Prediction Of Welding Distortion Research Articles

Prediction of Laser Welding Distortion in Cylindrical Shell Structures Using Direct Application of Inherent Strain

In this study, a simplified analysis method by directly applying inherent strain (DIS) at integration points to predict welding distortion of cylindrical shell structures was suggested. The 3D thermo-elastoplastic method demands substantial computational time. The strain as direct boundary (SDB) simplified method using virtual temperature encounters challenges in consecutive thermal structural analysis including welding distortion. The suggested method (that is, DIS) offers the advantage of enabling continuous thermal structural analysis after welding distortion analysis, with computational efficiency. To calculate inherent strain, lap laser welding with 2 mm and 2.6 mm SUS304 plates was performed, measuring fusion and heat-affected zone sizes via cross-sectional observations. Using the calculated inherent strain and our suggested direct input method, we conducted welding analysis and welding test on cylindrical shell structures. Comparison of welding distortion under same conditions revealed radial distortion difference within approximately 10%, corresponding with the experimental result and confirming a computational time reduction by over 2,000 times than those of thermo-elastoplastic analysis. Therefore, an efficient and accurate prediction of welding distortion was achievable through the suggested method.

An Improved Method for Deriving the Heat Source Model for FCAW of 9% Nickel Steel for Cryogenic Tanks.

The International Maritime Organization (IMO) is tightening regulations on air pollutants. Consequently, more LNG-powered ships are being used to adhere to the sulfur oxide regulations. Among the tank materials for storing LNG, 9% nickel steel is widely used for cryogenic tanks and containers due to its high cryogenic impact toughness and high yield strength. Hence, numerous studies have sought to predict 9% nickel steel welding distortion. Previously, a methodology to derive the optimal parameters constituting the Goldak welding heat source for arc welding was developed. This was achieved by integrating heat transfer finite element analysis and optimization algorithms. However, this process is time-consuming, and the resulting shape of the weld differs by ~15% from its actual size. Therefore, this study proposes a simplified model to reduce the analysis time required for the arc welding process. Moreover, a new objective function and temperature constraints are presented to derive a more sophisticated heat source model for arc welding. As a result, the analysis time was reduced by ~70% compared to that previously reported, and the error rates of the weld geometry and HAZ size were within 10% and 15% of the actual weld, respectively. The findings of this study provide a strategy to rapidly predict welding distortion in the field, which can inform the revision of welding guidelines and overall welded structure designs.

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.

A Study on the Enhanced Process of Elaborate Heat Source Model Parameters for Flux Core Arc Welding of 9% Nickel Steel for Cryogenic Storage Tank

Various regulations are being devised and implemented to prevent the environmental pollution that is threatening mankind. The International Maritime Organization has strengthened regulations on sulfur, a notorious pollutant, to prevent sea pollution. In addition, the production of LNG fueled ships is increasing. Among various metals, 9% nickel steel is widely used in the shipbuilding industry because it is advantageous in terms of material strength and cryogenic impact toughness. Various studies are being carried out to predict and prevent its distortion, caused by welding, in the design. To predict welding distortion during flux core arc welding, this study found a way to refine the parameters constituting the Goldak welding heat source. The optimal heat source parameters were derived by using BOP experiments, cross-sectional analysis, finite element analysis and global optimization algorithm. When re-analyzed and verified based on the values, an error of up to 6.3% was found between simulation results and experimental values. The process was improved by clarifying the objective function and reducing the range of candidate welding efficiencies during global optimization and the process efficiency was also improved by reducing analysis time with a simplified model. Therefore, it is thought that this study can contribute to the productivity improvement of LNG storage containers, helping engineers apply it immediately in the industrial field.

