Sensitivity analysis for process parameters in GMA welding processes using a factorial design method

Generally, the quality of a weld joint is strongly influenced by process parameters during the welding process. In order to achieve high quality welds, mathematical models that can predict the bead geometry and shape to accomplish the desired mechanical properties of the weldment should be developed. This paper focuses on the development of mathematical models for the selection of process parameters and the prediction of bead geometry (bead width, bead height and penetration) in robotic GMA (Gas Metal Arc) welding. Factorial design can be employed as a guide for optimization of process parameters. Three factors were incorporated into the factorial model: arc current, welding voltage and welding speed. A sensitivity analysis has been conducted and compared the relative impact of three process parameters on bead geometry in order to verify the measurement errors on the values of the uncertainty in estimated parameters. The results obtained show that developed mathematical models can be applied to estimate the effectiveness of process parameters for a given bead geometry, and a change of process parameters affects the bead width and bead height more strongly than penetration relatively.     

Optimization of welding parameters for laser bead-on-plate welding using Taguchi method

This paper presents the results obtained by the optimization of laser bead on plate welding parameters for 3.5 kW cooled slab laser using Taguchi technique. The trials were conducted on two different shielding gases 100% Nitrogen and 50% Nitrogen + 50% Argon. The input process parameters such as beam power, travel speed and focal position are selected suitably in order to obtain the desired output i.e., bead width and depth of penetration. The quality of the weld is evaluated by studying the features of weld bead geometry. Grey relational analysis is applied to optimize the input parameters simultaneously considering multiple output variables. In this investigation the nearest optimal solution which would improve the weld quality was found out. Experimental trial on super austenitic stainless steel has been conducted to validate the optimized parameters. Further, the optimized parameters were evaluated through the microstructural characterization and hardness measurements across the weld zone.     

Prediction of bead geometry in pulsed GMA welding using back propagation neural network

This paper presents the development of a back propagation neural network model for the prediction of weld bead geometry in pulsed gas metal arc welding process. The model is based on experimental data. The thickness of the plate, pulse frequency, wire feed rate, wire feed rate/travel speed ratio, and peak current have been considered as the input parameters and the bead penetration depth and the convexity index of the bead as output parameters to develop the model. The developed model is then compared with experimental results and it is found that the results obtained from neural network model are accurate in predicting the weld bead geometry.     

Role of Welding Parameters Using the Flux Cored Arc Welding Process of Low Alloy Steels on Bead Geometry and Mechanical Properties

Welding parameters have direct effects on the bead geometry, microstructure, and mechanical properties of low alloy steels. A series of experiments have been carried out to examine some of these parameters using the flux cored arc welding process (FCAW). In this article, an experimental study was conducted to investigate the influence of welding parameters in FCAW process particularly welding voltage and travel speed on weld bead dimensions. The study also includes the effects of bead overlap and deposition sequence on the parent material and the heat-affected zone (HAZ) properties. It was found that an increase in the welding voltage leads to an increase in the weld bead width, and the increase in the welding traverse speed leads to a decrease in the weld bead width. When studying the bead overlap percentages, it was found that the 50% bead overlap can be considered to be practically a better option than the higher percentages of bead overlap (i.e., 70-90%). The experimental investigation of studying the deposition sequence showed that there were no significant differences in the microstructure, hardness, and the size of the refined HAZ between the two proposed deposition sequences. However, a significant improvement in the microstructure and the size of the refined HAZ, and a reduction in the hardness were achieved after depositing the second welding bead, irrespective of the depositing sequence.     

Electron beam welding of precipitation hardened CuCrZr alloy: Modeling and experimentation

In order to maintain the structural consistency during the welding of precipitation hardened copper− chromium−zirconium (PH-CuCrZr) alloy components, electron beam welding (EBW) process was employed. Experimental study and numerical modeling of EBW process during welding of PH-CuCrZr alloy components were carried out. A 3D finite element model was developed to predict the output responses (bead penetration and bead width) as a function of EBW input parameters (beam current, acceleration voltage and weld speed). A combined circular and conical source with Gaussian heat distribution was used to model the deep penetration characteristic of the EBW process. Numerical modeling was carried out by developing user defined function in Ansys software. Numerical predictions were compared with the experimental results which had a good agreement with each other. The developed model can be used for parametric study in wide range of problems involving complex geometries which are to be welded using EBW process. The present work illustrates that the input current with a contribution of 44.56% and 81.13% is the most significant input parameter for the bead penetration and bead width, respectively.     

