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。     

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.     

“<Emphasis Type="SmallCaps">disassembly plan approach based on subassembly concept</Emphasis>”

A three-dimensional numerical model is established to study the temperature and fluid flow fields in the twin-wire gas metal arc welding (GMAW) process. The high-speed photography system is used to capture the images of the weld pool during the welding. Based on simulation and experimental results, the weld pool formation, convection, and stability in twin-wire GMAW process are investigated. Both “push-pull” and outward flow patterns exist in the twin-wire GMAW weld pool, which can contribute to decreasing the height of the bulge and increasing the width of the pool. The convection in the weld pool can proceed adequately, the arc force between the leading and trailing arcs is relatively balanced, surface tension normal force is uniform along the liquid channel, and the liquid channel is capillary stable, all of those contribute to the stability of the weld bead. The simulation results are in good agreement with those in the experiment.     

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.     

Effect of shielding gas mixture on gas metal arc welding of HSLA steel using solid and flux-cored wires

In this work, gas metal arc welding of high strength-low alloy (HSLA) steel with solid- and flux-cored arc welding wires using different shielding gas compositions was performed. The composition of filler wire and shielding gas in gas metal arc welds of HSLA steel determines the inclusion characteristics, microstructure and mechanical properties. Thus, acceptable weld metal properties in HSLA steel using gas metal arc welding (GMAW) process could be achieved with the proper combination of filler wire and shielding gas composition.     

Effect of forces on dynamic metal transfer behavior of cable-type welding wire gas metal arc welding

A cable-type welding wire (CWW) gas metal arc welding (GMAW) method was proposed as a novel approach, using CWW for the consumable electrode. Droplet transfer influences the welding process, and the forces on the droplet were analyzed to elucidate the metal transfer phenomenon observed during the welding process. The effects of the arc pressure, rotating force, and welding parameters were analyzed to understand the metal transfer. The special structure of the CWW affected the arc characteristics and forces during metal transfer as part of the welding process. The droplet formed by droplets from each thin wire, the arc, and electromagnetic forces on droplet formation and the coupling process were analyzed. The arc pressure and rotating forces are beneficial to metal transfer and increase the droplet transfer frequency. The droplet size decreases with increasing welding parameters.     

Effect of process parameters and mathematical model for the prediction of bead geometry in pulsed GMA welding

Pulsed gas metal arc welding is one of the most widely used processes in the industry. It offers spray metal transfer at low average currents, high metal deposition rate, versatility, less distortion, and the ability to be used in automated robotic welding systems. The weld bead plays an important role in determining the mechanical properties of the weld. Its geometric parameters, viz., width, reinforcement height, and penetration, are decided according to the welding process parameters, such as wire feed rate, welding speed, pulse current magnitude, frequency (cycle time), etc. Therefore, to produce good weld bead geometry, it is important to set the proper welding process parameters. In the present paper, mathematical models that correlate welding process parameters to weld bead geometry are developed with experimental investigation. Taguchi methods are applied to plan the experiments. Five process parameters, viz., wire feed rate, plate thickness, pulse frequency, pulse current magnitude, and travel speed, are selected to develop the models using multiple regression analysis. The models developed were checked for their adequacy. Results of confirmation experiments show that the models can predict the bead geometry with reasonable accuracy.     

双丝旁路耦合电弧GMAW高效焊接工艺

在介绍了双丝旁路耦合电弧熔化极气体保护焊(双丝旁路耦合电弧(Double-electrode gas metal arc welding,DE-GMAW))高效焊接工艺原理的基础之上,采用双闭环反馈解耦智能控制系统,进行双丝旁路耦合电弧GMAW高速焊接工艺试验,测量双丝旁路耦合电弧GMAW母材热输入,分析双丝旁路耦合电弧GMAW高效焊接工艺机理,并对双丝旁路耦合电弧GMAW高效焊接工艺方法进行改进,进一步研究混合气体保护下的双丝旁路耦合电弧GMAW及其熔滴过渡行为,且开发出单电源双丝旁路耦合电弧GMAW。研究表明:采用双闭环反馈解耦智能控制系统使双丝旁路耦合电弧GMAW焊接过程稳定性更好、精确度更高且响应速度更快;旁路分流是实现高效焊接的同时降低母材热输入的关键;采用混合气体保护下的双丝旁路耦合电弧GMAW能进一步提高焊接过程稳定性,单电源双丝旁路耦合电弧GMAW能形成良好的焊缝成形,且设备成本低。     

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.     

