Simulation and Analysis of Electrolyte Flow Pattern in ECM for L-Shaped Tool Using CFD

IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 14, Issue 1 Ver. V (Jan. - Feb. 2017), PP 70-74
www.iosrjournals.org
DOI: 10.9790/1684-1401057074 www.iosrjournals.org 70 | Page
Simulation and Analysis of Electrolyte Flow Pattern in ECM for
L-Shaped Tool Using CFD
Gali Chiranjeevi Naidu1
, U Sainadh2
, K Dharma Reddy3
123
Department of Mechanical Engineering, SVU College of Engineering, Tirupati, Andhra Pradesh, India
Abstract: Electrochemical machining (ECM) is a non-traditional machining method based on principle of
reverse electroplating (anode loses metal to cathode). ECM uses principal of electrolysis to remove metal from
the work piece. Due to improper tool design of complicated shapes, there are chances of passivation and boiling
of electrolyte in ECM process that causes poor machining. In this present study three dimensional flow pattern
of ECM process has been simulated using Computational Fluid Dynamics (CFD) in L-shaped tool models. This
work is for optimizing the design of L-shaped tool and to study the flow pattern, current density distribution,
velocity profile, temperature pattern, turbulence and final shape change of workpiece top surface. ANSYS was
used for design and simulating this CFD problem, the geometrical model consists of a circular workpiece made
with Iron, 20% brine solution (NaCl) as electrolyte and L-shaped copper tool with different kind of grooves.
Keywords: CFD, ECM, flow pattern; IE, MRR, passivation, temperature profile, velocity profile.
I. Introduction
Electrochemical machining (ECM) is a method based on electrochemical process for removing metals
in production. It is working with hard materials which are impossible for conventional machining process. This
method is useful for all conducting metals. Now a day we use high strength, low weight metallic and
intermetallic alloys for many applications. High cutting forces and imperfection in cutting give low preference
to conventional milling and turning process. This is uneconomical too due to tool wear and low machining rates.
ECM is opposite of electrochemical or galvanic coating or deposition process. Thus ECM is the controlled
removal of metal by anodic dissolution in an electrolytic cell in which the work piece is the anode and the tool is
cathode. The electrolyte is pumped through the gap between the tool and the work piece, while direct current is
passed through the cell, to dissolve metal from the work piece. Material removal rate in electrochemical
machining is analyzed in context of over voltage and conductivity of the electrolyte solution. Electrolyte has
three main functions in ECM: It carries the current between the tool and work piece, it removes the products of
the reaction from the cutting region, and it removes heat produced in operation. Normal electrolyte used for
ECM for all common metals & alloys is solution of Sodium Chloride (NaCl) in water. They react with the work
piece and form a salt which dissolves in electrolyte. Thus if a job is steel (Fe) and electrolyte is common salt
(NaCl) the following reacting takes place at the anode.
II. Working Principle
Electrochemical machining removes material from the work piece by electrochemical process. The
working principle is anodic dissolution in which the work piece as anode and the tool as cathode. Both
electrodes are immersed in the electrolyte and electrical applied to these electrodes. The electric conduction is
achieved through the movements of ions between the anode and cathode through the electrolyte. The current is
passing through the system of arrangements will cause the dissolution of anode. This process of electrolysis is
working based on Faradays law of electrolysis. The principal and process detailing of ECM for steel is shown in
Fig. 1, generally a neutral salt solution of sodium chloride (NaCl) is taken as the electrolyte.
Fig. 1: Principle of ECM

