micromanufacturing lab, i.i.t. kanpurhome.iitk.ac.in/~jrkumar/download/chapter 6 - ecsm.pdf ·...

Chapter 6

Electrochemical Spark Machining

Dr. J. Ramkumar1 and Vyom Sharma2

1Professor and 2Research Student

Department of Mechanical Engineering

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

Chapter 6

Electrochemical Spark Machining

Dr. J. Ramkumar

Professor, Department of Mechanical Engineering

Micro machining Lab, I.I.T. Kanpur

Micromanufacturing Lab, I.I.T. Kanpur

Organization of the presentation

1. Overview of Electrochemical Spark Machining Process

(Introduction to Machining Process, Mechanism of spark formation and material removal)

2. Process and performance parameters of ECSM

3. Machining system of ECSM process

4. Variants of ECSM process

5. Hybridized ECSM processes

6. Future scopes of research

3 Micromanufacturing Lab, I.I.T. Kanpur

1. Overview of Electrochemical spark machining (ECSM) process

4

ECSM process is a novel combined/hybrid machining method developed tomachine electrically nonconductive materials. Generally, it comprises thermalenergy based on two unconventional machining processes, that is, ECM and EDM.

Due to the combined effect of EDM and ECM, the ECSM process successfullyovercomes the drawbacks of the constituting processes (EDM and ECM) asrequirement of the electrically conductive materials for machining. The processcapabilities are not only limited to nonconductive materials and also applied forshaping of electrically conductive materials.

Generally, process capability in terms of material removal of ECSM process is muchhigher (approx. 5 and 50 times) as compared to ECM and EDM, respectively, atsame machining conditions.



5

Comparison between ECM, EDM, and ECSM



6

Spark formation phenomenon in ECSM

In ECSM process, the combined effects of

constituent processes (ECM and EDM) are

responsible for material removal. Generally,

hydrogen (H2) gas bubbles are generated due to

electrolysis process or electro-chemical reaction

while electrical discharge/spark is produced between

gaseous layer formed by gas bubbles and tool

electrode (cathode) in the presence of electrolyte.

Therefore, two phenomena, that is, hydrogen (H2) gas

formation and spark generation, cause material

removal in ECSM. The material is removed due to

simultaneous effect of melting, vaporization and

chemical etching processes.



7

Spark formation phenomenon in ECSM

The temperature of plasma channel is in the range of 800–20,000K. At this temperature, any non-

conductive material is placed near the sparking zone with appropriate inter electrode gap (IEG) and then

material removal takes place from workpiece surface due to melting and vaporization. Such phenomenon

is known as material removal mechanism of ECSM process. Generally, IEG between tool-electrode and

workpiece is in few micro-meters and depends on the machining conditions. The IEG between tool

electrode and workpiece is 20mm or less than 25mm for machining of glass.



8

Equivalent circuit for ECSM process

At critical accumulation condition

No sparking

At the time of sparking

Circuit used for calculation of

spark energy

2. Process and Performance parameters of (ECSM) process

9

Process

Parameters

Electric

ParametersNon-electric

Parameters

Current

density

Discharge

voltage

Pulse

duration

Pulse

interval

Frequency

Polarity Electrolyte

FlushingTool

electrode


2. Process and Performance parameters of (ECSM) process

10

Performance

Parameters

Material

removal rate

Surface

roughness

Tool wear

rate


3. Machining system of Electrochemical Spark Machining Process

11

Following are the constituents of a typical machining system used in a ECSM process:

3. Machining system of Electrochemical Spark Machining Process

12

Experimental setup of Electrochemical Spark Machining process:


4. Variants of Electrochemical Spark Machining Process

13

Drilling ECSM: It can be used in different configurations such as through-holedrilling, blind hole drilling, counter drilling and percussion drilling. In drilling,flushing capability is highly affected by peripheral velocity of drilling toolresulting in enhancement in machinability with higher material removal withbetter surface quality. Instead of this, the rotational speed of the tool leads to areduction in stray corrosion resulting in improvement in the circularity of drilledhole. Generally, low rotational speed is better for higher material removal withgood surface finish and vice versa at higher speed.

Sinking ECSM: Sinking ECSM process can be used to create micro holes in theworkpiece with application of stationary tool-electrode (reciprocating type) formanufacturing of moulds and dies. Generally, sinking ECSM process has beenused for making of through- and blind micro holes in the workpiece to achievehigher aspect ratio. It also shows their potential to make small and shallow (ultra-precision) features for nozzles, orifices, dies and moulds made of non-conductive,semi-conductive or conductive materials.



14

Turning ECSM: The feeding mechanism for workpiece during turning ECSM isnot required resulting in reduction in the complexity. This process becomesbeneficial for turning of different profilers such as cylindrical turning, taperturning, step turning and thread turning operations.

Milling ECSM: Milling ECSM process shows their potential to create three-dimensional (3D) micro structures, cavities and profiles on the surface of non-conductive materials by adopting the strategy of tool-electrode movement similarto conventional milling.

