Numerical analysis of thermal fluid transportation during electron beam welding of 2219 aluminum alloy plate and experimental validation

A three-dimensional mathematical model using volume-of-fluid method is developed to investigate the heat transfer,fluid flow and keyhole dynamics during electron beam welding of 2219 aluminum alloy plate.In the model,an adaptive heat source is employed to simulate the heating process of electron beam.Fluid flow is mainly driven by surface tension,thermo-capillary force,recoil pressure,hydrostatic pressure and thermal buoyancy.The thermal-fluid transport behaviors of welding pool during the drilling and backfilling stages of keyhole and the formation reason of the nail-shaped weld with an arc crater are systematically analyzed.Finally,all calculation results are validated by experiments and show good agreements.     

2219铝合金电子束焊接匙孔演变过程的数值模拟

文中主要借助Fluent软件,基于有限体积离散方法建立了2219铝合金电子束点焊熔池传热、流动和匙孔演变的二维耦合数学模型.在模型中,考虑了表面张力、Marangoni剪切力、流体静压力、金属蒸气反冲压力的作用,并采用VOF(volume of fluid)方法跟踪了匙孔的形成与演变过程.结果表明,反冲压力钻取和涡旋输运的综合作用是匙孔加深的根本原因;沿深度方向热源功率密度的降低会导致前者钻取速度的减小.铝合金的点焊工艺试验表明,数值计算结果与实际吻合较好.     

电子束焊熔池温度场及小孔演变的数值模拟

针对2024铝合金电子束定点焊物理输运特点,在质量守恒、动量守恒、能量守恒以及VOF方程的基础上,建立了电子束深熔焊三维数学模型,系统描述了加热阶段以及冷却回填阶段点焊熔池的温度场以及小孔的演变过程,并通过焊缝形貌对比对计算结果进行了试验验证.结果表明,蒸汽反冲压力是小孔形成和加深的主要驱动力;在小孔出现以后,加热阶段的熔池最高温度区间位于瞬态小孔的底部,而当熔池冷却时冷却速度由上至下逐渐增加,并导致了焊缝微观组织的晶粒细化.     

铝合金激光-MIG复合焊熔滴对匙孔作用的模拟

将复合焊接过程中的反冲压力、表面张力等驱动力及熔滴过渡行为考虑在内,建立5A06铝合金激光-MIG复合焊接数值模拟热流耦合模型,由于熔池内的流动及匙孔稳定性对焊接性能有重要影响,因此针对熔滴与匙孔及熔池稳定性的影响进行了系统讨论,并且通过采用不同的熔滴落入位置进行计算.结果表明,当熔滴落入位置距激光中心较近时,熔滴对匙孔的冲击作用较大,匙孔壁的平均流速和波动频率有所增加,匙孔更易由于周期性的熔滴过渡而产生液桥发生闭合,熔滴落入位置还会影响匙孔深宽比,进而影响激光能量的菲涅尔吸收.     

穿孔型等离子弧焊接热-力耦合模型优化

K-PAW的焊接过程是等离子电弧对被焊工件热与力的耦合作用.文中基于FLUENT软件,依据流体动力学理论,对穿孔型等离子弧焊接过程熔池、流场和小孔进行了热-力耦合模型分析,提出了随穿孔深度增加,能量和电弧压力二次变化的计算优化模型,使维持小孔壁面稳定的力同时作用在小孔内部和物理边界上,初步实现了穿孔型等离子弧焊接从开始到穿透工件及穿孔后焊接过程的数值模拟.计算结果表明,焊接时间为0.25 s时,熔池已开始熔化并出现下凹变形,穿孔型等离子弧焊接穿孔时间为2.15 s,焊接3.00 s后小孔和熔池达到稳定状态,与试验测得的穿孔时间吻合良好,在穿孔动态过程中穿孔形态吻合良好,熔合线走势基本相同.另外,在平行于焊缝的截面上观察,熔池内部易出现逆时针环流.     

电子束扫描横焊薄铌板的熔池动力学行为

在电子束焊接过程中,金属液体蒸发的反冲压力、表面张力、重力等驱动力共同作用于熔池,对焊缝成形有显著影响. 在扫描横焊的情况下,电子束作用范围的扫描摆动和重力方向的旋转使熔池的动力学行为变得更复杂. 采用试验和数值计算方法对电子束扫描横焊薄铌板的熔池形态和凝固后熔合区形貌进行研究,数值模拟得到的熔池形态和熔合区形状与试验结果吻合. 熔池流场分析结果表明,半熔透熔池的驱动力主要为液态金属蒸发引发的反冲压力;全熔透熔池的上表面Marangoni流动占主导,表面张力与反冲压力共同作为熔池流动的驱动力;重力与焊接扫描共同作用使得熔池两侧的质量分布和流场分布不对称,造成了焊缝两侧熔合线的不对称.     

Numerical simulation of molten pool dynamics in high power disk laser welding

A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed.     

