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Recent Developments in Electro Chemical Machining-A Review

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 International Journal of Technical Innovation in Modern
Engineering & Science (IJTIMES)
Impact Factor: 5.22 (SJIF-2017), e-ISSN: 2455-2585
Volume 5, Issue 04, April-2019

Recent Developments in Electro Chemical Machining- A Review

Ashish Kumar1, P.S. Rao2
1
ME Student, Department of Mechanical Engineering, NITTTR Chandigarh,
2
Assistant Professor, Department of Mechanical Engineering, NITTTR Chandigarh

Abstract- Electrochemical machining (ECM) is a technique of removing metal by an electrochemical method. It is

typically used for mass production and is used for working enormously hard materials or materials that are difficult to
machine by conventional techniques. ECM give an enhanced alternative in producing precise 3-D complex shaped
and components which are difficult-to-machined by conventional methods.
The aim of this paper is to study some electrochemical processes for material removal. The parameters such as tool
feed rate and the applied voltage also plays a vital role in increasing the material removal rate. Higher surface quality,
low tool wear, higher in material removal rate have been studied by using modern unconventional machining process
like electrochemical machining operations.

Keywords- Electrochemical machining, Electro chemical honing, Electrochemical Micro Machining, Electro
Chemical Drilling, Electro Chemical jet machining

I. INTRODUCTION

1.1 Principle of ECM

Electrochemical machining is a technique of removing metal by an electrochemical process. It uses an electrolyte and
electrical current to ionize and remove metal atoms. ECM is a reverse process of electrochemical coating. The important
process parameters in electrochemical machining are tool feed rate, material removal rate, electrolyte flow rate, surface
roughness and applied voltage. In electrochemical machining, there is a reaction occurring at the electrode or workpiece
and at the cathode or tool along within the electrolyte. As the potential difference is applied between the tool (cathode)
and the workpiece (anode), the negative ions move towards the workpiece and positive ions move towards the tool as
shown in figure 1.
The main focus on electrochemical machining is to find out the optimum process parameter with various electrolyte
material, varying the electrode gap and applied voltage.

Figure 1: Schematic diagram of ECM

1.2 Literature review

The improvement in the material removal rate of electrochemical machining experimentally was investigated. The
Material Removal Rate (MRR) calculated for different electrolytes condition on aluminium and stainless steel.
The experimental results shows that the theoretical and actual material removal rates by using sea water as an
electrolyte in electrochemical machining on aluminum alloy and steel alloy gives better MRR [1].

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Volume 5, Issue 04, April-2019, e-ISSN: 2455-2585, Impact Factor: 5.22 (SJIF-2017)

The metal removal rate(MMR), overcut and surface roughness (Ra) of mild steel work piece of diameter 50 mm as
by using copper electrode and brine solution as electrolyte by using Taguchi L9 orthogonal array approach was
determined. Then optimized the best setting of process variables for higher MRR, lower surface roughness and
overcut. Three parameters selected as process variables are tool, feed rate, voltage, and electrolyte concentration.
Investigation has been done on Mild steel of 50mm diameter by electrochemical machining. Three factors were
considered that are voltage, tool rate and electrolyte concentration. These experiments were conducted to obtain
high MRR, low overcut and low surface roughness. Feed rate is typically affected process parameter in metal
removal rate (MRR), then comes voltage and at last electrolyte concentration.. For surface roughness, feed rate
effects it most then concentration and at last voltage. Tool feed rate effects most to overcut at second rank is
voltage and at third rank is concentration which affects most to overcut [2].
Electro chemical machining of Special stainless steel Cr 12 Ni9 MO4 Cu 2, which has multiple composition and
inhomogeneous tissues; short circuiting frequently occurred during machining when using conventional
electrolyte processing was described. They analyzed the reason of machining is difficult from the material
composition and structure. They used the NaNO 3 and NaClO3 electrolyte composite to select the appropriate
concentration, and then by using the orthogonal experiment and gray relational analysis method. Under optimum
conditions of 20 V, an electrolyte composite concentration of 41 gram per litre NaClO3 and 178 gram per litre
NaNO3 , a feed rate of 0.7 mm/min, and an electrolyte pressure of 0.8 MPa, a material removal rate of 100.8 mm3
/min, a surface roughness of Ra 0.8, and a side gap of 0.16mm were produced. At the same voltage, with an
increasing cathode feed rate, the metal removal rate was shown to decrease in side gap while increase the surface
roughness. Under the same cathode feed rate, the metal removal rate decreased, while the side gap and the surface
roughness increase as the electrochemical machining application voltage increases. Their studies proves that using
a certain concentration of electrolyte composite is a simple, low-cost, and feasible approach in improving
efficiency and quality [3].
The Electro Chemical Machining for machining of LM25 al/10% SiCp composites during electrolysis with sodium
chloride as electrolyte and copper as tool was investigated. The process parameters such as applied voltage, MRR,
electrolyte concentration, tool feed rate and electrolyte flow rate were determined by performing experiments on
METATECH ECM equipment. The mathematical models were developed based on response surface methodology
and were tested by ANOVA and the parameters were optimized by NGSA-2 approach. The results showed
optimized Metal removal rate and surface roughness. Optimization will increase production rate considerably by
reducing machining time [4].
The Electro Chemical machining of stainless steel EN series 58 A (AISI 302 B) was described. They investigated
the effect of voltage variation on metal removal rate. Inter electrode gap (IEG) was maintained constant during the
experimentation. They found that the MRR improved significantly by increasing the voltage [5].
The material removal rate by controlled anodic dissolution at atomic level of the work -piece with a hollow
cylindrical copper electrode electrically conductive, stainless steel electrode and aluminium electrode, Mild Steel
as work piece was investigated. The investigation carried out to find the influence of machining parameters such
as Electrolyte concentrations, current density and electrodes. From the experiment, they determined that by the
use of different electrolyte concentrations there is a change in MRR. It increases as electrolyte concentration
increases. Also by using various types of tools like stainless steel, aluminium and copper it affects the material
removal rate. Out of which copper tool material showed good results as compared to the aluminium and stainless
steel. By increasing in current density, the material removal rate is also increases. At 10 amp metal removal rate is
greater than at 5 amp for given tool material and electrolyte concentration [6].
The Electro Chemical Machining of SS AISI 30 4 work piece Taguchi approach of experimentation showed the
best performance in terms of MRR, and surface roughness can be obtained by variation in current, feed rate and
electrolyte concentration. It was observed that metal removal rate increased with increase in current. while, high
MRR is achieved by increasing the speed of chemical reaction [7].

