铝合金T型接头激光+GMAW复合热源焊温度场的有限元分析

FINITE ELEMENT ANALYSIS OF TEMPERATURE FIELD IN LASER+GMAW HYBRID WELDING FOR T-JOINT OF ALUMINUM ALLOY

从宏观传热学出发,综合考虑焊缝横断面形状特点及接头形式对焊接热流的影响,建立了适用的T型接头激光+GMAW复合热源焊的组合式热源模型.利用双椭球体热源模型描述电弧热流和熔滴热焓,采用热流峰值指数递增-锥体热源模型表征激光热输入,并通过坐标系转换的方法旋转热源模型,以考虑焊枪倾斜对焊接热流分布的影响,推导出适用于T型接头复合焊的热源模型表达公式,从而简化了T型接头焊接数值模拟中的模型加载过程.将所建立的模型用于不同焊接条件下铝合金T型接头激光+GMAW单侧双面焊接焊缝形状和尺寸的模拟计算,计算结果与实验结果吻合较好,从而证明了模型的准确性和适用性;利用该模型计算了铝合金T型接头复合焊近缝区不同位置的热循环曲线,分析了铝合金T型接头复合焊热循环特征,为其组织和性能的预测奠定了基础.

T-welded structures of aluminum alloy are increasingly used in automotive, railway vehicles, aerospace and bridges. However, compared with the simple joint, the T-joint of aluminum alloy is more difficultly welded due to its complex temperature distribution and fluid flow mode in the weld pool. Whether using laser welding or the conventional arc welding process, aluminum alloy T-wleded joint is more prone to welding defects such as crack, pore, undercutting, joint softening, and so on. As a promising joining technology, laser＋gas metal arc welding （laser＋GMAW） hybrid welding not only combines the advantages of laser welding with those of GMAW, but also overcomes their shortcomings, thus having great potential to achieve high efficiency and high quality welding of aluminum alloy T-joint. So far, however, there is a lack of fundamental investigations involving math- ematical modelling and understanding of the hybrid welding process of aluminum alloy T-joint. As key factors determining the weld quality, thermal field has a significant influence on microstructure and properties of T-welded joint. In this work, using the numerical simulation method, the temperature distribution in laser＋GMAW hybrid welding of aluminum alloy T-joint was studied. Considering the influence of joint form on welding heat flux, an adaptive combined volumetric heat source model for laser＋GMAW hybrid welding for T-joint is developed based on macroscopic mechanism of heat trans- fer. The arc heat flux and heat content of overheated droplet are described using an double ellipsoid body heat source model, and the laser power is regarded as peak density exponentially increasing-conic body distribution. To take into account the effect of inclination of welding gun on heat flow distribu- tion in T-joint welding, the heat source model is rotated by way of coordinate transformation, thus deducing the formula of combined heat source model suitable to hybrid welding for T-joint. The built model is used to calculate the geometry and dimensions in laser＋GMAW hybrid both-sided welding for T-joint of aluminum alloy under different welding conditons, and the simulated resluts agree well with the experimental ones, which indicates the accuracy and applicability of the combined model. Besides, the thermal cycles at different positions in hybrid welding for T-joint of aluminum alloy are computed, and the characteristics of the thermal cycles are analyzed, which will lay the foundation for prediction of microstructure and properties of welded joint.