Effects of activating flux on the welded joint characteristics in gas metal arc welding

This paper presents the effect of each welding parameter on the weld bead geometry, and then sets out to determine the optimal process parameters using the Taguchi method to determine the parameters. Three kinds of oxides, Fe₂O₃, SiO₂, and MgCO₃, were used to investigate the effect of activating flux aided gas metal arc welding (GMAW) on weld bead geometry, angular distortion and mechanical properties in AISI 1020 carbon steel. During welding, a charge coupled device (CCD) camera system was used to observe and record images of the welding arc and analyze the relationship between penetration increase and arc profile. The experimental results showed that activating flux aided GMAW increased the weld area and penetration and tended to reduce the angular distortion of the weldment. The MgCO₃ flux produced the most noticeable effect. Furthermore, the welded joint presented better tensile strength and hardness.     

Vision-based weld seam tracking in gas metal arc welding

A low-cost visual sensing system is developed to realize weld seam tracking in gas metal arc welding (GMAW). The system consists of a commercial CCD camera, narrow-band composite filter lens, an image capturing card, an industrial computer, a welding control unit, a GMAW power source, and a worktable. Images of root gap and its vicinity are captured in the GMAW welding process by the system. The captured images are processed by an algorithm on the basis of the analysis of gray characteristics of the root gap to get the offsetting information between torch and root gap centerline. The offsetting information is then used to realize weld seam tracking in the GMAW process. Welding seam tracking experiment is conducted by a simple proportional (P) controller. The results show that tracking error is basically less than ± 0.5 mm.     

铁路钢轨与辙叉过渡层焊接的研究

钢轨与辙叉的焊接 ,属于高碳钢和高锰钢异种金属材料的焊接 .由于二者材料本身的焊接性都较差 ,而且所要求的焊接工艺差异很大 ,再加上钢轨的被焊截面形状不规则 ,所以给焊接带来很大的难度 .采用手工电弧焊的方法 ,通过增加过渡层可降低焊接难度 ,简化焊接工艺 .对 60 0mm长的钢轨与辙叉试件进行了实焊 ,其结果达到或超过了相关标准的技术要求 ,从而证明采用增加过渡层的办法来解决高碳钢和高锰钢焊接是一种可行的办法 .     

Modelling the arc heat flux distribution in GMA welding

The spatial distribution of the heat flux falling on the weldpool surface has a marked effect on the weldpool shape and on the subsequent solidification process, which in turn affects the structure and properties of the weldment produced. A heat flux distribution model of gas metal arc (GMA) is developed in this paper. This model is suitable for larger surface deformation of GMA weldpool. It is found that when the free surface of the weldpool is significantly deformed, the resultant heat flux falling on the workpiece may be markedly modified. It follows that a bimodal distribution of arc heat flux may be applicable for a significantly deformed GMA weldpool.     

Role of arc mode in laser-metal active gas arc hybrid welding of mild steel

Arc mode plays an important role in joint characterizations of arc welding, but it has been seldom considered in laser-arc hybrid welding. This paper investigated the role of arc mode on laser-metal active gas (MAG) arc hybrid welding of mild steel. Three arc modes were employed, which were cold metal transfer (CMT), pulsed spray arc and standard short circuiting arc. Microtexture of the joints were observed and measured via electron back scattering diffraction (EBSD) system to reveal the effect of arc mode on microstructure. Mechanical properties of the joints were evaluated by tensile and Charpy V-notch impact tests. It was found that both the stability and mechanical properties of laser-CMT hybrid welding (LCHW) is the best, while those of laser-standard short circuiting arc welding (LSHW) is the worst. OM and EBSD results showed that the fraction of acicular ferrite and high-angle grain boundaries in fusion zone decreases gradually in the sequence of LCHW, laser-pulsed spray arc welding and LSHW, while the mean grain size increases gradually. Finally, the microstructure formation mechanisms and the relationship between microstructure and mechanical properties were summarized by the loss of alloying element and the stirring effect in molten pool.     

Determining the critical transition current for metal transfer in gas metal arc welding (GMAW)

It is of great significance to determine the critical transition current from globular transfer to spray transfer in gas metal arc welding (GMAW) because metal transfer modes affect the weld quality and welding productivity. In this study, a simple model is developed to calculate the critical transition current based on the analysis of various forces exerted on a pendent droplet at the electrode tip. It is found that the force exerted by the incoming molten metal from the wire on the drop, i.e., the term ṁ _c v _c, plays an important role in determining the critical transition current. For mild steel wires and argon shielding gas, the critical transition current is predicted with different levels of wire diameter and extensions. The calculated results match the experimental ones.     

Numerical analysis of weld pool geometry in globular-transfer gas metal arc welding

The weld pool geometry and its dimension in the globular-transfer mode during gas metal arc welding (GMAW) were numerically analyzed by using the thermal conduction model, which considered the influence of the deformation of weld pool surface on heat flow in the quasi-steady state. According to the features of the globular-transfer mode, the additional heat energy from molten metal droplets was treated as a plane or volumetric heat source term to correspond to different welding conditions. The weld pool surface profile was predicted while considering the effect of droplet impingement on the depression of the weld pool. The bead-on-plate GMAW experiments were performed under different welding conditions to validate the model of numerical analysis. It has been found that the predicted results agree well with the measured ones.     

