【作者】 张顺善；

【导师】 邹增大；

【作者基本信息】 山东大学 ， 材料加工工程， 2010， 博士

【摘要】 随着焊接技术的发展,如何提高电弧焊的生产率、焊接质量以及拓展其应用领域成为研究者们关注的焦点。传统电弧焊工艺由于熔敷系数低,使其提高焊接生产效率受到了一定限制,合理分配电弧热在母材和焊丝的热能比成为近年来电弧焊的重要研究方向。双丝间接电弧气体保护焊是一种新的焊接工艺,属于熔化极气体保护焊,焊接过程电弧在工件与焊丝间燃烧,双丝间接电弧焊电弧形成于两焊丝端部；其接线方式不同于传统电弧焊,双焊丝分别与电源的正负极相接,双丝均为熔化极,电弧能量主要熔化焊丝,只有很少一部分电弧热量用于熔化母材,因此其熔敷速度高,电能利用率高；由于母材几乎没有电流通过,该方法还具有熔合比小、焊接应力和变形小的特点,是一种具有良好应用前景的高效焊接工艺。双丝间接电弧焊焊接设备异于传统电弧焊焊接设备。本文首先对双丝间接电弧焊设备的关键部件焊枪进行了优化设计。双丝间接电弧焊,电弧形态直接影响熔深和焊接接头质量。间接电弧的本质与传统电弧焊相同,其形态受诸多因素影响。本文围绕主要工艺参数及磁场对间接电弧形态影响规律开展研究,并对不同电弧形态下焊接熔深的变化规律进行了试验研究。研究借助的主要设备和仪器包括FASTCAMSuper-10KC高速摄像系统、Agilent54624A数字示波器、LZ-630数字特斯拉计、自行设计外部励磁设备及NBC-350型逆变式CO2气体保护焊电源等；采用的试验材料为Φ1.2mm的H08Mn2SiA焊丝,3mm厚的Q235试板,保护气体为Ar及与CO2的混合气体,试验方法为平板堆焊。在对焊枪的设计中,主要对焊枪部件结构、联结方式及保护罩气室结构进行优化设计和数值模拟。焊枪设计中综合考虑两焊丝的对中性、与导电嘴之间的相互绝缘、形状尺寸的灵活性、工艺可达性、送丝阻力及气体的保护效果等诸方面,以保证焊接过程稳定；利用有限元分析的方法对不同形状保护罩出口处及罩内区域的气体流动状态进行了模拟计算。研究结果表明,圆柱形内气室保护罩的保护气体流场可减小出口处气流紊乱程度,但出口处气体流速和气流压力都很低,保护效果受限；收缩形内气室保护罩的保护气体流场容易在保护罩出口处形成湍流,使空气混入而降低保护效果；变截面形状内气室的保护罩既有效地改善了出口处气流紊乱现象,又能增加气体流速和气流压力,是一种较理想的保护罩内气室设计。决定变截面保护罩内气室结构的主要参数是圆柱形柱面高度h及收缩处坡度θ,研究表明h、θ分别设计为20mm及45°为宜。对双丝间接电弧特性的研究试验发现,双丝间接电弧焊阴极焊丝熔化速度远大于阳极,二者与其焊丝送进速度相等是间接电弧稳定燃烧的前提,在送丝速度发生微小变化的情况下,由电弧的自调节作用,能使电弧恢复和保持稳定燃烧,但送丝速度与熔化速度相差较大时,电弧将不稳定甚至断弧。影响双丝间接电弧气体保护焊焊丝熔化及熔深的主要工艺参数包括焊丝伸出长度L、两焊丝夹角α、两焊丝交点到工件距离d、焊接电流I、电弧电压U、焊接速度v及选用的保护气体成分等。在其它焊接参数相同条件下,焊丝伸出长度越大,焊丝熔化速度越大,这主要是由于电阻热的原因,本文研究选用的焊丝伸出长度为10mm；随着两焊丝夹角变小,电磁收缩力增大,间接电弧形态变细变长,焊接熔深增加,同时夹角的变化还会对电弧静特性产生影响。试验研究表明夹角选为20°-40°为宜；两焊丝交点到工件的距离对焊接熔深大小有决定性影响,随着距离的减小对间接电弧机械压缩作用增大,熔深增加。试验表明,两焊丝交点到工件距离选择在6-8mm时,易于获得较大的焊接熔深；随焊接电流的增加,焊接熔深增加,但增加至一定值时,电弧出现分散现象而导致熔深减小随电弧电压的增加熔深变化不大,熔宽增加较明显；焊接速度为10mm/s-11mm/s时有利于获得较大的焊接熔深；保护气体中加入CO2可使电弧变收缩,电弧热量变集中,焊接熔深增加,但当CO2比例在50%以上时,飞溅量增加,焊接过程不稳定,75%Ar+25%CO2为较理想的保护气体组分。双丝间接电弧中带电离子的运动轨迹决定了电弧的形态,本文对双丝间接电弧焊焊接电流产生的自身磁场分布状态进行了研究,并对xoz面内各点的自磁场强度进行了计算和测量。利用外加磁场改变电弧内部离子运动的轨迹,以改变电弧形态进而改变熔深。研究指出对间接电弧施加横向磁场时,随正横向磁场磁感应强度增加,电弧变得细长,焊接熔深增加；施加纵向磁场时,电弧发生偏转,电弧绕轴线旋转,旋转半径与磁场大小有关。随外加纵向正磁场强度增加,焊接熔深略有减小；随外加纵向负磁场强度增加,焊接熔深也略有减小。双丝间接电弧焊的熔滴过渡形式包括大滴过渡、短路过渡、射滴过渡和射流过渡。由示波器记录不同过渡形式下电弧电压及焊接电流变化可知,射流过渡时焊接过程较稳定,可获得良好焊缝成形。双丝间接电弧焊其射流过渡的临界电流值决定于工艺参数,在一定参数下,两焊丝夹角的减小及保护气体成分中C02含量的增多使得射流过渡临界电流值降低,而焊丝长度的增加则使临界电流值升高。在一定的焊接工艺参数下施加横向磁场,随正向磁场强度增加熔滴直径变小,熔滴过渡频率增加；而随反向磁场强度增加,熔滴变大,过渡频率降低。施加纵向正、负磁场,熔滴脱离丝极其运动轨迹分别向阴阳极焊丝侧偏转,并随磁场强度增加,偏转程度增加,熔滴直径变大。更多还原

【Abstract】 With the development of welding technology, it has become the research focus how to improve the welding efficiency and quality and broaden its application scope. Traditional welding methods are limited in the application because of low deposition coefficient, so it is necessary to find a new way to distribute the energy between wires and base metal more properly. Twin-wire indirect arc welding is a new fusion welding method. In the process of twin-wire indirect arc welding, the welding arc burns between the twin wires instead of between the wire and the base metal. So the arc is called indirect welding arc. In this method, the twin wires are connected with the negative pole and the positive pole of the DC power source respectively, and the base metal is an independent unit. Most of the energy is used to melt the wires while a little for base metal, so the deposition coefficient is higher. What’s more, because there is almost no current passing the base metal, the penetration ratio, residual stress and welding deformation is lower in this new method. So