On line Optimization of the Manufacturing process of Solar Thermal Absorbers

PRIME LASER TECHNOLOGY is an OEM manufacturer of solar thermal absorbers, established in 2006 by C. Travasaros and E. Hontzopoulos. PRIME is using innovative methods in the production line, and one these is the laser welding of similar (Cu tube to Cu sheet) or dissimilar materials (Cu tube to Al sheet), constitutes the state of the art in solar thermal absorber production. It should be stated that PRIME founders, developed the laser welding method of solar absorbers in 1995-97 and they were the first who incorporated this technology in the production line worldwide within 2003, when they worked at FOCO SA.

Laser welding of solar thermal absorbers is used to produce around 30% of the European absorbers market, mainly Cu-Aluminum absorbers. Manufactures in Germany, Austria and Greece use this new technology. For these developed market, quality and efficiency of the product are key issues. Up to now the quality of the welds is evaluated on an empirical basis, and there isn’t any quantitative correlation of the welding conditions (laser power, welding speed, focal point position) to the quality of the welding products. It is pointed out that the efficiency of the solar absorber depends directly on the quality of the welding, which has to fulfil certain metallurgical and mechanical requirements.

Συγκόλληση Laser

Laser spot welding on a Cu-Al absorber

Within the frame of the proposed program the welding parameters will be correlated quantitatively to the quality and the performance of the final product. In order to achieve this, a wide experimental investigation will be carried out. For each set of experimental parameters, the quality of the weld will be evaluated (both metallurgically and mechanically) by using European quality standards. The appropriate, for the process, real-time optical system will be used to monitor the optical spectra of the plasma plume generated during the welding process. The spectroscopic changes will then correlated with the quality of the laser welds.

Following the above methodology, a set of “qualitative rules” will be developed based on the metallurgical and mechanical characteristics of the laser welding spots. These “qualitative rules” will be monitored by optical means in real time, offering a unique opportunity to introduce innovation in the production process. Towards this scope PRIME will collaborate in the frame of this proposal, with well experienced partners. More specifically with the Laboratory of Materials, University of Thessaly (EΥΠΘ), the Mechatronics Institute, Centre for Research and Technology – Thessaly (ΚΕΤΕΑΘ), as well as the Institute of Electronic Structure and Laser of FORTH (ΙΗΔΛ-ΙΤΕ). The role of each Research Group is distinguishable and complementary, as the scientific knowledge and expertise will be exploited for the achievement of the above described objectives.

More specifically EΥΠΘ will undertake the metallurgical characterization of the welds, ΙΗΔΛ-ΙΤΕ will carry out the characterization of plasma’s optical characteristics, while ΚΕΤΕΑΘ will perform the evaluation of the mechanical properties. The results of program will be particularly useful and immediately exploitable from PRIME, since “qualitative rules” will be developed that will correlate laser welding conditions directly and on real production time to the quality (metallurgic and mechanic) of the final product. This will offer to PRIME important qualitative advantage and prestige in the local and international competition.