Tack Welding Research Articles

선체 블록의 판접 위치 획득을 위한 센서 모듈 시제품 개발

Alignment of the main plates during the tack welding is essential to block assembly since most of the curved blocks and outfitting parts are assembled on the jigs and fixtures. Tact welding of main plates is the initial process of the curved hull block assembly. Due to the heavy weight of the main plates it is difficult to locate the plate on the accurate position of the jig and fixtures before welding. The conventional masonry process requires much time and manual work in order to achieve the accurate alignment. This labour-intensive process results in relatively high errors and correction works. Due to their larger dimensions and heavier weights, these hull blocks are not ergonomically desirable and, therefore, various mechanical devices such as hydraulic balancers or hydraulic jigs are used for the plate alignment. In this study, the position-sensing scheme implemented by sensors is presented in order to align the main plates on the accurate position during the hull block assembly. Integrating the Infrared photo sensors and micro processor unit, a small scaled prototype of the position-sensing module is developed to determine the alignment of main plates.

Multi-Robot Assembly of High-Performance Aerospace Components

Abstract This paper presents an automated assembly and tack welding operation of high performance aerospace components using two real-time controlled industrial robots and a high-precision non-contact measurement system. The system was able to align two components with an offset distance less than 0.1 mm, well within manufacturing tolerances.

The effect of tack welding on numerically calculated welding-induced distortion

A single-layer pulsed gas metal arc weld of structural steel S355J2+N with a thickness of 5mm is experimentally and numerically investigated. Two tack welds are considered in the numerical simulation into two different ways. First, the tack welds are represented by elements belonging to the initial material. This implies that the “tack weld material” was not exposed to any thermal load or phase transformation before actual welding was performed. The weld seam is shortened and there is an influence on the stiffness of the whole structure affecting the calculation result. Secondly, the tack welds were simulated as conducted in the experimental welding procedure. The cases considering tack welding are compared to a simulation neglecting tack welding and to the experimental results.The influence of tack welds on the calculated welding-induced distortion is clarified and a contribution to an improved simulation-based prediction of welding-induced distortion is possible by modeling tack welding according to the realistic fabrication procedure.

MicroTack technology: revolution in tack welding of thin-walled structures

Kemppi in co-operation with its clients has developed a new MicroTack technology, which eases tack weld of the low-carbon and corrosion-resistant steel, accelerates the process, and improves the quality of the tack welds that results in speeding up of the further main welding. The technology is available on the new MasterTig MLS™ 3000/3003 ACDC welding apparatus, which does for welding low-carbon and corrosion-resistant steel, as well as aluminium.

Small Batch Laser Welding Using Light Fasteners and Laser Tack Welding

Laser welding is known for its low heat input compared to arc welding methods. This could enable laser welding of sheet metals with lighter fastening solutions and less time-consuming tack welding alternatives. A feasibility study was carried out to study four different corner joint types for 2 mm thick cold rolledcold-rolled steel sheet by using filler-free laser welding. The aim of the research was to get more experimental knowledge about the laser welding of corner joints. Also possible benefits concerning faster manufacturing times and smaller costs by developing fastening applications for small batch laser welding was to be studied in practice. The 170 mm long joints were welded without air gap or pressing. All corner joint types proved to be weldable with a continuous wave Yb:YAG diode-pumped disk laser. It was also found during the With the experiment it was also found out that laser welding enables the use of light and inexpensive fasteners such as magnetic holders in steadinstead of traditional clamps and fixturing. With some joint types, the insufficient fastening power of magnetic fasteners against distortions was compensated by making a spot-like laser tack weld toat the end of the weld before welding the actual seam. This showed that it is possible to make precise and small tack welds with a laser and to use laser -tacking in sheet metal assembly.

Optimizing Tack Welding Fabrication Procedures Using Numerical Finite Element Models

The aim of this study was to investigate the influence of different tack welding fabrication procedures on the final deformations of seam welded plate structures. In this study the length of the tacks, number of tacks, and position of tacks with respect to the final seam weld are altered, and their sensitivity with respect to out-of-plane deformation is established. A parametric study of these three different procedural variations is performed via finite element models to identify which fabrication procedures would lead to minimal out-of-plane distortion.

Effect of Welding on the Slip Damping of Layered and Jointed Structures

A mathematical model has been presented for the mechanism of interfacial slip damping in layered and jointed cantilever beams with continuous and tack welds. The pressure distribution at the interfaces, number of contacting layers, techniques of welding, length and thickness of the beam specimen, and amplitude and frequency of vibration are found to be the dominating factors influencing the damping capacity of such welded structures. The results can be exploited positively in the design of machine tools, aircraft, spacecraft, satellites, automobiles, missile systems, etc. for maximizing their damping capacity.

