考虑金属蒸汽气氛下电弧等离子体数值模拟
发布时间：2018-08-22 09:31
【摘要】：在采用以惰性气体为保护气的焊接工艺方法时,如MIG焊,气体经电离形成电弧等离子,必然会有金属蒸汽进入电弧等离子体内,进而影响电弧特性。若不考虑金属蒸汽的影响,会对电弧温度场等一系列物理场的认识造成偏差,甚至导致焊接过程效率低,影响焊缝美观甚至导致质量低下。由于电弧等离子温度极高,形成过程极其复杂,通过试验手段难以进行观察和测量,因此,为了深入研究此课题,本文就以计算机数值模拟技术为手段,探究考虑金属气氛下电弧等离子的行为特性,有助于更好选择电弧焊接参数,稳定焊接过程,保证焊接质量。首先,以熔化极气体保护焊(MIG焊)为主要研究载体,不考虑熔滴过渡这一物理化学过程,掌握和运用连续性方程、动量守恒方程、能量守恒方程和电磁场方程以及组分输运方程组成方程组,在深刻理解电弧等离子原理、组成和产生机理的前提下,应用FLUENT仿真软件,建立考虑金属蒸汽下电弧等离子二维轴对称数学模型,简化阴极,并选取合理的计算方法进行计算。其次,从两个方面入手来进行本课题的研究。一方面,模拟计算出无金属蒸汽典型电弧等离子温度场与有金属蒸汽但不考虑辐射能损失电弧等离子温度场,对比得出结论:金属蒸汽会使电弧形态明显收缩且电弧整体温度明显下降,在研究电弧等离子体特性时,尤其是熔化极气体保护焊,将金属蒸汽考虑在内十分有必要;另一方面,在考虑金属蒸汽气氛下这个大前提之下,模拟计算不考虑辐射能电弧的一系列物理场(温度、电势、电流密度和金属蒸汽的摩尔分数)与考虑辐射能电弧的一系列物理场(温度、电势、电流密度和金属蒸汽的摩尔分数)后,对应比较,得出结论:考虑辐射能下的电弧等离子体温度进一步下降,电弧形态进一步收缩;电弧电压和电流的峰值和整体范围都增大;Fe蒸汽分布更为广泛。确定当有金属蒸汽进入电弧时,必须将辐射能考虑在内。最后,研究焊接电流、金属蒸汽蒸发率和保护气体流量对考虑金属蒸汽下电弧等离子体的影响。结果表明:增大焊接电流,电弧温度升高,形态收缩,辐射能损失加剧;增大金属蒸汽蒸发率,电弧温升高,但幅度不大,形态收缩,辐射能加剧;低气流量下,增大惰性保护气体流量,电弧温度略微升高,形态收缩,辐射能加剧。三种焊接参数对电弧影响程度依次减弱。
[Abstract]:In the process of welding with inert gas as protective gas, such as MIG welding, the arc plasma is formed by ionization of the gas, and the metal vapor will inevitably enter into the arc plasma, which will affect the arc characteristics. If the influence of metal vapor is not considered, the understanding of a series of physical fields such as arc temperature field will be deviated, and even the efficiency of welding process will be low, the appearance of weld will be affected and even the quality will be low. Because the arc plasma temperature is extremely high and the formation process is extremely complex, it is difficult to observe and measure by means of experiment. Therefore, in order to study this subject in depth, the computer numerical simulation technique is used in this paper. Considering the behavior of arc plasma in metal atmosphere is helpful to select arc welding parameters, stabilize welding process and ensure welding quality. First of all, taking MIG welding as the main research carrier, regardless of the physical and chemical process of droplet transfer, the continuity equation and momentum conservation equation are grasped and applied. The energy conservation equation, the electromagnetic field equation and the component transport equation form equations. On the premise of deeply understanding the principle, composition and generation mechanism of arc plasma, the FLUENT simulation software is used. A two-dimensional axisymmetric mathematical model of arc plasma with consideration of metal vapor is established to simplify the cathode, and a reasonable calculation method is selected for calculation. Secondly, from two aspects to carry out the study of this subject. On the one hand, the typical arc plasma temperature field without metal vapor and the arc plasma temperature field with metal vapor without taking into account the radiation energy loss are simulated and calculated. It is concluded that metal vapor can obviously shrink the shape of the arc and decrease the whole arc temperature. It is necessary to take metal vapor into account when studying the characteristics of arc plasma, especially the gas shielded electrode welding. On the other hand, a series of physical fields (temperature, potential) without taking into account the radiation energy arc are simulated and calculated under the premise of considering the metal vapor atmosphere. The current density and the mole fraction of metal vapor are compared with a series of physical fields (temperature, potential, current density, and molar fraction of metal vapor) taking into account the radiation energy arc. It is concluded that the arc plasma temperature decreases further and the arc shape shrinks further considering the radiation energy, and the peak value and overall range of arc voltage and current increase the distribution of Fe vapor more widely. It is determined that radiation energy must be taken into account when metal vapor enters the arc. Finally, the effects of welding current, evaporation rate of metal vapor and flux of shielded gas on arc plasma under metal vapor are studied. The results show that the welding current increases, the arc temperature increases, the shape shrinks, the radiation energy loss intensifies, the evaporation rate of metal vapor increases, the arc temperature increases, but the amplitude is small, the shape shrinks and the radiation energy intensifies. With the increase of inert gas flow, the arc temperature increases slightly, the shape shrinks and the radiation energy intensifies. The influence of three welding parameters on the arc is weakened in turn.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444.74
