Stability Of Welding Process Research Articles

Analysis and improvement of laser wire filling welding process stability with beam wobble

The reasonable selection of laser welding modes, namely keyhole mode and heat conduction mode, is based on the practical application requirements. The results show that the heat flux rapidly decreases and beam moving velocity increases with the beam wobble amplitude of 2.0 mm and frequency of 150 Hz, promoting the transformation of keyhole mode to heat conduction mode. Wider and shallower weld morphology is obtained. The improvement of keyhole stability and modification of liquid metal fluidity promote the overflow of bubbles. In case of beam wobble welding, the movement and turbulence of weld pool driven by the beam wobble help to break the columnar crystals. Welding of 40-mm thick plates without incomplete fusion and pore defects is achieved by suitable beam wobble parameters.

Microstructure and Mechanical Properties of Al/Steel Butt Joint by Hybrid CMT Welding with External Axial Magnetic Field.

The 6061 aluminum alloy and 304 stainless steel were welded by hybrid cold metal transfer (CMT) welding with external axial magnetic field. The effects of magnetic intensity and frequency on joint microstructure and mechanical properties were studied. It was found that the magnetic field can promote the spreading of aluminum weld metal on the steel surface and thus increase the bonding area of Al/steel butt joint. The welding process stability improved, while the wetting behavior worsened with the introduction of alternating frequencies. The thickness of the intermetallic compound (IMC) layer at Al/steel interface was reduced to 3 μm with the coil current of 2 A. The application of the magnetic field promoted the aggregation of Si atoms at the interface and inhibited the formation of brittle (Al, Si)13Fe4 phase. The fracture paths were transformed from (Al, Si)13Fe4 layer to Al8Fe2Si layer with the application of the magnetic field. The maximum tensile strength reached 130.2 MPa, an increase of 61.6% in comparison to the normal CMT process.

Influence of interwire angle on undercutting formation and arc behavior in pulsed tandem narrow-gap GMAW

The tandem narrow-gap gas metal arc welding was adopted in this study. The effects of interwire angle on the welding process stability and arc behavior were investigated. With the interwire angle increasing, the welding process stability gets improved. The arc interruptions which frequently occur in the leading arc are eliminated when the interwire angle is >0°. The mutual electromagnetic attraction between the two arcs decreases with the interwire angle increasing due to the increased arc distance. The two arcs move from the groove bottom to the sidewalls, which transfer more heat to the sidewalls resulting in increased weld width. This leads to serious undercutting defects especially when the interwire angle is 20°. The molten metal under the arcs flows to the rear of welding pool under the action of plasma drag force, arc pressure and droplet impingement. As a result, there is no adequate molten metal to fill the sidewalls, giving rise to undercutting defects. The undercutting at the groove sidewall close to the trailing arc is smaller. This is because the liquid metal under the trailing arc is more massive, which means more molten metal flows to the sidewall, alleviating the undercutting defect.

Effects of Cr2O3 active agent on the weld process dynamic behavior and joint comprehensive properties of fiber laser welded stainless steel thick plate

In this study, the dynamic behaviors of metal vapor, plasma, keyhole, and weld pool during activating laser welding of stainless steel thick plates are monitored in real time by employing a novel "sandwich" method in combination with a high-speed camera system. Meanwhile, the welding quality of specimens is inspected and analyzed from the aspects like joint weld formation, mechanical properties, microstructure, and element distribution. The effects of Cr2O3 active agent on the welding stability and quality of specimens are explored. According to the results, adequate coating of active agent on the specimen surface can weaken and suppress the generation and drastic changes of metal vapor and plasma inside and outside the keyhole, increase the keyhole depth, improve the keyhole shape, weaken the oscillation amplitude of weld pool, and prolong the change cycles of keyhole and weld pool. Consequently, the stability of welding process is enhanced, the generation of porosity and splash defects is inhibited preferably, the quality of weld formation is improved, the weld penetration is increased, the grain structure in weld zone is refined, the width of heat affected zone is narrowed, and the joint strength and toughness are enhanced, without showing apparent change of the relative element contents in the welded joint. In conclusion, coating of Cr2O3 active agent on the specimen surface is effective in improving the welding properties of laser welded stainless steel plates.

