焊接变形预测技术研究进展

焊接变形是影响焊接结构质量和生产率的主要问题之一，焊接变形的存在不仅影响着焊接结构的制造过程，而且影响着焊接结构的使用性能。一般认为，焊接过程中材料的不均匀受热、板厚方向的热梯度、材料的局部非协调塑性应变以及焊接残余应力的作用是产生各种焊接变形的根本原因。焊接变形预测方法大都基于有限元分析。文中详述了国内外有关焊接变形预测技术的最新研究进展，具体介绍了热弹塑性有限单元法、固有应变法以及基于传统有限元的优化设计法与人工神经网络模型等先进的焊接变形预测方法。     

随焊冲击旋转挤压控制TC4薄板焊接失稳变形工艺

薄板钛合金在焊后存在较大的残余压应力,使其发生失稳变形,很多情况下,结构不能满足设计要求,必须采取措施减少失稳变形.文中采用随焊冲击旋转挤压的方式,对焊接过程中尚处于较高温度的焊缝部位进行塑性延展,减少焊接时发生的塑性收缩量,降低残余压应力的值,从而减少焊接变形量.对焊后薄板的变形挠度和残余应力进行了测量,变形挠度下降...     

TC4薄板随焊旋转挤压工艺

薄板钛合金由于在焊后存在较大的残余压应力,使得其易发生失稳变形.采用随焊旋转挤压方式,对焊缝高温部位进行塑性延展,减少焊接时所发生的塑性收缩量,降低残余压应力的值,从而降低焊接变形量.采用拉伸试验、拉伸断口SEM分析和焊后薄板的变形挠度的测量等试验.结果表明,随焊旋转挤压焊件的变形挠度可以下降到常规焊件挠度的2/3,并且随着加载应力的增加,变形的挠度可以进一步下降.说明在焊接过程中采用随焊旋转挤压方式控制薄板TC4失稳变形是可行的.     

Experimental and computational analysis of residual buckling distortion of bead-on-plate welded joint

A test specimen with a thickness of 2.28 mm was selected as the examined object, to investigate welding induced buckling. Bead-on-plate welding was conducted on the test specimen and residual buckling distortion was observed. A thermal-elastic-plastic (TEP) FE analysis using solid elements model was carried out to predict welding induced buckling after cooling. The inherent deformation of the examined welded joint was also evaluated from the computed results of TEP FE analysis. A shell elements model of the test specimen was used for eigenvalue and elastic FE analyses based on the inherent deformation theory. Eigenvalue analysis predicted the buckling mode and corresponding tendon force in the examined welded joint. Considering large deformation and initial deflection, an elastic FE analysis was carried out to predict the out-of-plane welding distortion, which showed a good agreement with measured distortion.The generation mechanism of buckling in bead-on-plate welded joint was clarified employing the inherent deformation theory. The tendon force (longitudinal inherent shrinkage) is the dominant reason to produce buckling and the disturbance (initial deflection or inherent bending) triggers buckling but does not influence the buckling mode.     

Efficient Simulation of Welding Distortion in Large Structures and Its Reduction by Jig Constraints

Two large construction machinery structures were welded separately with and without jig constraints. The welding distortion of the entire structure was measured by a 3D coordinate measuring system and simulated by elastic FEM using the inherent deformation method. To obtain an accurate inherent deformation, a thermal elastoplastic FE analysis of simple one-side fillet joints with and without jig constraints was performed. Efficient simulation of welding distortion in large structures was accomplished by applying inherent deformation in a localized region, and the effect of jig constraint on the reduction of welding distortion was clarified. The computation of inherent deformation, the weld zone definition and the conversion of inherent deformation into inherent strain were automated. Measured and computed welding distortions in large structures had a good correspondence with respect to both tendency and magnitude. Further investigation of jig configuration was performed for enhanced reduction of welding distortion. Alternative controlling techniques for common welded structures were also addressed.     

