Brazing of metals – consumables,technologies and standardisation

For predicting welding distortion and residual stress generated by laser–arc hybrid welding, a series of experiments and analyses were carried out. A bead-on-plate welding was performed on SM490 steel by using a fibre laser and CO₂ arc welding by changing their heat input ratio. The experiment was simulated by thermal elastic–plastic analysis with the proposed simulation model considering the penetration shape by laser and arc separately. By using this model, the experimental results could be simulated with high accuracy. Therefore, the validity and generality of the numerical simulation model could be verified. The tendency and magnitude of angular distortion varied with the heat input ratio of laser and arc. The results indicated the possibility of the ideal heat input ratio of laser and arc for controlling angular distortion generated by hybrid welding. On the other hand, it was confirmed that the heat input ratio of laser and arc did not affect residual stress generated by hybrid welding.     

钛合金带热沉钨极氩弧焊中热沉作用

采用数值模拟和实验相结合的方法研究了钛合金TC4薄板常规及带热沉的钨极氩弧焊焊接过程中温度及应力应变的分布,考察了热沉对温度场和应力应变场的影响规律,探讨了使用该技术实现应力和变形控制的机理.结果表明:带热沉的钨极氩弧焊焊接过程中,紧随热源之后热沉急冷作用使得试件形成马鞍形温度场,而热沉作用部位温度最低.热沉作用部位的急冷收缩对周围金属产生拉伸作用,使得焊缝及近缝区金属升温过程中产生的压缩塑性应变减小,冷却过程中产生的拉伸塑性应变增大,接头中不协调应变减小,残余应力降低.实验测量与有限元模拟结果吻合良好,证实了采用热沉控制应力与变形的有效性和有限元模型的正确性.     

Characteristics of welding distortion/residual stress generated by fillet welding with laser beam and verification of generality of its highly accurate prediction

It was found that the characteristics of welding distortion and residual stress generated by laser beam welding (LBW) had the same tendency as those by arc welding but that the absolute value was small. Moreover, the process of LBW is quite different from that of arc welding, the validity and generality of the dominant factors to predict high accuracy welding distortion and residual stress generated by welding could be verified by the high accurate prediction of welding distortion and residual stress which had been proposed based on arc welding. Inherent force was proposed as a parameter which could indicate the magnitude of compressive residual stress, which might influence the load-carrying capacity. Although inherent forces with LBW were 40% that of arc welding, it was found that control of welding heat input was important so as to improve the load-carrying capacity.     

Numerical simulation about the effect of fixture on the welding stress and distortion of thin aluminum plate joints

The effect of welding jig on the welding stress and buckling distortion of thin aluminum plate joints was simulated by finite element method （FEM）. The results show that the restraint distance and the heat conduction ability of the fixture do have essential effects on the residual stress and distortion. The residual compressive stress and distortion will be increasing with the increase of the restraint distance, while the residual compressive stress and distortion will be decreasing with the increase of the heat conduction ability of the fixture.     

Effect of trailing heat sink on residual stresses and welding distortion in friction stir welding Al sheets

Abstract

This paper investigates a trailing heat sink, which was designed and applied to friction stir welding (FSW) in order to control the residual stresses and welding distortion. Residual stresses, residual plastic strains and welding distortion of 2024-T3 and 5083-H321 Al sheets welded by FSW with and without the trailing heat sink were compared. The optimal placement of the heat sink was discussed. The results revealed that the reductions in peak tensile stresses were 66% for 2024-T3 and 58% for 5083-H321 by application of the trailing heat sink in FSW. In addition, the welding distortion could be reduced drastically by this method. The 5083-H321 sheet with a size of 1000×100×3·5 mm welded by this method was very flat and had almost no distortion. This method achieved in-process control of stresses and welding distortion, without additional complicated work before or after welding operation.     

振动埋弧焊工艺

振动埋弧焊工艺是一种在焊接过程中通过给焊件施加振动来改善焊接性能的新工艺.介绍了在西气东输阀门焊接中运用振动埋弧焊进行厚板焊接的试验,就残余应力、焊接变形、金相三个方面对常规埋弧焊和振动埋弧焊工艺进行比较,对振动埋弧焊工艺进行初步探讨.试验结果表明,振动埋弧焊工艺能有效地降低焊接残余应力和变形,并细化晶粒.     