Welding distortion prediction of ship plate frame structures based on a self-learning database

ABSTRACT Welding distortion will increase the shipbuilding cost. Therefore, it is important to accurately predict the welding distortion of a structure during the design stage. In this paper, a novel welding distortion prediction method for ship plate frame structures based on a self-learning database was proposed. Based on a typical plate frame structure in a shipyard, the applicability of the method was verified by comparing the prediction with on-site measurements. To solve the problem of choosing the welding sequences of structures with too many welds, the Latin hypercube sampling method was selected to arrange the weld samples in sequence. The results showed that the distortion of the structure was mainly concentrated on the upper shell. The numerical simulation coincided with the measurement results, and the accuracy was within 20%. Moreover, a reasonable welding sequence can decrease the distortion of a structure by 11.2%.

Welding distortion prediction and mitigation in thick steel plate structures on ships

ABSTRACT In the ship fabrication process, welding distortion will affect the dimension accuracy. In this paper, an industrialisation prediction method for thick steel plate structures on ships is proposed based on a combination of thermal-elastic-plastic finite element method and inherent deformation theory to reduce the welding distortion in the design stage, and its applicability is verified through a comparison of measurements in the shipyard and numerical simulations. The thick plate models produced by multi-pass welding technology are selected to analyse the welding distortion. The results show that the numerical prediction results are in good agreement with the measurement on site. The transverse bending distortion is the main factor that affects the fabrication accuracy. To mitigate welding distortion, the influence of welding sequence and flame heating is examined. This research may provide a macro concept for understanding the distribution characteristics of welding distortion and serve as a mitigation reference for manufacturing engineers.

Mitigation of welding induced buckling with transient thermal tension and its application for accurate fabrication of offshore cabin structure

Offshore cabin structure is usually fabricated by welding with 6–8 mm steel plates as lightweight application, and welding distortion is inevitable generated to influence its dimensional accuracy. In particular, welding induced buckling will occur under conventional welding procedure due to the geometric feature of cabin structure. Typical fillet welded joints in considered cabin structure were numerically examined beforehand, while thermal and mechanical behaviors were represented with non-linear thermal elastic plastic FE computation. Then, welding inherent deformation was proposed as driving force for welding distortion prediction, which can be evaluated by integration of residual plastic strain for each typical welded joint. Since transient thermal tension is applied during fillet welding with numerical investigation, self-constraint supported by base materials on welding line will become weak. Thus, less plastic strain is generated during welding process, and magnitude of welding inherent deformation will be significantly reduced. Elastic FE computation with welding inherent deformation as mechanical load was carried out to predict out-of-plane welding distortion of considered cabin structure, while cases of conventional welding and welding with transient thermal tension were examined. Better fabrication accuracy can be obtained with application of transient thermal tension due to less welding inherent deformation.

Welding Distortion Prediction for Multi-Seam Welded Pipe Structures using Equivalent Thermal Strain Method

Distortion prediction of a welded structure is an important way to improve work efficiency and ensure product quality during the fabrication process. Recently, the widely used approaches for evaluating residual deformation include the thermo-elastic-plastic finite element method (TEP-FEM) and the inherent strain method (ISM). The former can accurately simulate the entire welding process with excessive computational time, whereas the latter has great potential in the fast prediction of residual distortion in complex welded components. In this study, an equivalent thermal strain method based on inherent strain theory was proposed to predict residual deformation of the multi-seam welded pipe structures. Moreover, a full 3D TEP-FEM model was also developed to estimate the distributions of inherent strain in longitudinal (L-seam) and circumferential (C-seam) welds. To validate the accuracy of the proposed ISM, the welding distortion predicted by the proposed ISM is compared with the experimental data and TEP-FEM simulation results. It is discovered that the proposed ISM can be used to accurately predict welding-induced deformation in multi-seam welded pipe structures. Furthermore, compared with TEP-FEM simulation, the significant advantage of this approach is that the computing efficiency can be increased by about 50 times.

A Geometry-Based Welding Distortion Prediction Tool.

