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Applications of Acoustic Mapping in Electrical Discharge Machining

Applications of Acoustic Mapping in Electrical Discharge Machining. Craig Smith, Philip Koshy. McMaster University Canada. Acoustic emission monitoring of EDM. Relative to cutting, grinding and forming processes, little is known about acoustic emission (AE) in EDM.

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Applications of Acoustic Mapping in Electrical Discharge Machining

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  1. Applications of Acoustic Mapping in Electrical Discharge Machining Craig Smith, Philip Koshy McMaster UniversityCanada

  2. Acoustic emission monitoring of EDM • Relative to cutting, grinding and forming processes, little is known about acoustic emission (AE) in EDM • Information gleaned from AE could constitute an important additional dimension in advancing intelligent adaptive process control Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  3. Scope of present work Y X • This work proves the concept of the acoustic mapping of discharges in EDM (x,y) • Application of the concept towards the estimation of electrode length in fast hole EDM, and workpiece height in wire EDM are demonstrated jauvtismp.com practicalmachinist.com Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  4. Previous work on discharge location: 1 Han & Kunieda (2008) Kunieda & Kojima (1990) tool electrode tool electrode discharge discharge L1 R1 P1 P2 L2 R2 workpiece workpiece branch 2 branch 1 branch 1 branch 2 current sensor 1 current sensor 2 current method potential method Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  5. Previous work on discharge location: 2 Qiang et al (2002) Okada et al (2010) electromagnetic method high speed imaging Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  6. Previous work on discharge location: 3 Ydreskog & Novak (1989) Muto et al (1989) • AE sensor with a resonant frequency of 20 MHz t1 • Single spark experiments that did not consider the superposition of AE from successive discharges t2 acoustic emission method Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  7. Experimental AE acquired @ 10 MHz • wire and fast hole experiments were simulated on a sinker sensor 1 sensor 2 wire Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  8. AE discharge location AE sensor 2 AE sensor 1 discharge wire EMI 2 0 -2 2 signal voltage (V) 0 -2 1.0 current signal 0.5 0.0 0 50 100 150 200 time (µs) Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  9. Estimation of arrival time & time lag arrival time 2 0 -2 2 signal voltage (V) 0 50 100 150 200 0 time (µs) time lag -2 • Estimation of arrival time and time lag with reference to preset voltage thresholds and cross-correlation, respectively, referred to location errors > 10 mm Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  10. AE frequency content AE EMI amplitude (V) 0.20 0.20 0.15 0.15 0.10 0.10 0.05 0.05 0.00 0.00 0 250 500 750 1000 frequency (kHz) 0 250 500 750 1000 Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  11. Typical spectrogram AE EMI • The peak in the spectrogram serves a consistent reference for the reliable estimation of arrival time Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  12. Speed calibration 3300 m/s 3452 m/s • 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 Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  13. Electrode length estimation in fast hole EDM estimation error ~1 mm Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  14. 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 PSD (x10-6 V2/Hz) Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  15. Superposed AE 161.9 µs 169.1 µs ton 1 µs; toff 10 µs 4 AE sensor 1 2 sensor 1 105.8 µs 0 -2 current signal -4 0.6 x1 0 50 100 150 200 0.3 2 3 4 5 6 7 8 9 10 1 signal voltage (V) 250 mm 0.0 wire x2 4 AE sensor 2 2 0 sensor 2 -2 -4 0 50 100 150 200 time (µs) Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  16. Workpiece height identification in wire EDM 23 mm histogram of detected locations • 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 actual w/p height 90 mm cumulative distribution Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  17. Conclusions • 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 Applications of acoustic mapping in EDM C. Smith, P. Koshy 63rd CIRP General Assembly Copenhagen, August 20, 2013

  18. Canadian Network for Research & Innovation in Machining Technology Natural Sciences & Engineering Research Council of Canada Thank you for your kind attention!

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