1.3 Electro chemical honing

Electrochemical honing is a process in which the metal removal capabilities of electrochemical machining are combined
with the precision capabilities of honing. This process involves a rotating and reciprocating tool inside a cylindrical
component. The material is removed through anodic dissolution and mechanical abrasion 7.5% or more, of the material
removal, occurs through electrolytic action. As with conventional electrochemical machining, the workpiece is the anode
and a stainless steel tool is a cathode.

Electrochemical honing can offer a unique range of benefits to the machined surface which cannot be obtained by either
of the processes when applied independently [7]. The main benefits of ECH process are the complex geometry can be
finished with a single setting, high rate of finishing which is virtually independent of removal material without heat and
material hardness because the material is removed at an atomic level [8]. Electrochemical honing was used first time in
1979 for making helical gear using specially designed helical gear as cathode and NaNO3 as electrode [9]. A model was
established for metal removal rate using pulsed current, this system was successfully used for making micro-holes and
for profile refinement. They compared successfully experimental data to theoretical data within 9.99% [10]. A very
minor amount of material was removed from the workpiece by an electrochemical honing process and remaining by

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Volume 5, Issue 04, April-2019, e-ISSN: 2455-2585, Impact Factor: 5.22 (SJIF-2017)

electrolyte [11]. In 1963-65, the idea of micro material removal from the workpiece by anodic dissolution was developed.
This idea was used to improve the productivity and performance of manufacturing parts which was not possible with the
existing conventional honing process [12-15]. Electrochemical honing is a highly productive alternating finishing process
for the bevel gears [16]. The theoretical model was developed for material removal rate and surface roughness of the
bevel gear by an electrochemical honing and for fine finishing of all the teeth of a bevel gear eliminating need to provide
the reciprocating motion to the gear workpiece [17-18]. The input process parameters like electrolyte composition,
electrolyte temperature, processing time and electrolyte concentration were studied and they found a significant role in
minimization of roughness [19].

1.4 Electro Chemical Micro Machining

Electro Chemical Micro Machining (ECMM) is used to increase the production of complex micro structures such as
semi-conductors, ultra-precision machinery. A suitable manufacturing process for mass production of these micro scale
component needs to be established. The principle of electro Chemical Micro Machining has been investigated the
influence of ultrashort voltage pulse and the wire electrode amount on the machining process. In recent years, micro-
machining has increased the importance in mass production of micro complex components because manual drilling and
milling machines are unsuitable for many micromachining application due to the stress reported on the workpiece.

1.5 Electro Chemical Drilling (ECD)

Electrochemical drilling is a useful process to produce small holes with a large aspect ratio on hard-to-machine
materials. Recently, more research has focused on neutral salt electrolytes because they are less harmful to the
environment. Whereas, more problems have been caused to the removal of waste products, especially in deep-hole
drilling. Usually, an electrolyte flow with constant pressure control is adopted in Electro Chemical Drilling, which
might result in the poor removal of waste products at depth because of pressure loss. An electro chemical drilling
method with a constant electrolyte flow is obtain a consistent ability to remove insoluble waste products from
machining gap. Experiments of Electro Chemical Drilling with both constant flow electrolyte pressure are conducted
on workpieces. The results shows that when a constant electrolyte flow rate is applied, the machining currents are much
smoother and the profile of machined holes is also uniform. In addition, the pressure variation in the constant flow
method increases linearly with machining depth, electro Chemical Drilling with a constant flow also has an increased
feed rate [20].