Internal characteristic of droplet and its influence on the underwater wet welding process stability

Abstract Based on an X-ray imaging system, the characteristic of underwater wet welding droplets was revealed, which was deemed to be the essential factor contributing to the unstable underwater wet welding process. By observing the X-ray images, it is confirmed that the inflation-exhaustion process in the droplet occurred during the entire process from the droplet forming to entering into the molten pool. The void in the droplet leaded to lower gravity and greater repulsive force and deteriorated the welding process stability. On the one hand, the spatter-like droplet transfer mode was relatively easy to occur, increasing the frequency of the droplet repelled spatter. On the other hand, the arc easily broke and the arc stability was deteriorated. In addition, the droplet rupture process tended to promote the generation of gas escaping spatter. The process was effected by material gas solubility, the surface tension, the temperature according to the establishing force models.

A novel underwater submerged-arc welding acquires sound quality joints for high strength marine steel

The serious interferences from the surrounding water severely limit the process stability and joint quality of the current underwater welding technologies. To effectively isolate the welding area, a mixture of epoxy resin and submerged-arc flux was innovatively prepositioned in the welding area during underwater welding process. Butt welding experiments of a typical high strength marine steel were conducted to verify the advantages of this technique. Compared with the traditional underwater wet welding, underwater submerged-arc welding significantly optimized the arc burning environment due to the covering and isolation, which effectively improved the stability of welding process. Defectless joints with microstructure that full of fine acicular ferrite and high-quality mechanical properties, especially, outstanding performance of ultimate strength and plasticity were obtained. The results are expected to positively widen the practical application of underwater welding in many water related industries.

Optimization of the design of the plasma torch for using gas fluxes

The paper presents the results of plasma torch development and gas fluxes using possibility in plasma welding process. As part of the work, existing plasma torches were analyzed in order to identify opportunities for their modernization. The literature data was analyzed for identifying the optimal design of the plasma torch. During the study of literature data, it was found that the diameter of the nozzle tip has a great influence on the plasma welding process. Therefore, it was decided to model the processes occurring in the plasma torch using tips with different diameter sizes. Parameters that effects on the stability of plasma welding process were presented. Possible and potential effective plasma torch tip designs were proposed. The model of the behavior of argon in a plasma torch was constructed, which made it possible to draw conclusions about the optimum diameter of the plasma torch tip. Also, was shown the effect of the diameter of the plasma torch on the behavior of plasma gas.

Investigation of Arc Bubble Affecting the Arc Stability and Improvement of Weld Appearances Using Bubble Constraint Device in Underwater Wet Welding

The generating, floating and collapsing of arc bubble is a special phenomenon in underwater flux-cored wet welding. The configuration changing process of bubble will change the stress on droplet and influence the droplet transfer process. In this study, the shape changing of bubble is captured in graphic and the real-time electric signal data is obtained. The impact of bubble floating and collapsing results in the globular repelled transfer mode, which also reduces the arc stability. A self-designed gas-shield cover is used as a bubble constraint device to improve the welding process stability and weld appearances by limiting the free floating and expansion of arc bubble. The relationships between the cover diameter and the characteristics of weld appearance are studied.

