Evolution of magnetically rotating arc into large area arc plasma

An arc channel tends to shrink due to its conductivity increasing with the increase of temperature. In this study, to generate large area arc plasma, we construct a magnetically rotating arc plasma generator, which mainly consists of a lanthanide tungsten cathode （13 mm in diameter）, a concentric cylindrical graphite anode chamber （60 nun in diameter） and a solenoid coil for producing an axial magnet field. By controlling the cold gas flow, the magnetically rotating arc evolves from constricted mode to diffuse mode, which almost fills the whole arc chamber cross section. Results show that the diffuse arc plasma has better uniformity and stability. The formation mechanism of large area arc plasma is discussed in this paper.

The characteristics of welding currents in a rotating arc leadtandem GMAW process and the weld-seam tracking

Tandem gas metal arc welding （ T-GMAW） process shows a high deposition rate that up to three times o f the single electrode GMAW, so the welding speed could be significantly increased in this process. However, the majority o f this process applications are based on the pre-programmed robotic welding, which does not allow them to track the seam real-time during welding. Rotating arc sensor, sensing the seam position by detecting the changing of welding currents, has been widely adopted in the automatic robot welding process. It is proposed in this paper to integrate the rotating arc sensor with a trailing torch to develop a new approach of rotating arc lead tandem gas metal arc welding （RLT-GMAW） process. The characteristics of the welding currents in the proposed new welding process were firstly studied, and then a self-turning fuzzy control seam tracking strategy was developed for the mobile robot automatic welding. The experimental results showed that the proposed RLT-GMAW process had an excellent seam tracking performance and high welding deposition rate. Even if there were some electromagnetic interactions between the two arcs, the deviation of the welding seam could also be reflected by the fluctuation of the welding currents on the leading arc once the correct welding parameters were selected. Based on the detected deviation, the welding tracking experiments showed that the proposed self-turning fuzzy controller had a good performance for the RLT-GMAW process seam tracking.

A modified heat source model for rotating arc welding

A modified mathematical model of heat source for rotating arc welding （RAW） process was developed for investigating the heat and temperature distribution. The characteristics of temperature field based on the complex welding motion trajectory were studied. In this work, a transient three-dimensional （ 3D ） model was established and computed by a finite element analysis computer program MARC as well as its subroutine. In RA＇W process, the temperature changes in the style of stepladder. Moreover in the high temperature zone, there are multiple peak temperature points. These characteristics of temperature distribution are induced by the arc rotating which leads the repetitive heating or fasing during the welding process. In contrast with non-rotating arc （NRAW） process, the width of temperature distribution enlarges, and the peak temperature of weld pool decreases. Good agreement is shown between the computed results and experimental results of thermal cycle in RAW process.

Study on weld formation in a novel rotating arc horizontal GMAW

A novel rotating arc horizontal welding process was developed for solving the sagging of the molten pool which bottlenecks the application and the development of the horizontal welding. The principle of the effect of the rotating arc on the molten pool is that the rotating arc process not only can reduce the welding heat input by prolonging the welding path in the same welding distance cawed by the arc rotation, but also disperse the arc force to affect the sidewall periodically to support the molten metal near the upper sidewall. The effects of the rotating speed and arc voltage on the weld formation were studied. The results indicate that there is an appropriate range of the rotating speed and the arc voltage to obtain the defect free horizontal welding.

Application of RVM for prediction of bead shape in underwater rotating arc welding

Bead sttape in underwater rotating arc welding was affected by several welding parameters. RVM （ relevance vector machine） was used to build a model to predict weld bead shape. The training data set of RVM eortsists of the welding parameters which are rotational frequency, rotational radius, height of torch and welding current and the features of the bead shape. The maximum error and mean error for prediction of width are 0. 10 mm and 0. 09 mm, respectively, and the maximum error and mean error for prediction of penetration are 0. 31 mm and 0. 12mm, respectively, which are showed that the prediction model can achieve higher prediction precision at reasonably small size of training data set.

Rotating arc horizontal narrow gap welding of high strength quenched and tempered steel

Rotating arc borizontal narrow gap welding of quenched ＆ tempered （Q＆T） steel was innovatively performed for solving the bottleneck that the molten pool sagged due to the gravity. The shapely multilayer single pass horizontal joint could be obtairzed by using the rotating are welding process. The cold crack was not observed in the joint without controlling the heat input and selecting the consumables intentionally. Microstructure of the joint could be divided into three zones： base metal zone （BMZ） , heat-affected zone （ HAZ） and weld zone （WZ）. Because of the characteristic of the rotating arc horizontal welding process, the defects in the joints were slag inclztsion formed at the interlayer of lower side wall. Tbe tensile strength and hardness of HAZ and WZ were larger than those of BMZ. The impact toughness in WZ, HAZ and BM at 0 % is equal to 11.5, 212 and 236 J, respectively.

