铝锂合金电子束焊接数值模拟分析及工艺优化

采用组合热源模型对Al-Li合金电子束焊接温度场分布进行数值模拟分析,通过热-力耦合,模拟计算得到接头区域的残余应力分布.结果表明,Al-Li合金电子束焊接温度场沿焊接方向呈椭圆形分布,电子束热源中心的温度最高,其附近区域的等温线分布密集,随着与热源中心的距离增大,等温线分布逐渐稀疏,焊缝区存在较大的温度梯度,较好地模拟出了电子束焊缝的钉形分布特征.接头的残余应力分布模拟结果显示,残余应力主要集中于焊缝区,由于修饰焊的热作用,焊缝上部具有相对较大的应力值.利用模拟计算得到的结果进行焊接工艺及参数优化,焊接工艺试验表明,试验焊缝形貌与模拟熔池形貌相吻合,进一步验证了模拟计算结果的可靠性.     

A temperature dependent slip factor based thermal model for friction stir welding of stainless steel

This paper proposes a new slip factor based three-dimensional thermal model to predict the temperature distribution during friction stir welding of 304L stainless steel plates. The proposed model employs temperature and radius dependent heat source to study the thermal cycle, temperature distribution, power required, the effect of process parameters on heat generation per mm length of the weld and peak temperature during the friction stir welding process. Simulations of friction stir welding process were carried out on 304L stainless steel workpieces for various rotational and welding speeds. The predicted thermal cycle, power required and temperature distributions were found to be in good agreement with the experimental results. The heat generation per mm length of weld and peak temperature were found to be directly proportional to rotational speed and inversely proportional to welding speed. The rate of increase in heat generation per mm length of the weld and peak temperature are found to be higher at lower rotational speeds and lower at higher rotational speed. The heat generation during friction stir welding was found to be 80.8 % at shoulder, 16.1 % at pin side and 3.1 % at the bottom of the pin.     

U肋加劲板焊接残余应力数值模拟分析

通过数值模拟和实验方法对U 肋加劲板焊接残余应力进行了估算和分析,建立了三维热弹塑性有限元模型,采用生死单元法模拟焊缝填充和焊接热输入过程,实现了整个焊接过程中的动态应力和变形变化,得到了U肋加劲板的焊接温度场和应力场,分析了U 肋加劲板的焊接残余应力分布,并与残余应力测试试验结果比较.结果显示:U 肋加劲板近焊缝区残余拉应力达到材料屈服强度,母板远离焊缝区残余压应力平均值约为材料屈服强度的0.2 倍,其分布趋势与实验测试得到的残余应力分布比较接近,证明了所采用的焊接数值模拟方法的正确性.     

基于ANSYS 的D500 钢激光焊接温度场数值模拟

目的研究D500钢激光焊接温度场的变化。方法运用ANSYS有限元分析软件,以5 mm厚D500钢为研究对象,采用均匀分布的柱体热源与椭球热源组合的方法,建立了激光焊接热源模型。对D500钢激光焊接温度场进行了模拟计算,并与实验所得焊缝形状及尺寸进行了比较分析。结果结果表明,数值模拟所得焊缝截面尺寸与实验结果一致性达到95%以上。结论验证了柱体热源与椭球热源的组合热源模型在D500钢激光深熔焊接温度场模拟中的适用性,从而为不同焊接工艺条件下D500钢激光焊接焊缝形状和尺寸的预测,提供了一种有效的途径。     

等离子弧焊接熔池和小孔形成过程数值分析

目的 研究等离子弧焊接穿孔过程中熔池内部的金属流动情况和小孔动态变化过程。方法 通过“传热-熔池流动-小孔”之间的相互耦合关系,建立了等离子弧焊接穿孔过程的数值分析模型,通过VOF方法追踪了小孔界面,采用FLOW-3D软件模拟了等离子弧焊接熔池和小孔的形成过程,定量计算了等离子弧焊接温度场、熔池流场及小孔形状;分析了等离子弧焊接熔池和小孔行为;并通过等离子弧焊接实验数据验证了模拟结果。结果 当焊接时间为0~1.0 s时,小孔深度曲线与熔深曲线几乎相同,小孔底部紧贴熔池底部;在2.8 s以后,小孔深度曲线与熔深曲线有一定距离,小孔深度曲线在一定范围内波动,等离子弧焊接电弧挖掘作用到达极限,电弧压力与其他力达到平衡状态。模拟的焊缝熔深为8.04 mm、熔宽为13.20 mm,实验测得的焊缝熔深为8.00 mm、熔宽为13.42 mm。结论 构建的随小孔动态变化的曲面热源模型和电弧压力模型可以描述等离子弧焊接过程中的电弧热-力分布;模拟出了等离子弧焊接熔池和小孔动态演变过程;模拟得到的等离子弧焊接焊缝形貌与实验测得的焊缝形貌基本吻合。     

