Chenfu Fang

TANDEM and GMAW Twin Wire Welding of Q690 Steel Used in Hydraulic Support

Compared with using semi-automatic gas shielded arc welding, using automatic TANDEM twin wire welding and twin wire gas metal arc welding (GMAW) to weld Q690 steel, a low-alloy high-strength structural steel used in the hydraulic support in the fully-mechanized mining face, the welding speed, deposition rate, production environment and welding quality can be obviously improved. Compared with GMAW twin wire welding, a refined micro-structure in the weld and heat-affected zone (HAZ), narrow HAZ and improved joint strength were achieved with TANDEM on Q690. Also, due to the push-pull pulsed way in TANDEM welding, the droplet transfer, distribution on heat flow and interaction between two arcs were completely different from those in GMAW twin wire system. The heat input of TANDEM is only about 76. 6% of GMAW, and correspondingly, the welding speed and welding seam can be obviously improved. The complete oscillation caused by TANDEM pulsed current occurred in the welding pool, which refined the grains in the microstructure. The results show that TANDEM twin wire welding is very suitable in the welding of Q690 used in the hydraulic support.

Arc Behavior and Droplet Transfer of CWW CO2 Welding

Cable-type welding wire (CWW) CO2 welding is an innovative process arc welding with high quality, high efficiency and energy saving, in which CWW is used as consumable electrode. The CWW is composed of seven wires with a diameter of 1. 2 mm. One is in the center, while others uniformly distribute around it. The diameter of twisted wire is up to 3. 6 mm, which can increase the deposition rate significantly. With continual wire-feeding and melting of CWW, the formed rotating arc improved welding quality obviously. The arc behavior and droplet transfer were observed by the electrical signal waveforms and corresponding synchronous images, based on the high speed digital camera and electrical signal system. The results showed that the shape of welding arc changed from bell arc to beam arc with the increase of welding parameter. The droplet transfer mode changed from repelled transfer, globular transfer to projected transfer in turn. Droplet transfer frequency increased from 18. 17 Hz to 119. 05 Hz, while the droplet diameter decreased from 1. 5 times to 0. 3 times of the CWW diameter.

Comparative Study on Processing Property Between CWW CO2 Gas Shielded Welding and SAW

Cable welding wire (CWW) CO2 gas shielded welding is an innovative process arc welding with high efficiency, high quality and low consumption, in which cable wire is used as consumable electrode. CWW CO2 gas shielded welding and submerged arc welding (SAW) are used for contrast studies on processing property of high strength steel A36 used in ship structure. The results show that the shapes of weld seam, using CWW CO2 gas shielded welding and SAW, are good and no weld defect such as air hole, flaw, slag inclusion, incomplete fusion, lack of penetration and so on are found in the weld seam. Because the rotating of arc during CWW CO2 gas shielded welding process has a strong stirring effect on molten pool, the grain in the heat affected zone (HAZ) of the joints, using CWW CO2 gas shielded welding, is small. Tensile failure positions of joints by CWW CO2 gas shielded welding and SAW are all in the base metal, but tensile strength of CWW CO2 gas shielded welding joint is higher than that of SAW joint by an average of 2. 3%. The average impact energy of HAZ, using CWW CO2 gas shielded welding and SAW, is almost equal, but the average impact energy of the weld seam using CWW CO2 gas shielded welding is increased by 6%, and the average impact energy of the fusion line is increased by 7%. The 180° bending tests for the joints of CWW CO2 gas shielded welding and SAW are all qualified, and the joints hardness is all less than HV 355, but hardness of CWW CO2 gas shielded welding wire welding joint near the fusion line is obviously lower. It can be concluded that the properties of CWW CO2 gas shielded welding are better than those of the SAW joint, and CWW CO2 gas shielded welding is suitable for welding high strength steel A36 used in ship structure.

Arc ignition of CWW CO2 welding in A36 steel

ABSTRACT In gas metal arc welding, arc ignition significantly influences arc stability, droplet transfer, and the quality of welded joints. Cable-type welding wire (CWW) CO2 welding is an innovative welding method. This paper analyzes the arc ignition procedure for this type of welding based on experiments with three different wire end conditions: an unsmooth wire end, a smooth wire end, and a preheated smooth wire end. Smaller contact areas between the CWW and the workpiece led to higher arc ignition currents, and higher wire tip temperatures led to shorter arc ignition times (AITs) with the same chemical composition, diameter, and extension. Based on the characteristics of the welding wire end structures and the contact resistance between the CWW and workpiece, a suitable mathematical model of the AIT was developed. The model was validated using experimental arc ignition images. The AITs for the unsmooth smooth and preheated smooth wire ends were 14, 20, and 11 ms, respectively, essentially consistent with the model calculations.

A study on sidewall penetration of cable-type welding wire electrogas welding

Cable-type welding wire (CWW) electrogas welding (EGW) is an innovative process in which CWW is used as the consumable electrode. Seven wires can be melted simultaneously with only one welding power source, one wire feeder, and one welding torch. This paper reports a study of the sidewall penetration of CWW EGW. The results showed that all the mechanical properties of CWW EGW welded joints met the standards of the China Classification Society (CCS). The arc heating area of CWW EGW was large and that the unique rotating arc of CWW EGW had a strong stirring effect, enhancing convective motion of the molten pool and accelerating heat transfer between the superheated molten pool and the sidewall. The droplet of the CWW EGW appeared to be non-axial transfer due to the rotating force. The superheated droplet transferred to the sidewall or the molten pool near the sidewall directly, promoting the heating and melting of the base metal.