Study of mechanism of activating flux increasing weld penetration of AC A-TIG welding for aluminum alloy

When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld penetration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc constriction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(5): 45–49 [译自: 机械工程学报]     

基于Hammerstein模型的GMAW-P焊接熔深自适应预测控制

针对脉冲熔化极气体保护焊(Pulsed gas metal arc welding,GMAW-P)过程中焊接熔深的实时控制,使用脉冲峰值期间的电压变化幅值(ΔU)来表征焊接熔深变化,并且通过测量和控制ΔU的大小来间接达到熔深控制的目的。建立了以ΔU为输出和脉冲基值电流为输入的单输入单输出熔深控制系统。系统输入输出之间的静态关系模型显示该熔深控制系统具有一定非线性,因此,采用加入干扰的Hammerstein模型描述该非线性系统。在基于该Hammerstein模型的经典预测控制算法基础上,在控制过程中加入递推最小二乘法在线辨识模型参数,从而实现焊接熔深自适应控制。控制算法仿真和实时焊接试验表明该熔深控制算法能够较好地实现GMAW-P焊接过程中的熔深控制。变散热试验结果验证了该控制算法的有效性和适应性。     

Ultrasonic thermometry for friction stir spot welding

This investigation presents the feasibility of ultrasonic temperature measurement of friction stir spot welding (FSSW). FSSW is an automated solid state joining process. Thermal profiles of the weld zone are crucial for implementing informed process changes to improve weld quality. Ultrasonics present a novel and non-invasive method of monitoring changes in temperature.Ultrasonic time of flight (TOF) measurement method is used to calculate the temperature of Al 6061 as it is heated. Comparisons of the ultrasonic temperature calculations with thermocouple readings confirm the accuracy of the ultrasonic system. The ultrasonic signal is then recorded during spot welding and processed. The results show that ultrasonic technology is a feasible method of monitoring the heating and cooling profiles of the weld zone during welding. The paper also discusses challenges presented by the system as well as recommendations for its future implementation in the friction stir welding manufacturing industry.     

活性激光电弧复合焊接法研究

为了进一步提高激光电弧复合焊接的熔深,提出活性激光电弧复合焊接法。在氧气的保护下,用小功率光纤激光在待焊焊件表面进行预熔处理,使表面熔化生成一层氧化层,然后用激光电弧复合焊接覆盖氧化层,达到增加熔深的目的。结果表明,激光预熔后进行激光电弧复合焊接,电弧明显收缩,熔深增加1.5倍左右,表面成形良好。激光预熔后,焊缝含氧量增加,熔池表面张力温度系数由负变正,使得复合焊接熔深增加。研究工艺参数对焊缝熔深和熔宽的影响,随着激光预熔功率的增加,熔深增加熔宽减小;随着电流的增加,熔深熔宽都增加,但激光预熔后的焊道增加更快。随着复合焊接速度的增加,熔深和熔宽都减小。随着复合焊接中激光功率的增加,熔深增加,对熔宽的影响较小。利用活性激光电弧复合焊接法,可以得到较为细小的焊缝组织,提高焊接接头的抗拉强度,能达到母材抗拉强度的95%,且面弯和背弯180°后未出现裂纹,表明接头具有良好的韧性。     

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。     

Solving multiple response optimisation problems using adaptive neural networks

This paper describes an integrated methodology using experimental designs and neural networks technologies for solving multiple response problems. This new methodology consists of an experiment reference template for designing and collecting training data samples and a parallel distributed computational adaptive neural network system to provide a powerful tool for data modelling, guiding experimentation and empirical investigations. While the experiment reference template is for determining the measurements to adopt in order to extract maximum information within minimum experimental efforts, the adaptive neural network provides a nonlinear multivariate data-fitting algorithm for analysing the results of the experimental design and providing decision support. This integrated methodology is used to model and optimise a multiple response metal inert gas (MIG) welding process. The neural network is trained with optimum welding experimental data, tested and compared in an actual welding environment in terms of weld quality. The relevant data is established using experimental design methods and is highlighted in the case study. The implementation for this case study was carried out using a semi-automatic welding facility, to mass weld a 20 in.×0.438 in. pin/box onto a 20 in.×0.5 in.×37 ft pipe (tubular drilling products), in an actual workshop which makes oilfield equipment. The entire range of welding combination that the process might be subject to during actual welding operations is included to study the weld quality.     

