Microstructures of 2219 twin wire welded joints

With thick plates of 2219 high-strength alloy, the microstructures of welded joints with twin wire MIG welding were analyzed. Experimental results show that no hot crack was found in the weld due to discontinuous distribution of cocrystallization with low melting temperature, but porosity is serious in the first weld seam that is mainly composed of equiaxial grains with uneven sizes. As the poor position of the whole welded joint, fusion zone has big and coarse grains, uneven microstructures ; In quenching zone, there exist a lot of soaked microstructures that cocrystallizntion with low melting temperature solute into matrix, thus strengthening the metal in this zone; In excessive aging zone, much more phases that distribute evenly will be separated from the matrix; Ontside this zone, properties and microstructures of the metal are basically similar to matrix due to the relatively low temperature or unaffected heat in the zone during welding.

Micro-mechanical properties of 2219 welded joints with twin wire welding

Nanoindentation method was adopted to investigate the distribution regularities of micro-mechanical properties of 2219 twin wire welded joints, thus providing the necessary theoretical basis and guidance for joint strengthening and improvement of welding procedure. Experimental results show that in weld zone, micro-mechanical properties are seriously uneven. Both hardness and elastic modulus distribute as uneven sandwich layers, while micro-mechanical properties in bond area are much more uniform than weld zone;In heat-affected zone of 2219 twin wire welded joint, distribution regularity of hardness is similar to elastic modulus. The average hardness in quenching zone is higher than softening zone, and the average elastic modulus in solid solution zone is slightly higher than softening zone. As far as the whole welded joint is concerned, metal in weld possesses the lowest hardness. For welded specimens without reinforcement, fracture position is the weld when tensioning. While for welded specimens with reinforcement, bond area is the poorest position with joint strength coefficient of 61%. So, it is necessary to strengthen the poor positions--weld and bond area of 2219 twin wire welded joint in order to solve joint weakening of welding this kind of alloy.

FEM analysis of stress evolution in twin wire welding of Al alloy

Twin wire weld temperature results calculated by classical double ellipsoid heat source model are bigger than the experimental results. By analyzing the shape of twin wire welding arcs and the track of droplets transition, the phenomena that both the fore arc and rear arc of twin wire welding deflect to the middle of the two arcs is found. Based on this the double ellipsoid heat source model is amended, and a heat source model which can be applied to calculate the temperature field of twin wire welding was put forward. This model is testified by actual experiment of temperature sampling. Then, the evolution regularities of longitudinal and transverse stress for 2219 sheets were investigated under the condition of twin wire welding. The result shows that longitudinal residual stress value of twin wire welding is 10% higher than that of the single wire welding.

TANDEM and GMAW Twin Wire Welding of Q690 Steel Used in Hydraulic Support

Compared with using semi-automatic gas shielded arc welding, using automatic TANDEM twin wire welding and twin wire gas metal arc welding （GMAW） to weld Q690 steel, a low-alloy high-strength structural steel used in the hydraulic support in the fully-mechanized mining face, the welding speed, deposition rate, production environment and welding quality can be obviously improved. Compared with GMAW twin wire welding, a refined micro- structure in the weld and heat-affected zone （HAZ）, narrow HAZ and improved joint strength were achieved with TANDEM on Q690. Also, due to the push-pull pulsed way in TANDEM welding, the droplet transfer, distribution on heat flow and interaction between two arcs were completely different from those in GMAW twin wire system. The heat input of TANDEM is only about 76.6% of GMAW, and correspondingly, the welding speed and welding seam can be obviously improved. The complete oscillation caused by TANDEM pulsed current occurred in the welding pool, which refined the grains in the microstructure. The results show that TANDEM twin wire welding is very suitable in the welding of Q690 used in the hydraulic support.

Electromagnetic Characteristic of Twin-wire Indirect Arc Welding

Traditional welding methods are limited in low heat input to workpiece and high welding wire melting rate. Twin-wire indirect arc（TWIA） welding is a new welding method characterized by high melting rate and low heat input. This method uses two wires one connected to the negative electrode and another to the positive electrode of a direct-current（DC） power source. The workpiece is an independent, non-connected unit. A three dimensional finite element model of TWIA is devised. Electric and magnetic fields are calculated and their influence upon TWIA behavior and the welding process is discussed. The results show that with a 100 A welding current, the maximum temperature reached is 17 758 K, arc voltage is 14.646 V while maximum current density was 61 A/mm2 with a maximum Lorene force of 84.5 ~tN. The above mentioned arc parameters near the cathode and anode regions are far higher than those in the arc column region. The Lorene force is the key reason for plasma velocity direction deviated and charged particles flowed in the channel formed by the cathode, anode and upper part of arc column regions. This led to most of the energy being supplied to the polar and upper part of arc column regions. The interaction between electric and magnetic fields is a major determinant in shaping TWIA as well as heat input on the workpiece. This is a first study of electromagnetic characteristics and their influences in the TWIA welding process, and it is significant in both a theoretical and practical sense.

