In this paper we describe a novel spectroscopic closed loop control system capable of stabilizing the penetration depth during laser welding processes by controlling the laser power. Our novel approach is to analyze the optical emission from the laser generated plasma plume above the keyhole, to calculate its electron temperature as a process-monitoring signal. Laser power has been controlled by using a quantitative relationship between the penetration depth and the plasma electron temperature. The sensor is able to correlate in real time the difference between the measured electron temperature and its reference value for the requested penetration depth. Accordingly the closed loop system adjusts the power, thus maintaining the penetration depth.
References
[1]
Abderrazak, K.; Ben Salem, W.; Mhiri, H.; Bournot, P.; Autric, M. Nd:YAG laser welding of AZ91 magnesium alloy for aerospace industries. Metall. Mater. Trans. B. 2009, 40, 54–61, doi:10.1007/s11663-008-9218-7.
[2]
Lima, M.S.F.; Riva, R.; De Oliveira, A.C.; Siqueira, G.R. Laser beam welding aerospace aluminum using fiber lasers. Proc. SPIE 2009, 7131, 713128.
[3]
Liedl, G.; Bielak, R.; Ivanova, J.; Enzinger, N.; Figner, G.; Brickner, J.; Pasic, H.; Pudar, M.; Hampel, S. Joining of aluminum and steel in car body manufacturing. Proc. LIM. 2011, 12, 150–156.
[4]
Mikame, K. Application of Laser Material Processing in Toyota Motor Corporation. Proceedings of 4th International WLT Conference on Lasers in Manufacturing, Munich, Germany, 18–22 June 2007; pp. 1–4.
[5]
Dasgupta, A.K.; Mazumder, J. Laser welding of AM60 magnesium alloy. Magnes. Technol. 2004, 2004, 43–48.
[6]
Parionar, I.; Teleginski, V.; dos Santos, K.; Machado, S.; Zara, A.J.; Zurba, N.K.; Riva, R. Yb-fiber laser beam effects on the surface modification of Al-Fe aerospace alloy obtaining weld filet structures, low fine porosity and corrosion resistance. Surf. Coat. Technol. 2012, 206, 2293–2301, doi:10.1016/j.surfcoat.2011.10.007.
[7]
Mueller, S.; Bratt, C.; Mueller, P.; Cuddy, J.; Shankar, K. Laser Beam Welding of Titanium—A Comparison of CO2 and Fiber Laser for Potential Aerospace Applications. Proceedings of ICALEO 2008: 27th International Congress on Applications of Lasers and Electro-Optics, Temecula, CA, USA, 20– 23 October 2008; pp. 846–854.
[8]
Scintilla, L.D.; Tricarico, L.; Brandizzi, M.; Satriano, A.A. Nd:YAG laser weldability and mechanical properties of AZ31 magnesium alloy butt joints. J. Mater. Process. Technol. 2010, 210, 2206–2214, doi:10.1016/j.jmatprotec.2010.08.005.
[9]
Beersiek, J.; Devermann, T.; Behler, K. Practical Applications of In-Process Monitoring For Laser Processes—Not Only for Single Welds and Common Materials. Proceedings of ICALEO 2004: 23rd International Congress on Applications of Laser and Electro-Optics, San Francisco, CA, USA, 4–7 October 2004.
[10]
Kawahito, Y.; Ohnishi, T.; Katayama, S. In-Process Monitoring and Adaptive Control in Micro Lap Seam Welding with Fiber Laser. Proceedings of ICALEO 2008: 27th International Congress on Applications of Lasers and Electro-Optics, Temecula, CA, USA, 20–23 October 2008; pp. 94–98.
[11]
Kawahito, Y.; Kito, M.; Katayama, S. In-process monitoring and adaptive control for gap in micro butt welding with pulsed YAG laser. J. Phys. D Appl. Phys. 2007, 40, 2972–2978, doi:10.1088/0022-3727/40/9/045.
