Slag recycling in submerged arc welding and its influence on weld quality leading to parametric optimization

Slag generated during conventional submerged arc welding (SAW) has been recycled by mixing varying percentages of crushed slag with fresh flux to use in subsequent runs. The influence of using flux-slag mixture on various aspects of SAW weld parameters of bead geometry have been investigated in a quantitative basis. Slag has been reprocessed and reused in submerged arc welding to produce bead-on-plate weld on mild steel plates. Apart from conventional process parameters: voltage (OCV), wire feed rate, nozzle to plate distance (stick-out) and traverse speed, welding has been carried out using various percentages of flux-slag mixture; the % of fused flux in the mixture has been treated as a process parameter. Various bead geometry parameters viz. bead width; reinforcement, depth of penetration and depth of HAZ have been measured for each of weld prepared in the study. Using experimental data, a grey-based Taguchi approach has been applied for parametric optimization of this non-conventional SAW process. The aim was to reveal the optimal amount of slag-mix%, which could be applied in SAW process without imposing any adverse effect on features of bead geometry and HAZ. Optimal result has been checked through confirmatory test.     

Application of Taguchi philosophy for parametric optimization of bead geometry and HAZ width in submerged arc welding using a mixture of fresh flux and fused flux

Taguchi philosophy has been applied for obtaining optimal parametric combinations to achieve desired weld bead geometry and dimensions related to the heat-affected zone (HAZ), such as HAZ width in the present case, in submerged arc welding. The philosophy and methodology proposed by Dr. Genichi Taguchi can be used for continuous improvement in products that are produced by submerged arc welding. This approach highlights the causes of poor quality, which can be eliminated by self-adjustment among the values of the process variables if they tend to change during the process. Depending on functional requirements of the welded joint, an acceptable weldment should confirm maximum penetration, minimum reinforcement, minimum bead width, minimum HAZ width, minimum bead volume, etc. to suit its area of application. Hence, there exists an increasing demand to evaluate an optimal parameter setting that would fetch the desired yield. This could be achieved by optimization of welding variables. Based on Taguchi’s approach, the present study has been aimed at integrating statistical techniques into the engineering process. Taguchi’s L9 (3**3) orthogonal array design has been adopted and experiments have been accordingly conducted with three different levels of conventional process parameters using welding current and flux basicity index to obtain bead-on-plate weld on mild steel plates. Features of bead geometry and HAZ in terms of bead width, reinforcement, depth of penetration and HAZ width have been measured for each experimental run. The slag, generated during welding, has been consumed in further runs by mixing it with fresh unmelted flux. The percentage of slag in the mixture of fused flux (slag) and fresh flux has been defined as slag-mix%. Welding has been performed by using varying slag-mix%, treated as another process variable, in order to obtain the optimum amount of slag-mix that can be used without any alarming adverse effect on features of bead geometry and HAZ. This would lead to ‘waste to wealth’.     

Modeling and optimization of features of bead geometry including percentage dilution in submerged arc welding using mixture of fresh flux and fused slag

Quality has now become an important issue in today’s manufacturing world. Whenever a product is capable of conforming to desirable characteristics that suit its area of application, it is termed as high quality. Therefore, every manufacturing process has to be designed in such a way that the outcome would result in a high quality product. The selection of the manufacturing conditions to yield the highest desirability can be determined through process optimization. Therefore, there exists an increasing need to search for the optimal conditions that would fetch the desired yield. In the present work, we aim to evaluate an optimal parameter combination to obtain acceptable quality characteristics of bead geometry in submerged arc bead-on-plate weldment on mild steel plates. The SAW process has been designed to consume fused flux/slag, in the mixture of fresh flux. Thus, the work tries to utilize the concept of ‘waste to wealth’. Apart from process optimization, the work has been initiated to develop mathematical models to show different bead geometry parameters, as a function of process variables. Hence, optimization has been performed to determine the maximum amount of slag--flux mixture that can be used without sacrificing any negative effect on bead geometry, compared to the conventional SAW process, which consumes fresh flux only. Experiments have been conducted using welding current, slag-mix percentage and flux basicity index as process parameters, varied at four different levels. Using four³ full factorial designs, without replication, we have carried out welding on mild steel plates to obtain bead-on-plate welds. After measuring bead width, depth of penetration and reinforcement; based on simple assumptions on the shape of bead geometry, we calculated other relevant bead geometry parameters: percentage dilution, weld penetration shape factor, weld reinforcement form factor, area of penetration, area of reinforcement and total bead cross sectional area. All these data have been utilized to develop mathematical models between predictors and responses. Response surface methodology (RSM), followed by the multiple linear regression method, has been applied to develop these models. The effects of selected process parameters on different responses have been represented graphically. Finally grey relational analysis coupled with the Taguchi method (with Taguchi’s orthogonal array) has been applied for parametric optimization of this welding technique. Confirmatory experiments have been conducted to verify optimal results.     

