铝合金P-GMAW电

发布时间：2018-03-17 14:49

本文选题：P-GMAW　切入点：热惯性　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：脉冲熔化极气体保护焊(Pulsed current gas metal arc welding,简称PGMAW)热输入量小、焊接变形小、生产率高,被广泛应用于铝合金、高强钢等薄板及热敏感性材料的焊接生产中。然而,P-GMAW过程参数较多,焊接过程中电弧、熔池、熔滴过渡等多物理过程相互作用,电场、磁场、温度场、流场等相互耦合,且脉冲电流的快速变化给电弧及熔池行为带来影响,多物理过程、多因素耦合的复杂过程使得P-GMAW过程动态变化机理至今仍未被完全掌握。本文以数值模拟为主要研究手段,结合实验观察,研究P-GMAW过程中多因素耦合作用下焊接电弧行为,阐明脉冲电弧等离子体热惯性对焊接电弧及过程稳定性的影响机理。基于对脉冲电弧及熔池动态行为的观察和分析,以研究周期性变化的电弧对熔池振荡行为的作用机制。同时分析了金属蒸气对熔化极气体保护焊(Gas metal arc welding,简称GMAW)电弧特征的影响,以揭示金属蒸气对焊接电弧及熔池行为的影响机制。本文在综合考虑焊丝、电弧、熔池流体流动、熔池表面变形、金属蒸发以及熔滴与电弧、熔池之间的相互耦合作用下,建立了适合于描述P-GMAW电弧及熔池行为的三维动态自收敛数值模型。并基于实验所得的电弧轮廓、温度场、电压及焊缝成形,验证了模型的可靠性。表明该模型能较好地模拟P-GMAW焊接过程,以揭示该过程中复杂的物理现象及机理。基于该模型,所获得的研究结果如下:通过P-GMAW焊接电流下降过程中的热惯性及电弧特征的分析,研究了热惯性对焊接过程稳定性的影响机理。结果表明热惯性主要通过增加电弧-焊丝、电弧-熔池界面处的温度,提高电弧的导电性来实现稳弧作用。热惯性在焊接电弧区域存在两个高值区,一个位于焊丝的正下方,一个位于熔池的正上方,其最大值随着焊接电流下降速度的提高而升高。热惯性的稳弧作用存在临界值,电流下降速度越大热惯性作用越明显,对于本文给定的脉冲峰值电流220 A、基值电流90 A的指数型脉冲电流,当焊接电流下降速度大于260 A?ms-1,热惯性可显著提高电弧温度及焊接过程稳定性。研究了P-GMAW脉冲电弧的动态行为,以及其对熔池振荡的作用机制。结果表明电弧压力是熔池振荡的关键因素。P-GMAW焊接电弧形貌的周期性变化,使得热输入及作用于熔池表面的电弧压力交替变化,熔池表面发生不同程度的变形,最终导致熔池振荡。熔池的振幅取决于脉冲峰值电流及基值电流的差值,且随着脉冲峰值电流的增加而增加。对于本文给定的脉冲峰值电流220 A、基值电流90 A的指数型脉冲电流,脉冲峰值电弧压力为基值电弧压力的6倍,熔池振荡幅度为0.8 mm。分析了不同电流条件下,GMAW焊接过程中金属蒸气的分布及其对电弧特征、热输入及熔池行为的影响。结果表明焊接电弧中的金属蒸气主要来源于焊丝端部金属的蒸发,其蒸发率高于熔池表面金属蒸发率的12倍,因而金属蒸气集中分布在焊丝端部的周围及焊接电弧的中心,并且焊接电流越大,分布越集中。金属蒸气降低了焊接电弧的欧姆热,增加了电弧辐射热损失,从而降低了焊接电弧中心的温度,使得焊接电流更加均匀的通过电弧弧柱。电弧温度的降低大大减少了焊接热输入,并且随着焊接电流的增大金属蒸气的作用更加明显,且发现铝合金GMAW焊接金属蒸气对热输入的降低可达20%~30%。
[Abstract]:P-GMAW (Pulsed current gas metal arc welding, referred to as PGMAW) small amount of heat input, small welding deformation, high productivity, is widely used in Aluminum Alloy, welding production of high strength steel sheet and heat sensitive materials. However, more P-GMAW process parameters in the process of welding arc and weld pool so, droplet interaction processes, electric field, magnetic field, temperature field, flow field coupling, fast changing and pulse current to the influence of welding arc and welding pool behavior, multi physical process, the complex process of multi factor coupling mechanism of the dynamic process of P-GMAW has not yet completely understood. Based on numerical simulation as the main research method, combined with the experimental observation, the welding arc behavior of coupling effect of P-GMAW in the process of multi factors, clarify the pulsed arc discharge plasma thermal inertia effects on stability of arc welding machine and process Daniel. Observation and analysis of the pulsed arc and weld pool dynamic behavior based on periodic variation of arc on weld pool oscillation mechanism. At the same time analyzed the metal vapor of GMAW (Gas metal arc welding, referred to as GMAW) in order to reveal the influence of arc characteristics, the arc and metal vapor welding pool behavior influence mechanism. Based on the comprehensive consideration of welding arc and weld pool fluid flow, weld pool surface deformation, metal evaporation and droplet and arc, the coupling interaction between the weld pool, the self convergent numerical model is established for describing 3D dynamic P-GMAW of welding arc and welding pool behavior and arc. Based on the experimental