镁合金真空电子束深熔焊接及焊缝成形数值模拟

对10mmAZ61镁合金板材进行了真空电子束深熔焊接数值模拟研究.考虑到焊接过程中高温金属蒸气等离子体的热效应及真空电子束焊接"匙孔"深熔热效应特征,建立了高斯面热源与双椭球体热源复合的移动热源模型,采用数值模拟的方法研究了镁合金真空电子束焊接温度循环特征及不同焊接工艺对焊缝成形的影响.结果表明,建立的复合热源模型能够获得电子束深熔焊接的效果,并可模拟不同焊接工艺下的温度场分布与电子束热源作用下的焊缝成形,这也证明了该模型在AZ61镁合金电子束平板焊接的热效应模拟中有较好的适用性.     

真空电子束焊接热源建模及功率密度分析

分析了真空电子束深熔焊接的热源作用形成钉状焊缝的特征,建立了峰值功率递增型旋转高斯体热源,即热源作用半径在深度方向呈高斯规律递减,热源功率密度在深度方向呈指数函数规律递增.利用该热源模型计算了聚焦状态和散焦状态下,真空电子束焊接特殊热效应的功率密度分布.结果表明,热源数学模型得到的功率密度分布规律符合理想状态下的电子束热源作用特征,可用于不同聚焦状态下的真空电子束焊接的热效应数值模拟研究.     

激光穿孔点焊接瞬态过程数值分析

考虑工件表面等离子体作用，建立了小孔和熔池传热与传质耦合的穿孔点焊数值分析模型. 采用随小孔形状变化的自适应热源模型，热源形态依小孔形状变化而实时改变. 模型考虑了蒸发现象所引起的质量转换和能量损失，利用焓–孔介质法处理焊接过程动量损耗. 主要考虑液态金属蒸发所带来的反冲压力、表面张力和液体静压力并通过流体体积方程计算小孔壁面. 结果表明，小孔形成直至穿孔过程都可能产生向上和向下的飞溅、焊瘤和余高. 激光的瑞利散射、工件表面等离子体的热效应，激光束反射和等离子体膨胀作用，使得工件上/下的焊缝宽度比中间略大. 模拟计算值与试验结果比较，二者在形状和尺寸基本吻合.     

镁合金真空电子束焊接匙孔热效应数值模拟

分析了镁合金真空电子束焊接过程中的匙孔热效应特征,针对真空电子束焊接工艺建立了适用于镁合金焊接的复合热源模型.考虑到焊接过程中存在的高温金属蒸气等离子体及真空电子束焊接"匙孔"深熔效应特征,模型由高斯面热源和圆锥体热源复合而成,利用高斯面热源功率分配系数和圆锥体热源功率分配系数的不同取值,模拟电子束焊接的不同聚焦状态,并得到电子束聚焦状态与散焦状态下的焊接温度场变化,进而通过计算得到聚焦状态变化下的匙孔形状和焊缝成形.结果表明,模拟结果与其具有较好的一致性.     

穿孔等离子弧焊接热场和流场的数值模拟

考虑熔池和小孔的耦合作用,建立了穿孔等离子弧焊接热过程的三维瞬态模型.采用焓孔隙度法处理了凝固熔化过程中相变潜热以及动量损耗问题.基于流体体积函数法（VOF）对小孔界面实施追踪.对等离子弧焊从小孔形成到穿孔的瞬态演变行为、熔池流场的动态变化过程进行了数值模拟.开展了穿孔等离子弧焊接试验,对数值模拟结果进行了试验验证.结...     

A study on keyhole evolution and weld ripple formation in dissimilar welding under pulsed laser

A three-transient multiphase model is developed to study the dissimilar metal welding of pure niobium plate to titanium alloy Ti–6Al–4V sheet under pulsed laser. The physical process of dissimilar metal welding involves melting, resolidification, mass transfer, self-consistent keyhole, and weld bead formation. The major physical factors, such as recoil pressure induced by vapourisation, surface tension, heat transfer, fluid flow, Marangoni shear stress, buoyancy force, and their coupling are considered. The results show that the keyhole mainly occurs on the Ti–6Al–4V side due to the differences in physical properties of the materials. The effects of pulse overlapping factor on the weld bead are studied. It is found that the pulsed laser has a significant influence on the weld bead formation. The mixing of materials mostly occurred in the upper part of the molten pool. The simulated weld bead profile and the phase distribution agree well with the experimental results.     

真空电子束深熔焊接匙孔前沿蒸发传热分析模型

根据真空电子束焊接过程匙孔深熔效应的特点,建立简化的圆柱形匙孔物理模型.考虑到匙孔前沿的强烈蒸发现象,提出一种基于传热学理论的匙孔前沿气固界面传热分析模型.通过模型分析了AZ系列镁合金材料的主要金属元素Mg,Al,Zn和Mn在匙孔前沿的蒸发效应,以及匙孔半径变化对匙孔前沿气固界面处4种金属元素温度变化的影响.结果表明,...     