Figure 2: Processing principle of Electro Chemical Drilling [20]

Electrochemical drilling (ECD) uses metal tubes as cathodes, which allows electrolyte pumped through the pipe and
into the machining area. When the power is on, workpiece would start to dissolve. Then with the feeding of cathode,
the dissolve continues, and eventually, hole 3 with a shape similar to the cathode would be produced (Fig.1). As an
important branch of electrochemical machining, ECD was established for drilling holes with a large aspect ratio on
hard-to-machine metals. Though it would be difficult to fabricate holes with diameters smaller than 0.8mm, ECD
produces a good machined surface and has relatively high stock removal rates [21]. Due to its advantages, ECD has
various applications ranging from the aerospace and automotive industries to the die mould industry [22].

1.6 Electro Chemical jet machining

Electro-Chemical jet machining (ECJM) employs a jet of electrolyte for anodic dissolution of workpiece material but
there is a lost machining effect which leads to diminishing the effectiveness of machining. The primary method of
material removal occurs when an electrical potential is applied between the nozzle and workpiece resulting in anodic

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Volume 5, Issue 04, April-2019, e-ISSN: 2455-2585, Impact Factor: 5.22 (SJIF-2017)

dissolution. ECJM is very effective to manufacture complex shapes with the help of multi-dimension mechanical motion,
which can meet the complex design requirement [23]. Electro-Chemical jet machining is widely used for drilling small
cooling holes in aircraft turbine blade and for producing microelectronic parts. In Electrochemical Jet Machining (EJM)
material removal is limited to the exposed substrate directly below the electrolyte jet therefore not requiring additional
masking. This is due to the confinement of the current density field in the working gap [24].

Figure 3: Schematic of Electrochemical Jet Machining apparatus and process [25]

1.7 Electro Chemical Discharge Machining

A study of all machining processes indicates that any scheme for removing material in the form of small particles in a
controlled fashion can be used for the shaping of objects. To circumvent material and shape problems, quite often the
approach adopted for machining is to cause the melting of a small portion of the workpiece by means of intense localized
heat generation. By controlling the location of the heat source in a proper way, the required shape of the workpiece can
be achieved.
One phenomenon used to produce intense localized heat generation without using any sophisticated technology like
electron beam or laser beam is the electrochemical discharge. Figure 4 shows an electrochemical cell where one electrode
is very small and the other is relatively much larger. When these electrodes are connected to a voltage source (either AC
or DC) an electrical discharge can be seen at the tip of the smaller electrode if the supply voltage exceeds a critical value.
This is known as electrochemical discharge which takes place between the tip of the smaller electrode and the electrolyte
in its immediate neighbourhood [26].

Figure 4: Electrochemical discharge machining [27]

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Volume 5, Issue 04, April-2019, e-ISSN: 2455-2585, Impact Factor: 5.22 (SJIF-2017)

1.8 Electro Chemical Grinding

Electrochemical grinding (ECG) is a relatively new process which has a combination of electrochemical machining and
mechanical grinding processes. Nowadays, ECG is more important due to its industrial applications as material removal
is independent of the strength and prior treatment of workpiece materials. The electrochemical grinding process is
relevant for shaping or grinding an electrically conductive material.
The process of ECG is very similar to ECM except that the cathode is a specially constructed grinding wheel instead of a
cathodic shaped tool. Diamond and aluminium oxide are used as an insulating abrasive material for grinding wheel and
this grinding wheel is rotated tool with abrasive particles on its periphery as shown in fig.5. The abrasive wheel is
attached to a spindle, when the voltage is applied the rotary wheel is fed perpendicular to the workpiece surface as shown
in fig.5.The current density and applied voltage are used in the range of 45-350 amp and 5 to 45 V respectively.

Figure 5: Schematic diagram of electrochemical grinding [28]

II. CONCLUSION

The electrolyte concentration influenced the material removal rate were found by the researchers, hence, by obtaining the
favorable concentration of the electrolyte one can easily achieve the higher Material removal rate. The parameters such
as tool feed rate and the applied voltage also plays a vital role in increasing the material removal rate. Higher surface
quality, low tool wear, higher in material removal rate have been studied by using modern unconventional machining
process like electrochemical machining operation, Electro Chemical Drilling, Electro Chemical jet machining, Electro
Chemical Discharge Machining, Electro Chemical Grinding etc.

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