Numerical simulation of asymmetric fillet weld pool based on temperature field and flow field coupling

The temperature field and flow field were analyzed to solve the problems of unstable penetration and poor forming quality,which always happen in asymmetric fillet welding. In order to explore the effect of the welding parameters on welding and improve the quality of forming,a three-dimensional mathematical model of asymmetric fillet welding was established by using the finite element software COMSOL and the coupling equation. The model was considered about the surface tension gradient,the electromagnetic force,gravity and the effect of temperature,radiation and convection heat on physical properties of the material. The flow field and the growth pattern of the weld pool were analyzed,and the weld pool geometry under different welding currents was compared. The results show that,the thin metal was preferentially penetrated,and with the welding process the weld width expanded until the weld beam was fullpenetration. The heat affected zone was got from weld experiments,its shape and size agreed well with the simulation results,which verifies the validity of the theoretical analysis.

Numerical study of fillet weld leg height of sleeve repair welding for in-service pipeline

This paper presents a mechanical calculation and numerical simulation of the fillet weld of sleeve repair.The mechanical analysis based on the yield criteria is performed to obtain the minimum value of the fillet weld leg height to ensure the strength and loadbearing capacity of the weld. Within the framework of numerical simulation,the parameters of double ellipsoid heat source are determined by fitting method and the simulated molten pool morphology agrees well with the practical weld. Finite element models with various weld leg height are performed to predict the distribution and magnitude of the deformation and stress. The simulation takes into account thermal,metallurgical and mechanical factors,and the maximum value of the fillet weld leg height is obtained based on the magnitude of the deformation and stress.The mechanical calculation and numerical simulation results show that 1.2-2 times wall thickness is an optimal range of fillet weld leg height. And reasonable parameters of sleeve repair for in-service welding are provided for engineering field,which can improve the service life of the weld and production efficiency.

Polarities effect on arc interference in triple-electrode CO2 fillet welding

The occurrence of arc interference between the adjacent arcs becomes an important problem in triple-electrode high speed CO2 fillet welding. To clarify this problem, polarities effects on arc interference were investigated. The experimental results and theoretical analysis showed that the reverse magnetic field generated by the middle wire （ DCEN or DCEP ） decreased the arc deflection due to arc interference. The average arc voltage fluctuations induced by DCEP/DECN/DCEP and DCEN/DCEP/DCEN were smaller than those induced by the other polarities.

Evaluation model for arc fluctuations of triple-electrode high speed fillet welding

To improve the welding efficiency of conventional arc welding, triple-electrode fillet welding was proposed and developed. Stability of triple-electrode fillet welding process is the assurance for ideal joint. The evaluation model for arc fluctuations of triple-electrode fillet welding was established based on the characteristic parameters and their variation coefficients. This model indicated that variation coefficients could reflect arc voltage flnctuations of welding process, and its analysis result was consistent with the actual welding process.

Experimental study on the shear strength of side fillet weld of Q235B steel post high temperatures

In order to learn the variation laws of shear strength of side fillet weld post high temperatures, the tension tests were conducted after the double-strapped side fillet welded joints which were cooled down from different high temperatures with different cooling patterns. The tests indicate that specimens appear brittle fracture at the side fillet weld during the tension tests after cooling down. The fracture su（face is located in the welding throat. The maximum temperatures undergone and the cooling pattern are major factors influencing shear strength of side fillet welded joint post high temperatures. The shear strength reduces by 24% at most within 900 ~C. Based on the experimental results, the calculation formulas of shear strength of side fillet weld post high temperatures were proposed. Conclusions supply references for evaluation damage and reinforcement of steel structure post fire.

THE EXACT SOLUTION OF STRESS DISTRIBUTION IN FILLET WELDS

The exact solution of stress distribution in fillet welds under the action of bending moment M is presented in this paper. Together with the exact solution of stress distribution in fillet welds under the action of concentrated force P given in an earlier paper([1]), designers of weldments can improve their work on the foundation of exact analytical solutions.

Reduction of Undercuts in Fillet Welded Joints Using Taguchi Optimization Method

This project work focuses on the reduction of weld undercuts using the Taguchi method. The phenomenon of weld undercuts constitutes a major problem for the welding industry. When undercuts occur, and particularly when such cuts are deep, it has a negative impact on the weld as it lowers the integrity and quality of the weldment. Therefore, efforts are made globally to reduce the depth of such weld undercuts to the barest minimum. Several optimization methods have been adopted;however, in this study, the Taguchi method is applied. “The smaller the better components” of the Taguchi method is applied. From the results obtained from applying this Taguchi method, the optimum process parameters obtained are A2-B1-C2, which are a voltage of 20 V, a current of 180 A, and a welding speed of 130 mm/s, required to form an undercut of 0.03 mm. Whereas the existing process parameters used by the company are A1-B3-C, which make an undercut to a depth of 0.09 mm. It is concluded that the use of Taguchi method has been able to reduce the depth of undercut as shown in this study. A step-by-step approach is presented in the study.

