【作者】 王军；

【导师】 冯吉才； 李慕勤；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 博士

【摘要】 在传统电弧焊中,电弧的两极为焊枪与工件,由于直接接受电弧热,工件的热输入难以控制,稀释率过大。在某些要求焊缝熔敷率高且母材熔化量低的情况下,由于不能满足焊接要求,使得电弧焊的应用在一定程度上受到限制。如在航空、航天领域及兵器制造业,为改善钢材的导电、导热性能和表面硬度,通常需要在钢基体表面熔覆铜合金。为防止铁铜互熔引起偏析,要求在保证高焊缝熔敷率的情况下,减少基体的熔化,形成低稀释率的堆焊接头。本研究提出了钨极-熔化极间接电弧焊方法,期待解决上述问题。该方法使用单电源,电源不接工件,而是使两电极分别接熔化极焊枪和钨极焊枪,两焊枪之间成一定角度,电弧在焊丝端头与钨极之间燃烧,间接电弧热主要用于焊丝熔化,不产生熔池,间接电弧力主要用于熔滴过渡,使焊丝熔化后形成熔滴过渡到工件,实施焊接。该方法能够解决在高焊缝熔敷率情况下,最大限度降低工件母材热输入的问题。通过构建钨极-熔化极间接电弧焊系统,实现了间接电弧稳定燃烧,熔滴持续过渡。为进一步研究间接电弧焊电弧行为和实际应用奠定了基础。以铜焊丝为例,采用高速摄像技术对间接电弧焊的熔滴过渡行为及电弧形态进行了观察,并对电信号进行了采集。通过在钢表面堆焊铜合金的工艺试验,对堆焊接头的宏观形貌和微观组织进行了观察和分析。计算了熔滴的飞行速度和对工件表面的冲击力。采用红外测温仪对熔滴的温度进行了测量并计算了熔滴的热焓量。结果表明:采用平外特性电源和陡降特性电源实施该方法,均能实现熔滴的持续过渡。采用平特性电源时,熔滴过渡频率随送丝速度的增加而增加;焊接电压在16-20V时熔滴过渡频率及指向性都较高。采用陡降特性电源时,随送丝速度的增加,焊丝端头平衡位置从钨极端头的侧下方、正侧方向侧上方转变。随焊接电流的增加,熔滴的过渡频率也增加。当焊接电流大于140A时,熔滴过渡从大滴转变为射滴过渡。采用上述两种外特性电源,熔滴脱离焊丝前,间接电弧已从熔滴侧面爬升至熔滴与焊丝的界面处,降低了熔滴脱离焊丝时电弧的波动。电弧形态总体呈倒三角形,不同外特性电源、不同参数对电弧形态变化的影响规律也不同。当焊丝端头处于钨极的侧上方时,电弧形态为Y形;当焊丝端头处于钨极的正侧方时,为心形;当焊丝端头处于钨极的侧下方时,为笔尖形。焊接电压和电流的周期性波动引起了电弧形态的周期性变化,采用平特性电源的电弧形态波动较大,陡降特性电源的电弧形态波动较小。间接电弧由阴极区、阳极区和弧柱区组成,其中弧柱区的导电部分为弧芯区,不导电部分为弧焰区。电弧靠近熔化极一侧的部分为熔化极电弧区,靠近钨极一侧的部分为非熔化极电弧区,两区聚集产生倒三角电弧形态,此时电弧较亮,有利于焊丝的快速熔化。倒三角形电弧形态是磁场作用、阴极焰和阳极焰相互对冲共同作用产生的。间接电弧能够稳定燃烧是由于钨极的加入和电弧自身调节的综合作用的结果。当采用铜焊丝时,因电弧自身固有调节作用明显,使得采用陡降特性电源时电弧更加稳定。结合熔滴过渡行为和电弧形态分析熔滴受力情况及其过渡机制。熔滴受到重力、表面张力、电磁力、等离子流力和电弧力的综合作用。其中,在点对点电极排布方式中,电弧在熔滴侧面,很容易爬升到焊丝上,熔滴内部电磁收缩力主要集中作用于熔滴与焊丝相连的根部;熔滴长大过程中,焊丝端头从钨极的侧上方伸到钨极的正侧方,电弧力充当动力的成分增加,并对熔滴根部产生挤压作用,降低了表面张力,从而能够使熔滴顺利过渡。熔滴的飞行速度与电流密切相关,当焊接电流大于140A时,熔滴脱离焊丝后的飞行速度明显提高。随焊接电流的增大,冲击力先增大后减小,最后保持平稳。随焊接电流的增大,熔滴温度逐渐下降,达到1200℃后保持平稳。熔滴的热焓量较低,约为电源总输出能量的30%,熔滴未受到电弧的保温和加热作用,有效降低了工件表面的热输入。利用钨极-熔化极间接电弧焊方法在30CrMnSi钢表面采用CuSi3焊丝进行了堆焊试验。堆焊接头表面无明显缺陷,稀释率最低可达0.12%,有效抑制了偏析现象的发生。利用该方法不仅可用于堆焊,也可以用于薄板焊接。可以实现0.6mm厚薄镀锌钢板的搭接焊,钢板本身只发生了极少量的熔化。更多还原

