Improvement of Gas Shielding Effect in Vertical-position Laser Micro-welding of Titanium Alloy

High brightness lasers enable an efficient processing of wide area with high processing speed, but there are few effective supplying method of shielding gas for a wide area. It is difficult to fill up a wide processing area with a shielding gas, and the usage of shielding box might deteriorate the flexibility of remote laser welding method. In the case of titanium alloy, the oxidation and nitriding of weld area must be prevented due to the risk of strength reduction. In addition, for large and long size components, welding parts may be located in a vertical wall, which makes it difficult to keep a shielding gas at a processing area. Therefore, a proper shielding method of argon gas at a wide area is required in a vertical-position remote laser welding of titanium alloy for large size components.The shielding gas flow was numerically analyzed by computer fluid dynamics (CFD) method, and some shapes of ring-type shielding gas nozzle were investigated. Shielding gas flows from two layers of injection ports could increase the mass fraction of argon gas, and higher of ring-type nozzle led to the higher mass fraction. Moreover, it was suggested that a tilting of injection port against the center of ring-type nozzle was effective to keep the argon gas at a processing area, and the proper balance of flow rate between two layers could improve the mass fraction of argon gas. Laser irradiation experiments indicated similar effects of ring-type shielding gas nozzle shape, and the atomic percent of oxygen in vertical-position laser micro-welding of titanium alloy could be decreased by the newly designed nozzle shape.High brightness lasers enable an efficient processing of wide area with high processing speed, but there are few effective supplying method of shielding gas for a wide area. It is difficult to fill up a wide processing area with a shielding gas, and the usage of shielding box might deteriorate the flexibility of remote laser welding method. In the case of titanium alloy, the oxidation and nitriding of weld area must be prevented due to the risk of strength reduction. In addition, for large and long size components, welding parts may be located in a vertical wall, which makes it difficult to keep a shielding gas at a processing area. Therefore, a proper shielding method of argon gas at a wide area is required in a vertical-position remote laser welding of titanium alloy for large size components.The shielding gas flow was numerically analyzed by computer fluid dynamics (CFD) method, and some shapes of ring-type shielding gas nozzle were investigated. Shielding gas flows from two layers of injection ports c...