Study correlating the bubble phenomenon and electrical signals in underwater wet welding with covered electrodes

The bubble phenomenon in underwater wet welding is very important to the final quality of the weld. A good understanding of the formation and collapse of the bubbles and knowledge of the behaviour of welding parameters during the process can improve the practices used in underwater welding and, consequently, improve the final quality of the weld. This study was developed to understand and try to correlate the phenomenon of growth, detachment and frequency of bubbles with electrical signals during the welding process. Beads were made on plate metal at a depth of 0.50 m, with three types of commercial coated electrodes: E6013, E7024 and E7018. High-speed filming to visualize the process of formation, detachment and counting of the bubbles was performed, along with acquisition of their electrical signals. Thus, it was possible to try to correlate the bubble frequency with the electrical signals observed during the process. It was observed in the current data that the mean number of variations under 5% of the mean current is similar to the mean detachment rate of the bubbles. Therefore, it was concluded that there is a possible relationship between bubble detachment and a determined variation in the current.     

Self-feed device behaviour evaluation designed for assessment of operability of coated electrodes

The objective of the present work is to evaluate the effectiveness of a self-feed device for coated electrodes. This device is able to eliminate disturbances from manual operation or the use of automatic control systems during the study of coated electrode behaviour. The conjugation of different methods such as short-circuit time statistical analysis and metallographic analysis (penetration, heat-affected zone, shape and mean distance between successive solidification fronts) together with the analysis of the electric arc and electrode melting parameters allows us to obtain relationships between arc behaviour, mass transfer processes and bead appearance. This permits the extraction of criteria to describe process stability and the behaviour of the feed device employed. An appropriate statistical methodology was obtained to process the ‘duration of the short-circuit’ parameter through an appropriate adjustment of empirical distributions to a log-normal model. The self-feed device for coated electrode welding allows the repeatable and reproducible execution of welding beads in the flat position, keeping the arc length based on physical and chemical characteristics of the electrode during welding trials using 125, 140 and 160 A.     

Effect of welding conditions on reduction in angular distortion by welding with trailing heat sink

Abstract

The effectiveness of welding with a trailing heat sink in reducing the angular distortion of a weld has been experimentally investigated with focus on the cooling position. A numerical model of welding with a trailing heat sink is constructed through the comparison of measured values of weld penetration, thermal cycles and angular distortion with those calculated. On the basis of this model, the effect of welding heat input conditions on the reduction in angular distortion is discussed to evaluate the versatility of welding with a trailing heat sink. The results indicate that the choice of an appropriate cooling position behind the welding heat source is essential for the effective reduction in angular distortion. The reduction in angular distortion by the heat sink at the appropriate cooling position increases with the heat input parameter Q_net/h, where Q_net is the weld heat input and h is the thickness of the plate.     

浅谈电力行业焊接人员的培训考核与管理

本文介绍了电力行业焊接的特点和焊接技术人员的层次,重点介绍了各类人员的培训、考核方式和以及管理效果,分析了这种培训管理模式的优势,对其他行业的培训有一定的借鉴意义。     

Controlling the composition of welding fume in welding with coated electrodes for special applications

A technology of ultrasound seam welding of polyethylene terephthalate films has been developed and ultrasound welding equipment and waveguides with spherical working ends constructed. The amplitude–frequency characteristics of acoustic systems are analysed. The dependence of the strength of welded joints on frequency, welding pressure, welding speed and the amplitude of ultrasound oscillations is determined.     

焊接线摇杆部件焊缝强度校核及焊接工艺改进

针对卡车厂焊装车间主焊线摇杆部件损坏状况,对各杆件和焊缝强度进行受力分析和强度校核,采用新材料和焊接工艺进行改进。改进后摇杆满足了正常工作强度要求。     

Improving the service properties of metal structures working in the conditions of low climatic temperatures by methods of adaptive pulsed-arc welding

Experimental results confirm that the application of adaptive pulsed-arc welding with regulated heat input to welded material refines the structure of the metal, lowers the degree of softening of the fusion zone of the welded joint and greatly increases the mechanical properties of the welded joints, including structures working at low temperatures.     

Influence of welding position and parameters in orbital tig welding applied to low-carbon steel pipes

The most notable characteristic of Orbital TIG welding is the constant geometric profile of the tubes. In the context of orbital TIG welding of tubes with a large diameter and thick walls, the relationship between the welding position, the use of constant or pulsed current and also the value of the average current on the geometric characteristics of the beads obtained was studied. We deposited welds on SAE 1020 carbon steel tubes, as well as taking macrographs of the cross-sections of the beads using optical microscopy. High-definition films were used to understand the behaviour of the weld pool in different welding positions. The geometric characteristics were quantified using macrographs and software, and the relationship between these characteristics and the above-mentioned variables were traced. In addition, an analysis of the microstructure of the samples was carried out, correlating with Vickers microhardness. It was concluded that the beads welded with pulsed current were more reinforced and wider, as well as being harder and having a finer microstructure. The vertical up position resulted in beads with a lower shape factor and more penetration, and the overhead position resulted in beads with a low shape factor.     

