基于SYSWELD的焊接工艺参数对多道焊焊接残余应力的影响

文章以某型动车组中间车KK端中T型焊接接头为例,通过数值仿真,分析了不同预热温度与不同焊接速度对焊接残余应力的影响。利用双椭球形热源模型校核得到了与实验拟合度较好的温度场,保证了后续计算焊接残余应力的准确度。通过三种多道焊速度方案,计算T型焊缝焊接残余应力可知:在给定的预热温度前提下,在一定范围内减小焊接速度,可减小焊缝残余应力;分析了预热温度对焊接残余应力的影响,在一定范围内提高预热温度,可以有效地降低焊接残余应力。     

奥氏体不锈钢纵向焊接残余应力分布的有限元模拟

以LED集鱼灯基板与灯壳的搭接接头为例,建立了热力学耦合的三维有限元模型,运用SYSWELD焊接专业软件,对316L奥氏体不锈钢薄板焊接件在不同焊接条件下纵向残余应力分布进行有限元模拟与分析,研究了预热温度和焊接顺序对纵向残余应力分布的影响,并将模拟结果与实测结果进行了对比。结果表明:采用预热可以有效降低焊接件的纵向残余应力;随着预热温度的升高,纵向残余应力降低;焊接顺序对纵向残余应力的影响不大;模拟结果与实测结果比较吻合,验证了计算用模型的准确性。     

钛合金薄板激光焊接和TIG焊接残余应力数值模拟

基于有限元分析软件ANSYS，以激光焊接和TIG焊接温度场模拟为基础，对钛合金薄板的焊接残余应力进行了数值模拟，并分析了不同焊接工艺参数对激光焊接和TIG焊接残余应力分布的影响。数值模拟中考虑了材料参数的温度相关性，并与小孔释放法测试的焊接残余应力进行比较，结果表明：计算结果和测试结果吻合较好。     

钛合金大厚度试件电子束焊接残余应力有限元分析

基于热弹塑性有限元理论,建立了钛合金大厚度试件电子束移动热源的焊接残余应力三维数值分析模型,分析研究了厚度为75 mm的TC4电子束焊接试件残余应力分布规律。计算结果表明,大厚度电子束焊接试件在焊缝及其附近宽度约40 mm的范围内存在极其复杂残余应力,试件表面的焊缝及其附近20 mm左右的区域存在着对结构强度有利的横向残余压应力,但试件内部残余应力水平要高于表面的残余应力,尤其是在距起始和收尾端10mm及约1/4厚度处的区域,存在着三向的残余拉应力,且数值较高,对钛合金平板电子束焊接接头力学性能将具有重要影响,应引起足够的重视。钛合金平板电子束焊接残余应力的计算结果与实测结果基本一致。     

紫铜板搅拌摩擦焊接温度场有限元分析

FSW传热过程直接决定工件所经历的热循环,进而影响焊接接头的微观组织和力学性能。同时温度场的分析对于预测接头残余应力和变形,以及焊缝区硬度都具有重要意义。本文在工艺研究基础上,分析了FSW的产热过程;根据搅拌头形状与尺寸,建立了FSW三维传热有限元模型。使用Ansys有限元分析软件,结合有限几个测量点温度变化的实验数据,对6 mm厚度紫铜板FSW焊接过程的温度场进行了有限元分析和计算,获得了该焊接过程的温度场分布与变化规律。计算过程中考虑了工件下表面与支撑板接触热传导对温度场的影响,以及温度对紫铜材料热传导系数的影响,有限元计算结果与实验测量结果接近。     

基于显微照片的增层模型涂层温度场模拟

熔射成形中涂层的使用性能与其残余热应力密切相关,而残余热应力则是由于沉积过程中温度场分布不均匀导致的,因此,研究涂层温度场是分析其残余热应力的基础。针对现有涂层沉积温度场模拟普遍采用的增层模型不能考虑涂层孔隙的缺陷,提出一种基于显微照片的含孔隙涂层生长增层模型,并使用该模型对其温度场进行模拟。计算结果表明,孔隙不仅对沉积过程中的涂层温度场具有重要影响,而且对基体温度场也有影响。涂层中靠近孔隙的位置其温度下降比远离孔隙位置更慢,且沉积初期这种差异更明显。含孔隙涂层温度场的模拟为含孔隙涂层残余热应力的研究及涂层起翘、开裂和剥落等失效机理的分析提供了基础。     

基于单元生死焊接温度场应力场模拟研究

在用有限元进行焊接温度场的数值计算中，通过“控制单元的生死”来模拟焊缝的形成和焊接热量的输入，利用计算结果对焊接结构的温度场及残余应力进行分析，模拟结果与实测结果吻合较好，表明本计算方法能够准确计算焊接温度场，是一种实用的工程计算方法，对于优化焊接工艺设计具有较好的指导作用。     

高强钢T形接头焊接残余应力的数值模拟

焊接过程中不均匀的温度场及局部塑性应变导致了残余应力的产生,从而影响焊接结构的疲劳强度及承载能力.应用ABAQUS的焊接子程序DFLUX,结合单元“生死”技术对高强钢焊接流程进行数值分析.获得了焊接温度场和应力场的动态变化过程,计算出焊接温度场及残余应力的分布,绘制出焊接残余应力分布曲线,为优化焊接工艺,控制焊接残余应力提供理论依据.     