Calculation of the Strengths of Jointswith Fillet Welds in Welded Structure

In the paper, the finite element method (FEM) , engineering calculationmethod (ECM) and empirical fromular method (EFM) were used to calculatethe strengths of fillet joints in an Al-alloy vehicle. The results obtained withdifferent calculation methods were analysed, and then each method wasreviewed and assessed. FEM is accurate, but complicated, and its results haveno strength reserve; ECM and EFM are simple and convenient, butconservative.

压力容器小径支管角焊缝相控阵检测埋藏缺陷回波特性研究

采用CIVA仿真软件对实际规格的压力容器小径接管角焊缝模型进行了仿真分析,研究了球孔、横通孔、未熔合、未焊透和裂纹等典型缺陷的回波响应规律及特征,结果表明,相对于端角结构信号,不同缺陷的回波强度不同,面积型缺陷与声束角度90°时回波强度最大,同一类型缺陷位于不同位置时的回波强度差距明显,最大达到了13 dB。设计加工了典型缺陷的模拟试件,对5种典型缺陷的检测结果开展了试验分析,结果表明,试件中的缺陷均可被有效检测。总结了不同缺陷的回波特性变化规律,可为现场检测中的缺陷定性提供参考和依据。

局部干法水下激光焊接装置研制及工艺试验

针对核电站乏池边角位置的水下修复需求,研制了一套局部干法水下激光焊接装置,可在实现常规水下平焊位置焊接的同时,重点兼顾角焊缝的局部干法水下焊接作业需求。同时,该装置还具备水下焊接位置的照明、焊接环境和焊接过程的实时监控、焊接区域的温湿度监测等功能。采用研制的局部干法水下焊接装置,对核电站乏池常用的304不锈钢材料进行了水下焊接工艺试验,结果表明:水下焊接焊缝的成形良好,水下焊缝的宏观形貌、截面形貌和金相组织与空气环境成形焊缝无显著差异。

航空发动机叶片微束等离子堆焊转角焊缝模型研究

航空发动机叶片修复时,将受损部位切除后在新平面上进行多层多道焊接,在焊缝转角区域特别是转角点,因焊接工艺难以匹配导致过多熔滴进入熔池增加了焊缝熔高与熔宽,造成焊缝凸起,影响焊接质量。针对微束等离子焊接叶片转角区域焊缝的这种特征,建立了转角区域焊缝模型。首先利用抛物线曲线拟合建立了单道焊缝模型,并通过实验验证该模型能准确地表征单缝外形轮廓。然后提出了一种双焊缝转角重叠的焊缝成型模型。实验表明,采用该转角焊缝模型能够极大地降低转角区域焊缝的凸起,能满足航空发动机叶片修复精度的要求。

激光-MIG复合角焊缝成形工艺研究

目前,复合焊接技术研究多关注于薄板拼接焊,角焊缝焊接仍采用单热源,焊缝成形效果差。针对8 mm厚的Q235低碳钢板角焊缝,研究了激光-MIG复合焊接时,各工艺参数对角焊缝成形尺寸及熔池状态的影响。结果表明:MIG弧焊熔池飞溅较大,焊缝熔深、熔宽均较小,加入激光热源后,激光对电弧有一定的稳定作用,熔深、熔宽均增大,余高减小。弧焊熔池尺寸随电流增大而增大,当激光熔池与弧焊熔池耦合较好时,有利于稳定熔池、减少飞溅;随热源间距增大,熔滴不再滴入激光作用区,耦合作用下降;随焊接速度提升,热源在单位长度焊缝作用时间变短,熔深、熔宽下降。当激光功率为1.5 kW,焊接电流为220 A,热源间距为2 mm,焊接速度为600 mm/min时,弧焊熔池与激光熔池耦合好,熔池最为稳定,焊缝成形最佳。

