Gap Welding Research Articles

A comparative study on microstructure and mechanical properties near interface for dissimilar materials during conventional V-groove and narrow gap welding

Low alloy steel and 304 LN austenitic stainless steel pipes were welded together by gas tungsten arc and narrow gap welding. The aim of investigation was to identify particular welding technique, which may able to deliver better joint quality over the other considering mechanical properties of assemblies. Welding consumable was IN82 for both of them. Multilayered buttering was done over low alloy steel prior to welding for conventional GTAW. Microstructural characterisation was done and tensile strength was determined through in-situ deformation of miniature samples for welded joints. Low alloy steel consisted of heat affected zone close to interface. Near fusion boundary between low alloy steel and IN82, islands of martensite, complex alloy carbides, Types-I and II boundaries were formed. Width of heat affected zone and martensite layer was more for conventional welding in comparison to narrow gap welding. During in-situ tensile testing crack was initiated from stress concentration site and propagated through IN82. Joint strength and strain hardening co-efficient for narrow gap welded specimen was higher than conventional welded sample. This indicated better formability of narrow gap welded assembly with respect to gas tungsten arc welded specimen.

An infrared visual sensing detection approach for swing arc narrow gap weld deviation

The present work develops a weld deviation detection system based on infrared visual sensing for swing arc narrow gap weld tracking, proposes a local pattern recognition (LPR) algorithm to detect groove edge position, and experimentally investigates their adaptabilities. This approach captures welding image synchronously with the base current period of pulsed arc as the arc swings to stay at groove sidewall, and extracts weld deviation feature from the relative distances of electrode wire center to the opposite sidewall of arc staying position, thus reducing arc light disturbance. The LPR algorithm seeks the straightest line segment by finding the minimum standard variance of groove edge pixel distribution in moving LPR window, and can adaptively acquire sidewall edge true position from the straightest segment regardless of size-varying spatters. It is shown that this approach is obviously superior to conventional mean algorithm in the precision and efficiency of weld deviation detection.

Thermophysical parameters of additive gap welding with the laser cladding of powders

The simulation and optimization of the main process variables of gap welding with the laser cladding of metallic powders is considered. The adsorption coefficient of powdered particles as a function of particle radius is analyzed for powder feeding via a metering unit. Optimum particle velocities and the weight flow rate of the metering device are determined. Preliminary experimental results are presented.

Quasi-cyclic fracture studies on stainless steel welded straight pipes with circumferential through-wall crack in the weld

Fracture studies were carried out on 170 mm OD welded straight pipes having circumferential through-wall crack in the weld under quasi-cyclic loading. The specimens were made of Type 304 LN stainless steel and welded using conventional Shielded Metal Arc (SMA) welding or Narrow Gap (NG) welding. The specimens were subjected to different amplitudes of load/displacement, which was decided based on the monotonic load carrying capacity of the specimens. It was found that the failure load reduces to 78.5% and 74.0% of the monotonic failure load for resisting 50 and 100 loading cycles, respectively in the case of NG welded pipes. The NG welded specimens showed more energy absorbing capability and crack growth resistance, when compared with SMA welded specimens. Crack growth was more stable in the case of specimens tested under displacement control; whereas the same was unstable in the case of load-controlled experiments and specimens failed by sudden collapse.

Development of narrow gap multi-layer welding process using oscillation laser beam

The oscillation laser beam is considered to be effective as a heat source of narrow gap multi-layer welding because oscillation laser welding can control the penetration shape and prevent the lack of fusion. In this study, in order to establish a narrow gap welding process by oscillation laser beam, butt welding experiments of 50 mm thickness carbon steel plate were performed. By the appropriate control of the heat input area using the in-process sensor for recognizing the groove shape, narrow gap welding of a thick plate with groove which was cut by gas cutting was achieved. Properties of the welded joint had been confirmed by nondestructive testing, tensile test and side bend test. A two-dimensional numerical calculation model for welding deformation was developed. This calculation model was used for investigation of the optimal groove angle. The results of calculations were in quantitative agreement with the experimental results. Microstructure of the weld zone had multiple thermal histories. According to the hardness test results, maximum hardness of the heat affected zone of the upper layer has been lowered than that of the lower layer.

