Laser welding of the synchronizer stop ring and the rear gear in a manual transaxle

The focused laser beam is one of the highest power density sources available to industry today. When the “keyhole mode” is used for welding the result is characterized by a parallel-sided fusion zone, narrow width, and deep penetration. Therefore, a higher value of the joining efficiency (i.e., the reciprocal of the specific welding energy) is obtained and less energy is necessary for heating which generates a large heat affected zone and low mechanical distortion. This article focuses on the application of the CO2 seam laser welding of the stop ring of the synchronizer hub and the rear idle gear in a five-speed manual transaxle. This weld requires precision, repeatability, and welding efficiency. Unfortunately, stresses generated by the thermal cycle can produce cold cracks in the fused zone, which was highly stressed during the cooling phase. The different thermal expansion coefficients of the metals can also produce misalignment during the welding cycle. Here, the welding process was investigated with experimental tests and finite element numerical analysis. In particular a finite element model supported the decisional process of selecting parameters that minimize the crack risk and thermal induced misalignment during the welding process.