Suggestion of welding procedure for compressive residual stress induction by using low transformation temperature welding materials

ABSTRACT

To understand the cause of compressive residual stress in welded joints, we analysed by numerical analysis the effect of welding pass sequence using low transformation temperature (LTT) welding materials on residual stress around the weld toe of boxing fillet welded joints. It was determined by numerical analysis that the produced compressive residual stress and the influence of the stiffeners are reduced in the equivalent position of the weld toe in a fillet welded joint because of the influence on the behaviour of the stiffener in the weld being due to residual stress distribution around the weld toe. The residual stress reduction method of extending the length of the welded bead and releasing the weld toe from the stiffener, similar to the concept of discarding a bead to reduce tensile residual stress, was effective in fillet welded joints. Numerical analysis of the relationship between residual stress around the weld toe and width of the weld bead in the bead-on-plate welding model clarified that compressive residual stress can be introduced around the weld toe by having a wide width weld bead. In addition, a fully penetrated welded joint was very effective for causing compressive residual stress around the weld toe.     

Prediction of welding distortion during assembly process of thin plate structures

0IntroductionApplication of welding process in fabricating largestructures offers several advantages over mechanical joiningmethods such as improved structural performance,flexibil-ity of design,weight reduction and cost savings etc.Inship and automobile …     

Artificial neural networks – an aid to welding induced ship plate distortion?

Abstract

A preliminary study on the potential application of artificial neural networks in welded structures was expanded to metal inert gas welding of steel plates of grades D and DH 36. The main controllable variables were plate thickness, steel grade, plate cutting process, and heat input. A series of welded plates of each grade was manufactured, covering plate thicknesses of 6 and 8 mm. The topography of each welded plate was evaluated after tacking the plates together and after welding, allowing the actual distortion to be calculated. It was established that a multilayer perceptron network architecture configuration accurately represented the distortion for the 6 mm thickness plate, and for the 8 mm thickness plate after treatment of the data. The data generated were used to develop the PREDICTOR software package, which allows a distortion prediction to be produced, and to carry out a sensitivity analysis. Heat input was found to be the most sensitive factor related to distortion, with carbon content of the plates, yield/tensile strength ratio, carbon equivalent, and steel grade also having significant effects. Some test plates were modelled using finite element method software packages: the initially poor agreement was improved via the addition of significant detail, but the finite element model by its nature will normally predict symmetrical distortion from a symmetric weld, whereas the artificial neural network model developed was capable of predicting the asymmetric distortion observed in reality.     

Comparative study on evaluation of tendon force for welding distortion prediction in thin plate fabrication*

Tendon force is an essential concept to predict welding distortion such as longitudinal shrinkage and welding induced buckling in thin plate fabrication.In this study,three approaches with experimental,theoretical and computational analysis,are examined to evaluate the magnitude of tendon force.In detail,inherent deformation theory is introduced first,the theoretical analysis to obtain the inherent strain solution is also reviewed;and then analytical solution for tendon force is achieved.Also,the theory of FE analysis for welding is introduced and implemented in a computation to obtain the transient temperature distribution,plastic strain,residual stress and welding distortion in a bead-on-plate welded joint with 2.28 mm in thickness.The longitudinal displacement is employed to evaluate tendon force directly,and these computed inherent strain and inherent stress can also be employed to evaluate tendon force by integration approach later.All the evaluated magnitudes of tendon force have a good agreement with each other.     

电渣焊接头焊接残余应力与变形的数值模拟

为研究电渣焊接头焊接残余应力的分布规律及变形特征,基于有限元分析软件MSC. Marc,开发了用于模拟电渣焊接头温度场、残余应力与焊接变形的热-弹-塑性有限元计算方法. 在所开发的计算方法中,采用全椭球等密度体积移动热源模型来模拟电渣焊的热输入,并以生死单元技术考虑焊缝成形,数值模拟了箱型柱中的腹板与隔板处电渣焊接头的焊接残余应力与变形. 同时,采用试验方法实测了电渣焊接头的横向收缩及角变形. 结果表明,横向收缩和角变形的计算结果都与试验值比较吻合,验证了所开发的数值计算方法的妥当性. 此外,利用数值模拟方法详细研究了电渣焊接头焊接残余应力的分布特征.     