Осесимметричная интегральная модель распределения синусоидального сварочного тока при дуговой сварке зазора в пластине

Осесимметричная интегральная модель распределения синусоидального сварочного тока при дуговой сварке зазора в пластине

Effect of pass increasing on interpass stress evolution in nuclear rotor pipes

The purpose of this study is to investigate the evolution of residual stress during designing a 89-pass narrow gap welding of nuclear rotor pipes. A two-dimensional finite element model is employed to calculate the residual stress in welding process and heat treatment process, and then the evolution of residual stress during the welding process was discussed in detail. The investigated results show that the overall trend of hoop stress on the inner surface decreases gradually before pass 30, while the trend remains unchanged after pass 30. The through wall axial residual stress at the weld centreline demonstrates a distribution of bending type before pass 38, while this bending type distribution turns into a clearly self-equilibrating type after pass 38.

Characteristics of welding and arc pressure in TIG narrow gap welding using novel magnetic arc oscillation

Tungsten inert gas (TIG) narrow gap welding using magnetic arc oscillation is one of the most important methods for joining thick components. Today’s developments are aimed at increasing a sophisticated process understanding, especially concerning the physical effect of arc behavior, which can provide many strategies to enhance weld prediction and joint quality. In this article, the arc behaviors studied by its arc pressure, static characteristic, and arc profile in terms of arc force are presented. With the help of the forces acting on the welding arc, arc profile can be considered separately to allow an improved investigation of narrow gap welding involved. Measurements of arc pressure distribution are used to validate the weld formation and the final welding result. Under the same conditions, the uniformity of arc pressure distribution in both the bottom and sidewall improved with the increase in magnetic flux density. Furthermore, a comparative study of arc static characteristic with magnetic field and non-magnetic field has also been carried out. The reduction in the difference of arc static characteristic is attributed to the inverse effect between electromagnetic pinch force and Lorentz force with the increasing welding current.

Ultra-narrow gap welding of thick section of austenitic stainless steel to HSLA steel

A substantially narrow GMAW torch nozzle head has been designed that enables narrowing down of weld groove up to a limit of just accommodating the nozzle in it where the groove wall of thick section virtually acts as a side wall of the nozzle head to produce a narrowest possible butt welding. A model of shielding gas flow dynamics and its flow rate in case of employing newly developed GMAW nozzle head has been studied at different projection angle of torch nozzle inside the narrow groove of butt joint by using ANSYS-CFX(14.5) software. The utility aspect of such a narrow nozzle head from the view point of smooth flow of shielding gas inside a close fitted ultra-narrow weld groove has also been studied. The outcome of the analytical studies has been used to produce a defect free ultra-narrow multi-pass weld by employing P-GMAW process with vertically placed electrode depositing single bead per layer in weld groove.

Development of gap sensing system for narrow gap laser welding

Narrow gap welding with an oscillation laser beam is one of the effective processes for thick plate welding. To put this welding process into practical manufacturing, a groove-sensing system using image processing for narrow gap welding with an oscillation laser beam is used. This developed system uses still images of the weld zone taken by a coaxial CMOS camera. It can recognize the position of the groove wall by analysing the brightness distribution in the still image. It can then control the oscillation width and the laser-irradiated area by calculating the groove width and the groove centre position. Some narrow gap welding experiments were performed to evaluate the performance of the developed system. The results revealed that the developed system is effective for narrow gap welding with an oscillation laser beam. Using this system, the narrow gap groove can be welded even if the groove width has changed during the welding process.

Detection of micro gap weld joint by using magneto-optical imaging and Kalman filtering compensated with RBF neural network

An approach for seam tracking of micro gap weld whose width is less than 0.1mm based on magneto optical (MO) imaging technique during butt-joint laser welding of steel plates is investigated. Kalman filtering(KF) technology with radial basis function(RBF) neural network for weld detection by an MO sensor was applied to track the weld center position. Because the laser welding system process noises and the MO sensor measurement noises were colored noises, the estimation accuracy of traditional KF for seam tracking was degraded by the system model with extreme nonlinearities and could not be solved by the linear state-space model. Also, the statistics characteristics of noises could not be accurately obtained in actual welding. Thus, a RBF neural network was applied to the KF technique to compensate for the weld tracking errors. The neural network can restrain divergence filter and improve the system robustness. In comparison of traditional KF algorithm, the RBF with KF was not only more effectively in improving the weld tracking accuracy but also reduced noise disturbance. Experimental results showed that magneto optical imaging technique could be applied to detect micro gap weld accurately, which provides a novel approach for micro gap seam tracking.

