铝合金点焊熔核流场及热场的有限元分析

Finite element analysis of thermal field and flow field in spot welding for aluminum alloys

关键词:  铝合金  电阻点焊  流场  热场  有限元

Key words:  aluminum alloys  resistance spot welding  flow field  temperature field  finite element

摘要:

根据计算流体力学与传热学原理,建立了描述铝合金电阻点焊液态熔核流动行为和传热过程的轴对称有限元模型。模型中考虑了移动边界层内部液态金属的对流传热和层外固体导热、材料热物理性能参数和接触电阻随温度的变化、焊件表面通过对流和辐射向周围环境的散热、球面电极传热以及熔化/凝固相变潜热对熔核形成热过程的影响,并采用有限元法对铝合金点焊熔核形成过程温度场和流场分布进行了数值计算。计算结果表明,强烈的对流位于熔核中心沿轴线附近区域,其流速最大值数量级为1×10^-1 mm/s;在直流焊接条件下,5 ms时间内开始形成液态熔核,并迅速沿轴向和径向扩展;回流环速度矢量将能量从熔核中心通过对流传热方式传递到熔核边缘,降低熔核内部温度梯度,促进熔核生长。试验表明,计算结果与实测值吻合良好。

Abstract:

Based on theories of computational fluid dynamics and heat transfer, an axial symmetry finite element model of velocity and temperature field of spot welding for aluminum alloy is established. In the model, many factors are considered including both convection heat transfer inside moving boundary layer and heat conduction of solid metal, material property and contact resistance which are the function of temperature, the effect of the loss of heat by convection, radiation and conduction through spherical electrode, and latent heat of phase transformation. The model is discretized with finite element method. The calculated results show that the prominent convection cell is observed at the center of the molten pool and the maximum value of flow velocity is 0.1 mm/s. With direct current power supply, fusion nugget starts to generate within 5ms and expands rapidly along axial and radial directions. Circumfluence velocity vector delivers energy from fusion nugget center to nugget fringe by convection, which reduces temperature gradient inside nugget and drives nugget to grow. The calculated results agree well with measured value.