High Efficiency and Quality of Multi-Pass Tandem Gas Metal Arc Welding for Thick Al 5083 Alloy Plates

Multi-pass tandem gas metal arc welding (TGMAW) for Al 5083 alloy plates with 30mm thickness is carried out to study its high efficiency and high quality. The welding process is evaluated by high-speed photographs and electrical signals. The deposition rate and welding time are calculated to characterize the welding efficiency. The bead formation, porosity, microstructure and mechanical properties are tested and analyzed. The results indicate that though arc deflection occurs due to the electromagnetic interference between two arcs during TGMAWprocess, it does not affect the welding process stability significantly. The deposition rate and welding time of TGMAW process are about 15 g/min larger and about 16.7% less than those of gas metal arc welding (GMAW) process respectively, accompanied by the reduction of heat input. The TGMAW welded joint has less porosity and more refined microstructure to contribute to the improvement of mechanical properties (micro-hardness, tensile strength and ductility). It can be concluded that TGMAW process yields excellent performance of welded joint with improved welding efficiency, which makes it extremely practical during welding of thick plates.

Pulsed laser enhanced metal transfer of aluminum alloy in GMAW

Pulsed laser enhanced metal transfer of gas metal arc welding (GMAW) is a recent modification of conventional GMAW that applies a relatively low-power pulsed laser to the droplet. Previously current-independent metal transfer of carbon steel, in free-flight or short-circuiting mode, was achieved by utilizing single-side pulsed laser irradiation on the droplet. However, there are few studies on laser enhanced aluminum alloy metal transfer of GMAW due to the high reflectivity of aluminum alloy. In addition, the low melting point of aluminum alloy makes it possible to cut off the welding wire (irradiate on the wire) directly by pulsed laser with high energy density, instead of irradiating on the solid-liquid interface of the droplet. Hence, the laser-enhanced aluminum alloy metal transfer process is studied in this paper. The results demonstrate that when the pulsed laser irradiated the solid-liquid interface of the droplet, the laser was found to lead to a significant increase in the stability of welding process as an additional detaching force and change the transfer mode and flight path of the droplet. Both the short-circuiting (SC) transfer and the spray transfer processes were promoted by changing the stress state of the droplet, and the transfer frequency was effectively increased. Moreover, when the pulsed laser irradiated the welding wire, the welding wire was cut off and the arc climbed to the laser incident point. The cut wire-droplet (W-D) changed into a molten droplet by the heating of the arc and entered into the molten pool. A new spray transfer balance formed at the incident point and the restriction that the laser must impinge on the solid-liquid (S-L) interface of the droplet was released.

Investigation of acoustic radiator affecting bubble-acoustic interaction in ultrasonic wave-assisted UWW at shallow water

The evolution mode of the dynamic bubble around the arc burning zone plays an essential role in adversely affecting the stability of underwater wet welding (UWW) process. Ultrasonic wave-assisted UWW (U-UWW) provides such a promising approach to control the bubble evolution and achieve a large and stable bubble. In fact, the enhancement of bubble-acoustic interaction capabilities by optimization of acoustic radiator also provides chances for the development of U-UWW. In this work, acoustic radiator with a concave surface has been designed in order to investigate the effect of curvature radius on the bubble-acoustic interaction. Analysis of the high-speed imaging in conjunction with welding current and arc voltage waveforms was carried out to understand the variation in bubble evolution for process control and how the bubble evolution was affected by varying curvature radii. The study indicated that stable bubble can be more easily achieved in U-UWW because it minimizes the extent of the undesirable bubble evolution occurring in an erratic and time-variant behavior. The difference in the shape and motion track of the bubble is also observed in different curvature radii. Acoustic field simulations confirm the acoustic pressure changes with curvature radius, consistent with experimental result that the maximum degree of ultrasonic control of the bubble indeed appears in practice. Observations and analysis of arc stability and weld morphology revealed that the addition of ultrasonic wave in UWW contributes to an improvement in the welding process. Due to varying curvature radii, the degree of improvement also produces significant differences. Furthermore, in terms of bubble evolution, arc stability, weld morphology and acoustic field simulation, the degree of bubble-acoustic interaction follows the order: R = 38 mm > R = 30 mm > R = 46 mm > conventional UWW, suggesting that curvature radius of 38 mm exhibits a better interaction performance.

