Laser beam micro-welding of dissimilar metals

The combination of dissimilar materials like brass and stainless steel is often needed in watch movements due to tribologic aspects. For mass production in automotive applications, a joining technique for alloyed copper with alloyed steel is needed. Laser beam micro welding offers an alternative to conventional joining techniques like press fit or soldering. Depending on the joining geometry, two different welding techniques are investigated: seam and spot welding. High strength and reproducibility are the main objective of joining dissimilar metals. Cracks and spillings are affected by the metallic continuity and should be avoided. Lap- and T-joints can be produced by the SHADOW-Welding technique. The length of the continuous welding seams are up to 15.7 mm at a feed rate of up to 60 m/min with a pulsed laser source. The weld width attained ranges from 50 to 250 µm and a weld depth from 20 to 150 µm. This low energy joining process with minimized heat input results in low distortion of the parts joined. Applying spot welding, the pulse forming capability is needed especially for highly reflective metals like copper. The welded joints have a higher strength than the basic material