Resistance spot welding and the effects of welding time and current on residual stresses

A 2-D finite element model is developed based on fully coupled electrical-thermal and incrementally coupled thermal-mechanical analysis. The growth rate of the weld nugget as a function of welding time and current is studied. Comparison of the predicted results with the experimental data shows good agreement. Contact area variations and pressure distribution between the sheets’ faying surface and electrode-sheet interfaces during the welding process are studied. Compressive radial residual stress on the surface of the specimen obtained in the center region of the nugget while it becomes tensile and rises toward the nugget edge. The maximum tensile residual stress occurs outside of the nugget, near the edge region. The effects of welding time and current on distribution and magnitude of welding residual stresses are also investigated. The magnitudes of radial residual stresses in the inner and outer areas of the weld nugget grow with increasing the welding time and current while they decrease slightly in the edge regions of the weld nugget. The growth rate of the maximum residual stress reduces with increase in the welding time and current. This fact is more tangible for welding time.     

焊缝底片数字化系统及其评价方法

建立了一套针对焊缝底片的数字化系统,该系统由企业级CCD相机、高亮线形LED光源、底片传送机构、STM32嵌入式控制器、PC等组成。针对工业底片数字化的高空间分辨力、高密度对比灵敏度、大动态范围、高光学密度、大位深、高效率等要求,开展了各项关键技术的研究,实现了X射线焊缝底片的高质量数字化。对底片数字化设备的评价方法进行了研究,分析底片数字化设备的关键指标及其评价实现方法,利用数字图像处理方法对底片数字化系统进行客观评价。     

Wave formation in impact welding: Study of the Cu–Ti system

The cause of wavy interface morphology during impact welding is debated in the literature. In this paper, the effect of internal stress waves is investigated by varying the target (Cu 110) thickness during vaporizing foil actuator welding with constant thickness CP-Ti flyers. Experiments and smooth particle hydrodynamics simulations show that increasing target thickness causes the interfacial wavelength to increase, until it reaches about two times the flyer thickness. Also, to demonstrate the effects of consistency and transients of interfacial parameters, i.e., flyer velocity and wavy interface morphology, multi-probe photon Doppler velocimetry, electron microscopy and X-ray computed micro-tomography results are presented.     

基于DSP-MCU实现焊接电源系统数字化控制的设计

基于DSP-MCU实现焊接电源系统数字化控制的设计采用TMS320F240数字信号处理器和80C196KC单片机，设计成实现多功能IGBT逆变焊接电源双机控制系统。其中，TMS320F240主要用于焊接参数的采样、控制算法的运算，80C196KC用于完成人机接口的功能，包括键盘和显示，与上位机的通信等。设计中人机界面采用液晶显示。系统设计的关键是双机之间的通信技术，为了确保通信的可靠及快速性采用双口RAM(IDT7005)来完成。数字PWM控制单元采用复杂可编程逻辑器件(CPLD)完成，整个系统中所有逻辑控制也由此芯片来完成，设计完成的DSP-MCU双机控制系统实现了焊机的多功能全数字化控制。     

Effects of welding velocity on the impact behavior of droplets in gas metal arc welding

The influence of welding velocity on the impact behavior of the globular metal transfer was studied by high speed video photography with a laser source during gas metal arc welding of E36 steel. The welding current and voltage were 180 A and 30 V during the welding process. The results indicated that the impact location of a droplet depended strongly on the welding velocity. There was a critical welding velocity (0.4 m/min) that when the welding velocity was lower than this value the droplet impacted inside the weld pool, while the welding velocity was higher than this value the droplet impacted outside the weld pool. The results showed that when a droplet impacted outside the weld pool it would rebound or adhere on the workpiece, which was depended on the kinetic energy of the droplet. The rebound percentage of droplets increased with increasing kinetic energy. With increasing welding velocity, the mass of droplets was not changed obviously, but the flight velocity of the droplet increased, i.e. the kinetic energy of droplets increased with increasing welding velocity. The results also showed that when a droplet impacted outside the weld pool, the droplet which rebounded away from the workpiece surface formed weld spatters, resulting in discontinuous weld appearance, while the droplet which adhered on the workpiece surface streamed to the weld pool and good weld joint would still be obtained. Molten metal decreases with increasing welding velocity. When the welding velocity increases from 0.4 m/min to 2.0 m/min, the weld width decreases from 12.9 mm to 6.3 mm and the weld penetration decreases from 5.4 mm to 2.1 mm.     

