外加横向磁场作用电弧增材成形过程中的传热传质仿真

为了揭示外加横向磁场对电弧增材成形过程中电弧和熔池传热传质以及成形件微观组织影响的内在机理,建立基于GMAW电弧增材成形过程中电弧和熔池的弱耦合数值模型,通过数值模拟对比分析了有/无外加横向磁场作用下熔池电磁力分布、电弧和熔池传热传质的差异,发现横向磁场作用使电弧向熔池后方偏转,使熔池发生单向强制对流并驱动熔融金属和热量向熔池后方运动,从而更加直接地冲刷熔池结晶面。由此预测横向磁场作用能降低熔池凝固过程中枝晶前沿温度梯度和溶质浓度,提高枝晶前沿的成分过冷,使得靠近熔池中心的枝晶前端生长加速并细化晶粒。相同工艺条件的对比试验表明:相比无外加磁场的普通熔积,横向磁场作用下熔池底部等轴晶区域减小,整个结晶面上细密的胞状枝晶区域面积增大,验证了数值模拟的预测。研究结果可为外加磁场在电弧增材成形微观组织控制中的应用提供依据和参考。     

磁场作用下铝/钢CMT焊接温度场及熔池流动行为

为探究纵向磁场在铝/钢冷金属过渡(Cold metal transfer,CMT)焊接过程中的作用机理,采用ANSYS软件对纵向磁场作用下电弧形态、温度分布和熔池流动行为进行数值模拟,重点研究不同线圈励磁电流对焊接温度场和熔池流动行为的影响。结果表明,外加磁场可以改变电弧等离子体的运动行为,进而影响了焊接电弧在基板表面和熔池内部的热量传导行为。施加磁场后,熔池中的峰值温度发生下降,峰值温度区域由熔池中心转向熔池外围,铝/钢界面处的高温停留时间和温度也随之下降。此外,外加磁场改变了铝液熔池内部的流动行为。熔池内部的流动特征由无磁场时的单一环流,转变为有磁场作用时的双环流流动特征。随着励磁电流的增加,熔池内部的流速和流动范围有增大的趋势。     

外加纵向磁场GTAW焊接熔池流动机理

以外加纵向磁场GTAW (钨极氩弧焊 )焊接LD10CS铝合金过程为研究对象 ,建立外加纵向磁场GTAW焊接熔池流体流动和传热数学模型 ,对固定电弧的外加纵向磁场GTAW焊接熔池流体流动过程进行数值分析 ,研究外加纵向磁场GTAW焊接熔池流体流动和传热行为。     

稳态磁场对激光熔注球形WC颗粒分布的影响机理研究

利用稳态磁场对金属流体的粘滞效应,在316L不锈钢基体上制备颗粒梯度分布的WC/316L复合涂层.为研究稳态磁场对激光熔注球形WC颗粒分布的影响机理,建立了考虑固液相变、流动以及洛伦兹力的熔注熔池多物理场模型,分析稳态磁场对流场,洛伦兹力分布以及等效黏度的影响.采用多颗粒动力学模型与熔池模型耦合计算,研究稳态磁场对熔池颗粒运动的影响.实验与仿真结果均证实,随着磁场强度从0T增大至1.2T,WC颗粒集中分布在复合涂层表层的趋势增大.分析结果表明:稳态磁场可有效增加熔池流体的等效黏度,使得颗粒在熔池中对流体的跟随性增强;同时,外加稳态磁场可以明显抑制熔池Marangoni对流,进一步降低了颗粒的运动能力,使得颗粒难以运动至熔池内部,大部分增强颗粒集中于熔池上表层.     

纵向稳态磁场对电弧增材成形零件表面质量和性能影响的研究

外加磁场作用是影响电弧增材成形过程与成形零件性能的有效方式之一。为了研究外加纵向稳态磁场对低碳钢电弧增材成形零件表面质量和力学性能的影响,搭建基于GMAW的纵向稳态磁场辅助电弧增材成形装置,采用形貌分析、金相观测、性能测试的方法对比分析有/无外加磁场作用下成形试样表面质量、微观组织及力学性能差异。结果表明:相比普通熔积,外加磁场作用下,单焊道宽高比增大,形成宽而平的焊道横截面形貌,从而有效地改善搭接精度并提高熔积层表面质量,电磁搅拌作用还能够细化晶粒,减少熔积缺陷以及多道搭接区域的晶粒分布的不均匀性。此外,外加磁场作用还改变了铁素体和珠光体的占比和分布形态。力学性能测试显示,磁场作用使得成形样件在熔积方向和搭接方向的力学性能有一定的提升,力学性能的各向异性减小。     

