40Cr轴面激光熔覆Ni60数值模拟

目的 针对激光熔覆过程中熔池内部复杂的传热和对流现象,分析激光功率和扫描速度对熔池内部温度场、流场演变和分布的影响.方法 采用双椭球热源模型,建立了40Cr轴面基体激光熔覆Ni60粉末过程的三维温度场流场数值模型,并进行试验验证.结果 熔覆过程形成了近似椭球体的熔池,最高温度位于移动光斑中心偏后方,达到了2080.4 ...     

TC4合金等离子–MIG复合焊过程温度场的数值模拟

目的 研究TC4合金在等离子-MIG复合焊(Plasma–MIG Hybrid Welding)过程中的温度场特性,探究不同电弧功率对熔池形貌的影响。方法 进行了2组4 mm TC4合金板堆焊试验,根据实验结果提出了一种改进的复合热源模型并进行了相应的仿真分析。结果 仿真与实验获得的焊缝截面相吻合;等离子电流的增大使熔池尺寸增大且余高减小,等离子电弧功率的变化对熔池宽度的影响相对较小。结论 等离子–MIG复合电弧对工件的热作用非常集中,更易实现深熔焊、焊接效率更高;所提出的热源模型适用于TC4合金等离子–MIG复合焊温度场模拟。     

焊接数值模拟中热源的选用原则

热源模型是焊接过程数值模拟的基础,其选择直接影响模拟结果的准确性。综述了焊接数值模拟热源模型的研究进展,着重分析了Rosenthal-Rykalin热源、平面高斯热源、双椭圆热源、均匀体热源、半球状热源、旋转高斯体热源、双椭球热源和组合热源的应用现状,最后总结了热源模型的选用原则。最后指出,建立更精确的三维热源模型,从而分析焊接熔池的熔化与凝固过程,已成为焊接数值模拟热源模型的发展方向。     

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。     

卷边接头激光钎焊复合热场模型的数值计算

为了研究卷边接头激光钎焊热现象,进行了母材为镀锌板,CuSi3作为钎料的激光钎焊实验.基于激光钎焊原理和卷边接头焊缝成型特点,通过有限元分析法对激光钎焊温度场进行了数值模拟,采用高斯双椭球复合热源模型模拟了钎料融化铺展流动的传热行为,模型考虑了材料热物理属性随温度变化的问题以及相变潜热、辐射和对流对传热的影响,对不同激光钎焊工艺参数下的温度场进行计算,结果表明:当激光功率为1200W,焊接速度为1.5 m/min,离焦量为30 mm时,卷边接头的峰值温度和温度梯度较低,对于获得成形质量良好的钎焊接头更为有利.     

T型接头旋转激光+GMAW复合焊熔池动态行为数值分析模型

目的 研究T型接头旋转光纤激光+GMAW复合焊熔池的温度场和流态特征,揭示气孔缺陷的产生及抑制机理。方法 依据光学、电磁学、传热学及流体动力学机理,建立T型接头旋转光纤激光+GMAW复合焊熔池数值分析模型。使用Fluent软件对旋转频率分别为50 Hz和100 Hz的T型接头旋转激光+GMAW复合焊进行温度场以及流态特征的模拟,对比不同频率下T型接头横、纵截面,从工艺和焊缝成形角度出发,针对不同频率对熔池、小孔成形以及气孔抑制的影响进行讨论。结果 当旋转频率为50 Hz时,纵截面内小孔最大深度为5.4 mm,横截面熔池内小孔开口直径相对较大,旋转一周后,小孔远离气泡,气泡无法逸出,形成气孔;当旋转频率为100 Hz时,纵截面内小孔深度显著降低,熔池体积明显减小,横截面内小孔最大开口直径和深度均降低,熔池尺寸也有所减小,在时间为0.097 s时,小孔上方区域出现的顺时针涡流不仅能抑制气孔,还能改善熔池的下垂以及立板焊趾处的咬边。结论 随着旋转频率的增大,小孔的最大开口直径和深度均降低,还对熔池具有搅拌作用,使熔池体积变小。     

921A舰船钢激光–MAG复合焊接过程数值模拟分析

目的 对厚度为16 mm的921A舰船钢进行激光–MAG复合焊接,得到最佳工艺参数,从数值模拟的角度验证焊接工艺的可靠性。方法 利用SYSWELD+Visual–Environment软件对激光–MAG复合焊接过程进行数值模拟,选用3D高斯热源与双椭球热源相结合的复合热源模型对激光–MAG复合焊接过程进行仿真,绘制不同时刻及不同焊缝区域的时间–温度曲线,采用热弹塑性有限元法对应力变形场进行仿真计算。结果双椭球热源模型与3D高斯热源模型相结合的复合热源模型能够获得较为理想、接近真实热源形貌的热源形态;焊缝区域的焊接热源在行进过程中温度稳定,模拟热源温度可达3 200℃,具有典型的焊接热循环曲线特征,且距离焊缝越远,升温速率和冷却速率越慢;焊接残余应力主要集中在焊缝处,约为440 MPa,且焊缝两端的结合部位具有较高的残余应力。结论 复合热源模型适用于16 mm厚的921A钢激光–MAG复合焊接数值模拟,焊后板材的残余应力低于材料的屈服强度,冷却后板材的变形程度较小,最大变形量为1.13 mm,表明激光–MAG复合焊接方法及工艺适用于16 mm厚921A钢的焊接。     

