抄録
An ultra-high vacuum diode laser welding system capable of performing a diode laser (DL) welding experiment at the International Space Station orbital pressure of 10−5 Pa was developed for investigating the effect of environmental pressure on DL welding phenomena. A DL welding experiment with a power density of about 100 kW/cm2 was conducted on 304 stainless steel at pressure levels between 105 Pa and 10−5 Pa. Although a laser-induced plasma plume was observed during welding at environmental pressures, 105 Pa and 103 Pa, no laser-induced plasma plume was found in the pressure range from 10 Pa to 10−5 Pa. The mode of the melting process (weld pool shape) under these experimental conditions was a keyhole-type melting mode or a transition-type melting mode at environmental pressures of 105 Pa and 103 Pa. However, the melting mode at pressures lower than 10 Pa changed to a heat-conduction-type melting mode. Although the penetration depth decreased when the environmental pressure was dropped to 103 Pa, it did not change at pressures lower than 10 Pa. We also determined that the prevention technology of metal vapor deposition on optical devices needs to be developed for DL welding technologies used in space.
