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Chapter 5

Electrochemical Based Hybrid Machining

Dr. J. Ramkumar1 and Prabhu Dayal2

1Professor and 2Research Student

Department of Mechanical Engineering

Micromanufacturing Lab, I.I.T. KanpurMicromanufacturing Lab, I.I.T. Kanpur

Organization of the presentation

1. Introduction-Electrochemical Based Hybrid Machining

2. Classification of Ecm-Based Hybrid Machining Process

3. Assisted ECM Based Hybrid Process (Laser-assisted jet ECM, Ultrasonic-assisted ECM, Abrasive-assisted ECM )

4.Combined ECM Based Hybrid Process(Laser-ECM, Electrochemical Discharge Machining(ECDM), Combined Electrochemical

Grinding, Mechano- Electrochemical Machining, Electrochemical honing )

5. Concluding Remarks

6. Summary of ECM-Based Hybrid Process

7. References

2Micromanufacturing Lab, I.I.T. Kanpur

Introduction-Electrochemical based Hybrid Machining

Several hybrid machining process are resorting

to ECM as one of the candidate process

because of the following advantages of ECM;

1. Independent of workpiece hardness.

2. Complex shapes can be machined.

3. ECM has no tool wear and high surface

finish as dissolution occurs at atomic level.

4. Material removal rates can be controlled

from electrical parameter( voltage , current ,

energy) and pulse characteristics ( pulse

frequency , on time , duration , duty cycle).3

Fig: Ultrasonic – two axis vibration Assisted Polishing[1]

ECM- based hybrid machining process will

combine other types of energies( mechanical,

Abrasive, lase/ heat , ultrasonic) to enhance the

material removal of ECM process. Based on the

types of combined energies, ECM based hybrid

machining process can be classified as-

1. Assisted ECM

2. Combined ECM

ECM BASED HYBRID MACHINING PROCESS CLASSIFICATION

Assisted ECM based hybrid process Combined ECM based hybrid process

Laser-assisted jet ECM

Ultrasonic-assisted ECM

Abrasive-assisted ECM

Laser-ECM

Electrochemical Discharge Machining(ECDM)

Combined Electrochemical Grinding

Mechano- Electrochemical Machining

Electrochemical honing


Laser assisted jet electrochemical machining

(LAJECM) is a hybrid process, that combines

a laser beam with an electrolyte jet thereby

giving a non-contact tool electrode that

removes metal by electrochemical dissolution.

The laser beam effectively improves the

precision of LAJECM as it is able to direct the

dissolution to specifically targeted areas. This

prevents the machining from unwanted areas

due to stray current.

Assisted ECM Based Hybrid Process-(1) LAJECM

5

Fig : LAGECM Apparatus Layout (a) Machining Chamber(b) Jetcell [1]

Fig : Energy Balance of LAJECM[1]Micromanufacturing Lab, I.I.T. Kanpur

LAJECM PROCESS PRINCIPLES

LAJECM combines two different sources of energy simultaneously: energy of ions (ECM) and

energy of photons (a laser beam). The main aim of combining a laser with a jet of electrolyte

(giving a laser-jet) is to assist electrochemical dissolution from a specific workpiece surface area.

Electrochemical dissolution is the main material removal mechanism supported by the parallel

action of the low power (average power of 375 mW) laser beam.

Fig. : illustrates the principles of hybrid LAJECM [1]6

Fig: Volumetric Removal Rate Vs. Voltage and

IEG for Stainless Steel Micromanufacturing Lab, I.I.T. Kanpur

Thermal energy enhances the kinetics of

electrochemical reactions providing faster

dissolution. It also aids in breaking down the oxide

layer found on some materials in certain

electrolytes that inhibit efficient dissolution.

The advantage of LAJECM is that the laser beam

can be easily aimed on the workpiece surface and

therefore, together with the flushing electrolyte

jet, dissolution can be accelerated in any desired

direction. This ‘localisation effect’ enhances

accuracy by limiting stray machining action .

Fig. 2. (a) Jet-ECM without directed dissolution, and

(b) LAJECM with intensified dissolution in the

localised zone.[1]

7

Fig: Micrograph of a hole drilled with LAJECM [1]

Micromanufacturing Lab, I.I.T. Kanpur

1. Basically the laser beam must be maintained

coaxially with an electrolyte jet and in a single

spot on the workpiece. This is obviously

difficult due to the hydrodynamic behaviour of

the jet as well as the gas evolution at the

cathode.

2. Gas evolution may also disturb a jet making

the electrolyte flow more turbulent and thus

causing the laser-jet spot to drift.