预拉伸对铝合金焊接残余应力和变形的影响

在预拉伸应力作用下，进行了厚度为4mm的5A05铝合金试板的焊接，焊后残余应力及变形的测定结果表明．预拉伸焊接法可有效减小铝合金薄板焊后的纵向残余应力、纵向挠曲变形和平面变形。在弹性应力范由内，随着预应力的增大，试板的残余应力峰值、纵向挠曲变形及平面变形均逐渐减小。分析认为，预拉伸应力部分抵消了焊接区热膨胀产生的压缩应力，从而减小了压缩塑性变形，进而减小了冷却时焊接区域的拉伸应力水平，相应地远离焊缝区域的压缩应力也随之减小。     

大型电机转子焊接残余应力的数值分析

利用轴对称模型研究了大型电机转子焊接残余应力分布规律 ,探讨了单层单道焊情况下两侧同时焊接、热套、预热等工艺以及三层四道焊情况下焊接顺序对焊接残余应力的影响。研究结果表明 ,磁轭圈与辐板焊接后在焊缝及其周围区域产生较大的三向残余拉应力 ;两侧同时焊接可大大降低径向残余应力 ;热套可降低三向残余拉应力 ,热套后直接焊与热套后先冷却后焊相比效果更佳 ;预热可以降低周向残余拉应力 ;多道焊时径向残余应力主要取决于最后一层 ,尤其是最后一道焊缝 ;两侧的最后一道焊缝同时焊接可显著降低径向残余应力 ,而前面的焊道同时焊接与否并不重要。研究结果为优化生产工艺 ,降低残余应力提供了理论依据     

A mechanism of formation of a single section of a vacuum discontinuous coating

A welding distortion prediction method based on the inherent strain concept is presented. In the proposed method, welding distortion of large-welded structures could be estimated by elastic analysis using the result of thermal-elastic–plastic analysis and the result of smaller welded joints or components. Thermal-elastic–plastic analysis is performed to calculate residual plastic strain distribution, which is the input data for the elastic analysis of welding distortion. The obtained residual plastic strain distribution is mapped to non-deformed finite element models to calculate welding distortion by elastic analysis. The mapping procedure is done in different ways for welding start/end parts and the rest of the weld length in order to take into consideration the unsteady strain distribution at the start/end of welds. For start/end parts, strain distribution used is identical with thermal-elastic–plastic analysis. For the part except start/end parts, strain distribution obtained by thermal-elastic–plastic analysis is extracted from the centre of weld length and is extruded along the welding direction.

The proposed method was applied to the welding distortion prediction of joints with weld length of 900 and 1200 mm based on the thermal-elastic–plastic analysis result of a joint with weld length 600 mm. The estimated results were in good agreement with the thermal-elastic–plastic analysis results of models of corresponding weld length to show the validity of the proposed method.     

Radial basis function neural network model based prediction of weld plate distortion due to pulsed metal inert gas welding

Abstract

Welding shrinkage and distortion affect the shape, dimensional accuracy and strength of the finished product. This work concerns the prediction of welding distortion in a pulsed metal inert gas welding (PMIGW) process. Six different types of radial basis function network (RBFN) models have been developed to predict the distortion of welded plates. Six process parameters, namely, pulse voltage, background voltage, pulse duty factor, pulse frequency, wire feed rate and the welding speed, along with the root mean square (RMS) values of two sensor signals, namely, the welding current and the voltage signals, are used as input variables of these models. The angular distortion and the transverse shrinkage of the welded plate are considered as the output variables. Inclusion of sensor signals in the models, as developed in this work, results in better output prediction.     

