A seminar on electrochemical spark machining

PRESENTED BY:BHAWNA GOKANIIII B.TECH MES.R NUMBER:280/07

CONTENTSCLASSIFICATION OF UNCONVENTIONAL PROCESSES

ELECTRO DISCHARGE MECHINING(EDM)

ELECTRO CHEMICAL MACHINING(ECM)

ELECTRO CHEMICAL SPARK MACHINING(ECSM)

COMPARISON OF EDM , ECM & ECSM

PARAMETRIC ANALYSIS OF ECSM

EXPERIMENTAL SET – UP AT IIT KANPUR

CURRENT & TEMPERATURE WAVEFORMS

INFERENCES

MECHANISM OF THE PROCESS

MICROCHANNEL FABRICATION

FUTURE POSSIBILITIES & LIMITATIONS

CONCLUSIONS

WHAT IS

ECSM??

ECSM:ELECTRO CHEMICAL SPARK MACHINING

MANUFACTURING PROCESS

UNCONVENTIONAL

MECHANICA

L

THERMOELEC

TRIC (EDM)HYBRID (ECS

M)

ELECTROCHEMICAL(ECM)

TRADITIONAL

EDM:ELECTRICAL DISCHARGE MACHININGWorking Principle: Powerful spark causing

erosion.

Advantages: The melting point, hardness, toughness, brittleness of the material poses no problem.

Characteristic surface obtained improves component life.

Major limitation:

The process cannot be applied to

machine non-conducting materials.

ECM:ELECTRO CHEMICAL MACHININGWorking Principle: Faraday’s classical law of electrolysis.

Advantages:

Metals and alloys impossible to machine by mechanical means can be machined.

MRR is quite high for HSTR materials compared to conventional machining processes.

No direct contact between tool and workpiece facilitates least wear, friction generation and heat build-up.

Very thin metal sheets can easily be worked out without distortion.

Electro chemical machining cell

ECM:ELECTRO CHEMICAL MACHINING

Schematic of ecsm

Typical applications:

Machining of hard heat resistant alloys

Machining of complex external shapes like that of turbine blades, aerospace components and in electronic industry.

Major limitation:

The process cannot be applied to

machine non-conducting materials.

ECSM:ELECTROCHEMICAL SPARK MACHININGECSM has been defined as “ An innovative hybrid machining

process comprising the techniques of electrochemical machining (ECM) and electro discharge machining (EDM) “

“HYBRID PROCESS”

Hybrid processes are those in which two or more machining processes are combined to take advantage of the worthiness of each by overcoming the individual limitations.

Example : ECG(electrochemical grinding)=conventional grinding process + electrochemical machining.

Similarly : ECSM = ECM + EDM.

PROCESS COMPONENTS MECHANISM OF DISCHARGE

MECHANISM OF MATERIAL

REMOVAL

ECM Electrodes and

electrolyte

Not applicable as there is no discharge

Electrochemical reaction

EDM Electrodes and dielectric

Breakdown of the dielectric between

the electrodes

Melting and vaporization of the work piece due to

electrical discharge

ECSM Electrodes and

electrolyte

A high electric field in the vicinity of

the cathode

Melting and vaporization of the work

piece

Comparison of the three processes

ECSM

WHETHER THE SPARK OCCURS CONTINUOUSLY OR IN SHORT

BURSTS??

IN CASE IT IS A BURST

PROCESS,DOES THE TEMPERATURE OF

THE WORKPIECE RISE QUICKLY IN

RESPONSE TO THESE SHORT BURSTS OF

CURRENT??

WHAT IS THE ACTUAL

MECHANISM OF THE PROCESS??