3. Electrolyte boiling and electrical discharges

8

Disadvantages of LAJECM Electrical Discharge

crater Located to one

side of the cavity edge

Cavity Edge

Fig: Spark damage due to electrolyte boiling [1]


Ultrasonic Assisted Electrochemical Machining (USAECM)

1.To improve technological factors in electrochemical

machining, introduction of electrode tool ultrasonic vibration

is justifiable. This method is called as ultrasonically assisted

electrochemical machining (USAECM).

2.The objective of ultrasonic assistance in ECM is multifold.

The ultrasonic vibration facilitate removal of reaction by-

product and heat from machining zone , favors diffusion ,

minimizes passivation , creates optimal hydrodynamic

conditions, improve aspect ratios, and influences electrolytic

reactions through sonochemical reaction.

9

Fig : Schematic of ultrasonic-assisted

electrochemical machining [2]


Fig. Ultrasonic Assisted Electrochemical Machining[2]

The set mainly consist of a direct current (DC) pulsed power supply, motion control system,

electrolyte circulation system, ultrasonic head, which consist of a transducer coupled with

ultrasonic generator, and horn for transmitting ultrasonic energy to the tool. The use of

ultrasonic frequencies of 28 kHz, 40kHz, 20kHz, and 1.7 MHz depending on the process

configuration and method of actuation .10


Thus, the electrolyte flow and electrochemical reactions are benefited. The ultrasonic wave

traveling in Z direction can be represented as a longitudinal wave as in --

……………………………(1)

In the above equation, P is the pressure acting on the upper surface of the micro-cell, 𝐏𝟎is the

pressure acting on the boundary surface between the electrolyte and air, ρ is the density of the

electrolyte, g is the acceleration due to gravity, ω is the frequency of the ultrasonic wave, c is the

wave speed, t is the time, A is the amplitude of the wave, and h is the distance between the fluid

surface and the end of the electrode. The higher the frequency of the ultrasonic vibrations, the

greater the pressure on the micro-cell. The maximum or minimum pressure with respect to the

frequency can be obtained by partial differentiation of Eq. (1):

…………….……………….(2)


12

From equation (2), applying the condition of maxima – minima, it can be deduced that maximum

and minimum pressure occurs at points which satisfy the following equation (3).

……………………………………(3)

From equations (2) and (3), it can be inferred that the maximum pressure occurs a given point (z)

increases with the ultrasonic frequency.

1.Hence, ultrasonic vibrations are responsible for frequent and larger pressure increases in the

machining gap and this leads to enhanced electrolyte diffusion and elimination of bubble.

2.Besides the process parameters (current density, voltage, pulse parameters, and electrolyte

concentration) involved in ECM, the amplitude of ultrasonic vibration plays an important role.

3.Low amplitudes don’t give additional benefits. Too high amplitudes affect machining precision

especially while machining microdimensional features.Micromanufacturing Lab, I.I.T. Kanpur

ABRASIVE –ASSISTED JET – ELECTROCHEMICAL MACHINING

In abrasive –assisted jet ECM , abrasive are used

to facilitate material removal by jet ECM. One

such example is electrochemical slurry jet

machining. The abrasive (𝐀𝐥𝟐𝐎𝟑) slurry in the

electrolyte( NACl) facilitates removal of a

passivating layer by impact action on the

workpiece . This process is particularly suitable

for machining of WC ( tungsten carbide) which

undergoes excessive corrosion and passivation

under jet-ECM. The working voltages ranges

from 60 V to 120 V.

Fig; Schematic of electrochemical slurry jet micro-machining (ESJM)[3]


14

ABRASIVE FEEDER

MIXING CHAMBER

PUMP

NOZ-ZLE

WORKPIECE

FILTER

Fig : Schematic of electrochemical slurry jet micro-machining

Electrolyte flow

Valve


COMBINED ECM BASED HYBRID PROCESS

1. Mechano-Electrochemical Milling (MECM)1.This hybrid machining process combines the effect of both the conventional milling process

and the Electrochemical Machining process (ECM). The MECM is under development with an

objective to machine difficult-to-cut materials with improved productivity and better surface

quality .

Fig: Schematic overview of a MECM setup[4]

2.The MECM process is especially useful in

machining of hard metal such Ti6Al4V which suffers

from surface passivation during the ECM process.

The mechanical process facilitates removal of

passivation by a cutting edge , thereby enhancing

the surface quality and process stability . The process

needs dedicated tool design of a tools. 15

2.Electrochemical Grinding (ECG)

1.In ECG , the material removal is achieved by

combined action of abrasive and electrochemical process

energy. The resulting surface has high surface integrity,

is burr free, and has negligible distortion.

