Laser welding of EGR coolers - a new process technology for heat exchanger manufacturing

摘要

Laser welding is a joining process, which is comparatively new to industrial production and especially to heat exchanger manufacturing. Due to the high energy density of the laser beam, the process is characterized by faster welding speeds with deep penetration as compared to the conventional welding processes. Therefore laser-welding technology is widely used in the automotive industry on a variety of different applications. This paper describes the application of laser welding as possible joining technology for exhaust gas heat exchangers made of stainless steel. The cooled exhaust gas recirculation (EGR) technology shows good potential for meeting the actual and future emission targets of diesel engines combined with acceptable fuel consumption. It will be shown that the selection of the base metal and the joining technology are extremely important for the durability of the product because of the severe operating environment the EGR cooler must endure. The consecutive manufacturing steps starting with the block assembly, the welding of the tubes to the header as well as the combined header to shell welding and cutting process will be described. In addition some typical laser welding results for the different processing steps will be shown. An important factor for the technical and economical success of laser welding of EGR coolers is given by the used systems engineering. As an example the application of a new kind of focusing optics for the tube-to-header welding process will be introduced. Based on the experience of the serial production of EGR coolers for passenger cars and commercial vehicles, the importance of laser welding as joining technology for other types of heat exchangers will be evaluated.