【作者】 李大森；

【导师】 赵朋成；

【作者基本信息】 青岛科技大学 ， 材料学， 2011， 硕士

【摘要】 为了优化高速脉冲熔化极气体保护焊(GMAW)焊接工艺,本文建立了三维高速脉冲GMAW焊接熔池流体流动和传热过程的瞬态数值模型,对高速脉冲GMAW焊接熔池动态行为进行了研究。本文首先根据高速脉冲GMAW焊接热过程中伴随周期性熔滴过渡、熔池自由表面发生变形以及液面波动的特点,建立了变形熔池自由表面受迫振动及熔池自由表面波动模型,并在此基础上建立了适合于描述变形及波动熔池表面上方电弧空间内热流密度分布的新型热源模型,即热流密度在电弧空间内分布模型。然后从能量守恒定律、动量守恒定律和质量守恒定律的角度出发,建立了高速脉冲GMAW焊接热过程的控制微分方程组,并给出了相应的初始条件和边界条件,对控制方程组进行了离散化。最后用FORTRAN语言编制了相应的计算程序。利用新建的变形熔池表面受迫振动及熔池自由表面波动模型、热流密度在电弧空间内分布模型和热过程数值模型,对焊接熔池的动态行为进行了数值分析。应用变形熔池表面受迫振动及熔池自由表面波动模型,模拟了熔滴过渡引起的熔池自由表面的波动,获得了不同时刻下熔池自由表面的准确形貌。在此基础上,建立了电弧热流密度分布在三维电弧空间中的分布模型。应用该热输入模型研究了高速脉冲GMAW焊接工件的温度场和流场随时间的变化。将应用新型热源模型条件下数值模拟结果与实验测得结果相比较,结果表明新型热源模型适合于高速脉冲GMAW焊接传热、传质过程的数值模拟。本文采用显热容法处理了高速脉冲GMAW焊接过程中的相变潜热问题。计算了不同焊接工艺参数(焊接电流、焊接速度)条件下高速脉冲GMAW焊接熔池的动态行为,得到不同焊接电流和焊接速度条件下熔池三维温度场、流场和形状随时间的瞬时演变规律。分析了不同焊接电流和焊接速度条件下熔池三维温度场、流场和形状的变化趋势,与实验结果吻合良好。本文的工作能够为高速脉冲GMAW焊接工艺的工业化生产和焊接工艺参数的优化提供基础数据和理论指导。更多还原

【Abstract】 In order to optimize the welding parameters, a 3D transient numerical model for the fluid flow and heat transfer in high-speed pulsed gas metal arc welding (GMAW) is established to investigate the dynamic behaviors of weld pool.First, according to the features of periodical droplet transfer, deformation and fluctuations on weld pool free surface in high-speed pulsed GMAW, a forced vibration model and a wave fluctuation model on deformed weld pool free surfaces are established. On this basis, a new heat source model that can describe the heat flow density distribution in arc spaces above the deformed and fluctuated weld pool free surfaces is developed, which is called heat flow density distribution model in arc spaces. Second, the governing differential equations are derived as the energy conservation, momentum conservation and mass conservation, respectively. After that, corresponding initial conditions and boundary conditions are given and the governing equations are discretized. Finally, the calculating software written in FORTRAN is programmed.The dynamic behaviors of weld pools are analyzed numerically by using forced vibration and wave fluctuation models on deformed weld pool free surface, heat flow density distribution model in arc spaces and numerical model of the thermal process. The vibration and wave fluctuation of the free surface of weld pools are simulated by the established models above, so accurate morphology of weld pool free surface at different time is obtained. Therefore, the heat flux distribution of arc in 3D space is grounded on the wave behaviors of deformed weld pool free surfaces. By utilizing the heat input model, the heat and fluid flow fields of high-speed pulsed GMAW workpiece are studied carefully with time changes. Comparison between predicted data and measured ones are performed, and the results show that the new established heat source model is suitable for the numerical simulation of heat and mass transfer in high-speed pulsed GMAW. Apparent heat capacity method is used to deal with the latent heat of phase transformation.The dynamic behaviors of weld pools in different welding parameters such as welding current and welding speed are predicted, thus the transient developments of 3D heat field, fluid field and shape of weld pool with different welding parameters are obtained. The changing tendency of the 3D heat fields, fluid fields and shapes of weld pool with different welding parameters are analyzed and the predicted results show a good agreement with the experimental data.This study could provide basic data and theoretical instruction for the industry application and optimization of welding parameters of high-speed pulsed GMAW.更多还原