Control Of Welding Distortion Research Articles

Prediction of distortion in a thin-plate structure with intermittent fillet joints using a local-to-global approach

Fillet welds by intermittent welding are widely used in the welding of centrifugal fans, such as attaching a fan blade to the rear plate. The intermittent welding method transforms the full-length continuous weld into multiple short welds to minimize distortion by reducing the total heat input for a welded joint to control welding distortion. An infinite number of short welds are created during this process. However, depending on the complexity of the model, the computational cost of predicting welding distortion based on full-scale modeling is considerable. These numerous short welds undoubtedly complicate modeling and computations, limiting rapid distortion prediction for large and complex structures. This study develops an equivalent deformation calculation approach based on a local-to-global technique and applies it to predict distortion of a fillet joint welded specimen. The approach consists of two steps. First, the welding-induced structural deformation is calculated for a two-dimensional (2D) weld and a 2D heat-affected zone (local calculation). Second, the 2D structural deformation is applied to the full-scale welded structure using a nearest-point spatial interpolation algorithm to acquire the three-dimensional (3D) equivalent deformation (global calculation). Note that the weld shape was considered in both local and global calculations. In addition, welding tests were performed, and the coordinates of the key points were measured. The geometric parameters of the welds used in the numerical simulations were obtained from experimental observations. Finally, the key point coordinates obtained by the proposed approach were compared with experimental measurements. Furthermore, the distribution of out-of-plane distortion caused by the new approach was compared with the simulation results of the thermo-elastic-plastic method performed on a full-scale welded structure. The proposed approach can be verified by both comparisons.

Simulation and control of welding distortion for the CFETR equatorial port extension mock-up

The CFETR equatorial port extension is a double-walled stepped structure like the main body of the vacuum vessel (VV). During the 1/8 VV mock-up fabrication, this part will be connected to the main vessel by welding. The high-density welded joints in the equatorial port extension mock-up will badly affect the overall profile of the whole structure. The shrinkage of the open end makes the fit-up accuracy unable to meet the requirement. In this paper, to accurately predict the welding distortion of the equatorial port extension mock-up, the distortions of local models were evaluated by the thermo-elastic-plastic (TEP) method first to validate the results obtained by the inherent strain method. Then the welding distortions in three stages without external constraints conditions were simulated and analyzed for the design of the welding tooling. The comparison between the welding deformation with and without tooling presents that the dimensional accuracy of the whole structure is basically within the tolerance, proving that the designed tooling is effective. The simulated results were also validated by the actual measured results. The predictions and designs in this article can provide theoretical guidance for the practical processing of the CFETR equatorial port extension mock-up.

Welding distortion control technology in CFETR vacuum vessel

The vacuum vessel is very important component for China Fusion Engineering Test Reactor (CFETR), it is a double-layer shell structure with complex contour. The vacuum vessel is mainly formed by welding, which requires high precision of forming dimension. Welding distortion brings difficulties to the forming dimension control of vacuum vessel, so it is necessary to control the welding distortion in the progress of vacuum vessel welding. In this paper, many kinds of welding distortion control methods used in CFETR vacuum vessel manufacturing are introduced, and the application objects and key technology of each welding distortion control method are given. To accumulate experience for the formal CFETR vacuum vessel construction, and provide reference for other similar engineering construction.

Improvement of manufacturing jigs design for reduction of welding distortion in Vacuum Vessel PS1 through finite element analysis

One of the principal means of controlling welding distortion of metallic welded components is the use of assembly jigs. The knowledge about the effect of jigs on weld distortion is based in the qualitative, generally neither systematic nor documented experience of each manufacturer. Such knowledge needs to be complemented by specific research for components with the tight tolerances, intricate geometry, complex manufacturing sequence, size, and wall thickness of the ITER vacuum vessel. The influence of the assembly jigs has been investigated through finite element analysis, leading to jig design modifications. The conclusions of the research show that jig design is the main contributor to control weld distortion of PS1, when compared to welding sequence. Results and conclusions obtained provide highly valuable information to the manufacturer during the design phase, in terms of jig behavior, jig re-design and distortion control.

