焊接结构变形预测及控制的研究现状

本文综述了国内外对于焊接变形预测和控制的主要方法及其研究现状。首先介绍了预测焊接变形的几种方法：解析法、热弹塑性有限元法、固有应变法（固有应变有限元法、热弹塑性有限元获得固有应变法）等;其次简述了工程中一些常用的控制焊接变形的措施：制定合理的焊接工艺规程、反变形法、系统综合分析法等;最后对焊接变形的预测与控制提出了展望。     

高强度钢T型接头焊接变形固有应变数值模拟

以固有应变理论为基础,介绍了两种固有应变模拟焊接变形的计算和加载方法;以高强度钢T型接头焊接变形为算例,讨论了两种模拟方法的差异;通过与相同实体模型热弹塑性变形结果的分析比较,验证了固有应变法预测焊接变形的合理性与准确性,为更合理的利用固有应变法预测大型焊接结构残余变形提供了有益的参考.     

固有应变法在T型接头焊接变形研究中的应用

本文以固有应变理论为基础,介绍了两种固有应变模拟焊接变形的计算和加载方法,并通过对T型接头焊接变形的分析实例讨论了两种模拟方法的差异,并与相同实体模型热弹塑分析的变形结果进行比较,验证了固有应变法计算焊接变形的合理性与准确性,为预测大型焊接结构变形提供了参考方法。     

采用固有应变法预测铝合金焊接变形

伴随焊接过程而产生的焊接变形和残余应力是影响焊接产品精度和性能的重要因素,至今仍然是工业生产中迫切需要解决的重要课题。目前常用的预测焊接变形的方法是三维热弹塑性有限元法,但是由于现有计算机计算能力的限制,还不能预测很多复杂结构的焊接变形。固有应变法是由日本学者提出的解决复杂结构焊接变形的方法,它忽略了整个焊接过程,直接将固有应变施加于壳单元上,经过一次弹性计算就可得到焊接变形。本文用三维热弹塑性有限元和试验相结合的方法获得了平板对接接头形式下的固有应变,运用固有应变法预测铝合金5052平板对接后的焊接变形,通过计算和试验相结合的方法验证了固有应变法预测铝合金焊接变形的可行性,结果表明,固有应变法能够较准确地预测焊接变形,且所用的时间短。     

基于等效载荷法的复杂结构焊接变形预测

采用固有应变等效载荷法,对复杂结构焊接变形进行预测.以焊接热过程产生的广义固有应变作为等效载荷,通过确定等效载荷的大小、加载区域和方式,编制等效载荷的施加程序,经过一次弹性有限元计算出焊接变形.以某51 000t散货船的双层底分段为例.采用等效载荷法对其焊接变形进行预测计算结果与实测数据进行比较,验证了固有应变等效载荷法预测船体双层底结构焊接变形的可行性,结果表明,固有应变法预测焊接变形结果与实测数据具有良好的一致性,且预测效率较高.     

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。     

基于固有应变的大型焊接结构变形的预测

首先用热弹塑性有限元法研究了铝合金对接焊的固有应变的变化规律，得到了固有应变，即纵向收缩力Tendon Force，横向收缩和角变形与热输入参数Q／h^2之间关系曲线。在掌握了同有应变的变化规律的基础上，通过简化焊接结构，用弹性板单元有限元法，对大型铝合金机车车顶盖的部分结构的焊接变形进行了预测。研究表明，用基于固有应变的弹性板单元有限元法对大型焊接结构的焊后变形预测足可以实现的。     

基于固有应变法预测双丝CO_2气体保护焊液压支架顶梁变形

采用双丝CO2气体保护焊方法焊接30 mm厚Q690D钢板全尺寸液压支架顶梁.基于温度热源和热弹塑性算法对局部顶梁结构焊接变形进行计算,获得焊接固有应变,然后将固有应变施加在全尺寸壳单元顶梁模型上进行弹性计算,最终得到液压支架顶梁结构的焊接变形.结果表明,结合小结构模型的热弹塑性法和大结构固有应变法,能高效预测大型结构的焊接变形且能保证一定精度,预测的液压支架顶梁焊接变形结果与试验结果符合较好;液压支架顶梁的焊接变形主要为角变形,且两侧分布不对称.     

考虑夹具接触约束的FSW焊接变形的固有应变法预测

为高效高精度地预测大尺寸结构FSW焊接变形,基于考虑夹具接触约束的热弹塑性仿真结果,在分析塑性应变的区域分布特点的基础上运用固有应变法进行分区映射,发展了一种有效的焊接变形预测方法.针对小尺寸6061-T6铝合金板材FSW焊接,将接触约束状态和固定约束状态下的焊后变形预测值与实验值进行了对比分析,结果表明接触约束状态的...     

