Influence Of Additional Electric Field On Low Power Pulsed YAG Laser+TIG Arc Hybrid Welding Process

Compared with single laser welding and single arc welding, laser+arc hybrid welding possesses the merits of higher welding speed, more stable welding process, greater energy utilization ratio, lower assembling accuracy acquirement and enhanced heat penetrability, so it is widely concerned by researchers. However, the studies on the hybrid heat source are still on the level of technique application, and mechanisms referring to the interactions taking place in the heat source treating material are relatively limited. Based on the above-stated situations, this paper performs the investigations on the interaction between laser and arc plasma during welding from the view point of electric field, where an additional electric field (AEF) is introduced into the laser+arc hybrid welding process. The influence of additional electric field on single laser welding process, single tungsten inert gas (TIG) welding process and the hybrid process is comparablely studied. According to the welding penetration depth, the plasma behavior and plasma spectral information, the effect of AEF on the hybrid welding process is disposed. Consequently, together with the electromagnetics theory, the role of arc electric field in the laser+arc interactions and hence the hybrid welding process is discussed.1. Investigations on the penetration depths and formations of single laser, single TIG and hybrid laser+arc welding show that there is hardly effect of AEF on the weld formation of TIG welding, laser welding and hybrid welding; AEF does not affect the TIG welding penetration depth, but has effect on that of single laser welding. Penetration depth increases with the increase in AEF intensity and larger laser power leads to greater penetration depth. Whether or not the AEF has effects on the hybrid welding penetration depth depends on the given parameters. When AEF effects on hybrid penetration depth, the depth value also increases with the increase in laser power and AEF intensity.2. By the observation of welding plasma behavior and acquisition of plasma, the effect of AEF on welding plasma is researched and the results show that AEF hardly influences the direct current TIG arc plasma; AEF strongly influences the laser induced plasma behavior. Under the AEF, the brightness of laser induced plasma increases and the volume is enlarged as well as the arc stiffness. Still, whether or not the AEF influences the hybrid welding plasma depends on the parameters. At the parameters by which the welding penetration depth can be improved by AEF, the hybrid welding plasma brightness and the stiffness increase under the AEF action. Meanwhile, spectral diagnosing shows that there is hardly change of particle species in the welding plasma with and without AEF action. At the parameters by which the welding penetration depth can be improved by AEF, spectral intensity of Mg atom lines increases when AEF is added and electron temperature of arc plasma decreases while the electron density is increased. 3. The effects of AEF on single TIG welding, laser welding and hybrid laser+arc welding are discussed as well as the role of electric field of arc plasma in hybrid welding. The nature of effect of AEF on the welding process is the behavior variation of charged particles in the AEF. The reason for the neglectable influence of AEF on TIG welding and TIG plasma is the automatic self-adjustment function of the welding machine, which keeps the output current constant. In single laser welding with AEF, the charged particles (mainly the electrons) in the laser induced plasma are sped in the AEF, and extra energy gained from AEF is delivered to the material, resulting in the increased welding penetration depth. For the laser+arc hybrid welding process, the interaction between the AEF and charged particles in the plasma is strictly depends on the welding parameters. If the laser induced plasma in the keyhole connects with the arc plasma, the speeding effect of AEF on electrons disappears, leading to the unobvious variation of welding depth and plasma behavior. When the arc plasma separates with the laser keyhole plasma, the AEF effects as in the situation of single laser welding. Therefore, whether or not the AEF affects the plasma and penetration depth of hybrid welding depends on the interaction between laser keyhole and arc plasma. Consequently, in laser+arc hybrid welding, the electric field of arc plasma can serve as the AEF when arc plasma combines with laser keyhole plasma, and the electrons in the keyhole gains extra energy from arc electric field, and at last this part of energy is converted into the heat to form an extra welding penetration depth.