Development Of Physical And Numerical Simulation Platform For Local Dry Underwater Laser Welding

As a new type of automatic production process,underwater laser welding technology has the advantages of high heat input,low loss,high precision and fast cooling rate.It has a broad application prospect in the fields of underwater mineral development,submarine oil and gas pipelines,large equipment,and even the construction and maintenance of green nuclear power projects.However,the deep-sea underwater environment is characterized by high humidity and low temperature.Hydrogen and oxygen from water and electricity can cause serious ablation of alloy elements,and the low water temperature can easily lead to the formation of brittle and hard tissue in the weld.At the same time,the presence of water can also shield the laser.It is very difficult to carry out laser welding directly in water environment.The local dry laser welding technology is to reduce the influence of water on the laser welding process by installing the drainage device artificially.However,the existing local dry underwater laser welding equipment is usually suitable for the shallow water environment,so it cannot be used to study the laser welding technology in the deep water environment.The boiling point of the material will increase with the increase of the depth of water and the interaction between the laser and the material will be significantly affected.For this reason,this paper focuses on the development and design of a local dry underwater laser welding ground simulation device which can be used in the deep water environment,so that it is possible to simulate the laser welding process in the deep sea environment on the ground.By establishing a 3d simulation model of local dry underwater laser welding,the mesoscopic physical process of laser welding in different deep-water environments was analyzed in depth,and a research method combining physical simulation and numerical simulation of local dry underwater laser welding in deepsea environment was formed on the ground.First of all,a ground simulation device of local dry laser welding was designed to simulate the deep sea environment.In this paper,the pressure resistance performance and adjustable pressure range of the simulation device are comprehensively considered,and the pressure adjustment integrated system of the simulation device,laser perforation and movable moving platform are designed.Through the comprehensive performance verification of the simulation device,the results show that: the ground simulation device independently developed and designed can withstand the pressure of more than 10 MPa,that is,it can simulate the deep-water environment with a depth of more than 1000 meters.Moreover,it has good sealing performance and can adjust and change the internal environmental pressure of the device according to the experimental requirements.Through the study of the related experimental verification of analog device,the results show that the use of analog device for local dry method underwater laser welding experiment,can stay above the weldment form local stable drying space successfully,and get the experiments of laser welding seam weld appearance and atmospheric environment morphology is very close to,further proves the feasibility and effectiveness of the local drainage of ground simulation device.Then,based on the self-developed ground simulation device,a local dry underwater laser welding test operation platform was established to study the local dry underwater laser welding process under different welding speed parameters.The results show that: under the condition that the technological parameters such as power and defocusing amount remain unchanged,the surface of the welding seam of underwater local dry laser welding is well formed,and the weld morphology is in the shape of "T",the upper part is wider,the lower part is long and narrow and straight,and the cross-sectional area of the whole weld morphology decreases with the increase of welding speed.In addition,the penetration depth of the weld gradually decreases with the increase of the welding speed.When the welding speed increases from 1.0m/min to 3.0 m/min,the penetration depth decreases from 4.1 mm to 2.8 mm,and the weld width also shows a downward trend,decreasing from 3.6 mm to 2.8 mm.Through the analysis of the residual stress,it can be seen that the equivalent stress of atmospheric and underwater laser welding processes under atmospheric pressure is equivalent,both of which can reach about 600 MPa.Finally,by using the method of simulation,the mathematical model considering the conditions of local dry welding space and pressure environment is established,and the recoiling pressure model is modified,so as to further reveal the evolution process of the hole in the local dry underwater laser welding pool.The results show that the maximum flow rate in the keyhole molten pool is 2 m /s in both water and atmosphere.Although the local dry underwater laser welding process is similar to the atmospheric environment,the presence of water will have an impact on the flow characteristics of the keyhole molten pool.The counterclockwise vortex in the upper part of the molten pool in the atmospheric environment is more intense,and the underwater vortex is only concentrated in the smaller area above the molten pool.And the environmental pressure has a significant impact on the weld.With the increasing of the environmental pressure,the weld penetration depth decreases,the surface bulge of the hole decreases,and the surface temperature of the weld pool increases gradually.