RBF-NN-based model for prediction of weld bead geometry in Shielded Metal Arc Welding (SMAW)

Welding processes are considered as an essential component in most of industrial manufacturing and for structural applications. Among the most widely used welding processes is the shielded metal arc welding (SMAW) due to its versatility and simplicity. In fact, the welding process is predominant procedure in the maintenance and repair industry, construction of steel structures and also industrial fabrication. The most important physical characteristics of the weldment are the bead geometry which includes bead height and width and the penetration. Different methods and approaches have been developed to achieve the acceptable values of bead geometry parameters. This study presents artificial intelligence techniques (AIT): For example, radial basis function neural network (RBF-NN) and multilayer perceptron neural network (MLP-NN) models were developed to predict the weld bead geometry. A number of 33 plates of mild steel specimens that have undergone SMAW process are analyzed for their weld bead geometry. The input parameters of the SMAW consist of welding current (A), arc length (mm), welding speed (mm/min), diameter of electrode (mm) and welding gap (mm). The outputs of the AIT models include property parameters, namely penetration, bead width and reinforcement. The results showed outstanding level of accuracy utilizing RBF-NN in simulating the weld geometry and very satisfactorily to predict all parameters in comparison with the MLP-NN model.

Ensuring High Performance Characteristics For Explosion-Welded Bimetals

Analytical relations are found for determining the rotation-angle and contact-point-velocity values that the flying plate in explosion welding must have to obtain the limiting uniform strains in the cladding layer. These values determine the parameters of explosion welding and the size of the weld gap. Laminated metallic composites obtained by the explosion-welding regimes proposed in this article have superior wearresistance characteristics during service.

Finite element analysis of deformation in early stage of multi-pass circumferential dissimilar welding of thick-walled pipes with narrow gap

Three-dimensional thermal elastic-plastic finite element analyses were conducted in order to reveal the mechanism of gap shrinkage in early stage of multi-pass narrow gap welding of thick-walled dissimilar pipes and thick plates. The gap shrinkage up to the 8th pass indicates that the shrinkage of plates becomes to be much larger than that of pipes with increasing the weld passes. In addition, through the decomposition of gap shrinkage to transverse shrinkage and angular distortion, it is found that the gap shrinkage of pipes is mainly governed by the transverse shrinkage, while the shrinkage of plates is influenced by both the transverse shrinkage and angular distortion. Moreover, the serial computational results with various groove shapes suggest that the transverse shrinkage of pipes almost linearly increases with increasing the weld pass, and its increment can be predicted by a linear approximation function obtained by the transverse shrinkage of plates regardless of the groove shape.

Special features of thermal and deformation processes in welding high-strength steels with different edge preparation

Investigations were carried out into the special features of thermal and deformation processes in single- and twin-arc welding of joints with different edge reparation. On the basis of the experimental results it was established that deformation of all types when using the constricted shapes of the welding gap is lower than when using the standard welding gaps. The level of strain in the component can be additionally reduced by the application of twin-arc welding. The investigation results also show that in the final stage of welding it is necessary to correct the welding conditions in the immediate vicinity of the edge of the welded component in order to eliminate the superheating effect caused by the reflection of the heat flow from the welding edge.

A complex response inductive method for improved gap measurement in laser welding

Laser welding needs precise measurement of weld gap position to avoid weld defects. Most often, optical measurement methods are used, but well-aligned narrow gaps can be difficult to detect. An improved inductive method capable of detecting zero gaps in square butt joints is proposed. The new method uses two eddy current coils, one on each side of the gap, and measures the complex response of the individual coils, i.e. both the inductive and resistive response. By combining the coil responses, both the position and the geometry of the weld gap can be estimated. The method was experimentally investigated by traversing a single coil over an adjustable gap between two plates and combining the measured coil responses into a simulated two-coil probe. The gap was adjusted in both misalignment and gap width up to 0.4 mm. Comparing the results to known settings and positions shows that gap position is measured to within 0.1 mm, if the probe is within a working area of 1 mm from the gap in both position and height. Results from the new method were compared to simulations, from the same experimental data, of a previously reported method where the coils were electrically combined by wiring them together. The previous method can give accurate results but has a much smaller working area and depends on servo actuation to position the probe above the gap. The improved method gives better tolerance to varying misalignment and gap width, which is an advantage over previous inductive methods.

