The arc characteristic of ultrasonic assisted TIG welding

Many applications of ultrasonic-assisted methods were used during metal solidification, but they could not be introduced into weld pool. In this paper, a way of ultrasonic assisted TIG welding is introduced. By directly imposed ultrasonic vibration on welding arc, the vibration interacts with arc plasma and passes to the weld pool. Measurement results show that arc pressure is significantly increased with the ultrasonic vibration and the arc pressure distribution models are changed. Bead-on-plate welding tests on SUS304 confirm that this technology can influence the style of metal melting and increase weld penetration depth.

Research on the Mechanism of Penetration Increase by Flux in A-TIG Welding

The mechanism of penetration depth increased by activating flux in activating tungsten inert gas(A-TIG)weldingwas studied by measuring the distribution of trace element Bi in the weld and monitoring the change of arc voltageduring A-TIG welding of stainless steel 0Crl8Ni9 with fluxes SiO_(2)and TiO_(2).The results show that the mechanismof penetration depth in A-TIG welding depends on the sort of flux used.The weld pool convection after coating theflux SiO_(2)and flux TiO_(2)is changed inversely compared with convectional TIG welding without flux.The arc voltageis increased by flux SiO_(2)whilst flux TiO_(2)does not have effect on the arc voltage.The reason of penetration depthincrease for SiO_(2)is due to the constriction of arc plasma and the change of surface tension gradient.The increaseof weld penetration depth with TiO_(2)only ascribes to the change of surface tension gradient.

Realizing precision pulse TIG welding with arc length control and visual image sensing based weld detection

Methods of arc length control and visual image based weld detection for precision pulse TIG welding were investigated. With a particular all hardware circuit, arc voltage during peak current stage is sampled and integrated to indicate arc length, deviation of arc length and adjusting parameters are calculated and output to drive a step motor directly. According to the features of welding image grabbed with CCD camera, a special algorithm was developed to detect the central line of weld fast and accurately. Then an application system were established, whose static arc length error is ±0.1 mm with 20 A average current and 1 mm given arc length, static detection precision of weld is 0.01 mm , processing time of each image is less than 120 ms . Precision pulse TIG welding of some given thin stainless steel components with complicated curved surface was successfully realized.

Experimental investigation and optimization of weld bead characteristics during submerged arc welding of AISI 1023 steel

Submerged arc welding(SAW), owing to its high deposition rate and high welding quality, is widely used in the fabrication of pressure vessel, marine vessel, pipelines and offshore structures. However, selection of an optimum combination of welding parameters is critical in achieving high weld quality and productivity. In this work, initially, the SAW experiments were performed using fractional factorial design to analyze the effect of direct and indirect input parameters, namely, welding voltage, wire feed rate,welding speed, nozzle to plate distance, flux condition, and plate thickness on weld bead geometrical responses viz. bead width, reinforcement, and penetration. The bead on plate technique was used to deposit weld metal on AISI 1023 steel plates. The effect of SAW input parameters on response variables were analyzed using main and interaction effects. The linear regression was used to develop the mathematical models for the response variable. Then, the multi-objective optimization of input parameters was carried out using desirability approach, genetic algorithm and Jaya algorithm. The Jaya algorithm offered better optimization results as compared to desirability approach, genetic algorithm.

Gas Pool Coupled Activating TIG Welding Method with Coupling Arc Electrode

Gas pool coupled activating TIG(GPCA?TIG) welding put forward in?house can dramatically enhance weld penetration of TIG welding through introducing active element oxygen to reverse the Marangoni convection flow in the molten pool. In order to further improve the welding productivity, the normal solid tungsten electrode is replaced by a kind of coupling arc electrode. The changes of arc pressure distribution along anode surface and the weld appearance were evaluated. On this basis, the dependences of weld shape characterized with weld depth, width and undercut on the main welding parameters were discussed. The results indicate, the substitution of coupling arc electrode can lead to an obvious decrease of arc pressure. Compared to hollow tungsten electrode and twin tungsten electrodes, the coupling arc electrode is much easier to manufacture and has more compacter structure. Combined with the symmetric distribution of arc pressure in di erent directions, this electrode has extensive adaptability. In the GPCA?TIG welding with coupling arc electrode, both the substitution of coupling arc electrode and the introduction of outer active gas oxygen can reduce the possibilities of producing humping bead and undercut. Their joint action makes this welding method have the capability of realizing high travel speed and deep penetration welding.