Numerical investigation of droplet impact on the welding pool in gas metal arc welding

A transient three‐dimensional model that describes physical phenomena inside a welding pool during gas–metal arc welding process is presented. The model considers such phenomena as heat‐mass transfer, electromagnetics, hydrodynamic processes and deformation of the weld pool free surface. The fluid flow in the weld pool is induced due to the presence of the mechanical impact of the droplets, thermo‐capillary surface tension, thermal buoyancy and electromagnetic forces. The weld pool surface deformation is calculated by considering arc pressure and droplet impact force. A comparative analysis of the impact of the electric current of the welding arc and different force factors causing the motion of liquid metal in the weld pool on the shape of the welded seam was carried out and discussed.     

Investigation on gas metal arc weldability of a high strength tool steel

In this paper, gas metal arc weldability results of a particular advanced tool steel are presented. Indeed, the study was focused on the weld profile, microhardness and microstructure of the joints. The aim was to identify an appropriate filler material and optimize the process parameter.The validation of results started with a careful metallographic analysis of the joints, in order to verify that the metallurgical properties of the material were not compromised by the welding process. In the following step, all the non-destructive and mechanical tests, imposed by procedure qualification, were performed in order to have a complete characterization of the joints. For all the wires used, hardness tests highlighted that the use of low heat input and a high number of beads causes an increase in the Heat Affected Zone (HAZ) hardness up to values equal to or exceeding the limits imposed by the European standard on the process qualification. To avoid this problem, it was therefore necessary to adopt high electric parameters and thus high heat inputs. The filler material that gave the best results, in terms of uniformity of mechanical properties, is the rutile flux wire.     

Real-time monitoring of abnormal conditions based on Fuzzy Kohonen clustering network in gas metal arc welding

A real-time monitoring system based on through-the-arc sensing is developed for detecting abnormal conditions in gas metal arc welding. The transient signals of welding voltage and current during the welding process are sampled and processed by statistical analysis methods. It is found that three statistical parameters (the standard deviation, variance, and kurtosis of welding current) show obvious variations during the step disturbance, which is intentionally introduced into the T-joint test pieces by cutting a gap in the vertical plane. A Fuzzy Kohonen clustering network (FKCN) is put forward to monitor the abnormal conditions in real-time. Ten robotic welding experiments are conducted to verify the real-time monitoring system. It is found that the correct identification rate is above 90%.     

核电设备用SA738Gr.B复合钢板的爆炸焊接试验研究

为了开发高强核电压力容器用复合钢板,实现核电设备压力容器关键部件国产化,对核电设备用SA738Gr.B复合钢板的爆炸焊接和热处理工艺进行了研究,通过试验验证了爆炸焊接理论参数的正确性,对爆炸焊接后的核电设备用SA738Gr.B复合钢板提出了合理的正火和回火工艺,从而实现了核电设备用SA738Gr.B复合钢板各项力学指标...     

核电设备用SA738Gr.B复合钢板的爆炸焊接试验研究

为了开发高强核电压力容器用复合钢板,实现核电设备压力容器关键部件国产化,对核电设备用SA738Gr.B复合钢板的爆炸焊接和热处理工艺进行了研究,通过试验验证了爆炸焊接理论参数的正确性,对爆炸焊接后的核电设备用SA738Gr.B复合钢板提出了合理的正火和回火工艺,从而实现了核电设备用SA738Gr.B复合钢板各项力学指标的最优化。     

Numerical investigations of arc behaviour in gas metal arc welding using ANSYS CFX

Current numerical models of gas metal arc welding (GMAW) are trying to combine magnetohydrodynamics (MHD) models of the arc and volume of fluid (VoF) models of metal transfer. They neglect vaporization and assume an argon atmosphere for the arc region, as it is common practice for models of gas tungsten arc welding. These models predict temperatures above 20 000 K and a temperature distribution similar to tungsten inert gas (TIG) arcs. However, current spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to TIG arcs they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in a very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the work piece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2000 to 5000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, and the evaporation rate relative to the wire feed. Finally the model predictions are compared with the measuring results of Zielińska et al.     

Investigation on various welding consumables on properties of carbon steel material in gas metal arc welding under constant voltage mode

In this present work, the influence of different consumables on weld properties of carbon steel plate was studied by automatic gas metal arc welding under constant voltage mode. For all experiments, the process parameters such as welding current of 200 A, voltage of 28 V and welding speed of 200 mm/min were kept constant. The results indicate that the angular distortion remained higher for solid wire, whereas it was minimum for flux-cored wire and the lowest in metal-cored wire. Mechanical properties such as yield strength, tensile strength, elongation and joint efficiency remained high for solid wire relative to cored wire. Excellent impact toughness of the weld metal and heat-affected zone was reported for the flux-cored welds compared with solid wire and metal-cored welds.     

