Abstract

Any reliable automated production system must include process control and monitoring techniques. Two laser processing techniques potentially lending themselves to automation are percussion drilling and cutting. For drilling we investigate the performance of a modification of a nonintrusive optical focus control system we previously developed for laser welding, which exploits the chromatic aberrations of the processing optics to determine focal error. We further developed this focus control system for closed-loop control of laser cutting. We show that an extension of the technique can detect deterioration in cut quality, and we describe practical trials carried out on different materials using both oxygen and nitrogen assist gas. We base our techniques on monitoring the light generated by the process, captured nonintrusively by the effector optics and processed remotely from the workpiece. We describe the relationship between the temporal and the chromatic modulation of the detected light and process quality and show how the information can be used as the basis of a process control system.

© 2002 Optical Society of America

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References

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  1. E. J. Lerner, “Industrial laser cutting goes mainstream,” Laser Focus World 35, 113–118 (1999).
  2. H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.
  3. W. W. Duley, Laser Processing and Analysis of Materials (Plenum, New York, 1993).
  4. W. M. Steen, Laser Materials Processing, 2nd ed. (Springer-Verlag, New York, 1998).
    [CrossRef]
  5. J. Powell, CO2 Laser Cutting, 2nd ed. (Springer-Verlag, New York, 1998).
    [CrossRef]
  6. M. H. H. van Dijk, G. de Vlieger, J. E. Brouwer, “Laser precision hole drilling in aeroengine components,” in Proceedings of the Sixth International Conference on Lasers in Manufacturing, W. M. Steen, ed. (IFS Ltd., Birmingham, UK, 1989), pp. 237–247.
  7. P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.
  8. 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.
  9. Laser Vision process monitor, Modular Vision Systems, 4830 Cousens, Montreal, Quebec H4S 1X7 Canada.
  10. F. M. Haran, D. P. Hand, C. Peters, J. D. C. Jones, “Focus control system for laser welding,” Appl. Opt. 36, 5246–5251 (1997).
    [CrossRef] [PubMed]
  11. W. Koechner, Solid State Laser Engineering (Springer-Verlag, New York, 1996).
    [CrossRef]

1999 (1)

E. J. Lerner, “Industrial laser cutting goes mainstream,” Laser Focus World 35, 113–118 (1999).

1997 (1)

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.

Brouwer, J. E.

M. H. H. van Dijk, G. de Vlieger, J. E. Brouwer, “Laser precision hole drilling in aeroengine components,” in Proceedings of the Sixth International Conference on Lasers in Manufacturing, W. M. Steen, ed. (IFS Ltd., Birmingham, UK, 1989), pp. 237–247.

Byrd, P.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

de Vlieger, G.

M. H. H. van Dijk, G. de Vlieger, J. E. Brouwer, “Laser precision hole drilling in aeroengine components,” in Proceedings of the Sixth International Conference on Lasers in Manufacturing, W. M. Steen, ed. (IFS Ltd., Birmingham, UK, 1989), pp. 237–247.

Duley, W. W.

W. W. Duley, Laser Processing and Analysis of Materials (Plenum, New York, 1993).

French, P. W.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

Goede, M.

H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.

Haferkamp, H.

H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.

Hand, D. P.

F. M. Haran, D. P. Hand, C. Peters, J. D. C. Jones, “Focus control system for laser welding,” Appl. Opt. 36, 5246–5251 (1997).
[CrossRef] [PubMed]

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

Haran, F. M.

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.

Koechner, W.

W. Koechner, Solid State Laser Engineering (Springer-Verlag, New York, 1996).
[CrossRef]

Lerner, E. J.

E. J. Lerner, “Industrial laser cutting goes mainstream,” Laser Focus World 35, 113–118 (1999).

Peters, C.

F. M. Haran, D. P. Hand, C. Peters, J. D. C. Jones, “Focus control system for laser welding,” Appl. Opt. 36, 5246–5251 (1997).
[CrossRef] [PubMed]

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

Powell, J.

J. Powell, CO2 Laser Cutting, 2nd ed. (Springer-Verlag, New York, 1998).
[CrossRef]

Shannon, G. J.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

Steen, W. M.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

W. M. Steen, Laser Materials Processing, 2nd ed. (Springer-Verlag, New York, 1998).
[CrossRef]

Thürk, O.

H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.

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.

van Dijk, M. H. H.

M. H. H. van Dijk, G. de Vlieger, J. E. Brouwer, “Laser precision hole drilling in aeroengine components,” in Proceedings of the Sixth International Conference on Lasers in Manufacturing, W. M. Steen, ed. (IFS Ltd., Birmingham, UK, 1989), pp. 237–247.

von Busse, A.

H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.

