Welding Sequence Research Articles

Numerical and parametric modeling and analysis of weld-induced residual stresses

A three-dimensional thermo-elasto-plastic finite element analysis is used to determine the residual stress distribution and the distortion field in butt and fillet plates. The employed finite element model is first verified against existing experimental results of thermal distortion and then is used for analyzing 12 case studies accounting for various plate thicknesses and welding sequences. Weld induced residual stress distributions have been estimated and discussed. The effects of thickness, welding sequences and finite element size have been investigated. A two-dimensional parametric relationship of residual stresses has been developed.

Progress of Manufacturing Trials for the ITER Toroidal Field Coil Structures

Japan Atomic Energy Agency (JAEA) has been conducting manufacturing feasibility trials of the toroidal field coil structures since 2009. Their feasibility was confirmed; however, since the structures were welded by using a one-side welding method, welding deformation was much larger than expected. By using a double-side welding method and optimizing the welding sequence, welding deformation can be minimized. Therefore, JAEA conducted full-scale trial manufacturing of basic segments to optimize the double-side welding sequence. After optimization, welding deformation was reduced. As a result, the double-side welding method will be used to manufacture the toroidal field coil structures as a manufacturer's selection.

Method for Handling Model Growth in Nonrigid Variation Simulation of Sheet Metal Assemblies

In automotive industry, virtual tools and methods are becoming increasingly important to ensure robust solutions as early as possible in the development processes. Today, techniques exist that combine Monte Carlo simulations (MCS) with finite element analysis (FEA) to capture the part's nonrigid geometric behavior when predicting variation in a critical dimension of a subassembly or product. A direct combination of MCS with full FEA requires high computational power and the calculations tend to be very time consuming. To overcome this problem, the method of influence coefficients (MIC) was proposed by Liu and Hu in the late 1990s. This well-known technique has since then been used in several studies of nonrigid assemblies and sensitivity analysis of the geometric fault propagation in multistation assembly processes. In detailed studies of the resulting subassemblies and levels of variation, functionality for color plots and the ability to study the geometry in arbitrary sections are desired to facilitate the analysis of the simulation results. However, when including all part nodes in combination with methods for contact and spot weld sequence modeling, the required sensitivity matrices grow exponentially. In this paper, a method is proposed, describing how traditional MIC calculations can be combined with a separate detailed subassembly analysis model, keeping the model sizes down and thus facilitating detailed studies of larger assembly structures.

Predicting residual stresses and distortion during multisequence welding of large size structures using FEM

A three-dimensional thermomechanical finite element (FE) analysis is carried out to model and predict the influence of welding sequence on the generation of distortions and residual stresses in large size T-joints. To simulate industrial welding conditions, the influence of nine welding sequences on the magnitude of distortion in both the plate and the stiffener was investigated. The addition of new material during welding was simulated using an element “birth and death” technique, while the moving welding arc was considered as a volumetric heat source with a double ellipsoidal distribution. The investigated material is a structural steel used for fabrication of large size structures in the hydroelectric industry. To calibrate the model and validate the simulation results, welding-induced distortion for one sequence was initially modeled and the results were compared with experimental measurements. The optimum welding sequences for the base plate and the reinforcement plate were determined. The results indicated also that the predicted distortions obtained from three-dimensional FE analysis are in reasonable agreement with experimental measurements.

Design, Manufacturing and Welding of Aluminum Alloy UHV Chambers for Taiwan Photon Source

This paper describes the design, manufacturing and welding sequence for the aluminum alloy vacuum chamber for Taiwan Photon Source. The vacuum chamber composes of aluminum extrusion chamber of A6063 and BPM chamber of A6061 aluminum alloys. The straightness and flatness of these extrusion chambers are controlled under 0.1mm/m and 0.2mm/m, respectively. The BPM chambers are manufactured precisely in oil-free environment, which provide clean surface and a precise sealing surface after machining. All the components are assembled in pre-aligned support system through the welding process, and then the results show the straightness of < 0.15mm/m, flatness of < 0.3mm/m, and leakage rates of < 2 × 10-10 mbar‧l/sec. were achieved.

Process modelling and optimization of keyhole plasma arc welding of thin Ti-6Al-4V

This article presents a comprehensive piece of research work focused on the development, validation and application of finite element modelling capability for the prediction and optimization of robotic keyhole plasma arc welding of Ti-6Al-4V thin structures. Experimental and computational investigations were carried out to characterize, develop, optimize and validate various aspects of the finite element modelling. The experimental investigations cover the determination of welding parameter envelopes using a robotic welding cell and the measurements of thermal history, distortion, residual stress and weld pool profile. The computational investigations include the development and validation of finite element models as well as the development and validation of a fully automated welding sequence optimization tool using a genetic algorithm approach. The work provides useful guidance and generic methodologies for optimum design of thin and complex lightweight structures and has formed a basis for the development of a framework on structural integrity assessment and component lifing of thin structures fabricated by welding. The optimization tool has significant potential to be conveniently modified to suit other optimization objectives and/or welding processes.