On the estimation and control of welding distortion of guide blade carrier for a 660 MW turbine by using inherent strain method

While predicting the welding distortion for a complex welded structure like the guide blade carrier assembly of power generation turbine, the traditional thermo-mechanical models commonly utilized for geometrically simple welded butt and T joints may not be adequate. For large and complex welded structures,the thermo-mechanical elasto-plastic analysis can be computationally prohibitive. Other than simplistic butt and T joints, the aforementioned distortion prediction technique is not so suitable to provide reliable results when applied to large complex 3-D welded structures. Hence, inherent strain method is proposed here to predict distortion in an outer ringof GBC (Guide Blade Carrier) of a steam turbine. Such welded outer rings of GBC are large welded structures having many welded joints of different weld geometries at several planes. In the present study, inherent strain based technique was utilized for the aforementioned welded structure in elastic finite element analysis for the accurate prediction of 3-D distortion patterns with reduced computational time. The predicted and measured values of 3-D distortions of GBC were observed to be in good agreement with the ones provided from the shop floor, indicating the adequacy of inherent strain based method for the prediction of welding distortion in large and complex welded structures. As part of this investigation, a suitable welding fixture was also designed and welding sequence was modified, which were verified through inherent stain method to aid in minimizing the distortion of welded GBC.

Finite element simulation and experimental investigation of thermal tensioning during welding of DP600 steel

The locally introduced heating and cooling cycle of welding generates residual stresses and distortion. Costly post-weld heat treatments are required in order to reduce welding residual stresses and distortion. Thermal tensioning is one of the more promising in-process techniques to control welding distortion and can be classified into transient thermal tensioning (TTT) and side heating (SH). In thermal tensioning additional heat sources are applied during welding. If the additional heaters are close to the weld centre line and influence the thermal field of the weld, the process is called TTT. If there is no interference to the thermal field of the weld, the process is called SH. In this work, the SH during welding of 2 mm thick DP600 steels has been extensively investigated using numerical and experimental approaches. The thermal and mechanical fields during conventional welding and SH were examined by means of finite element models, and validated by comparison with experimental observation of temperature, distortion and residual stresses. The microstructure was investigated experimentally.

Control of welding distortion during gas metal arc welding of AH36 plates by stress engineering

Welding residual stress and distortion are strongly linked together. One of the ways to control or reduce the welding distortions is the manipulation of the generated stresses during welding, and final residual stresses exist in the workpiece (stress engineering). In this paper, the control of gas metal arc butt welding distortion of 500 × 250 × 6 mm3 AH36 plates by means of additional heat sources is studied using experimental and numerical approaches. To understand the distortion reduction mechanism, 3D finite element model has been constructed and validated by temperature, distortion and residual stress measurements together with microstructure investigation. The numerical results are compared to that of the experimental measurements.

Investigating the influence of external restraint on welding distortion in thin-plate bead-on joint by means of numerical simulation and experiment

The main objective of this study is to clarify the influence of external restraint on welding deformation in thin-plate bead-on joint by means of both experiment and numerical simulation. In the current study, an advanced computational approach based on ABAQUS code with considerable moving heat source, material nonlinearity, and geometric nonlinearity was developed to simulate welding-induced distortion in thin-plate joints. Meanwhile, experiments were carried out to measure the out-of-plane deformations in the corresponding mock-ups. Based on the experimental and numerical results, the mechanisms of the out-of-plane deformation in the thin-plate joints were discussed. In addition, the influence of external restraint on welding distortion in thin-plate bead-on joints was clarified by means of both numerical simulation and experiment. Both numerical models and experiments show that external restraint can mitigate the magnitude of the final deformation to some extent; however, it is difficult to satisfactorily eliminate welding distortion in the thin-plate joints only by external restraint. The results obtained from this work will be meaningful in understanding the features of welding distortion in thin-plate weldments, and will also be helpful in controlling welding distortion.

Numerical simulation and control of welding distortion for double floor structure of high speed train

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code. Then, the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software. The effects of welding sequence, clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically. The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure. Compared with the welding sequence, the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure. In the case of 30 mm reverse deformation, the maximum deformation can be reduced about 70% in comparison to an actual welding process.

Buckling of Stiffened Panels and Its Mitigation

The increased use of thin plates, like in ships for high-speed operation, results in significantly increased distortion. In-process control of welding distortion is more desirable than postwelding rectification from the point of manufacturing efficiency. This can be achieved by suitably designing and also implementing one or more of the distortion control measures as is suitable for a particular manufacturing situation. In this study, an investigation on buckling phenomenon in fabrication of stiffened panels was carried out. Analytical formulae were used to calculate the weld-induced compressive stresses. Critical buckling stresses considering appropriate buckling coefficient for typical stiffened panels as used in shipbuilding practice were calculated. The predictions from these analytical tools were compared with experimental observations. The experimental results compared fairly well with those of the calculated ones. In the present study the panel design aspect as well as thermomechanical tensioning scheme were studied with regard to buckling mitigation. It was observed that when choosing suitable stiffener spacing in conjunction with plate thickness, buckling distortion can be significantly reduced. Distortion mitigation through thermomechanical tensioning was also found to an effective yet simple-to-implement method of buckling distortion control. However, further investigation is necessary toward fully establishing the method of thermomechanical tensioning. Once this method is established, this pretensioning technique can be applied as an active in-process control method to avoid buckling distortion in stiffened panels.