本文编号：2196697
[Abstract]:In the process of welding with inert gas as protective gas, such as MIG welding, the arc plasma is formed by ionization of the gas, and the metal vapor will inevitably enter into the arc plasma, which will affect the arc characteristics. If the influence of metal vapor is not considered, the understanding of a series of physical fields such as arc temperature field will be deviated, and even the efficiency of welding process will be low, the appearance of weld will be affected and even the quality will be low. Because the arc plasma temperature is extremely high and the formation process is extremely complex, it is difficult to observe and measure by means of experiment. Therefore, in order to study this subject in depth, the computer numerical simulation technique is used in this paper. Considering the behavior of arc plasma in metal atmosphere is helpful to select arc welding parameters, stabilize welding process and ensure welding quality. First of all, taking MIG welding as the main research carrier, regardless of the physical and chemical process of droplet transfer, the continuity equation and momentum conservation equation are grasped and applied. The energy conservation equation, the electromagnetic field equation and the component transport equation form equations. On the premise of deeply understanding the principle, composition and generation mechanism of arc plasma, the FLUENT simulation software is used. A two-dimensional axisymmetric mathematical model of arc plasma with consideration of metal vapor is established to simplify the cathode, and a reasonable calculation method is selected for calculation. Secondly, from two aspects to carry out the study of this subject. On the one hand, the typical arc plasma temperature field without metal vapor and the arc plasma temperature field with metal vapor without taking into account the radiation energy loss are simulated and calculated. It is concluded that metal vapor can obviously shrink the shape of the arc and decrease the whole arc temperature. It is necessary to take metal vapor into account when studying the characteristics of arc plasma, especially the gas shielded electrode welding. On the other hand, a series of physical fields (temperature, potential) without taking into account the radiation energy arc are simulated and calculated under the premise of considering the metal vapor atmosphere. The current density and the mole fraction of metal vapor are compared with a series of physical fields (temperature, potential, current density, and molar fraction of metal vapor) taking into account the radiation energy arc. It is concluded that the arc plasma temperature decreases further and the arc shape shrinks further considering the radiation energy, and the peak value and overall range of arc voltage and current increase the distribution of Fe vapor more widely. It is determined that radiation energy must be taken into account when metal vapor enters the arc. Finally, the effects of welding current, evaporation rate of metal vapor and flux of shielded gas on arc plasma under metal vapor are studied. The results show that the welding current increases, the arc temperature increases, the shape shrinks, the radiation energy loss intensifies, the evaporation rate of metal vapor increases, the arc temperature increases, but the amplitude is small, the shape shrinks and the radiation energy intensifies. With the increase of inert gas flow, the arc temperature increases slightly, the shape shrinks and the radiation energy intensifies. The influence of three welding parameters on the arc is weakened in turn.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444.74
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相关期刊论文 前4条
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