A study of droplet transfer behavior in ultra-narrow gap laser arc hybrid welding

Laser arc hybrid welding became a useful method to weld thick plates. But a sound weld is not so easy to obtain because of the uncontrollability of droplet transfer state, especially in ultra-narrow gap welding process. In this study, V-like ultra-narrow gap welds were carried out using 80 % Ar + 20 % CO2 blend as shielding gas. A high-speed video system was used to observe the droplet transfer behaviors. The results showed that the transfer mode did not change with the same welding current. The transfer mode changed from the short circuiting transfer to the mixture of the short circuiting and the globular transfer and then to spray transfer as the welding current increased. The relationship between the droplet transfer process and the welded defects was studied to obtain high-quality weld joint with a stable transfer process. The optimal parameter window between welding current and groove size was found. Only when the welding current was 200 to 270 A and groove gap was 2 to 3 mm, can a good welded joint be got. Finally, 30-mm-thick plate with 5.49-mm maximum groove gap was welded well by one pass laser autogenous welding and seven passes laser arc hybrid welding process.

New technology for measuring resistance of electrical contact and estimating welding quality

Incomplete penetration is a common defect in the welding gap of large size (welding area is over 100 mm2) electrical contact, which leads to an instability of welding quality. Nevertheless, there was limited research dealing with non-destructive quality inspection of electrical contact. In this research, the resistance of CJ400 electrical contact was measured with the device medium frequency inverter resistance spot welding (MFI-RSW) machine. Multipulse measuring method was designed and proved efficient to reach a higher accuracy by restraining the influence of the contact resistance between electrodes and electrical contact. Moreover, the error of resistance caused by temperature rising in the measuring process is also eliminated effectively. Therefore, more accurate resistance of electrical contact could be extracted compared to the method of single pulse measuring. Then, the relationship between resistance and welding quality was studied and a new quality inspection method was proposed.

Advanced submerged arc welding processes for Arctic structures and ice-going vessels

The Arctic region is expected to play an extremely prominent role in the future of the oil and gas industry as growing demand for natural resources leads to greater exploitation of a region that holds about 25% of the world’s oil and gas reserves. It has become clear that ensuring the necessary reliability of Arctic industrial structures is highly dependent on the welding processes used and the materials employed. The main challenge for welding in Arctic conditions is prevention of the formation of brittle fractures in the weld and base material. One mitigating solution to obtain sufficiently low-transition temperatures of the weld is use of a suitable welding process with properly selected parameters. This work provides a comprehensive review with experimental study of modified submerged arc welding processes used for Arctic applications, such as narrow gap welding, multi-wire welding, and welding with metal powder additions. Case studies covered in this article describe welding of Arctic steels such as X70 12.7-mm plate by multi-wire welding technique. Advanced submerged arc welding processes are compared in terms of deposition rate and welding process operational parameters, and the advantages and disadvantages of each process with respect to low-temperature environment applications are listed. This article contributes to the field by presenting a comprehensive state-of-the-art review and case studies of the most common submerged arc welding high deposition modifications. Each modification is reviewed in detail, facilitating understanding and assisting in correct selection of appropriate welding processes and process parameters.

Narrow Gap 맞대기 TIG 용접에서 생산성 향상을 위한 연구

Abstract Adoption of narrow gap welding shall be increased for the butt joint of thick plate, because the deformation and welding cost is reduced by decrease of cross-sectional area. However, sometimes narrow gap causes defects such as lack of fusion since it has small groove angle and narrow groove width. Therefore, GMAW, GTAW and SAWprocess shall be adopted to narrow gap welding with small bead hight and low deposition rate. In this study, Super-TIG welding using C-type strip was applied to semi-narrow gap butt joint in order toincrease the welding productivity. High deposition rate 10kg/hr was obtained by high current 600A without undercut, humping bead and other welding defects. Measuring the mean and standard deviation of the meltingdepth to evaluate the developed processes, the fusion line type was determined by measuring the difference betweenmaximum and minium melting depth. Furthermore, a model on arch fusion line and linear fusion line was suggested in order to prevent LF on groove wall in narrow gap butt welding. Key Words : Narrow gap, Butt welding, TIG welding, Super-TIG welding, Deposition rate, Melting depth, Fusion lineISSN 1225-6153Online ISSN 2287-8955