Research On The Breakdown Mechanism Of Powder Mixing Assisted Underwater Wet Welding Based On PIC-MCC

Underwater wet cored welding involves the liquid breakdown mechanism based on the composite liquid conductive medium(including water,bubbles and impurities),which involves a variety of complex particle physical and chemical reactions.In order to solve the dilemma of deep-water wet welding,we must start with the different physical essence of wet welding and land welding,that is,the physical problem of welding arc.Based on the experimental data obtained from the experimental platform and through the method of numerical simulation,this paper studies the dielectric breakdown mechanism of arc plasma in high-pressure deep-water and powder mixing assisted underwater wet welding from the perspective of micro particles,in order to provide theoretical guidance for enhancing the energy efficiency of arc liquid breakdown in water and improving the quality of wet welding.Based on the arc spectrum signal acquisition system and high-speed camera signal acquisition system,the arc spectrum and bubble information of underwater welding are obtained,and the principal components of arc plasma particles and bubble evolution process are analyzed.According to the principal components of arc plasma particles obtained from arc spectrum,five particles of electron,H,O,H~+,and O~+are selected to calculate the conductivity of arc plasma under different water depths.Water vapor is selected as the component of bubble gas,and the dielectric constant under different water depths is calculated,so the plasma conductivity and dielectric constant under different water depths are obtained,which lays a foundation for establishing the dielectric breakdown model of arc plasma under different water depths.According to the experimental parameters of underwater wet welding and the characteristics of underwater wet welding,reasonable assumptions and simplification are made.Based on PIC-MCC method,a three-dimensional numerical analysis model of arc plasma dielectric breakdown under high pressure and different water depth is established.Firstly,the experimental spectral diagnostic analysis results are compared with the numerical simulation results to verify the rationality and correctness of the model.Secondly,by comparing the numerical simulation results under different water depths,the micro analysis of the dielectric breakdown discharge process of high-pressure underwater wet welding arc is realized.The research shows that with the increase of water depth,the number of arc electrons increases,and with the increase of water depth pressure,the electron avalanche effect at the cathode welding head becomes more intense,producing more electrons.The electrons are dense in the middle and sparse around,resulting in more drastic fluctuations in the electric field intensity near the cathode welding head.When the water depth is 100m,the particle distribution depth on the polar plate is greater than 40m,which is consistent with the result that the penetration depth increases with the increase of water depth.In addition,compared with 40m water depth,the plasma electron temperature and electron number density at 100m water depth increase at all times.Based on the mechanism of improving liquid breakdown energy efficiency and machining quality by powder mixing EDM process,a powder mixing assisted underwater wet welding method is proposed.According to the ionization energy and precipitation characteristics of mixed powder,aluminum powder is selected as mixed powder additive.The dielectric constant and conductivity of the mixed phase after adding mixed powder were analyzed quantitatively.Considering the dielectric constant and conductivity under different powder mixing conditions,a powder mixing assisted wet welding arc plasma dielectric breakdown model based on PIC-MCC method is established.The water depth condition is0.3m and the powder concentration is selected as 4g/L and 8g/L.The effects of powder mixing and different powder concentration on underwater wet welding arc dielectric breakdown discharge are explored.The results show that the addition of aluminum powder is conducive to enhance the electric field strength between electrodes,and with the increase of powder concentration,the number and density of electrons in the arc increase accordingly,which finally promotes the breakdown of background gas dielectric.With the increase of powder concentration,the number of particles on the electrode plate decreases,the depth of particle distribution decreases,and the particle distribution on the transverse section widens,which is reflected in the reduction of weld penetration and the increase of weld width on the machined surface,which is conducive to improving the welding quality.