Yoshinobu Makino

Combination welding between CO2 laser beam and MIG arc

With the development of high power lasers in recent years, 45 kW class CO2 lasers are now employed on line in the steel industry for welding plates greater than 20 mm thick; in addition, in the automobile industry many 3-4 kW class YAG lasers are in practical use for high speed welding of thin sheets of approximately 3 mm or less. However, the practical application of laser welding in Japan remains small compared with that in the West and the following factors are often considered:

High-temperature mechanical properties of laser welds in Co-base superalloy and its improvement by laser surface melting

Summary The high-power CO2 laser is extensively used for practical applications such as cutting and welding of metals. Laser welding of superalloys requiring high-quality and high-efficiency welding, however, is seldom employed in heavy industry. Conventional laser welding of metals with filler wire produces the columnar structure which meets at the weld bead centre and leads to deterioration of creep properties. To improve the creep rupture behaviour of joints within this context, this paper describes the development of a laser surface melting technique involving the weld bead surface being remelted by laser. In the experiments described, Haynes 188 Co-base superalloy with a thickness of less than 3 mm is used as the base metal. The spot size of the laser beam used to irradiate the first layer of the weld bead surface is around 3 mm. The depth of the surface melting layer is varied by the travelling speed. The results suggest that both the elongation at fracture and creep rupture life after laser surface...

Development of laser welding technology for fully austenitic stainless steel

Abstract The radial stainless steel plates (RPs) used for Toroidal field (TF) coils in the International Thermonuclear Experimental Reactor (ITER) are 13 m long, 9 m wide and 10 cm thick, which are quite large. Even though they are very large structures, high manufacturing tolerances and high mechanical strength at 4 K are required. It is also required that each RP should be fabricated every three weeks. Therefore, the authors intend to develop efficient manufacturing methods for an ITER TF coil RP. Laser welding is then selected as a welding method for RP. Especially, the development of high technology laser welding is necessary to prevent hot cracking in the material used for the RP; namely, fully austenitic stainless steel with high nitrogen content. The authors carried out trial laser welding experiments aiming at its application to RP. As a result, it was effective to make the angle of back inclination of the weld head at a uniform welding speed. It also seemed that the sensitivity of hot cracking could be reduced by optimizing the chemical compositions of material used for RP. The base material and the welded joints satisfied mechanical properties in 4 K. The application of the laser welding technology to the fully austenitic stainless steel was therefore demonstrated.