The influence mechanism of variable polarity plasma arc pressure on flat keyhole welding stability

The variable polarity plasma arc (VPPA) welding process is well suited for the welding of aluminum alloy, but the stable welding process and good-quality weld bead are difficult to be obtained in the flat position. The purpose of this work is to study the characteristic of variable polarity plasma arc pressure with different polarity time and find the key fact to achieve welding process stability and good quality welding joint in the flat position. The arc shape variation, arc pressure evolution and the molten pool behavior were observed and measured to discover the relationship to the weld joint formation. It was found that the small plasma arc pressure in the center with a similar affected region and enough upward shear force of arc plasma are the necessary conditions to get a stable keyhole process, which could drive the liquid metal of the back side weld pool converges at the bottom of the keyhole and flows upward and form a high-quality weld bead. Comparing the welding stability and quality, adjusting polarity time is the good method for completing the necessary conditions. With the variable polarity time decreasing, the stable keyholes process and acceptable weld quality were obtained in the flat position.

Lyapunov exponent analysis for the evaluation of hybrid laser double-arc welding process stability.

Hybrid laser double-arc welding is a complicated process with many random and uncertain influencing factors because of the interactions of energy, forces, and fields. The wire spacing is one of the main factors affecting the coupling behavior of laser and arc plasma and the stability of welding process. However, it is difficult to establish a precise mathematical model for evaluation of welding stability. In this paper, the largest Lyapunov exponent (LLE) of characteristic currents during the welding process under different wire-wire distances were numerically evaluated by the phase space reconstruction technique. Synchronous high-speed photography was adopted to observe arc shape and droplet transfer. The experimental and calculated results indicate that hybrid laser double-pulsed arc welding is a complex process of chaos. The LLE can provide a criterion for welding stability and can agree well with the observation of electrical signal, arc shape, and droplet transfer. Research results are needed to understand the welding process and to guarantee a stable and safe joining.

Influence of calcium fluoride on underwater wet welding process stability

To explore the influence of calcium fluoride on underwater wet welding process stability, the relevance of calcium fluoride in the flux to metal transfer mode and arc stability was discussed in the process of underwater wet welding using a set of wires with various calcium fluoride contents. The metal transfer images were obtained using X-ray imaging system and the electric signal detection system was used to collect arc voltage and welding current signals synchronized with the film frames. Three metal transfer modes, i.e., repelled globular transfer, surface tension transfer, and spatter-like metal droplet transfer, were observed during the underwater wet welding process. The spatter-like metal droplet transfer mode was put forward firstly. Increasing the contents of calcium fluoride in the wire from 0 to 65%, the proportion of surface tension transfer mode steadily climbed from approximately 15 to 40% while that of spatter-like metal droplet mode declined from 53 to 35%. The arc stability of the welding process firstly deteriorated and then ameliorated with the increasing calcium fluoride content.

Analysis and improvement of underwater wet welding process stability with static mechanical constraint support

A process variant of underwater wet welding (UWW), i.e., mechanical constraint-assisted UWW process, was developed. Through the visual sensing of arc bubble and welding electrical signals, the optimum parameters of mechanical constraint system were determined. Variations of arc stability, arc burning process, and weld morphology with arc voltage were investigated under the same mechanical constraint condition. Results indicated that the coefficients of variation for the two processes initially dipped to a minimum and then gradually increased to a higher value with increasing arc voltage, but the change rate of variation coefficient in UWW was much more pronounced than that in mechanical constraint-assisted UWW (MC-UWW). When the arc voltage was lower, the proportion of short circuiting process was so high. Thus, there was room for further reduction by mechanical constraint. But the further reduction room became still effective when the arc voltage was larger because the proportion of arc extinction process was already large enough. Weld morphology results showed that the increment of weld penetration decreased from 0.91 mm to 0.18 mm with the increase of arc voltage when mechanical constraint was applied. In addition, the increment trend was very significant when arc voltage was within the range of 20 V to 28 V. For the welding conditions in this study, a suitable voltage range in conjunction with optimum mechanical constraint condition can be determined to achieve a more stable welding process in MC-UWW.

