Application of Laser Welding to Stainless Steel Light Rail Vehicle

Abstract

In 2003 AnsaldoBreda, a Finmeccanica company operating in the rail vehicle transportation sector, and Centro Sviluppo Materiali, an industrial research centre, started to investigate the possibility to apply laser technology to replace resistance spot welding process for stiffeners assembly on rail vehicle side panels. Goals of the activities were:

• to increase the aesthetics of the car body by eliminating visible indentation on the surface

• to increase flatness of the skin reducing welding deformations

• to increase welding productivity and quality in terms of soundness and repeatability.

This work summarises the main results obtained in the programme conducted to evaluate laser welding possibilities and welded joint properties. Different process parameters were explored for producing lap joints aiming to eliminate visible indentation on the external sheet and, at the same time, to optimise the welding properties and fabrication process robustness. The weld quality was assessed by metallurgical investigations and mechanical tests such as: hardness profiles, tensile and fatigue tests. The obtained results were compared with strength and fatigue behaviour of spot welded joints. Finally, by using optimised and qualified welding procedures, the real components were manufactured obtaining high quality and productivity levels (welding speed up to 5 m/min). Afterwards AnsaldoBreda started to manufacture, committed by the Los Angeles County Metropolitan Transportation Authority, fifty Light Rail Vehicle trams for the Californian city using the new assembly technology and the manufacturing facilities available at Centro Sviluppo Materiali.