Effect of auxiliary TIG arc on formation and microstructures of aluminum alloy/stainless steel joints made by MIG welding-brazing process

A new hybrid welding process was successfully used to join aluminum alloy and stainless steel. In the MIG welding-brazing process, the lower thermal conductivity of steel can cause dramatic change of temperature gradient on steel surface, while the auxiliary TIG arc can change this phenomenon by heating the steel side. The auxiliary TIG improved the wettability of molten metal, resulting in the molten metal spreading fully on upper surfaces, front and back surface of steel, forming a sound brazing joint; the content of Cr and Ni elements in IMCs layer was increased, which can enhance the quality of the layer; and the microstructure of IMCs layer also was improved, increasing the bonding strength with the weld seam. The average tensile strength of the joint obtained with auxiliary TIG arc（146.7 MPa） was higher than that without auxiliary TIG arc（96.7 MPa）.

Research for the method of image acquisition of the molten pool in the TIG welding of aluminum alloy

Obtaining the image of molten pool aluminum alloy’s tungsten inert gas(TIG)welding becomes a challenging problem in the welding field. In this paper, a bran-new optical sensor based analyzing the light spectrum was designed, and the clear image of the molten pool during the aluminum alloy’s welding using the common industrial CCD camera was obtained. And with the new algorithm provided by myself, the desirable characteristic parameters of the molten pool of aluminum alloy’s welding were obtained, and it provides a good base for advanced monitor welding quality.

Microstructure and property research on welded joints of 7xxx aluminum alloy welding wire TIG for 7075 aluminum alloy

7 xxx welding wire was self-made by spray forming ingots drawn to series welding wires products,and then TIG butt welding test is used for 5 mm thick 7075 high-strength aluminium alloy.After welding,the stress relief+solid-solution aging heat treatment(T6)were performed to joints,and the mechanical properties and microstructure of the joints before and after heat treatment were comparative analyzed.The results show that the properties of the heat-affected zone(HAZ)of the joint before heat treatment decreas,and the joint is softened.The welded joints tensile strength is 271.8 MPa,the elongation is 5.6%,and the average hardness of the weld is 118.4 HV.The second phase particles such asη(Mg Zn2),S(Al2 Cu Mg),Al13 Fe4 are distributed in a network layer,with no apparent element segregation.After heat treatment,the structure of each area of the joint is coarsened,and a small amount of Fe-containing impurity phases are distributed.Theηand S phases are dissolved in the matrix.The hardness of each area of the joint is increased to 155 HV,and the softening zone is disappeared,this leads the joint elongation close to 16.9%.The tensile strength is increased to 511.8 MPa,reaching 94%of the base metal tensile strength.

Physics characteristic of coupling arc of twin-tungsten TIG welding

Twin-tungsten TIG welding was developed, in which two electrodes were placed in a single welding torch. In order to master this process, the arc physics characteristic was studied. The twin-tungsten coupling arc shape was observed by using CCD camera, and the arc pressure was measured. The results show that the coupling arc includes two arcs that pull each other according to Lorentz force and one big coupling arc is formed; the coupling arc pressure is much lower than that of conventional TIG arc. In the end, a simple welding experiment was carried out. This proves that stable welding process can be achieved by twin-tungsten TIG at higher current than that of conventional TIG because of its low arc pressure and the high efficiency welding is realized.