Travelling Wire ECSM: In TW ECSM, the spark is generated between movingwire made of copper, brass or tungsten and at the surface of workpiece as a resultof melting, vaporization and erosion of workpiece material. It is widely applicablefor shaping of complex profile in non-conductive materials with application ofmovable wire (tool-electrode) on any surfaces (internal or external) for micro-cutting such as gear cutting, comb profiles, chutes or channels.



15 Micromanufacturing Lab, I.I.T. Kanpur

5. Hybridizations of Electrochemical Spark Machining Process

16

To enhance the performances of ECSM process and to minimize/eliminate thedrawbacks, the researchers combined or hybridized ECSM process with othermachining processes. Such combined processes are called as hybridized ECSM orECSM-based hybrid machining processes.

The purposes of the hybridization of ECSM with different machining processes areto utilize the potential merits and at the same time dismiss the demerits of theconstituent processes as a result enhancement in the machinability of the hybridizedECSM processes.

Hybridized ECSM processes are classified based on (a) Energies or (b) Involvementof constituent processes in machining.

On the basis of energy sources, the mechanical or magnetic force is used forhybridization of ECSM process.

Based on involvements, the hybridized ECSM can be classified as associated andassisted type hybridized ECSM.



17

Hybridization of ECSM based on energy source:

Mechanical Energy based

hybrid ECSM process

Magnetic Energy based

hybrid ECSM process

Ultrasonic assisted sinking ECSM

Ultrasonic assisted drilling ECSM

Electrochemical spark abrasive

grinding (ECSAG)

Ultrasonic assisted ECSAG

Magnetic force assisted ECSM

Magnetic force assisted abrasive

grinding ECSM

Ultrasonic magnetic force assisted

abrasive grinding ECSM


18

Hybridization of ECSM based on involvement:

Associated type hybrid

ECSM process

Assisted type hybrid

ECSM process

All the constituent processes

directly involve to improve the

machinability and continuously

make their efforts toward that

direction.

Ex: ECSAG

UA-ECSAG

MA-ECSAG

PM-ECSAG (Powder mixed)

The constituent processes are not

directly involved in improving the

machinability, and among them

only one process is directly

involved in machining, while

other processes facilitate or assist

the machining method.

Ex: UAS ECSM

UAD ECSM

MA ECSM


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Classification of Hybridized ECSM process:



20

Electrochemical Spark Abrasive Grinding Process (ECSAG):

In this process, the material removal occurs due to chemical dissolution, sparkerosion and abrasive abrasion, that is, three different energies such as chemical,thermal and mechanical are responsible for material removal.

To implement the abrasion action of grinding ECSM process, a metallic wheel withabrasive (metal bonded) aided has been applied during machining and the processbecomes as ECSAG.

Spark phenomenon occurs between bond material (metallic part) and gas bubblesdue to which the workpiece material melted and vaporized.

Simultaneously, abrasive particles make contact with workpiece surface and softenmaterial removed due to abrasion action of abrasive particles.



21

Electrochemical Spark Abrasive Grinding Process (ECSAG)



22

Powder Mixed Electrochemical Spark Machining Process (PM ECSM):

In PM ECSM, loose conductive particles are mixed with electrolyte to improve thesurface integrity of ECSM process.

Generally, the generation of fine spark with uniform energy and their fine controlare highly desired to get higher machinability and surface finish.

Due to the presence of loose abrasive particles in electrolyte, a lot of particles makecontact with workpiece surface freely resulting in small amount of material beingremoved from workpiece surface. This phenomenon leads to improve the SQ andhelp to achieve the SQ up to micro/nano level.

The abrasion action of abrasive particles also minimized/removed the micro-cracks on the machined surface.



23

Electrochemical Spark Abrasive Drilling Process (ECSAD):

Electro-chemical spark abrasive drilling (ECSAD) is the implementation ofabrasive-based tool-electrode in drilling ECSM process.

In this process, three different energies such as chemical, electrical and mechanicalare used to perform chemical dissolution, spark erosion and abrasive abrasionphenomena.

Abrasive particles make sufficient gap between the workpiece and bond materialsdue to effective protrusion heights, and as a result huge amount of bubble areformed during chemical reaction.

Material removal decreases with an increase in depth, and after a certain depth, themachining becomes much difficult. This is due to lack/insufficient formation of gasbubbles at higher depth.



24

Ultrasonic assisted Electrochemical Spark Drilling Process (UA ECSD):

Ultrasonic assisted electro-chemical spark drilling (UA ECSD) is an application ofmechanical energy in the form of vibration (ultrasonic) in drilling ECSM process.

Ultrasonic vibration in ECSM effectively changes the discharge behaviour andimproves the electrolyte circulation, as a result no accumulation of debris takesplace as which stable sparks are generated.

