【摘要】：在采用以惰性氣體為保護氣的焊接工藝方法時,如MIG焊,氣體經(jīng)電離形成電弧等離子,必然會有金屬蒸汽進入電弧等離子體內(nèi),進而影響電弧特性。若不考慮金屬蒸汽的影響,會對電弧溫度場等一系列物理場的認識造成偏差,甚至導(dǎo)致焊接過程效率低,影響焊縫美觀甚至導(dǎo)致質(zhì)量低下。由于電弧等離子溫度極高,形成過程極其復(fù)雜,通過試驗手段難以進行觀察和測量,因此,為了深入研究此課題,本文就以計算機數(shù)值模擬技術(shù)為手段,探究考慮金屬氣氛下電弧等離子的行為特性,有助于更好選擇電弧焊接參數(shù),穩(wěn)定焊接過程,保證焊接質(zhì)量。首先,以熔化極氣體保護焊(MIG焊)為主要研究載體,不考慮熔滴過渡這一物理化學(xué)過程,掌握和運用連續(xù)性方程、動量守恒方程、能量守恒方程和電磁場方程以及組分輸運方程組成方程組,在深刻理解電弧等離子原理、組成和產(chǎn)生機理的前提下,應(yīng)用FLUENT仿真軟件,建立考慮金屬蒸汽下電弧等離子二維軸對稱數(shù)學(xué)模型,簡化陰極,并選取合理的計算方法進行計算。其次,從兩個方面入手來進行本課題的研究。一方面,模擬計算出無金屬蒸汽典型電弧等離子溫度場與有金屬蒸汽但不考慮輻射能損失電弧等離子溫度場,對比得出結(jié)論:金屬蒸汽會使電弧形態(tài)明顯收縮且電弧整體溫度明顯下降,在研究電弧等離子體特性時,尤其是熔化極氣體保護焊,將金屬蒸汽考慮在內(nèi)十分有必要;另一方面,在考慮金屬蒸汽氣氛下這個大前提之下,模擬計算不考慮輻射能電弧的一系列物理場(溫度、電勢、電流密度和金屬蒸汽的摩爾分數(shù))與考慮輻射能電弧的一系列物理場(溫度、電勢、電流密度和金屬蒸汽的摩爾分數(shù))后,對應(yīng)比較,得出結(jié)論:考慮輻射能下的電弧等離子體溫度進一步下降,電弧形態(tài)進一步收縮;電弧電壓和電流的峰值和整體范圍都增大;Fe蒸汽分布更為廣泛。確定當有金屬蒸汽進入電弧時,必須將輻射能考慮在內(nèi)。最后,研究焊接電流、金屬蒸汽蒸發(fā)率和保護氣體流量對考慮金屬蒸汽下電弧等離子體的影響。結(jié)果表明:增大焊接電流,電弧溫度升高,形態(tài)收縮,輻射能損失加劇;增大金屬蒸汽蒸發(fā)率,電弧溫升高,但幅度不大,形態(tài)收縮,輻射能加劇;低氣流量下,增大惰性保護氣體流量,電弧溫度略微升高,形態(tài)收縮,輻射能加劇。三種焊接參數(shù)對電弧影響程度依次減弱。
[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.
【學(xué)位授予單位】：中北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG444.74

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