The effect of arc behavior on weld geometry by high-frequency pulse GTAW process with 0Cr18Ni9Ti stainless steel

Based on 0Cr18Ni9Ti austenitic stainless steel plate (h?=?6 mm), a study on arc behavior by ultrasonic frequency pulse gas tungsten arc welding (GTAW) process has been carried out. The results show that with the increasing pulse frequency, an obvious pinch effect of arc plasma has been detected and also the increment of arc voltage, stiffness, and force. Then, the method, combining weld appearance and numerical simulation, has been adapted for weld behavior on the basis of arc behavior by ultrasonic frequency pulse GTAW process. As a result of arc shrinkage, the root radius of arc decreased, which caused narrower weld bead. The larger arc force led to more depression of pool surface that made the downward heat source and external force point, which had been important to increasing weld penetration. Meanwhile, the mobility of molten pool was enhanced by weld behavior compared with conventional GTAW process.     

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.     

Understanding the process parameter interactions in multiple-pass ultra-narrow-gap laser welding of thick-section stainless steels

In laser welding, typical welding penetration depths are in the order of 1–2 mm/kW laser power. The multipass laser welding technique, based on the narrow-gap approach, is an emerging welding technology that can be applied to thick-section welds by using relatively low laser power, but the process is more complicated since it is necessary to introduce filler wire to narrow-gap weld configurations. The aim of this work was to understand significant process parameters and their interactions in order to control the weld quality in ultra-narrow-gap (1.5 mm gap width) laser welding of AISI grade 316L stainless steel. A 1-kW IPG single-mode fiber laser was used for welding plates that were 5 to 20 mm in thickness using the multiple-pass narrow-gap approach. Design of experiments and statistical modelling techniques were employed to understand and optimise the processing parameters. The effects of laser power, wire feed rate, and welding speed on the weld homogeneity, integrity, bead shape, gap bridgability and surface oxidation were studied. The results were evaluated under different optimising constraints. The results show that the models developed in this work can effectively predict the responses within the factors domain.     

Penetration Estimation of GMA Backing Welding Based on Weld Pool Geometry Parameters

Penetration estimation is a prerequisite of the automation of backing welding based on vision sensing technology.However, the arc interference in welding process leads to the di culties of extracting the weld pool characteristic information, which brings great challenges to the penetration estimation. At present, most researches focus on the extraction of weld pool geometry parameters, and the visual sensing systems are complex in structure and complicated in the image processing algorithms. The research of penetration estimation based on weld pool geometry parameters is still in the exploratory stage. The purpose of this paper is to research the relationship between the weld pool geometry parameters and the penetration during backing welding and to estimate penetration using the weld pool geometry parameters. A passive vision sensing test system for gas metal arc(GMA) backing welding was established. An image processing algorithm was developed to extract the weld pool geometry parameters, namely,the area, maximum width and length, half-length, length-width ratio and advancing contact angle(simplified as AWP,MWWP, MLWP, HLWP, LWR and ACA, respectively). The corresponding relationships between the weld pool geometry parameters and the penetration state were explored by analysing their changes with the welding current and speed. The distribution of the weld pool geometry parameters corresponding to penetration was determined. When the AWP of the weld pool is within a certain range and the values of LWR and ACA are close to their maximum and minimum respectively, the penetration is in good condition. A mathematical model with the weld pool geometry parameters as independent variables and the back-bead width(the indicator of the penetration state) as a dependent variable was established based on multivariable linear regression analysis, and relevant statistical tests were carried out. Multivariable linear regression equations for the weld pool geometry parameters and the back-bead width were deduced according to the variations in the current and speed, and the equations can be used to estimate the penetration of backing welding. The study provides a solution to penetration estimation of GMA backing welding based on automatic vision sensing.     