Simulation and Analysis of Electrolyte Flow Pattern in ECM for L-Shaped Tool Using CFD
1.1. Power Supply
Power supply is required with low value of voltage and high value of current. Current of the order of 1000-
40,000 A is generally required and 5-25 V is applied to overcome the resistance at the gap.
1.2. Servo System
The servo system controls the tool motion relative to the work piece to follow the desired path. It also
controls the gap width within such a range that the discharge process can continue. If tool moves too fast and
touches the work piece, short circuit occurs. Short circuit contributes little to material removal because the
voltage drop between electrodes is small and the current is limited by the generator. If tool electrode moves very
slowly, the gap becomes too wide and electrical discharge never occurs.
1.3. Tool Feed Rate
In ECM process, an inter electrode gap of about 0.01 to 0.05 mm is maintained between the tool and
work piece. For smaller gap, the electrical resistance between the tool and work-piece is least and the current is
the maximum and accordingly maximum metal is removed. The tool is feed in to the work-piece depending
upon how fast the metal is to be removed. The movement of the tool slide is controlled by a hydraulic cylinder
giving some range of feed rate.
1.4. Electrolyte Flow Rate
Electrolyte flow is a very important and critical parameter in the analysis of electrochemical
machining. Insufficient and improper electrolyte flow in the IEG may cause poor machining. The effect of
cavitation, stagnation, and vortex flow can avoid up to a certain extent by avoiding sharp corner. The entire flow
path has an approximate radius of 0.7 to 0.8 mm. Flow will not cover all area of the work-piece initially. These
difficulties can be avoided by using restriction techniques. Fig. 1.2 shows a tool with no sharp corners.
1.5. Material Removal Rate
Material removal rate (MRR) is the rate at which the work-piece material is dissolved per unit time. It
is primarily a function of feed rate which signifies the current passed between the work-piece and the tool. As
the tool advances towards work, inter electrode gap decreases and current increases which cause more metal
removal at a rate corresponding to the tool advance. A stable spacing between the tool and work is thus
established. It may be noted that high feed rate not only is productive but also produces best quality of surface
finish.
III. Modelling And Simulation
The analysis techniques, geometric modeling and boundary conditions are explained in this chapter.
ECM set up consists of a work-piece, tool and an electrolyte solution. Work-piece should be electrically
conducting material and the tool may or may not be. Commonly used electrolytes are NaCl solution and
NaNO3. To get required shape in the work-piece, tool should be designed properly. The shape of the tool affects
the critical parameters of machining. Another important aspect in the modelling of ECM is the flow pattern of
electrolyte and the various intervening factors those are affected by the two phase flow pattern of electrolyte.
1.6. Geometrical Modelling
Finite element based commercial CFD software package, ANSYS, which operated under the
Windows7 64-bit operating system, was used for the simulation study. In the present simulation process, the
modelling is done with ANSYS design modeler Module of ANSYS software. The L shaped tool with central
through hole model is used for the simulation study. The initial shape of the work-piece is circular in shape with
60 mm diameter and 20 mm height. Model of work-piece is shown in Fig. 2. Electrolyte used for this simulation
is brine solution (15% NaCl). The electrolyte starts flowing with a constant diameter of 3 mm from the inlet of
the tool. The long side of the L-shape is having 30 mm length and short side of 15 mm length and the central
hole has diameter of 3mm. Top view of the tool is shown in Fig. 3 and 3D view is shown in Fig. 4. Inter
electrode gap (IEG) for all the models is kept constant at 0.5 mm. The key dimensional feature of the physical
model is as shown in table 1. The complete physical model of workpiece tool set up is as shown in Fig. 5.

Table 1: Element type
Sl.No Component Material Physical state Shape Dimension(mm)
1 Work-piece Iron Solid Cylindrical 60 dia. X 20 ht.
2 Tool Copper Solid L-shaped Arm 30 X Width 15 X Height 50 X central
hole 3Ø
3 Medium Brine Fluid - -
1.7. L-Shaped Tool with Central Through Hole
A simple L shaped model having a central through hole with a diameter of 3mm and height of 50 mm.
This centre of the hole is fixed on (-7.5,-7.5) coordinate in the XZ plane. Fluid is flowing through the through
hole and flow out through the IEG. Top view of the tool is shown in Fig. 3 and 3D view is shown in Fig. 4. Inter
electrode gap (IEG) is kept constant as 0.5mm.
1.8. Meshing
Model is meshed using ANSYS Mesh Module in ANSYS commercial software. The quality of mesh is
a relevant factor in the case of appropriate geometry of the model and accuracy of the results. This can be
expressed in terms of orthogonal quality. If the value of orthogonal quality is coming near to one then our mesh
quality is good and it gives better results. At the same time if it is coming near to zero, then the mesh gives bad
results. Advantages of this method is that it uses the geometry only to associate the boundary faces of the mesh
to the region of interest there by ignoring gaps, overlaps and other issues that present in other meshing tools.
However, the required timing of simulation for the finer meshes was found to be 35% higher than intermediate
mesh and 190% higher than the coarse mesh. Materials used are copper for tool, iron for work piece and brine
(15% NaCl) as the electrolyte solution.
1.9. Boundary Conditions
Before considering the boundary conditions, the computational domains should be specified. In this
simulation three domains are being used such as two solid domains and a fluid domain. One solid domain for
work-piece and other is for tool. Materials of solid domain are considered as pure solids. Morphology of
materials in the solid domain is given as continuous solid and reference temperature is given 298K. Electric
potential model with automatic value is chosen from Electromagnetic model. Fluid domain is constructed for
electrolyte. Two materials are taken for fluid domain as it is a two phase flow analysis. Morphology for fluid
domain is taken as continuous fluid for brine and dispersed fluid for hydrogen bubbles. The properties of the
materials used in these domains are set as per the values in the Table 2.

