Automatic MIG Welding Process For Invar Steel Used In Manufacturing Of Molds For Civil Airplane

With high specific strength, good fatigue properties and other characteristics, the composite materials played more and more important role in aircraft manufacturing industry. It will deform uncontrollable when the composite materials cool down to the natural temperature after molding in high temperature environment, but it will be positively controlled by using the Invar steel mold. The Invar steel mold employed in large civil airplane manufacturing is generally produced by traditional manual arc welding method with low efficiency, unstable quality and high requirements for welding workers. This paper studies the related problems of automatic welding for Invar steel systematically with experiment and simulation method, and investigates the weldability of the Invar steel, the path planning in robot welding and welding process optimization.Firstly, the weldability of Invar steel is studied through the welding test and with the energy spectrum analysis method and it is confirmed that the welding porosity is mainly caused by CO. As a result, the welding of Invar steels should be protected by inert gas. Through comparing of welding deformations with different angle grooves, this paper has found that the 60 degrees groove can promote the spreading of the Invar steel as well as the controlling of welding deformations.Secondly, the studies of the influence of the robot automatic welding process parameters on the shape of weld beads have been carried out with the orthogonal test method. Then this paper makes the welding path planning of the multilayer multi-channel swing welding of Invar steel plates. The filling strategy design was established. And against the weave bead welding, the quantitative role of the torch pose during forming welding passes was established as well as the amplitude of swing. In addition, verification welding experiments were carried out to reach the conclusions. Using triangle swing mode with 0.1s residence time at the amplitude point can make the best shape of welding beads.Finally, the finite element model of the Invar steel welding process was established. The material model for calculation was established and the heat source model was checked by the verification of the shape of the welding bead and the welding deformation. And then, the welding optimization of Invar 19.05 mm steel thick plates was studied with the finite element method. The results show that the minimum welding stress and welding deformation was got with five filler and fifteen layers welding strategy at welding of Invar 19.05 mm steel thick plate. Consequently, with comprehensive using the welding bead sequence planning from sides to the middle and the welding sequence selection of alternating welding can provide another 12.2% reduction of welding deformation. And the prestrain method was studied for controlling welding deformation and good quality welding specimens were obtained.This paper adopts the technical route of experiment researches as well as simulation analysis for welding of Invar steel. with the defect control, welding path planning and welding process optimization and so on, effective controls of the welding deformation and improvements of the production efficiency were accomplished which laid the foundation for the automatic welding manufacturing technology of the Invar mold.