Abstract

We describe a focus control system for Nd:YAG laser welding based on an optical sensor incorporated into the fiber delivery system to detect light generated by the process. This broadband light is separated into two wavelength bands, and simple electronic processing gives a signal proportional to focal error as a result of chromatic aberrations in the optical delivery system. Focus control is demonstrated for bead-on-plate welds in different thicknesses of titanium alloy, aluminum alloy, mild steel, and stainless steel. The control system works for both pulsed and continuous laser radiation.

© 1997 Optical Society of America

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References

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  1. S. Beirmann, A. Topkaya, M. Jagiella, “Capacitive clearance sensor system for high quality Nd:YAG laser cutting and welding of sheet metals,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 51–55.
  2. I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).
  3. A. Otto, G. Deinzer, M. Geiger, “Control of transient processes during CO2-laser beam welding,” in Symposium on Laser Materials Processing: Industrial and Microelectronics Applications, E. Beyer, M. Cantello, A. V. Larocca, L. D. Laude, F. O. Olsen, G. Sepold, eds., Proc. SPIE2207, 282–288 (1994).
    [CrossRef]
  4. A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
    [CrossRef]
  5. T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.
  6. M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980), p. 174.
  7. T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
    [CrossRef]
  8. N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
    [CrossRef]

1996 (1)

T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
[CrossRef]

1992 (1)

A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
[CrossRef]

1989 (1)

N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
[CrossRef]

Beirmann, S.

S. Beirmann, A. Topkaya, M. Jagiella, “Capacitive clearance sensor system for high quality Nd:YAG laser cutting and welding of sheet metals,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 51–55.

Boechat, A. A. P.

A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
[CrossRef]

Born, M.

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980), p. 174.

Deinzer, G.

A. Otto, G. Deinzer, M. Geiger, “Control of transient processes during CO2-laser beam welding,” in Symposium on Laser Materials Processing: Industrial and Microelectronics Applications, E. Beyer, M. Cantello, A. V. Larocca, L. D. Laude, F. O. Olsen, G. Sepold, eds., Proc. SPIE2207, 282–288 (1994).
[CrossRef]

Dowden, J.

N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
[CrossRef]

Geiger, M.

A. Otto, G. Deinzer, M. Geiger, “Control of transient processes during CO2-laser beam welding,” in Symposium on Laser Materials Processing: Industrial and Microelectronics Applications, E. Beyer, M. Cantello, A. V. Larocca, L. D. Laude, F. O. Olsen, G. Sepold, eds., Proc. SPIE2207, 282–288 (1994).
[CrossRef]

Ishide, T.

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

Jagiella, M.

S. Beirmann, A. Topkaya, M. Jagiella, “Capacitive clearance sensor system for high quality Nd:YAG laser cutting and welding of sheet metals,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 51–55.

Jones, J. D. C.

A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
[CrossRef]

Kaminuki, A.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

Kapadia, P.

N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
[CrossRef]

Klien, T.

T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
[CrossRef]

Maruo, H.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

Matsumoto, O.

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

Miyamoto, I.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

Mori, K.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

Nagashima, T.

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

Nagura, Y.

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

Otto, A.

A. Otto, G. Deinzer, M. Geiger, “Control of transient processes during CO2-laser beam welding,” in Symposium on Laser Materials Processing: Industrial and Microelectronics Applications, E. Beyer, M. Cantello, A. V. Larocca, L. D. Laude, F. O. Olsen, G. Sepold, eds., Proc. SPIE2207, 282–288 (1994).
[CrossRef]

Postacioglu, N.

N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
[CrossRef]

Sakamoto, M.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

Simon, G.

T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
[CrossRef]

Su, D.

A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
[CrossRef]

Topkaya, A.

S. Beirmann, A. Topkaya, M. Jagiella, “Capacitive clearance sensor system for high quality Nd:YAG laser cutting and welding of sheet metals,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 51–55.

Vicanek, M.

T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
[CrossRef]

Wolf, E.

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980), p. 174.

Yokoyama, A.