45钢电子束相变硬化温度场数值模拟与实验验证

建立了移动电子束高斯热源作用下的三维相变硬化过程中温度场的数学模型,分析过程中考虑了热源分布、热物性参数、热辐射等因素对温度场的影响,得到了电子束扫描相变硬化温度场的分布规律和硬化层的形态,并进行了实验验证;探讨了电子束工艺参数对硬化区深度和宽度的影响。结果表明:移动电子束高斯热源作用下的温度分布等值线呈勺状,表面最高温度滞后于束流中心,且处理后硬化层横截面呈月牙状;在固态相变条件下,硬化层的宽度和深度随着扫描功率的增加呈非线性增加,随着扫描速度的增加呈非线性减小。     

Simulation of vapour keyhole and weld pool dynamics during laser beam welding

To help get a deeper insight into highly-complex characteristics of laser beam welding, a mathematical model, closely mapping all prominent phenomena, is useful. Some phenomena such as surface tension induced forces, recoil back pressure, multiple reflections of laser rays and angle dependent energy absorption of hot surfaces are all crucial. Encompassing all those presences, a simulation model has thereby been developed. A laser power transmission model built in conformity with the ray tracing scheme is proposed along with a consistently-adaptive system of time stepping and meshing. The simulation results demonstrate a tailing, deepening weld pool wrapping around an unsettled vapour keyhole forming and collapsing in a fickle manner. Besides, the development pattern of the total laser power literally conveyed to the workpiece seems well matching with the prevalent understanding on broad deep-penetration welding processes. Experimental verification comes in the end. The simulated weld pool shape at its presumably-mature state is compared with that from the laboratory. A continuous-wave multimode Ytterbium-doped fibre laser was employed in the experiment to weld a plain 6-mm-thick stainless steel plate. Apart from the computed weld pool depth appearing somewhat deeper than it is supposed to be, the calculated weld pool width and length are in good agreement with the measured ones.     

12 mm厚钛合金平板电子束焊接的数值模拟

采用ANSYS有限元分析软件,建立12 mm厚TC4钛合金平板电子束焊接温度场和应力场的三维有限元数值计算模型。模型采用圆锥体热源考虑电子束焊接时的小孔效应;材料的热学、力学性能参数随温度变化;相变和熔池内液体的对流散热通过比热和热导率的变化实现。计算结果表明：钛合金电子束焊接时,熔池呈典型的卵形分布。高值纵向残余拉应力集中分布在焊缝中心线两侧距焊缝中心线4 mm的区域内,平板内部出现接近材料屈服极限的局部三维残余拉应力状态。实验得到的焊缝宏观形貌和小孔释放法检测到的焊接残余应力对计算结果进行验证,实验结果和计算结果吻合较好,证明了有限元模型的正确性。     

激光焊接瞬态小孔与运动熔池行为模拟

提出了一种三维瞬态小孔与瞬态熔池相结合的激光小孔焊接耦合数学模型.该模型综合考虑了多重反射菲尼尔吸收、小孔界面上的间断边界条件、金属蒸气/等离子体的辐射传热、Marangoni力、固-液相间的摩擦力、浮力、粘性力、蒸发潜热、熔化/凝固潜热,以及热传导、对流、辐射等多种因素对激光小孔焊接过程的耦合作用.采用水平集方法和快速扫描方法对小孔演化方程进行求解,得到了三维瞬态小孔形貌;并采用SOLA方法求解了瞬态熔池的三维传热和流动过程.结果表明,该模型能够较好地模拟激光小孔焊接中瞬态小孔和熔池的动态演化行为.     

驱动力对2219铝合金DLBSW焊接熔池行为的影响

为了探索激光焊接熔池驱动力与焊接过程中熔池流动之间的关系,构建2219铝合金T型结构双激光束双侧同步焊接(Dual Laser-beam Bilateral Synchronous Welding,DLBSW)过程热-流耦合模型。分析表面张力、反冲压力、重力及热浮力对熔池流动的驱动作用,并阐述这些驱动力共同作用下的熔池流动机理。结果表明,熔池表面的流体,其主要受到表面张力的驱动作用;对于熔池下端左侧及后方形成的环流,其主要受到表面张力、热浮力及重力的共同驱动作用;匙孔下方熔池底部在重力及热浮力的共同作用下沿熔池边缘流动。     

驱动力对2219铝合金DLBSW焊接熔池行为的影响

为了探索激光焊接熔池驱动力与焊接过程中熔池流动之间的关系,构建2219铝合金T形结构双激光束双侧同步焊接(dual laser-beam bilateral synchronous welding,DLBSW)过程热-流耦合模型.分析表面张力、反冲压力、重力及热浮力对熔池流动的驱动作用,并阐述这些驱动力共同作用下的熔池...