Faraday’s constant= 96500 coulomb.
The various process parameters which influence the machining process are:
• Nature of power supply and machining pulse- DC power supply and DC
pulsed power supply.
• Inter- electrode gap
• Electrolyte type- Passivity and Non-Passivity Electrolyte
• Electrolyte concentration and flow
• Size shape and material of the tool

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Various applications of EMM for micro fabrication are:
• Nozzle plate for ink jet printer head
• Production of high accuracy holes
• 3 dimensional micro machining
As the days are passing by there are numerous no. of things developing in
EMM. The recent advancements of these EMM process are magnificently noted
in:
• Micro Electrochemical Milling
• Wire Electrochemical Machining
• Solid Electrochemical Drilling
• Oxide Film Laser Lithography (OFLL)
• Micro and Nanometer scaled surface structuring
• Laser Electrochemical Micro Machining (LECMM)

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2. Different Techniques Of Surface Structuring
The different techniques of surface structuring can be broadly classified
into two categories viz.
i. Conventional techniques:
Conventional techniques are those techniques which uses conventional
machining processes such as grinding, honing, lapping etc. for surface
structuring purpose. Also it can be stated that these processes use mechanical
energy for machining. Frankly speaking, surface structuring is the process of
developing surface in miniaturized level. But these processes are often used
mainly for surface finishing which is imperative in precision manufacturing
process. So these processes can be termed as conventional processes for
surface structuring.
The major advantages of these conventional surface structuring processes
are mentioned below:
a) These processes are suitable for almost all types of materials.
b) These processes are very effective to economy i.e. they’re very economical.
c) Capital cost of performing these operations are low.
d) Easy setup of equipment are noted.
e) Can be operated by anyone, be him or her high skilled or low.
However there are some disadvantages of these conventional processes
which has led to applications of non-conventional techniques. The major
disadvantages are:
a) Lower accuracy and poor surface finish is obtained sometimes.
b) Higher wastage of material due to high wear rate.
c) Noisy operation cause sound pollution.
d) Tool life is less due to high wear.
e) Cannot be used to operate on very small parts, like in micro and Nano range.
f) The processes are manual, hence there’re chances of human error.

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ii. Non-Conventional techniques:
Non-Conventional techniques are those techniques which uses non-
conventional machining processes such as Electric Discharge Machining etc. for
surface structuring purpose. There is no direct contact between tool and work
piece in most cases, and hence it uses some kind of energy like thermal energy,
chemical energy etc. material removal purposes.
The major advantages of these non-conventional machining processes are
mentioned below:
a) Higher accuracy and surface finish can be obtained here with compared to
the conventional processes.
b) Tool life is far more than the former.
c) Lower wastage of material due to low or no wear.
d) Operation is quiet, mostly no sound is produced.
e) Fully automated process; hence there’re no chances of human error.
f) Can operate into small ranges, even in the micro or Nano range. Prototypes
can be machined here too.
Just like all other processes, the non-conventional processes have some pitfalls
too. These are mentioned below:
a) Capital cost is high.
b) Not suitable for all types of material e.g. EDM or ECM processes require
electrically conductive materials to be operated on.
c) These processes are economical mainly for precision manufacturing
processes.
d) Complex setup of equipment.
e) Only experts can perform these operations.
It has been seen that though non-conventional techniques have some
disadvantages, their weight of advantage is much more than the other sides. Hence
for the surface structuring process, non-conventional techniques are more used
than the former. Among all the non-conventional techniques, ECM, more
specifically EMM has shown excellent performance to be operated under
predefined suitable conditions for this surface structuring purposes. That is why
ECM or EMM has got most attention for this operations.

