Arc Stiffness Research Articles

The differential analysis for temperature distribution diagnostics of arc current-carrying region in sheet slanting tungsten electrode inert gas welding with the electrostatic probe

Abstract An electrostatic probe differential analysis method is used to diagnose the arc current-carrying region of the sheet slanting tungsten electrode. Based on the local thermal equilibrium condition and energy transition model with charged particles collision, the temperature distribution in the current-carrying region of different welding process parameters is solved by saturated ion current. The results show that the temperature distribution range in the width direction of sheet slanting tungsten electrode expands, the arc high-temperature region shifts integrally, and the temperature in the thickness direction of sheet slanting tungsten electrode would be symmetrical. The guide effect of the hypotenuse of sheet slanting tungsten electrode for arc current and the inertia drag effect of arc would mainly change the temperature distribution. The variation of the inclination angle of the hypotenuse of sheet slanting tungsten electrode will aggravate the shift of the arc high-temperature region. The larger inclination angle will enhance the guiding effect, and then the inertia drag effect would be in a dominant position with a smaller inclination angle. With the increase of welding current, both the arc stiffness and the guiding effect would be intensified, the latter should make the arc high-temperature zone shift to the position with a small discharge gap.

Effect of Alternating Magnetic Field on Arc Plasma Characteristics and Droplet Transfer during Narrow Gap Laser-MIG Hybrid Welding

In this paper, the morphological characteristics of arc plasma and droplet transfer during the alternating magnetic field-assisted narrow gap groove laser-MIG (metal inert gas) hybrid welding process were investigated. The characteristics of arc plasma and droplet transfer, electron temperature, and density were analyzed using a high-speed camera and spectrum diagnosis. Our results revealed that the arc maintained a relatively stable state and rotated at a high speed to enhance the arc stiffness, and further improved the stability of the arc under the alternating magnetic field. The optimum magnetic field parameters in this experiment were B = 16 mT and f = 20 Hz, the electron temperature was 9893.6 K and the electron density was 0.99 × 1017 cm−3 near the bottom of the groove, which improved the temperature distribution inside the narrow gap groove and eliminated the lack of sidewall fusion defect. Compared to those without a magnetic field, the magnetic field could promote droplet transfer, the droplet diameter decreased by 17.6%, and the transition frequency increased by 23.5% (owing to the centrifugal force during droplet spinning and electromagnetic contraction force). The width of the weld bead was increased by 12.4% and the pores were also significantly reduced due to the stirring of the magnetic field on the molten pool.

Welding procedure Research of Niobium Heat Exchanger

The weldability of R04200 niobium tube-to-tubesheet is analyzed. The macroscopic examination, penetration testing, hydrostatic testing and metallographic examination are tested by the method of GTAW. The results show that specific welding structures with He-Ar mixed gas as shielding gas can improve the arc stiffness, thermal efficiency and penetration. It expresses the great significance of formulating the welding methods guidance of niobium pressure vessels.

Research status and future perspectives on ultrasonic arc welding technique

In recent years, ultrasonic arc welding technology, a novel and promising welding process, has been widely applied in the welding of steel, aluminum alloy, titanium alloy, nickel base alloy and composite materials to improve the welding efficiency and quality of the welded joints. This paper reviews the research status of ultrasonic arc welding technology, systematically classifies and summarizes the process of ultrasonic arc welding in terms of different ultrasonic energy forms, and evaluates the limitations of the processes. Based on the experiment and simulation results, this paper summarizes the effect mechanisms of ultrasonic on the arc characteristics and molten pool behaviors during arc welding, namely the theories of ultrasonic vibration and electromagnetic field, and briefly discusses the association mechanism of ultrasonic vibration and electromagnetic field. Finally, we summary the systematic results supporting the association mechanism. On the one hand, ultrasonic energy leads to arc compression, which can effectively improve the arc stiffness, arc pressure and energy density, thus improving the arc thermal efficiency and welding efficiency. On the other hand, the ultrasonic stirring and mixing effects as well as the high-frequency pulsed electromagnetic field force introduced by the ultrasonic energy accelerate the thermal convection circulation and the flow of the molten pool, and affect the solidification and crystallization behavior of the molten pool, thus improving the formation, microstructure and mechanical properties of the weld. The paper aims to comprehensively review the ultrasonic arc welding process and mechanisms, and provide guidance for the future research and development in ultrasonic arc welding technique.

