Experimental investigation on mechanical and metallurgical properties of super duplex stainless steel joints using friction welding process

Friction welding is one of the most economical and highly practicable methods in joining similar and dissimilar metals. In this study, high-quality welds are produced in the super duplex stainless steel by continuous drive friction welding successfully. Design of experiment was done using central composite design of response surface methodology. In the present work, the microstructure and mechanical properties of friction welded super duplex stainless steel (UNS S32760) were examined. The base material has a microstructure consisting of the ferrite matrix with austenite islands. Ferrite content was analyzed through the phase analyzer software and found that it is in the range of 42–55% in all weld metals. The phases were further analyzed through X-ray diffraction method. All the weld metals have higher hardness than the base metals. Weld transverse tensile failures consistently occurred away from the weld zone and exhibit more hardness, yield and ultimate tensile strengths than the base material. The austenite content increases with nitrogen concentration. Nitrogen could enhance the yield stress and ultimately tensile strength of super duplex stainless steel. Secondary phase precipitation is not observed in the welded joint probably due to the shorter heating times.     

Vibrational energy loss analysis in battery tab ultrasonic welding

In ultrasonic metal welding processes, high-frequency ultrasonic energy is used to generate friction and heat at the interface between weld parts to produce solid-state bonds. It has been observed that sufficient energy is required to produce proper bonding, while excessive energy can cause such quality issues as weld fracture and perforation. Therefore, it is important to have a product/process design in ultrasonic welding to ensure efficient energy conversion from ultrasonics to welding energy, minimizing energy loss in the process. In this work, vibrational energy loss associated with the longitudinal and flexural vibrations of the Cu coupon during ultrasonic welding is studied by applying one-dimensional continuous vibration models. To facilitate our modeling, experimental results from the free response of Cu coupon were obtained to determine the damping characteristics of the Cu coupon in the welding process. Our analysis shows that substantial energy loss can occur during welding due to the flexural vibration of the Cu coupon, especially when the overhang (the upper part of the Cu coupon extended from the anvil) of the Cu coupon resonates at or close to the welding frequency (about 20 kHz), degrading the weld quality of battery tabs. This study contributes to understanding the fundamental dynamics of the Cu coupon during ultrasonic welding and its impact on weld quality.     

Strength assessment using destructive testing on MIAB welded alloy steel tubes and subsequent techno-economical evaluation

In this study, an attempt is being made to determine the feasibility of Magnetically Impelled Arc Butt (MIAB) welding process for joining alloy steel tubes in pressure parts. In view of this, a specially made state of art MIAB welding unit (MD1) available at WRI, BHEL, Tiruchirappalli has been employed and adequate number of welding trials is conducted to weld alloy steel tubes of 6–7 mm thickness for boiler applications. The combination of a set of values provided as input is varied for each trial. The welding current and the welding time are divided into three and four stages respectively. For each trial, either the current in stage II is varied or the time for stage III is varied while maintaining the other input parameters constant. These trials are carried out mainly to develop an optimum window (working range) for the process parameters. Further, the strength of MIAB welded specimens are examined by subjecting the welded specimens to various destructive tests. It is observed that the weld region is stronger than the base metal in most of the cases.In the next part of the study, the characteristics of MIAB welded joints for T11 steel tubes are compared with those using flash butt welding and induction pressure welding that is presently employed for alloy steel tube joining in pressure parts. It is found that the manufacturing time and incurred cost per weld drastically reduces while simultaneously increasing the productivity. Hence, the feasibility of MIAB welding process for pressure part is established.     

A method for double-sided friction stir spot welding

A rotating anvil similar to a pinless friction stir welding (FSW) tool can be applied to friction stir spot welding (FSSW) of thin metal plates. FSSW is a solid-state joining process that is currently being used by automotive manufacturers as an alternative to rivets and traditional resistance spot welding. The principal detractor of this process is the keyhole left by pin extraction, which can be detrimental to the weld strength. A pinless tool can be used to eliminate the keyhole. However, this approach is limited to joining thin sheet (≤1 mm). Using a rotating anvil with the FSSW process permits the joining of thicker cross sections, improves the mechanical strength of the spot weld and reduces the reaction forces on the spot welding frame. A numerical model of the process, tensile shear tests and macrosection analysis are used to evaluate the spot welds.Macrosection and numerical analysis reveals that the material flow between the pinless tool and rotating anvil is complex and unique to this process. It has been found that the use of a rotating anvil for FSSW is a viable means to create quality spot welds in thicker weldments.     

