Laser Brazing with Diode Lasers

High process speed, low heat input, and smooth, tight and clean brazed seams are the main characteristics of diode laser brazing.

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Braze welding for car body construction

Laserline’s diode lasers have established themselves in more than 800 systems worldwide with different applications for their practical use in the field of brazing welding within the automotive industry. There, galvanized steel sheets or lightweight components made from aluminum are usually joined together. Major advantages of this process include the strikingly calm melt pools and the visually attractive brazed seams.

Laser brazing has been used in car body construction since as far back as the mid-90s. Laser brazing offers beneficial properties, especially for visible seams on the outer skin: low deformation, a stiff lacquerable joint, and almost no post-processing make this brazing process unique. Compared to laser beam or spot welding, brazing welding improves the aesthetics of the joint so much that a roof seam no longer has to be covered by a plastic strip.

This technique was made possible by the first fiber-coupled processing lasers, the lamp-pumped Nd:YAG lasers. The first Laserline diode laser for laser brazing in the tailgate production of the Audi A3 were used in 2001.

Diode Laser Brazing – the Technique

Joining methods, in which the brazing solder is melted by an industrial laser, have mainly been used in the mass production of vehicle bodies. There, laser beam brazing is mostly used for joining galvanized steel sheets or lightweight components made from aluminum, but also for other brazing material. Laser automobile brazing is usually carried out with a brazing optic that is integrated into a robot. The laser beam is guided along the joint where it melts the brazing solder – e.g. a copper-silicon wire – and in so doing, connects the components together. The success of the brazing process depends on whether the firmness is similar to the welding seams and on the high aesthetic quality of the joints: brazing seams that were generated with lasers are known for their sealed, smooth and clean structures. They are visually appealing and reduces post-processing to a minimum. The car body can often be lacquered immediately after cleaning, for example.

Brazing Process Advantages of a Diode Laser

The global practical usage of Laserline’s diode lasers has been established in the field of laser brazing. More than 800 LDF diode lasers are in successful permanent use for different brazing applications within automotive body assembly around the globe. Besides the requirements of higher firmness and a heat-affected zone that is as small as possible, there are particularly high standards in terms of the appearance of the joint for visible seams. A key process advantage of diode lasers is the strikingly calm melt pools.

Furthermore, the multi-spot module developed by Laserline has achieved enormous process advantages for triple-spot brazing. Brazing hot-galvanized sheets is often difficult, but as usual, this technology can achieve top-quality brazing seam qualities without reducing the process speed.

Examples of brazing applications

Hot Dip Galvanized Brazing with Triple-Spot

Laser brazing has long since secured a well-established place in terms of the manufacturing of vehicle bodies. However, the increased use of hot-galvanized sheets has led to problems, recently: the number of micro splashes and wavelets has grown, forcing a reduction in process speed. Laserline has developed a ground-breaking solution with its variable multi-spot module, in which side-spots are positioned in front of the main-spot: the pre-spots ablate the galvanizing at the brazing seam and thus calm the brazing process, which can be undertaken at the usual speed, as a result. This is viewed as a trend-setting process.

Brazing Galvanized Sheets

When galvanized sheets (that is, on an electrolyte basis) are processed as before – people call them “elo-zinc” – brazing diode lasers with the classical single-spot are sufficient. Here, the beam source is mostly integrated into special brazing robots. Thanks to the calm melt pools created by diode lasers, the melting of typical brazing solders based on silver or whitish silver poses no problem at all, resulting in attractive, high-quality seams.

The process stability of the LDF diode laser in mass production was able to be tested as part of a laser brazing process comparing a 4 kW YAG and a 6 kW diode laser during the process of manufacturing the VW Touran in Wolfsburg, Germany.