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3. Fundamental Aspects Of Electrochemical Surface Structuring
Electrochemical processes for shaping and surface structuring of metals by
controlled anodic dissolution include electrochemical machining (ECM),
electrochemical polishing (EP) and electrochemical micromachining (EMM).
These processes find many applications in the manufacturing industry and several
reviews discussing fundamental and applied aspects are available.
Among the named processes EP has been known for the longest time. The
invention of EP as an industrial surface treatment process is usually attributed to
Jacquet who took a patent in 1930, but the first recorded publication dealing with
electro polishing (EP) goes back even further. EP is widely used for surface
finishing of metallic objects of any shape and for deburring. Overviews of
electrolytes commonly used in practice are given in references. EP involves
levelling and brightening of surfaces. The former is usually associated with a
decrease in roughness in the micrometer or larger range, the latter with achieving
specular reflectivity by surface smoothing in the sub micrometer range.
ECM was developed in the late fifties and early sixties for the shaping of
difficult to machine metals and alloys. In the ECM process the shape of the
cathode is reproduced on the anode by high rate anodic dissolution. During
dissolution the cathode is progressively advanced to maintain a constant electrode
spacing, typically on the order of one or several tenth of a millimeter. Extremely
high current densities, up to 100 A/cm2
or more, are applied to achieve high
machining rates. Such high current densities require flow rates of several meters
per second in the inter-electrode gap in order to evacuate the reaction products and
the heat produced in the process. Mostly neutral salt solutions such as NaCl or
NaNO3 are used as electrolytes. ECM was originally developed for the aerospace
industry, but has found applications also in other industries, especially in the
automobile industry, which in the sixties and early seventies developed an active
research program in this field. Subsequently, due to the development of computer
controlled electric discharge machining (EDM), the industrial importance of ECM
has decreased somewhat. However, the process still presents advantages for
certain applications, especially when a smooth surface finish is required.
EMM is a relatively recent method originally developed as an environment
friendly alternative to chemical milling for the electronics and micromechanics
industry. An important advantage of EMM compared with chemical milling is that
it requires no oxidizing agent that must be disposed of with the spent solutions. In
addition, EMM is faster and permits machining of chemically resistant metals

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such as super alloys, stainless steels or titanium. Similar as in chemical milling, in
EMM a photosensitive polymer (photoresist) is applied to the metal. Irradiation of
the photoresist through a suitably designed mask leads to formation of a pattern.
The irradiated (positive resist) or the non-irradiated (negative resist) parts of the
photoresist are then chemically dissolved in a suitable solvent. Finally, the
exposed metal is subjected to electrochemical dissolution forming the desired
shapes. Depending on the application, thin metal sheets are machined by one sided
or two sided attack.
From a fundamental point of view EP, ECM, and EMM have much in
common. They can be understood and theoretically modelled based on the same
principles provided one takes duly into account scale effects resulting from
differences in the rate of material removal, the size of the system and the relevant
geometry. To be focused into our topic, recent results on EMM and surface
structuring of titanium will be presented here only.

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4. New Development Of EMM For Titanium Surface Structuring
The recent researches on EMM on titanium has opened new directions in the
field of mechanical engineering, more specifically manufacturing processes. The
various new developments mainly comprise of:
• Oxide film laser lithography: This does not much differ with
original lithography process except the fact that the layer by layer
development is made with typical laser spot diameter used for Oxide film
laser lithography or OFLL.
• EMM of multilevel structures: EMM using the photoresist
technique is usually applied to single step etching of flat surfaces, using one
sided or two sided attack of thin sheet samples. Different examples of such
applications have been given in the literature. More recently, the application
of EMM to the fabrication of two level structures has been explored.
• Scale dependent surface structuring: Control of surface
topography on the micrometer and the nanometer scale is of importance in
many applications and for that purpose this is a recently developing
technique. Our discussion is focused on this matter.

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5. Scale Dependent Surface Structuring
Control of surface topography on the micrometer and the nanometer scale is of
importance in many applications. Electrochemical etching can for example be
used for producing polished or grained surfaces of aluminum. The surface
topography of biomedical implants plays an important role for cell attachment and
differentiation. For example, the surfaces of dental implants made of titanium are
subjected to physical and chemical treatments that produce finely textured
surfaces in order to reduce the time of recovery for the patients. In our laboratory
we develop electrochemical methods for the fabrication of titanium surfaces of
defined micro- and nanostructure in order to produce model surface topographies
that can be tested for cell response by biologists. Typically, EMM using the
photoresist technique serves for the fabrication of micrometer sized hemispherical
cavities of different size and separation. Since biological testing requires large
numbers of samples of identical surface structure the EMM process had to be
optimized. Using an ethanol cooled sample holder and an optimized voltage
function well defined regular surface structures on 1.5 cm diameter polished disks
were made as illustrated by the SEM micrograph of the below figure.
The sample surface outside the cavities is the original mechanically polished
surface, whereas the inside of the cavities has an electro polished surface finish.
Varying the cavity size and distance one, therefore, also varies the ratio between
electro polished and mechanically polished surfaces. The effect of these variables
on cell response is being tested at present. Surface topography at the nanometer
scale is thought to be at least as important for cell response as micrometer scale
topography. For titanium, chemical etching in hot sulphuric and hydrochloric acid