Analysis of circumferentially welded thin-walled cylinders to study the effects of tack weld orientations and joint root opening on residual stress fields

In recent years, the demand for resilient welded structures with excellent in-service load-bearing capacity has been growing rapidly. The operating conditions (thermal and/or structural loads) are becoming more stringent, putting immense pressure on welding engineers to secure excellent quality welded structures. The local, non-uniform heating and subsequent cooling during the welding processes cause complex thermal stress—strain fields to develop, which finally leads to residual stresses, distortions, and their adverse consequences. Residual stresses are of prime concern to industries producing weld-integrated structures around the globe because of their obvious potential to cause dimensional instability in welded structures, and contribute to premature fracture/failure along with significant reduction in fatigue strength and in-service performance of welded structures. Arc welding with single or multiple weld runs is an appropriate and cost-effective joining method to produce high-strength structures in these industries. Multi-field interaction in arc welding makes it a complex manufacturing process. A number of geometric and process parameters contribute significant stress levels in arc-welded structures. In the present analysis, parametric studies have been conducted for the effects of a critical geometric parameter (i.e. tack weld) on the corresponding residual stress fields in circumferentially welded thin-walled cylinders. Tack weld offers considerable resistance to the shrinkage, and the orientation and size of tacks can altogether alter stress patterns within the weldments. Hence, a critical analysis for the effects of tack weld orientation is desirable.

Residual Stress Fields due to Varying Tack Welds Orientation in Circumferentially Welded Thin-Walled Cylinders

The local, nonuniform heating and subsequent cooling during the welding processes causes complex thermal stress/strain fields to develop that finally leads to residual stresses, distortions, and their adverse consequences. Residual stresses are of prime concern to the industries producing weld-integrated structures around the globe because of their obvious potential to cause dimensional instability in welded structures, contribute to premature fracture/failure, along with the significant reduction in fatigue strength and in-service performance of the welded structures. Arc welding with single or multiple weld runs is an appropriate and cost effective joining method to produce high-strength structures in these industries. A multifield interaction in arc welding process makes it a complex manufacturing process. A number of geometric and process parameters are contributing to significant stress levels in arc-welded structures. In the present analysis, parametric studies are conducted for the effects of a critical geometric parameter, that is, tack weld on the corresponding residual stress fields in circumferentially welded thin-walled cylinders. Tack welds offer a considerable resistance to the shrinkage and the orientation, and size of tacks can alter altogether the stress patterns within the weldments. Hence, a critical analysis for the effects of tack weld orientation is desirable.

A control system for uniform bead in fillet arc welding on tack welds

Positioning a workpiece accurately and preventing weld distortion, tack welding is often adopted before main welding in the construction of welded structures. However, this tack weld deteriorates the final weld bead profile, so that the grinding process is usually performed for a uniform weld bead profile. In this study, a control system for uniform weld bead is proposed for the fillet arc welding on tack welds. The system consists of GMA welding machine, torch manipulator, laser vision sensor for measuring the tack weld size and the database for optimal welding conditions. Experiments have been performed for constructing the database and for evaluating the control capability of the system. It has been shown that the system has the capability to smooth the bead at the high level of quality.

Procedural influences on non-linear distortions in welded thin-plate fabrication

Fusion welding is the most common and convenient method used for the fabrication of large, thin-plate welded structures. However, the resulting tendency to out-of-plane distortion exacts severe design and fabrication penalties in terms of poorer buckling performance, lack of fairness in external appearance, poor fit-up and frequent requirements for expensive rework. This study forms part of a long-term project that has the aim of modelling welding and related fabrication processes computationally with particular emphasis on the out-of-plane distortion outcomes. Throughout the present work the computational models have been cross-referenced to realistic experimental test cases. A repeated finding of the trials was that minor variations in fabrication procedures, were found to have significant effects on distortion. In particular, the pre-fabrication procedures, including spot and tack welding, have a significant effect on the initial out-of-plane distortion leading to differences in distortion of the post-welded structures. The support and clamping conditions during welding and cooling of welded thin-plate structures were also found to have a considerable influence on the final predicted out-of-plane distortion. The outcomes often result in different buckling instability behaviour. This paper concentrates on these aspects and draws on studies of buttwelding between plates of thicknesses 3–8 mm.