Research evolution on intelligentized technologies for arc welding process

This paper presents some new evolutions of research works in the IRWTL at SJTU on intelligentized technologies for arc welding dynamic process and robot systems, including multi-information sensing of arc welding process, such as characteristic extraction of weld pool image, voltage, current, and sound, arc-spectral features; multi-information fusion algorithms for prediction of weld penetration; intelligentized modeling of welding dynamic process; intelligent control methodology for welding dynamic process; intelligentized technologies for robotic welding, such as guiding and tracking seam technology and intelligent control of weld pool and penetration in robotic welding process; and development of autonomous welding robot system for the special environment. The ideas of intelligentized welding manufacturing technology (IWMT) and intelligentized welding manufacturing engineering (IWME) are presented in this paper for systematization of intending researches and applications on intelligentized technologies for modern welding manufacturing. The studies of intelligentized welding presented in this paper establish the foundation work of intending researches and applications on intelligentized technologies for modern welding manufacturing.     

Feasibility Study of 316L Stainless Steel for the Ultrasonic Consolidation Process

The viability of using 316L stainless steel in the ultrasonic consolidation process was examined in this work. Ultrasonic consolidation is an additive, free-form manufacturing process that employs ultrasonic welding and machining to form a part. The process ultrasonically joins layers of metal together by welding them one at a time. Once four layers of metal foil are welded together, welding is suspended and the system machines the part outline, and repeats this cycle until a component is completed. Experiments were conducted to determine the feasibility and processing parameters for ultrasonically welding stainless steel. Mechanical testing and optical microscopy were conducted. 316L stainless steel was successfully welded. Increasing welding amplitude and decreasing welding speed were the most effective way to increase weld peel strength. Unlike work in aluminum alloys, these experiments found no relationship between horn force and peel strength. Rough processing windows for ultrasonically welding 316L were identified.     

硫酸盐还原菌对EH40焊接钢海水腐蚀的影响

目的研究无菌和SRB体系中EH40钢焊接接头的母材区、热影响区和焊缝区腐蚀差异。方法利用金相显微镜观察、失重法、电化学测试、扫描电镜和X射线光电子能谱仪等分析手段。结果焊缝区微观组织由块状铁素体(BLF)和魏氏组织(W)组成;热影响区可再分为粗晶区(CGHAZ)和细晶区(FGHAZ)两个区;母材区主要由BLF、AF和少量珠光体组成。在无菌对照体系中,焊缝区腐蚀速率为0.0026 mm/a,混合区次之,为0.0023 mm/a,母材区最小,为0.0019 mm/a。含SRB体系中,各区的腐蚀速率为:焊缝区(0.0037 mm/a)混合区(0.0034 mm/a)母材区(0.0030 mm/a)。热影响区腐蚀产物形貌粗大,点蚀孔也较大。结论焊缝区比母材区容易腐蚀,由此易造成小阳极大阴极加速腐蚀,热影响区容易发生点蚀。SRB能促进三个区域试样腐蚀加速。     

Double-electrode arc welding process: Principle,variants, control and developments

Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100 A base current for 1.2 mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment.     

某站场对焊法兰环焊缝缺陷原因分析

目的研究法兰环焊缝缺陷产生的原因,采取相应针对性措施,预防泄露事故发生。方法通过宏观分析、超声检测、化学成分分析、金相分析、能谱分析对环焊缝裂纹形成原因进行分析。结果裂纹起源于根焊焊材与母材间,两端较为平滑,沿环焊缝周向方向扩展。焊缝中夹渣的残留药皮和层间未熔合缺陷,是形成裂纹的内在原因。结论焊缝产生裂纹由焊接参数控制不当引起的。     