twin-wire indirect arc welding is a high efficiency method of good prospect.The equipment of indirect arc welding is different from conventional fusion welding equipment. In this study, the key component of the equipments-the welding torch was optimized firstly. On one hand, the welding arc shape in the indirect arc welding process affects the weld penetration and weld quality, on the other hand, the arc shape is affected by many factors. In this paper, the affecting laws of process parameters and magnetic field on the indirect arc shape were studied. Meanwhile, the penetration changes with different indirect arc shapes were discussed by experiments. The main devices in the experiments include FASTCAMSuper-10KC high-speed camera, Agilent54624A digital oscilloscope, LZ-630 teslameter, the self-designed external excitation equipment, twin-wire indirect arc welding equipment. The welding consumables include H08Mn2SiA wires ofΦ1.2, Q235 plate of 3 mm thick, shielding gases of pure Ar or compound of Ar and CO2. The welding experiments were carried out on plates by surfacing.While designing the welding torch, the torch structure, component connection and the boot cap shape were simulated and optimized. Many factors were considered, such as the centration of twin wire, insulativity of wire from the contacts, flexibility of the shape, the reliability and gases’protective effects. The new structure of twin severely bended contact matching insulated parts by vertical thread is replaced by twin slightly bended contacts matching insulated parts by horizontal thread, and the new structure is easy for operation and maintenance. The protective effects of three boot caps were contrasted by numerical method. And the varied cross-section boot cap was chosen finally for better protective effect, with its cylindrical surface length of 20mm and included angle of 45°.The experiments on indirect arc characteristics show that the melting rate of negative wire is highly faster than positive wire. It is the premise for arc burning stably that the wire melting rate is the same as the wire feeding rate for both poles. When the wire feeding rate is changed a little, the arc could be adjusted by itself and remain stable. However, the arc would burn unsteadily, even out if the wire feeding rate is severely higher or lower than the melting rate.In twin-wire indirect arc welding process, there are several parameters that could affect the appearance of the welds and the welding quality. The parameters include wire extension, included angles of twin wires, the distance from wires’ crossing point to base metal, welding current, arc voltage, welding speed and percentage of CO2 in protective gas, called L,α, d, I, U, v, CO2%, respectively. Experiments show that the wires’melting rate increases with increasing of wire extension, which is mainly caused by increasing resistance heat, and the welding process would be unstable when the wire extension is too long. The proper value of L for good appearance of weld and welding quality is 10mm. The change of the included angle of twin wires would affect indirect arc shape and arc forces on base metal, and then the penetration depth of the joint. The arc shape turns thinner and longer and the arc forces on base metal turns bigger with decreasing of included