2.The abrasive particles of the grinding wheel make a

contact with the workpiece and the gap between the

wheel and workpiece makes passage for electrolyte

circulation. The gap voltages range from 2.5V to 14V. At

the start of machining process, the material removal is

achieved by the action of electrochemical process and

this is followed by the development of passivating layer

on the workpiece surface.16

Fig : Schematic of electrochemical grinding

Fig: Burr Free Electrochemical Grinders

Image source: Tridex Technology

Fig Schematic of electrochemical grinding fordrilling [5]

3.The MRR in ECG is a result of synergic interaction

of three subprocesses, i.e., electrochemical dissolution,

mechanical abrasion, and erosion process and can be

estimated using a simplified model as ……..

The MRRs due to individual process energy can be

estimated using following equations:

………………(4)

where, η, I, A, z, ρ, F, 𝑽𝒆, 𝐊𝐩, w, 𝐅𝐚, and IEG are current efficiency, machining current,

molecular weight of anode, valency of positive or negative ions, density of workpiece, Faraday’s

constant, applied voltage across electrodes, degree of polarization, specific conductance of

electrolyte, active surface area of anode, and size of interelectrode gap, respectively. 17

Fig. Schematic of flow of electrolyte gas mixture incylindrical micro-ECG [6]

where dg, dl/dt, 𝐝𝐦𝐞𝐚𝐧 𝐝𝐦𝐚𝐱 , 𝒅𝐜𝐨𝐧𝐭𝐚, and ρ are average size of abrasive grain, feed rate, mean

grain diameter, maximum grain diameter, the diameter of grain just contacting the workpiece

surface, and density of electrolyte, respectively. 𝐍𝐭𝐨𝐭𝐚𝐥 is total number of grains coming into the

machining zone per unit time. a is machining gap. 18

Fig : Schematic of electrochemical grinding

Image source : Tridex Technology

…………..(5)

where, 𝐀𝐬 is shear area (width of grinding wheel x projected contact length). 𝐀𝐈𝐄𝐆 is area of

interelectrode gap (product of IEG and width of grinding wheel). ρ is density of electrolyte.

H: is head. Fs :is shear force, C : is correction factor.

19

Applications Of ECG

Fig: Point Grinding through ECG

Fig: Miscellaneous product made through ECG

Image source: Tridex Technology Micromanufacturing Lab, I.I.T. Kanpur

20

3. Orbital Electrochemical Abrading

1.In orbital ECA, a three-dimensional abrasive

cathode is used which has a multiaxis orbital

motion and is oscillated mechanically .

2.The tool and workpiece also undergo

reciprocating motion which facilitates

electrolyte flow in the gap.

3.The orbital motion of the abrasive cathode

facilitates the removal of a passive layer of

formed on the workpiece surface . The orbital

motion of the tool enables uniform distribution

of electrolyte and improves ECM performance.

Fig. Sketch of orbital electrochemical abrading [7]

4.The areas where abrasive action has not acted

retain the passive layer. This helps in

preventing stray machining.

5.Therefore, orbital ECA offers controlled and

localized removal of workpiece material.

4. ELECTROCHEMICAL HONING (ECH)

1. Electrochemical honing (ECH) is a hybrid process of ECM and mechanical honing and is used

in finishing of complex shaped products, such as helical and bevel gears, external and internal

cylindrical surfaces.21

Fig :Proposed process principle of Ultrasonic ECH

of bevel gear.[8]

Fig : Schematic view of the ECH setup used for finishing of

workpiece . [8]


Fig. Sketch showing working principle ofelectrochemical honing for finishing of bevel gears[9]

3.The electrolyte is supplied in the interelectrode gap and the workpiece gear undergoes finishing

by electrochemical dissolution. This is followed by development of a passivating oxide layer on

the gear teeth and this prevents further electrochemical dissolution.

22

2. The setup consists of two cathodic bevel

gears (I and II) meshing with the

workpiece bevel gear which acts as an

anode. The cathode gear-I consists of an

insulating layer of Metalon sandwiched

between two conducting layers of copper

with a 1-mm undercut.


4. Subsequently, the mechanical honing action comes into the picture which removes the

passivating layer. The mechanical honing action is accomplished by using a honing gear which is

mounted in a tight mesh and perpendicular to the workpiece as well as cathode gears.

5.The material removal in ECH is the sum of volumetric material removal due to electrochemical

action and mechanical honing as in Equation given below.