Modelling weld bead geometry using neural networks for GTAW of austenitic stainless steel

Abstract

The authors analyse the importance of different weld control parameters on the weld pool geometry of gas tungsten arc welding using an online feature selection technique that suggests weld voltage and vertex–angle pair as more important than the weld voltage and torch speed pair. Using the selected features multi layer perception and radial basis function networks are developed for prediction of bead width, penetration depth, and bead area. With cross-validation the authors have extensively studied the performance of composite models (one model for all outputs) and individual models (one model for each output). The individual models are found to work better than composite models. Usually, radial basis function networks are found to work better than the multi layer perception networks. To assess the influence of weld control parameters the authors have studied the performance of both networks using different combination of inputs. Overall, the performance of the proposed models is found to be quite satisfactory.     

基于支持向量机的焊缝尺寸预测

焊缝尺寸是决定焊接接头强度及有关性能的重要因素,因此也是焊接质量控制的重要内容.分别以焊接电流、电弧电压以及焊接速度作为输入向量构造样本集,建立CO2焊接焊缝尺寸支持向量机模型,分别运用线性核函数,多项式核函数、高斯径向基核函数以及指数径向基核函数对焊缝熔宽、焊缝熔深以及焊缝余高进行预测.结果表明,采用指数径向基核函数所建立的支持向量机模型可以有效地对焊缝尺寸进行预测,为进一步实现焊缝质量的在线控制提供依据.     

铝合金同轴式等离子-MIG焊接工艺

使用同轴式等离子-MIG焊枪,对防锈铝LF5进行工艺试验,研究其工艺参数对焊缝成形及组织的影响,并检验了组织中的缺陷.结果表明,同轴式等离子-MIG焊接铝合金时能够获得较为理想的焊缝;与偏置式等离子-MIG焊接低碳钢相比,用同轴等离子-MIG焊接铝合金时等离子电流的增加对焊缝影响更大,而对熔宽的影响相对较小;焊接过程中,焊丝与母材在高温时熔敷共同形成焊缝中过渡;等离子弧清理范围变小,易形成氧化物夹渣.     

Comparison of multiple regression and back propagation neural network approaches in modelling top bead height of multipass gas metal arc welds

Abstract

With the advanced developments and automation of the welding process, the use of process optimisation techniques has increased. The objective of the present paper is to describe process optimisation techniques for the gas metal arc (GMA) welding process, based on experimental results generated by the process. Back propagation (BP) neural network and multiple regression methods are employed to study relationships between process parameters and top bead height for robotic multipass welding process, and to select a suitable model that provides the weld final configuration and properties as output and employs the process parameters as input. The process parameters, namely pass number, arc current, welding voltage and welding speed are optimised to produce the required top bead height. These techniques have achieved good agreement with the experimental data and yielded satisfactory results. Also, the BP neural network that was developed was compared to the empirical equations for predicting top bead height through additional experiments, and it was evident that the BP neural network was considerably more accurate than multiple regression techniques.     

Influence of process variables on weld bead quality in two wire tandem submerged arc welding of HSLA steel

Two-wire tandem submerged arc welding process involves simultaneous depositions from two electrode wires with the leading wire usually connected to a DC power source and the trailing wire connected to a pulsed AC power source. The weld bead profile and mechanical properties in the tandem submerged welding are significantly affected by the leading and trailing wire current transients and the welding speed. We present here a detailed experimental study on the influence of leading wire current, trailing wire current pulses, and welding speed on the weld bead dimensions and mechanical properties in single-pass tandem submerged welding of a typical HSLA steel. It is realized that the weld bead penetration is primarily influenced by the leading wire current while the weld bead width and the reinforcement height are sensitive to the trailing wire current pulses. Greater magnitude of trailing wire current pulses and shorter negative pulse duration increase the weld pool volume leading to reduced cooling rate and poor mechanical properties as the formation of the strengthening phases like acicular ferrite is inhibited. In contrast, increase in welding speed reduces the rate of heat input thereby enhancing the cooling rate and the weld bead mechanical properties. A set of empirical relations are developed to estimate the weld bead dimensions and mechanical properties as function of the welding conditions. The predictions from the empirical relations and the corresponding measured results are observed to be in fair agreement.     