Modelling the effects of constraints and single axis welding process parameters on angular distortions in one-sided fillet welds

Welding process parameters and joint fit-ups significantly affect angular distortion patterns. By using constraints at proper positions the angular distortion can be minimized. In the present work the effect of constraints in the form of tack welds to minimize angular distortion in one-sided fillet welds has been analysed. It has been observed that proper positioning of tacks plays an important role in controlling angular distortion. The process was modelled using the three-dimensional finite element technique. Three-dimensional transient thermal analyses were done for predicting temperature distributions by considering a moving heat source. The element birth and death technique was used for simulating filler material deposition. The fillet welds were sectioned and microstructure zones were measured. The thermal model was verified by comparing the temperatures obtained from the thermal analysis with experimental results. Transient thermal and non-linear structural analyses were carried out in order to predict angular distortions.

溶接変形の高精度予測における支配因子の正当性と一般性の検証

When out-of-plane distortion was measured objecting to butt welding, if tack welding was easily performed, the position of a neutral axis was variously changed by the linear misalignment. Out-of-plane distortion was generated in the unexpected direction because the neutral axis changed. From such as bitter experience, a test specimen to measure out-of-plane distortion was proposed so as to solve this problem. Using the proposed specimen, out-of-plane distortion was measured for butt welding.In the high accurate prediction of welding distortion, the dominant factors, which were satisfying the yield condition (especially at high temperature above 700 degree Celsius) and regarding the weld metal as welds, had been specified in fillet welding previously. So as to verify the validity of the dominant factors, the experiment and thermal elastic plastic analysis by FEM were carried out using newly developed specimen for butt welding. The validity of the dominant factors in the high accurate prediction of welding distortion objecting to fillet welding was verified by the results of butt welding and its generality was confirmed. It was confirmed that residual stress was also highly predicted because welding distortion was highly predicted.

Image processing and control of weld pool in switch-back welding without backing plate

To achieve high quality in multilayer welding, it is important to obtain stable weld results for the first layer.1–5 For this reason, welding is usually conducted by using a backing of the same kind as the base material or a ceramic backing plate. In using a backing metal, the weight of the base material increases. Also it sometimes induces notches to occur at the weld joint between the base material and the backing. This can cause cracking. On the other hand, in using the backing plate, its removal is required after welding, and this makes the method unsuitable for automating the process. Therefore, in the authors' previous report, a proposal was made of the switch-back welding method in which welding is executed without using a backing plate, and also an investigation was made of the welding conditions for the root gap.6 In this welding method, it is necessary to adjust the wire feeding rate, the torch motion and the power property in accordance with the gap so that the back bead and the deposit can be controlled. Even if the gap is measured before welding, it may change owing to welding distortion. Hence, when welding is conducted by fixing the welding conditions, the change in the gap causes the back bead to become unstable. For this reason, in this study, a method is discussed to detect the gap on-line by processing images of the molten pool observed by a CCD camera. Then, using the results, the back bead was feed-forward-controlled in real time. Moreover, to examine the controlling performance, welding was conducted by varying the gap between 4.6 mm and 2.5 mm without tack welding. Very good weld results were obtained.

Numerical simulation to study the effect of tack welds and root gap on welding deformations and residual stresses of a pipe-flange joint

This paper presents a three dimensional sequentially coupled non-linear transient thermo-mechanical analysis to investigate the effect of tack weld positions and root gap on welding distortions and residual stresses in a pipe-flange joint. Single-pass MIG welding for a single ‘V’ butt-weld joint geometry of a 100 mm diameter pipe with compatible weld-neck ANSI flange class # 300 of low carbon steel is simulated. Two tack welds at circumferentially opposite locations, with the crucial effect of the tack weld's orientation from the weld start position is the focus in this study. Four different angular positions of tack welds (0 and 180°, 45 and 225°, 90 and 270°, 135 and 315°) are analyzed. In addition, four cases for root gaps (0.8, 1.2, 1.6, 2.0 mm) are considered and computational results are compared. A basic FE model is also validated with experimental data for temperature distribution and deformations. From the results, the axial displacement and tilt of the flange face are found to be strongly dependent on the tack weld orientation and weakly dependent on the root gap.

Finite-element simulation of tack welds in girth welding of a pipe-flange joint

Welding deformations play an important role in sealing capabilities and service life of welded pipe-flange joints. A numerical procedure for modeling of tack welds in girth butt-welding of such joints is of vital importance for the prediction of transverse shrinkage and flange face deformation, which is directly related to the joint sealing capability. This paper presents a 3-D finite element simulation of a pipe-flange joint to describe the numerical procedure for modeling of tack welds in circumferential joints. Sequentially coupled nonlinear transient thermo-mechanical analysis is performed to simulate Metal Inert Gas (MIG) welding. Single pass butt weld geometry with single “V” for 100 mm nominal diameter pipe with same sized weld neck type ANSI flange of class no. 300 is used. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. The peak temperature of the tack during the butt-welding of the tacked model is concluded a key parameter for numerical prediction of deformations, whereas tack temperature has negligible effect on the residual stresses.

