Study On Arc And Droplet Transfer Behavior Of Sandwich Panels T-joints In Flux Bands Constricting Arc Welding

As a new type of lightweight structural material,high-strength steel sandwich panels have wide application prospects in the fields of shipbuilding,rail transit,automobile and heavy machinery because of its high specific strength,high specific gravity and good energy absorption.For solving the problem of connection of face-plate and core-plate in metal sandwich panel,this paper puts forward a new welding method to manufacture high-strength steel sandwich panel,which is Flux Bands Constricting Arc Welding(FBCA).This method can make up for the defects of gaps at the root of the weld bead of the T-joint in the high-strength steel sandwich panel.This paper mainly researches the arc behavior,droplet tr ansfer and arc stability in FBCA welding T-joint process by the ways of high-speed camera system and welding electric signal acquisition system in order to obtain a well-formed T-joint.At the same time,the microstructures and performances of the FBCA welding T-joint were analyzed and tested.This study not only provides a theoretical basis for improving the arc and droplet transition stability in FBCA welding T-joints,but also improves the quality of joints.It also established a processing foundation to realize steady welding high-strength steel sandwich panels.At first,the complete equipment of FBCA welding T-joint system and the flux bands coating process was developed,the T-joint assembly fixture was optimized,and the welding process of FBCA welding T-joint was designed.Through a large number of welding experiments,good formed T-joints and optimum process range was obtained.Based on the high-speed camera image acquisition system,the interaction between the flux bands and welding arc was studied.In the welding process,on the one hand,arc heated and melted the flux bands,which shows different melting states.On the other hand,welding arc was affected by the hot compression and solid wall constraints of the flux bands,which change the arc burning position and the arc shape.The experimental results show that the distance from the arc to the sidewall and the distance from the arc to the bottom of the groove are the main factors affecting the arc burning position.By adjusting the arc voltages,welding currents,and groove widths,the melting height of the flux band affecting the distance from the arc to the sidewall and the bottom of the groove is affected.Thereby,when the arc voltages are 23-29 V,the welding currents are 240-320 A,and the groove widths are 3-7mm,the flux bands melting height is moderate,and the arc burns at the bottom and side walls of the groove.Furthermore,the effects of arc behavior on weld formation under different welding process parameters were studied.The results s how that the arc heating position significantly affects the cross-section morphology of the T-joint weld.The degree of flux bands constricting arc and welding arc heating root of T-joint can be quantified by the difference between the maximum sidewall pen etration and the minimum sidewall penetration “?L” and the ratio of the root bead width to the groove width “K” respectively.Based on the high-speed camera and welding electric signal synchronous acquisition system,the FBCA droplet transfer modes and arc stability were analyzed.The results show that there are four different modes of droplet transfer under different FBCA welding process parameters,which are arc bridge coexistence transition,short circuit transition,repulsion transition,fine droplet transition.The fine d roplet transition can be divided into free fine droplet transition and rejection fine droplet transition according to the droplet transition angle.The arc is pretty stability when the droplet transfer are the arc bridge coexistence transition and the fine droplet free transition,At last,the microstructure of the T-joint was studied,and the tensile,shearing and bending tests of corresponding T-joint was experimented.The results show that the weld microstructure of the T-joint is a mixture of needle-shaped ferrite and fine pearlite,the heat affected zone is consisted with martensite and bainite,and the base metal zone is lath martensite.The average hardness of welded joints represented following relation: base metal(325HV)>heat affected zone(298HV)> weld zone(256HV).In the mechanical tests,the failure position of the T-joint occurs mostly in the fusion zone.Compared with the performance of the T-joint with the same thickness by the laser welded,the bearing capacity of the T-joint by FBCA welding method can be significantly improved,which indicates that FBCA is a promising method for manufacturing metal sandwich panels.