MRRECH = VECM + Vhoning ……………………(6)

where, VECM can be computed from Faraday’s Law of electrochemical dissolution, and Vhoning can

be calculated from Archard law of wear. Substituting the expressions for MRR for

electrochemical dissolution and mechanical honing, Equation (6) can be rewritten as Equation (7).

MRRECH (mm3/s) = ηEJAs

Fρ+ KFnSH

………………………….(7)


where, η denotes current efficiency, E stands for electrochemical equivalent of workpiece material

(g), F denotes Faraday’s constant (96500 C), ρ is density of workpiece gear material (g/cu.mm),

As is surface area of gear tooth (depends on type of gear and its geometry), J is current density in

this area (A/ mm2); K denotes wear coefficient of the workpiece material, Fn is the total normal

load acting along the line of action, S is total sliding distance (mm), and H stands for Brinell

hardness number of the workpiece material (N/sqa.mm).

24

Application of ECH

Fig : Schematic of a typical tool for ECH of internal cylinders

Fig :Photograph of a typical tool for ECH of internal

cylinders

Image source: tridex technology

5. ELECTROCHEMICAL DISCHARGE MACHINING (ECDM)1.In electrochemical discharge machining (ECDM) process, the capabilities of ECM and EDM

processes are combined with each other to expand the processing window from conductive to

nonconducting materials as well as to fabricate deep microholes, microchannels, etc. .

Fig.Sketch showing setup and process mechanism forelectrochemical discharge machining [10]

2.The setup consists of two electrodes, i.e., tool as cathode and an auxiliary electrode (anode),

and the workpiece is kept below the tool electrode. A pulsed DC current is supplied between

cathode (tool) and anode.

25Fig. Schematic of ECDM setup [12]

3.An optimum gap is maintained and electrolyte is passed through the gap. The ECDM process

involves two major phenomenon: electrolysis leading to generation of gas bubbles and arc

discharge due to breakdown of gas film.

Fig. Current and voltage waveforms forelectrochemical discharge machining[11]

26

Fig:(a) Micro-grooves, (b) enlarged figure of micro-grooves, (c) micro-pillar,

(d) micro-wall, and (e and f) micro-pyramid machined on glass by ECDM

(KOH 30 wt%, 23 V pulse voltage, 1 ms/1 ms pulse on/off-time ratio, Ø 30–

33 μm tool, 3 μm/s feedrate and 300 rpm rotational speed)[11]

4.The wettability of tool electrode affects

micromachining resolution . It has been

observed that applied voltage is the influential

parameter which influences MRR, HAZ

thickness as compared to electrolyte

concentration, tool immersion depth, and

interelectrode gap in micro-ECDM drilling.

ECDM micromachining has been demonstrated

on a variety of nonconducting materials, such

as glass , pyrex wafer, alumina , quartz, and in

trueing and dressing of metal-bonded diamond

grinding 27

Fig : Micro ECDM experimental setup [12]

Fig : Tool rotation effects (a) no rotation and (b) with tool

rotation at 1500 rpm [12]


Concluding Remarks

This chapter presented a discussion the fundamental aspects of electrochemical-based hybrid

machining processes. The main benefits of hybridizing ECM with other processes are restated

below:

1. To combine high MRR and high surface finish during deep hole drilling (ECDM).

2. To achieve better process localization and minimize lateral machining (LAJECM).

3. To achieve better flushing/circulation of electrolyte in the machining gap (UAECM).

4. To break the passive layer formed on the workpiece in ECM process (UAECM, ECG).


29

For successful hybridization of micro-ECM with other process energies and to realize it in

machining, several technological requirements have to be met and are listed below :

1. Development of Universal machine tool capable of combining ECM with two or more

processes.

2. Synchronization of ECM process energy with other process energies such as laser,

micromilling, EDM by parametric optimization for better process and shape control.

3. Better understanding of material removal mechanisms under the simultaneous action of two or

more process energies.

Concluding Remarks


ECMM-basedhybrid process

Process Energies involved

Main process Parameters

Advantages

Laser-assistedelectrochemicalmachining

Laser,electrochemical

laser pulse energy, repetition rate,ECM parameters (voltage, currentdensity, electrolyte type,concentration, pulse parameters)Laser average power,

Improved reactionkinetics, localizedmaterial removal

Ultrasonicassistedelectrochemicalmachining

Ultrasonic vibration

(mechanical) and

electrochemical

Ultrasonic frequency andamplitude, tool design, ECMparameters (voltage, currentdensity, electrolyte type,concentration, pulse parameters)

Improvedelectrolyticdiffusion, improvedmass and chargetransport, reducedpassivation

