【作者】 霍玉双；

【导师】 武传松；

【作者基本信息】 山东大学 ， 材料加工工程， 2010， 博士

【摘要】 穿孔等离子弧焊接过程中,小孔的形成与维持涉及到复杂的物理机制。小孔的形状和尺寸直接决定着工件沿厚度方向的热作用、熔深大小以及焊缝成形质量。深入分析和研究等离子弧焊小孔的形成过程及其对焊缝成形的影响对于拓宽其工艺裕度和提高其过程稳定性,具有重要的理论意义和工程实用价值。本研究首先分别对6 mm和8 mm厚度的不锈钢板进行了穿孔等离子弧焊接工艺实验,测量了不同工艺条件下的等离子弧尾焰电压、焊缝轮廓形状和尺寸,为对小孔和熔池的建模获得了实验数据。在深入分析等离子弧焊接熔池受力状态的基础上,根据小孔壁面上的力平衡条件,建立了等离子弧焊小孔模型。利用模型,分别对6 mm和8 mm厚不锈钢板PAW焊接准稳态小孔的形状和尺寸进行了数值计算。计算结果与实验测试的穿孔情况吻合良好,证明了所建立的小孔模型的合理性和适用性。根据达到准稳态时小孔壁面各点的受力状态,对PAW焊接过程中小孔从“盲孔”到“穿孔”的转变机制进行了初步的探讨,分析计算了小孔壁面上各点的作用力的大小。计算结果表明,穿孔等离子弧焊接过程形成穿孔主要是由于电弧力随焊接电流增加发生剧烈变化,而小孔深度突变的原因是在一定条件下电弧力在熔池局部的进一步集中。采用小孔模型与组合式体积热源模型相结合的方式,利用计算出的小孔形状与尺寸,对组合式体积热源模型的热源参数进行标定。分别计算了6 mm和8 mm厚不锈钢板的焊接温度场,将焊缝横截面的实验测试结果与数值模拟结果进行了对比,结果表明,两者基本吻合。更多还原

【Abstract】 In keyhole plasma arc welding (PAW), the forming and sustaining of the keyhole involves complicated physical mechanism. The shape and dimensions of the keyhole directly determine the heat interaction along the thickness direction of the workpiece, the penetration depth and the weld bead quality. It has theoretical and practical significance to deeply analyze and study the keyhole behaviors and its effect on the forming of the weld bead.First of all, the experiments of Keyhole PAW on the 6 mm-thickness and 8 mm-thickness stainless steel workpieces are conducted. And the efflux plasma voltage, and the shape and sizes of PAW welds are measured under different welding conditions in order to get the experimental data to verify the models of the keyhole and the weld pool.Based on in-depth analysis of the forces acting on the weld pool, the keyhole model is established according to the force-balance condition on the keyhole wall. The shape and dimensions of quasi-steady state keyhole are calculated. And the results of the simulation agree well with the experimental measured keyholing cionditions which demonstrate the rationality and applicability of keyhole model.Primary discussion on the transformation mechanism of the keyhole from "blind (partial)" to "open (complete)" in PAW process is conducted based on the each action force on the keyhole wall. The magnitude of each force is calculated. The results indicate that the forming of the open keyhole is caused by the drastic change of the arc force with increasing the welding current, and the sudden transformation of the depth of the keyhole is owing to the concentration of the arc force in partial areas. To integrate the keyhole model with the model of combined volumetric heat source, the shape and dimensions of the keyhole are used to calibrate some parameters of the combined volumetric heat source. The temperature fields of the 6 mm-thickness and 8 mm-thickness stainless steel plates are calculated respectively. The calculated fusion line at the transverse cross-section of PAW welds are compared with the experimental measurements. It is found that the predicted results are in agreement with the experimental data.更多还原