Wire Edm, Edg, Eddg

8/13/2019 Wire Edm, Edg, Eddg

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WIRE ELECTRIC DISCHARGE MACHINING(WIRE EDM)


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Wire EDM

Electrical discharge machining wire cutting (EDM-WC) is a thermalmass-reducing process that uses a continuously moving wire to

remove material by means of rapid controlled repetitive sparkdischarges.

Process Characteristics Utilizes a traveling wire that is advance within arcing distance of theworkpiece (0.001 in.)Removes material by rapid, controlled, repetitive sparkUses dielectric fluid to flush removed particles, control discharge, andcool wire and workpieceThe wire and workpiece must be electrically conductive.Can produce complex two-dimensional shapes


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WIRE - EDM

POWER SUPPLY - PULSATING DC. DIELECTRIC DEIONISED WATER

WORKING PRINCIPLE OF WIRE EDM SAME AS EDM.

COMPARED WITH BAND SAW MRR & QUALITY = (WIRE).

SPARKING BETWEEN WIRE & WORKPIECE ERODES BOTH WIRE & WORKPIECE.


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WORKPIECE MATERIAL ELECTRICALLY CUNDUCTIVE.

TOOL 0.05 - 0.30 mm DIA. WIRE

DIELECTRIC DEIONSED WATER

MATERIAL REMOVING MELTING / VAPORISATION

CONSTANT IEG COMPUTER CONTROLLED POSITIONING SYSTEM

HIGH DEGREE OF ACCURACY AND GOOD SURFACE FINSH

WIRE ELECTRIC DISCHARGE MACHINING (WIRE EDM)

CAN CUT COMPLICATED CONTOURS


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POWER SUPPLY SYSTEM

POWER SUPPLY SYSTEM

DIELECTRIC SYSTEM

POSITIONONG SYSTEM

DRIVE SYSTEN

WIRE ELECTRIC DISCHARGE MACHINING (WIRE EDM)

PULSE FREQUENCY 1 MHz reduced crater size or better surface finish

SMALL WIRE SIZE CURRENT CARRYING CAPACITY < 20 A .


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DIELECTRIC SYSTEM

WATER AS DIELECTRIC (substitute for kerosene )

More efficient way of dielectric delivery is to provide a stream of deionizedwater along the axis of the wire.Cost of the dielectric can be lowered down by reusing it after filtration

5 m size disposable paper filterAdditives are mixed to minimize rusting

low viscosity efficient flow

easy availability, desirable thermal properties

pollution-free working

no fire hazardhigh cooling rate very thin recast layer

high MRR, better surface finish and high tool wear rate

high TWR does not adversely affect performance as wire is not reused


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POSITIONING SYSTEM

CNC 2 AXES TABLE Operates in adaptive control mode

IN CASE OF SHORT CIRCUITING ( debris bridging gap / wire workpiece too

close) MOVES BACK TO RE-ESTABLISH PROPER CUTTING GAP CONDITIONS.

WIRE DRIVE SYSTEM

FUNCTIONSDELIVERS FRESH WIRE

keeps wire always under tension moves in m/cing zone as straight wirefor better quality of the machined surface

For high quality avoid taper, streaks, vibration marks etc.

Minimizes wire breakage frequently

o WIRE GUIDED BY WIRE GUIDESSAPPHIRE

DIAMOND

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WIRE MOVEMENT TOWARDS TAKE UP SPOOL SERIES OF TENSIONING ROLLERS


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o WIRE MATERIALSMALL DIAM. (< 0.15 mm) MOLYBDENUM STEEL

LARGE DIAM. (0.15 0.3 mm) COPPER OR BRASS

o AUTOMATIC RELOADING OF BROKEN WIRE

TO ENHANCE PRODUCTIVITY

TO RUN THE M/C UNATTENDED

WIRE DISCARDED AFTER USED ONCE After wear at leading surface due tosparking, no longer remains round


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Automatic wire threading, self restarting and improved tensioning devices.

incorporation of CNC features operator can input for wire compensation at the m/c.

Easy to interrupt the process and change the m/cing parameters (V, I) and othersettings more easily

Program wire to follow a complex path in 2 axes for making dies for stamping fine

blanking and extrusion , 2-D through holes

Possible to tilt wire in positions other than perpendicular to X and Y axesHave facility for speedy automatic realignment of wire

Perform 3-D cutting using 2 additional axes (U and V). Drive motors tilt wire towards

front or back (V axis) and left or right (U axis). Extent of tilt (say, 10 or so) gives

limitation of m/t.In versatile m/t, all 4 axes (X, Y, U, V) can be controlled simultaneously using closed

loop control arrangement for work table and wire guide positions to make, a draft or

relief in the mould, and constant radius corners along the tapered walls of molds and

dies in one stroke.

Advances in WC- EDM


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CNC WIRE EDM / CNC EDM

POSSIBLE TO ACHIEVE 0.1m FEED

1.0 m TABLE POSITIONING.

TAPER CUTTING USING WIRE EDM

REDUCES CORNER ERROR

SUPPRESSES WIRE VIBRATION REDUCES

CRACKED SURFACE.

FINE FINISHING POWER SUPPLY HIGH

QUALITY SURFACE FINISH ( 0.1 m )

Mitsubishis approach to taper cutting on a traveling wire EDM involves drive motors that shiftthe position of the upper wire guide along two axes, called U and V. These shifts must be coordinatedwith X and Y travel by the CNC for versatile three dimensional machining.


