In this study, we propose a technique to detect the weld morphology between deep penetration mode and shallow penetration mode in CW 4kW YAG laser welding by monitoring an optical and acoustic emissions. Both signals were analyzed by Fast Fourier Transform (FFT) program and their frequency spectra were obtained. Mild steel, stainless steel and aluminum alloy were used for workpiece. When the weld morphology changed from deep penetration mode to shallow penetration mode in mild steel, main frequency components of the acoustic spectrum, which appeared in 1 to 10 kHz, became smaller and a flat spectrum was obtained. The similar change of the main frequency components was observed for FFT spectra of optical emission intensity. This phenomenon was also observed for other two materials examined. We found that the intensity ratio of lower frequency components versus higher frequency components of the spectrum correlated well to the aspect ratio of welding bead. The ratio of the optical emission intensity measured in the range of 23 - 25 kHz to that measured in the range of 2 - 4 kHz showed a good correlation with the aspect ratio, and the ratio of 32 - 35 kHz to 2 - 4 kHz correlated well to the aspect ratio for the acoustic emission. Thus we could evaluate whether the welding was deep penetration mode or shallow penetration mode by analyzing the frequency components of the signals in YAG laser welding.

1.
Mao
Y L
,
Kinsman
G
and
Duley
W W.
Real-Time Fast Fourier Transform Analysis of Acoustic Emission During CO2 laser Welding of Materials
.
J. Laser Applic.
Vol.
5
:
1993
; pp.
17
22
.
2.
Duley
W W
and
Mao
Y L.
The Effect of Surface Condition on Acoustic Emission During Welding of Aluminium with CO2 Laser Radiation
.
J. Phys. D: Appl. Phys.
Vol.
27
:
1994
; pp.
1379
1383
.
3.
Gu
H
and
Duley
W W.
Resonant Acoustic Emission During Laser Welding of Metals
.
J. Phys. D:Appl. Phys.
Vol.
29
:
1996
; pp.
550
555
.
4.
Gu
H
and
Duley
W W.
A Statical Approach to Acoustic Monitoring of Laser Welding
.
J. Phys. D:Appl. Phys.
Vol.
29
:
1996
; pp.
556
660
.
5.
Gu
H a
nd
Duley
W W.
Discrete Signal Componets in Optical Emission During Keyhole Welding
.
Proceedings of the Laser Materials Processing Conference ICALEO’97
LIA
Vol.
83
Part1 Section C:
1997
; pp.
40
46
.
6.
Watanabe
M
,
Okado
H
,
Inoue
T
,
Nakamura
S
and
Matsunawa
A.
Features of Various In-Process Monitoring Methods and Their Applications to Laser Welding
.
Proceedings of the Laser Materials Processing Conference ICALEO’95
LIA
Vol.
80
:
1995
; pp.
553
562
.
7.
Nakamura
S
,
Ito
Y
,
Nakabayashi
T
,
Watanabe
M
,
Inoue
T
and
Matsunawa
A.
Analysis of Optical and Acoustic Emissions During CO2 Laser Welding of a Stainless Steel
.
Proceedings of the Laser Materials Processing Conference ICALEO’97
LIA
Vol.
83
Part2 Section G:
1997
; pp.
256
262
.
8.
Nakamura
S
,
Sakurai
M
,
Ito
Y
,
Kamimuki
K
,
Inoue
T
and
Matsunawa
A.
Detection of Transition from Keyhole-type to Heat Conduction-type Welding in CO2 Laser Welding of Metals
.
Proceedings of the Laser Materials Processing Conference ICALEO’99
LIA
Vol.
87
Part2 Section E:
1999
; pp.
28
33
.
9.
Nakamura
S
,
Sakurai
M
,
Kamimuki
K
,
Inoue
T
and ItoY.
Detection Technique for Transition between Deep Penetration Mode and Shallow Penetration Mode in CO2 Laser Welding of Metals
.
J. Physics D: Applied Physics
Vol.
33
No.22:
2000
; pp.
2941
2948
.
This content is only available via PDF.
You do not currently have access to this content.