Mechanism of Metal Transfer in DE-GMAW

Modification of conventional gas metal arc welding (GMAW) process is of great potential to achieve high productivity with low cost and strong usability.Double-Electrode GMAW (DE-GMAW) is such a modified arc welding process which is formed by adding a bypass torch (gas tungsten arc welding torch) to a conventional GMAW system.The mechanism of metal transfer in DE-GMAW was proposed and verified in this paper.Experiments show that the critical current is decreased so that spray transfer can be obtained at a lower current level in DE-GMAW.Analysis of this significant change in metal transfer phenomena is conducted, and explanation is given out.It is found that the bypass arc in DE-GMAW lifts the anode point on the droplets such that the electromagnetic force becomes larger and squeezes the droplets so that spray transfer can take place under welding current lower than that in conventional GMAW.     

电弧增材制造成形工艺影响因素研究

采用Ti6321A焊丝进行电弧增材制造,研究了焊枪姿态和摆动参数等工艺因素对成形的影响。结果表明,不同的焊枪角度对增材制造焊缝堆焊成形形貌具有显著的影响,当焊枪姿态由推焊变化到拉焊时,焊缝熔宽减小,余高变高,即焊缝表面铺展能力减弱;焊缝熔深在焊枪垂直时达到最大值。焊枪摆动会使增材制造表面呈现纹路特征,纹路之间的宽度直接由摆长参数决定,摆宽对焊缝熔宽有显著影响,呈近似线性关系。     

TC4金字塔点阵结构的激光焊接及其平压性能

基于用高温节点下压法成形的TC4钛合金芯体,用面芯激光焊接制备了钛合金金字塔点阵结构。用响应曲面法优化激光焊接参数,实现了点阵结构面芯连接,分析焊接节点的微观组织并进行了点阵结构平压实验。结果表明：激光功率对焊接效果有显著的影响。点阵结构面芯激光焊接的优化工艺参数为：上面板的焊接功率为1.4 kW,下面板的焊接功率为1.2 kW,离焦量为30 mm,停留时间为1 s。在激光焊接热影响区发生了马氏体转变,分布着大量的针状马氏体;熔焊区的组织为粗大β相+针状α相。在焊接节点处,从熔焊区到母材的显微硬度随着马氏体相的减少而降低。根据平压实验结果分析了金字塔点阵结构变形和破坏的规律,桁架杆失效断裂发生在热影响区。用激光焊接制备的TC4钛合金点阵结构,其平压强度为3.09 MPa,平压模量为153.25 MPa。     

焊枪倾角对熔池振荡的影响

本文利用焊枪倾角的办法,解决了快速焊接时,熔振荡信号的可靠提取问题。焊枪前倾可以有效的抑制熔池后拖现象。为了保证熔透熔池可靠的振荡,焊枪倾角θ与焊接速度 V_w 之间有一定的匹配区间,在此区间内焊枪倾角θ的变化,对熔池振荡特性没有影响,对接焊缝实验时发现,装配间隙和错边对焊接熔池振荡特性没有明显的影响。     

Diamond synthesis using an oxygen-acetylene torch

Diamond microcrystallites and polycrystalline films were grown on various substrates in the ambient atmosphere with an oxygen-acetylene welding torch. Growth is examined as a function of substrate position and temperature, and gas flow ratio. The deposited material was analyzed with Raman spectroscopy, X-ray diffraction and electron microscopy.     

On the weldability of grey cast iron using nickel based filler metal

Shielded metal arc welding process using nickel based filler metal was used to join grey cast iron. The effect of post weld heat treatment (PWHT) on the microstructure and hardness was studied. PWHT included heating up to 870 °C, holding for 1 h at 870 °C and then furnace cooling. By using nickel based filler metal, formation of hard brittle phase (e.g. carbides and martensite) in the fusion zone is prevented. Before PWHT, heat affected zone exhibited martensitic structure and partially melted zone exhibited white cast iron structure plus martensite. Applied PWHT resulted in the dissolution of martensite in heat affected zone and graphitization and in turn the reduction of partially melted zone hardness. Results showed that welding of grey cast iron with nickel based filler metal and applying PWHT can serve as a solution for cast iron welding problems.     

