Megumi Ohmine

Welding Characteristics of Mild Steel by CW-YAG Laser.

Penetration mechanisms of welding by continuous wave (CW) YAG laser beam for mild steel were discussed. Bead-on-plate tests were carried out varing laser beam power and welding speed, and the cross-sectional shapes of the welds were measured. The fundamental welding characteristics for mild steel by YAG laser beam were estimated in comparison with those by CO2 laser beam. The results obtaine are as follows. (1) The penetration mechanism of key-hole welding in a steady state by YAG laser beam agrees with the heat conduction theory for a wedge type volume heat source model, like that by CO2 laser beam. (2) YAG laser beam has lower threshold power to enter fusion of mild steel and its absorption efficiency is less dependent upon the cavity depth of molten pool than CO2 laser beam. Then, input power can be controlled to adjust the irradiating beam power, that is necessary to slow down penetration depth at the end of weld.

Development of automatic beam focus detecting system for electron beam welding.

In electron beam welding, it is very important to set focal position of beam on work piece appropriately. However, it is very difficult to set one accurately in case of complex joint geometry.New beam focus detecting system have been developed as part of intelligent welding system for electron beam welding.When electron beam is irradiated on work poece, backscattered electron, thermoelectron, secondary electron, ion or X-ray emitted from work piece are observed. Among these, thermoelectron is much affected with surface condition of a work piece. That is, as soon as the surface melted, thermoelectron increased rapidly.The results obtained are as follows.1. In case that the condition of beam convergency on work piece is shifted from out of focus to in focus, signal of thermoelectron shows peak value when beam focal position coincide with the surface of work piece.2. It is possible to obtain high S/N ratio by employing positive collector bias by which thermoelectron gathered easily to the collector.3. The detecting accuracy is within ±1% in the case that ab factor is 1.0.

Improved metal processing with high power CO2 lasers (I) - Welding and cutting

Improved metal welding and cutting technology with high power CO2 lasers has been developed. On the basis of the results, the laser processing mechanisms for FMSC test plant including automatically interchangeable laser processing heads (i.e. welding head and heat treating head) have been produced and their performances have been evaluated.Improved metal welding and cutting technology with high power CO2 lasers has been developed. On the basis of the results, the laser processing mechanisms for FMSC test plant including automatically interchangeable laser processing heads (i.e. welding head and heat treating head) have been produced and their performances have been evaluated.