Droplet transfer and spatter generation in DC–AC pulse tandem gas metal arc welding

Tandem welding increases productivity in gas metal arc welding (GMAW). We investigate asynchronous DC–AC pulse tandem GMAW. We analyse welding arc and droplet behaviour for two tandem welding processes, DC standard-AC pulse and DC pulse-AC pulse. Spatters were generated by attractive and repulsive arc interferences. The attractive arc interaction hinders stable droplet transfer and the repulsive one can induce short-circuiting of the hanging droplets. We examine the effect of process parameters on droplet transfer and spatter generation. During DC pulse-AC pulse tandem GMAW, high peak current of the DC pulse increases arc stiffness and enhances droplet detachment. The observed consistency in arc length, droplet formation, and droplet transfer confirms the stability of asynchronous DC pulse-AC pulse tandem GMAW.

Investigation of double arc interaction mechanism and quantitative analysis of double arc offset in high-power double-wire DP-GMAW

In this paper, the double arc interaction mechanism is investigated and the double arc offset is quantitatively analyzed in the high-power double-wire double pulsed gas metal arc welding (DP-GMAW). Arc offsets in the synchronous and alternating phases were captured using high-speed photography and corresponding voltage and current waveforms were simultaneously recorded during the welding process. Experimental results show the arc offset behavior is affected by the electromagnetic field, arc pressure, and arc stiffness. In the alternating phase, offset of the base arc is largest and offset of the peak arc is smallest. In the synchronous phase, the base and peak arc offsets are somewhere between those in the alternating phase. Dimensional analysis method was used to analyze the factors influencing arc stiffness and in addition, the effects of arc stiffness on arc offset were examined. Increasing the arc stiffness can prevent arc offset, by reducing measurement and experimental errors. Furthermore, the arc stiffness effects were found to be more prominent during the strong pulse compared with the weak pulse, and the arc offsets were smaller in the strong pulse. In the alternating phase, the base arc promotes the formation of molten metal deposits, resulting in the appearance of more prominent fish scales compared with the synchronous phase. Marangoni convection in the weld pool becomes stronger as the phase difference between the two arcs decreases. Moreover, the weld width increases, weld penetration becomes shallower and the weld reinforcement will be lower.

Arc Controllers for TIG Welding Applications:A Review

An arc welding joint could utilize the features of discretely different arc welding methods to obtain the desired joint characteristics. The continuous improvement in arc welding controllers has helped redefine the need of proper parametric control of the process. For efficiency and productivity improvement, modern arc controllers come handy to re-define various aspects of the process (e.g. metal transfer, arc stiffness, etc.). One fascinating outcome is the virtual convergence of complete multi-functional arc welding process to GMAW. Still, there are applications where SMAW and TIG welding processes are regularly being used. Like other welding methods, TIG welding, as well, consists of several derivative approaches. For example, for creating joints of reactive metals (aluminum or magnesium), the AC-TIG welding is commonly employed. Here, the role of arc controller is to generate consistent pattern of desirable rectangular shape AC current waveform through the arc gap. It could cause severe stress (during polarity transition) in all secondary side components of the controller. This review, using indigenously designed peripheral interface controller (PIC) based arc welding inverter, explains the role of arc controllers to handle issues of majority of TIG welding applications.

Arc Controllers for TIG Welding Applications:A Review

An arc welding joint could utilize the features of discretely different arc welding methods to obtain the desired joint characteristics. The continuous improvement in arc welding controllers has helped redefine the need of proper parametric control of the process. For efficiency and productivity improvement, modern arc controllers come handy to re-define various aspects of the process (e.g. metal transfer, arc stiffness, etc.). One fascinating outcome is the virtual convergence of complete multi-functional arc welding process to GMAW. Still, there are applications where SMAW and TIG welding processes are regularly being used. Like other welding methods, TIG welding, as well, consists of several derivative approaches. For example, for creating joints of reactive metals (aluminum or magnesium), the AC-TIG welding is commonly employed. Here, the role of arc controller is to generate consistent pattern of desirable rectangular shape AC current waveform through the arc gap. It could cause severe stress (during polarity transition) in all secondary side components of the controller. This review, using indigenously designed peripheral interface controller (PIC) based arc welding inverter, explains the role of arc controllers to handle issues of majority of TIG welding applications.