Optimization of Inconel 718 alloy welds in an activated GTA welding via Taguchi method, gray relational analysis, and a neural network

The purpose of this work is to optimize the weld bead geometry of Inconel 718 alloy gas tungsten arc (GTA) welds that are coated with activating flux before welding. In order to obtain the optimal welding parameters with multiple quality characteristics (QCs) such as penetration and depth-to-width ratio (DWR) of weld bead, the Taguchi method (TM), gray relational analysis (GRA), and a neural network (NN) are employed in this work. The TM is first used to construct a database for the NN. The GRA is adopted to solve the problem of multiple QCs. The gray relational grade (GRG) obtained from the GRA is used as the output of the backpropagation (BP) NN. Then, a NN with the Levenberg–Marquardt BP (LMBP) algorithm is used to provide the nonlinear relationship between welding parameters and GRG of each specimen. The optimal parameters of the activated GTA welding process are determined by simulating parameters using a well-trained BPNN model. The experimental procedure of the proposed approach not only improves the DWR of weld bead but also increases the penetration of Inconel 718 alloy welds.     

Multi sensor data fusion for improving performance and reliability of fully automatic welding system

This paper presents a new generation of system for pressure vessel and shipbuilding. Typical pressure vessel and ship building weld joint preparations are either traditional V, butt, fillet grooves or have narrow or semi narrow gap profiles. The fillet and U groove are prevalently used in heavy industries and shipbuilding to melt and join the parts. Since the wall thickness can be up to 6 in. or greater, welds must be made in many layers, each layer containing several passes. However, the welding time for the conventional processes such as submerged arc welding (SAW) and flux cored arc welding (FCAW) can be many hours. Although SAW and FCAW are normally mechanized processes, pressure vessel and ship structures welding up to now have usually been controlled by a full time operator. The operator has typically been responsible for positioning each individual weld run, for setting weld process parameters, for maintaining flux and wire levels, for removing slag and so on. The aim of the system is to develop a high speed welding system with multi-torch for increasing the production speed on the line and to remove the need for the operator so that the system can run automatically for the complete multi-torch multi-layer weld. To achieve this, a laser vision sensor and a special image processing algorithm have been made. Also, the multi-torch welding system can be applicable for fine grained steel because of the high welding speed and lower heat input compared to a conventional welding process.     

Some investigations on microstructure and mechanical properties of submerged arc welded HSLA steel joints

This paper investigates the influence of the submerged arc welding (SAW) process parameters (welding current and welding speed) on the microstructure, hardness, and toughness of HSLA steel weld joints. Attempts have also been made to analyze the results on the basis of the heat input. The SAW process was used for the welding of 16 mm thick HSLA steel plates. The weld joints were prepared using comparatively high heat input (3.0 to 6.3 KJ/mm) by varying welding current (500–700 A) and welding speed (200–300 mm/min). Results showed that the increase in heat input coarsens the grain structure both in the weld metal and heat affected zone (HAZ). The hardness has been found to vary from the weld centre line to base metal and peak hardness was found in the HAZ. The hardness of the weld metal was largely uniform. The hardness reduced with the increase in welding current and reduction in welding speed (increasing heat input) while the toughness showed mixed trend. The increase in welding current from 500 A to 600 A at a given welding speed (200 mm/min or 300 mm/min) increased toughness and further increase in welding current up to 700 A lowered the toughness. Scanning electron microscopy of the fractured surfaces of impact test specimen was carried out to study the fracture modes. Electron probe micro analysis (EPMA) was carried out to investigate the variation in wt.% of different elements in the weld metal and HAZ.     

Development of Adaptive Fill Control for Multitorch Multipass Submerged Arc Welding

A significant portion of the total manufacturing time for a pipe fabrication process is spent on the welding following the primary machining and fit-up processes. To achieve a reliable weld bead appearance, automatic seam tracking and adaptive control to fill the groove are urgently required. For seam tracking in the welding processes, vision sensors have been successfully applied. However, the adaptive filling control for a multitorch system for the appropriate welded area has not yet been implemented in the area of submerged arc welding (SAW). This paper describes several advances in sensor and process control techniques for applications in SAW which combine to give a fully automatic system capable of controlling and adapting the overall welding process. This technology has been used in longitudinal and spiral pipe mills and in pressure vessel production.     