双丝旁路耦合电弧高效熔化极气体保护焊过程模拟及控制

采用等效电流路径的方法建立双丝旁路耦合电弧高效熔化极气体保护焊耦合电弧的动态数学模型,模拟表征焊接过程稳定性的电流、净干伸长信号的变化,得到与实际焊接过程相似的模拟结果。在此基础上,针对焊接过程中耦合电弧形态的剧烈变化会影响焊接过程稳定性与焊接质量的问题,提出通过调节旁路弧长控制耦合电弧稳定性的方案,并利用Matlab/Simulink软件和xPC-target快速原型控制平台,对控制方案进行模拟、分析、预测与试验。结果表明:所建立的数学动态模型能很好地反映双丝旁路耦合电弧高效GMAW焊接过程;模拟分析旁路弧长控制方案可以有效地解决焊接过程稳定性的问题;控制试验实现了焊接过程的稳定控制并获得了成形良好的焊缝形貌,验证了模拟阶段的分析与预测。     

Effect of welding processes on tensile properties of AA6061 aluminium alloy joints

The present investigation is aimed at to study the effect of welding processes such as GTAW, GMAW and FSW on mechanical properties of AA6061 aluminium alloy. The preferred welding processes of these alloys are frequently gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties and poor resistance to hot cracking. Friction stir welding (FSW) is a solid phase welding technique developed primarily for welding metals and alloys that heretofore had been difficult to weld using more traditional fusion techniques. Rolled plates of 6 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA4043 (Al-5Si (wt%)) grade aluminium alloy. In the present work, tensile properties, micro hardness, microstructure and fracture surface morphology of the GMAW, GTAW and FSW joints have been evaluated, and the results are compared. From this investigation, it is found that FSW joints of AA6061 aluminium alloy showed superior mechanical properties compared with GTAW and GMAW joints, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.     

Prediction of metal deposition from arc sound and weld temperature signatures in pulsed MIG welding

The weld deposition efficiency is an important economic factor like productivity and weld quality in gas metal arc welding (GMAW). There is a strong relationship between arc sound signals and arc stability (or deposition efficiency) in GMAW. In this work, the variation of weld deposition efficiency with various pulse parameters in pulsed metal inert gas welding was investigated. The arc sound signal along with current and voltage signals were acquired and analyzed in time domain as well as in frequency domain. The sound signal kurtosis and arc power were found to be highly correlated with welding process stability. The weld deposition efficiency was also related to weld surface peak temperature. Finally, an attempt was made to correlate the sound time domain as well as frequency domain features of sound signal with the deposition efficiency. The variation of pulse shape with the duty factor also influenced the deposition efficiency as evidenced by in fast Fourier transform analysis.     

双丝旁路耦合电弧高效熔化极气体保护焊双变量解耦控制模拟与试验分析

双丝旁路耦合电弧高效熔化极气体保护焊是一种新型、高效的焊接方法。针对其在开环条件下焊接过程不稳定、焊缝成形差的问题,提出通过旁路送丝速度控制旁路弧长从而保证焊接过程稳定性、通过控制旁路电流调节流经母材电流的双变量解耦控制方案并进行模拟与分析。在此基础上,采用快速原型控制系统,设计双丝旁路耦合电弧高效熔化极气体保护焊试验系统并进行双变量解耦控制焊接试验。结果表明,双丝旁路耦合电弧高效熔化极气体保护焊双变量解耦控制方案可以有效地保证焊接过程与流经母材电流的稳定,与模拟结果基本一致;并且由于采用解耦算法,控制过程稳定性更好、响应速度更快、精度更高,并得到成形良好的焊缝,焊接过程飞溅也较小。     

Welding of thin sheet of Al alloy (6082) by using Vario wire DC P-GMAW

This paper describes an investigation on the micro-structure, weld bead geometry, dilution rate and mechanical properties of the butt and overlap weld joints of 1-mm-thick 6082 aluminium alloy sheet. Weld joints were produced with the help of a variant of gas metal arc welding (GMAW) process, i.e. direct current-pulsed GMAW (DC P-GMAW), using a Vario wire. The capability of the new process has been assessed in terms of dilution, weld bead geometry, mechanical properties and porosity. The welding results with this new process showed good process stability in the welding of thin sheets of aluminium, while weld mismatch was found to increase with an increase in heat input. Weld bead geometry parameters such as weld size, throat and weld convexity increases with the increase in heat input. The dilution in case of lap joints (10–25%) was less than that of butt joints (60–80%). The increase in factor Φ (summarizing the effect of pulse parameters) increases the form factor and lowers the toe angle. Mechanical properties of the welds are poor as the tensile strength of 6082 alloy welds was around 150 MPa, and the percent elongation was about 1.3%, and it was primarily due to high porosity. Porosity (%) in weld joints was found in the range of 0.33–11.59%. The porosity is a major issue with DC P-GMAW welds.     