Buckling of Stiffened Panels and Its Mitigation

The increased use of thin plates, like in ships for high-speed operation, results in significantly increased distortion. In-process control of welding distortion is more desirable than post welding rectification from the point of manufacturing efficiency. This can be achieved by suitably designing and also implementing one or more of the distortion control measures as is suitable for a particular manufacturing situation. In this study, an investigation on buckling phenomenon in fabrication of stiffened panels was carried out. Analytical formulae were used to calculate the weld-induced compressive stresses. Critical buckling stresses considering appropriate buckling coefficient for typical stiffened panels as used in shipbuilding practice were calculated. The predictions from these analytical tools were compared with experimental observations. The experimental results compared fairly well with those of the calculated ones. In the present study the panel design aspect as well as thermomechanical tensioning scheme were studied with regard to buckling mitigation. It was observed that when choosing suitable stiffener spacing in conjunction with plate thickness, buckling distortion can be significantly reduced. Distortion mitigation through thermomechanical tensioning was also found to an effective yet simple-to-implement method of buckling distortion control. However, further investigation is necessary toward fully establishing the method of thermomechanical tensioning. Once this method is established, this pre-tensioning technique can be applied as an active in-process control method to avoid buckling distortion in stiffened panels.

Verification of possibility for controlling welding distortion generated by laser-arc hybrid welding

For predicting welding distortion and residual stress generated by laser-arc hybrid welding (HYBW) with high accuracy by the 3D thermal elastic-plastic analysis based on FEM, a heat input model considering the dual heat source of HYBW was proposed. By using the proposed model, welding distortion and residual stress generated by HYBW on the general structural steel under several welding conditions, in which the heat input ratio of laser and arc were variously changed, were obtained. Comparing with the results obtained by experiments and analyses, the validity and generality of the proposed heat input model could be verified. The tendency and magnitude of welding distortion varied with the heat input ratio of laser and arc. The results indicated the possibility for controlling welding distortion generated by HYBW with the optimum heat input ratio of laser and arc.

Optimization and Control of Welding Distortion in Hatch Cover Girders

An in-process method for controlling welding distortion in Hatch Cover Girders due to fillet welds is developed. It particularly reduces linear and angular distortion by performing FAIRING (triangular heating and triangular cooling) after the weld process. Various heating conditions are examined by experiment and by the lab test analysis (Geographic information system) in order to determine appropriate conditions and to study the mechanism by which welding distortion is reduced. It is consequently found that this mechanism is a result of two main effects: triangular heating effect on one side and triangular cooling effect on other side, which produces the opposite linear and angular distortion.

Challenging Experiences in the Usage of Stainless Steels in a Heavy Fabrication Industry

Stainless steels are regularly used as one of the preferred material of construction in the pressure vessels and heat exchangers manufactured by welding for process plants and energy sector at BHEL, Tiruchirappalli. They are considered mainly because of their corrosion resistance and high temperature suitability. But the practising welding engineers have to face innumerable challenges with stainless steel with regard to defects minimization, distortion control and dimensional stability on large and complex assemblies. Use of Nickel based filler wires or development of welding procedures simulating the true configuration of the product and by conducting specific tests and NDE are followed for weld defects control. Sequence welding, development of special fixtures, etc have come as handy options for welding distortion control of SS. Innovative inspection techniques for the certification of dimensions including geometrical tolerances especially on large constructions using SS welding and evolution of special Helium leak testing procedures for certain in-process checks in critical products are inevitable in the SS fabrication industry as a part of Quality Assurance programme. As a pioneer in SS fabrication, some of our challenging experiences pertaining to these three areas are discussed in this paper.

The applicability of using low transformation temperature welding wire to minimize unwanted residual stresses and distortions

Fusion welding of steel pressure vessels provides one of the most economic methods for creating such structures. However, the highly localised heat distribution, at the fused region gives rise to non-uniform heating/expansion and cooling/contraction of the weld and the surrounding base material, consequently giving rise to residual stresses and distortion. Several techniques are available to minimize welding distortions and residual stresses [1]. One feasible and efficient mitigation technique, that alters the inherent residual stresses developed during welding, includes the use of low transformation start temperature welding wire [2–4]. By altering the filler material and metallurgical transformations developed at the fusion zone and heat affected zone, wielded regions at the weld line can give rise to compressive residual stresses [2]. Consequently by establishing the appropriate chemical composition of the welding wire, a significant reduction in welding distortions can be achieved. This study focuses on establishing the merits of using different filler materials to minimize welding residual stresses and distortion through a thermal-metallurgical-elasto-plastic numerical parametric study. Numerical modelling of butt welded structures using three different filler materials is considered and the applicability of using low transformation temperature welding wire is investigated. The predicted residual stresses and distortions give a significant advance in understanding and control of welding distortion in welded fabrications. The chemical composition of the filler material and ultimately fused zone composition, leading to reductions in residual stresses and distortions is identified.