The prediction of welding distortion requires expertise in computer simulation programs, a clear definition of the nonlinear material properties, and mesh settings together with the nonlinear solution settings of a coupled thermal–structural analysis. The purpose of this paper is to present the validation of an automatic simulation tool implemented in Ansys using Python scripting. This tool allows users to automate the preparation of the simulation model with a reduced number of inputs. The goal was, based on some assumptions, to provide an automated simulation setup that enables users to predict accurate distortion during the welding manufacturing process. Any geometry prepared in a CAD software can be used as the input, which gave us much geometrical flexibility in the shapes and sizes to be modeled. A thermomechanical loosely coupled analysis approach together with element birth and death technology was used to predict the distortions. The automation of the setup enables both simulation and manufacturing engineers to perform welding-induced distortion prediction. The results showed that the method proposed predicts distortion with 80–98% accuracy.

Novel welding distortion analysis method for large welded structures using orthotropic thermal expansion coefficients

Abstract This paper proposes an effective numerical method to predict welding distortion for large welded structures. To predict welding distortions, inherent strain-based methods are computationally efficient and widely used in engineering fields. However, there are some drawbacks such as the generation of undesirable longitudinal forces and the use of vector-type input variables. Equivalent loads are derived through finite element formulation considering orthotropic thermal expansion conditions. Unlike previous methods, the proposed method predicts transverse shrinkage and angular distortion accurately, removing the undesirable longitudinal forces. In addition, scalar-type input variables are employed, which results in a convenient design procedure. The performance of the proposed method is verified through various examples including complex and large welded structures.

Multi-Pass Welding Distortion Analysis Using Layered Shell Elements Based on Inherent Strain

In this article, a layered shell element-based, elastic finite element method for predicting welding distortion in multi-pass welding is developed. The welding distortion generated in each pass can be predicted by employing layer-by-layer equivalent plastic strains as thermal expansion coefficients and using the heat-affected zone (HAZ) width as the mesh size. The final distortion can be expressed as the sum of the distortions for each pass. This study focuses on extraction of the equivalent plastic strain and HAZ width through 3D thermal elastic plastic analysis (TEPA) for each pass. The input variables extracted from each pass can be converted and added to simulate the final distortion of the multi-pass welding. A 10 mm thick, multi-pass butt-welded joint, subjected to three passes, is simulated via the proposed method. The predicted welding distortion is compared with the 3D TEPA results and the measured experimental data. The outcome indicates that good agreement can be obtained.

Geometry and Distortion Prediction of Multiple Layers for Wire Arc Additive Manufacturing with Artificial Neural Networks

Wire arc additive manufacturing (WAAM) is a direct energy deposition (DED) process with high deposition rates, but deformation and distortion can occur due to the high energy input and resulting strains. Despite great efforts, the prediction of distortion and resulting geometry in additive manufacturing processes using WAAM remains challenging. In this work, an artificial neural network (ANN) is established to predict welding distortion and geometric accuracy for multilayer WAAM structures. For demonstration purposes, the ANN creation process is presented on a smaller scale for multilayer beads on plate welds on a thin substrate sheet. Multiple concepts for the creation of ANNs and the handling of outliers are developed, implemented, and compared. Good results have been achieved by applying an enhanced ANN using deformation and geometry from the previously deposited layer. With further adaptions to this method, a prediction of additive welded structures, geometries, and shapes in defined segments is conceivable, which would enable a multitude of applications for ANNs in the WAAM-Process, especially for applications closer to industrial use cases. It would be feasible to use them as preparatory measures for multi-segmented structures as well as an application during the welding process to continuously adapt parameters for a higher resulting component quality.

Numerical Prediction of Welding Distortion Considering Gravity Force on General Ship Grillage Structure by Elastic Finite Element Method Using Inherent Strain

The accurate numerical prediction of welding deformation is important to improve the structural safety of ships and offshore structures in heavy industries. The precise reflection of the real working condition in the numerical prediction is an essential factor to improve its result. In the present study, the effect of the gravity force on numerical prediction of the optimal welding sequence of a general ship grillage structure was validated with the introduction of a new boundary condition in which the structure is placed over rails. Additionally, the direction of the gravity force of welded structures could be changed at the final assembly process according to the production plan. The effect of the gravitational orientation on the final welding displacements was also investigated herein. The elastic finite element method using the inherent strain, interface element, and multipoint constraint function was introduced to analyze the welding deformation. This study validated the influence of the gravity force on the numerical prediction of welding displacements in a general ship grillage structure.