外加稳态磁场作用下的焊接电弧数值仿真

为了揭示外加静态磁场对焊接电弧形态及传热传质的影响规律,建立了焊接电弧的数值模型,对比分析了普通熔积、外加纵向磁场作用以及横向磁场作用下的电弧传热传质过程。结果显示:相比普通熔积,外加纵向磁场作用下,靠近基板的位置电流密度和温度减小,电弧的温度和压强峰值减小,中心处出现负压;外加横向磁场作用下,电弧整体偏向一侧,电弧中心的电流密度、温度和电弧压强都小于未施加外加磁场情况。外加磁场对电弧形态及传热传质的改变,将导致电弧和金属之间的热和力相互作用改变,从而使得熔池的传热传质过程相应的发生改变。     

活性剂钨极惰性气体保护电弧焊接熔池行为的观察

利用高速数字摄相机对涂敷活性剂与不涂活性剂条件下的熔池表面流体流动形态及等离子体行为进行观察.利用X射线实时焊缝数字观察系统,用钨粒子示踪法测试熔池流体流动的规律.试验结果表明,活性剂使电弧收缩、改变熔池流体的流动方向并使流体流动速度加快,有活性剂时的涡流流动速度比无活性剂的涡流流动速度增加4倍,强烈的熔池流体向内对流是活性剂钨极惰性气体保护电弧焊熔深增加的主要原因,验证了数值模拟得到的结果.     

外加磁场对高速GMAW电弧和熔池行为的主动调控效应

在熔化极气体保护焊(Gas metal arc welding,GMAW)过程中,当焊接速度超过临界值后,焊缝成形变差,出现咬边和驼峰焊道,无法满足生产要求。研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因。自主研发外加磁场发生装置,向熔池施加横向电磁力,对后向液体流进行主动干预,并调控熔池流态,从而抑制驼峰焊道的形成。在Q235低碳钢板上开展焊接工艺试验,获得了不同磁感应强度下的焊缝表面成形;采用高速摄像技术,拍摄焊接过程中的电弧和熔池图像,分析外加磁场对电弧形态、熔池流场和焊缝成形的影响规律,初步揭示外加磁场抑制驼峰焊道的机理。试验结果表明,外加横向磁场能明显调控熔池流态,减小后向液体流的动量,并能有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度。     

交变磁场对激光熔覆铁基复合涂层宏观形貌的影响及其微观组织演变

通过特殊设计的电路及作用线圈制作了交变磁场发生装置,并用其研究了不同磁场强度对激光熔覆铁基涂层宏观形貌和显微组织的影响。基于电磁学及金属凝固原理,揭示了激光熔覆涂层的固化过程和磁场诱发熔覆涂层柱状树枝晶向等轴晶转变的主要机制。实验结果表明:在交变磁场作用下,熔池金属液表面产生的趋肤效应和交变电磁力使凝固后熔覆层的表面形态呈波浪式,熔高和横截面积均随磁场电流的增加而减小,但熔宽变化不大。熔池内部产生的电磁力驱动熔体流动使树枝晶熔蚀和机械折断,游离的破碎枝晶成为新的形核核心,增加了形核率,从而促使熔覆层顶部组织由树枝晶向等轴晶转变。随着磁场电流的增加,等轴晶区扩大,但涂层底部的组织变化不明显。     

基于TIG焊电弧-熔池统一模型分析焊接电弧

以TIG焊电弧为研究对象,建立了电弧—熔池的统一模型,并在此模型的基础上对焊接电弧进行了分析。建立此模型就避免了对阳极表面温度的假定,使得对焊接电弧的分析与实际情况更近了一步,从而也为将焊接电弧和熔池作为一个整体来进行分析奠定了基础。采用ANSYS软件分析并得到了阳极表面温度的变化情况,阳极表面电流密度的分布状况,得出热流密度与电流密度分布规律的一致性。并从电磁力和流体流动的角度揭示了电弧压力产生的原因,并通过试验验证了电流密度和电弧压力的分布情况。     

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

This paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved.     

Numerical analysis of a moving gas tungsten arc weld pool with an external longitudinal magnetic field applied

Mathematical models of the electromagnetic field, fluid flow and heat transfer of a three-dimensional moving gas tungsten arc (GTA) weld pool with external longitudinal magnetic field applied are established in the paper. Using a multi-coupled analysis function of ANSYS finite element code, distributions of current density and magnetic field, as well as fluid flow and heat transfer in a moving weld pool, were systematically studied and investigated to understand and reveal the effect of an external longitudinal magnetic field on liquid metal in a moving GTA weld pool and also to supply a basis for the application of an external longitudinal magnetic field in welding technology .     

“<Emphasis Type="SmallCaps">disassembly plan approach based on subassembly concept</Emphasis>”

A three-dimensional numerical model is established to study the temperature and fluid flow fields in the twin-wire gas metal arc welding (GMAW) process. The high-speed photography system is used to capture the images of the weld pool during the welding. Based on simulation and experimental results, the weld pool formation, convection, and stability in twin-wire GMAW process are investigated. Both “push-pull” and outward flow patterns exist in the twin-wire GMAW weld pool, which can contribute to decreasing the height of the bulge and increasing the width of the pool. The convection in the weld pool can proceed adequately, the arc force between the leading and trailing arcs is relatively balanced, surface tension normal force is uniform along the liquid channel, and the liquid channel is capillary stable, all of those contribute to the stability of the weld bead. The simulation results are in good agreement with those in the experiment.     