Table 2: Material properties
IV. Results And Discussions
The analysis of the results and discussion of the model generated in ANSYS as per the modelling. It shows the
crucial parameters affecting overall machining process of ECM in terms of contours from which we can predict
the variation of these parameters in the IEG and their effects.
4.1. Critical Parameters Analysed In Simulation
4.1.1. Volume Fraction Profile
Fig. 6 shows the volume fraction profiles of the model generated. The inlet velocity for this simulation study
was taken as 40 m/s. The volume fraction contour has shown the volume fraction of brine in the homogenous
mixture of continuous fluid brine and a dispersed fluid hydrogen bubble.
4.1.2. Velocity Profile
Fig.7 show the velocity profile for model respectively with an inlet velocity of 40 m/s, which indicates that
velocity of two phase electrolyte is increased from the groove to the boundary partly due to reduction in area of
flow and partly due to formation of hydrogen bubbles resulting in more turbulence.
4.1.3. Pressure Profile
The pressure profiles describe about the variation in pressure in the IEG on the plane of machining area. As in
model, there is very large amount of production of hydrogen bubbles and because of cavitation effect, the
pressure increases at a large number of nucleus sites from the groove outlet towards the outer boundaries
showing the places of hydrogen bubbles and hence high pressure zones as shown in Fig. 8.
4.1.4. Temperature Profile
Pattern is a very crucial aspect for this study. As can be seen from the Fig. 9, the temperature is least at the
groove outlet and goes on increasing rapidly as we move to outside for model. It crosses the boiling point of
brine which in turn produces phase change and production of hydrogen bubbles as secondary dispersed phase.
Properties Brine Copper Iron Air
Molar mass (kg/kmol) 58.44 63.55 55.85 -
Density (kg/m3
) 1050 8933 7860 -
Specific heat (J/kgK) 3760 385 460 -
Dynamic viscosity (Pa s) 0.001 - - -
Thermal conductivity (W/m K) 0.6 401 80 -
Electrical conductivity (S/m) 8.43 5.96E+07 1E+07 -
Convection coefficient (W/m2
K) 1000 - - 100

4.1.5. Heat Flux Pattern
Heat is generated in the IEG due to joule’s heating. By appropriately designing tool shape, the heat
generated and thus the overheating can be avoided. It describes the heat flux pattern for the model. In this
simulation, we have assumed that the heat generated in the IEG is only due to Joule’s heating. Heat flux is
nothing but the heat generated per unit machining area. For model, the value is less near the groove outlet. But
as we proceed towards the outer, the heat flux increases to a very high amount. This higher value of heat flux
exists all over the outer boundary of L-shape in a comparatively larger area. The minimum amount of heat flux
is -2.823 W/m2
and maximum amount is 3.763 W/m2
.
V. Conclusion
Three dimensional two phase flow pattern analysis of electrochemical machining with L-shaped tool
provides fundamental idea of velocity distribution, pressure pattern, temperature profile, turbulence etc. in the
IEG. A cylindrical Iron work-piece, L-shaped Copper tool and 20% brine solution as electrolyte was considered
in this analysis. This tool slot design was modeled using Design Modeler of ANSYS and subsequently analysed.
To get consistent and good results, the Model was meshed with Fine mesh resolution. The model is analysed
with inlet velocity of 40 m/s and with a residual target of 1x10-4
. Volume fraction profile for brine indicates that
more hydrogen bubbles are generated and the velocity profile indicate very high value at the outer side of
groove due to the turbulence created because of the generation of hydrogen bubbles. Pressure profile describes
the pressure in the machining area and it has randomly generated high pressure spots throughout the machining
area except at groove outlet because of the cavitation effect at the points of hydrogen bubbles generation.
Similarly, temperature pattern indicates boiling effect in the machining area resulting in the generation of
hydrogen bubbles.
References
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International Mechanical Engineering Congress & Exposition IMECE, November 13-19, Lake Buena Vista, Florida, USA.
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[5] Mukherjee, S.K., Kumar, S., Srivastava, P.K. and Kumar, A. (2008) Effect of valency on material removal rate in electrochemical
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Simulation and Analysis of Electrolyte Flow Pattern in ECM for L-Shaped Tool Using CFD

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