Effect of welding sequence on residual stress in thin-walled octagonal pipe–plate structure

A three-dimensional finite element approach based on ABAQUS code was developed to investigate the effect of welding sequence on welding residual stress distribution in a thin-walled 6061 aluminum alloy structure. To obtain sound numerical results, the thermo-mechanical behaviour was simulated using a direct-coupled formulation. Nine different simulation sequences were carried out by single-pass TIG welding of an octagonal pipe–plate joint, and the distributions of longitudinal and transverse residual stresses both on the outer and inner surfaces of the pipe were analyzed. The results suggest that the final residual stresses in the weld and its vicinity are not affected by the initial residual stresses of the structure. Selecting a suitable welding sequence can reduce the final residual stress in an octagonal pipe–plate joint.

A new algorithm on welding process of T-shaped plates in ship hull structure to minimize distortion based on thermal simulation

In this paper, the influence of welding sequence on the distribution of distortion on a T-shaped plate bar is investigated. The simulation consists of sequentially coupled thermal and mechanical analyses using an element birth and death technique to model the addition of welding metal to the work piece. Thermal distribution in steel T-shaped plate subjected to gas metal arc welding is determined through finite element method (FEM) in numerical simulations. Three-dimensional (3D) thermal model is simulated in ANSYS FEM commercial code. A macro code programme based on Goldak model is developed to apply thermal loading generated by the heat sources. The analyses are planned to be performed for 3D, transient and non-linear conditions. Temperature distribution during welding, welding-induced distortion fields and thermal graphs are predicted. The results are compared with the predictions from mechanical analyses. The results of four welding sequences on the magnitude of distortion in the plate are discussed and their effects on the thermal smooth distribution for special points in the plate are studied. Evaluation of the results with minimum distortion represents proper predictions and proves applicability and simplicity of the new introduced algorithm in this paper.

Numerical Simulation for Residual Stress and Deformation of Surface Welding on Membrane Water-Wall

Automatic MIG was adopted to weld Inconel 625 alloy on 20 G Membrane Waterwall, which can improve the capacities of high temperature corrosion resistance and wear resistance. To study the influence of Membrane Waterwall surface welding sequences on residual stress and residual deformation, this paper utilized finite element software ABAQUS and segmented moving heat source model to simulate the sequence welding, balanced welding from the middle to sides, balanced welding from sides to the middle, balanced skip welding from middle to sides and balanced skip welding from sides to the middle and studied their residual stresses and deformations. The simulation results indicated that there was a great influence of welding sequences on the residual stress and deformation. The optimal welding sequence was balanced skip welding from middle to sides and balanced skip welding from sides to the middle, which could change the stress distribution, decrease the welding residual stress by 17%, realize the even deformation of the whole welding section and decrease the bending deformation by 50%.

Minimizing Dimensional Variation and Robot Traveling Time in Welding Stations

Complex assembled products as an automotive car body consist of about 300 sheet metal parts joined by up to 4000 spot welds. In the body factory, there are several hundred robots organized into lines of welding stations. The distribution of welds between robots and the welding sequences have a significant influence on both dimensional quality and throughput. Therefore, this paper proposes a novel method for quality and throughput optimization based on a systematic search algorithm which exploits properties of the welding process. It uses approximated lower bounds to speed up the search and to estimate the quality of the solution. The method is successfully tested on reference assemblies, including detailed fixtures, welding robots and guns.

Thermo-mechanical Analysis of Multi-pass Bead-on-Plate Welding

This paper presents an investigation of the multi-pass bead-on-plate welding sequence modeled and simulated using thermal-elastic-plastic approach with Ferritic stainless steel UNS40900 (FSS) as specimen material. The welding simulation was considered as a sequential coupled structural/thermal analysis. A sequentially coupled structural/thermal analysis is the combination of analysis from different engineering disciplines which interact to solve a global engineering problem i.e. welding performed using ANSYS software. To validate the software results, a series of experiments was conducted with three different welding sequences using Shielded metal arc welding (SMAW). It was established based on the results that the experimental results show decent agreement with thermo-elastic-plastic 3D FEM analysis. The objective of this work is to compare the experimentally obtained weld bead geometry of FSS material with simulated results from ANSYS software for various weld parameters.

