Characterising thermoacoustic emission in alternating current spot welding process

The acoustic emission of spot welding with thermoacoustic theory was studied in this paper, which provides new basis to analyze the quality of nugget with acoustic signal. The result shows that the thermoacoustic emission exists in both 5052 Al alloy and cold-rolled steel AC spot welding process and this process takes place later than the load of welding current, and the frequency of thermoacoustic is twice as that of the welding current. The amplitudes of thermoacoustic signals detected from different angles are different, which undergo an up-down-up process. The thermoacoustic emission shows different trends with the thickness increase in AC resistance spot welding experiment for 5052 Al alloy and cold-rolled steel.     

Welding deformation control of medium-thickness structures made by advanced high strength steel

In order to investigate the residual angular deformation in fillet welding of T-joint of HG785 high strength steel with a medium thickness plate, both detailed thermo-mechanical finite element simulation and conventional gas metal arc welding experiment were carried out in the present study. In-process deformation control method using backheating method to reduce the residual deformation was discussed.     

Effects of welding voltage on process stability in hyperbaric gas metal arc welding

Based on hyperbaric gas metal arc welding （GMAW） experiments at ambient pressure of 0. 8 MPa, the process stability of different welding voltages was studied. The experiments were carried out with a high speed camera system including infrared laser backlight and electric signal acquisition system. Keeping wire feed speed at 8 m/min, arc length increases linearly with the increase of welding voltage in O. 8 MPa argon environment. Under this condition, all the metal transfer modes are droplet repelled transfer and the transfer frequency increases with increasing welding voltage. The number of deviating spatter is less with relatively high welding voltage. The results of electric signal waveforms show that the probabilities of short circuit and arc interruption decrease firstly and then increase with increasing welding voltage. When the welding voltage is 37 V, the hyperbaric welding process is the most stable with no probability of short circuit and arc interruption.     

Study of microstructures and of domestic X70 properties for girth welding pipeline steels

With the development of domestic pipeline steels, it is necessary to develop suitable welding technology which can improve the properties of the welded pipeline. In this paper, the microstructures and mechanical properties of domestic XTO pipeline steels and welded joints are discussed. The welding consumables of BOHLER E6010 and HOBART 81N1 are matched for girth welding. The following characteristics in heat-affected zone（ HAZ） are indicated that microstructures of intercritical HAZ（ ICHAZ） is finer and more uniform, the grain sizes of fine-grain HAZ （ FGHAZ） and subcritical HAZ （ SCHAZ） are smaller than that of coarse-grain HAZ（ CGHAZ）. The hardness, tensile strength and toughness of welded joints come up to the standard. The micrographs of impact specimens in welded joints are cleavage, quasi-cleavage and dimple which shows there is typical ductile rupture.     

Study on intelligent image recognition for the tube welding defects in pressure vessels

Currently, the welding defects recognition of X-ray nondestructive inspection is principally carried out by manual work, which highly depends on the experience of the inspectors and costs plenty of workload. In this paper, an intelligent image processing and recognition method for the tube welding radiographic testing in large-scale pressure vessels is proposed. Firstly, the raw image is preprocessed by median filtering, pseudo point removing and non-lincar image enhancement. Secondly, the welded joints parts are separated from the whole image by edge detection and threshold segmentation algorithms. Then, the separated images are handled by FFT transformation. Finally, whether defects exist and the specific type of defects are judged by Support Vector Machine. Software developed basing on this method works stably on site, and experiments demonstrate that the recognition results are compliance with the JB/T 4730. 2 or ASME standards.     

Sequence optimization of hull structure assembly based on prediction of welding deformation

Optimization of assembly process is significant for ship construction, thus reducing the time and related costs of construction. Welding Structure Deformation Analysis （Weld-sta） was used to predict welding deformation of a hull block. After the reliability of simulation was proved by comparing with measured results, four kinds of welding sequences was determined. By considering welding deformation and assembly process with the e]ficieney of automation, decreasing the overturn times （times of turning the erections upside down during welding） and working hours etc, one of the welding sequences is assumed to be the most reasonable one. The study shows this method is very useful in optimal assembly program determination of practical engineering structures.     