A Structural Design Approach for Controlling Welding Distortion at the Upper Deck of a Hull Structure in the Erection Stage

An effective design method for controlling the transitional welding distortion at the aft upper deck occurring in the erection stage of the hull structure has been established using FEA and measured distortion database. Variation of distortion at the aft upper deck was measured according to the progress of the manufacturing process. This was done in order to clarify the 2nd distortion of the upper deck, defined as the increment of welding distortion developed after the assembly stage, The amount and distribution of the 2nd load causing the 2nd distortion were identified with a non-linear buckling FEA. The distribution of the welding distortion and the residual stress were assumed to be initial imperfections, which were identified with STEM (simplified thermoelastic method) based on inherent strain. Based on these results, the modification of structural design parameters such as plate thickness and the attachment of carling were made, in order to prevent the excessive 2nd distortion which requires costly flame correction work in the erection stage.

A Research on Prediction and Control of Welding Distortion and Residual Stress for an All-Welded Steel Bridge

A typical case of integral all-welded panel joints on Shanghai Minpu Second Bridge is discussed in this paper. The prediction of welding residual stresses at joints is achieved by thermal elasto finite element analysis, and the research reveals that a proper scheme of multi-layer welding craft will reduce welding distortions and residual stresses through mutual offset. The welding distortions at upper and lower chord joints (Type I) and those of the overall structural model are predicted with the distribution of residual stresses obtained. The research aims to provide a theoretical basis for the control of welding distortion, the optimization of welding craft and the constitution of optimal assembly welding craft.

A Research on Prediction and Control of Welding Distortion and Residual Stress for an All-Welded Steel Bridge

A typical case of integral all-welded panel joints on Shanghai Minpu Second Bridge is discussed in this paper. The prediction of welding residual stresses at joints is achieved by thermal elasto finite element analysis, and the research reveals that a proper scheme of multi-layer welding craft will reduce welding distortions and residual stresses through mutual offset. The welding distortions at upper and lower chord joints (Type I) and those of the overall structural model are predicted with the distribution of residual stresses obtained. The research aims to provide a theoretical basis for the control of welding distortion, the optimization of welding craft and the constitution of optimal assembly welding craft.

Study on FEM Numerical Simulation Method for the Welding Distortion

The control of welding distortion during assembly process is very important. At present, there are mainly two numerical simulation methods for the welding distortion which are thermo-elastic-plastic finite element method and its simplified approach of inherent strains. At first, taking T-joint as an example, the welding distortions were computed using two methods mentioned above. Based on thermo-elastic-plastic finite element method, welding process was simulated by life and death element, moving heat source and transient state thermal field etc. Then, the welding distortion was calculated by inherent strains method after thermo-elastic-plastic computation. It was concluded from the comparison that the simulation results by using the two methods are consistent. Therefore, the inherent strains method can be conveniently and economically applied to prediction of structural welding distortion in engineering. Applied the inherent strains method, welding deformation was predicted for the bogie frame side beam of high speed train. According to the deformation results from the finite element analysis, the welding deformation of the bogie frame side beam was lager than the tolerance of quality and in reasonable agreement with the experimentally determined distortion values. The work in this paper indicated that the inherent strains method was effective to predict the welding deformation so as to control the welding quality in large complex structures, such as the bogie frame of railway vehicle. Key words: welding distortion; thermo-elastic-plastic method; inherent strains approach; numerical simulation; bogie frame;

Prediction and Control of Welding Distortion in "U" Rib Orthotropic Plate

Prediction and control of welding distortion is an important stage to guarantee manufacturing quality of steel structures. Thermo-elasto-plastic finite element method is employed to analyze the model of "U" rib orthotropic plate. Through this method, inherent strain in the weld zone is extracted. Inherent strain obtained which is regarded as known conditions is put on the weld zone of "U" rib orthotropic plate. Elastic finite element analysis is employed to predict the welding distortion of the plate. According to the prediction result, control scheme of welding distortion is made and a curvilinear equation is provided. The equation elaborates the shape of the welding jig controlling welding distortion. Numerical simulation method is applied to analyze the control scheme and the steps of the method are given. The numerical simulation result meets the quality request of welding deformation control. The method provides important reference for the control of the welding distortion in complex components.