Inclusion behavior and microstructure of weld metal with Ce in twin wire high heat input submerged-arc welding

In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al_2O_3,MnO,SiO_2,TiO,Ce_2S_3,CeS,Ce_2O_2S and Ce_2O_3. Under the effect of welding thermal cycle,oxy-sulfides inclusions of Ce,the diameter of which was less than 2. 0 μm,slightly grew larger,but the composition and type of the inclusions didn't change. The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite. In the coarse-grained heat affected zone of weld metal,home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed. It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite. Meanwhile,sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries,where high dislocation density was located,and grew inside the neighboring carbon-depleted austenitic regions. The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.

Microstructures and Properties of Copper-steel Welded Joint by Twin Wire Welding

The paper studies the twin wire butt welding of 6mm-thick T2 copper and Q235 steel plate by using the twin wire consisting of one copper-plated welding wire and one steel welding wire.According to the appearance detection,the weld joint gained is sound in shape without crackles,pores,incomplete fusion and other defects.As shown by the mechanical property,SEM and EDAX and in the metallographic analysis and test,the rupture position of copper-steel welded joint is located in the copper-part HAZ when the tensile strength reaches above 210MPa and Fe content of the welded joint involved in 1# test specimen reaches around 22.78%-26.75%,with the hardness achieving between 102～107HB and the weld structure being (α+ε) duplex solid solution.

Prediction of cooling time t8/5 in twin wire submerged arc welding of intermediate thickness plate

Twin wire submerged arc welding （SAW） is widely used in oil or gas line pipe fabrication because of its high productivity. To investigate the strength and toughness of the heat-affected zone （HAZ） in twin wire SAW, the cooling time t8/5 of the coarse grained zone must be studied. The authors presented a method of predicting the cooling time in twin wire SAW of intermediate thickness plate. Based on Rosenthal analytical solutions, an energy factor was introduced to describe the energy contribution of the two wires, equations of thermal cycle and cooling time in twin wire SAW of both thick, and thin, plates were developed. Weighting factors determined by actual thickness and critical thickness were adopted to represent the thermal cycle and cooling time of intermediate thickness plate through linear interpolation with thick, and thin, plate solutions. The predicted cooling time for an intermediate thickness plate was verified experimentally, and the predicted results agreed therewith.

Study on twin-wire pulsed MIG welding power supply based on DSP and CAN

A design proposal for twin-wire pulsed MIG welding power supply based on DSP （ digital signal processor） and CAN （ controller area network ） is put forward. By ase of the CAN bus, the synergic control between the master and slave power supplies can be realized. And in this way, their peak currents can be guaranteed to be alternative and the interference between the two arcs can be decreased efficiently. The hardware design, software design and relative tests are provided in this paper. Tests show that the power supply can meet the design requirements of twin-wire welding.

Arc characteristics of twin-wire indirect arc gas shielded welding

Twin-wire indirect arc gas shielded welding is a novel welding method. By recording the arc shape and welding parameters, the effects of welding parameters and included angle on arc characteristics are discussed in this paper. The experimental results show increasing welding current can prompt centralized and straight of arc due to increasing plasma force and electric magnetic pinch effect. Increasing arc voltage can increase the size and brightness of the arc, as a result of increasing arc energy. The reducing of included angle increases the electric magnetic pinch effect, the arc becomes slender and supplies higher energy. It is thought the smaller included angle is beneficial to obtain perfect weld bead.

Twin-wire Submerged Arc Welding Process of a High-strength Low-alloy Steel

The measurement of thermal cycle curves of a high-strength low-alloy steel （HSLA） subjected twin-wire submerged arc welding （SAW） was introduced. The thermal simulation test was performed by using the obtained curves. The impact toughness at -50 ℃ temperature of the simulated samples was also tested. OM, SEM and TEM of the heat-affected zone （HAZ） of some simulation specimens were investigated. The results showed that the HSLA endured the twin-wire welding thermal cycle, generally, the low-temperature toughness values of each part of HAZ was lower than that of the parent materials, and the microstructure of coarse-grained zone（CGHAZ） mainly made up of granular bainite is the reason of the toughness serious deterioration. Coarse grain, grain boundary carbide extract and M-A island with large size and irregular polygon, along the grain boundary distribution, are the reasons for the toughness deterioration of CGHAZ. The research also showed that selected parameters of twin-wire SAW can meet the requirements to weld the test steel.

Twin-wire SAW welding of 70 kg class high strength steel

The twin-wire SAW welding process was investigated using Baosteel 70 kg class high strength steel, and the properties of the joints were studied using conventional single and double-faced grooves as well as an optimized groove. The results showed that by using an optimized double-faced groove, a small root face, and no back gouging, a small welding heat input was achieved and thus the joint strength and toughness were improved significantly. Also, removing back gouging reduced the labor required in the process. The weld reinforcement and deformation were observed to be rather small.