Laser beam welding of dissimilar stainless steels in a fillet joint configuration

This paper investigates laser beam welding of dissimilar AISI 304L and AISI 430 stainless steels. Experimental studies were focused on effects of laser power, welding speed, defocus distance, beam incident angle, and line energy on weld bead geometry and shearing force. Metallurgical analysis was conducted on a selected weld only to show various microstructures typically formed at different zones and consequent change in microhardness. Laser power and welding speed were the most significant factors affecting weld geometry and shearing force. All the bead characteristics but radial penetration depth decreased with increased beam incident angle. The focused beam allowed selecting lower laser power and faster welding speed to obtain the same weld geometry. Weld shape factor increased rapidly due to keyhole formation for line energy input ranging from 15 kJ/m to 17 kJ/m. Fusion zone microstructures contained a variety of complex austenite-ferrite structures. Local microhardness of fusion zone was greater than that of both base metals.     

铝合金变极性TIG焊接电弧行为

分别采用正弦波变极性和方波变极性氩弧焊对铝合金试板进行了焊接试验,利用高速摄像机和汉诺威分析仪分别对焊接过程中变极性电弧形态及电信号进行采集分析. 结果表明,电弧电压概率密度分布和高速摄像图证实了较小焊接参数条件下正弦波变极性比方波变极性电弧稳定性差的现象. 正弦波变极性TIG电弧随EP(反极性)的增加清理宽度增加,但熔宽未增加,证明此条件下正弦波变极性TIG电弧过于发散;焊接参数较大时,随EP的增加,正弦波变极性熔宽变宽,证实正弦波变极性TIG电弧稳定性随之提高,证明了铝合金变极性TIG焊接过程中EP极性电弧产热大于EN极性电弧能量的本质特征.     

Experimental study of laser welding with applied electrical potential

Abstract

The objective of the present study is to develop laser welding with an applied voltage potential, to increase the weld bead root size in laser welding and thereby to improve the welding speed and the butt joint gap tolerance. The influences of the experimental conditions, namely, input laser power, applied voltage between plate and backside electrode, welding speed, plasma operating gaseous species (air, argon, or argon–helium), and the butt joint gap, on the plasma stability and the weld bead were investigated. The weld beads are evaluated from the point of view of the bead appearance, the penetration depth, the ratio of the widths of the weld bead root and weld bead face, and the smoothness of the bead surface. It is found that to stabilise the plasma, it is preferable to set the plate polarity as the cathode (electrode positive), and to use argon or helium gas as a plasma operating gas. Also, it is concluded that this novel method is effective in increasing the bead root/face width ratio, and the melting area. Although it is necessary to optimise the experimental conditions to avoid overheating and melting of the plates, the present method is applicable for higher speed and wider gap butt joint welding than in conventional laser welding.     

Experimental investigation on laser beam welding of martensitic stainless steels in a constrained overlap joint configuration

This paper presents experimental investigation of laser beam welding of martensitic stainless steels in a constrained overlap configuration. Experimental studies were focused on the effects of laser power, welding speed and fiber diameter on bead geometry and mechanical properties of the weld. Metallurgical study of a selected welded joint was done only to show various microstructures typically formed at different zones. Laser power and welding speed were found the most significant factors affecting the weld geometry and shearing force. The contour plots showing constant response lines indicated the evidence of two-factor interaction effects of laser power-welding speed, welding speed-fiber diameter, and fiber diameter-laser power on all the responses except the weld width. Moreover, energy density plots illustrated its linear relationship with penetration depth and limited nonlinear effects on others. Additionally, metallurgical analysis of fusion zone showed dendritic structures consisted of martensitic with eutectic ferrite along solidification grain and subgrain boundaries.     

TIG arc characteristics in different atmospheres (part 1)

Summary

The physical properties of gases such as density, thermal and electrical conductivity, as well as ionisation potential, determine to a great extent the operational characteristics of welding arcs. These properties may vary widely for different gases. As a result, arc voltage, heat output, mean radius, thermal profile, performance and other parameters which influence bead geometry (shape, width and penetration) depend on the chemical composition of the shielding gas. Rather complex physical models have been proposed to explain and quantify the effects of shielding gas chemical composition on welding arc performance. The influence of arc atmosphere may also be easily predicted by empirical methods. However, only changes in arc operational parameters and weld bead geometry due to variations in gas composition appear in the literature. This article presents an optical study of the TIG welding arc, based on a digital system of image capture and welding parameter recording, during arc operation. Variations in arc aspect, dimensions and electrical parameters were observed, and the results related to the physical properties of gases and mixtures used, as well as forecasts by theoretical models.     