PARAMETRIC ANALYSISSynchronized measurements of time varying current and temperature have been performed

No particular mechanism for the process proposed till date

EXPECTED RESULTS

If the discharge is in short bursts

if temperature rise were related to this burst of current

Expected synchronized time varying current and temperature waveform in ECDM process

Control PC

Z Assembly

X-Y Stage

Machining

Chamber

Power Supplies

Exhaust

System

EXPERIMENTAL SET-UP

Ref. defense science journal .Kulkarni A.V,vol57,no5,sep2007,pp768

Main components

Machining chamber

ECS cell

Exhaust system

Control PC

Power supply system

Designed and developed at IIT Kanpur.

Exhaust system especially designed and developed to take away the fumes rapidly out of the machining chamber

CURRENT AND TEMPERATURE WAVEFORMSSnapshots of the stored waveforms of time varying current and temperature respectively taken by a digital camera(upper one for copper and lower one for tantalum).

Upper waveform corresponds to current and the lower one shows the temperature.

Pyrometer registers the temperature reading only when the temperature of the sensing area is above its sensing limit(here 815 degrees centigrade)

When the temperature is above the sensing limit , there is a sharp rise in the temperature pulse. Temperature starts falling due to quenching in ECDM.

Scale for current:1V=1A;for temp:0.1V=100degrees centigrade.

Ref.Kulkarni A.V(2009)’systematic analysis of ecsm’vol 6,nos3/4,pp 197

RESULTS AND INFERENCESEach current spike represents occurrence of discharge at the cathode tip followed by the ensuing temperature rise.

Thus, discharge takes place in short bursts and there is an instantaneous temperature rise in the work piece surface.

If the spark is strong enough, the temperature reached by the work piece surface in that localized region is very high of the order of evaporation temperature of the material.

This is generally outside the sensing limit of the pyrometer(shown by the open temperature spike).

Thus material removal takes place in that localized region.

Ref.Kulkarni,A.V.(2009)’systematic analysis of ecsm’vol 6.nos3/4,pp296

SURFACE TOPOGRAPHY RESULTS OF THE DISCHARGE AFFECTED ZONE BY SEM

A clear ring pattern is seen

Formed by melting and solidification due to quenching at the work piece surface

The inner shining spot is due to the removal of material

100*magnification for CU surface with 4 prominent discharges striking the work piece.

The geometry of the single discharge affected zone is almost circular in nature.

Smaller circular zones are due to the low energy discharges striking the surface.

RESULTS AND INFERENCES

Ref.KulkarniA.V.(2009)’systematic analysis of ecsm’vol6,nos3/4,pp211

Ref.KulkarniA.V.(2009)’systematic analysis of ecsm’vol6,nos3/4,pp211

MECHANISM OF MATERIAL REMOVALThe potential drop across the cathode-electrolyte interface appears on

application of a DC voltage causing a small ionic current to flow due to electrochemical reaction.

Hydrogen bubbles evolve as per the reaction at the cathode: 2H2O+2e- = H2 + 2OH-

Size of bubbles within the interface region grows over the time.

No bubbles Small ionic current

Current decreasesBubbles formationBubbles grow in

numberCurrent further

decreases

MECHANISM OF MATERIAL REMOVAL CONTINUED..An isolating film of hydrogen gas bubbles covers the cathode tip portion in the electrolyte, abruptly a large dynamic resistance is present and the current through the circuit becomes almost zero

A high electric field (10^7 V/m) gets generated causing discharge within the gas layers covering the tip.At the instant when discharge occurs, a large current flows through the spark channel for a very short duration of time as can be seen by the current spike.

Complete isolation Current is almost zero

Discharge at the tipA large current spike due to huge number of

electrons created by ionization

The bombardment of electrons on the work piece surface results in intense heating and hence metal removal takes place.

Workpiece

Anode given positive and cathode negative supply.

“Critical voltage” applied.

“Spark” occurs at the interface of cathode and electrolyte together with the electrochemical reaction.

Energy of spark then utilized for micromachining.

SCHEMATIC OF ECSM PROCESS

MECHANISM OF MATERIAL REMOVAL CONTINUED..

Schematic of ECSM

APPLICATIONS OF ECSM

The process is potentially useful for machining non-conducting materials such as alumina ,quartz , ceramics , composites.

