Copper alloys are often found in electronics, sensors and precision engineering applications. Here, high demands are placed on the heat and mechanical stress resistance of spot welds, and laser micro-welding has very good weld qualities. However, non-ferrous metals are difficult to weld, due to high reflectivity, and a sudden jump in energy absorption when the melting temperature is reached. It is difficult to repeat good welding results, and with low process stability, up to now lasers have only been used following complex surface treatment, or for manual applications.

 

Researchers at the Department of Production and System Technology at the LZH have developed a new process, which uses a laser pre-pulse with a peak output of no more than 1 MW and a pulse length of only a few nanoseconds to initiate the welding process. This short-pulsed, solid-state, frequency converted laser has a high degree of absorption, and provides stable conditions for the subssequent high-output welding using a conventional IR laser. The welding energy can be easily controlled after pre-pulsing.

 

Experiments using the pre-pulse prototype of the company neoLASE were carried out on an 80 µm thick, 2mm wide copper band. After 200 repetitions, the welding results were constant, implying that the welds were 100% good. "This result is already a great success," says engineer Anas Moalem, who is responsible for the development of the process. Apart from improved precision and quality, the process window for the laser parameters could be expanded considerably. Depending on the weld spot diameter, the laser output power could be reduced by up to 40%, meaning that using the compact pre-pulse module (13 x 9 x 4 cm) could result in energy savings in the kilowatt range for the IR welding lasers.

 

Developments took place within the framework of the SME-innovation project "Supreme", which was financed by the BMBF (German Federal Ministry of Education and Research) under supervision of the PTKA-Project Management Agency Karlsruhe. Support was also given by the companies Arteos GmbH, Ilfa GmbH, neoLASE GmbH and Sill Optics GmbH & Co. KG.