Research On Root Humping Suppression Of Medium-thick Plate By Laser-arc Hybrid Welding

Laser-arc-hybrid welding is a high-efficient welding method applying the laser-heat and arc-heat on one same molten pool.For the advantages of large single penetration depth and good welding joint performance,it has great potential in the welding of medium plates.After 10,000-watt laser device entering the market,the welding depth of laser-arc-hybrid single-line welding grows again.But with the thickness of welding plates increasing,the welding defects such as splashes,holes,cracks,undercuts and humping always comes up.Root humping defects is hard to suppress and seriously affects the performance of weld joint made by single-sided-welding-double-sided-molding forming technology of laser-arc hybrid welding.In view of the current situation that the bottom hump defect is difficult to suppress in the single-sided-welding-double-sided-molding forming technology of laser-arc hybrid welding medium thick plates,this paper has conducted in-depth research on the bottom hump from the three aspects:bottom hump suppression mechanism,single-sided-welding-double-sided molding process optimization,and laser-arc-hybrid welded joint performance research.The main contents are as follows:（1）A mechanical model for the formation of the bottom hump in the hybrid weld pool was constructed,and combined with the melt pool model,the mechanism of the bottom hump formation was analyzed from the imbalance of the bottom of the weld bead and the extrusion of the bottom melt pool.The pressure and the thrust of the laser deep-melting small hole on the bottom of the weld bead are the root causes of the formation of the bottom hump in the double-sided forming of the single-side welding of the laser-arc composite welding.Based on finite element simulation and mechanical analysis,it is found that under the condition of ensuring full penetration,the minimum value of laser power,the minimum value of arc power₍（6）,and the maximum value of welding speed(1 can effectively reduce the pressure of the molten pool on the bottom of the weld bead;Under the condition of full penetration,the minimum value of laser powerand the minimum value of welding speed(1 can guarantee the stability of laser"deep-melt holes"in laser-arc composite welding.（2）The effects of laser-arc hybrid welding process parameters,welding structure and heat-source-guiding-mode on the formation of bottom hump were studied.The results show that in10mm-thick-plate welding,root humping can be suppressed by adjusting process parameters such as laser power,wire feed speed(1,welding speed(1 and other,but when the plate thickness increased to 12mm,it is difficult to suppress the formation of the bottom hump by simple process parameter optimization;when welding 12mm-thick-plate,root hump can be suppressed only when9..5k,,(19mmmmin,(1 92.1mmmin;compared with the bottom hump characterization under different process methods in 12mm-thick-plate welding,founding that when using I-shaped grooves and Y-shaped grooves,the formation of root humping can effectively suppressed at high welding speeds,but defects such as surface underfill and undercut defects will occur respectively;the root humping forming can be suppressed under most welding parameters,showing the arc-leading-laser mode is significantly better than the laser-guided arc mode on the suppression of root humping forming.（3）The structure and properties of laser-arc hybrid welding single-sided-welding-double-sided-molding welded joints were analyzed.The results show that in laser-arc middle-thick plate single-sided welding-double-sided-molding,the filling effect of the welding wire on the weld and the strengthening of the joint performance are limited to the upper layer of the weld,so the tensile resistance of the middle and lower layer welds is significantly lower than that of the upper layer Seam;the main components of the weld are austenite and ferrite.Due to the precipitation of chromium carbide on the upper and lower layers of the weld,the grain boundary is not obvious,and it will cause cleavage fracture during the lifting process and reduce the extension of the weld.The test of the overall performance of the weld shows that the composite welded joints have good mechanical properties including tensile strength,toughness,elongation,porosity,and impact resistance.The tensile strength is 6.0Mpa,and the elongation after break is 45.5%.There is no crack under the condition of 180°bending,no pores of more than 0.1mm in the weld,and it can resist 1.3.5KV2 impact energy.