Summary of ECM-Based Hybrid Process

30

ECMM-basedhybrid process

Process Energies involved

Main process Parameters

Advantages

Abrasiveassistedelectrochemicalmachining

Abrasive impact(mechanical) andelectrochemical

Concentration of slurry, abrasiveparticle size, speed, stand-offdistance, ECM parameters (voltage,current density, electrolyte type,concentration, pulse parameters)

Removal ofpassivating layer,stabilization ofelectrochemicaldissolution

Laserelectrochemicalmachining

Laser,electrochemical

Laser average power, laserwavelength, laser pulse energy,repetition rate, ECM parameters(voltage, current density, electrolytetype, concentration, pulseparameters)

High MRR withgood surfacefinish, reducedthermal defectsof laser, i.e.,spatter, recastlayer, HAZ

Summary of ECM-Based Hybrid Process

31

ECMM-based hybrid process

Process energies involved

Main process parameters Advantages

ECDM Electrochemicaland arcdischarge

Gap voltage, gas film thickness,pulse duration, electrolyte type,concentration, conductivity andflow rate, tool material

Machining ofnonconductivematerials, high MRR,and good surfacefinish

Combinedelectrochemicalgrinding

Electrochemical,abrasive cutting(mechanical)

Grinding wheel type (grit size,bond type), wheel RPM, ECMparameters (voltage, currentdensity, electrolyte type,concentration, pulseparameters)

Removal ofpassivating layer,stabilization ofelectrochemicaldissolution, improvedMRR

32

ECMM-based hybrid process

Process energies involved

Main process parameters Advantages

Mechano-Electrochemic-al machining

Electrochemic-al andmechanical(cutting edge)

Cutting edge radius, RPM, toolfeed rate, ECM parameters(voltage, current density,electrolyte type, concentration,pulse parameters)

Removal of passivatinglayer, high MRR

Electrochemic-al honing

Electrochemic-al, mechanicalhoning

Tool RPM and reciprocation,abrasive type and grit size,processing time, ECMparameters (voltage, IEG,current density, electrolyte type,concentration, pulseparameters).

Finishing of complexshaped parts such ashelical or bevel gears,external cylindricalsurfaces.

33

REFERENCES

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laser assisted jet electrochemical machining, Precis. Eng. 30 (2006) 288298.

[2] S. Skoczypiec, Research on ultrasonically assisted electrochemical machining process, Int. J.

Adv. Manuf. Technol. 52 (5-8) (2011) 565574.

[3] Z. Liu, H. Nouraei, J.K. Spelt, M. Papini, Electrochemical slurry jet micro-machining of

tungsten carbide with a sodium chloride solution, Precis. Eng. 40 (2015) 189198.

[4] D. Van Camp, J. Bouquet, J. Qian, J. Vleugels, B. Lauwers, Investigation on hybrid

mechano-electrochemical milling of Ti6Al4V, Proc. ISEM XIX (2018).

[5] D. Zhu, Y.B. Zeng, Z.Y. Xu, X.Y. Zhang, Precision machining of small holes by the hybrid

process of electrochemical removal and grinding, CIRP Ann. - Manuf. Technol. 60 (1) (2011)

247250.


[6] K.S. Gaikwad, S.S. Joshi, Modeling of material removal rate in micro-ECG process, J. Manuf.

Sci. Eng. 130 (3) (2008). 34502.

[7] K.P. Rajurkar, D. Zhu, J.A. McGeough, J. Kozak, A. De Silva, New developments in electro-

chemical machining, CIRP Ann. - Manuf. Technol. 48 (2) (1999) 567579.

[8] Harpreet Singh and Pramod K Jain, Study on ultrasonic-assisted electrochemical honing of

bevel gears , journals.sagepub.com/home/pib.

[9] J.H. Shaikh, N.K. Jain, Modeling of material removal rate and surface roughness in finishing of

bevel gears by electrochemical honing process, J. Mater. Process. Technol. 214 (2) (2014) 200209 .

[10] T. Singh, A. Dvivedi, Developments in electrochemical discharge machining: a review on

electrochemical discharge machining, process variants and their hybrid methods, Int. J. Mach.

Tools Manuf. 105 (2016) 113.

REFERENCES


36

[11] M. Scho ¨pf, I. Beltrami, M. Boccadoro, D. Kramer, B. Schumacher, ECDM (Electro

Chemical Discharge Machining), a new method for trueing and dressing of metal bonded diamond

grinding tools, CIRP Ann. - Manuf. Technol. 50 (1) (2011) 125128.

REFERENCES

[12] S.K. Jui et al. / Journal of Manufacturing Processes 15 (2013) 460–466.


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