Numerical simulation of influence of nozzle structure on arc characteristics of GPCA-TIG welding

This work mainly articulated the effects of nozzle structure on arc characteristics in gas pool coupled activating TIG （GPCA-TIG） welding process by using Fluent Software. Different models were set up to adapt the different torch structure during computer progress. The specific configuration of the welding torch made the gas flow in outer gas passage constrained. The nozzle structure has great influence on outer gas distribution because of the changing of coupling region between the outer active gas and molten pool surface. When the coupling degree is reduced or the outer gas passage become smaller, the oxygen in outer gas penetrates into the arc plasma and spreads to the arc region more easily. Owing to its cooling effects, the morphology of arc is contracted, and the arc temperature is increased. When the inner wall and the outer wall of outer gas passage are not parallel, the wide top and narrow bottom nozzle shape can bring more oxygen into the arc plasma, the arc is contracted and the peak temperature of arc rises a little more comparing to the narrow top and wide bottom one.

Study on arc-ultrasonic TIG welding of titanium alloy

TC4 alloy was welded by conventional TIG welding and arc-ultrasonic TIG welding respectively. The microstructure of joint was analyzed by means of optical-microscope, scanning electron microscope in order to study the relationship between the macro-properties of joint and the microstructure. The results show that the joints were all welded successfully by conventional TIG welding and arc-ultrasonic TIG welding. With the increment of ultrasonic frequency and activated voltage, the width of joint became narrow step by step. The microstructure became more and more fine and was inclined to equiaxed crystal. Moreover, the dendrite depredation was not observed obviously. The properties of welded joint were improved markedly compared with that of conventional TIG welding.

Investigation on the stepping arc stud welding process

Through the investigation on traditional arc stud welding process, a new welding gun and its control system were developed in this paper. The stepping arc stud welding gun was mainly made by a stepping motor as actuating unit and a screw-driven device as moving unit. A control system with a MCS-51 single-chip microcomputer as main control component was used to realize the new stud welding procedure. This new welding process with stepping stud welding gun is named as stepping arc stud welding. In the new welding process, the stud action can be looked as constituted by some micro steps. The setting and adjusting of the stepping arc welding gun behavior parameters are accomplished independently. It is indicated from the results of process tests and bending test that the stepping arc stud welding process is practicable.

Simulation on Dynamic Characteristic of Negative Resistance Arc in Pulsed TIG Welding

A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the mathematical model is run in MATLAB environment, and the discussion is focused on the way the peak current ranging from 29 A to 50 A and the time constant of arc in the span of 0.003—0.006 s influence the simulating results and the dynamic characteristic. The simulating data are close to that of welding experiments and correspond to the theoretical conclusion.

Optimization of back bead geometry in the PMAG-TIG twin arc hybrid root welding process using grey based Taguchi method

This study investigated multi-response optimization of the pulse metal active gas-tungsten inert gas( PMAG-TIG) twin arc hybrid root welding process for an optimal parametric combination to yield favorable back bead geometry of welded joints using grey relational analysis and Taguchi method.Eighteen experimental runs based on an orthogonal array following the Taguchi method were performed to derive objective functions to be optimized within the experimental domain.The objective functions were selected in relation to parameters of PMAG-TIG twin arc root welding back bead geometry: back bead width to root reinforcement ratio and deposited metal height.The Taguchi approach was followed by grey relational analysis to solve the multi-response optimization problem.The significance of factors on overall quality characteristics of the weld joint was also evaluated quantitatively using analysis of variance.Optimal results were verified through additional experiments,and showed to feasibility of applying grey relation analysis in combination with Taguchi technique for continuous improvement of product quality in the manufacturing industry.

Experimental Investigation on the Performance of Armour Grade Q&T Steel Joints Fabricated by Flux Cored Arc Welding with Low Hydrogen Ferritic Consumables

Quenched and Tempered （Q＆T） steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking （HIC） and softening in the heat affected zone （HAZ） after welding. The use of austenitic stainless steel （ASS） consumables to weld the above steel was the only available remedy to avoid HIC because of higher solubility for hydrogen in austenitic phase. Recent studies revealed that low hydrogen ferritic （LHF） steel consumables can also be used to weld Q＆T steels, which can give very low hydrogen levels in the weld deposits and required resistance against cold cracking. Hence, in this investigation an attempt has been made to study the performance of armour grade Q＆T steel joints fabricated by flux cored arc welding with LHF steel consumables. Two different consumables namely （i） austenitic stainless steel and （ii） low hydrogen ferritic steel have been used to fabricate the joints by flux cored arc welding （FCAW） process. The joints fabricated by LHF consumable exhibited superior transverse tensile properties due to the presence of ferrite microstructure in weld metal. The joints fabricated by ASS consumable showed higher impact toughness due to the presence of austenitic phase in weld metal microstructure. The HAZ softening in coarse grain heat affected zone （CGHAZ） is less in the joints fabricated using LHF consumable due to the lower heat input involved during fabrication compared to the joints fabricated using ASS consumables.