Stress and distortion mitigation technique for welding titanium alloy thin sheet

Abstract

A stress and distortion mitigation technique for Gas Tungsten Arc Welding (GTAW) of titanium alloy Ti–6Al–4V thin sheet is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch, and it is also called the Dynamically Controlled Low Stress No-Distortion (DC-LSND) technique. The development of this mitigation technique is based on both detailed welding process simulation using the advanced finite element technique and systematic laboratory experiments. The finite element method is used to investigate the detailed thermomechanical behaviour of the weld during conventional GTAW and DC-LSND GTAW. With detailed computational modelling, it is found that by the introduction of a heat sink at some distance behind the welding arc, a saddle shaped temperature field is formed as a result of the cooling effects of the heat sink; the lowest temperature exists in the zone where the heat sink is applied. High tensile action on the surrounding zone is generated by abrupt cooling and contraction of the metals beneath the heat sink, which increases the tensile plastic strain developed during the cooling process and decreases the compressive plastic strain developed in the heating process, and therefore mitigates the residual stresses and plastic strains within and near the weld. The experimental results confirmed the effectiveness of the DCLSND technique and the validity of the computational model. With a proper implementation of the DC-LSND technique, welding stress and distortion can be reduced or eliminated in welding titanium alloy Ti–6Al–4V thin sheet, while no appreciable detrimental effects are caused on the mechanical properties of welded joints by applying the heat sink in the GTAW process.     

Studies on multipass welding with trailing heat sink considering phase transformation

A two pass butt welding of 6 mm mild steel plates was simulated using 3D finite element model using temperature and phase dependent material properties. Material phase transformations were simulated using suitable phase transformation kinetic models. Mechanical analysis is carried out using nodal temperature and phase proportions as input. Experiments were carried out using liquid nitrogen (LN2) as trailing heat sink. Trailing heat sink helped to reduce the residual stress in the fusion zone (FZ) and heat affected zone (HAZ) although distortions were found be increasing. A parametric study was conducted to study the effect of distance between weld arc and trailing heat sink. The heat sink closer to weld arc reduced both distortions and residual stresses.     

Effect of welding conditions on reduction in angular distortion by welding with trailing heat sink

Abstract

The effectiveness of welding with a trailing heat sink in reducing the angular distortion of a weld has been experimentally investigated with focus on the cooling position. A numerical model of welding with a trailing heat sink is constructed through the comparison of measured values of weld penetration, thermal cycles and angular distortion with those calculated. On the basis of this model, the effect of welding heat input conditions on the reduction in angular distortion is discussed to evaluate the versatility of welding with a trailing heat sink. The results indicate that the choice of an appropriate cooling position behind the welding heat source is essential for the effective reduction in angular distortion. The reduction in angular distortion by the heat sink at the appropriate cooling position increases with the heat input parameter Q_net/h, where Q_net is the weld heat input and h is the thickness of the plate.     

Controlling welding residual stress and distortion by a hybrid technology of transient thermal tensioning and trailing intensive cooling

ABSTRACT

A new method of hybrid technology for controlling welding residual stress and distortion is proposed, which contains the transient thermal tensioning with two symmetrical heat sources ahead and the trailing intensive cooling with a cooling source behind the welding heat source during the welding process. Welding temperature, stress and distortion were compared and discussed under different welding processes by experimental and numerical methods. The results reveal that the hybrid technology adjusted the temperature field during welding and redistributed the longitudinal residual stress of welding joint. Thus, the welding residual distortion was reduced. Compared with conventional metal inert gas welding, the reductions of the welding residual stress and distortion of joint by the hybrid technology reached 65% and 58%, respectively.     

动态控制的低应力无变形焊接新技术

在成功地研究并开发了薄壁构件低应力无变形焊接新技术的基础上，把靠预置温度场静态控制焊接应力与变形的方法发展到动态控制法。这一新构思所形成的动态控制焊接应力与变形的新技术的原理在于：不再依赖预置温度场，而是直接利用电弧在薄壁构件上所形成的焊接温度，建立一个特殊构造的热潭跟随电弧，板成“热源－热潭“多源系统，在熔池后的高温焊缝区产生强烈的局部急冷拉伸作用，控制和补偿焊接时产生的压缩塑性变形，达到薄壁构     

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.     

