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ABSTRACT Titanium alloy is the main material of pressure-resistant shell of underwater submarine. Although the design and manufacturing technology of spherical pressure-resistant structure of manned submersibles has matured, the domestic large-scale ring rib shell processing and construction technology is not mature enough, especially the titanium alloy welding technology. The high concentration argon welding workshop designed in this paper is mainly aimed at the overall welding of the typical titanium alloy large ring ribbed column shell, and the key technology is verified by the principle prototype. Finally, the mechanical properties of welding samples are evaluated.
INTRODUCTION Titanium alloy is mostly used as the pressure-resistant shell material of large-depth manned equipment. The design, processing and construction technology of spherical pressure-resistant structure of manned submersible is approaching maturity, while the processing and construction technology of large ring-ribbed cylindrical shell in China is not perfect, especially the titanium alloy welding technology (SOHU news, 2021). Due to the large size of the pressure-resistant structure and the large thick thickness of the plate and shell, the existing technology of large-depth manned equipment cannot achieve integrated forming, and the forming of pressure-resistant cylindrical shell, ribs and hemispheric sealing head unit structures all need welding. Welding technology is one of the core technologies in the manufacturing process of titanium alloy pressure shell. The maturity and perfection of titanium alloy welding technology directly affects the safety and reliability of titanium alloy pressure shell of manned equipment.
DEMAND ANALYSIS The pressure shell material of large-depth manned equipment is mainly titanium alloy, with large volume, various welding joints and great difficulty in construction. The welding workload accounts for more than 40% of the total construction workload. The welding environment is complicated, and the temperature and humidity are greatly different. Titanium has strong chemical activity and is sensitive to impurities and water. It is easily polluted by air, water, grease and oxide scale during welding, leading to impurities such as oxygen, hydrogen, nitrogen and carbon dissolved in the weld, thus deteriorating the joint performance (Li DD et al., 2003). In order to avoid material contamination, the whole welding process needs to be separated from the steel operation area and carried out in an independent clean workshop (Jia HT et al., 2020). The working environment temperature is not less than 5°C, the relative humidity is not more than 80%, the wind speed at construction site is not more than 1.5m/s. Different from steel, repairing times of titanium alloy weld at the same position should not exceed two times, which requires higher quality of weld. At present, mature welding methods for titanium alloy are mainly GTAW and ELECTRON beam welding, but the protective effect of GTAW is limited and electron beam welding is limited by vacuum chamber (Chen FL, 2019). GTAW technology in high concentration argon gas environment does not need high vacuum chamber and overcomes the shortcoming of traditional GTAW welding seam protection. Therefore, the construction of titanium alloy argon welding workshop can provide an ideal welding environment for the integral welding of titanium alloy pressure-resistant structure of underwater manned equipment.
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