Influência dos procedimentos e modos de transferência no processo MAG na redução de deformações em painéis de estruturas navais

Juntamente com o crescimento da indústria naval brasileira surgiram problemas provenientes dos processos de produção na forma de distorções e tensões residuais. Neste trabalho foi estudada a influência de procedimentos de soldagem (sequência e direção de soldagem e uso do passe reverso) e modos de transferência (MAG-CC, MAG-STT e MAG-CW) sobre os valores de distorções. Todas as soldagens foram realizadas com o arame ER70S-6 e gás de proteção CO2 puro no modo curto-circuito. Ao final das soldagens, observou-se que a variável mais importante foi a mudança de direção de soldagem, que está ligada diretamente aos níveis de restrição do painel teste. As sequências utilizadas surtiram pouco efeito nos valores de distorção. O passe reverso obteve valores baixos de distorção, contudo, mostrou-se improdutivo. Observou-se que os valores de distorção para os processos e MAG-STT resultaram em valores de distorção semelhantes. Os painéis soldados pelo processo MAG-CW obtiveram os menores valores de distorção mensurados.

Simulation of Arc Welding Process

This paper presents a program for modeling and optimization of the arc welding process. Interface of the program is divided: time-synchronized monitoring multiple welding robots, a quick calculation options are various parameters, quickly replace the original design parameters (sequence of welding, etc.), the high degree of reliability modeling of welding defects, overheated regions, distortion and residual stresses in structures, intuitive visualization and control mechanism of the modeling process. Process variables are easy to evaluate quickly by changing the welding parameters, leading to systematic optimization of fusion zones, heat-affected zones, residual stress, and distortions. The software provides tools for reporting display of distortion, temperature distribution, residual stresses, and curve progression of physical factors on fixed measuring points. As a production process tool, simulation offers an interface to RoboCad, as well as an export interface to robots. Welding paths can be simulated in real speed, direction, and inclination, and the program is capable of tracking different heat sources (Goldak model, volume sources, surface heat sources with Gauss distribution, and combinations of this). This paper presents RobotStudio simulation of welding of parts. Optimum welding parameters are set using Simufact.welding modeling.

Distortion and its Control in Welding of Stainless Steel Structures - Case Studies

Distortion is a perennial problem faced by engineers engaged in welding fabrication. The shape change deformations and change in the dimensions that occur after welding is termed as distortion, leading to various undesirable consequences. So there exists a necessity to control distortion within limits. When distortion exceeds acceptable limits, correction of distortion after the complete fabrication results in major reworking operation that consumes both fabrication time and cost. Distortion control in complex structures has always been a challenge to fabrication engineers, dealing with stainless steels. To arrive at an appropriate control method, an in-depth analysis of the shape change deformation behavior of the component and adaptation of appropriate methods to control distortion are essential. In this study, two circular components made of stainless steel have been taken up for control of distortion. The first structure is the labyrinth used in hydro turbine assembly that consists of a ring type of flange made of martensitic stainless steel (ASTM grade A240 S41500) welded with a shell type web using grooved fillet welds. The size of the welded assembly is huge and the quantum of weld is very high leading to heavy distortion that often required to be corrected by way of weld build-up and subsequent machining. The second one is the vortex finder assembly which is a part of cyclone separator that is used to separate the fine particles of coal from coarse ones for use in the combustion chamber of typical Circulating Fluidised Bed Combustion (CFBC) boilers. This is again a cylindrical structure with three shells joined with three flanges and supported by stiffeners. The structure is made of special grade Austenitic stainless steel to withstand high temperature. In both the structures, most of joints are of Tee-joints with fillet welds. During fabrication of these assemblies, the angular tilt, local waviness and the diameter variation were the major issues. Correction after fabrication is not viable considering the configuration and shape of the component. This calls for control of distortion during fabrication itself. Towards this, a suitable welding procedure using an appropriate weld sequence was evolved after studying the weld details of the components. This weld sequence was implemented in-situ in actual components. During fabrication on-line monitoring was carried out and course corrections were provided. After implementation of the weld sequence, it was found that the distortion of the component could be reduced and contained well within the permissible limits. This made the extra rework redundant thus leading to a significant reduction in the cycle time of manufacture of the component. The details of the methodology adopted are described in this paper. Keywords: Labyrinth assembly, vortex finder assembly, stainless steel welding, distortion, T joint, grooved fillet weld, angular tilt, weld sequence.

Numerical Simulation of CO<sub>2</sub> Welding 409 Stainless Steel Multi-Crossed Parts

A dynamic 3D thermal and mechanical Simulation of CO2 welding 409 stainless steel multi-Crossed parts was carried out by using the software SYSWELD. A double ellipsoid heat source model of CO2 arc welding was explored and fitted with the Heat Source Fitting tool. The transient stress and strain fields of 409 stainless steel multi-crossed weld joint under two kind of welding sequences were obtained by loading the simulated temperature field, which helps to decrease the residual stress and deformation of 409 stainless steel multi-Crossed parts welding.