Optimization of Plasma Arc Welding Parameters by Using the Taguchi Method with the Grey Relational Analysis

The optimal parameters process of plasma arc welding (PAW) by the Taguchi method with Grey relational analysis is studied. The Grey relational grade is used to find optimal PAW parameters with multiple response performance characteristics. The welding parameters (welding current, welding speed, plasma gas flow rate, and torch stand-off) are optimized with consideration of the multiple response performance characteristics (the penetration of root, the weld groove width, and the weld pool undercut). As a result, the improvement percentage of the Grey relational grade with the multiple performance characteristics is 31.8%. It is shown that the multiple response performance characteristics are greatly improved through this study.     

XRD and TEM analysis of microstructure in the welding zone of 9Cr-1Mo-V-Nb heat-resisting steel

Under the condition of tungsten inert gas shielded welding (TIG) + shielded metal arc welding (SMAW) technology, the microstructure in the welding zone of 9Cr-1Mo-V-Nb (P91) heat-resisting steel is studied by means of X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The test results indicate that when the weld heat input (E) of TIG is 8.5 ∼ 11.7 kJ/cm and the weld heat input of SMAW is 13.3 ∼ 210 kJ/cm, the microstructure in the weld metal is composed of austenite and a little amount of δ ferrite. The substructure of austenite is crypto-crystal martensite, which included angle. There are some spot precipitates in the martensite base. TEM analysis indicates that the fine structure in the heat-affected zone is lath martensite. There are some carbides (lattice constant, 1.064 nm) at the boundary of grain as well as inside the grain, most of which are Cr₂₃C₆ and a little amount of (Fe, Me)₂₃C₆.     

U75V轨道钢线性摩擦焊工艺研究

目的 提高及改善目前轨道连接与修复的质量。方法 采用线性摩擦焊（LFW）的方法,对高碳轨道钢（U71Mn）在不同参数下进行了焊接试验,并对其微观组织和力学性能进行了表征。结果 焊接参数对接头质量起着决定性的作用。根据焊后接头的微观组织差异,可将其分为4个部分：焊缝中心区（WCZ）、热力影响区（TMAZ）、热影响区（HAZ）和母材（BM）。BM为珠光体和上贝氏体的混合组织,TMAZ由珠光体和少量马氏体组成。在WCZ中,由于受到的热力耦合作用的增强和更高的冷却速率,该区域马氏体含量进一步增加。在拉伸试验中,所有试样均在WCZ处发生断裂,接头的最大抗拉强度达到BM强度的86.6%。此外,WCZ中存在大量马氏体,在增加焊缝显微硬度的同时也降低了焊缝的冲击韧性。结论 采用LFW的方法可以得到焊接质量优良的轨道钢接头。     

Narrow-gap tungsten inert gas welding of 78-mm-thick Ti–6Al–4V alloy

Narrow-gap tungsten inert gas welding with in situ protective system is applied to 78-mm-thick Ti–6Al–4V alloy. The martensite basketweave microstructure is formed in fusion zone (FZ), and heat-affected zone (HAZ) near FZ consists of acicular martensite and a small portion of primary alpha phase. The HAZ near base metal (BM) consists of primary alpha and transformed beta phase. Microhardness values of FZ and HAZ are relatively higher, and peak values appear at HAZ near FZ. The mechanical heterogeneity is dependent on variation of beta phase and martensite, which in turn depend on specific thermal cycle(s). The average tensile strength reaches 783.3?MPa and is 91.2% of BM, which appears in the middle of the weld with orthogonal martensites.     