Numerical simulation of bending deformation induced by multi-seam welding of a steel-pipe structure

Longitudinal bending deformation, often induced during gas metal arc welding of long pipe structures, plays a negative role in the accuracy of assembly, external appearance, and various strengths of welded pipe components. In this paper, an experimental and numerical study of pipe welding distortion is presented. A 3D thermo-elastic-plastic finite element model for multi-seam welds (composed of longitudinal (L-seam) and circumferential (C-seam) welds) of pipe components was developed to predict longitudinal bending deformation. The finite element method and experimental results demonstrate good agreement. Therefore, the proposed model can accurately predict welding distortions in multiseam welded pipe structures. Moreover, the results reveal clear distinctions between the longitudinal bending deformations induced by L-seam and C-seam welds due to different selfrestraint strengths. Finally, another characteristic, the bending angle, is analyzed. Linear and nonlinear relationships are observed between the sine of the bending angle and weld length for L-seam and C-seam welds, respectively.

Dimensional precision controlling on out-of-plane welding distortion of major structures in fabrication of ultra large container ship with 20000TEU

Ultra large container ship as an essential role during international trade, is required for precision fabrication due to highly efficient TEU loading and unloading. In this study, two major structures, so called watertight transverse bulkhead structure and torsion box structure of ultra large container with 20000TEU were examined for out-of-plane welding distortion prediction and mitigation with measurement and computational analysis. Based on the welding inherent deformation theory, typical welded joints of two major structures were systematically classified with the different material, thickness, welding condition and joining form; and the relationships between welding heat input and inherent deformations were also presented. Elastic FE analysis with shell elements model and welding inherent deformation as input loading was employed for welding distortion prediction. Not only the distributions but also the magnitudes of predicted out-of-plane welding distortions of considered major structures have a good agreement comparing to the measurements. Furthermore, welding sequence influence was considered for dimensional precision controlling during the watertight transverse bulkhead structure fabrication, and welding groove optimization of thick plate was examined for out-of-plane welding distortion mitigation during the torsion box structure fabrication. Computational results show that welding distortions of both ship block structures can be significantly reduced for requirement of fabrication precision.

Application of efficient TEP FE computation on accurate fabrication of cylindrical leg structure of jack-up rig

Cylindrical leg structure is an essential component of jack-up rig, and its fabrication accuracy will significantly influence the operation performance and service lift. Due to the welding distortion generated during rack and cylinder joining and its effect on dimensional profile of cylindrical leg structure, the experiment to fabricate the cylindrical leg structure and dimensional measurement were conducted in advance, and highly efficient Thermal Elastic Plastic (TEP) FE computation with Iterative Substructure Method (ISM) and OpenMP parallel computation was proposed and employed for welding distortion prediction. Simplified cylinder FE model was considered to clarify the mechanism of dimensional variation in advance, and efficiency of proposed TEP FE computation was also demonstrated. Quarter FE model of rack and cylinder welded structure was then employed due to its symmetrical feature while computed results have a good agreement comparing to the measurement. Meanwhile, in order to improve the fabrication accuracy, bead-on-plate welding on inner surface of cylindrical leg structure was numerically examined, while inverse deformation can be generated and has significant influence to mitigate welding distortion during rack and cylinder joining.

