Design And Research Of Local Dry Drainage Cover Assisting Underwater Laser Additive Manufacturing

The demand for underwater welding is increasing with more attention put on the exploration of ocean and the application of nuclear power plants.Coaxial-powder-feeding laser additive manufacturing technique is an advanced welding technique,which is easy to integrate and realize automation.It can reach deep sea and areas with high temperature or radiation.Now,it has been considered one of the best tool for long-distance manufacturing.Underwater local dry welding has good flexibility and is able to achieve higher welding quality than traditional methods,and the combination between this method and laser additive manufacturing technique is worth investigating.In this paper,gas curtain drainage cover assisting underwater laser additive manufacturing by coaxial powder feeding was investigated.Firstly,factors in the quality of dry areas were analyzed in order to reveal the general performance of gas curtain drainage cover.The results showed that water depth,surface conditions,surface angle,working distance,velocity,gas flow rate etc.have different effect on the drainage quality.Secondly,VOF model and RNG k-? turbulent model were applied to simulate the fluid domain of drainage in Workbench 15.0,assisting the design of drainage cover.After that,first version was finished and manufactured.Drainage experiments were conducted to prove the feasibility of the method of simulation analysis,and experiments of underwater laser welding were carried out to show its effectiveness.The results turned out that the simulation outcomes were independent of the number of grid and the size of the time step,that the results of simulation was consistent with those of drainage experiments,and that defects like porosity could be found easily using this cover.Therefore,the first drainage cover was unqualified.Thirdly,uneven buffer was proposed to improve drainage performance,which was then demonstrated by a group of drainage cover with gas outlet of different structure.It was proved that uneven buffer was able to deepen dry areas and make dry areas more stable.Next,the second drainage cover was designed,and experiments for drainage and underwater laser welding were conducted respectively to check the drainage capacity.The consequence was that uneven buffer could decline the direct impact from turbulent water,and that the welding quality was much better than the previous one.Therefore,the second drainage cover with uneven buffer was capable of assisting underwater laser additive manufacturing.