angle, accordingly, the penetration depth increases. The distance of the two wires’ crossing point to the base metal is a critical factor for penetration depth, when the distance becomes short, the indirect arc is compressed severely and the welding penetration would be increased. The proper value range of the distance is 6-8mm. The arc shape turns centralized and the penetration depth increases with the increasing of welding current. However, the arc shape turns dispersed and the penetration depth decreases when the current is too high. The arc shape turns large and bright and the weld width increases with the increasing of arc voltage while penetration depth changes little. The welding speed of 10mm/s-11mm/s is proper for higher penetration. Different composition of the protective gas affects the arc shape because of different physical and chemical properties, the arc turns thinner and the penetration depth increases with the increasing of CO2 percentage in Ar-CO2 mixed shielding gas. However, when CO2 percentage is higher than 50%, the amount of spatter increases, and weld appearance is bad. The proper composition of mixed shielding gas is 75%Ar+25%CO2.The change of magnetic field distribution around the twin wires would affect the motion of particles and the arc shape, and the arc force on the base metal and the penetration depth would alter too. By the self-designed external excitation equipment, external magnetic field including transverse magnetic field and longitudinal magnetic field was applied to change the magnetic field distribution around the twin wires in order to get ideal indirect arc shape. All the magnetic fields affect the arc shape and the process property. The arc shape turns thinner and the penetration depth increases with the increasing of forward direction transverse magnetic field intensity, inversely, the arc turns shorter and the penetration depth decreases. The penetration and the weld width affected by the longitudinal magnetic field were studied. The mechanism of the effect of applied magnetic fields on arc was discussed and the steady-state model of indirect arc was established, and indirect arc can be expressed by axial and radial component of current vector and external magnetic field vector.The modes of metal transfer in twin-wire indirect arc welding include globular transfer, short circuiting transfer, projected transfer and spray transfer. Usually, the transfer modes of twin wires are different because of different heat production of two poles, so there are totally seven different kinds of transfer mode considering different matching modes of two poles. The welding current and arc voltage recorded by the oscilloscope with different transfer modes show that the mode of spray transfer is the most stable mode, which is considered as the precondition for good weld appearance and stable welding process. The influence of the process parameters and the applied transverse magnetic field on the critical current value was investigated. The critical current value becomes lower with decreasing of included angle and increasing of CO2 percentage in the mixed shielding gas. Applied forward transverse magnetic field would refine the droplets and promote droplets transfer, and the reverse transverse magnetic field would hinder droplets transfer, inversely.更多还原