Research On New Technologies Of Single Pass Welding And Double Backside Shaping For T-structure Of Titanium Alloy

In the aeronautical manufacturing industry, the main developing trend of aircraft is to lighten the structural components. Because of the excellent properties such as low density, high specific strength and high-temperature stability, titanium alloys have been widely applied to the structural parts of aircraft manufacturing, including the bulkhead, beam, and wallboard in the rear part of fuselage. Titanium alloy aircraft wallboard is commonly composed of thin-wall skin and purlin T-structure. At present, riveting is the main connecting method of such structural parts. However, there exist some disadvantages of riveting such as discontinuous joint, easy dropping and weight increment of structural parts. Therefore, welding is applied to the structural parts instead of riveting, and could make the T-structure as a whole part, reduce the aircraft weight, increase the structural strength, and decrease the manufacturing cost. And this effect has been validated in the aircraft manufacture of Airbus corporation. Recently this point has also been the main developing trend of aeronautical manufacture.In this paper, the new methods of TIG welding and laser-TIG hybrid welding have been presented to solve the problem of single pass welding and double backside shaping for T-structure of thin-wall titanium alloy. The formation characteristic and conditions of single pass welding and double backside shaping, and the distortion discipline and methods of reducing distortion are all studied, through the technology experiment, numerical simulation and general mechanical performance tests. Additionally the formation process of actual parts has also been carried out. The main conclusions are listed as follows:TIG welding and laser-TIG hybrid welding experimental systems are developed, in which every welding parameter could be expediently adjusted. The TIG welding and laser-TIG hybrid welding processes of titanium alloy T-structure are researched, and the optimal welding parameters are obtained. And the problems of titanium alloy T-structure welding protect and back forming control are resolved by applying numerical simulation to design optimal welding protect equipment.A new laser-TIG hybrid welding method of single pass welding and double backside shaping in helium and argon mixed gas is proposed, and the influences of the multiple factors on weld shaping are researched. The optimal technology conditions of single pass welding and double backside shaping for laser-TIG hybrid welding are acquired. From the comparison of TIG welding and laser-TIG hybrid welding of titanium alloy T-structure, the result shows that the hybrid welding technology has obvious advantages such as improving microstructure and properties of welding seam, reducing the welding distortion,and increasing welding efficiency and gap flexibility.The 3D finite element model of single pass welding and double backside shaping for titanium alloy T-structure is developed. The welding temperature field and stress and strain field of TIG welding for titanium alloy T-structure are researched in the method of numerical simulation. And additionally the stress and strain distributions of the welding processes of an actual airplane TA15 titanium alloy wallboard in different welding sequences are also simulated. The research results show that the welding residual stress and welding distortion of the head and tail symmetry welding are relatively lower, which has been proved and applied to guide the actual production.The general mechanical properties of titanium alloy T-structure in TIG welding and laser-TIG hybrid welding have been compared. The testing results of tensile and bending properties show that the difference between tensile strengths of two welding parts is small, and whereas the section shrinkage of component in laser-TIG hybrid welding is larger than in TIG welding. The bending strength of laser-TIG hybrid welding T-structure is obviously higher than that of TIG welding. The comparing results of fatigue performance show that the fatigue life of laser-TIG hybrid welding joint is 50% more than that of TIG welding joint. The above testing results show that the general performance of laser-TIG hybrid welding joint is better than that of TIG welding. Therefore, this technology has large application potential in the welding of large-scale titanium alloy thin-wall skin and purlin T-structure of airplane.