Comparison of 2A12 aluminium alloy joint by ultrasonic assisted friction stir welding and friction stir welding

Ultrasonic assisted friction stir welding （UAFSW） is a recent modification of conventional friction stir welding, which adds ultrasonic energy directly into the friction stir welding area by the pin. In this study, 2A12 aluminum alloy was welded by this process and conventional, respectively. The tensile tests, microstructure and fracture surface of FSW joint and UAFSW joint were analyzed. The research results show that the surface forming texture of ultrasonic assisted friction stir welding joint, compared with conventional, is finer and more uniform, showing metallic matte color. The grains are much finer in weld nugget zone, thermo-mechanically affected zone and heat-affected zone; S-phase particles size is much smaller and distribution is more homogeneous in the matrix. The tensile strength of UAFSW joint is 94. 13% of base metal, and the elongation is 11.77%. The tensile strength of FSW joint is 83.15% of base metal, and the elongation is 8.81%. The tests results reveal that ultrasonic vibration can improve the tensile strength and the elongation of welded joints.     

Numerical analysis of reverse dual-rotation friction stir welding process

A three-dimensional model of reverse dual-rotation friction stir welding （RDR-FSW） is developed to conduct the numerical simulation of heat generation and material flow during the process. The reverse rotation of the assisted shoulder and the tool pin is considered to model the heat generation rate. The predicted temperature difference between the advancing side and the retreating side in RDR-FSW is less than that in conventional FSW. There are two reverse flows during the RDR-FSW which is beneficial to the uniformity of the temperature profile. Due to the reverse rotation effects of the assisted shoulder, the predicted shape and size of thermal-mechanically affected zone （TMAZ） based on the iso-viscosity line are decreased greatly compared to the conventional FSW. It lays solid foundation for optimizing the process parameters in RDR-FSW.     

基于最小二乘法的脉冲MIG焊参数一元化调节

针对数字化焊机焊接参数复杂繁琐,不易于实现大规模工艺试验的特点,提出了一种基于最小二乘法的脉冲MIG焊参数一元化调节方法.该方法利用经工艺试验得到的大步距标定的焊接电流与各种焊接参数的拟合关系,得到最佳的拟合曲线,充分利用了所有的经试验得到的理想数据,并且容易实现软件编程,算法简便,可快速实现大范围内对焊接参数的连续调节.通过对单脉冲、双脉冲焊接参数的拟合处理并且进行试焊,焊接过程稳定,能够得到成形美观、飞溅较少、鱼鳞纹清晰的焊缝.结果表明,该拟合方法稳定、可靠、可行.     

Microstructure and mechanical properties of laser welded joints of pure copper and 304 stainless steels

A continuous wave diode laser with an output power of 2.8 kW was used to join pure copper and 304 stainless steel with a thickness of 1 mm. The focused laser beam with a diameter of O. 8 mm was irradiated on the copper side of the butt joints. In process of laser welding, effects of processing primary parameters on tensile strength of the joints were investigated. The interfacial characterizations of the joints were investigated by metallographic microscope, scanning electron microscope （SEM） and energy dispersive X-ray spectroscope （EDS）. The results showed that the element diffusion and solution occur and metallurgical bonding was achieved between pure copper and 304 stainless steel. The maximum tensile strength of the joints was 209 MPa when the laser power of welding was 2. 4 kW and welding speed was 12 mm/s.     

Numerical analysis of transient keyhole shape in pulsed current plasma arc welding

Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresponding heat source model. And considering the effects of gravitational force, plasma arc pressure and surface tension on the weld pool surface, the dynamic change features of the keyhole shape in a pulse cycle are calculated by using surface deformation equation. Experiments are conducted and validate that the calctdated weld fusion line is in good agreement with the experimental results.     

Experimental study of electron beam welded titanium alloy to chromium bronze joint with a vanadium sheet

Electron beam welding experiment of titanium alloy to chromium bronze with a vanadium filler metal was carried out. Microstructure of the joint was observed by optical microscopy and scanning electron microscopy. Tensile strength of the joint was evaluated. The fracture surface of the joint was also analyzed. The results showed that the addition of vanadium filler metal reduced the brittleness of joint by increasing the amount of vanadium-based solid solution in the weld. But the melting point of vanadium.filler metal was so high that large heat input was needed to completely melt the filler metal. Thus, a large amount of interfacial compounds were produced. The tensile strength of joint was 280 MPa with a brittle fracture mode.     

Effect of Zr-Ti combined deoxidation on impact toughness of coarse-grained heat-affected zone with high heat input welding

In this study, the effects of Zr-Ti combined deoxidation and AI deoxidation on the impact toughness of coarse- grained heat-affected zone in high-strength low-alloy steels were investigated. More fine oxides were formed in the Zr-Ti-killed steel than in Al-killed steel. It was also found that more acicular ferrite grains were formed in the coarse-grained heat-affected zone in the Zr-Ti-killed steel than in Al-killed steel. The impact toughness of coarse-grained heat-affected zone of Zr-Ti-kiUed steel was higher than that of Al-killed steel. The good impact toughness was attributable to the pinning effect of fine oxides and the formation of acicular ferrite grains on fine oxides.     