旋风分离器管屏智能焊接设备的开发与应用

针对目前旋风分离器管屏角焊缝采用机械龙门焊或手工焊接,存在焊缝质量差、焊接飞溅多和焊工作业环境差等问题,设计开发了一种旋风分离器管屏机器人智能焊接设备,可实现对管屏角焊缝的自动定位、自动起弧、自动调整焊枪姿态、自动焊接的全过程智能化控制。对其硬件系统、软件系统和辅助装置进行了介绍,并设计了管屏焊接工艺流程。焊接工艺试验和应用结果表明,设备运行稳定,激光寻位准确,焊缝成形良好,焊接飞溅少,烟尘处理效果好,焊角尺寸满足标准要求,焊接速度可达800 mm/min以上,焊接综合效率提高40%以上。旋风分离器管屏智能焊接设备实现了管屏角焊缝的自动化焊接,提高了焊接效率,降低了劳动强度,改善了作业环境。

钛材阀门角焊缝连接件焊接性能研究

阀门焊接结构中角焊缝连接件的焊接难度较大,通过对TA2阀门氩弧焊角焊缝焊接性试验研究,解决阀门TA2角焊缝焊接的技术难题.

单道角焊缝焊接工艺的试验研究

核岛安装现场涉及角焊缝焊接的工作量非常大,角焊缝焊接工艺评定的完成是保证现场角焊缝焊接进度及质量的关键性因素。主要针对现场工艺评定过程中单道角焊缝屡次存在的未焊透缺陷,从人、机、料、法、环五个方面分析讨论,并制定相应纠正措施进行试验验证,提高角焊缝焊接宏观腐蚀试验合格率,以保证现场角焊缝焊接工作的顺利进行。

石化装置小接管隐患分析及检测与管理对策

由于石化装置小接管结构独特,服役环境恶劣,在其设计制造、焊接安装、检验检测和运行管理方面存在很多问题,与设备及管道本体相比,小接管更容易发生腐蚀破坏,形成安全隐患,小接管已经成为石化装置腐蚀和安全管理中的重点和难点。该文分析了石化装置小接管的结构特点和服役环境,从设计、制造、安装和运行等四个方面对常见的小接管隐患问题的来源进行了阐述;并根据具体隐患问题来源提出了相应的管理建议和检测措施,从而减少了事故隐患,保障了石化装置的安全运行。

结构件角焊缝表面参数检测算法研究

针对多种类结构件角焊缝特征曲面变化小,设计了一种基于线激光的角焊缝检测方法。利用机器人搭载线激光相机扫描焊缝获取点云,预处理后采用确定随机种子的RANSAC算法分割,基于最小二乘算法拟合母材平面与焊缝二次曲面,提出一种基于临域迭代均值法求取焊趾方法,计算角焊缝特征。以角焊缝工件作为实验对象,与传统结构光角焊缝检测算法对比,结果表明,该算法可以将检测进度误差控制在0.1mm以内;且重复检测偏差在±0.03mm,具有较好的准确性与稳定性。

储罐大角焊缝结构多参数响应面优化分析

为有效降低储罐大角焊缝结构处的应力强度水平,将GB 50341—2014《立式圆筒形钢制焊接油罐设计规范》中只给出取值范围的边缘板外伸长度、边缘板内伸长度、大角焊缝在罐壁内侧的焊缝长度设置为输入可变参数,将大角焊缝结构处的最大应力强度设置为输出参数,优化目标设置为大角焊缝结构处的最大应力强度最小。经ANSYS响应面优化分析,最大应力强度在选择不同的结构参数时变化范围较大,优化分析可以确定出多参数的最佳组合,提出了优化和结果选择建议。

散货轮甲板角焊缝失效原因分析

利用无损探伤、光学显微镜、扫描电镜和EDS能谱仪等检测仪器,分析了开裂的甲板角焊缝的宏观形貌、显微组织、断口形貌及化学成分。分析结果显示:甲板角焊缝裂纹断面无金属光泽,伴随有高温氧化色,且内部有较多夹渣;在裂纹断面发现大量淤泥状液态薄膜,液态薄膜中富集低熔点的硫化物。因此该裂纹属于典型的热裂纹。焊接工艺实施不当,是导致该角焊缝产生裂纹的主要原因。

超超临界锅炉集箱角焊缝开裂分析及优化

针对某电厂超超临界锅炉延伸侧墙出口集箱角焊缝开裂的问题,从材料成分、显微组织、硬度测试及运行工况等方面综合分析该集箱角焊缝失效的原因,并且从焊接工艺、热处理工艺及焊缝形式出发综合提出优化方案。结果表明:集箱管材料为12Cr1MoVG,失效集箱角焊缝的化学成分、显微组织及硬度均符合标准,裂纹起裂于角焊缝外表面,并向内表面扩展。开裂原因为焊接残余应力与服役过程应力产生复杂叠加。通过采用降低角焊缝处应力集中的优化措施,延长材料使用寿命,可以为同类型电站锅炉管道的日常监督与质量控制提供重要的借鉴。