용접구조물의 변형 최소화를 위한 최적 용접순서의 해석적 방법

Abstract Several methodologies analyzing welding distortions of large shell structures like ship blocks have been developed and utilized in shipyards for a long times ago. In general, one of objects of thermal distortion analysis is to find welding sequence making least-deformation without any suppliance, and it can be solved easily and rapidly by EP strain-boundary method. But after assembly construction, there are usually more than 10 weldments in each process, and the number of sequence will follow the Factorial calculation. In this research, a method has been suggested to decide the best welding sequence by minimum analysis. Using this method, welding deformation could be reduced just analyzing some cases as many as the number of weldments. Experiments and Analysis of all cases were also done, and their best results are good agreements with predictation by suggested methodology.Key Words : Ship block, Wedling distortion, Shell element, FEM, Sequence 1. 서 론 선박의 건조과정에 적용되는 생산기술 중 과거에는 경험으로 진행되던 많은 분야가 현재는 상당 부분 공학적 시뮬레이션의 범위 내에 포함되어 합리화 및 최적화의 과정을 거치고 있다. 대표적으로 용접 열변형 해석

Welding distortion analysis of multipass joint combination with different sequences using 3D FEM and experiment

This paper presents an investigation of the welding sequence effect on induced angular distortion using FEM and experiments. The specimen of a combined joint geometry was modeled and simulated using Multipass Welding Advisor (MWA) in SYSWELD 2010 based on the thermal-elastic-plastic approach with low manganese carbon steel S3355J2G3 as specimen material and Goldak's double ellipsoid as heat source model. To validate the simulation results, a series of experiments was conducted with two different welding sequences using automated welding process, low carbon steel as parent metal, digital GMAW power source with premixed shielding gas and both-sided clamping technique. Based on the results, it was established that the thermo-elastic-plastic 3D FEM analysis shows good agreement with experimental results and the welding sequence “from outside to inside” induced less angular distortion compared to “from inside to outside”.

Weld distortion prediction of the ITER Vacuum Vessel using Finite Element simulations

The as-welded surfaces of the ITER Vacuum Vessel sectors need to be within a very tight tolerance, without a full-scale prototype. In order to predict welding distortion and optimize the manufacturing sequence, the industrial contract includes extensive computational simulations of the weld processes which can rapidly assess different sequences. The accurate shape prediction, after each manufacturing phase, enables actual distortions to be compared with the welding simulations to generate modified procedures and pre-compensate distortions. While previous mock-ups used heavy welded-on jigs to try to restrain the distortions, this method allows the use of lightweight jigs and yields important cost and rework savings. In order to enable the optimization of different alternative welding sequences, the simulation methodology is improved using condensed computation techniques with ANSYS in order to reduce computational resources. For each welding process, the models are calibrated with the results of coupons and mock-ups. The calibration is used to construct representative models of each segment and sector. This paper describes the application to the construction of the Vacuum Vessel sector of the enhanced simulation methodology with condensed Finite Element computation techniques and results of the calibration on several test pieces for different types of welds.

Optimization of Spot Welding of An Assembly Like B-pillar of a Car For Minimum Distortion, By Sequencing Technique

The aim of this paper is to achieve optimisation of spot welding sequence to minimise the distortion of a sheet metal assembly. The distortion of the assembly involving number of spot welds is different for different sequences of welding The assembly consists of sheet metal components which are joined by using various welding sequence schemes. The components are manufactured in quantity and welding with various sequences. After welding the distortions in an assembly due to welding sequence change are worked out and compaired. The sequence with minimum distortion is suggested a solution for the quality manufacturing with minimum distortion induced in it.

Electron beam welding–brazing of hard alloy to steel with Ni–Fe intermediate

The direct welding of hard alloy to steel by electron beam was carried out. The weld was mainly composed of molten steel. The microstructure of joint mainly consisted of the cellular dendrites and the eutectic phases. A transition layer enriched with large amounts of carbides formed at the interface of hard alloy. Finite element analysis of the welding sequence indicated that the maximum residual stress distributed at the weld or the hard alloy base metal where the macroscopic cracks tended to generate. According to the metallurgical compatibility principle, the cracks can be avoided by a powder metallurgy Ni–Fe intermediate during electron beam welding–brazing of hard alloy to steel. The microstructure of the joint was composed of (Fe,Ni) solid solution and carbides. The transition layer enriched with brittle phases did not form at the interface in the hard alloy side. Therefore, the microhardness of the weld was reduced and the compatible deformation ability of the weld was improved, and thus macroscopic cracks could be avoided.