An experimental and theoretical study of gas tungsten arc welding of stainless steel plates with different sulfur concentrations

During fusion welding, the presence of sulfur in steel often affects heat and fluid flow in the weld pool and its geometry. While the role of sulfur during welding of stainless steel plates with the same sulfur content is well understood, welding of stainless steel plates containing different concentrations of sulfur has not yet received proper attention. Here we report an experimental and modeling investigation of gas tungsten arc butt welding of stainless steel plates containing different sulfur concentrations. The main variables studied were sulfur concentrations in the two plates, welding current and welding speed. The results show significant shift of the fusion zone toward the low sulfur steel. The asymmetric fusion zone profile with respect to the original joint interface could be quantitatively explained through numerical modeling of heat transfer and fluid flow considering a bead shift observed experimentally.     

Detection of GTA welding quality and disturbance factors with spectral signal of arc light

By just artificially causing disturbance factors, the change in the spectrum of the welding arc is studied in order to identify special spectral processing zones that could provide signals, with high signal to noise ratio, for a proper evaluation of the GTAW (gas tungsten arc welding) process. Furthermore, the selected spectral processing zones were applied for in situ detection of the welding trails with the disturbance factors. The results have shown that by using suitable spectral processing zones (250-300 nm, 750-830 nm, 776.6-777.6 nm, 867.5-868.5 nm, 900-1000 nm), welding defects, such as bead face discontinuity, poor weld and porosity, which are usually caused by different disturbance factors, could be detected and identified. The present study is an attempt to put on theoretical basis the in situ detection and control of GTAW process.     

Effect of trailing heat sink on residual stresses and welding distortion in friction stir welding Al sheets

Abstract

This paper investigates a trailing heat sink, which was designed and applied to friction stir welding (FSW) in order to control the residual stresses and welding distortion. Residual stresses, residual plastic strains and welding distortion of 2024-T3 and 5083-H321 Al sheets welded by FSW with and without the trailing heat sink were compared. The optimal placement of the heat sink was discussed. The results revealed that the reductions in peak tensile stresses were 66% for 2024-T3 and 58% for 5083-H321 by application of the trailing heat sink in FSW. In addition, the welding distortion could be reduced drastically by this method. The 5083-H321 sheet with a size of 1000×100×3·5 mm welded by this method was very flat and had almost no distortion. This method achieved in-process control of stresses and welding distortion, without additional complicated work before or after welding operation.     

渣金间辅助外电场提高焊接工艺稳定性分析

为探索焊接过程实现高稳定性工艺的潜在途径,最大限度地减少重要钢结构制造中焊缝咬边及成形缺陷带来的焊后返修工作,提出并试验了一种利用埋弧焊渣金间随焊施加辅助外电场对渣金电导载流进行导流,进而提高焊接工艺稳定性的方法,并应用焊接电信号分析仪对弧压信号进行了采集统计分析.结果表明,以钨电极作阴极利用电场在渣金熔体内部形成稳定的电导载流,可使熔渣电导性能得以改善,并引导电子进入电弧阴极中心以增强电弧的集聚程度.同时外电场作用也使渣金内部的带电粒子形成有序运动并在界面结合成低表面能的活性氧化物,又可改善液态熔渣在焊缝金属表面的润湿铺展性能.实施辅助电场引入的这些有益作用使焊缝形状、表面光洁度、尤其是焊缝边缘平直均匀性得到较好地改观,焊接过程工艺稳定性得以进一步提高.     

渣金间辅助外电场提高焊接工艺稳定性分析

为探索焊接过程实现高稳定性工艺的潜在途径,最大限度地减少重要钢结构制造中焊缝咬边及成形缺陷带来的焊后返修工作,提出并试验了一种利用埋弧焊渣金间随焊施加辅助外电场对渣金电导载流进行导流,进而提高焊接工艺稳定性的方法,并应用焊接电信号分析仪对弧压信号进行了采集统计分析.结果表明,以钨电极作阴极利用电场在渣金熔体内部形成稳定的电导载流,可使熔渣电导性能得以改善,并引导电子进入电弧阴极中心以增强电弧的集聚程度.同时外电场作用也使渣金内部的带电粒子形成有序运动并在界面结合成低表面能的活性氧化物,又可改善液态熔渣在焊缝金属表面的润湿铺展性能.实施辅助电场引入的这些有益作用使焊缝形状、表面光洁度、尤其是焊缝边缘平直均匀性得到较好地改观,焊接过程工艺稳定性得以进一步提高.