New technique to control welding buckling distortion and residual stress with non-contact electromagnetic impact

Abstract

A new technique using non-contact electromagnetic forces has been proposed for controlling welding buckling distortion and residual stresses in welded thin plates. The experimental results show that the method can successfully eliminate the buckling distortion and reduce the residual stresses. Three-dimensional finite element modelling has been developed to study the evolution of the stress and strain throughout the welding and electromagnetic impacts. The predicted welding distortion and residual stresses are in good agreement with the experimental results. The numerical analyses show that the reduction in distortion and stress is a result of the change of the plastic strain field in the weld region: electromagnetic impacts reduce longitudinal compressive plastic strain in the local region near the weld, and even produce the tensile plastic strain. Moreover, it is found that the residual stress can promote the changes of the longitudinal plastic strain state under electromagnetic impact.     

基于固有应变法筒体对接多道焊焊接变形的预测

对于全焊接阀体球阀,由于最后一道工序是焊接,为了确保焊后阀芯的转动和阀门的密封,焊接变形应该严格的控制,选择一个有效的方法准确地预测焊接变形,为焊前阀体的加工提供参考数据.采用了基于固有应变理论的有限元法预测与阀体结构相似的筒体对接多道焊的焊接变形.对于多道多层焊,轴向变形采用了分层计算的方法,径向变形进行一次计算.与试验测量的结果比较,计算值与测量值比较吻合,验证了固有应变法的准确性及可靠性,为阀体焊接工艺参数的优化和焊接结构的加工提供了重要的参考依据.     

Q345钢对接接头残余应力与变形的预测

以ABAQUS软件为平台,开发了用于模拟多层多道焊接头温度场、残余应力和焊接变形的热-弹-塑性有限元计算方法. 利用所开发的计算方法对板厚为16 mm的Q345钢平板对接接头的温度场、应力场和变形进行了数值模拟. 采用试验方法测量了对接接头的残余应力和角变形. 试验结果与数值结果比较吻合,验证了所开发方法的有效性. 结果表明,在板厚相同的条件下角变形和横向收缩随着焊接层数的增多有增大的趋势;焊缝附近的纵向拉伸应力区域分布范围随焊接层数的增加略有减小;焊接层数对纵向残余应力的峰值影响较小.     

线能量对TC4钛合金激光焊接残余应力和变形的影响

利用有限元分析和实验测试，研究了TC4钛合金平板激光焊接线能量对变形和残余应力的影响规律，并通过焊缝金相实验分析了线能量与焊接残余应力和变形的内在关系。结果表明：钛合金激光焊接产生的纵向残余拉伸应力约700MPa～850MPa，而横向残余拉伸应力只有50MPa～80MPa。激光焊接线能量增加时，纵向残余应力拉伸区域变宽，峰值应力降低，而横向残余应力随线能量的增加而升高。在临界焊透规范以上焊接时，角变形随线能量的增大而减小，但横向收缩变形增大。试件被完全穿透焊接时，线能量对角变形的影响作用降低。     

Numerical and experimental study of thermally induced residual stress in the hybrid laser-GMA welding process

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser-gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.     

大面积拼焊平台结构的焊接变形预测

为了对大面积厚板拼焊平台结构进行焊接变形预测,首先进行了缩比件焊接试验,并测试了焊接过程中的角变形,然后进行了实际焊道数量及焊道集中分组后缩比件的焊接数值模拟,验证了焊接有限元模型输入的准确性及焊道集中分组方案的合理性;最后根据建立的焊道集中规则建立了平台结构的焊接有限元模型,进行了焊接变形的预测.结果表明,实际焊道数量及焊道集中分组后缩比件焊接角变形的数值模拟结果与测试结果一致,角变形约为1.6°,验证了将实际焊接工艺中15层27道简化为5层5道的焊道集中方案的准确性;平台结构的焊接变形表现为局部下塌或上凸的面外变形,是由上下坡口不对称产生的焊接角变形及底部钢架支撑作用共同产生的,面外变形范围为−5.2 ~ 4.4 mm.