The effect of arc behavior on weld geometry by high-frequency pulse GTAW process with 0Cr18Ni9Ti stainless steel

Based on 0Cr18Ni9Ti austenitic stainless steel plate (h?=?6 mm), a study on arc behavior by ultrasonic frequency pulse gas tungsten arc welding (GTAW) process has been carried out. The results show that with the increasing pulse frequency, an obvious pinch effect of arc plasma has been detected and also the increment of arc voltage, stiffness, and force. Then, the method, combining weld appearance and numerical simulation, has been adapted for weld behavior on the basis of arc behavior by ultrasonic frequency pulse GTAW process. As a result of arc shrinkage, the root radius of arc decreased, which caused narrower weld bead. The larger arc force led to more depression of pool surface that made the downward heat source and external force point, which had been important to increasing weld penetration. Meanwhile, the mobility of molten pool was enhanced by weld behavior compared with conventional GTAW process.     

Analysis of weld pool dynamic during stationary laser–MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary laser–metal inert gas (MIG) hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow pattern; moreover, typical phenomena of MIG welding such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding such as recoil pressure, inverse Bremsstrahlung absorption, and Fresnel absorption were all considered in the model. The laser beam and arc couple effect was introduced into this model by the plasma width during hybrid welding. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds of weld pool to a unified weld pool were calculated. Furthermore, the simulated weld bead geometries were in good agreement with experimental measurement.     

Development of a MIAB welding module and experimental analysis of rotational behavior of arc—simulation of electromagnetic force distribution during MIAB welding of steel pipes using finite element analysis

Magnetically impelled arc butt (MIAB) welding is a unique forge welding process in which an arc is drawn in the gap between the two tubes to be welded in order to raise them to a high temperature to allow forging to form a solid-state weld. In this case, the arc is rotated with a high speed around the weld line by an electromagnetic force resulting from the interaction of the magnetic field and the arc current. This paper presents the details of the results and the conclusions of the experimental trials conducted on the MIAB module designed and developed based on the principle. Further, nonlinear electromagnetic analysis has been performed to determine the magnetic field and electromagnetic force distribution in MIAB process using finite element package ANSYS. Typical results of this analysis pertaining to magnetic field are compared with the experimental data for steel tubes (outer diameter 47 mm and thickness of 2 mm). It is observed that the results from finite element analysis and the experimental trials are in excellent agreement. The proposed three-dimensional finite element method model for electromagnetic force distribution facilitates comprehensive understanding of the arc rotation process in MIAB welding.     

Prevention of humping bead associated with high welding speed by double-electrode gas metal arc welding

Manufacturing productivity can be improved by increasing the welding speed. However, humping bead will occur when welding speed is beyond a certain value. An experimental system of double-electrode gas metal arc welding (DE-GMAW) was developed to implement high speed welding and prevent from humping bead formation. The DE-GMAW appropriately partition the heat energy between the wire and the base metal so that higher deposition rate of filler wire and suitable shape and size of weld pool are ensured. The arc images captured during DE-GMAW process were used to optimize the geometric parameters between the gas tungsten arc welding and the gas metal arc welding (GMAW) torches. The main arc and bypass arc integrated well and satisfactory weld bead formation was obtained. Through observing the weld pool behaviors from side view during DE-GMAW process, it was found that the height of both solidified and molten region at the pool tail is almost flat so that no humping bead was formed during DE-GMAW with the welding speed up to 1.7?m/min. The side view images of weld pool in DE-GMAW were compared with those in conventional GMAW, and the reason why DE-GMAW can suppress humping bead is shortly discussed.     

Numerical simulation of laser�Ctungsten inert arc deep penetration welding between WC�CCo cemented carbide and invar alloys

In order to optimize the laser?Ctungsten inert arc (TIG) welding process of cemented carbide to steel, a novel combined model consisting of circular disk source, line source, and double ellipsoidal TIG heat source was put forward to simulate the deep penetration phenomena and bead profile. In contrast, laser heat source model was validated using macrostructure analysis results. The effects of the circular disk of radius and the material properties on the bead profile were discussed. For mechanism surface formation, surface depression or humps was discussed based on the high-speed photography technique to verify bead profile characterization. The results manifested that in the model, the circular disk radius played a key role in the formation of bead profile. And the penetration coefficient chiefly affected the root of weld and the keyhole formation. During the hybrid welding, the main forces influencing the surface depression or humping were intrinsic stress from coefficient of thermal expansion gradient, surface tension, buoyancy force, stirring action, and shock waves at the end of the keyhole. Before the solidification of the upper part of the melt, the melt was driven by the fluctuated plasma, plumes, or other forces. While the amount of melt filling the back welds metal of keyhole was larger than that caused by plume losses and the shrinkage of weld metal, the humps came into being.