Weldability of Copper-bearing Aging Steel

The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm,oblique Y-groove cracking test,heat-affected zone (HAZ) maximum hardness measurement,submerged arc welding (SAW) test and gas metal arc welding (GMAW) test.The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility.SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature.The HAZ has no hardening but there exists a slightly softening phenomenon.Thus,line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW.GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa,higher than the stipulated strength requirement of base metal.The average impact energy at-40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin.There are no hardening and softening behaviors in the heat-affected zones of GMAW.All weld metals exhibit acicular ferrite (AF) plus small amount of proeutectoid ferrite (PF) structure,of which the former can significantly improve impact toughness of weld metal.The predominant microstructure in coarse grain HAZ is bainite.     

A105钢振动焊接接头的性能与组织分析

采用阀门用钢A105作为试验材料,采用机械振动焊接与常规埋弧自动焊接相结合的方法进行对比试验。试验结果表明:振动焊接后,焊接变形和残余应力明显降低,焊接结构尺寸稳定性和使用安全性大大提高,振动焊接后焊缝试样的冲击吸收功平均值比常规焊接下冲击吸收功的平均值提高了21%,且振动焊接对焊缝冲击性能的影响要明显大于对热影响区冲击性能的影响;振动焊接使得焊缝和热影响区的组织明显细化,熔合区和过热区变窄,魏氏组织减小或消失。     

外加磁场对高速GMAW电弧和熔池行为的主动调控效应

在熔化极气体保护焊(Gas metal arc welding,GMAW)过程中,当焊接速度超过临界值后,焊缝成形变差,出现咬边和驼峰焊道,无法满足生产要求。研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因。自主研发外加磁场发生装置,向熔池施加横向电磁力,对后向液体流进行主动干预,并调控熔池流态,从而抑制驼峰焊道的形成。在Q235低碳钢板上开展焊接工艺试验,获得了不同磁感应强度下的焊缝表面成形;采用高速摄像技术,拍摄焊接过程中的电弧和熔池图像,分析外加磁场对电弧形态、熔池流场和焊缝成形的影响规律,初步揭示外加磁场抑制驼峰焊道的机理。试验结果表明,外加横向磁场能明显调控熔池流态,减小后向液体流的动量,并能有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度。     

Grey-based taguchi method for optimization of bead geometry in submerged arc bead-on-plate welding

A multi-response optimization problem has been developed in search of an optimal parametric combination to yield favorable bead geometry of submerged arc bead-on-plate weldment. Taguchi’s L25 orthogonal array (OA) design and the concept of signal-to-noise ratio (S/N ratio) have been used to derive objective functions to be optimized within experimental domain. The objective functions have been selected in relation to parameters of bead geometry viz. bead width, bead reinforcement, depth of penetration and depth of HAZ. The Taguchi approach followed by Grey relational analysis has been applied to solve this multi-response optimization problem. The significance of the factors on overall output feature of the weldment has also been evaluated quantitatively by analysis of variance method (ANOVA). Optimal result has been verified through additional experiment. This indicates application feasibility of the Grey-based Taguchi technique for continuous improvement in product quality in manufacturing industry.     

一种高效焊接技术——添加合金粉末埋弧焊

采用普通埋弧焊和添加合金粉末埋弧焊技术,焊接了２０Ｇ和１６ＭｎＲ钢,结果表明,添加合金粉末埋弧自动焊技术能够采用大线能量（因为添加的合金粉末改善了焊缝组织,焊缝深宽比显著提高,而焊缝及ＨＡＺ组织晶粒没有粗化）,焊接工艺性能良好,焊接熔敷速率是传统埋弧焊的２倍,接头角变形明显减小,焊接接头的力学性能满足要求。     

Study on arc characteristics and their influences on weld bead geometry in narrow gap GMAW of 5083 Al-alloy

As an efficient process, narrow gap gas metal arc welding (NG-GMAW) was employed to join thick plates of 5083 Al-alloy. In this paper, arc characteristics in NG-GMAW of 5083 Al-alloy and their influence on the weld bead geometry were studied with synchronous acquisition system for various groove types, welding modes, welding current levels, and swing frequencies. The arc profiles were measured and appear to be entirely different compared with that in bead-on-plate GMAW process, meanwhile the arc size changes with varied welding mode, welding current, and arc swing frequency. Arc characteristics highly affect the weld bead geometrical parameters such as bead width, welding penetration, sidewall penetration, and weld surface concavity. Linear regressions were made between the arc characteristics and the weld bead geometrical parameters both in swing and non-swing arc process. It showed that a negative linear correlation exists between welding penetration and arc length, sidewall penetration, and arc warpage, while a positive linear correlation exists between weld surface concavity and arc warpage in non-swing arc process. In contrast, a non-linear correlation exists among them and the variation tendency remains the same in swing arc process.     