Research and engineering application of the arc welding pulsed controller technology

The tenacity of heat-affected zone （HAZ） will decline and the size of grains will increase, because of the overheating on HAZ when submerged are welding （SAW） is ased to thick plate with high heat input. The shaping will worsen when SAW is used to thin plate with high current at high speed. A new SAW technology, the pulsed direct current （DC） automatic SAW, will be put forward in this paper in order to overcome the above shortcomings. And a pulsed controller with micro-controller unit （MCU） as the core, nixie tube （NT） and keyboard as the man-machine conversation interface is developed. The main functions of the pulsed controller include the output of pulsed welding current and the working with twinwire. The research has widely prospects in application with significant meanings in theory and practical engineering.

双丝三电弧焊热源优化及数值模拟

为研究双丝三电弧焊焊接温度散布规律,根据其电弧形态和脉冲频率建立了适用于双丝三电弧焊接的体+面热源,并根据焊丝的倾角对其进行了旋转计算,利用有限元技术模拟了6 mm厚Q235碳素钢的双丝三电弧焊焊接温度场,通过遗传算法对其热源参数进行了迭代优化,提高了计算效率。计算结果表明:温度场呈长椭圆状分布,且最高温度和最大温度梯度都出现在R弧热源处,其原因是此处同时积累了R弧电弧热量和L弧焊后凝固时的热量;有限元模型温度场与实验温度场结果对比吻合度较高,其结果可为拓展双丝三电弧焊的应用和优化工艺参数提供仿真基础。

双丝窄间隙焊接工艺参数对焊缝成形的影响

通过工艺试验,研究了双丝共熔池窄间隙焊焊丝与侧壁间距、双丝前后间距和双丝倾角3个工艺参数对焊缝成形的影响。结果表明,焊丝与侧壁间距减小,侧壁熔深和表面下凹增加;沿焊接方向双丝倾角为零时,侧壁熔深和表面下凹达到最大值;而在电弧和熔池热量的共同作用下,双丝前后间距增大,侧壁熔深和表面下凹先增大,后减小,在5~10 mm内达到最大值。在不形成指状熔深时,这3个参数对焊缝熔深影响不大。采用I形坡口会出现底部未熔合,调节这3个参数不能消除未熔合现象。

双丝焊热源模型

利用经典的双椭球形热源模型进行双丝焊温度场的计算,模拟结果与测量结果的对比表明此模型应用在双丝焊温度场的数值模拟中存在很大误差。通过对双丝焊电弧形态及熔滴过渡路径进行分析,发现双丝焊时前丝和后丝的电弧均向两丝中间偏转,利用此现象解释了模拟结果误差产生的原因。并以此为基础,对双椭球形热源模型进行修正,提出了双丝焊的热源模型,利用提出的模型进行计算得到的结果和测量结果吻合良好。

双丝高速软开关脉冲MAG焊装备

将CAN(局域控制网)总线技术、软开关技术、脉冲焊技术等有机地结合,研制了结构紧凑、一体化、协同控制的TANDEM型双丝焊装备。在深入分析双丝焊工艺要求的基础上,引入新型双闭环控制模式,实现了适合双丝焊要求的脉冲焊电源动特性、外特性。为减少双丝焊电弧之间的干扰,将CAN总线技术成功应用于双丝焊装备的通信控制中,设计了双丝焊装备的协同控制装置。结果表明,电源各项电气性能都满足了设计要求,且焊接过程稳定、飞溅小、焊缝成形好、焊接速度快、热输入小、变形小,突出显示了双丝高速焊的优点。

焊接残余应力的测试及研究

依据应力测量的基本理论,采用LabView语言编程自行设计制备了焊接残余应力测量系统。对45号钢和22SiMn2TiB钢焊缝的焊趾处进行超声冲击处理,并测量处理前、后的残余应力。结果表明,超声冲击处理能够将焊接残余拉应力转变为压应力,45号钢和22SiMn2TiB钢处理前、后的纵向残余应力均值为169、-63、296、-49MPa,下降率分别为137%和117%。

单丝、双丝MIG对7A52铝合金焊缝性能和变形的影响

采用单丝、双丝MIG两种焊接工艺研究7A52铝合金焊缝抗拉强度和硬度分布以及平板对接产生的自由变形特点。结果显示:5A56、5356焊丝形成的焊缝强度低于母材;单、双丝焊缝截面硬度分布规律基本相同,但双丝焊较单丝焊热影响区减小1/3;单丝焊对接缝的自由变形远大于双丝焊。

磁场对双丝间接电弧形态的影响

对双丝间接电弧在自身磁场及外加磁场变化的情况下,电弧形态随磁感应强度值的变化规律进行了研究.自身磁场变化通过改变两焊丝夹角角度实现,外加磁场由励磁线圈产生,对间接电弧施加横向及纵向磁场,磁场强度利用特斯拉计测出,并借助高速摄像系统对磁场变化时的电弧形态进行拍摄.研究表明,通过改变两焊丝夹角及施加横向磁场的方式,可使两焊丝所夹区域内外磁场强度之差变大,使得电磁力的外扩作用增大,电弧变细长;施加纵向磁场时,电弧在与两焊丝垂直的平面内发生偏转,其偏转程度随纵向磁场强度增加而增加.