Snaking around in a nuclear jungle

PurposeThe paper describes a pipe repair conducted in August 2004 using two types of snake‐arm robot. The pipe was located 5 m below the reactor core of Ringhals 1 nuclear reactor.Design/methodology/approachThe two types of robot worked co‐operatively to replace a section of critical pipe. The 23‐degree of freedom arm snaked around obstructing pipes to positions cameras in a humanly unreachable location in order to give the ideal view of the work site. The more substantial second arm used 13 degrees of freedom to deliver fixtures, cutting tools, gas shields, inspection equipment and also conducted both tack welding and continuous welding.FindingsThe leaking pipe was repaired manually during the 2004 outage. The robots successfully completed the externally assessed Factory Acceptance Tests which involved copying the complete procedure on a purpose built mock‐up. The robots are now on standby for 2005 and beyond.Practical implicationsThe successful completion of this extremely difficult task indicates that snake‐arm robots are now a viable solution to a variety of complex access tasks in all industries including aerospace, pharmaceuticals, the miltary sector and nuclear industries.Originality/valueThe paper describes a procedure that has never been attempted before using two completely new designs of redundant snake‐arm robot.

バッキングレスＶ開先溶接におけるギャップセンシングと溶融池の制御

The formation of stable back beads in the first layer weld during one side multilayer welding is important to achieve high quality welded metal joints. The authors thus employed the switch back welding method for V groove joints without backing plates. In this method, the power source, wire feed motor, and robot manipulators were controlled by the computer based cooperative control. The torch is moved backward and forward like switch back. First, the torch is moved forward with high speed. The arc is discharged to the each root edge of the groove. The droplet is deposited to each root edge, too. After that, the torch is moved backward with the same high speed. During the backward motion, the deposited metal makes the bridge between the both edges due to the surface tension. Next, the torch is moved forward with slow speed to form the bead. The mentioned torch motion is repeated. When constant welding conditions are used, the back bead becomes unstable by affection of the disturbances such as gap variations due to the welding distortion. In this method, it is important to measure the gap. The authors discuss a method to detect the gap and to get the stable back bead by using a visual sensor, the CCD camera. During the slow forward torch motion, the weld pool can be observed. The shape in the front part of the weld pool depends on the gap. It can be detected by processing the weld pool images. The authors investigate the method to take the gap from the weld pool image. The use of feed-forward control of back beads to compensate for variations of root gaps was also tested. In order to verify the performance of the feed forward controller, the gap is changing from 4.6 mm to 2.5 mm without the tack welding.

A Modeling and Simulation of Production Process in Subassembly Lines at a Shipyard

In order to simulate material flow in a subassembly line at a shipyard, the product, process, and resources are modeled for the subassembly process. The subassembly line is selected from a large shipyard and consists of several subprocesses, such as base joining, piece alignment, tack welding, and robot welding processes. The analysis and modeling procedure were carried out using the Unified Modeling Language (UML), an object-oriented modeling methodology, and Integration Definition (IDEF), a functional modeling tool. Initially, the characteristics of the shop resources were analyzed using the shipyard data and the layout of the subassembly line was designed with the resources. A production process was then modeled using the resources and the layout. The production process modeling of the subassembly lines was performed using the discrete event simulation method. Using the constructed resource and process model, the productivity and efficiency of the line were investigated. Variations in the resource performance, such as a new welding robot and the number of workers, were examined to simulate changes in productivity. It can be seen that bottlenecks occur in different places according to the nature of new resources. The proposed model is viewed three-dimensionally in a virtual environment so that space allocations for the resources and interferences between objects can be easily investigated.

Improvements of Flux-Copper Backing Welding Quality

Flux-copper backing process welding is a high-speed, one-sided automatic welding process that is a type of submerged arc welding. Although it has been widely applied for the joining of flat skin plates in shipbuilding, a couple of problems with this process still exist: longitudinal cracks occur in the vicinity of the end point, and transverse cracks occur on the back surface. The data in this study were collected in the production site of Ishikawajima-Harima Heavy Industries Company Ltd, Kure Shipyard. The causes of failures were examined, and countermeasures were studied. Concerning the longitudinal cracks, the behavior of plate deformation during welding was investigated, and the end tab plates and the tack welding method were improved in order to reduce the rapidly increased transverse distortion of the joining plates. Concerning the transverse cracks, the dispersal figure of the reverse flux to form the backing bead was observed, the relation between the flux spraying height and the welding quality was investigated, and the height was standardized. In addition, welding heat input was also examined and regulated to avoid the transverse cracks.