Research On Deflection Control Of Laser Welding Of Hastelloy Thin Sheet With Filler Wire

The economic is developing,that makes the demand for energy increase.Nuclear energy has attracted the attention of countries all over the world for its cleanliness and sustainability.AP1000 is the representative of the third generation nuclear power plant.AP1000 has high safety and reliability,that makes it become one of the main development directions of nuclear power plants.The can of nuclear coolant pump is an important component in AP1000 nuclear power plant.It is made of Hastelloy C-276 thin plate by welding after rolling.The can needs high manufacturing precision to meet the requirements of matching,installation and service.The welding deflection control requirement of the can is extremely high.In this paper,the laser welding with filler wire technology was used to weld Hastelloy C-276 thin sheet.The influence of welding parameters on the longitudinal deflection of the sample was studied.The generation mechanism and change law of deflection during the welding with filler wire were analyzed.The welding deflection control method based on realtime ultrasonic effectily control the deflection of welding.That provided theoretical guidance for improving the manufacturing accuracy of the nuclear main pump can.The main research contents are as follows:(1)A numerical model of the pulse laser welding with filler wire in Hastelloy C-276 was developed.The model considered the cooling and restraining effects of shielding gas and fixtures on the workpiece during the actual welding process.Temperature and deformation fields were obtained by experiments to verify the accuracy of the simulation results.(2)Combined with the generation mechanism of longitudinal deflection,the influence of process parameters on the longitudinal deflection was studied.With the increasing of linear heat input,the equivalent load increased,the bending stiffness of the sample changes in a decreasing-increasing-decreasing trend.That made the longitudinal deflection of the sample overally increase,and its increasing trend slowed down when the weld was fully penetrated.With the relative wire speed increased,the bending stiffness of the sample increased,and the longitudinal deflection gradually decreased.The relative wire speed amount increasing from 0.48 to 0.99 made the longitudinal deflection reduce from 1.87 mm to 0.49 mm,reduced by 73.8%.The change of the defocusing had little effect on the entirestiffness of the sample.It had little effect on the amount of longitude deflection,and changed the direction of longitudinal deflection.(3)Combined with the generation mechanism of longitudinal deflection,welding with realtime ultrasonic was proposed.The influence of realtime ultrasonic parameters on deflection was analyzed.With the increase of the preset plastic deformation and ultrasonic power,the longitudinal deflection firstly increased and then decreased.Welding with 0.25 mm preset plastic deformation and 1400 W ultrasonic power can reduce by 55.0%compared with as-welded sample.(4)The effect of realtime ultrasonic on the microstructure of the weld was researched.The deflection suppression mechanism of realtime ultrasonic was verified through the change of the microstructure.The main texture at the center of weld changed to {100}<130> texture.The texture strength was reduced to 4.92.The average grain size is reduced to 78.5 ?m.The proportion of low angle grain boundaries was reduced.The weld structure transfomed to rolling structure.That showed realtime ultrasonic could produce plastic deformation by applying pressure to the weld,and suppressed the longitudinal deflection.