Dynamic Balancing Structure Optimal Design for the Rotating Arc Sensor

Rotating arc sensor is a key device for automation welding. The vibration has a big influence on signal's correct collection and reliable automatic welding. In order to solve the vibration problem and the dynamic balancing design with the restricted space,a bearing force analysis based dynamic balancing structure optimal design is proposed and implemented with the help of Pro/Engineer( PROE) and automatic dynamic analysis of mechanical systems( ADAMS) virtual prototype technology, in which three parameters of the counterbalance are considered. The method is suitable for the practical online adjustment. The simulation result shows that optimal design based counterbalance structure and parameters can satisfy the space requirement with lower vibration. The methodology provides a new idea for dynamic balancing design and adjustment of rotating arc sensor with adjustable rotation radius.

Sensitivity analysis of rotating flux-cored arc welding process parameters

Empirical models were developed using curvilinear regression analysis to predict bead geometries of rotating fluxcored are welding （FCAW）. Parameters, such as rotational frequerwy, rotational radius, torch height and welding current, are used as design variables. The objective function is formed using bead width and penetration. Experiments of rotating FCAW were conducted based on orthogonal experimental design of four process parameters. A sensitivity analysis was also conducted and the effects of four process parameters on bead geometries were compared. The results show that the sensitivity of rotational radius on bead width is much higher than those of rotational frequency, torch height and welding current on bead width. Welding current is insensitive to bead width. The sensivity of rotational frequerwy on weld penetration is higher than those of other three parameters.

Characteristics of Atmospheric Pressure Rotating Gliding Arc Plasmas

In this work, a novel direct current （DC） atmospheric pressure rotating gliding arc （RGA） plasma reactor has been developed for plasma-assisted chemical reactions. The influence of the gas composition and the gas flow rate on the arc dynamic behaviour and the formation of reactive species in the N2 and air gliding arc plasmas has been investigated by means of electrical signals, high speed photography, and optical emission spectroscopic diagnostics. Compared to conventional gliding arc reactors with knife-shaped electrodes which generally require a high flow rate （e.g., 10-20 L/min） to maintain a long arc length and reasonable plasma discharge zone, in this RGA system, a lower gas flow rate （e.g., 2 L/min） can also generate a larger effective plasma reaction zone with a longer arc length for chemical reactions. Two different motion patterns can be clearly observed in the N2 and air RGA plasmas. The time-resolved arc voltage signals show that three different arc dynamic modes, the arc restrike mode, takeover mode, and combined modes, can be clearly identified in the RGA plasmas. The occurrence of different motion and arc dynamic modes is strongly dependent on the composition of the working gas and gas flow rate.

Dynamic behavior of a rotating gliding arc plasma in nitrogen:effects of gas flow rate and operating current

The effects of feed gas flow rate and operating current on the electrical characteristics and dynamic behavior of a rotating gliding arc （RGA） plasma codriven by a magnetic field and tangential flow were investigated.The operating current has been shown to significantly affect the time-resolved voltage waveforms of the discharge,particularly at flow rate =21 min^-1.When the current was lower than 140 mA,sinusoidal waveforms with regular variation periods of 13.5-17.0 ms can be observed （flow rate =21 min^-1）.The restrike mode characterized by serial sudden drops of voltage appeared under all studied conditions.Increasing the flow rate from 8 to 121 min^-1 （at the same current） led to a shift of arc rotation mode which would then result in a significant drop of discharge voltage （around 120-200 V）.For a given flow rate,the reduction of current resulted in a nearly linear increase of voltage.

Simulation of Arc Rotation and Its Effects on Pressure of Expansion Volume in an Auto-Expansion SF_6 Circuit Breaker

A 3D Magnetohydrodynamics （MHD） arc model in conjunction with an arc move- ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The rotation of the arc driven by an external electromagnetic force is simulated in the case with 200 kA of the short circuit current and 16 ms of arc duration. The arc rotating process and the speed of arc rotation have been obtained in the simulation. A comparison of the pressure in the expansion volume with and without an external magnetic field has been carried out based on the calculation results of two cases. The results of the simulation reveal that the arc rotation, which causes more energy exchange between the arc and its sur- rounding gas, can evidently bring about the pressurization in the expansion volume, which would contribute to more effective arc quenching at current zero and further reducing operation power.

Grain refinement and improved properties through electromagnetic stirring in Al alloy MIG welds

This paper described the effects of external excitatory parameters of current and frequency on the microstructure and mechanical properties of weld metal in MIG welding with longitudinal electromagnetic field. With a high speed video camera capturing the images of arc shape, the mechanism of arc rotation and how the periodic contraction and expansion of arc affected the movement of molten pool were investigated. The technique resulted in fine equiaxed grains in weld metal and optimum parameters of electromagnetic stirring were suggested based on the extent of refinement. Fine-grained weld metal exhibited better yield strength and significant improvement in elongation.