变极性等离子弧焊接熔透信息的检测与分析

通过对铝合金3003变极性等离子弧穿孔立焊熔池振荡行为的研究,发现熔池振荡频率与焊接熔透之间的内在规律。在变极性电流的作用下,焊接熔池产生振荡,可以通过对电弧电压频谱分析获得熔池固有振荡频率。分别建立变极性等离子弧穿孔立焊未熔透及完全熔透熔池模型,并分析焊接电流的变化对熔池固有振荡频率的影响,发现焊接电流大小对其影响很小,可以忽略。为了验证该模型的准确性,进行理论与实测分析,结果表明,理论值与实测值相吻合。熔池固有振荡频率主要取决于熔池宽度、深度及材料密度等参数,而其他焊接参数对其没有直接影响。因此,熔池振荡频率可间接反映焊接熔透信息,为焊接质量自动控制提供了理论支持。     

Nd:YAG激光+脉冲MAG电弧复合热源焊接参数对焊缝熔深的影响

试验研究Nd:YAG激光 脉冲MAG电弧复合热源焊接过程中焊接参数对焊缝熔深的影响.研究结果表明,复合热源焊缝熔深随电弧功率和激光功率的增大而增大,随焊接速度的增大而减小,并且在相同参数下,复合热源焊缝熔深稍大于激光焊缝熔深而显著大于脉冲MAG焊缝熔深.对于不同焊接电流,光丝间距在0～3 mm内复合热源焊缝取得最大熔深,且取得最大熔深的光丝间距与焊接电流大小有关;复合热源焊缝熔深在离焦量为2 mm时取得最大值.试验结果分析表明,在激光 电弧复合热源焊接过程中激光功率不仅决定复合热源焊缝熔深,而且可以极大地提高焊接速度:MAG电弧也可提高Nd:YAG激光焊的热效率.     

连续脉冲GTAW不同熔透状态熔池振荡 频率特征及分析*

熔池振荡频率与熔池尺寸具有直接物理对应关系,但常规弧压、弧光方法很难实现连续焊接振荡频率提取。提出一种激光视觉测量方法用于连续焊接振荡频率检测。对连续焊接条件下部分、临界及全熔透状态下的熔池振荡激光条纹进行采集,通过图像处理算法提取不同熔透状态下的频率特征,并从激光条纹变化形态、熔池表面振荡和液态金属内部流动对不同频率特征进行分析。结果表明,激光视觉法能够精确检测熔池表面金属轴向及横向的流动;在部分和全熔透状态下熔池表面及内部金属以单一模式进行振荡,存在单一特征频率;在临界熔透状态下由于熔池约束条件的变化,使其表面振荡及内部金属振荡具有部分和全熔透的振荡特征,表现出两种特征频率;不同熔透状态的振荡频率特征可为精确检测不同熔透状态提供依据。     

大功率盘形激光焊焊缝背面宽度预测

提出了通过视觉传感获取焊接过程中的焊接特征信息并利用神经网络模型预测焊缝背面宽度的方法。利用大功率盘形激光器焊接了低碳钢SS400焊件,在焊接过程中改变焊接功率、焊接速度和焊接路径,并利用两台高速摄像机同步获取焊件正面和侧面出现的焊接特征信息。对获取的图像进行色彩空间转换、分层、滤波去噪和空域图像处理,提取飞溅、熔池和金属蒸气等焊接特征信息,观察焊接路径对各个特征的影响。最后,建立了一个三层的LMBP(LevenbergMarquardt Back Propagation)神经网络模型,将提取的特征信息作为输入量,预测焊缝的背面宽度。结果显示:当熔透不稳定或出现未熔透状态时,LMBP神经网络拟合度大于0.83,最大训练误差均值为0.002 8mm,最大实际误差均值为0.225 6mm。试验结果表明所建立的预测模型具有良好的准确性和稳定性。     

304不锈钢大功率光纤激光焊成形研究

为了研究大功率光纤激光焊在304不锈钢上的焊缝成形,使用5~7kW的激光功率,10~100mm/s的焊接速度在16mm厚的304奥氏体不锈钢上进行全覆盖参数试验。随后观察了焊缝的熔深、熔宽、焊缝形状等成形参数。结果表明,焊接速度低于20mm/s时,焊缝表面会形成隆起,熔深随速度减慢,迅速增加;焊接速度在30~40mm/s时,焊缝表面变得凹凸不平且两边存在咬边,熔深随速度减慢且小幅增加;焊接速度介于50mm/s和90mm/s之间时,焊缝的熔深和熔宽几乎不变;而当速度达到100mm/s时,熔深急剧减小,且钉头形焊缝的形状发生了很大的改变。通过以上试验结果结合小孔效应和熔池特性分析了激光焊缝的成形机理,对大功率光纤激光焊接形成了更全面的认识。     

Characterization and mechanical properties of TiN/TiAlN multilayer coatings with different modulation periods