铝合金T型接头激光+GMAW复合焊残余应力数值分析

目的 研究激光+GMAW复合焊中不同激光功率参数对铝合金T型接头残余应力的影响,从而提高焊接性能。方法 分别考虑了热弹塑性理论、传热学以及T型接头几何特性,建立了铝合金T型接头激光+电弧复合焊残余应力的数值分析模型。采用双椭球体热源模型表征电弧热输入与熔滴晗,采用锥体热源模型对激光深熔焊进行描述。基于所建立的T型接头模型,使用ANSYS有限元软件对12 mm厚铝合金激光+ GMAW焊T型接头残余应力进行模拟计算,并研究其分布特征;使用X射线衍射法对T型接头处的残余应力进行测量从而对所建模型的准确性进行验证。同时,对比了不同激光功率下铝合金T型接头对残余应力的影响规律。结果 当激光功率分别为2、3、4、5 kW时,铝合金T型接头路径L3上的纵向残余应力最大值分别为270、263、258、251 MPa,米塞斯-等效应力最大值分别为265、261、257、250 MPa。结论 后焊的焊缝A对焊缝B有明显的热处理作用,使应力明显降低;在T型接头焊缝及近缝区,横向残余应力和厚度方向残余应力峰值均比纵向残余应力峰值小,且随着激光功率的增大,焊缝及近缝区拉应力峰值不断减小。     

基于Fluent的钛合金激光氮化机理及数值模拟

基于非等温产生的表面张力梯度导致熔池区域内的马兰戈尼对流对激光氮化传热和传质过程有重大的影响。本文采用计算流体软件Fluent对钛的激光氮化过程进行探究和重现,结合传热过程中材料温升引起的相变模型及流体体积函数(VOF)模型分析气—液降膜传质机理,通过建立瞬态激光氮化温度场和浓度场的耦合模型,对激光氮化过程的传热,熔池流动和传质机理进行数值模拟。分析结果给出了钛工件的熔池形成、内部流动、氮化层的氮含量及其分布与激光参数之间的关系,为激光氮化工艺参数优化提供了理论依据。     

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。     

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 Analysis of Two-Way Interaction between Weld-Pool and Arc for GTA Welding Process

［1］H.G.Fan, S.J.Na and Y.W.Shi: J. Phys. D: Appl. Phys., 1997, 30, 94. ［2］Y.P.Lei and Y.W.Shi: Numerical Heat Transfer B,1994, 26, 455. ［3］R.T.C.Choo, J.Szekely and R.C.Westhoff: Metall. Trans. B, 1992, 23B, 357.     

Numerical simulation of fluid flow and temperature field in keyhole double‐sided arc welding process on stainless steel

Double‐sided arc welding process powered by a single supply is a type of novel high‐production process. In comparison with the conventional single‐sided arc welding, this process has remarkable advantages in enhancing penetration, minimizing distortion and improving welding production. In this paper, a three‐dimensional steady numerical model is developed for the heat transfer and fluid flow in plasma arc (PA)–gas tungsten arc (GTA) double‐sided keyhole welding process. The model considers the surface tension gradient, electromagnetic force and buoyancy force. A CCD camera is used to observe the size and shape of the keyhole and weld pool. The acquired images are analysed through image processing to obtain the surface diameters of the keyhole on the two sides. A double‐V‐shaped keyhole geometry is then proposed and its characteristic parameters are derived from the images and cross‐section of weld bead. In the numerical model, the keyhole cavum within the weld pool is treated as a whole quality, whose temperature is fixed at the boiling point of the workpiece material. The heat exchange between the keyhole and weld pool is treated as an interior boundary of the workpiece. Based on the numerical model, the distributions of the fluid flow and temperature field are calculated. A comparison of cross‐section of the weld bead with the experimental result shows that the numerical model's accuracy is reasonable. Copyright © 2005 John Wiley & Sons, Ltd.     

Hybrid laser/arc welding of advanced high strength steel in different butt joint configurations

An experimental procedure was developed to join thick advanced high strength steel plates by using the hybrid laser/arc welding (HLAW) process, for different butt joint configurations. The geometry of the weld groove was optimized according to the requirements of ballistic test, where the length of the softened heat affected zone should be less than 15.9 mm from the weld centerline. The cross-section of the welds was examined by microhardness test. The microstructure of welds was investigated by scanning electron microscopy and an optical microscope for further analysis of the microstructure of fusion zone and heat affected zone. It was demonstrated that by changing the geometry of groove, and increasing the stand-off distance between the laser beam and the tip of wire in gas metal arc welding (GMAW) it is possible to reduce the width of the heat affected zone and softened area while the microhardness stays within the acceptable range. It was shown that double Y-groove shape can provide the optimum condition for the stability of arc and laser. The dimensional changes of the groove geometry provided substantial impact on the amount of heat input, causing the fluctuations in the hardness of the weld as a result of phase transformation and grain size. The on-line monitoring of HLAW of the advanced high strength steel indicated the arc and laser were stable during the welding process. It was shown that less plasma plume was formed in the case where the laser was leading the arc in the HLAW, causing higher stability of the molten pool in comparison to the case where the arc was leading.     

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.