Kawahito, Y.; Ohnishi, T.; Katayama, S. In-process monitoring and feedback control for stable production of full-penetration weld in continuous wave fibre laser welding. J. Phys. D Appl. Phys. 2009, 42, 085501, doi:10.1088/0022-3727/42/8/085501.
[14]
Zaeh, M.F.; Huber, S. Characteristic line emissions of the metal vapour during laser beam welding. Prod. Eng. 2011, 6, 667–678.
[15]
Sibillano, T.; Ancona, A.; Berardi, V.; Lugara, P.M. Optical detection of condution/keyhole mode transition in laser welding. J. Mater. Process. Technol. 2007, 191, 364–367, doi:10.1016/j.jmatprotec.2007.03.075.
Zhang, Y.; Li, L.; Zhang, G. Spectroscopic measurements of plasma inside the keyhole in deep penetration laser welding. J. Phys. D Appl. Phys. 2005, 38, 703–710, doi:10.1088/0022-3727/38/5/007.
[18]
Sibillano, T.; Ancona, A.; Berardi, V.; Schingaro, E.; Basile, G.; Lugarà, P.M. A study of the shielding gas influence on the laser beam welding of AA5083 aluminium alloys by in-process spectroscopic investigation. Opt. Lasers Eng. 2006, 44, 1039–1051, doi:10.1016/j.optlaseng.2005.09.002.
Postma, S.; Aarts, R.G.K.M.; Meijer, J.; Jonker, B. Penetration control in laser welding of sheet metal. J. Laser Appl. 2002, 14, 210–214, doi:10.2351/1.1493764.
[21]
Graaf de, M.W.; Olde Benneker, J.; Aarts, R.G.K.M.; Meijer, J.; Jonker, J.B. Robust Process-Controller for Nd:YAG Welding. Proceedings of ICALEO'05: International Conference on Applications of Lasers and Electro-Optics, Miami, FL, USA, 31 October–3 November 2005.
[22]
Bagger, C.; Olsen, F.O. Laser welding closed-loop power control. J. Laser Appl. 2003, 15, 19–24, doi:10.2351/1.1536651.
[23]
Bautze, T.; Kaiser, T.; Huber, S. Focal Shift Monitoring and Cognitive Closed-Loop Control by Analysis of Co-Axial Video Data. Proceedings of ICALEO 2009: 28th International Congress on Applications of Lasers and Electro-Optics, Anaheim, CA, USA, 23–27 September 2009; pp. 849–855.
[24]
Zhang, X.; Chen, W.; Jiang, P.; Liu, C.; Guo, J. Double closed-loop control of the focal point position in laser beam welding. Meas. Sci. Technol. 2003, 14, 1938–1943, doi:10.1088/0957-0233/14/11/011.
[25]
Haran, F.M.; Hand, D.P.; Peters, C.; Jones, J.D.C. Focus control system for laser welding. Appl. Opt. 1997, 36, 5246–5251, doi:10.1364/AO.36.005246. 18259340
[26]
Sibillano, T.; Rizzi, D.; Ancona, A.; Saludes-Rodil, S.; Rodriguez Nieto, J.; Chmelickova, H.; Sebestova, H. Spectroscopic monitoring of penetration depth in CO2, Nd:YAG and fiber laser welding processes. J. Mater. Process. Technol. 2012, 212, 910–916, doi:10.1016/j.jmatprotec.2011.11.016.
[27]
Rizzi, D.; Sibillano, T.; Calabrese, P.P.; Ancona, A.; Lugarà, P.M. Spectroscopic, energetic and metallographic investigations of the laser lap welding of AISI304 using the response surface methodology. Opt. Lasers Eng. 2011, 49, 892–898, doi:10.1016/j.optlaseng.2011.02.014.
[28]
NIST Database. Available online: http://physics.nist.gov/PhysRefData/ASD/linesform.html (accessed on 20 June 2012).
[29]
Griem, H.R. Plasma Spectroscopy; McGraw-Hill: New York, NY, USA, 1964.