Micro fabrication of miniature machine tools for micromachining as in aeronautics, electrical and mechanical engineering.

Micro – fabrication of array of holes in SU-8 material( high aspect ratio, polymer, dielectric photoresist material) to fabricate micro-filters needed in micro-EDM process.

Micro seam welding of copper plates and foils.

Fabrication of miniature components.

Heat treatment.

COMPLEX SHAPED MICRO CHANNEL FABRICATION

Micro channels find use in optical sensing , photonic, and in BioMEMS devices.

ECSM acts as an innovative, cost effective , and straight forward process without employing intermediate processing steps for micro channel fabrication.

For circle diameter of 2500um each it took 8 minutes of total time to machine the micro channel in the form of “8”.

A micron region application of ECSM

Kulkarni,A.V.(2009)’systematic analysis of

ecsm’,int j.machining,vol6,nos3/4,pp19

9

MICROCHANNEL FABRICATION CONTINUED……Dial gauge mounted on EDM machine used to measure the depth of micro

channels at various locations.

photograph of the depth measurement set-up close-up of the tip of the dial gauge on the work piece under measurement

microstructure of the micro machined glass surface at 1000* magnification. Visible cracks are formed due to the impact of the sparks. Dimensions of cracks are of the order of few tens of micrometers.

WIDTH , DEPTH AND HAZ MEASUREMENTSResults of micro channels fabricated on glass substrate

NaOHConc %

Avg.MaxDia

Avg.MinDia AvgWidthJunction

. AvgWidth circle,(AvgHAZ)

Avg. Depth of Channel, µm

Photograph

µm µm µm µm LeftCircle

At Junction

RightCircle

14 2300 1650 198 150(279)

- 110 70

16 _ 140 120

18 2342 1602 344 175(210)

70 140 80

20 2850 1442 50 (?) 107(562)

240 340 270

MEASUREMENTS CONTINUED…..

NaOHConc %

Avg. MaxDia

Avg.MinDia

Avg.WidthJunction

AvgWidthCircle

Avg. Depth of Channel, µm

Photograph

µm µm µm µm LeftCircle

At Junction RightCircle

14 2280 1614 320 125(265)

75 100 50

16 2514 1516 182 120(383)

130 180 120

18 2240 1658 394 145(280)

140 100 110

20 2308 1572 254 127(481)

235 400 115

MICRO CHANNEL MEASUREMENT RESULTS FOR V=50V ON GLASS WORKPIECE

future possibilities…….Extension of the process for layered deposition and hence for micro fabrication are being studied

.Multi layer deposition of the desired shape and size can result in the evolution of micro fabrication of miniature structures.

Flowing electrolyte ECSM can also be researched for further improvements.

Both machining and deposition process are in infancy for the industrial purposes.

ED samples with air as medium and copper wire of 0.2 mm dia as work piece.ref V.K.Jain’microfabrication using ecsm’defense science journal.vol57,no.5.sept2007,pp766

LIMITATIONS…….Beyond a certain value of electrolyte temperature , ECSM performance starts deteriorating.

Since a high voltage greater than that in ECM is required to produce the spark , therefore the process is potentially useful and cost effective mainly for non-conducting materials and machining in the micron region.

CONCLUSIONS….The discharge in ECSM is a discrete phenomenon.

Synchronized study of the process revealed that the discharge temperature rise is due to bombardment of electrons generated during the discharge process. When the discharge temperature is of the order of boiling temperature of the work piece material, metal removal takes place.

ECSM can be performed in the micron region and the dimensions can be further reduced by reducing the geometry of the cathode tip and by careful design of process parameters.

The process is a stand alone process requiring no other intermediate steps as masking, pattern transfer, passivating.

It is a competitive process in the sense that the machining time required to have a complex micro channel is very small.

Hence , it’s a potential candidate for micro machining in a cost effective manner.

THANK YOU

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