汽车排气管焊缝断裂的失效分析

某汽车用排气管使用不久焊缝处断裂。对失效排气管焊缝进行化学成分、金相组织和断口的微观分析。发现该排气管焊缝柱状组织粗大,断口微观形貌为沿晶断裂,柱状晶贯穿整个断裂面,断口有较明显的脆性特征。分析认为该排气管属于早期失效,是由于薄壁的排气管焊接时温度过高,导致焊缝柱状组织粗大,加之薄壁管冷却又快,致使焊缝产生较大的内应力。建议改进焊接工艺,控制较低的层间温度,使焊缝组织细化,解决焊缝断裂问题。     

Geometry Regulation of Material Deposition in Near-Net Shape Manufacturing by Thermally Scanned Welding

This paper introduces a thermally scanned material deposition control method for near-net shape manufacturing of metal parts by welding. To eliminate thermal distortion and the required intermediate-layer milling steps, and to control the material structure, plasma arc scan welding under infrared pyrometry sensing regulates the temperature field by providing in-process heat treatment of the part. In laboratory tests, the material is simultaneously deposited by a gas metal arc welding torch, with monitoring of the weld profile by two laser stripe profilometers. These sensors provide measurements of the bead width for its feedback control by modulation of the wire feed. To compensate for measurement delays, real-time prediction by a deposition model is employed, with its parameters identified during the process. Preview of the geometric surface irregularities in front of the deposition is used as feedforward to ensure the desired layer deposition patterns in adjacent beads. The performance of this bead-size control scheme is assessed experimentally on a robotic laboratory station, and applications of the thermally scanned material deposition technique are explored in rapid manufacturing of customized metal products.     

Effect of oxide-based fluxes on mechanical and metallurgical properties of Dissimilar Activating Flux Assisted-Tungsten Inert Gas Welds

Present investigation is to study the “Effect of Activating Fluxes on Mechanical and Metallurgical Properties of Dissimilar Activated Flux-Tungsten Inert Gas Welds”. Effect of current, welding speed, joint gap and electrode diameter on weld bead dimensions on 6 mm thick dissimilar weld between carbon steel to stainless steel, was studied under Activated Flux-Tungsten Inert Gas Welding process. During this investigation three different types of oxide powders were used-TiO₂, ZnO and MnO₂. After welding samples were subject to mechanical testing, in addition to characterization via micro hardness and microstructures of Normal Tungsten Inert Gas Welds and Activated Flux-Tungsten Inert Gas Welds. Activating fluxes TiO₂ and ZnO are effective fluxes for Activated Flux-Tungsten Inert Gas Welding of dissimilar weld between CS to SS. Highest depth/width (D/W) ratio reported under TiO₂ and ZnO fluxes compare to Normal-Tungsten Inert Gas Welds. Lowest angular distortion was observed under TiO₂ flux compare to Normal-Tungsten Inert Gas Welds. Mechanical properties, Joint Efficiency of Activated Flux-Tungsten Inert Gas Welds are higher than normal-Normal Tungsten Inert Gas Welds. Tensile Test specimens of both the processes failed from the parent metal (carbon steel side). Carbon migration from CS to SS, had occurred which led to failure of weld joints from CS side.     

Comparison of mechanical properties of pure copper welded using friction stir welding and tungsten inert gas welding

The objective of this research is to investigate the mechanical properties including bonding, tensile strength, and impact resistance of pure copper welded using friction stir welding (FSW) method and compare them with that of tungsten inert gas (TIG) welding. Micro-hardness tests are performed on pure copper, TIG welded copper and FSW welded copper to determine the effect of heat on the hardness of welded coppers. Tensile strength tests and notch tensile strength tests are performed to determine the mechanical properties of different weld process.In this experiment, it is found that the notch tensile strength and the notch strength ratio for FSW (212 MPa, 1.10) are significantly higher than those (190 MPa, 1.02) of TIG welding. For the impact tests, the weld zone and heat-affected zone energy absorption values for FSW (2.87 J, 2.25 J) are higher than those (1.32 J, 0 J) of TIG welding. XRD tests are performed to determine components of copper before and after welding process for TIG and FSW.     