Accurate FE Computation for Out-of-plane Welding Distortion Prediction of Fillet Welding with Considering Self-Constraint

Inherent deformation as key parameter plays an essential role in elastic finite element (FE) analysis for welding distortion prediction. In this study, the self-constraints supported by surrounding base material and lateral stiffener were presented, where their influences on magnitudes of inherent deformation components were qualitatively examined. In detail, self-constraint supported by the surrounding base material will distinguish the inherent deformation as an individual physical representation; and self-constraint supported by the lateral stiffener will significantly influence the bending component and final deformed mode. Taking into account fillet welding and orthogonal stiffened welded structure as the application, experiments were conducted for out-of-plane welding distortion measurement. Transient nonlinear thermal elastic-plastic FE analysis of fillet welding was carried out to evaluate inherent deformation after validation with the measured data; then, elastic FE analysis with inherent deformation was carried out to accurately predict the out-of-plane welding distortion and welding buckling behavior in fabrication of an orthogonal stiffened welded structure which is a part of typical ship panel, and there is a good agreement between the predicted and measured welding distortion. 1. Introduction Up to now, fusion welding which is considered as a main joining method because of its practical and high productive features is almost employed for component assembly in fabrication of marine structures, automobiles, trains, aircraft, bridges, pressure vessels, and others. However, during the fast heating and cooling processes, a narrow region near the welding line will expand and subsequently shrink because of the constraint of the surrounding base material, and then plastic strains are generated which are the primary cause of welding distortion and residual stress. Therefore, welding-induced distortion is inevitably generated during the welding process, and it will result in loss of dimensional control and structural integrity, trouble of subsequent alignment with the adjacent component, and increment of fabrication cost with straightening such as flame heating (Wang et al. 2015).

Welding Distortion Prediction and Process Optimization of Turbine Component by Electron Beam Welding

A turbine component with 130 blades requests high dimensional precision to ensure the assembly requirements. The dimensional precision is significantly influenced by welding distortion. In this research work, welding distortion in the turbine component by electron beam welding was predicted through elastic finite element method based on inherent strain theory. The inherent strains of single blade welding joints with different welding process and fix condition were obtained through thermal elastic plastic finite element method calculation. The simulation results indicated coherence between the predicted and measured distortion value. The final welding distortion of turbine component in different assembly sequences were compared, by utilizing the inherent deformations of optimized single blade welding joints simulation. An optimized welding procedure and assembly sequence was proposed to reduce the welding distortion. The results verify that 180-degree symmetrical welding can significantly reduce the plastic deformation.

Investigating the influence of external restraint on welding distortion in thin-plate welded structures by means of numerical simulation technology

Welding-induced deformation not only degrades the fabrication accuracy of a welded structure but also decreases the productivity due to correction work. Accurate prediction of welding distortion will be helpful in controlling the dimension accuracy.In this study, the main objective is to clarify the influence of external restraint on welding distortion in three different thin-plate steel welded structures by means of numreical simulation technology. A two-step computational approach was employed to simulate welding distortion in each welded structure. In the first step, the theranal ealstic plastic finite element method (T-E-P FEM) was used to obtain inherent deformation for each typical joint. In the second step, an elastic FEM based on inherent strain theory was used to compute welding deformation for three thin-plate panels with different tihickness and shape. In addition, the effects of external restriant on welding deformation in a thin-plate panel with 5 mm thickness, a thin-plate panel with 10 mm thickness, and an asymmetric curved panel with 10 mm thickness were investigated.

Comparative study of welding deformation of a stiffened panel under various welding procedures

The welding distortions of large-scale structures are extraordinary complicated. If an effective tool of predicting welding distortion is available, then marine design and manufacturing engineers can use this to improve production quality and reduce costs. This article focuses on the comparative studies of welding procedure of a stiffened panel. An efficient thermal elasto-plastic finite element method–based procedure is developed to predict the welding deformation and residual stress of structures. A combined shell/solid model is adopted to enhance modeling and calculation efficiency. The welding process of a stiffened panel is simulated. Three welding procedures of simultaneous, successive and bidirectional welding are studied. The results show that welding distortion can be well controlled by adjusting the welding procedure.