钢件淬火过程温度场的数值模拟

利用ANSYS软件的热分析模块对某钢件淬火过程进行建模、分网、加栽及求解,得到了钢件淬火不同时刻的温度场、在某一时刻沿钢件内壁温度分布,以及钢件上所选特殊点的温度分布;同时还建立了淬火过程的数学模型。模拟过程对于淬火液的选取及淬火工艺的优化提供了参考依据,对淬火过程中的热应力、残余应力计算提供了温度边界条件。     

多道焊三维残余应力场有限元模拟

运用大型有限元计算软件ABAQUS，对316L不锈钢平板多道焊接头的温度场和残余应力场进行模拟。有限元模型中选用三维实体单元，考虑材料物理性能随温度的变化和周边对流、辐射散热的影响。运用内生热的加载方法模拟焊接热源，运用单元激活技术模拟多道焊焊接过程。获得了三维多道焊焊接温度场和残余应力场，并对计算结果进行分析。     

Investigation on the process of laser surface melting using two sequential scans

Laser melting as a flexible and economical surface treatment technology is of significant value to industries. Many efforts have been taken on purpose to gain such desired machining goals and reliable service performances; yet, beneficial and efficient melting strategy is still needed. In studies of some other processes such as multi-pass laser cladding, it is found that the preheating effect of a previous scan can contribute to achieve better results like increasing dilution and improving thermal stress status. Hence in this investigation, for laser surface melting with single track, a helpful preheating process is performed by proposing an approach of using two sequential scans and the effects of preheating laser are further clarified. To this end, a three-dimensional non-linear, indirectly coupled thermal?Cstructural model for the sequential combined process is established accounting for temperature dependency of material properties. Then, investigations are carried out to examine temperature and residual stress fields under different preheating laser power and interval distance. The results show that this melting strategy can improve the residual stress distribution state. In addition, a high thermal stress distributes between two scans and the tensile stress component is released by rapid two-time fusions. Besides, the different combinations of preheating parameters take diverse effects on heat-affected and -remelted zone as well as residual stress distribution.     

热辐射处理制备VC涂层的温度-应力场有限元分析

利用ANSYS有限元软件对热辐射处理制备VC(碳化钒)涂层进行建模,分析了涂层厚度、加热温度及加热时间对VC涂层温度场-应力场的影响规律。结果表明,不同温度下涂层沿x轴方向温度变化的趋势均呈上升趋势;涂层最高温度(837℃)与加热温度(850℃)相差15℃左右,温度差值约1.52%;不同厚度下温度的变化趋势均为递减,当厚度为6μm时,温度递减的趋势较平稳,未出现峰值,当涂层厚度增加时,应力值先增加然后减小,在厚度为6.3μm时发生突变,而后呈递增趋势;考虑应力、厚度因素对涂层性能的影响,涂层最佳厚度应为5～6μm。     

Study on strengthened layer of workpiece in prestress dry grinding

The prestress dry grinding which combines with prestress grinding and surface strengthening is an innovative approach to substitute conventional grinding process. The residual stress and the thickness of strengthened layer have an important effect on surface performance of workpiece. In order to analyze the effect mechanisms of prestress on residual stress and thickness of strengthened layer, experiment and simulation are carried on for 45 steel. The result of prestress dry grinding experiment shows that the grains in the strengthened layer are refined with increase of prestress. The thickness of strengthened layer tends to decrease first and then increase with increase of prestress. The simulation model of temperature field is created. The effect of temperature field on the thickness of strengthened layer and different grinding parameters especially the prestress on temperature field are analyzed. Then, the relationship between prestress and residual stress on different directions are analyzed. The variation curve of residual stress shows that tensile residual stress can transform to compressive residual stress on the surface of workpiece by controlling the prestress. Besides, compressive residual stress increase first and then decrease with the increase of depth.     

The effect of DSAW on preheating temperature in welding thick plate of high-strength low-alloy steel

Double-sided double arc welding (DSAW), a high efficiency method requiring no back chipping for welding thick plate of high-strength low-alloy steel was used in this study. Gas metal arc welding is employed for backing run and filler passes. The effect of DSAW on preheating temperature is investigated. Meanwhile, numerical simulation has been performed to predict transient temperatures, which are in good agreement with the experimental results. The critical stress in DSAW without preheating is 528.31 MPa, while in conventional welding with 100 °C preheating temperature, it is 393.44 MPa. The higher critical stress implies that the samples in DSAW without preheating have better cold crack resistance than those in conventional welding with 100 °C preheating temperature. Y-slit type cracking test indicates that the samples welded by double-sided double arc demonstrate better cold crack resistance than conventional welding at the same preheating temperature. Therefore, DSAW can realize welding thick plate of high-strength low-alloy steel with lower preheating temperature or even without preheating.     