海洋用钢焊接接头的海水腐蚀行为研究

目的研究海洋用钢焊接接头的海水腐蚀行为。方法采用海水暴露试验、电偶腐蚀试验和腐蚀电位测量等方法。结果获得了5种海洋用钢焊接接头的海水腐蚀结果。结论海洋用钢焊接接头的熔合区易产生腐蚀沟槽。在全浸区、潮差区和飞溅区条件下,同一焊接接头的腐蚀行为相同,焊接接头的腐蚀严重程度顺序为全浸区>潮差区>飞溅区。焊缝-母材的电偶腐蚀试验结果与焊接接头的暴露腐蚀结果一致。     

铁氧体工艺处理含重金属污水研究现状及展望

本文对近年来该工艺中铁氧体沉渣的生成机理和生成条件等方面的理论研究、工艺流程的发展及实际应用情况、铁氧体沉渣的综合利用等方面的发展现状加以综述。指出对铁氧体生成机制和沉渣的组成、结构和性能开展深入研究,将对铁氧体工艺处理含重金属污水应用起推动作用。     

In-Process Joint Strength Estimation in Pulsed Laser Spot Welding Using Artificial Neural Networks

Pulsed laser spot welding is used in the manufacture of many goods. Because weak joints can lead to product defects, it is important to monitor and control the joint strength precisely. This paper introduces a method to estimate the joint strength of spot welds during the welding process. A point infrared sensor is used to measure temporal radiation on the top face of the spot weld. Because variable measuring conditions affect the radiation power, a scale-free radiation feature is extracted from the measured radiation and used as a monitoring criterion. An artificial neural network (ANN) uses this feature to estimate joint strength. In experiments, significant welding parameters are varied within a controllable range, and 640 weld parts are used for ANN learning. The correlation coefficient between the estimated and measured strength is more than 0.98 for learned parts. Another 180 weld parts are used to appraise the efficiency of the learned ANN, and the mean square error of estimation is 0.78 kgf.     

Efficient welding conditions in magnetic pulse welding process

This study investigates the experimental research of the appropriated conditions for the magnetic pulse welding of AA6060T6 tubular assembly. Some welding tests were performed with two process parameters: the charging voltage and the width of the air gap between the two parts to be welded. A torsion-shear test, associated with the material fracture surfaces observation, gives an insight about the appropriateness of the welding conditions. The failure mode of the destructive test gives a dimensional criterion of the weld that is used as weld quality. It appears that the voltage does not strongly affect the weld quality for a low gap. It is possible to find an optimal gap range giving a high weld length. When the gap is too small, it is necessary to increase the pressure on the flyer, and some cracks appear in the material. Similarly, when the gap is too large, the high impact energy damages the welded interface.     

Geometric variability and surface finish of weld zones in Yb:YAG laser welded advanced high strength steels

Laser welding is used for joining advanced high strength steels (AHSS) to improve formability and performance. In this paper, the geometric variability observed in the fusion zones and heat affected zones of several combinations of AHSS (different types, coatings and thicknesses), which were butt welded using a Trumpf TRUDISK 6000^® Yb:YAG laser beam, is presented. The surface texture parameters such as roughness and waviness of laser welds were also measured and correlated with geometric variability. Results indicate that although high quality welds with minimal defects can be obtained using the Yb:YAG laser welding process, there is considerable variation in both the shape and the dimensions of weld zones. The variability increased with an increase in thickness differentials between the sheets being welded. Analysis of the top of the weld surfaces also suggested that aluminum coating on USIBOR samples contributes significantly to increased roughness. An increase in laser power coupled with corresponding increase in welding speed did not impact variability. A fair correlation between the surface roughness and weld region variability exists, although this needs further study.     

A tutorial on learning human welder's behavior: Sensing,modeling, and control

Human welder's experiences and skills are critical for producing quality welds in manual GTAW process. Learning human welder's behavior can help develop next generation intelligent welding machines and train welders faster. In this tutorial paper, various aspects of mechanizing the welder's intelligence are surveyed, including sensing of the weld pool, modeling of the welder's adjustments and this model-based control approach. Specifically, different sensing methods of the weld pool are reviewed and a novel 3D vision-based sensing system developed at University of Kentucky is introduced. Characterization of the weld pool is performed and human intelligent model is constructed, including an extensive survey on modeling human dynamics and neuro-fuzzy techniques. Closed-loop control experiment results are presented to illustrate the robustness of the model-based intelligent controller despite welding speed disturbance. A foundation is thus established to explore the mechanism and transformation of human welder's intelligence into robotic welding system. Finally future research directions in this field are presented.