高强钢激光电弧复合焊接温度场的数值模拟与试验研究

目的 对厚度为12 mm的HG785D高强钢进行复合焊接,获取最佳焊接工艺参数,建立适用于激光-MIG(Metal Inert Gas Welding)复合焊接的热源模型.方法 采用激光-MIG复合焊接方法进行焊接试验,建立适用于HG785D高强钢激光-MIG复合焊接的"高斯锥形体+均匀锥形体+高斯柱形体"复合热源模型...     

等离子+缆式焊丝脉冲GMAW复合焊熔池流体行为研究

目的 研究等离子+缆式焊丝脉冲GMAW复合焊过程的熔池流体行为.方法 综合考虑传热学以及流体动力学,建立Fluent数值分析模型.使用双椭球–锥体热源模型代表等离子弧焊传热模型,用双椭球热源表征GMAW电弧传热并考虑熔滴传热,同时考虑熔池受到的电磁力、浮力、表面张力、等离子流力等作用力.基于Fluent软件,对复合焊过...     

Solidification behaviour in plasma are welding

Melting and solidification behaviour in the deep penetrution welding process is different from that in conventional welding process in deep penetration processes there is keyhole formation and the full thickness of the plate receives the are heat input unlike conventional processes in which the heat input is received only by the surface nodes. In the present study, the thermal analysis of molten pool formation and solidification keyhole welding using plasma are welding has been done using the finite element method. The model accounts for the several phenomena associated with welding, like the distributed are heat input over the top surface and along the thickness, the temperature-dependent material properties. convection and radiation heat losses etc. The analysis is performed for different combinations of parameters. viz welding current and welding speed, which have the maximum influence on molten pool shape and solidification behaviour. The model has also been validated by conducting experimental measurement of thermal cycles experienced by the plate for different welding parameters. The weld pool dimensions. viz. the length and widlh are found to increase with inincreasing current and decereasing welding speed. Thermal cycles at locations close to the weld reach a higher value of temperature and the time for peak temperature is also less but at farther locations the peak temperature reached is lower and the time for peak temperature is higher. Details of the model, the experimental results obtained and the solidifications charateristics of the pool are discussed in this paper.     

Influence of focusing thermal effect upon AZ91D magnesium alloy weld during vacuum electron beam welding

The influence of focusing thermal effect upon the weld shape, microstructure and alloying elements distribution in the welded joints during vacuum electron beam welding on AZ91D magnesium alloy was studied. The results show that the focus state affects the offset of DOF, and further significantly affects the actual welding heat input in the process of vacuum electron beam welding. The sharp focusing state is characterized with higher welding energy density, but the welding energy density of defocusing state is lower. Therefore, the welding process with sharp focusing state and smaller calculation welding heat input can obtain the same weld penetration as the welding process is the conditions of defocusing state and larger calculation welding heat input. And the welding process of sharp focusing state and smaller calculation welding heat input can induce more strongly burning loss of Mg element than the conditions of defocusing state and larger calculation welding heat input. Then, which will affect the distribution of alloy elements in weld seam.     

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn₂ .     

初始应力对三维光学轮廓法测试焊接接头残余应力的影响

目的研究不同初始应力状态下,三维光学轮廓法测试焊接接头残余应力的变化规律。方法采用MIG焊分别对供货态与去应力退火态试板进行多层多道焊,焊后试板经慢走丝切割,经三维光学测量技术扫描切割面轮廓,将所得轮廓数据经所建立的数据处理平台处理,将其结果作为有限元计算的边界条件,经应力反算得到残余应力分布。最后再进行有限元模拟,计算焊接接头残余应力。结果含初始应力、去应力退火和数值模拟的焊缝中心均为拉应力区,最大拉应力分别为480, 450, 523 MPa,且都位于焊缝根部区域。三者试板两侧为压应力区域,最大压应力分别为380, 280, 157 MPa,三者数值相差较大。结论将含有初始残余应力试板、退火处理试板与数值模拟结果的残余应力分布进行对比,可以发现三者在焊缝中心处的残余应力分布较为一致,但沿着焊缝向两侧的区域内,应力差别逐渐变大。主要原因为焊接热循环温度高于金属再结晶温度时可以消除部分残余应力,而温度循环较低时对应力消除不明显,导致实验结果相差较大。     