Influence of thickness of flange plate on the reduction of angular distortion by welding with trailing reverse-side flame line

In manufacturing of the steel bridge, fillet welded T-joint is widely used and angular distortion is often generated. So, reduction or control of angular distortion without additional processes to welding is strongly demanded because it takes great time and effort to correct the angular distortion. In this study, the effectiveness of welding with trailing reverse-side flame line heating for preventing angular distortion was investigated through the welding experiment and numerical simulation in submerged arc welding of fillet T-joint with three different thick flange plate. First, the heat source models for numerical analysis of both submerged arc welding and flame line heating were constructed based on the comparison with the measured temperature histories and angular distortion. And then, these heat source models were used in combination with various kinds of distance between two heat sources to make clear the appropriate distance condition for smallest angular distortion was 150 mm, and it does not depend on thickness of flange plate. It was also confirmed that the experimental angular distortions were in good agreement with those calculated. With a focus on the influence of thickness of flange plate, the reduction of angular distortion by welding with trailing reverse-side flame line heating becomes smaller with increasing thickness of flange plate. However, angular distortion could be adequately prevented under the appropriate flame line heating condition in either thickness of flange plate because the welding-induced angular distortion also becomes smaller with increasing thickness of flange plate. Thus, it was concluded that welding with trailing reverse-side flame line heating could be useful for preventing angular distortion of fillet T-joint, which is a component of steel bridge, enough not to correct it after welding.     

焊接电弧热效率的力学测试方法

基于焊接残余应力与外载荷应力叠加产生残余变形的原理，在焊接试件拉伸试验过程中，测量加载、卸载时试件的位移。并通过计算，可以确定焊接电弧的热效率，同时与焊接热源有效利用率的测试计算方法所得到的焊接热效率值进行了比较。研究结果表明，两种方法得到的焊接热效率值十分接近，因而为焊接热过程计算提供了一种新的确定焊接热效率的方法。     

钛合金薄板带热沉的TIG焊温度场

采用数值模拟和试验相结合的方法比较研究了钛合金薄板常规钨极氩弧焊(TIG)及带热沉的TIG焊焊接过程中温度场的形态与演变历史。相对于预置温度场的静态焊接应力和变形控制技术,带热沉的TIG焊接技术又称动态控制低应力无变形焊接技术(DC-LSND,Dynamically controlled low stress no-distortion)。该技术中。在热源之后紧随起冷却作用的热沉装置。研究结果表明。采用DC-LSND技术在热沉附近形成了中间低两边高的马鞍形温度场,热沉作用部位存在温度低谷,该温度区冷却收缩造成对附近高温区的拉伸作用,使焊缝不协调应变减小,焊缝中的残余拉应力降低,防止了焊接变形的产生。对DC-LSND畸变温度场的研究是了解这种方法控制变形机理的前提。     

焊接变形的控制和预防

焊工常常要面对焊接变形问题(焊接电弧产生的热量引起的基板变形).产生焊接变形的原因有多种,最关键的因素并不是结构问题.在此借助于焊接变形定义,提供多种焊接方式引起的焊接变形实例及其控制方式,介绍了焊接变形的各种控制方法.     

焊接过程三维应力变形数值模拟研究进展

焊接非平衡加热、冷却过程导致产生焊接应力与变形，严重影响焊接过程及结构的服役行为，是焊接结构生产制造过程中必须解决的关键技术问题之一。作者对目前国内外焊接过程中焊接应力与变形的数值模拟研究及工程应用进行了分析。结合研究小组的研究工作，对大型复杂结构焊接过程中三维焊接应力变形数值模拟存在的困难、需要解决的主要技术问题进行了评述，并介绍了几个工程应用实例。     

沟槽蒙皮结构激光焊接应力和变形的数值模拟

利用有限元分析软件MARC对"沟槽-蒙皮"结构的激光焊接过程进行三维数值模拟,涉及了激光焊接复合热源模型的确定,热力学边界条件的简化,数值模拟温度场的验证,以及残余变形和应力分布结果的分析和讨论.研究了结构上规则排列的多道焊缝的施焊顺序对焊接残余应力和变形的影响.结果表明,不同焊接顺序所产生的变形态相同,变形量有区别,而残余应力的分布则不同,以由外向中的对称顺序进行焊接时,结构的焊后残余变形最小,残余应力的分布比较均匀,峰值最小.     

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。