Effect of hydrostatic pressure on protective bubble characteristic and weld quality in underwater flux-cored wire wet welding

The metal transfer and protective bubble images, real-time electric signal data and weld appearance were obtained in different simulated water depth wet flux-cored arc welding. The electric signal results showed that the high hydrostatic environment deteriorated the stability of the wet welding process. The poor weld appearances with porosity were displayed when it was welded in deep water. The weld dilution rate descended from 51% to 40% with increasing water depth from 0.5 m to 90 m because of arc shrinking and heat input reduction. The reduction of protective bubble size and duration caused by high water pressure was unable to maintain a stable burning arc. With increasing water depth, the increase of pores in welds strongly deteriorated the mechanical property of joints. The process of gas generation and its escape from the droplet during the droplet transfer were observed. The rise of pressure compressed gas pores and prevented the gas from escaping, which resulted in the increase of pores.

Analysis of welding process stability and weld quality by droplet transfer and explosion in MAG-laser hybrid welding process

The metallic vapor and molten pool include plenty of welding information in the manufacturing process of MAG (Metal Active Gas Arc Welding)-laser hybrid welding. In this work, double high speed cameras are used to take the real-time images of the top-vapor and bottom-molten pool in the hybrid welding process. In order to monitor welding process status and weld quality, this paper proposes a method which combines the period of droplet transfer and droplet explosion. In time domain, the morphological features include the area of top-vapor, area of spatters, number of spatters and the average gray value of the bottom-molten pool, those features are used to research the stability of short circuiting transfer as well as the mechanism of the welding process. Besides, the welding process stability and weld quality are analyzed by features including the period of droplet transfer and droplet explosion in time and frequency domain. The experimental results show the period of droplet transfer and droplet explosion can effectively reflect welding process and weld quality. It provides a basis for monitoring and controlling MAG-laser hybrid welding process status.

Investigation on Underwater Wet Welding Process Stability Based on the Arc Bubble Control

Investigation on Underwater Wet Welding Process Stability Based on the Arc Bubble Control

Effect of water flow on the arc stability and metal transfer in underwater flux-cored wet welding

The influences of flow rate and direction on metal transfer mode and molten pool shape in underwater wet flux-cored arc welding (FCAW) process were studied. Real-time electric signal data, metal transfer images and weld appearances at different flow rates and directions were obtained. The electric signal results showed that the increase of flow rate would deteriorate stability of the wet welding process. Two typical modes of metal transfer, globular repelled transfer mode and surface tension transfer mode were observed. Their proportion would change with increasing of flow rate. When flow rate increased from 0m/s to 2.5m/s, the proportion of globular repelled transfer mode increased from 71.5% to 100%. When welding direction was downstream, the proportion of spatter increased from 4.23% to 56% with the flow rate adding to 2.5m/s. The variation of flow direction would change position of molten pool, which result in the change of spatter lose rate. The depth-to-width radio of weld bead which was welded upstream increased from 0.13 to 0.8 with the increase of flow rate. As welding downstream, the depth-to-width radio didn’t change obviously. The method to overcome adverse effects of flow was discussed, and an acceptable appearance of welding seam was obtained.

Arc Length Control of Pulsed MIG Welding Based on Two Dimensional Fuzzy Control

In the process of the pulse MIG power supply welding, the arc length will change dynamically due to various environmental disturbances. Therefore, how to realize the real-time control of the arc length is the key to the stability of the pulse MIG welding process, and it is also an important guarantee of the welding quality. In this paper, the three voltage loop control methods of no arc length control, one-dimensional fuzzy control and two-dimensional fuzzy control are compared through matlab simulation. The simulation results show that the arc length control scheme of welding power supply based on two-dimensional fuzzy control can achieve better dynamic response when the stepwise mutation occurs in the arc length.