wire edm, edg, eddg
TRANSCRIPT
-
8/13/2019 Wire Edm, Edg, Eddg
1/23
1
WIRE ELECTRIC DISCHARGE MACHINING(WIRE EDM)
-
8/13/2019 Wire Edm, Edg, Eddg
2/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
3/23
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.
-
8/13/2019 Wire Edm, Edg, Eddg
4/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
5/23
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 .
-
8/13/2019 Wire Edm, Edg, Eddg
6/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
7/23
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
o
WIRE MOVEMENT TOWARDS TAKE UP SPOOL SERIES OF TENSIONING ROLLERS
-
8/13/2019 Wire Edm, Edg, Eddg
8/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
9/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
10/23
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.
-
8/13/2019 Wire Edm, Edg, Eddg
11/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
12/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
13/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
14/23
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.
-
8/13/2019 Wire Edm, Edg, Eddg
15/23
WIRE - EDM
Stator core stamping die machined by wire - EDM
-
8/13/2019 Wire Edm, Edg, Eddg
16/23
WIRE EDM + TAPER CUTTING MECHANISM
Example of the complex shapes that can be cut with wire EDM and a taper cutting mechanism
-
8/13/2019 Wire Edm, Edg, Eddg
17/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
18/23
Rotating diskelectrode for EDG
-
8/13/2019 Wire Edm, Edg, Eddg
19/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
20/23
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.
-
8/13/2019 Wire Edm, Edg, Eddg
21/23
EDDG setup
-
8/13/2019 Wire Edm, Edg, Eddg
22/23
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
-
8/13/2019 Wire Edm, Edg, Eddg
23/23
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