| The thick plate welding technology has become the main method to build ship,pipeline,nuclear submarine and some other national defence equipments.However,the stability of welding process is hard to control,many researchers focused on the research.The unstable welding process may interrupt the arc existing status and disturb the droplet transfer behavior actuating some welded defects,which significantly affect property the property of welded joint.Accordingly,the systematic thick plate welding experiments and simulation research are essential to be conducted so as to analyse the arc stability,droplet transfer behavior,welded defects forming mechanism and the temperature/stress field druing laser-arc hybrid welding.The appropriate processing window should be established to obtain good quality welded joint with different thickness.The mian result and the innovative points are listed as below.(1)Research on stability mechanism of narrow gap laser-arc hybrid welding.Several key process parameters like:laser power,welding current,groove gap and laser-arc distance were detected to find the influence on arc stability using a high-speed camera,explaining the mechanism of arc stability.A multivariate nonlinear regression analysis model was established to quantify the relationship between the process parameters and the arc stability.The optimal process parameters combination could be obtained efficiently in actual productions by using this methods.Details are clarified in Chapter 3.(2)Research on droplet transfer behavior during narrow gap laser-arc hybrid welding.High-speed camera was applied to study the influences of groove gap,welding current and laser-arc distance on droplet transfer behavior.The general rule and the stress state of droplet transition were concluded and analyzed with an external magnetic field.Details are clarified in Chapter 4.(3)Research on the defect formation and inhibition methods of welded joint during narrow gap laser-arc hybrid welding.Laser cleaning method was proposed for slag cleaning between weld layers due to its flexibility in the narrow gap and less slag generation.Due to the incomplete fusion between layers,two growth types of opposite growth and unilateral growth were discussed,the inhibition methods of which were also proposed in Chapter 5.(4)Research on thick plate multi layers laser-arc hybrid welding of different thicknesses.Thick plates with different thicknesses were successfully welded with appropriate process parameters and groove types based on the stability mechanisms of arc/droplet transfer and the defect formation/inhibition methods of welded joints.The mechanical properties,microstructures of a 40mm thick plate welded joint were detected,indicating a high quality weld.All these results were discussed in Chapter 6. |
