Low-power Laser-induced TIG Arc In Unequal Thickness Titanium Alloy Structure Welding Process Research

As the "space" metal and "ocean" metal of the 21 st century,titanium alloy has many advantages such as high toughness,high specific strength,good high temperature resistance,fatigue resistance,etc.Titanium alloy welded structural parts are widely used in military affairs involving national defense and security.Equipment manufacturing field.With the acceleration of the modernization of military manufacturing,the R&D and production cycle of equipment has been shortened,and higher requirements have been put forward for advanced manufacturing technologies of various new materials.Titanium alloy welding structure is not only limited to the butt joint of flat plates of various thicknesses,so more stable and efficient technical means are required for connection.Traditional arc welding method prosses the disperse heat energy distribution and weak penetration force,and the low thermal conductivity of titanium alloy itself,the molten pool is larger when welding special structural parts,and it is more sensitive to changes in process parameters,which can easily cause instability of the molten pool and lead to continuous Burn through defects.In response to such problems,this paper proposes to use low-power laser-induced TIG arc heat source to weld various titanium alloys with different thicknesses of complex structural parts to reduce the sensitivity of special titanium alloy structures to welding process parameters and improve the stability of the welding process.Titanium alloy materials are expensive,and the thermal processing performance is not good.In order to explore the welding process in the special structure of unequal thickness and reduce the test cost as much as possible,We first used the low-power laser-induced TIG heat source to conduct a preliminary surfacing test on an 8mm thick TC4 titanium alloy to study the influence of welding process parameters on the size of the weld seam.Then we applied the BP neural network optimized based on the genetic algorithm to the experimental results to realize the prediction of the welding process parameters on the weld profile size,to verify the model's application in the TC4 titanium alloy material and the low-power laser-induced TIG arc welding method Applicability of the upper pair of weld size and morphology prediction.The experimental results show that the average absolute percentage difference and standard deviation are both less than 0.15,and the correlation coefficients of the linear regression of training and prediction samples are very close to 1,which indicates that the GA-BP model has high prediction accuracy and stability and can be used for subsequent TC4 Provide guidance on selection and optimization of low-power laser-induced TIG arc welding process parameters for titanium alloy plates with special unequal thickness structures.Based on the 8mm thick TC4 titanium alloy plate surfacing process and GA-BP neural network research,we respectively carried out welding process design and bottom welding experiments on the corner joint structure composed of 15 mm and 6mm plates,and the butt joint structure composed of 25 mm and 12 mm plates.The experimental results show that the addition of low-power pulsed laser will attract the TIG arc to the position of the laser action point to discharge,realize the macroscopic arc contraction,and can effectively enhance the penetration ability of the TIG arc and reduce the welding heat input.The butt joint structure composed of25 mm and 12 mm plates can achieve continuous and smooth weld formation and reasonable penetration of the back when the laser power is 296-336 W and the TIG current is 250-280 A.The corner joint structure composed of 15 mm and 6mm plates can get a good bottom weld formation when the laser power is 485-545 W,the TIG current is 210-240 A,and the welding gap is 0-0.3mm.It shows that the low-power laser-induced TIG arc heat source has lower sensitivity and stronger applicability when welding special structural parts of titanium alloy.After TC4 titanium alloy is welded by low-power laser-induced TIG arc heat source,the structure of the weld area grows up obviously as a coarse columnar crystal structure,and is accompanied by the appearance of "net basket structure".This makes the hardness of the weld zone higher than that of the base material and the heat-affected zone.The tensile strength of the specimen can reach 1011.54 MPa,and the fracture position is at the base material.The measured results of thermocouples with unequal thickness butt joint structure show that: the welding process of titanium alloy is very rapid,and the heating rate is much faster than the cooling rate after welding,and the heating rate and cooling rate on the side of the 25 mm thick plate are greater than those on the side of the 12 mm thin plate.