Study On Plasmashapeand Weld Characteristic During Laser-Tig Hybrid Welding

Laser-TIG hybrid welding is an advanced welding technology which couple two different heat sources. In the result, advantages of the two welding process can be obtained. Because of the synergetic effects of laser and arc, hybrid welding makes its own benefits, such as enhanced efficiency, deeper penetration depth and increased gap tolerances, etc. So, hybrid welding is very attractive for industrial applications. Plasma is an important phenomenon observed during hybrid welding. The shape of plasma have a close relationship with the stability of hybrid welding and weld quality. The study on plasma property and its relationship with the welding seam can help to understand the process of hybrid welding.In this dissertation, digital image processing algorithms such as adaptive threshold edge detection and mathematical morphology were used to get the characteristic information of plasma pictures. Those pictures were shot by fast camera during Laser-TIG hybrid welding. This experiment was conducted by CO₂ laser-TIG and Fiber laser-TIG hybrid welding. The material were chosen steel and aluminum alloys 6061. The variation of the characteristic information of plasma and its relationship with the feature of welding seam was studied. The following are the main results:During CO₂ laser-TIG hybrid welding, the plasma height at the position of the laser incident can be used to reflect the penetration depth of the welding seam. The phenomenon of LSC(Laser-supported Combustion) can be observed when laser power is above 1500W, which absorbed a large amount of laser energy. Thus the height of plasma increased and penetration decreased when Ar as shielding gas. The addition of some He can weaken the absorption and lead to the increase of penetration. The plasma become unstable when the distance of heat sources is D=4mm, which affect welding penetration depth and width,. The synergetic effect of laser and arc is disappeared.During Fiber laser-TIG hybrid welding, the interaction between metal vapor and arc is quite obvious. Metal vapor is suppressed near the surface of metal targets, and it become brighter. The height of plume/plasma is quite low compared with that of Fiber laser welding. The ionization of metal vapor which gets into the arc reduces the volume of arc and changes the shapes of arc. The voltage of arc during hybrid welding is decreased compared with that using arc welding. During hybrid welding, the area of plasma can be used to reflect the penetration width of weld. In Laser-TIG welding direction, the penetration width is wider compared with the using TIG-Laser welding direction. The area of arc is bigger in Laser-TIG welding compared with TIG-Laser welding. Fiber laser-TIG hybrid welding have a higher efficiency compared with CO₂ laser-TIG hybrid welding. During CO₂ laser-TIG hybrid welding, He should be used as shielding gas, as well as Ar should be used as shielding during Fiber laser-TIG hybrid welding.