航空发动机转子组件电子束焊变形预测

航空商用发动机组件尺寸精度要求较高,且组件焊接后盘心位置不能进行机械加工,因此采用数值模拟的方法对转子组件进行焊接变形预测. 试验将基于热弹塑性理论计算提取固有应变数值;通过理论计算得到GH4169合金电子束焊缝的固有应变值,分析焊接工艺参数对焊缝固有应变的影响规律;建立结构件模型,分析焊接工艺、焊接顺序及工装条件下组件焊接变形. 结果表明,相比于第一,第二和第三级盘,第四级盘心轴向变形最大,且通过增大扫描速度和改变约束方式的方法可以有效减小焊接变形,从而完成对转子组件焊接变形进行预测和控制.     

Cr2N沉淀相对2101双相不锈钢焊接接头综合性能的影响

对经济型2101双相不锈钢焊接接头1050℃固溶后在700℃进行不同保温时间的时效处理.采用光学显微镜、SEM和TEM观察接头各区域的组织演变,对接头进行低温冲击试验和动电位极化腐蚀试验.结果表明,1050℃固溶处理改善了接头的组织和性能;700℃时效处理后焊缝和HAZ析出Cr₂N沉淀相,随着时效时间延长,沉淀相长大,数量变多并向铁素体内部生长,使接头冲击韧性降低,断口由塑性断裂的韧窝状转变为脆性断裂的解理状;固溶处理试样点蚀发生在铁素体内部,时效处理后点蚀发生在Cr₂N周围的二次奥氏体区,时效时间越长,接头的抗点蚀能力越差.Cr₂N的析出对接头焊缝区的影响最为显著.     

薄板搭接接头固有变形逆解析方法

文中采用变形测试和数值模拟技术相结合的研究手段对低碳钢薄板搭接接头固有变形的求解方法进行了研究,提出了该接头的固有变形分布简化模型,并利用固有变形逆解析方法推定了3 mm低碳钢薄板的固有变形.使用该方法得到的固有变形值来预测焊接变形能较好的再现试验结果.结果表明,采用文中提出的固有变形分布简化模型能获得高精度的固有变形值,搭接接头固有变形的逆解析算法是正确有效的.     

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.     

焊接应力变形原理若干问题的探讨(二)

提出焊接残余应力形成和消除原理:焊接残余应力不是压缩塑性应变引起的,而是由于焊缝和近缝区金属在"力学熔点"及以下温度冷却收缩受阻产生的;消除焊接残余应力不是产生拉伸塑性应变以减少、抵消和补偿压缩塑性应变,而是将残余弹性应变转变为塑性应变;消除焊接残余应力并不是必须去除固有应变,部分去除或完全不去除固有应变也能完全消除残余应力.提出随焊后热精确控制应力变形焊接法,既可实现无应力焊接和无应力无变形焊接,也可实现适当压应力无变形焊接和较大压应力微变形焊接;并对传统方法与有限元法进行了分析比较.     

关于焊接应力应变问题的再探讨

由于认为焊缝存在加热过程和忽视熔化现象的存在,导致传统观点认为的焊缝存在压缩塑性应变的错误.传统观点尚不能解释液化裂纹出现于熔合线处和裂纹很短的现象,用作者给出的高温应变分布图可很好解释.消除焊接残余应力并不是一定要去除固有应变源,有时不去除固有应变源仍可消除残余应力.消除残余应力的过程实质上都是将残余弹性应变转变为塑性应变的过程.     

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.     

薄壁GH3536尾喷管组焊变形控制工艺优化仿真

基于SYSWELD仿真平台,利用热-弹-塑性有限元法和固有应变法进行仿真优化,研究焊接工艺对薄壁GH3536尾喷管组件焊接变形的影响。首先进行平板对接工艺试验和热-弹-塑性有限元仿真计算,对焊接热源模型进行校核,获得不同焊接工艺下典型接头的平均固有应变和修正的材料热膨胀系数。建立全尺寸三维尾喷管组件的焊接有限元模型,基于固有应变理论的弹性有限元方法,利用平板对接获得的材料热膨胀系数,计算焊接工艺参数与焊接约束对尾喷管组件焊接变形的影响。结果表明,焊接电流为40A时,薄壁GH3536平板对接焊接头固有应变值最小为0.00660mm,此时尾喷管焊后变形也最小,为推荐使用的最优焊接工艺。在焊缝、进气口和排气口同时进行夹持,尾喷管焊后变形最小,整体变形1.39mm。     

采用固有应变法预测超薄板的焊接变形

文中以汽车制造中常用的1 mm厚的薄板为分析对象，采用热-弹-塑性有限元分析了焊缝长度对固有变形分布特征的影响，通过比较热-弹-塑性有限元法及固有应变法预测的变形结果，定量分析了焊缝长度对固有应变法预测超薄板焊接变形时计算精度的影响.结果表明，当焊缝长度达到一定临界长度时，固有应变法可适用于板厚为1 mm左右超薄板焊接接头的焊接变形预测.     

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.