Optimization of weld bead geometry in the activated GMA welding process via a grey-based Taguchi method

We optimized the weld bead geometry of 6061 aluminum alloy welds pre-coated with activating flux before gas metal arc (GMA) welding. In this activated GMA welding process, there were five single component fluxes used in the initial experiment to evaluate the penetration capability of bead-on-plate GMA welds. Based on the higher penetration of weld bead, two single component fluxes were selected to create mixed component flux in next stage. The grey-based Taguchi method was employed to obtain the optimal welding parameters that were considered with multiple quality characteristics such as penetration, depth-to-width ratio (DWR) and fusion area of GMA welds. The experimental procedure of the proposed approach not only increases penetration of 6061 aluminum alloy welds, but also improves the DWR and fusion area of GMA butt-joint welds simultaneously.     

活性剂增加铝合金交流A-TIG焊熔深机理研究

采用多组元活性剂AF305进行铝合金交流A-TIG焊时,熔深达到传统TIG焊的3倍以上。进行了交流、直流正接和直流反接A-TIG焊,发现极性不同时活性剂对熔深的影响也不同。研究了强制电弧收缩对交流焊熔深的影响,发现弧根整体收缩并不是AF305增加交流A-TIG焊熔深的主要机理,熔深显著增加主要与焊渣成片分布有关。对焊渣进行了SEM形貌观察和EDS成分分析,并采用氦弧焊证实了焊接过程中焊渣在熔池表面成片分布,电弧斑点极大收缩。向AF305活性剂中添加铝粉改变焊渣分布,研究焊渣分布与熔深的关系,证实了焊渣成片分布能增加焊接熔深。认为焊渣成片分布使得电弧斑点极大收缩,斑点压力以及电弧和熔池内的Lorentz力增强,最终焊接熔深显著增加。     

Optimisation of the weld bead geometry in gas tungsten arc welding by the Taguchi method

In this paper, determination of the welding process parameters for obtaining an optimal weld bead geometry in gas tungsten arc welding is presented. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each welding process parameter on the weld bead geometry, and to predict the optimal setting for each welding process parameter. Experimental results are presented to explain the proposed approach.     

窄间隙埋弧焊的特点及未来发展

本文对在我国应用逐渐广泛的窄间隙埋弧焊的产生与发展进行了回顾,介绍了窄间隙埋弧焊产生的原因及其特点,对其在实际应用中表现出的优点和缺点进行了总结。优点包括更好的焊接质量、更小的焊接变形和残余应力以及节省焊接填充材料和能源,缺点包括熔合问题、脱渣问题以及使用何种焊剂。阐述了目前市场上销售与企业中实际应用最广泛的窄间隙埋弧焊机的特点以及未来窄间隙埋弧焊技术与自动焊机的发展方向,对于进一步的研究具有借鉴意义。     

Mathematical models for control of weld bead penetration in the GMAW process

This paper presents the effects of welding process parameters on weld bead penetration for the gas metal arc welding (GMAW) process. Welding process parameters included wire diameter, gas flow rate, welding speed, arc current and welding voltage. The experimental results have shown that weld bead penetration increased as wire diameter, arc current and welding voltage increased, whereas an increase in welding speed was found to decrease the weld bead penetration. However, the weld bead penetration is not affected significantly by gas flow rate changes. Mathematical equations for study of the relationship between welding process parameters and weld bead penetration have also been computed by employing a standard statistical package program, SAS.     

A control system for uniform bead in fillet arc welding on tack welds

Positioning a workpiece accurately and preventing weld distortion, tack welding is often adopted before main welding in the construction of welded structures. However, this tack weld deteriorates the final weld bead profile, so that the grinding process is usually performed for a uniform weld bead profile. In this study, a control system for uniform weld bead is proposed for the fillet arc welding on tack welds. The system consists of GMA welding machine, torch manipulator, laser vision sensor for measuring the tack weld size and the database for optimal welding conditions. Experiments have been performed for constructing the database and for evaluating the control capability of the system. It has been shown that the system has the capability to smooth the bead at the high level of quality.     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part I—the mathematical model

In this work, the oscillating arc narrow gap all-position gas metal arc (GMA) welding process was developed to improve efficiency and quality in the welding of thick-walled pipes. The statistical models of narrow gap all-position GMA weld bead geometry were developed using response surface methodology (RSM) based on central composite design (CCD). The developed models were checked for their adequacy and significance by ANOVA, and the effects of wire feed rate, travel speed, dwell time, oscillating amplitude and welding position on weld bead dimension were studied. Finally, the optimal welding parameters at welding positions of 0° to 180° were obtained by numerical optimization using RSM.