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based electrolytes can produce roughness on a sub micrometer scale. By
superposing this type of nano-roughness with electrochemical micro structuring
one can produce surfaces with controlled roughness at two different scales. An
example of such a surface is given in the below figure.
Another way to produce nanometer topography is based on the formation of
porous oxides by anodisation. Porous oxide films are well known for anodized
aluminum where regularly shaped pores can be formed with well-controlled pore
size. Apparently, in the sulphuric acid electrolytes typically used for aluminum
anodisation, the pores form as soon as oxide film starts to grow and their size
depends on the applied voltage. For titanium a similar pore formation mechanism
has very recently been reported in presence of fluoride at very long anodisation
times. Anodisation in sulphuric or phosphoric acid, on the other hand, leads to the
formation of a compact film, which at sufficiently high voltage undergoes
dielectric breakdown leading to formation of a multitude of pores, the size and
number of which depends on experimental conditions. The breakdown events
manifest themselves by marked current fluctuations. As an illustration, the SEM
picture of the below figure shows the surface of a porous anodic oxide film
formed in 1 M H2SO4 by sweeping the voltage up to 125 V.

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Interestingly, on mechanically polished samples the pores were quite regularly
distributed, almost independent of the grain structure of the underlying substrate.
On the other hand, pore formation on flat electro polished surfaces was in general
less regular. By porous anodizing of electrochemically structured titanium
surfaces containing 30 mm size cavities, scale resolved surface structuring on the
micrometer and the nanometer scales could be achieved. An example of such a
surface is shown in the below figure.

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The ability to fabricate well-defined surface topographies will be useful for
reaching a better understanding of the complicated interactions of living cells with
implant materials.

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6. Conclusion
In the present paper a brief overview has been given first of the basic principles
governing the performance of ECM and further the discussion has been
concentrated to EMM. Several characteristics of ECM, EMM and further EP
process are discussed. Most important are the consideration of current distribution,
mass transport and the behavior of passive oxide films which are not discussed
here due to the fact this will be beyond the scope of this topic. Taking into account
the relevant scales ECM, EP and EMM exhibit many similarities. Recent studies
on EMM of titanium with and without photoresist discovered, which demonstrate
the many possibilities of the process for biomedical and micromechanics
applications. In particular, EMM can be used for scale resolved surface structuring
on the micrometer and nanometer scales. Using oxide film laser lithography
instead of conventional photoresist technique, the usefulness of EMM can be
extended to non-planar surfaces and to the machining of multilevel structures for
device fabrication. These developments together with a better theoretical
understanding of the critical electrochemical parameters are expected to
eventually open new fields of application for EMM. Future work should be aimed
at finding ways to accelerate the different steps involved in resist-free EMM in
order to improve the economic attractiveness of the process. Another possible
development could be to use other means of oxide sensitization such as electron or
ion beams, which would permit to extend OFLL to machining of nano size
features. The techniques described here for titanium can probably be extended to
other valve metals such as tantalum or niobium, although the specifics of oxide
sensitization may require further study and optimization of the interaction of laser
radiation with oxide films.

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7. References
1. “Advancement in Electrochemical Micro Machining” by Dr. B.
Bhattacharyya, J. Munda, M. Malapati.
2. “Electrochemical micromachining, polishing and surface structuring of
metals: fundamental aspects and new developments” by D. Landolt, F.
Chauvy, O. Zinger.
3. “Electrochemical Micro Machining” by Todkar Mahesh.
----------THE END----------

Technical report on Electroc

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