Adaptive control strategy of the welding current

The welding process essentially is a complicated nonlinear system with time-varying, uncertain, strong-coupling characteristics, so it is difficult to get high welding quality by traditional control approaches such as the standard proportionalintegral （ PI） algorithm. A new algorithm based on artificial neural network （ANN） is presented to achieve optimal P1 parameters and improve its adaptability. First, main parameters of artificial neural network are researched to improve the convergence rate and system stability. Then, six expert rules are proposed to constitute the expert adaptive ANN-PI algorithm. Experimental results show that the welding current control system＇has high dynamic response rate, and the welding process is stable.     

Research on droplet transfer in oscillating arc narrow gap GMA welding

In this paper, the droplet transfer in oscillating arc narrow gap gas metal arc （ GMA ） welding was studied. According to the experimental results, the oscillating arc has effect on the droplet transfer mode. The droplet transfer frequency in narrow gap groove is higher than that in bead-on-plate welding. Because of the change of arc location in narrow gap groove, the droplet transfer in oscillating arc narrow gap changes regularly. The droplet transfer frequency near groove sidewall is higher than that at the middle of narrow gap groove.     

Numerical analysis of temperature profile and weld dimensions in laser ＋ GMAW hybrid welding of aluminum alloy T-joint

The temperature fields in the transient state and weld dimensions in laser ＋ gas metal arc welding （GMAW） hybrid welding of aluminum alloy T-joint for different welding conditions were calculated using the developed heat source model, and the effect of welding speed on them was analyzed. The results show that the temperature field for the first weld pass only shows the feature of GMAW and the one for the second weld pass has the characteristics of both laser welding and GMAW. Welding speed can affect greatly weld dimensions and temperature distribution. When welding speed reaches 3.5 m/min, the fusion zones of two weld passes are separated and the maximum peak temperature of thermal cycle on the workpiece surface decreases largely.     

Effect of groove angle and preheating temperature on temperature profile and fluid velocity in weld pool

The three dimensiotud transient weld pool dynamics are numerically analyzed ,for Forcearc welding, which is a new gas metal arc welding technology to get deep fusion penetration with smaller angle sf V groove to enhance welding efficiency significantly. The influence of groove angle and preheatin,g temperature on heat and .fluid .flow is studied and compared to get an optimal welding parameter. Good agreement is shown between the predicted and experimental results, such as weld bead cross-section and thermal cycles. It can he seen that an apprpriate groove angle could be used to replace high preheating temperature to get inproced penetration and thermal cycles.     

Exploring material flow in friction stir welding using stacked structure of 2024 and 6061 aluminum alloys

An experimental technique based on stacked structures was developed to observe the material flow behavior of the friction stir welding （FSW） process. Analysis of section views along different directions revealed important new details of the material flow in FSW process. In this work, a general flow model of FSW was constructed based on the analysis of different static section views of stacked structure weld. The formation of onion rings was found to be a geometric effect due to layered deposition attd the extrusion occurred at the interface between flow arm （FA） and stirring zone （SZ）.     

A new post-weld heat treatment to improve toughness of 9Cr-1Mo steel weld metals

9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable coarse columnar grains in weld metal whieh ean severely compromise the toughness. A new post-weld heat treatment （PWHT） is developed in the present work. Unlike the conventional processes in which the post-weld heat treatment is carried out below Ac1 , the use of temperatures above the Ac1 of 9Cr-1Mo alloy is considered. The new PWHT at a temperature above Ac1 improves the toughness of 9Cr-1Mo weld metals effectively. The improvement in toughness is mainly due to refinement and homogenization of mierostruetures. Key words     

Investigation on process and microstructure of Ti/Ni/Cu joints by electron beam welding

In this article, the electron beam welding of the Cu alloy （ QCrO. 8） with Ti alloy （TC4） sheet was processed and the joint microstructure as well as the welding process were studied. The results show that brittle reaction layer which was mainly composed of TiCu, Ti2Cu, Ti2Cu3 and TiCu2formed at the weld fusion line, regardless of welding on the middle or on the Cu side. The mechanical properties of the joint were severely deteriorated by the layer that tensile strength was only 89. 4 MPa for welding on the Cu side. The microstructure of the joint was improved with pure nickel as filler metal for the electron beam welding. The weld was mainly composed of solid solution. Intermetallic compound phase decreased signifwantly in fusion line compared with the joint without filler metal. The mechanical properties of the joint were obviously improved that the average tensile strength was 205.2 MPa and the bending strength was 413.3 MPa with O. 5 mm offset of electron beam on the Cu side.