International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 5 - Dec 2013
Application of Electrochemical Machining to
Produce Micro Hole on Micro Structure
Mahesh Gupta1 , Diwakar Singhal2, Vikas Sharma3, Lekhraj Kumawat4, Siddharth Sharma5
1, 2, 3
Department of Mechanical Engineering, MAIET, Jaipur, Rajasthan, India
Department of Mechanical Engineering, JIT, Jaipur, Rajasthan, India
4, 5
Abstract— The aim of this paper to use the application of
electrochemical in micromachining to produce micro hole, in
which cathode is closely attached to work piece plate. In this
process cathode make by patterned insulation plate coated with
metal film. When potential difference is applied across the work
piece and patterned plate over which the electrolyte flow at a
high speed due to this process micro hole will be produce. Using
this application we can reduce the lead time and cost. This
application can be demonstrated by numerically and
experimentally.
Keywords— Micro hole, Through-mask
through-mask EMM, Ansys.
EMM,
Modified
I. INTRODUCTION
Surface texturing is an attractive approach for the reduction
of friction in mechanical components. Micro dimples
distributed in a frictional surface are expected to act as fluid
reservoirs and help to promote the retention of a lubricating
thin film between mating components. It was found that a
friction reduction of 30% and even more was feasible with a
dimpled surface [1]. Additionally, recent progress made in the
field of aviation (cooling holes in jet turbine blades), space,
automobile, optics, miniature manufacturing and others has
created the need for parts with small and micro-size holes in
extremely hard and tough materials [2,3].Various techniques
have been developed to produce micro dimples and holes in
different ways, including laser machining, electrical discharge
machining, electrochemical machining (ECM),etc.
ECM is an electrochemical dissolution process that can
remove electrically conductive materials regardless of their
hardness and toughness. Application of ECM in micro
fabrication is referred to as electrochemical micromachining
(EMM). Micro fabrication by EMM might involve mask less
or through-mask material removal [4–8].
Through-mask EMM is a high throughput process for
micro device fabrication. It is now receiving considerable
attention in the electronics and other high-tech industries to
produce metallic parts with microstructures. The standard
through-mask EMM begins by bonding a sheet of inert photo
resist on the metal anode work piece. Lithography, which
includes procedures of spin coating, prebaking, exposure,
development, and post baking, is employed to pattern the
photo resist. The photo resist, however, is only one-time mask
and must be peeled off from the anode work piece after
machining. Therefore, it would cost a lot for mass production
[8].
ISSN: 2231-5381
In this study, a modified through-mask EMM has been
developed to produce micro dimple and hole array, in which a
mask with patterned insulation plate coated with metal film as
cathode is closely attached to work piece plate instead of
bonding photoresist layer on the work piece in the standard
through-mask EMM. Compared with the standard throughmask EMM, the modified process offers unique advantages
such as short lead time and low cost because the mask could
be re-used.
II. PRINCIPLE AND SHAPE EVOLUTION MODELLING
The mask developed in the modified through-mask EMM,
as shown in Fig. 1, consists of a conductive metal layer and an
insulation layer. Both the conductive layer and the insulation
layer have the same pattern which will be transferred to the
anode work piece. The mask is not bonded to the anode. As
illustrated in Fig. 2, the mask patterns the anode by simply
pressing and clamping the mask against the anode during
EMM. The metal layer serves as the cathode tool. The
electrolyte flows onto the surface of the mask at a high speed
and fills in all features in the metal and the insulation layer.
Then the areas on the anode exposed in the electrolyte would
dissolve when sufficient voltage was applied. After the
desired microstructure is obtained, the mask is removed from
the anode work piece. Since there is no tool wear in EMM, the
mask is preserved and could be re-used in the production of
other samples.
When the flexible material of the mask is used, a cylinder
or other non planar surface might be patterned by wrapping
and clamping the mask on the target surface.
In the proposed micromachining, the current distribution
defines the profile of micro dimple and hole. Therefore,
analysis of current density has been carried out. Modelling
and simulation have been done to observe the current density
distribution. The assumptions were made as follows:
1. The current density distribution at the anode surface is
determined solely by the Ohmic effects,
2. The conductivity of electrolyte, k, is uniform,
http://www.ijettjournal.org
Page 261
International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 5 - Dec 2013
Fig. 1: Schematic of electrode arrangement of the modified through-mask
EMM
Fig. 3: Electric potential distribution
The normalized current density is defined as i/imax ,where
imax : the maximum current density and i: current density of
every key point on the surface. As shown in Fig. 4,
Fig. 2: Schematic of the modified through-mask EMM
3. The temperature of electrolyte, T, is uniform,
4. The concentration gradient in the bulk electrolyte is
negligible.
