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Applications of Acoustic Mapping in Electrical Discharge Machining
Craig Smith, Philip KoshyMcMaster University
Canada
2/18
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Acoustic emission monitoring of EDM
Information gleaned from AE could constitute an important additional dimension in advancing intelligent adaptive process control
Relative to cutting, grinding and forming processes, little is known about acoustic emission (AE) in EDM
3/18
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Scope of present work
This work proves the concept of the acoustic mapping of discharges in EDM
(x,y)
XY
Application of the concept towards the estimation of electrode length in fast hole EDM, and workpiece height in wire EDM are demonstrated
practicalmachinist.comjauvtismp.com
4/18
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Kunieda & Kojima (1990)
current method
discharge
tool electrode
R1 R2
workpiece
branch 1 branch 2
current sensor 1 current sensor 2
Han & Kunieda (2008)
potential method
L1 L2
workpieceP1 P2
branch 1 branch 2
discharge
tool electrode
Previous work on discharge location: 1
electromagnetic method
Qiang et al (2002)
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Previous work on discharge location: 2
Okada et al (2010)
high speed imaging
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Previous work on discharge location: 3
Ydreskog & Novak (1989) Muto et al (1989)
t1
t2
acoustic emission method
AE sensor with a resonant frequency of 20 MHzSingle spark experiments that did not consider the superposition of AE from successive discharges
7/18
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Experimental
AE acquired @ 10 MHz
sensor 1 sensor 2
wire
wire and fast hole experiments were simulated on a sinker
8/18
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
AE discharge location
AE sensor 2
wire
AE sensor 1
0 50 100 150 200
0.00.51.0
time (µs)
current signal
discharge
-2
sign
al v
olta
ge (
V)
0
2
-2
0
2
EMI
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Estimation of arrival time & time lag
-2
sign
al v
olta
ge (
V)
0
2
-2
0
2
0 50 100 150 200time (µs)
Estimation of arrival time and time lag with reference to preset voltage thresholds and cross-correlation, respectively, referred to location errors > 10 mm
arrival time
time lag
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
AE frequency content
EMI AE
0.20
0 250 500 750 1000
0.00
0.05
0.10
0.15
frequency (kHz)
am
plit
ude
(V
)
0 250 500 750 1000
0.00
0.05
0.10
0.15
0.20
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Typical spectrogram
The peak in the spectrogram serves a consistent reference for the reliable estimation of arrival time
EMI AE
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Speed calibration
Propagation of AE entails shear, longitudinal and surface (Raleigh) wave modes that travel at different velocities; the sensor used responds to the latter two
Use of relative rather than absolute speeds enables the use of commercial AE sensors
3300 m/s
3452 m/s
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Electrode length estimation in fast hole EDM
estimation error ~1 mm
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Handling wave superposition
AE from discharges struck 12.9 µs apart
spectrogram
computed time lag 81.5 - 68.8 = 12.7 µs
power spectral density @ 300 kHz
PS
D (
x10-6
V2/H
z)
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Superposed AE
0.0
0.3
0.6 current signal
1 2 3 4 5 6 7 8 9 10
105.8 µs
ton 1 µs; toff 10 µs
time (µs)0 50 100 150 200
-4
-2
0
2
4 AE sensor 2 169.1 µs
4161.9 µs
sign
al v
olta
ge (
V)
-4
-2
0
2AE sensor 1
0 50 100 150 200
Current spike
x1 (mm)
x2 (mm)
x1+ x2 (mm)
5 216.9 240.6 457.56 159.1 183.9 343.17 112.9 136.7 249.78 103.0 126.8 229.93
x1
x2
sensor 1
sensor 2
wire
250 mm
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Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Workpiece height identification in wire EDM
The envelope of discharge locations refers to the workpiece height in wire EDM
Identification of workpiece height is important for on-line process optimization
50 mm
90 mm
23 mm
actualw/p height
cumulativedistribution
histogram ofdetected locations
17/18
Difficulties associated with handling the superposition of acoustic wavetrains from successive discharges have hitherto hindered the development of AE discharge location
The maximum intensity in the spectrogram of the AE signal constitutes a reliable frame of reference for the determination of acoustic time lag, even when several signals are superposed
The proof-of-concept of the application of the determination of acoustic time lag in the estimation of electrode length and workpiece height in fast hole EDM and wire EDM, respectively, highlight the potential of the technique
Fundamental investigations into the nature of acoustic emission in EDM is warranted
Conclusions
Applications of acoustic mapping in EDMC. Smith, P. Koshy
63rd CIRP General AssemblyCopenhagen, August 20, 2013
Thank you for your kind attention!
Natural Sciences & Engineering Research Council of Canada
Canadian Network forResearch & Innovation in
Machining Technology
