# High-Speed Welding of Stainless Steel with Additional Compensatory Gas Jet Blow Molten Pool
## 3 Experimental Materials and Equipment  
The test platform includes the digital arc welding power source, wire feeder, industrial personal computer, wavelet analyzer, velocity measurement system, and the self-modified compensatory gas jet control system. As shown in Figure 3, the outer part of the compensatory shielding gas nozzle is horn-shaped, aiding in preventing the flow of air towards the impact area. The welding technology test platform uses the intelligent digital signal processing (DSP) arc welding power source as the core. This is a fully functional and relatively complex system that can realize the real-time adjustment and optimization of multiple welding parameters and peripheral welding equipment [31].  
Figure 3: Self-made compensatory gas jet test platform: (**a**) Diagram of the compensatory gas jet system; (**b**) diagram of compensatory gas jet nozzle structure.  
Figure 2: Schematic of the molten pool blown with compensatory gas jet during welding.  
Applied to a traditional gas-protected welding system, the method of molten pool blown by a compensatory gas jet should solve the problem of establishing and controlling the new gas flow branches without affecting the adjustment and control of the main gas flow path. The compensatory gas jet system comprises a gas source, pressure-reducing valve, gas flow divider, flow control valve, and compensatory gas jet nozzle. The maximum output current of the arc welding power source is 500 A, which is in line with the high heat input conditions used for high-speed welding.  
In the experiment, the angle of base metal for impact of jet flow is 90 degrees while the distance between nozzle and base metal is 8 mm. The gas jet will form vertical impact for formation of liquid metal, which changes the balance of molten pool and causes geometric deformation. After complete solidification, the appearance of the weld joint is better than that of a weld joint without the impact of a gas jet. The hump is formed due to excessive localized accumulation of metal and it is a relatively common weld defect. The compensating gas jet will have an impact on the molten pool of liquid which flows out of the electric arc area of the molten pool. It has the effect of driving metal in the hump location downwards, thus avoiding formation of a hump.  
A total of 304 stainless steel sheets were used as the welding workpieces. The welding wire was 308 stainless steel solid-core wire with diameter \(\Phi\) = 1.6 mm. The chemical composition is shown in Table 1. The thickness of the experimental parent materials was 2.5 mm. Both the main path gas and the compensation gas were argon. The main path gas flow was 20 L/min and the compensation gas jet flow was 15 L/min. Butt welding was performed at speeds of 154 cm/min and 167 cm/min, with peak current Ip = 390 A, base current I\({}_{\text{b}}\) = 118 A, average current I\({}_{\text{v}}\) = 268 A, average voltage U = 32 V, and pulse frequency f = 77 Hz. For the convenience of comparison, the heat input line energy of the arc welding power source under the two welding speeds was held constant. Table 2 shows the main welding parameters. In Table 2, sample 1#S and sample 1#B were obtained at the first half and the latter part of the same weld, respectively, as were sample 2#S and sample 2#B.