An investigation of weld fracture surfaces and mechanical properties of two gamma titanium aluminide alloys

Two gamma titanium aluminide sheet materials were investigated to characterize the fusion zone cracking and mechanical properties that occur for specimens subjected to gas tungsten arc welding (GTAW). The materials used in this study consisted of essentially the same composition; however, one was received in the primary annealed (PA) condition and the other in the designed fully lamellar (DFL) condition. For both materials, all of the specimens welded with a stationary torch (spot welds) cracked catastrophically immediately after welding. The PA specimens exhibited a different mechanism of fracture in the fusion zone compared with the DFL specimens. The fractures that occurred in the PA specimens followed an interdendritic path through regions that did not completely solidify prior to the occurrence of cracking, whereas for the DFL specimens the primary mechanism of fracture was cleavage. For the butt welded specimens, no cracking occurred. For both materials, specimens welded parallel to the rolling direction exhibited more distinct preferred growth of columnar grains than those welded perpendicular to the rolling direction. The weld structure/property relationship is also discussed.     

高强焊丝用H10Mn2SiNiMoTi盘条拉拔横裂分析

某高强焊丝用盘条在拉拔过程中出现很多横向断裂裂纹,采用扫描电镜、金相显微镜、直读光谱仪、显微硬度计等设备对断裂试样进行检测分析,结果表明,断裂的盘条化学成分和金相组织正常,夹杂物不严重,引起横裂产生的主要原因是边部的马氏体组织。焊丝在拉拔过速或者拉拔时润滑条件差的情况下,焊丝圆周与模具的接触位置摩擦生热,在高温下发生奥氏体相变,后续冷却又形成了马氏体组织。马氏体组织硬度高、脆性大,在焊丝拉拔轴向拉应力的作用下产生了横向开裂。     

Microstructure and mechanical properties of dissimilar materials joints between T92 martensitic and S304H austenitic steels

In this paper, T92 martensitic steel and S304H austenitic steel were welded by gas tungsten arc welding (GTAW) process. Microstructural features and mechanical properties of T92 and S304H dissimilar materials joints were investigated. The results showed that the part of the joints with relatively weak tensile strength was T92 coarse-grained heat affected zone (CGHAZ), while the part of the joints which revealed relatively weak toughness was weld metal. The decrease of tensile strength in T92 CGHAZ was due to its coarse tempered martensite structure. Weak toughness of the joints was resulted from the coarse dendritic austenite of the weld metal. However, the weld metal in transverse direction of the joints was provided higher tensile strength by the orientation distribution of grains compared with T92 CGHAZ.     

基于超声波电机的移动焊接机器人焊枪精密定位控制系统研制

为了实现移动焊接机器人焊枪的精密定位控制,提出了焊枪跟踪控制时基于调整电机微步导通时间实现无位置传感器开环精密定位控制的控制系统设计方法.在控制系统设计中充分利用EDA和单片机技术各自的优点,采用CPLD和单片机相结合,实现了双行波超声波电机微步控制.实验证明该控制器可控精度高、可靠稳定、可维护性强,不需要高精度位移传感器就可控制焊枪达到很高的定位精度.研究所得的方法和结论具有较强的通用性,在基于环形行波超声波电机驱动的XY平面精密定位控制中具有普遍的应用意义.     

Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys

This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor (BPM).The welding parameters include the modes of laser output (pulsed wave and continuous wave),welding speed,shield gas flow,welding bead structure,and focusing distance.The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type.The crack in the welding bead reduced with decreasing welding speed.The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material.Weld morphology during the experimental process revealed the proper flow of shield gas.The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.     

多元气体大电流MAG焊试验系统

本文研制开发了一套多元气体大电流MAG焊试验系统 ,它包括一元化控制的IGBT逆变电源 ,电枢电压与速度反馈双闭环控制的双驱动送丝系统 ,双水冷焊枪以及质量流量闭环控制的精密气体配比供给系统。多元气体大电流MAG焊接试验证明 ,该系统具有焊接电源动态响应速度快 ;送丝速度稳定 ,调速范围宽 ,气体配比精密的特点 ,实现了1.2mm焊丝大电流MAG焊接高效的目标 ,其熔敷速率为普通MAG焊的2～ 3倍。     

