Effect Of Welding Parameters On The Porosity Of High Power Fiber Laser Welding And Laser-TIG Hybrid Welding With Filler Wire

In the manufacturing of welding, arc welding method is still the main stream. But the traditional method of arc welding in solving the problem of welding deformation, thermal damage of components, welding efficiency and the controlling of single side welding forming under the condition of big deviation of component assembly meet the technical bottleneck in the welding of high performance materials. Laser-arc hybrid welding method, with both the high efficiency characteristics of laser welding and high adaptive characteristic of arc welding and also with high stability in the process of high speed welding process provide the effective solutions of the problems mentioned above. "process-type" porosity is a common problem in the process of laser deep fusion welding. The current ways to restrain the "process-type" porosity is laser scanning welding, big spot welding, double focus laser welding, etc, the essence of the ways above is through increasing the heat input to reduce depth- wide ratio, Although these ways can effectively inhibit the production of porosity defects, they simultaneously weaken the characteristics of low heat input and high efficient of high power laser welding. How to give full play of the characteristics of the low heat input and high efficient of high power laser welding and inhibit the generation of porosity defect at the same time are the main issue of this paper.In the paper, 304 stainless steel and 6kw fiber laser were used to carry out the experiments of laser welding and laser-TIG hybrid welding with filler wire, systematically studied the influence of the matching of key process parameters such as laser power and welding speed on welding porosity. Study found that for the full penetration of laser welding of thick 304 stainless steel, fixed other welding parameters, every welding speed matched a certain threshold laser power(critical porosity inhibiting power), when higher laser power than the threshold laser power was used, the porosity defect can be effectively inhibited; The faster the welding speed, the higher the matching threshold laser power will be; Analyzing the mapping rules of the porosity with the welding parameters and the weld shape showed that no matter what the welding parameters were, as long as the back weld width and front weld width ratio close to 1, the weld porosity rate was less than 0.1%;Compared with the welding process of low power matching low welding speed, larger depth-width ratio weld can be got under the process of high laser power matching high speed welding, the heat input of which was lower, which was more advantageous to control the welding deformation and improve welding efficiency; the regularity of the effect of welding parameters on welding porosity and appearance keeps the same in both laser welding and laser-TIG hybrid welding with filler wire but laser-TIG hybrid welding with filler wire can effectively solve the problem of surface sag and can significantly improved welding speed compared with the conventional TIG arc.On the basis of the effect of process parameters on "process-type" porosity using high speed camera and methods of mathematical statistics, the fluctuation characteristics of laser-caused plasma and laser keyhole under the conditions of different parameters were studied, study show that the fluctuation of laser-caused plasma under large laser power was more stable and there was no disappearing process of the holes in the big laser power welding which was the main reason that the big laser power welding can restrain the occurrence of "process-type" porosity.