HAZ microstructure simulation in welding of a ultra fine grain steel

In the present work the evolution of grain structure in the weld HAZ (heat affected zone) under welding thermal cycle was simulated. Especially the grain growth in the HAZ of a SS400 ultra fine grain steel was investigated. An integrated 3-D Monte Carlo (MC) simulation system for grain growth of the weld HAZ was developed based on Microsoft Windows. The results indicate that MC simulation is an effective way to investigate the grain growth in weld HAZ. The method not only simulates the non-isothermal dynamics process of the grain growth in the weld HAZ, but also visualizes the austenite grains realistically. Moreover, the thermal pinning effect can be easily included in the simulation process. The grain sizes of the CGHAZ (coarse grain heat affected zone) obtained from MC simulation are basically in agreement with the experimental measurement of the real welded joints under different heat input. Furthermore, the simulation indicates that the grain growth degree is higher for the SS400 ultra fine grain steel compared to conventional steel. With the increase in the heat input, the grain growth of the CGHAZ rapidly increases. Because the activation energy of the grain growth is lower for the SS400 ultra fine grain steel, austenite grains can grow at a relatively lower temperature, hence the range of the CGHAZ becomes wider.     

纯铝板搅拌摩擦焊温度场数值模拟

建立了搅拌摩擦焊热源模型,利用有限元分析软件ABAQUS模拟了搅拌摩擦焊的温度场,研究了焊接速度、搅拌头轴肩尺寸和垫板材质对搅拌摩擦焊接过程中试板的温度场的影响。结果表明：随着焊接速度的提高,焊件上各点的峰值温度降低,经历高温区的时间减少;轴肩摩擦热是热输入的主要来源,随着搅拌头轴肩尺寸的增加,焊缝中心高温区同一等温线上宽下窄的分布特征越来越明显;垫板材质明显影响焊件底部的温度和分布;适当的焊接参数、搅拌头尺寸及散热条件对获得较好的焊缝质量极为重要。     

Virtual welding equipment for simulation of GMAW processes with integration of power source regulation

A two dimensional transient numerical analysis and computational module for simulation of electrical and thermal characteristics during electrode melting and metal transfer involved in Gas-Metal-Arc-Welding (GMAW) processes is presented. Solution of non-linear transient heat transfer equation is carried out using a control volume finite difference technique. The computational module also includes controlling and regulation algorithms of industrial welding power sources. The simulation results are the current and voltage waveforms, mean voltage drops at different parts of circuit, total electric power, cathode, anode and arc powers and arc length. We describe application of the model for normal process (constant voltage) and for pulsed processes with U/I and I/I-modulation modes. The comparisons with experimental waveforms of current and voltage show that the model predicts current, voltage and electric power with a high accuracy. The model is used in simulation package SimWeld for calculation of heat flux into the work-piece and the weld seam formation. From the calculated heat flux and weld pool sizes, an equivalent volumetric heat source according to Goldak model, can be generated. The method was implemented and investigated with the simulation software SimWeld developed by the ISF at RWTH Aachen University.     

Numerical investigation of droplet impact on the welding pool in gas metal arc welding

A transient three‐dimensional model that describes physical phenomena inside a welding pool during gas–metal arc welding process is presented. The model considers such phenomena as heat‐mass transfer, electromagnetics, hydrodynamic processes and deformation of the weld pool free surface. The fluid flow in the weld pool is induced due to the presence of the mechanical impact of the droplets, thermo‐capillary surface tension, thermal buoyancy and electromagnetic forces. The weld pool surface deformation is calculated by considering arc pressure and droplet impact force. A comparative analysis of the impact of the electric current of the welding arc and different force factors causing the motion of liquid metal in the weld pool on the shape of the welded seam was carried out and discussed.     