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

J. Phys. D (2)

T. Klien, M. Vicanek, G. Simon, “Oscillations of the keyhole in penetration laser beam welding,” J. Phys. D 29, 322–332 (1996).
[CrossRef]

N. Postacioglu, P. Kapadia, J. Dowden, “Capillary waves on the weld pool in penetration welding with a laser,” J. Phys. D 22, 1050–1061 (1989).
[CrossRef]

Meas. Sci. Technol. (1)

A. A. P. Boechat, D. Su, J. D. C. Jones, “Bi-directional cladding power monitor for fibre-optic beam delivery systems,” Meas. Sci. Technol. 3, 897–901 (1992).
[CrossRef]

Other (5)

T. Ishide, Y. Nagura, O. Matsumoto, T. Nagashima, A. Yokoyama, “High power YAG laser welding and its in-process monitoring using optical fibers,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 81–86.

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980), p. 174.

S. Beirmann, A. Topkaya, M. Jagiella, “Capacitive clearance sensor system for high quality Nd:YAG laser cutting and welding of sheet metals,” in European Conference on Laser Treatment of Materials, B. L. Mordike, ed. (DGM Metallurgy Information, New York, 1992), pp. 51–55.

I. Miyamoto, A. Kaminuki, H. Maruo, K. Mori, M. Sakamoto, “In-process monitoring in laser welding of automotive parts,” in Laser Materials Processing Conference (ICALEO ’93), P. Denney, I. Miyamoto, B. L. Mordike, eds., Proc. SPIE2306, 413–424 (1994).

A. Otto, G. Deinzer, M. Geiger, “Control of transient processes during CO2-laser beam welding,” in Symposium on Laser Materials Processing: Industrial and Microelectronics Applications, E. Beyer, M. Cantello, A. V. Larocca, L. D. Laude, F. O. Olsen, G. Sepold, eds., Proc. SPIE2207, 282–288 (1994).
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

Ray diagram of light propagating from the distal face of the delivery fiber onto the workpiece.

Fig. 2
Fig. 2

Laser/workpiece interaction zone.

Fig. 3
Fig. 3

Experimental setup.

Fig. 4
Fig. 4

Diagram illustrating the coupling of the optical radiation generated at the laser/workpiece interaction zone back into the power delivery fiber by way of achromats L 1 and L 2. F YAG, F IR, and F UV are the focal positions of the YAG, IR, and UV radiation, respectively.

Fig. 5
Fig. 5

Schematic of the closed-loop focus control system. LPF, low-pass filter.

Fig. 6
Fig. 6

Simulation of the experimental setup.

Fig. 7
Fig. 7

IR and UV/visible signals obtained when welding 1-mm-thick mild steel with 2 kW of Nd:YAG laser radiation. The plate was tilted at an angle of 2.5° and traversed through the laser beam at a speed of 6 m min-1. An argon shield gas was used.

Fig. 8
Fig. 8

Error signal obtained in open-loop tests when welding 1-mm-thick mild steel with 1.5 kW of Nd:YAG laser radiation. The plate was tilted at an angle of 2.5° and traversed through the laser beam at a speed of 2.5 m min-1.

Fig. 9
Fig. 9

Weld on 1-mm-thick mild steel with 2 kW of Nd:YAG laser radiation. The plate was tilted at an angle of 2.5° and traversed through the laser beam at a speed of 5 m min-1. An argon shield gas was used. The top weld was produced with open-loop operation and the bottom weld with closed-loop operation. The welds are 200-mm long.

Fig. 10
Fig. 10

Residual error signal obtained with loop closed when welding 1-mm-thick mild steel with 1.75 kW of Nd:YAG laser radiation. The plate was tilted at an angle of 2.5° and traversed through the laser beam at a speed of 3 m min-1. An argon shield gas was used.

Fig. 11
Fig. 11

Collection of closed-loop focus control error signals obtained for a range of different welding conditions and workpiece materials, as detailed in the figures. P is laser power, P ave is average laser power, ν is the welding speed, θ is the tilt angle, and σ is the standard deviation around the mean error signal value, expressed in millimeters.

Fig. 12
Fig. 12

Simulation experimental results showing the variation in the visible and IR signals as a function of translation in the direction of the optical axis.

Tables (1)

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Table 1 Positive Achromat Lens Specification

Equations (1)

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ε=GUVVUV-GIRVIR.

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