FEM prediction of welding residual stresses in a SUS304 girth-welded pipe with emphasis on stress distribution near weld start/end location

A finite element approach based on Quick Welder software is developed to simulate welding temperature field and welding residual stress distribution in a 3D multi-pass girth-welded pipe model. The characteristics of welding residual stress distributions in a SUS304 stainless steel pipe induced by heating with a tungsten inert gas arc welding torch are investigated numerically. Meanwhile, an emphasis is focused on examining the welding residual stress distributions in and near the weld start/end location. Moreover, the residual stresses predicted by the present computational approach are compared with the measured data; and the comparison suggests that the numerical simulation method has basically captured the feature of welding residual stress distribution near the weld start/end region. The numerical simulation results show that both the hoop and the axial residual stresses near the weld start/end region have sharp gradients and are significantly different from those in the steady range.     

马氏体含量对合金化热镀锌双相钢电阻点焊接头组织与性能的影响

目的 研究在双相钢电阻电焊过程中马氏体含量对点焊接头组织、性能的影响规律。方法 使用电阻点焊机对DP780、DP980、DP1180 3种马氏体含量不同的锌铁合金化热镀锌双相钢进行焊接,利用欧姆表、光学显微镜、扫描电镜、拉伸机和显微硬度计等设备,对基板的电阻率、工艺窗口、接头力学性能、焊点断裂模式、金相组织进行表征。结果 在AWS D8.9M-2012焊接标准体系下,DP780、DP980、DP1180焊接电流窗口依次减小,DP780、DP980、DP1180 3种材料在最大焊接电流下的焊核直径基本一致;熔核区硬度呈增大趋势,DP780点焊接头软化不明显,DP980和DP1180的热影响区出现明显的软化现象,这主要是由母材热影响区中的马氏体回火造成的。DP780、DP980、DP1180的最大剪切力分别为23 062、27 317、28 183 N。DP780为拔核断裂模式,DP980和DP1180为部分拔核断裂模式。结论 双相钢中马氏体含量的增加会使焊接电流窗口降低,整体向焊接电流减小的方向偏移,但是会提高上限电流的焊点承载强度。     

道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响

通过屈服强度和冲击韧性测试、组织分析,研究了两种焊接热输入条件下道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响。结果表明,随着道间温度从40℃提高到300℃,焊接热输入为8 kJ/cm和18 kJ/cm的焊缝金属屈服强度分别从868 MPa和855 MPa单调下降至728 MPa和693 MPa,-50℃冲击韧性分别从70 J和69 J升高至117 J和72 J(道间温度分别为200℃和100℃),然后降低至67 J和43 J;焊缝金属的组织差异是不同道间温度下焊接接头力学性能不同的原因。随着道间温度从40℃提高到300℃,焊缝金属中马氏体组织逐渐消失,粒状贝氏体组织逐渐增多,针状铁素体组织比例先增加再减少,含量最高时的道间温度与冲击韧性峰值水平相一致。     

Fusion Zone Microstructures of Laser and Plasma Welded Dissimilar Steel Joints

Dissimilar steel joints between 13CrMo44 low-alloyed ferritic steel and A1SI 347 austenitic stainless steel were produced using laser beam and plasma arC welding. Both autogenous welding (without Filler) and welding with nickel-based filler wire were employed in each process. Fusion zone microstructures were characterized using both optical and scanning electron microscopy. Compositional analysis was performed using scanning electron microscopy. Hardness was measured to provide data for identifying the microstructures. A clear correlation was observed between the composition, microstructure and hardness. The results show that both autogenous laser and plasma welding produce fusion zones with a mixed martensite/austenite microstructure. Autogenous plasma welds, however, possess less martensite than the laser welds. The formation of martensite was attributed to the material combination and the rapid cooling rate of the welding processes. The results also indicate that both laser and plasma welding with nickel-based filler wire can produce fully austenitic fusion zones. This is mainly due to the high nickel content in the filler wire. According to the results, laser and plasma welding with nickel-based filler wire are recommended as potential industrial processes.