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Laser brazing with diode lasers

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

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Automotive car body construction with diode lasers

In the field of brazing welding within the automotive industry, Laserline's diode lasers have established themselves with their practical use in more than 800 systems worldwide with different applications. There usually galvanized steel sheets or lightweight components made of aluminum are joined together. A major advantage of the process is the strikingly calm molten pools and the optically attractive brazed seams.

Already since the mid-1990s, laser brazing has been used in car body construction. Especially for visible seams at the outer skin, laser brazing offers beneficial properties. Low warpage, a stiff paintable 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 clearly that a roof seam no longer has to be covered by a plastic strip.

This technique has become possible with the first fiber-coupled processing lasers, the lamp-pumped Nd:YAG lasers. The first Laserline diode lasers 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 with the help of an industrial laser, have been used mainly in the mass production of vehicle bodies. There, laser beam brazing is mostly used for joining galvanized metal sheets or lightweight components made of aluminum, but also for other brazing material. Laser automobile brazing is usually realized with a brazing optic that is integrated in 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. The success of the brazing process is based on whether the firmness is similar to the welding seams and the high esthetic quality of the joints: brazing seams that were generated with lasers are known for their sealed, smooth and clean structures. This is visually attractive and reduces post-processing to a minimum. Car body construction, for example, can often be lacquered immediately after cleaning.

Brazing process advantages of a diode laser

In the field of laser brazing, the global practical usage of Laserline's diode lasers has been established. More than 800 LDF diode lasers are in permanent use successfully in different brazing applications within the automotive body assembly worldwide. Besides the requested higher firmness and a possibly small heat-affected zone, for these visible seams in particular, high demands are made on the appearance of the joint. A key process advantage of diode lasers is the striking calm molten pools.

Furthermore, the multi-spot-module developed by Laserline has achieved enormous process advantages during brazing with triple spot. At the often difficult brazing of hot-galvanized sheets, this technology can achieve, as usual, high brazing seam qualities without process speed reduction.

Brazing with triple spot

Examples of brazing applications

Hot dip galvanized brazing with triple spot

In the production of vehicle bodies, laser brazing has long since secured a well established place. However, the increased use of hot-galvanized sheets has of late led to problems: the number of micro splashes and wavelets has grown, forcing a reduction in the process speed. With a variable multi-spot module, in which side-spots are positioned in front of the main spot, Laserline has developed a groundbreaking solution: the pre-spots ablate the galvanizing at the brazing seam and thus calm the brazing process, which therefore can be done with the familiar speed. This is rated as a trend-setting process.

Brazing of galvanized sheets

When galvanized sheets (that is, electrolyte-supported) are still processed – we also talk about “elo-zinc” – brazing diode lasers with the classical single spot are sufficient. Here, the beam source is mostly integrated in special brazing robots. Thanks to the calm molten pools created by diode lasers, the melting of typical brazing solders based on silver or whitish silver poses no problem at all. Well-designed seams with high quality are the result.

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