【Abstract】 In traditional arc welding, the welding torch and the base metal act as the two electrodes of the arc. For some special occasions such as requiring the high deposition rate of the weld and small amount of fusion of the base metal, the heat input into the base metal is difficultly controlled because the base metal directly absorbs the arc heat. The large fusion of the base metal goes beyond the welding requirements and this restricts the application of the arc welding. For example, depositing Cu alloy onto steel is often applied in aviation, aerospace and weapon facture for improving the electric conductivity, thermal conductivity and surface hardness. To prevent the segreation for the mutal fusion between Fe and Cu, it is required that the fusion of the steel be decreased on condition that the high deposition ratio is ensured, and then the deposition weld with low dilution ratio be obtained.The tungsten-consumable indirect arc welding method has been presented. The base metal does not contact with the welding power source and the two output terminal connects with the consumable electrode and tungsten electrode of the weld power source. There is angle between the two welding torch and the indirect arc is generated between the two torches. The weld is created with the resultant droplets continuously transferring onto the base metal. This method can restrict the heat input into the base metal to the maximum extent while guaranteeing the deposition rate of the welding wire. The steady indirect arc and continuous metal transferring have been realized. These provide the basis for studying the arc behavior and application with the tungsten-consumable indirect arc welding.Take the Cu welding wire for example, the metal transfer behavior of the tungsten-consumable indirect arc welding is observed by high speed camera and the electrical signal is also acquired. The deposition of Cu onto steel substrate process experiment is conducted by this method. The macrostructure and the microstructure are observed. The droplet flying velocity and its impact force are calculated. By using the infrared temperature tester,the droplet temperature is obtained and its heat content is calculated.Result showed that: using constant voltage (CV) weld power source and the constant current (CC) weld power source can both realize continuous metal transfer. When using the CV power, the metal transfer frequency increases with the increase of the wire feeding speed. In 16-20V, the metal transfer frequency and its directionality can keep getting better. When using the CC power, the position of the tip of the welding wire changes from the lateral below the tip of the tungsten to the lateral upon the tip of the tungsten. The metal transfer frequency increases with the increase of the welding current. When the welding current goes beyond 140A, the metal transfer mode changed from globule transfer to spray transfer. Before metal transferred from welding wire, the indirect arc can climb to the interface between the welding wire and the droplet, decreasing the arc fluctuation.The arc shape presents inverted triangle. In different statistic characteristic of the weld power source and different parameters, the arc shape presents different patterns. When the tip of the welding wire is situated on the top left side of the tungsten, the arc shape presents Y shape; when the tip of the welding wire is situated on the left side of the tungsten, the arc shape presents heart shape; when the end of the welding wire is situated on the bottom left side of the tungsten, the arc shape presents pencil shape. The fluctuation of the arc voltage and the welding current correspond with the change of the arc shape. By using the CV power, the fluctuation of the arc is bigger than that by using the CC power.The indirect arc is composed of the cathode zone, the anode zone and the arc column zone. The arc column zone is also been composed of arc core zone and arc flame zone. According to the characteristic of the indirect arc, the whole indirect arc is also composed of consumable arc zone near the consumable electrode and the non consumable arc zone near the tungsten electrode. The convergence of the two zone produced heart arc shape, which can rapidly melt the welding wire. The integrated action by the magnetic field, the hedging between the cathode flame and the anode flame get into inverted triangle arc shape. The indirect arc is stabilized for the addition of the tungsten, the arc self-regulation. When using the Cu welding wire, the CC power is more suitable.The droplet is acted on by the gravity force, surface tension force, electromagnetic force, plasma force and arc force. The arc is situated on the right side of the droplet, and easily climbs to the welding wire. The electromagnetic force increases. The driving component of the arc force also increases,which increases extrusion on the droplet and then decreases the surface tension force.The droplet transfer rate is measured. When the welding current exceeds 140A the droplet transfers quickly. With the increase of the welding current, the impact force onto the base metal reaches the peak and then the impact force drops a little and then stabilized. With the increase of the welding current, the temperature of the droplet gradually fall and then remaining 1200℃. The heat content of the droplet metal is about 30% of the general energy of the arc. This proves that the method can decrease the heat input into the base metal effectively.The indirect arc heat mainly provides the fusion of the welding wire, and the indirect arc force mainly acts on the metal transfer. The tungsten-consumable indirect arc welding has been successfully applied on depositing CuSi3 onto 30CrMnSi steel. No obvious defect is observed and the dilution ratio is decreased at a minimum of to 0.12%. The segreation is restrained for low heat input into the base metal. This method is also successfully applied onto welding 0.6mm thin zinc coated steel plate. Small amount of fusion of the steel also proves that this methods’characteristic of decreasing heat input into the base metal.更多还原