Development of new processes for welding of thermal Al–Cu solar absorbers using diode lasers

Flat-plate solar collectors are favorable devices to generate heat from the energy of the Sun. The central part of a collector, the solar absorber, is a front-coated aluminum sheet with a copper tube fixed on the back side in order to transport heated liquid. Nowadays, the absorber is often fabricated by laser welding with two flashlamp-pumped neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers which provide high peak pulse powers. A disadvantage of this procedure is the high electrical energy consumption. Research on new laser welding processes is aimed to reduce the amount of energy required. Diode lasers allow processing with higher efficiency, due to a better absorption behavior of the aluminum sheet. Accordingly, two different processes have been developed. The first one, using two laser sources in pulsed mode, is similar to the industrial process, but enables an extension of the spot welds in order to increase the joint strength. In contrast, the second process requires only one laser source to weld the tube on both sides, using a scanner system which is integrated in a newly developed innovative laser processing head. By adopting these processes, significant energy savings during the production of solar absorbers can be achieved, ensuring high process reliability at the same time.