The potential ɸ obeys Laplace’s equation within gap domain
Ω [9] (see Fig. 3):
(in Ω)
(1)
Boundary conditions are as follows:
(2)
3˟4˟8˟9 =0 (at the cathode tool)
Γ1 =U (at the anode surface)
(3)
Γ2˟5˟6˟7˟10=0 (the boundary condition)
(4)
where U is the voltage between the anode work piece and the
cathode and n is the surface normal.
The current density, i, is then given by the Ohm’s law as the
normal derivative of the potential, i.e.
i = -K ɸ
(5)
The rate, r, at which the anodic surface recedes, is determined
as:
r= I
(6)
where M is the molecular weight of the anodic metal, n is
the metal dissolution valence, is the density of the anodic
metal, F is Faraday’s constant, and is the current efficiency
of anodic metal dissolution, which was assumed to be constant
at 100%.
The finite element method was employed to solve this
boundary problem, and the analysis was carried out in
ANSYS. For a trench like structure (see Fig. 3) with the scale:
w =200µm, h1 = 30 µm and h2 = 20 µm, 50 µm, 100 µm, 150
µm, respectively, the normalized current density distribution
on the initially flat metal surface is shown in Fig. 4.
ISSN: 2231-5381
Fig. 4: Current density distribution on the anode surface
The current density distribution on each surface is uneven
and the lowest current density is always on the center of the
trench. The thicker the insulation layer is, the more uniform
the current density distribution is observed. This non uniform
current density distribution will lead to a convex dimple
profile.
In order to predict the shape of the evolving cavity, the
boundaries were progressively updated using APDL (ANSYS
Parametric Design Language) in ANSYS. At each time step,
the electrode surface was displaced proportionally to current
density, i, using Faraday’s Law (Eq. 6). The Program flow
diagram of shape evolution simulating is shown in Fig. 5. The
thickness of the insulation layer is 100 µm in the simulation.
The time step is 0.2 s. With the material dissolution step by
step a given cavity evolves from an initially flat shape into a
hemispherical shape. The result of simulation is shown in Fig.
6.
III. EXPERIMENTAL SETUP
A. Electrochemical system
The ECM system (see Fig. 7) was constructed to generate
micro dimple and hole array in work piece. Direct current
controlled by a constant voltage is provided from the power
supply with 150 A maximum output current, 30 V maximum
output voltage. In addition, a time relay was synchronously
used to control machining time accurately during EMM. Table
1 lists the machining conditions.
http://www.ijettjournal.org
Page 262
International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 5 - Dec 2013
IV. EXPERIMENTAL RESULTS AND DISCUSSIONS
A. Electrochemical system effect of insulation layer thickness
on dimple machining
In order to optimize the insulation layer thickness
experiments on the influence of insulation layer thickness on
the etched dimple profile have been carried out.
Fig. 8 shows a convex structure in the middle of the dimple
measured by the three dimensional profile meter. The dimple
is produced by a mask with an insulation layer of 50 µm
thickness. The experimental result is accordant with the
current density distribution on the anode surface analysed
before. To solve this problem, a thicker mask is used. As
shown in Fig. 9, while the thickness of the insulation layer is
100 µm, the convex in the dimple centre will disappear.
Fig. 5: Program flow diagram of shape evolution simulation.
Fig. 8-a: 3D optical profile of a dimple with convex structure
Fig. 6: Shape evolution at the anode.
Fig. 8-b: The cross-sectional shape of a dimple with convex
Fig. 7. Sketch of ECM experimental system.
The size and spacing of the obtained dimple and hole were
measure with three-dimensional profile meter and scanning
electron microscope (SEM).
B. Friction tests
To verify the effect of micro-dimples array on the hard
chrome coating sample, friction tests were carried out using a
friction tester. The sample was driven by a motor to a certain
rotational speed which could be adjusted between 0 r/min and
1000 r/min. The sliding contact zone was fully soaked in
diesel oil. The temperature was kept at 25o C throughout the
tests. Each friction test was carried out with a normal load of
500 N, which was detected and controlled by load cells.
ISSN: 2231-5381
The parameters influencing the dimple dimensions, such as
cell voltage, current density, and machining time, were
studied and optimized. By controlling these parameters,
micro-dimple array with hundreds of micrometers in diameter
and several micrometers in depth, was produced as shown in
Fig. 10.
The proposed method could also be used to produce hole
array on thin metal sheet. For smaller taper of the hole and
shorter machining time, the modified through-mask EMM is
introduced in both the sides of the anode work piece plate (see
Fig. 11). The patterned features on the couple masks are
perfectly aligned by a special fixture. Electrochemical etching
is simultaneously taking place on both sides of the work piece
during machining. The SEM photograph of Fig. 12 shows that
http://www.ijettjournal.org
Page 263
International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 5 - Dec 2013
hole array with good circularity can be obtained by two-sided
process of modified through-mask EMM.