Simulation of Weld Depth in A-TIG Welding with Unified Arc-electrode model

Calculations have been made for weld depths occurring for TIG welding activated by a flux over the surface of the weld pool. In this case, the flux introduces an electrically insulating layer over the outer regions of the weld pool surface. There is then an increase in the current density at the surface of the centre of the weld pool with a consequent increase in the J×B forces, which drive a strong convective flow of the molten metal downwards, tending to make a deep weld. For a flux which produces an insulating layer for all but a central region of radius 2 mm, the calculated weld depth is 7 mm, and an arc spot is predicted at the centre of the weld pool surface. As yet we have not resolved the reason for significant differences that exist between our measurements of weld depth and the theoretical predictions.

Analysis of Aluminum Alloy Double-Pulse MIG Welding Arc Signal Characteristics Based on Broadband Mode Decomposition

Welding voltage and current in arc signals are directly related to arc stability and welding quality.Process experiments with different parameters were organized according to the orthogonal experimental design method by constructing an aluminum alloy double-pulse metal inert gas(MIG)welding arc electric signal test platform.The data acquisition system of the aluminum alloy MIG welding process was established to obtain real-time arc signal information reflecting the welding process.The aluminum alloy’s collected double-pulse arc current signals are decomposed adaptively by broadband mode decomposition(BMD).The direct current(DC)signal,pulse signal,distortion signal,ripple signal,and noise signal are separated and extracted,and the composite multiscale fuzzy entropy(CMFE)is calculated for the component set of the electrical signal.The experimental results show that the current waveform obtained by the double-pulse MIG welding current signal is consistent with the corresponding weld forming diagram.Simultaneously,the composite multiscale fuzzy entropy is calculated for the arc characteristic parameters.The rationality of matching process parameters and arc stability of aluminum alloy’s double-pulse MIG welding were evaluated.

Arc pressure of ultrasonic assisted TIG welding

In order to study the arc force distribution of ultrasonic assisted tungsten inert gas （U-TIG） welding and compare it with the conventional tungsten inert gas （TIC） welding, a series of experiments have been carried out, using our self- designed welding and testing system. The distribution of arc pressure is studied, under conditions as radiation distance, which is the distance between the ultrasonic horn tip and workpiece, and welding current. The values of arc pressure generally increase as the current increases. Other experimental phenomena are also accounted for in detail in this paper. Welding parameters are thought to be responsible for enhancing the welding efficiency and improving the appearance of weld.

Research of welding hyperbaric arc electron density in TIG welding

The arc spectrum of TIG welding in high pressure was analyzed by Stark broadening. Using the characteristic line of Arl in welding arc, a study of electron density in high pressure revealed that the electron density of the welding arc had an upward trend with the pressure increase. According to data analysis, a curve of relationship between electron density alwl environmental pressure was established. It has a universal significance for change of electron density in high pressure. Through the analysis of electron density changing in time-domain in different pressure, a theoretical basis was provided for the problem of poor arc stability in high pressure.

Numerical Simulation of the TIG Welding Arc Behavior

Achieving an effective utilization and exploitation of TIG welding arcs require a thorough understanding of the plasma properties and its physical processes. Through simultaneous solutions of the set of conservation equations for mass, momentum, energy and current, a mathematical model has been developed to predict the velocity, temperature, and current density distributions in argon welding arcs. The predicted temperature fields in arc regions, and the distribution of current density and heat flux at the anode agree well with measurements reported in literatures. This work could lay the foundation for developing a comprehensive model of the TIG welding process where a dynamic, two-way coupling between the welding arc and the weld pool surface is properly represented.