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Laser welding technique for solar absorbers

A new laser welding process, developed by Laser Zentrum Hannover (LZH), promises both an enormous potential for saving energy and higher welding strengths for the manufacturing of solar absorbers. The main element of this innovative process is a diode laser, which is used to join the copper tubes to the aluminum absorber sheet, instead of using the conventional solid-state laser.

Solar absorbers stand for energy savings. As the main element in solar collector systems, they use the sun's energy to warm up water and save on heating costs. However, much energy is needed to manufacture the solar absorbers. To weld the copper tubes to the absorber sheets, most manufacturers use two pulsed, solid-state lasers with peak energies up to 6kW. These flashlamp pumped lasers have a rather low working efficiency, making laser processing very energy intensive, and expensive.

The group 'Joining and Separating of Metals' of the Materials and Processing Department of the LZH uses only one 4kW diode laser for the welding process. This laser not only has a much higher efficiency rate, but it also uses the laser energy better, because copper and aluminum both have higher absorption characteristics for the typical diode laser wavelengths used (800 to 980nm). A further advantage is that the size of the welding spots can be increased, and wider welding spots mean higher weld stability. It is especially important that the thermal input can be regulated, as an excessive thermal load could damage the absorber coating.

The cooperative project between the Hannoverian laser researchers and the metal-working company Flexxibl from Brunswick, Germany, is now entering a decisive phase. Following the positive resonance to the welding results shown at the EuroBlech, the partners are now working on developing a new laser processing head for solar absorber welding. In the spring of 2011, they plan on presenting this new diode laser welding head to the absorber industry.

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