摘要
匙孔形态和熔池的流动形态是电子束焊接焊缝质量控制的关键,而表征焊缝成形质量的特征区域的选取以及计算较为繁琐.本文在电子束焊接匙孔壁面受力平衡研究基础上,利用ANSYS软件建立了电子束焊接过程温度场、熔池流场、匙孔形态演变耦合分析的数值计算模型。匙孔形态以及与之密切联系的金属蒸发、熔池流动的研究对于电子束焊接质量控制有着重要意义。
匙孔壁面力学平衡条件研究表明,在电子束焊接过程中,匙孔壁面法向主要受金属蒸气反冲压力、表面张力附加压力、流体静压力、熔池旋转向心力的作用;匙孔动态平衡时,法向上受力平衡;金属蒸气反冲压力和匙孔壁面表面张力是维持匙孔动态平衡的主要作用力。本文根据流体力学、流体动力学及传热学理论,建立了电子束作用下焊接熔池流场、温度场的二维瞬态数值分析模型。该模型综合考虑了熔池内部液态金属的对流传热和熔池外部的固体导热、材料热物理性能参数随温度的变化、焊件表面通过对流和辐射向周围环境的散热以及熔化/凝固相变潜热等对熔池流场与温度场的影响。利用ANSYS有限元软件对所建立的模型进行了求解。计算了焊接熔池温度场及其动态变化过程;研究了电子束作用下焊接熔池流体流场、熔池内金属的流动方式以及熔池流体运动速度的变化;分析了焊接工艺参数对匙孔的影响。在该模型中,对匙孔纵向深入过程与横向移动过程进行了模拟,采用匙孔自由界面跟踪算法(引入VOF模型)实现对匙孔形态变化的跟踪。结果表明,电子束焊接过程中驱动液态金属流动有三方面作用机制。一是与金属蒸发相关的金属蒸气反冲压力的驱动;二是与表面张力有关的附加压力以及Marangoni剪切力的驱动;三是熔池与工件的相对运动的驱动。三种驱动机制的共同作用导致了熔池内部复杂的流动特征。在验证试验中对熔池截面尺寸与模拟结果进行对比,能够达到预期效果。
The key of quality control are the flow shape of welding pool and the keyhole shape in electron beam welding.It is difficult to choose and calculate the characteristic area which can indicate the welding quality. In this paper, based on the force balance study of keyhole wall. ANSYS was used to build a coupled mathematical model to investigate the heat transfer, weld pool fluid flow and keyhole formation during electron beam welding. Investigation of keyhole behavior, metal evaporation and fluid flow played important part in the quality control of electron beam welding.
The driving forces distribution on the keyhole wall was confirmed through investigating of the mechanical equilibrium condition. It was indicated that the keyhole was mainly drove by metal vapor recoil pressure, surface tension pressure, hydrostatic pressure, centripetal force in the normal direction. When the welding process was stable, these forces were balanced. During electron beam welding, metal vapor recoil pressure and surface tension paid important part in the stabilization of keyhole. Based on theories of hydromechanics,hydrokinetics and heat transfer,a two dimensional transient numerical model of flow and temperature field of the electron beam welding molten pool is established. In the model,both convection heat transfer of the melted metal inside the pool and heat conduction of solid metal outside the pool,the variation of the rmophysical parameters of material with temperature,the effect of the loss of heat,including convection and radiation, and latent heat of Phase transformation on the temperature field are cansidered.In use of ANSYS,calculating software of finite element technology,the welding pool’two dimensional flow and temperature fields and their transient variation processes are calculated,the flow style and velocity of molten metal are researched,and the welding variables’infection of temperature field is alsoanalyzed
Based on the mechanical equilibrium condition, a coupled mathematical model was developed to simulate keyhole shape in longitudinal thorough process and level migration process. In this model, the volume of fluid method was used to trace the process of the keyhole formation. The results showed that there were three driving mechanisms for the weld pool flow. One was related to the metal evaporation and liquid metal was drove by the metal vapor recoil pressure; one was the effects of surface tension such as additional pressure due to surface tension and Marangoni shear stress; another was due to the relative motion between weld pool and work piece. Three kind of actuation mechanism's combined action has caused the molten bath interior complex mobile characteristic. In confirmatory test, carry on the contrast to the molten bath section size and the analogue result. it can achieve the anticipated effect.
引文
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