考虑熔池与小孔的耦合作用, 建立了穿孔等离子弧焊接三维瞬态熔池流体流动和传热过程的数学模型. 采用流体体积函数法追踪小孔的形状与尺寸, 利用焓--孔隙度法处理凝固熔化过程中的相变潜热以及动量损耗问题. 针对穿孔等离子弧焊接的工艺特点, 建立了随小孔深度动态调整的组合式体积热源模式. 对8 mm板厚的不锈钢工件进行了穿孔焊接工艺实验和数值模拟, 获得了等离子弧焊接过程中熔池出现、小孔形成、流场与温度场演变、工件熔透与穿孔等动态过程的基础数据, 展示了小孔穿孔前后熔池流体流动规律. 工件背面小孔形状尺寸以及焊缝横断面的数值模拟结果与实验测试结果基本吻合.
Because of its high gas velocity and heat input, plasma arc welding (PAW) can penetrate thicker workpieces with a single pass because PAW can operate in the keyhole mode. Compared with electron beam and laser beam welding, keyhole PAW is more cost effective and more tolerant of joint preparation, so that it is widely used in manufacturing structures with medium thickness. However, the keyhole establishment and sustainment during the initial stage of PAW process, i.e., the keyholing process, has a critical effect on the process stability and the weld quality. Thus, modelling and simulating of the keyholing process and its influence on fluid flow and heat transfer in keyhole PAW process is of great significance to completely understand the process mechanism. With considering the interaction between weld pool and keyhole, a three dimensional transient model of fluid flow and heat transfer in weld pool is developed for numerical analysis of keyholing process in PAW. The volume of fluid method (VOF) is used to track the keyhole shape and size. The latent heat and momentum sink due to solidifying and melting are dealt with by enthalpy-porosity technique. Considering the larger ratio of PAW weld depth to width, a combined volumetric heat source model is established, and one of its distribution parameters is adjusted dynamically with the variation of keyhole depth. The evolution of fluid flow and thermal field in weld pool, and the keyholing process are quantitatively analyzed on the stainless steel plates of thickness 8 mm. The feature of fluid flow in weld pool is revealed. The predicted keyhole size at bottom side of workpiece and fusion line at transverse cross-section of welds agree with the experimentally measured results.
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