| Thin-walled structures of titanium alloy have been widely used in aerospaceindustry because the excellent comprehensive performance of titanium alloy can meetthe requirement on the harsh working condition of the aircraft. The laser weldingtechnology has many advantages including small deformation and rapid weldingspeed, which make it more and more popular in titanium sheet welding. The lowelastic modulus of titanium alloy could cause significant welding stress anddeformation. Although the deformation of laser welding is much smaller than otherwelding methods, it is still difficult to meet some occasions that require tiny weldingdeformation. Thus, the means combining numerical simulation and experimentalanalysis were implemented to study the deformation control of titanium alloy sheetduring laser welding process in this paper.Firstly, a movable dial gauge measuring system was built to measure thelongitudinal welding deflection based on the welding deformation analysis of thetitanium alloy. In order to study the deformation characteristics and the influence ofthe line energy on the welding deformation, the process in laser welding of TC4titanium alloy and welding deformation measurement was also experimented. Theresults showed that the typical longitudinal welding deflection occurs in the coolingprocess. The longitudinal welding deflection of the test piece is reduced with thedecrease of inputted line energy during the welding process.Secondly, numerical simulation of the welding process was also analyzed in thispaper. The three-dimensional transient temperature field and stress field of laserwelding of titanium was simulated by the ANSYS software. The simulation resultsshow that the temperature field changes from non-steady state to steady, andeventually presents stable meteor-shape distribution with dense isotherms near theweld and narrow HAZ during the laser welding process. The weld profile obtai ned bythe simulation and the experiment results fits well. The stress near the HAZ reachespeak, and its value increases with the increase of the welding time. A pproaching tothe end of the welding process, the stress showed obvious boundary effects. Greatcompressive stress appears in the front region of molten pool and tensile stress occursin the tail region of molten pool.Finally, a method called synchronous gas cooling during welding or ‘SGCW’ for short have been proposed for the control of welding distortion. This method uses theargon gas cooled by liquid nitrogen to chill the region of the test piece at the back ofthe laser heat source during laser welding process. And some experiments based onthis method were carried out to study the effects of the cold source parameters on thedeformation control by comparing specimen obtained by laser welding and SGCW.The results indicated that deformation and residual stress of the specimen obtained bySGCW is smaller than that obtained by conventional laser welding. The longitudinalwelding deflection of the SGCW test piece is71%smaller than that obtained byconventional laser welding when d, the distance between the heat and cold source, is10~15mm and q, the cooled argon flow, is10L/min. The SGCW technology has noeffect on the microstructure and mechanical properties of the joint with properwelding and cold source parameters.The welding simulation results provide a theoretical basis for the present ofcontrol method of welding deformation. Deformation measurement results provide atechnical basis for the realization of control method of welding deformation. Thecontrast of the test piece obtained by conventional laser welding and SGCWdemonstrated the feasibility and effectiveness of SGCW deformati on controltechnology. Optimized welding and cold source parameters can provide the designbasis for the actual production, guiding the welding manufacture of thin-walledstructures of titanium alloy. |
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