厚板高强钢激光填丝多层焊接头特征及断裂机制研究

本文在11CrNi3MnMoV低合金高强钢激光填丝多层焊工艺优化的基础上利用电子万能试验机、HVS-5维氏硬度计、扫描电子显微镜和能谱分析仪等对焊缝接头进行了力学性能测试,并重点对断裂机制进行了分析.结果发现:激光填丝焊接头的HAZ很窄,约为1 mm.焊缝平均硬度值高出母材30%左右;顶层焊道硬度高于内层焊道;最高硬度值出现在熔合区附近;接头断裂机制为韧窝断裂;能谱分析发现韧窝中第二相粒子成分主要由母材和焊缝的合金元素决定.焊缝金属与母材界面处存在一层Fe、Mn等合金元素的氧化物,其导致侧壁未熔合,这是接头断裂的主要原因.     

Hybrid laser/arc welding of advanced high strength steel in different butt joint configurations

An experimental procedure was developed to join thick advanced high strength steel plates by using the hybrid laser/arc welding (HLAW) process, for different butt joint configurations. The geometry of the weld groove was optimized according to the requirements of ballistic test, where the length of the softened heat affected zone should be less than 15.9 mm from the weld centerline. The cross-section of the welds was examined by microhardness test. The microstructure of welds was investigated by scanning electron microscopy and an optical microscope for further analysis of the microstructure of fusion zone and heat affected zone. It was demonstrated that by changing the geometry of groove, and increasing the stand-off distance between the laser beam and the tip of wire in gas metal arc welding (GMAW) it is possible to reduce the width of the heat affected zone and softened area while the microhardness stays within the acceptable range. It was shown that double Y-groove shape can provide the optimum condition for the stability of arc and laser. The dimensional changes of the groove geometry provided substantial impact on the amount of heat input, causing the fluctuations in the hardness of the weld as a result of phase transformation and grain size. The on-line monitoring of HLAW of the advanced high strength steel indicated the arc and laser were stable during the welding process. It was shown that less plasma plume was formed in the case where the laser was leading the arc in the HLAW, causing higher stability of the molten pool in comparison to the case where the arc was leading.     

镀锌钢的液态金属脆现象及其在电阻点焊过程中的表现

液态金属脆是指通常具有韧性的固体金属或者合金与液态金属直接接触且受到拉伸应力时,其塑性降低并发生脆性断裂的现象。钢在液态锌中会发生液态金属脆现象,这在镀锌钢的热拉伸实验中得到了证实。此外,研究人员发现在镀锌高强钢的电阻点焊过程中也会出现液态金属脆现象,表现为在焊点表面出现大量裂纹,这些裂纹对焊点性能存在潜在危害。本文回顾了镀锌钢液态金属脆现象的热拉伸实验研究,阐明了影响脆化现象的实验因素;综述了镀锌钢在电阻点焊过程中发生液态金属脆现象的研究进展,分析了产生裂纹的位置及其影响因素,并总结了可能的解决方案。     

Study on arc and laser powers in the hybrid welding of AA5754 Al-alloy

In this paper a new generation of fiber laser assisted by a MIG source was used to weld AA5754-H111 aluminum alloy in 3 mm thick butt configuration. The effects of laser and arc powers on the weld geometry and properties were studied. Weld geometry and porosity were measured. The microstructure was investigated by optical microscope and Vickers micro-hardness was taken. The residual stress close to the heat affected zone was measured by the incremental hole-drilling method. Eventually, the tensile test was conducted in order to compare the mechanical properties of the weld with those of the parent metal.For the first time the sensitiveness of the hybrid welding of the 5754 aluminum alloy to the arc and laser powers was demonstrated. Higher laser power favored the stability of the process and provided good structural and geometrical properties of the weld. Further investigation can be performed in order to optimize the weld soundness and the energy efficiency of hybrid welding an aluminum alloy using a fiber laser.     

Modelling of arc welding: The importance of including the arc plasma in the computational domain

We present results of computational simulations of tungsten-inert-gas and metal-inert-gas welding. The arc plasma and the electrodes (including the molten weld pool when necessary) are included self-consistently in the computational domain. It is shown, using three examples, that it would be impossible to accurately estimate the boundary conditions on the weld-pool surface without including the arc plasma in the computational domain. First, we show that the shielding gas composition strongly affects the properties of the arc that influence the weld pool: heat flux density, current density, shear stress and arc pressure at the weld-pool surface. Demixing is found to be important in some cases. Second, the vaporization of the weld-pool metal and the diffusion of the metal vapour into the arc plasma are found to decrease the heat flux density and current density to the weld pool. Finally, we show that the shape of the wire electrode in metal-inert-gas welding has a strong influence on flow velocities in the arc and the pressure and shear stress at the weld-pool surface. In each case, we present evidence that the geometry and depth of the weld pool depend strongly on the properties of the arc.     

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160 pm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with 307Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.