Effects of different restraints on the weld-induced residual deformations and stresses in a steel plate

Effects of three different plate boundary constraints on the residual stress field and deformation are investigated numerically during butt-joint welding. For the numerical solution of the heat transfer equations, the finite element method is used to predict the temperature profile as well as residual stress field due to three different plate boundary conditions. The distortion of the welded plate is modeled as a nonlinear problem in geometry and material, adopting a finite element solution based upon the thermo–elastic–plastic large deflection theory. High-strength shipbuilding steel AH36 with temperature-depending material properties and nonlinear stress–strain material properties (bilinear isotropic hardening option uses the von Mises yield criteria) are assumed for the numerical analysis. For verifying the results, the temperature profile is compared with the result obtained in a previous research. In the mechanical analysis, three different boundary conditions are applied. Effects of plate thickness, plate width, and mesh model on the residual stress with boundary constraint are studied.     

球罐环焊缝接头残余应力的三维非线性有限元分析

建立了球罐环焊缝焊接温度场和焊接应力应变场三维移动热源有限元分析模型,考虑了材料的热物理性能和力学性能随温度而变化,应用单元生死技术模拟焊接填充过程,模拟计算出移动热源作用下的温度场,以及以温度场为基础的环焊缝接头焊接应力应变场的分布规律:温度场结果表明,由于焊接的热输入和速度不同,以及热源加载体积不相等,每道焊接的最高温度均不相等。应力场的分析结果表明,在球罐内表面的焊缝及近缝区,呈现双向残余拉应力(经向和周向),而在外表面的对应区域,经向残余应力是压应力,周向残余应力为拉应力。     

刹车盘成形热结构耦合分析

在有限元软件ANSYS中采用正交实验的方法确定了刹车盘成形的最佳温度参数为：浇注温度710℃、模具预热温度150℃、冷却水温度50℃。并用ANSYS对刹车盘成形过程的相变及热结构耦合进行了分析,得到了刹车盘毛坯和模具的温度场、应力场和变形。     

Experiment research on grind-hardening of AISI5140 steel based on thermal compensation

The grind-hardening process utilizes the heat generated to induce martensitic phase transformation. However, the maximum achievable harden layer depth is limited due to high grinding forces, and the tensile residual stress appears on the ground surface in the grind-hardening process. This paper proposes a new grind-hardening technology using thermal compensation. The workpiece of AISI5140 steel is preheated by electric resistance heating, and ground under the condition of the workpiece temperature 25°C, 120°C, 180°C and 240°C. The grinding force, harden layer depth and surface quality including residual stress on ground surface, surface roughness and micro-hardness are investigated. The experimental results show that a deep harden layer with a fine grain martensite can be obtained with the thermal compensation. The ground workpiece surface produces a certain compressive residual stress, and the residual compressive stress value increases with preheating temperature. As the preheating temperature increases, grinding force slightly decreases, while there is slightly increment of surface roughness. Compared with the conventional grind-hardening process, both the harden layer depth and residual stress distribution are significantly improved.

     

Thermo-mechanical coupled 3D-FE modeling of heat rotary draw bending for large-diameter thin-walled CP-Ti tube

The heat rotary draw bending of large-diameter thin-walled (LDTW) commercial pure titanium (CP-Ti) tube is a highly nonlinear thermo-mechanical coupled physical process. Developing a reliable finite element (FE) model for this process is an effective way to investigate the heat loading and the complex bending behaviors. In this study, considering the characteristics of multi-die constraints and local heating, a thermo-mechanical 3D-FE model was established for preheating and heat bending of LDTW CP-Ti tube in terms of both accuracy and efficiency. First, using the static implicit algorithm, a preheating model was developed to predict the temperature distribution of bending tools. In this model, the key issues such as the full-sized geometry modelling, thermal interaction definition, and automatic heating control were solved to increase the simulation accuracy and efficiency. Then, introducing the predictions of preheating model and using the dynamic explicit algorithm, a thermo-mechanical coupled 3D-FE model was established for the heat bending simulation via the geometry modelling simplification, temperature definition of bending tools, realization of non-uniform temperature distribution, etc. Considering the temperature history of bending tools and wall thickness changing of bent tube, the reliability of preheating model and heat bending model was verified by several experiments. The results showed that the maximum relative errors of both predicted temperature and wall thickness changing degree were less than 9 %. Based on the reliable models, the effects of preheating temperature on the temperature distribution of bending tools and wall thickness changing of tube were numerically evaluated. The established model provides the scientific basis for the prediction and control of bending qualities of the heat RDB process, and the modeling method is also of general significance to the other heat-aided forming process.     

激光熔覆成形预热基板设计及试验研究

为了降低激光熔覆成形过程中熔覆层热应力和减少裂纹的产生,以热传导理论和激光快速成形理论为依据,进行了预热基板的结构和控制设计;并进行了不同预热温度下单道熔覆和平面熔覆的试验研究.结果表明,通过智能PID控制器可对预热温度进行良好控制,通过热电偶温度采集模块可以实现对基板预热温度的连续、实时检测;在基板预热条件下进行激光熔覆成形可以显著改善试样的成形质量,并有效降低成形过程的热应力,减少了熔覆层裂纹的产生.