Correlation analysis in laser welding plasma T. Sibillano, A. Ancona, V. Berardi * , P.M. Lugara ` INFM-LIT 3 -Laboratorio Regionale di Ricerca, Formazione, Sviluppo e Trasferimento alle Imprese di Tecnologie Laser Innovative, Italy Dipartimento Interuniversitario di Fisica-Universita ` e Politecnico di Bari via Orabona 4, I-70126 Bari, Italy Received 11 October 2004; received in revised form 23 January 2005; accepted 21 February 2005 Abstract During the process of high power laser welding the interaction between laser beam and workpiece produces a plasma bunch, named plume which is ejected from the surface of the welded material. The efficiency of the welding process and the quality of the welded seams are influenced by the plasma plume which plays a fundamental role in coupling the incident radiation to the material. The aim of this work is to present an optical non-invasive spectroscopic approach for the investigation of plasma plume dynamics. In particular, we present data on optical spectroscopy of the plume produced during laser welding of aluminum–magnesium alloys of industrial interest. The dynamics of the plume during laser welding is investigated by performing a correlation analysis of the optical spectra (covariance mapping technique). Ó 2005 Elsevier B.V. All rights reserved. PACS: 81.20Vj; 52.50Jm; 52.38.Mf Keywords: Laser welding; Optical spectroscopy; Correlation analysis; Aluminum alloys 1. Introduction Because of its advantages over other joining techniques, laser welding is one of the most impor- tant manufacturing processes particularly in the automotive industry. Nevertheless laser-material interaction is very complex and the correlation between the various parameters characterizing the process is still not fully understood. Setting up a reliable procedure to obtain welds of acceptable quality is often a challenging prob- lem. Therefore there is a growing interest in devel- oping procedures for real-time monitoring of the weld quality by investigating the plasma plume produced in the laser-material interaction. It is well known that chemical composition, spatial and thermal characteristics of the plasma plume are related to the welding conditions and keyhole 0030-4018/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2005.02.076 * Corresponding author. Tel.: +39 080 5442363; fax: +39 080 5442434. E-mail address: v.berardi@poliba.it (V. Berardi). Optics Communications 251 (2005) 139–148 www.elsevier.com/locate/optcom