Investigation of melting dynamics of filler wire during wire feed laser welding

In order to investigate the mechanism of stability for the wire feed laser welding process, systematic experiments are carried out in this study for 5A06 aluminum alloy. By using high speed camera, the melting dynamics of filler wires with different feed positions and feed rates are studied. The results indicate that these two factors mainly influence the characteristics of the filler wire melting dynamics and determine the stability of the welding process. The melting dynamics of filler wire can be generally characterized by three different forms: explosion, big droplet and molten metal bridge. When the filler wire melts and transits to the molten pool in the forms of explosion or big droplet, the stability of the welding process is strongly disturbed, resulting in an undesirable weld quality. In contrast, when it is in molten metal bridge form, the welding process is more stable and a uniform weld bead is achieved.     

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.     

Real-time image processing for vision-based weld seam tracking in robotic GMAW

Image capturing and processing is important in using vision sensor to effectively track the weld seam and control the weld quality in robotic gas metal arc welding (GMAW). Using vision techniques to track weld seam, the key is to acquire clear weld images and process them accurately. In this paper, a method for real-time image capturing and processing is presented for the application in robotic seam tracking. By analyzing the characteristic of robotic GMAW, the real-time weld images are captured clearly by the passive vision sensor. Utilizing the main characteristics of the gray gradient in the weld image, a new improved Canny edge detection algorithm was proposed to detect the edges of weld image and extract the seam and pool characteristic parameters. The image processing precision was further verified by using the random welding experiments. Results showed that the precision range of the image processing can be controlled to be within ±0.3 mm in robotic GMAW, which can meet the requirement of real-time seam tracking.     

Gas Pool Coupled Activating TIG Welding Method with Coupling Arc Electrode

Gas pool coupled activating TIG(GPCA?TIG) welding put forward in?house can dramatically enhance weld penetration of TIG welding through introducing active element oxygen to reverse the Marangoni convection flow in the molten pool. In order to further improve the welding productivity, the normal solid tungsten electrode is replaced by a kind of coupling arc electrode. The changes of arc pressure distribution along anode surface and the weld appearance were evaluated. On this basis, the dependences of weld shape characterized with weld depth, width and undercut on the main welding parameters were discussed. The results indicate, the substitution of coupling arc electrode can lead to an obvious decrease of arc pressure. Compared to hollow tungsten electrode and twin tungsten electrodes, the coupling arc electrode is much easier to manufacture and has more compacter structure. Combined with the symmetric distribution of arc pressure in di erent directions, this electrode has extensive adaptability. In the GPCA?TIG welding with coupling arc electrode, both the substitution of coupling arc electrode and the introduction of outer active gas oxygen can reduce the possibilities of producing humping bead and undercut. Their joint action makes this welding method have the capability of realizing high travel speed and deep penetration welding.     

Analysis of weld pool dynamic during stationary laser–MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary laser–metal inert gas (MIG) hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow pattern; moreover, typical phenomena of MIG welding such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding such as recoil pressure, inverse Bremsstrahlung absorption, and Fresnel absorption were all considered in the model. The laser beam and arc couple effect was introduced into this model by the plasma width during hybrid welding. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds of weld pool to a unified weld pool were calculated. Furthermore, the simulated weld bead geometries were in good agreement with experimental measurement.     

Groove-center detection in gas metal arc welding using a template-matching method

To achieve welding automation, the center of the groove needs to be detected accurately during welding. We developed a method based on template-matching to detect the groove center during gas metal arc welding (GMAW). To avoid the negative influence of the strong GMAW arc light, a high-dynamic-range camera was used to capture details of the welding arc, molten pool, and the V-groove simultaneously in a single image. Two image-processing and object-detection algorithms were developed to detect the center of the welding pool and the groove based on template matching. The experimental results of the latter algorithm were more accurate for identifying the position of the groove center. However, interference in the welding process caused the template-matching method to fail under certain conditions. Therefore, the two detection algorithms were combined to improve the detection accuracy. After filtration of the detected welding-pool center, the groove-center detection algorithm based on template matching results in higher accuracy.