High power laser applications in Nippon Steel Corporation

Abstract

The full-scale use of lasers in the steel industry began 25 years ago with their applications as controllable light sources. The laser systems contribute to increase efficiency and quality of the steel making processes, and also save energy of resources and labor. Laser applications in the steel making process generally require high input energy, however, it is essential to consider the interaction between the laser beam and materials. In particular, the reflectivity of the laser beam on the surface of material and the quantity of the laser-induced plasma are critical parameters for high efficient processes. We newly developed methods and systems of high power 45 kW CO2 laser welding of hot steel specimens with their applications as welding characteristics of hot steel specimens that temperature is about 1000 degree C, have been examined. Using laser induced plasma as a secondary heat source, the penetration depth improves about 30% compared to that at room temperature. The bead width is also enlarged by 10%. The maximum depth is 38 mm at 1m/min welding velocity at 40 kW. A beam weaving method is adopted for further enlargement of bead width without degrading fusion efficiency. It is also effective for suppressing the bead depth deviation. Additionally, several new applications, for example, new type all-laser-welded honeycomb panels for high- speed civil transport, will be talked.