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STRATIFIED WIRE

CHARMILLES CORPORATION (SWTZERLAND)

Core made of copper drawn wire.

Outside thin layer of Zn or Zn alloy (low melt)

MRR higher (can carry more current ) than when using copper wire

Wire not-recycled not very expensive, gets eroded during process


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WHY TO USE STRATIFIED WIRE ?

Wire can carry heavier load if it can absorb more amount of heat without breaking

Heavier load high energy / spark high MRR (higher cutting speed) wirebreakage

To avoid wire breakage use stratified wire

Melting point of Zn


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BOWING OF WIRE

Distance between wire and workpiece 25 m in kerf.

W/p eroded by violent, extremely localized and momentary action of the spark

Gas bubbles rush to escape pressure on the wire wire bends (bowing of

wire) tends to drag on bends and sharp corners as it advances leads to inaccuracy

(due to different IEG)

Remedy

wire guiding and feeding mechanism should be designed to withstand higher tension

WIRE EDM m/c CNC WIRE EDM m/c


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PROCESS CHARACTERISTIC

APPLICATIONS

MATTE FINISH SURFACE.

CRATERS HELP IN RETAINING LUBRICATING OIL INCREASED DIE LIFE.

SURFACE IN FINISH PASS 0.1m

TOLERANCE 7m

Making dies

Fabrication of press tools

Electrodes for use in other areas of EDM

PROCESS VARIABLES

LINEAR CUTTING RATE THICKNESS OF WORKPIECE BUT NOT THE COMPLEXITY OF CUT

HIGHEST WIRE SPEED 40 mm/s.


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WIRE - EDM

Stator core stamping die machined by wire - EDM


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WIRE EDM + TAPER CUTTING MECHANISM

Example of the complex shapes that can be cut with wire EDM and a taper cutting mechanism


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ELECTRIC DISCHARGE GRINDING (EDG) Grinding conventional and hybrid grinding. Hybrid grinding mechanical grinding assisted by one or more (advanced) machining

techniques. Example: electrochemical grinding (ECG), ultrasonic grinding (USG), electric dischargegrinding (EDG), electric discharge diamond grinding (EDDG), etc.

EDG is a mass-reducing process that uses a rotating conductive wheel to remove electricallyconductive material by means of controlled, repetitive spark discharges. A dielectric fluid is usedto flush away the chips, regulate the discharge, and cool the wheel and the workpiece.

Process CharacteristicsA rotating wheel (electrically conductive material, usually graphite inexpensive and easy tomachine) used as a tool.

Wheel is kept within sparking (arcing) distance of the w/pPart of grinding wheel and w/p immersed in dielectric, connected to pulsed DC supplyRotating motion of wheel ensures effective flushing of dielectric in IEG

Mechanism of material removal same as in EDM except that rotary motion of the tool (i.e. wheel)helps in effective ejection of the molten material.

No direct physical contact between the tool and w/p unlike conventional grinding fragile andthin sectioned specimens can be easily machined without distortionEconomical compared to the conventional diamond grindingMaterial removal takes place due to melting and/or vaporization not by shearing.

EDG used for dressing metal bonded diamond grit grinding wheels removes bond material bymelting rather than mechanical shear as in conventional dressing

Can process very hard or difficult to machine metals


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Rotating diskelectrode for EDG


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Current in EDG m/t 0.5-200A, voltage 40-80V, pulse frequency 50-250 kHz.,

Maximum wheel surface speed 180 m/min.

EDG servo-system maintains a constant IEG by feeding workpiece into the wheel. If

debris somehow blocks the gap, the work-piece is retracted back to allow the debris to

be flushed out of the gap.

EDG capable to machine extremely hard materials, say, carbides at 2 to 3 times faster

than conventional diamond grinding.

Good surface finish (0.2 to 0.3 m) and high accuracy ( 2.5 m) is achieved


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ELECTRIC DISCHARGE DIAMOND GRINDING (EDDG)

Hybrid process involves machining of hard materials using advantages of EDM as

well as conventional grinding.

Water or water-based cutting fluid is used as dielectric.

Metal bonded diamond grit wheel is used in place of a simple electrically conductive

wheel (graphite) used in EDG.

Sparking takes place between metallic bonding material and W/P. Heat generated

during sparking softens the work material and hence machining by diamond

abrasive particles becomes easier.

Sparking in IEG during EDDG, results in continuous dressing of the grinding wheel

and hence the wheel does not clog. As a result, cutting properties of the grinding

wheel are stabilized.


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EDDG setup


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Used for precise trueing/dressing and profile generation of metal bonded

grinding wheels employing NC

EDDG also named as electro-contact abrasion finishing (ECAF) employed for

cutting blanks of various materials, profiles and dimensions.

Schematic diagram for on-machine electric dischargetrueing/dressing operation

Trueing/dressing operation


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Used for machining of cermates, super alloys, other metal matrix composites.

MRRV : 270 mm 3/min, wheel life: more than 120 min, and good surface finish (Ravalue as 10.32 to 0.15 m) without cracking.

Dressing/trueing of metal bonded diamond (or other abrasive) wheels.

wheel life in terms of the period between two dressings is increased by a factorranging from 5-10 in case of EDDG dressing, than after traditional abrasive dressing.

Accuracy achieved during electrical discharge diamond grinding is better than that inconventional diamond grinding.

Capabilities and Applications

Documents

Wire Edm, Edg, Eddg