The influence of the ratio between the wire and process velocities on the wetting process during laser brazing
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PRODUCTION PROCESS
The influence of the ratio between the wire and process velocities on the wetting process during laser brazing Thorsten Mattulat1 · Peer Woizeschke1 Received: 8 June 2020 / Accepted: 4 August 2020 / Published online: 17 August 2020 © The Author(s) 2020
Abstract Laser brazing is used in automotive production for the joining of car body parts with customer-visible seams, whereby the highest optical seam quality is demanded. During the wetting process, a constriction formation can occur within the molten brazing material, which subsequently collapses; this induces a stepwise progression of the wetting front, thereby decreasing the optical seam quality. The aim of this study is to investigate the influence of the wire and process velocities on this constriction formation. For this purpose, high-speed recordings of the process zone are performed during laser brazing and then evaluated concerning the wetting process. The results show that the constriction formation depends on the relationship between the process velocity and the process direction component of the wire velocity. The constriction formation only occurs when the process velocity exceeds the parallel-oriented component of the wire velocity. This constriction formation is unstable and collapses repeatedly. In this study, increasing velocity differences stabilizes the constriction existence. This stabilization correlates with a uniform wetting process and a reduced frequency of the occurrence of blowout events, probably due to improved outgassing of zinc bubbles from the melt pool. Keywords Joining · Laser material processing · Laser brazing · Wetting · Process monitoring
1 Introduction Laser material processing is a technology that is used for many applications in the production process of the automotive industry [1]. Here, laser brazing is used for the joining of car body parts [2], which are by default zinc-coated for corrosion protection [3]. Standard applications are a connection between the two-part trunk lid [4] or the connection of the roof and side panel [5]. The brazed seams remain directly visible (except for painting) to the customers [6], and hence, the highest optical quality standards are demanded for these seams [7]. This includes, for example, straight seam edges, a smooth seam surface, and the absence of adherent spatter or pores and holes [8]. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11740-020-00978-5) contains supplementary material, which is available to authorized users. * Thorsten Mattulat [email protected] 1
BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Klagenfurter Str. 5, 28359 Bremen, Germany
To ensure optical seam quality, the wetting process in laser brazing is of major importance [9]. As an example, the mechanism of pore formation is described by Frank et al. as the formation of constrictions in the area of the wetting front as a consequence of a temporary interruption of the wire feed [10]. However, such a constriction formation is no
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