Effects of shielding gas on GMAW of 10Ni5CrMoV HSLA steel using high Cr-Ni austenitic wire

The composition of shielding gas was investigated for gas metal arc welding (GMAW) of the 10Ni5CrMoV steel using high Cr-Ni austenitic wire. Adding CO2 into the inert shielding gas can improve the arc stiffness and reduce the incomplete fusion of sidewall. The optimal shielding gas of 40%Ar + 58%He + 2%CO2 was applied into multi-layer multi-pass GMAW of 10Ni5CrMoV steel with austenitic wire. No welding porosity, incomplete fusion and cracks were found in the welding joint. The chemical composition of the deposited metal reached the requirement for forming austenite weld. The highest hardness of welding joint was less than 350 HV and no obvious hardening tendency occurred in the welding joint. The tensile test and impact test indicated that the multi-layer multi-pass welding joint of 10Ni5CrMoV steel using austenitic wire had excellent comprehensive mechanical properties.

Double arc interference and dynamic behavior characteristics of double wire double-pulsed GMAW

The double wire gas metal arc welding (GMAW) technology combined with double pulse low-frequency modulation offers the benefits of the higher efficiency of double wire GMAW combined with superior weld joint quality offered by double pulse low-frequency modulation. However, the potential for severe double arc interference of double wire double-pulsed GMAW affects the stability of the welding process and has thus far limited its widespread use. In this study, high-speed photography was used to record the arc profiles and arc interference of double wire double-pulsed GMAW in the synchronous and alternant phases, while the voltage and current waveforms were simultaneously recorded. Experimental results demonstrated that the double arc deflection of the strong pulse was more severe than that of the weak pulse due to the high current associated with a strong pulse. It was also discovered that the trailing arc stiffness was lower than the leading arc stiffness. Moreover, the deflection of trailing arc was greater under the influence of the leading arc’s electromagnetic attraction. Whereas, the arc deflection of the pulse stage in the alternant phase was small, less than that of the pulse stage in the synchronous phase, the arc deflection of the background stage was much greater. Furthermore, the arc deflections of the pulse and background stages in the synchronous phase were smaller than the arc deflection of the background stage in the alternant phase. Finally, the leading and in the synchronous phase maintained their stiffness and demonstrated weaker magnetic arc blow, fewer spatters, a more refined fish-scale appearance, and weld beads with better uniformity.

The dynamic behavior of double arc interference in high-power double wire pulsed GMAW

High-power double wire pulsed gas metal arc welding (GMAW) exhibits higher welding efficiency than traditional double wire pulsed GMAW. However, severe interference caused by the high-power double arc impairs welding stability. Based on the analysis of the double arc interference forming principle, two phase modes were examined in this study: the alternating phase mode and the synchronous phase mode. In both phase modes, the welding arc voltage and current were recorded, and double arc profiles were also achieved using the high-speed photographic system. Comparison of the experimental results showed that in high-power welding, the electric arc processes produced superior arc stiffness in synchronous phase mode compared to the alternating phase mode, and the magnetic blow was alleviated. Therefore, it can be concluded that the double arc interference in the alternating phase mode was more severe, while the double arc interference in the synchronous phase mode was significantly reduced.

Numerical Analysis of Gas Tungsten Arc Welding with a Constricted Nozzle for Butt Joint of Thin-Sheet Metals

GTA (Gas Tungsten Arc) welding process has been studied as a higher level welding process. The “GTA welding process with constricted nozzle” is one of new welding processes [1]. In this new process, arc stiffness is greatly improved by attaching an additional gas nozzle which is called “constricted nozzle” inside the shielding gas nozzle. The design of a constricted nozzle is shown in Figure 1. With this new process, a butt joint of thin-sheet metals can be achieved although that is difficult with a conventional GTA welding process. In this study, numerical simulation is conducted to understand phenomena of arc plasma in a GTA welding process with a constricted nozzle scientifically.