异种钢激光-电弧焊复合焊接数值模拟

目的研究异种钢激光-GMAW复合焊接温度场以及应力场变化。方法运用ANSYS有限元分析软件,以5 mm厚D500钢和A514钢为研究对象,采用均匀分布的柱体热源与椭球热源组合的方法,建立了激光-GMAW焊接热源模型,对异种钢激光电弧复合焊接过程进行了模拟计算,并与实验所得的焊缝形状以及焊后残余应力进行了对比。结果结果表明,异种钢激光电弧复合焊接过程焊接变形以及残余应力实验结果与数值计算结果吻合较好。结论验证了锥体加柱体热源与椭球热源的组合热源模型在异种钢激光-GMAW复合焊接温度场及应力场模拟中的适用性,从而为不同焊接工艺条件下异种钢激光-GMAW复合焊接的焊缝形状和尺寸预测,提供了一种有效的途径。     

Generalized stress intensity factors due to steady and transient thermal loads with applications to welded joints

This paper deals with the elastic and plastic stress fields induced by thermal loads in the vicinity of sharp V‐notch tips in plates. Under the hypothesis of steady‐state heat transfer and plane‐strain conditions, the thermal and mechanical problem requires the numerical solution of an ordinary differential equation (ODE) system, obtained by extending the ‘stress function approach’. The intensity of the stress distributions ahead of V‐notch tips can be expressed in terms of thermal notch stress intensity factors (thermal NSIFs), as for external loads. The problem becomes much more demanding in the presence of transient thermal loads. The residual asymptotic stress distribution arising from the solidification of a fusion zone during an arc welding process is obtained by considering different boundary conditions. An aluminium butt‐welded joint is analysed after having modelled the weld toe region as a sharp V‐notch. A finite element (FE) simulation of the welding process is carried out by means of SYSWELD code (version 2004.1) modelling the arc welding torch by means of Goldak's source. Near the weld toe, the intensity of the residual stress field is given in terms of elastic or elastic—plastic generalized NSIFs.     

Numerical simulation of variable polarity vertical-up plasma arc welding process

Three-dimensional transient governing equations were developed based on conservation laws of energy, momentum and mass. These equations described physical phenomena of convection in weld pool and heat transfer in workpiece during variable polarity vertical-up plasma arc welding process. Boundary conditions for the developed governing equations were given. Welding energy input for variable polarity vertical-up plasma arc welding process was quantitatively expressed. Free surface deformation of the keyhole molten pool was coupled into calculation. Effect of wire filling on the geometry of molten pool and weld reinforcement was considered in the simulation. Correlations of temperature and thermophysical properties for aluminum alloy 2219 were quantitatively established. A control volume based finite difference method was used to solve the discrete governing equations. Moreover, dynamic evolutions of geometrical profile, dimension and fluid flow for the molten pool and keyhole were simulated through the developed computational routines, which achieved transient solution of fluid flow field coupling with thermophysical properties, temperature field and weld pool free surface deformation. Besides, the effect of the workpiece thickness on the moments of keyhole formation and stable keyhole establishment was analyzed, and thermal cycles for the main welding stage were calculated. In addition, experiments via variable polarity vertical-up plasma arc welding technique were conducted, and the established models were experimentally verified through weld cross-section profiles.     

Numerical analysis of weld pool geometry in globular-transfer gas metal arc welding

The weld pool geometry and its dimension in the globular-transfer mode during gas metal arc welding (GMAW) were numerically analyzed by using the thermal conduction model, which considered the influence of the deformation of weld pool surface on heat flow in the quasi-steady state. According to the features of the globular-transfer mode, the additional heat energy from molten metal droplets was treated as a plane or volumetric heat source term to correspond to different welding conditions. The weld pool surface profile was predicted while considering the effect of droplet impingement on the depression of the weld pool. The bead-on-plate GMAW experiments were performed under different welding conditions to validate the model of numerical analysis. It has been found that the predicted results agree well with the measured ones.     

Numerical and experiment analysis of residual stress on magnesium alloy and steel butt joint by hybrid laser-TIG welding

Hybrid welding technology has received significant attention in the welding of dissimilar materials recently. While, great welding residual stress and deformation often result by the difference of coefficient of thermal expansion This study describes the thermal elastic–plastic analysis using finite element techniques to analyze the thermo mechanical behavior and evaluate the residual stresses and welding distortion on the AZ31B magnesium alloy and 304L steel butt joint in laser-TIG hybrid welding. A new coupled heat source model was developed which combined by double-elliptic planar distribution, double-ellipsoid body distribution and Rotary–Gauss body distribution model. From the results, it can be concluded that the temperature distribution at the hybrid weld region is exposed to faster rate of heating and cooling in hybrid welding than TIG. Furthermore, compared to the welding stress distribution on the TIG weld, residual stress σ_y is found about 20% higher on hybrid weld joints, and the residual stress on the 304L steel plate is lower than that on the AZ31B magnesium plate.