The material of the work piece is 1Cr18Ni9Ti. The
thickness of the work piece is 0.3 mm. The cell voltage
applied is 18 V. In this way, the proposed method is a low
cost and efficient process in the production of metallic parts
with micro hole array.
(a) 3D optical profile of a dimple centre will disappear of a single dimple
Fig. 13: Effect of micro-dimple array on the friction coefficient under a
normal load of 500 N
(b) The cross-sectional shape of a single dimple.
Fig. 9: Profiles of a single dimple in chrome coated surface. (a) 3D optical
profile of a dimple center will disappear.single dimple, (b) the cross-sectional
shape of a single dimple.
Fig. 10: SEM micrograph of micro-dimple array in chrome coated surface.
Fig. 11: Schematic of two-sided process of modified through-mask EMM.
dimple depth of 10 mm. It was thus verified that the micro-dimples
B. Effect of micro-dimple array on friction coefficient
In order to assess the effectiveness of micro-dimple array
on friction coefficient, changes in friction coefficient under a
normal load of 500 N were evaluated using two types of
samples: one was the hard chrome coated surface without
micro dimples, and another was with micro-dimple array. The
dimple size was 240 µm in diameter and 4 µm, 10µm and 22
µm in depth, respectively.
The test results for the samples are shown in Fig. 13.
Compared to the non-dimpled surface, the samples with
micro-dimples array reduced friction coefficient successfully.
The friction coefficient decreases gradually with the dimple
depth when it ranges from 4 µm to 10 µm. However, it rapidly
increases as the dimple depth further increased to 22 µm. In
addition, with the sliding velocity increasing, the reduction in
friction coefficient was obvious with dimple depth of 10 µm.
It was thus verified that the micro-dimples array had a great
potential for reducing friction, if the micro dimples was set at
appropriate dimension.
V. CONCLUSIONS
A modified through-mask EMM has been developed.
Numerical simulation and experiments have demonstrate that
a sheet of insulation layer, coated with conductive metal layer
and perforated with through holes, could be used as a mask to
electrochemically etch microstructures while it is closely
attached to a work piece surface instead of being bonded to
work piece. Arrays of holes or dimples in the scale of several
hundred microns have been produced.
REFERENCES
(a) Hole array, (b) Amplified SEM photo of hole array, (c) Cross- sectional
shape of a single hole
Fig. 12: Photography of hole array fabricated by two-sided process of
modified through-mask EMM. (a) Hole array, (b) amplified SEM photo of
hole array, (c) cross- sectional shape of a single hole.
ISSN: 2231-5381
[1].
Bruzzone A-A-G, Costa H-L, Lonardo P-M, Lucca D-A (2008)
Advances in engineered surfaces for functional performance. Annals of
the CIRP 57/2:750–769.
[2].
Sen M, ShanH-S (2005) A reviewof electrochemicalmacro- to microhole drilling processes. International Journal of Machine Tools &
Manufacture 45:137–152.
http://www.ijettjournal.org
Page 264
International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 5 - Dec 2013
[3].
Li L, Diver C, Atkinson J, Giedl-Wagner R, Helml HJ (2006)
Sequential laser and EDM micro-drilling for next generation fuel
injection nozzle manufacture. Annals of the CIRP 55/1:179–182.
[4].
Rajurkar K-P, Levy G, Malshe A, Sundaram M-M, McGeough J, Hu X,
Resnick R, DeSilva A (2006) Micro and Nano Machining by ElectroPhysical and Chemical Processes. Annals of the CIRP 55/2:643–666.
[5].
Natsu W, Ooshiro S, Kunieda M (2008) Research on Generation of
Three-Dimensional Surface with Micro-Electrolyte Jet Machining.
CIRP Journal of Manufacturing Science and Technology 1(1):27–34.
[6].
Natsu W, Ikeda T, Kunieda M (2007) Generating Complicated Surface
with Electrolyte Jet Machining. Precision Engineering 31(1):33–39.
[7].
Kim B-H, Na C-W, Lee Y-S, Choi D-K, Chu C-N (2005) Micro
Electrochemical Machining of 3D Micro Structure Using Dilute
Sulfuric Acid. Annals of the CIRP 54/1:191–194.
[8].
Datta M, Landolt D (2000) Fundamental Aspects and Applications of
Electrochemical Microfabrication. Electrochimica Acta 45:2535–2558.
[9]
Zhu D, Wang K, Yang J-M (2003) Design of Electrode Profile in
Electrochemical Manufacturing Process. Annals of the CIRP 52/1:169–
172.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 265