In this paper, laser welding for the stainless steel lap joint used in the railway vehicle body has been studied based on the analysis of the ultrasonic test. The weld width is evaluated by the analysis of ultrasonic testing signals during the ultrasonic scanning process. The changes of the echo and main frequency are in good agreement with the positions of the probe. The semi-attenuation method and frequency domain analysis are established based on the A-scan signals and frequency spectrum characteristic curves. From the analysis of the error statistics, the frequency domain analysis has a higher accuracy and stability, which can meet the requirements of engineering applications. The equivalent weld width is defined based on the C-scan imaging and the quantitative ultrasonic test is achieved. The tensile shear measurements of welds show that the equivalent weld widths have the same change rules with the values of the tensile shear strength and provide an important basis for the quality evaluation of the laser welding.     

Data mining in resistance spot welding

Resistance spot welding is the dominant process in the present mass production of steel constructions without sealing requirements with single sheet thicknesses up to 3 mm. Two of the main applications of resistance spot welding are the automobile and the railway vehicle manufacturing industry. The majority of these connections has safety-related character and therefore they must not fall below a certain weld diameter. Since resistance spot welding has been established, this weld diameter has been usually used as the gold standard. Despite intensive efforts, there has not been found yet a reliable method to detect this connection quality non-destructively. Considerable amounts of money and steel sheets are wasted on making sure that the process does not result in faulty joints. The indication of the weld diameter by in-process monitoring in a reliable way would allow the quality documentation of joints during the welding process and additionally lead through demand-actuated milling cycles to a substantial decrease of electrode consumption. An annual, estimated reduction in the seven- to nine-figure range could be achieved. It has an important impact, because the economics of the process is essentially characterized by the electrode caps (Klages 24). We propose a simple and straightforward approach using data mining techniques to accurately predict the weld diameter from recorded data during the welding process. In this paper, we describe the methods used during data preprocessing and segmentation, feature extraction and selection, and model creation and validation. We achieve promising results during an analysis of more than 3000 classified welds using a model tree as a predictor with a success rate of 93 %. In the future, we hope to validate our model with unseen welding data and implement it in a real world application.     

大功率激光焊接光致等离子体的光谱分析

大功率激光焊接过程中,光致等离子体的粒子密度及温度对入射激光能量的传输效率及焊缝的熔深都有很大影响。采用光谱诊断、分析方法,利用谱线相对强度法对激光光致等离子体的温度及电子密度进行了测量与计算,给出了实验条件下光致等离子体电子密度与激光焊接能量及焊接熔深的量化关系。     

Investigation on droplet momentum in VPPA-GMAW hybrid welding of aluminum alloys

Variable polarity plasma arc-gas metal arc welding (VPPA-GMAW) is a superior technology for welding thick plates of high-strength aluminum alloys. It integrates the advantages of energy focusing and high penetration depth in VPPA welding, and those of high welding efficiency and wide range of technological parameters in GMAW process. In this work, we investigated the droplet momentum in paraxial VPPA-GMAW hybrid welding of 7A52 aluminum alloys, and the technological parameters of welding process was also optimized. The images of droplet transfer were captured by high-speed camera, while the droplet speeds and sizes were statistically analyzed by t tests of independent samples. The results showed that the speeds of droplet arriving at the weld pool were significantly between GMAW and VPPA-GMAW processes, and the droplet speed increases with increasing plasma currents within a certain range. Meanwhile, the droplet momentum in VPPA-GMAW process is larger than that in conventional GMAW process. We also found that as the droplet momentum increased, the depression of weld pool grew more obvious and greatly facilitated the deep-penetration welding. In VPPA-GMAW process, it became more and more easier for the droplet to fall off the wire when the electromagnetic force gradually increased during pulse period. Droplet movement through the arc zone was further accelerated since the central pressure of arc column increased during base period. This research can provide some theoretical support for thick plate welding of high-strength aluminum alloys and help for deeper understanding of the hybrid arc coupling mechanism.     

Automatic Detection of Spills and Gas Pockets upon Ultrasonic Checking of Welds in Zirconium Fuel Claddings

The problem of automating detection of flaws (gas pockets and spills) in welds obtained by electron-beam welding, using the ultrasonic echo method which is implemented by slanted introduction of ultrasonic waves into a thin zirconium fuel shell, is considered. Algorithms for automatic detection of flaws and evaluation of their relative dimensions are proposed. Experimental results confirming the efficiency of the algorithms proposed are reported.