| CMT Cold metal transition technology as one method of MIG/MAG welding, it has many advantages, such as,low heat input, high welding speed, Stable arc, small spatter, weld quality of high repetition accuracy, but it only can apply to thin, high-speed welding because of its low heat input and low melt depth.Laser-arc hybrid welding is an emerging specialty of laser processing technology, and it can compound laser and arc heat source together which are two completely different heat source in physical properties and energy transfer mechanism, while, the two heat sources act on the same processing location, not only give full play to their strengths of two heat sources, but also make up their own shortcomings with each other, thus forming a new and highly efficient heat source.Basing on the summarizing research of domestic and international laser-Arc hybrid welding, the paper firstly studies the welding process,arc characteristics and pool morphology of Nd:YAG laser+CMT hybrid welding using 18-8 stainless steel as test materials, with the help of laser-CMT arc hybrid welding equipment which independently developed by Harbin Welding Institute.The research shows that:Nd:YAG laser+CMT hybrid welding can stable arc better and improve the formation of weld compared with CMT. Because the laser provides charged particles and low-ionization potential of the particles for the burning of the arc, and also increases the temperature variation between the arc center and the surrounding environment, which make the resistance go low when the arc passing through this path, thus, the maintenance of the arc burning voltage decreases. So hybrid welding can stable arc better and improve the formation of weld.Mean while, it can improve the welding pool morphology and reduce spatter. Due to the adding of laser, the laser pool bath coupled with the CMT, which increases the distance between the action spot of wire and the pool edge, and extends the time of the melting episodes off the weld pool oscillation arising from the base material up to the leading-edge pool, leading to the energy weaken when the pool shock front to reach the base metal bath, and reduce the collision energy with the pool frontier, so the spatter reduced.It also increases the welding penetration. During the welding of 304 stainless steel, the laser power PL= 2kW, defocus amountΔz= 3mm, the welding current I= 150A, the penetration of the low-speed hybrid welding increases to 4 times of the CMT welding, and even increases to 9 times of the CMT welding under high-speed welding.Furthermore, it enhances the welding speed. It can not maintain arc burning stable under high-speed welding because of the inadequate concentration of the plasma between the electrode and the weldment. But the adding of laser enhances the plasma concentration of the weldment surface, playing a role in stabilizing the arc, and increases the offset degree of horizontal welding.It increases the offset degree of horizontal welding, too. Under the conditions of this experiment, CMT arc power is always less than 2kW laser energy, laser energy/ arc energy≥1:1, the adding of laser makes the temperature of the complex pool significantly higher than CMT, the surface tension of weld pool is also far less than the CMT, and the liquidity is better than CMT, too. Consequently, it increases the offset degree of horizontal welding.The application to the thick horizontal welding of Nd:YAG laser+CMT composite heat source can obtain stable arc and good weld bead formation under the protection of pure argon gas, avoiding the easily emerging of defects in "welding Valley" during the multi-layer multi-channel welding, such as non-fusion between layers, etc.
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