Pulsed Current Gas Metal Arc Welding under Different Shielding and Pulse Parameters; Part 2: Behaviour of Metal Transfer

The behaviour of metal transfer and arc stiffness understood in terms of arc pressure (Pa) of pulsed current gas metal arc welding (P-GMAW) using mild steel filler wire have been studied with respect to change in pulse parameters under different gas shieldings of Ar+2%CO2 and Ar+18%CO2. The arc environment revealing the droplet transfer from electrode to weld pool in bead on plate weld deposition has been studied by high speed video graphy. Effect of pulse parameters has been considered by their hypothetically proposed summarized influence defined by a dimensionless factor φ, mean current (Im) and arc voltage. The droplet diameter and velocity of droplet at the time of detachment are found to vary significantly with the variation of φ. At a given φ the experimentally measured behaviour of metal transfer is found well in agreement to their corresponding theoretical estimates. The average droplet diameter transferred per pulse predominantly reduces but, the velocity of metal transfer at the time of detachment enhances with the increase of φ under both the shielding gases. In general a higher values of φ, Im and arc voltage enhances the Pa depending upon type of gas shielding. The use of Ar+2%CO2 shielding gas reduces the droplet diameter and enhances the arc pressure than that observed under Ar+18%CO2 gas shielding.

Investigation into micro-tungsten inert gas arc behaviour and weld formation

Current pulsing patterns are defined for the micro-tungsten inert gas welding apparatus developed and are described as: no pulsation (NP), high frequency pulsation (HFP), slightly hybrid pulsation (SHP), and heavily hybrid pulsation (HHP). The characteristics of the microarc behaviour and weld formation are then investigated in detail for these patterns. The parameters and pattern of the pulsating current dominate arcing power and arc stiffness at a given average current, thus affecting arc state and bead formation. The arc image analysis shows that the HFP and HHP arcs can burn more steadily even at an average current of 2 A because of the arc stabilising effect from the superimposed high frequency components. During the on time of the pulse, the state of the hybrid pulsating (HP) arc varies successively from an apple like shape to a cone with an increased taper. Furthermore, this HP arc shrinks owing to the decreases in the peak current and arcing power with increasing frequency of the base pulse, but is still much greater in size than the NP and HFP arcs. Finally, welding experimental results demonstrate that the HP welds are the widest and become narrow with an increase in the pulse frequency, and the NP and HHP beads are somewhat wider than the HFP and SHP beads respectively.

交流パルスミグ溶接における微小スパッタ及びアーク切れ問題の対策

A general way of producing pulsed alternating current waveforms for metal inert gas welding is to reverse the polarity in part of the base current period from electrode positive (EP) to electrode negative (EN). In the case of reversing the polarity from EP to EN at the right beginning of a base current period, new cathode spots tend to be produced on the surface of elongated residual molten metal that remains on the tip of a welding wire right after the detachment of a droplet. A strong cathode jet breaks the elongated residual molten metal and the fragments deposit on both sides of weld bead as tiny spatters. Delaying the polarity reversing by a time of 1.5 ms at the beginning of a base current period can effectively reduce tiny spatters because in the delay time period the molten metal on the tip of a welding wire becomes steady with a hemispheric shape. At the end of EN current period the polarity is again switched from EN to EP and a new cathode spot is occasionally produced at a location away from the molten pool on the surface of base metal. Arc voltage becomes abnormally high so that the arc length control system extends automatically the base current period. If the cathode spot moves in a direction away from the molten pool arc interruption occurs in the extended base current period. Elimination of the abnormal arc voltage before it is used for arc length control can avoid the abnormal extension of base current period and probable arc interruption in the extended period as well. If the cathode spot moves more quickly in a direction away from the molten pool arc interruption occurs in the original base current period. In this case the rate of abnormal arc voltage increasing is very high. When the rate is higher than a preset value the present base current period is terminated immediately and arc current is switched from base current to pulse peak current. Consequently, the strong arc stiffness of pulse peak current brings the cathode spot back to the molten pool or its vicinities and arc interruption is avoided.

レーザ・アーク併用高速表面処理法の研究 ５ ＴＩＧアークの挙動から見た適正なレーザ照射位置

In the former reports, it was discussed that a TIG arc behavior was controlled by a CO2 laser when the traveling speed of a base metal was fast and the arc length was long. In this case, the bead width was different, although the experimental conditions were same except the traveling direction of the base metal. In this report, the behavior of the TIG arc only was investigated using high speed video images when the traveling direction was changed. Furthermore, the reasonable spot of CO2 laser was examined for stabilization of the arc. In this case, the backward direction meant that the traveling direction was same as the direction of a tungsten electrode. The opposite direction was called the forward direction. The main experimental conditions were as follows. The TIG arc current, the traveling speed of a SUS304 base metal, Ar gas flow rate and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 150 mm/s, 1×10-3 m3/s and 15 mm, respectively. When the base metal moved to the backward direction, a straight arc column bent smoothly at the point which was near to the base metal, and moved straightly to an anode spot. This spot existed in the circular molten pool and the shape of the pool did not changed. In this case, the bending point scarcely changed its position. On the other hand, in the case of the forward direction, the shape of the bending arc column, the position of the bending point and the shape of the melted part were different from ones of the backward direction. It was considered that arc stiffness at the bending point of the backward direction arc and preheat effect of arc plasma were less than the ones of the forward direction arc.