The purposes of ultrasonic vibration in drilling ECSM are to enhance machiningperformances such as material removal and surface quality of the drilled workpiecesby improving the circulation of electrolyte into the gap between tool-electrode andworkpiece during machining.

Vibration speeds up the machining discharge and also controls the hydrodynamicmachining process resulting in higher material removal.

Vibrational amplitude of 10mm creates the most uniform current signal inmachining zone resulting in uniform and stable sparks.



25

Ultrasonic assisted Electrochemical Spark Abrasive Grinding Process (UAECSAG):

UA ECSAG is the application of ultrasonic vibration in ECSAG process.

It is observed that after each spark, white oxide layer forms on the surface ofgrinding wheel, thus decreasing the protrusion heights of abrasive particles andreducing the material removal rate.

The thickness of oxide layer formation is inversely proportional to ultrasonicvibration (amplitude and frequency). Therefore, the application of ultrasonicvibration in ECSAG is an effective way of in-process dressing method of diamondgrinding wheel.



26

Magnetic field assisted milling ECSM process (MAM ECSM):

In this process, magnetic force is applied with milling ECSM process with anapplication of a permanent magnet.

The basic advantage of magnetic field in ECSM process is the development ofmagneto hydro-dynamic (MHD) convection into the gap between the workpiece andtool-electrode in the presence of electrolyte.

Due to this, there is effective circulation of electrolyte which facilitates deep holemachining and finally generates better geometry of machined surfaces.

Magnetic force assists to generate more stable spark and easily breaks of the gasbubbles away from the surface of tool-electrode. As a result, a uniform layer ofgaseous zone has been formed surrounding the surface of the tool-electrode whichcontributes to higher machining rate due to requirement of higher supply voltage inthe machining zone.



27

Magnetic field assisted Travelling wire ECSM process (MA TW-ECSM):

In TW ECSM process, the circulation of electrolyte into the gap defers in the closevicinity of the machining zone resulting in decline in material removal.

To overcome the above problem, the application of MHD convection in TW ECSMprocess becomes beneficial.

The MHD convection pushes the electrolyte into the sparking zone (gap betweentool-electrode and workpiece), and finally a uniform gaseous environment isobtained surrounding the tool-electrode.

Such a phenomenon leads to uniform presence of hydrogen gases resulting inuniform and precise formation of sparks.



28

Summary of Hybridized Electrochemical Spark Machining Processes:



29

After sophisticated studies, it is concluded that only limited hybridized ECSMprocesses are developed till now and several other new hybridized ECSM processescan be developed to improve the capabilities of existing processes.


30

Proposed hybridized ECSM processes to be developed are as follows:

Ultrasonic Vibration

based

Powder Mixture

based

Magnetic force

based

Magnetic force and

ultrasonic vibration

based

Ultrasonic assisted sinking

ECSM

Ultrasonic assisted milling

ECSM

Ultrasonic assisted turning

ECSM

Ultrasonic assisted TW

ECSM

Ultrasonic assisted saw-cut

ECSM

Ultrasonic assisted grinding

ECSM

Powder mixed sinking

ECSM

Powder mixed drilling

ECSM

Powder mixed milling

ECSM

Powder mixed turning

ECSM

Powder mixed saw-cut

ECSM

Powder mixed

ECSAG

Magnetic force assisted sinking

ECSM

Magnetic force assisted drilling

ECSM

Magnetic force assisted turning

ECSM

Magnetic force aided grinding

ECSM

Magnetic force aided

ECSAG

Magnetic force and ultrasonic

assisted sinking ECSM


assisted milling ECSM


assisted turning ECSM


assisted grinding ECSM


Conclusions

31

1. ECSM is a hybrid machining process that comprises the features of EDM andECM processes for shaping of electrically conductive and nonconductivematerials at micro-level machining.

2. ECSM process developed in different configurations such as drilling ECSM, TWECSM, milling ECSM, sinking ECSM, grinding ECSM and turning ECSMpositively create complex profiles with better surface quality during machining.

3. Hybridization with ECSM process is a novel trend to enhance the productivityof ECSM process. Grinding ECSM becomes an appropriate method to developmicro-tools for micro-machining related to EDM, ECM or ECSM process.

4. Saw-cut ECSM is a new configuration of ECSM and is a good approach forslice/disk cutting of difficult-to-cut non-conductive materials.

5. Ultrasonic vibration–assisted ECSM enhances the flow of electrolyte into thegap resulting in reduction in arcing phenomenon. Such an approach effectivelyimproves material removal, surface quality and reduces micro-cracks.


Conclusions

32

6. Abrasive-aided grinding ECSM shows their potential to remove micro-cracks andrecast layer formed due to spark energy at the workpiece surface. It significantlyenhances material removal and surface quality. It is a unique technique for dressingof micro-tools/wheels.

7. Several more hybridization of ECSM process can be possible to get betterperformances of the existing ECSM process. This becomes advantageous forresearchers to develop new process/method in the field of ECSM to machine thedifficult-to-machine materials.


33

Thank You


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