Watkins, K.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

Appl. Opt. (1)

Laser Focus World (1)

E. J. Lerner, “Industrial laser cutting goes mainstream,” Laser Focus World 35, 113–118 (1999).

Other (9)

H. Haferkamp, M. Goede, A. von Busse, O. Thürk, “On-line quality monitoring during laser beam cutting using a thermographic system,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1998), Vol. 1, Sect. C, pp. C11–C17.

W. W. Duley, Laser Processing and Analysis of Materials (Plenum, New York, 1993).

W. M. Steen, Laser Materials Processing, 2nd ed. (Springer-Verlag, New York, 1998).
[CrossRef]

J. Powell, CO2 Laser Cutting, 2nd ed. (Springer-Verlag, New York, 1998).
[CrossRef]

M. H. H. van Dijk, G. de Vlieger, J. E. Brouwer, “Laser precision hole drilling in aeroengine components,” in Proceedings of the Sixth International Conference on Lasers in Manufacturing, W. M. Steen, ed. (IFS Ltd., Birmingham, UK, 1989), pp. 237–247.

P. W. French, D. P. Hand, C. Peters, G. J. Shannon, P. Byrd, W. M. Steen, K. Watkins, “Investigation of the Nd:YAG laser percussion drilling process using factorial experimental design,” in Proceedings of the International Congress on Applications of Lasers and Electro-Optics (Laser Institute of America, Orlando, Fla., 1999), Sect. C, pp. 51–60.

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.

Laser Vision process monitor, Modular Vision Systems, 4830 Cousens, Montreal, Quebec H4S 1X7 Canada.

W. Koechner, Solid State Laser Engineering (Springer-Verlag, New York, 1996).
[CrossRef]

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Figures (16)

Fig. 1
Fig. 1

System outline for (a) fiber-optic delivery and (b) direct beam delivery.

Fig. 2
Fig. 2

Chromatic aberrations cause the beam waist to be in different positions for light at the short and long end of the spectrum.

Fig. 3
Fig. 3

(a) Workpiece at focus, zero error signal. (b) Workpiece too close to delivery lens; VIS light is coupled into fiber more efficiently than NIR, therefore positive error signal. (c) Workpiece is too far from delivery lens, negative error signal.

Fig. 4
Fig. 4

Workpiece used to set up the focus control. The plate is a 1.5-mm mild steel plate and the cut is made in the center. A, workpiece used for initial setup. Results are shown in Figs. 11 and 12. B, workpiece used to test focus control in a closed loop. A photograph is shown in Fig. 13. C, elevation view of the plate. D, plan view of the plate.

Fig. 5
Fig. 5

Focus control error signals for a hole drilled in a 4-mm-thick mild steel plate with a JK702, 1-ms, 1-J prepulse with an oxygen assist gas for fiber-optic beam delivery.

Fig. 6
Fig. 6

Integration of error signals shown in Fig. 5. Error signal increases with focal position.

Fig. 7
Fig. 7

Parameters as for Fig. 6, except the hole is drilled at an angle of 45°.

Fig. 8
Fig. 8

Integration of error signals shown in Fig. 7.

Fig. 9
Fig. 9

Focus control error signals for a hole drilled in a 4-mm-thick mild steel plate with a JK702, 1-ms, 1-J prepulse with an oxygen assist gas for direct beam delivery.

Fig. 10
Fig. 10

Integration of signals shown in Fig. 9.

Fig. 11
Fig. 11

Amplitude of NIR and VIS signals obtained when we produce a 100-mm cut in the workpiece using 2 kW of Nd:YAG laser radiation. The focal standoff was increased from 0.5 to 1.5 mm (optimal position 1.0 mm) as the plate was traversed through the laser beam at a speed of 7 m min-1. An oxygen assist gas was used.

Fig. 12
Fig. 12

Error signal of arbitrary units produced from signals shown in Fig. 11. The VIS signal was subtracted from the NIR to produce an error signal that can then be used to adjust the nozzle standoff.

Fig. 13
Fig. 13

Typical cuts produced with 2-kW of Nd:YAG laser radiation with initial focal position incorrectly set: (a) closed-loop, (b) open-loop 100-mm cut in workpiece. The focal standoff was increased from 1 to 3.5 mm and then back to 1 mm as the plate was traversed through the laser beam at a speed of 7 m min-1.

Fig. 14
Fig. 14

Optical signals obtained with system parameters varied. (a) Optical signals for a good cut with optimal parameter settings with power at 2 kW, a feed rate of 9 m min-1, and a gas flow rate of 45 l min-1 at 4 bars. (b) Parameters as in (a) but the gas flow rate is reduced to 35 l min-1 at 3.5 bars. (c) Parameters as in (a) but with feed rate increased to 13 m min-1. (d) Parameters as in (a) but with the power reduced to 670 W.

Fig. 15
Fig. 15

Diagrammatic beam waists for narrow and large NA.

Fig. 16
Fig. 16

For thick material, the cut front will vary according to the setup parameters, which may affect image position.

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