Prediction of weld quality in pulsed current GMAW process using artificial neural network

Abstract

Weld joint dimensions and weld metal mechanical properties are important quality characteristics of any welded joint. The success of building these characteristics in any welding situation depends on proper selection-cum-optimisation of welding process parameters. Such optimisation is critical in the pulsed current gas metal arc welding process (GMAW-P), as the heat input here is closely dictated by a host of additional pulse parameters in comparison to the conventional gas metal arc welding process. Neural network based models are excellent alternatives in such situations where a large number of input conditions govern certain outputs in a manner that is often difficult to adjudge a priori. Six individual prediction models developed using neural network methodology are presented here to estimate ultimate tensile strength, elongation, impact toughness, weld bead width, weld reinforcement height and penetration of the final weld joint as a function of four pulse parameters, e.g. peak current, base current, pulse on time and pulse frequency. The experimental data employed here are for GMAW-P welding of extruded sections of high strength Al–Zn–Mg alloy (7005). In each case, a committee of different possible network architectures is used, including the final optimum network, to assess the uncertainty in estimation. The neural network models developed here could estimate all the outputs except penetration fairly accurately.     

Optimization and Prediction of Angular Distortion and Weldment Characteristics of TIG Square Butt Joints

Autogenous arc welds with minimum upper weld bead depression and lower weld bead bulging are desired as such welds do not require a second welding pass for filling up the upper bead depressions (UBDs) and characterized with minimum angular distortion. The present paper describes optimization and prediction of angular distortion and weldment characteristics such as upper weld bead depression and lower weld bead bulging of TIG-welded structural steel square butt joints. Full factorial design of experiment was utilized for selecting the combinations of welding process parameter to produce the square butts. A mathematical model was developed to establish the relationship between TIG welding process parameters and responses such as upper bead width, lower bead width, UBD, lower bead height (bulging), weld cross-sectional area, and angular distortions. The optimal welding condition to minimize UBD and lower bead bulging of the TIG butt joints was identified.     

不锈钢激光焊焊缝成形的数学模型

在304不锈钢的激光深熔焊中,通过工艺试验,研究了激光焊接工艺参数与焊缝形状参数之间的关系.采用二次通用旋转回归设计方法设计了试验方案.通过对试验数据的统计检验,求出了置信度较高的以功率、速度和离焦量为因子的熔池形状回归方程.通过相关性分析,揭示了各个因子对焊缝成形的影响规律.随着激光功率的增大,熔深、熔宽、束腰高、束腰宽都增加;焊接速度增加时,熔深、熔宽、束腰高、束腰宽都减小,熔宽到一定水平后不再减小,而熔深则一直减小;当离焦量由负离焦向正离焦转变时,熔深和束腰高都呈现先增大后减小的趋势,而熔宽和束腰宽则呈现出相反的趋势.当离焦量水平为0时,熔宽达到最小值.     

铝合金脉冲YAG激光焊脉冲调制参数对焊缝形状参数的影响

以2mm厚LF3铝合金薄板为对象,研究了在平均功率和焊接速度不变时脉冲YAG激光焊脉冲调制参数(脉宽、频率及单脉冲能量)对热导焊缝形状参数(熔深、熔宽及深宽比)的影响规律,并结合脉冲激光焊间断作用的特征,引入"有效峰值功率密度"综合考虑焊接速度、频率、脉宽以及光斑大小对焊缝形状参数的影响.此外,还对脉冲激光焊所形成的特殊的层状焊缝形貌进行研究和分析.结果表明,焊缝形状参数受脉宽及峰值功率密度双重作用的影响.脉冲焊得到的焊缝呈现多层状形貌,层数随频率升高而增多.     

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process(HPVP-GTAW)is developed.High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration.The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5.8 Mg alloy plates.The arc characteristics studied by arc voltage and its profile,weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current.The experimental results show that the HPVP-GTAW process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input.The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.