profile, temperature field, forming and welding voltage, the reliability of the model was verified. The results indicated that the model can simulate the welding process of the P-GMAW, in order to reveal the process of complex physical phenomena and mechanism. In this model, the results of the study are as follows: through the analysis of P-GMAW welding current decreased the thermal inertia and arc characteristics in the process of research, the thermal inertia influence mechanism on the stability of the welding process. The results show that the thermal inertia mainly by increasing the arc welding, arc - welding pool surface temperature field, to achieve the stability of arc improve the conductivity of the arc. The thermal inertia in the welding arc region there are two high value areas, located in a wire just below, one in the molten pool is above the maximum value increased with the decrease of welding current speed increases. The effect of stabilizing arc thermal inertia has a critical value, the current decline rate is the heat inertia effect is more obvious, the pulse peak current to the given 220 A base value index type current 90 A pulse current, when the welding current rate of decline is greater than 260 A? MS-1, thermal inertia can significantly improve the arc temperature and welding The process of stability. To study the dynamic behavior of P-GMAW pulse arc, and the weld pool oscillation mechanism. The results show that the arc pressure is the periodic change of.P-GMAW key factors of weld pool oscillation of the welding arc shape, arc pressure variation makes the heat input and the effect on the weld pool surface, different degree of deformation of weld pool surface happen, resulting in weld pool oscillation amplitude depends on the weld pool. The peak current and base current difference, and increased with the increase of pulse peak current pulse peak current. For the given base value 220 A, 90 A power exponential flow pulse current, pulse peak arc pressure 6 times as the base the value of arc pressure, weld pool oscillation amplitude is 0.8 mm. analysis of the different current conditions, the distribution of metal vapor GMAW welding process and the influence of heat input on the arc characteristics and weld pool behavior. The results showed that Welding metal vapor arc mainly comes from the end of wire metal evaporation, the evaporation rate is 12 times higher than the surface of the molten pool of metal evaporation rate, so the metal vapor concentration distribution in the peripheral end of the wire and the center of the welding arc and the welding current is large, the distribution is more concentrated. The metal vapor reduced ohmic heat welding the increase of arc, arc radiation heat loss, thereby reducing the temperature of the arc center, the welding current is more uniform by the arc column. To reduce the arc temperature and reduces the welding heat input, and with the increase of welding current of metal vapor effect is more apparent, and found Aluminum Alloy GMAW welding of metal vapor the heat input decreased up to 20%~30%.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG457.14

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