レーザ・アーク併用高速表面処理法の研究 ３ 揺動レーザビームによるＴＩＧアークの制御

In the first report, stabilizing effects of a CO2 laser on a TIG arc behavior were discussed from the point of the arc voltage and of the interaction between the arc and the laser plume.In this report, the CO2 laser beam was scanned by a beam oscillator, and the shapes of melted parts of the base metal were investigated. Furthermore, the behavior of a TIG arc with a scanning CO2 laser beam was investigated by high speed video-pictures. The main experimental conditions were as follows. The TIG arc current, the laser output, the scanning frequency and the scanning width of a laser beam, the traveling speed of a SUS304 base metal and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 2 kw, 25 Hz, 8 mm, 20 mm/s and 15 mm, respectively.As a result, the arc could be controlled by the scanning laser beam, and wide and shallow beads were made using this method under the suitable conditions. Therefore, it was found that the arc with scanning laser beam is excellent as heat source for surface treatment.On the other hand, the arc voltage and the range of its change decreased according as the scanning frequency increased from 5 Hz to 20 Hz. According to the observation using high speed video-pictures, the arc went straight forwards from the electrode and bent toward the scanning laser plume, and the bending point of the arc became increasingly far from the tip of the electrode when the scanning frequency increased. It would be considered that the arc voltage was affected by the bending point of the arc column because of the arc stiffness.

レーザ・アーク併用高速表面処理法の研究（第１報） ＣＯ２レーザによるＴＩＧアークの安定化

In order to develop a fast surface treatment method or a fast welding method using an electric arc with a laser beam, stabilizing effects of a CO2 laser on a TIG arc were investigated. A TIG arc makes discontinuous molten pools even when the travelling speed of a base metal is high and the distance between a base metal and a tungsten electrode is large. In such a case, the behavior of an arc usually becomes unstable and the arc voltage changes in the range of 5-8 V. Whereas, the arc behavior became stable by using a CO2 laser beam simultaneously, and good continuous weld beads were made on conditions that the TIG arc current, the laser output, the distance between a SUS304 base metal and a tungsten electrode, and the travelling speed of a base metal were 100 A (DCEN), 2 kW, 15 mm and 200 mm/s, respectively.It was found that the anode spot was fixed on the molten pool formed by the laser beam, and, the molten pool, the laser plume and the metallic vapor affected the stabilization of the path of a TIG arc and its voltage. Therefore, it is effective to controle a long arc by a laser that the beam irradiates near the tip of the arc where the arc stiffness becomes weak.

The physics of fusion welding. Part 1: The electric arc in welding

The electrical characteristics of the arc as used in welding technology are considered, giving some attention to problems of arc reignition and stability, and to the means of assessing the suitability of power sources for welding operations. The behaviour of thermionic and nonthermionic cathodes is reviewed and recent developments in the investigation of nonthermionic cathodes are described. Work on the arc column is divided into sections on properties and fluid dynamics, following which the behaviour of the column during welding is reviewed in relation to specific problems such as arc force, arc stiffness, magnetic effects and arc blow. A final section covers the anode, particularly in relation to the tungsten/argon arc and its use in the gas tungsten arc welding process.

The Effect of High-Frequency Pulsing of a Welding Arc

Pulsed and nonpulsed nonconsumable electrode welding arcs are compared on the basis of equal average power input. A relationship is developed between the pressure of the high-frequency (typically greater than 5 kHz) pulsed arc and a dc arc with equal power input. It is shown that the arc pressure, and hence arc stiffness, of the pulsed arc may be as much as ten times that of the equivalent dc arc. As expected, the pressure ratio of the pulsed arc to nonpulsed arc decreases as the form factor of the pulsed arc decreases.