This paper introduces an intelligent system for monitoring and recognition of process disturbances during short-short-Cirutiong gas-metal arc welding. It is based on the measured and statisticlly processed dataof welding electrical parameters. A 12-dimensional array of process features is designed to describevarious welding conditions and is employed as input vector of the intelligent system. Three methods, Such as fuzzy c-means, neural netowrk and fuzzy Kohonen clustering network areused to conduct process monitoring and automatic recognition. The correct recoginition rates of these three methods are compared.

Double-sided arc welding (DSAW) is a novel process for joining metals that is capable of achieving deep narrow penetration in a single pass with minimized distortion. Aclear understanding of the process fundamentals is critical in order to fully examine the potential of DSAW, to guide the further developments of the process, to direct the practicability study, and to design the process parameters. This paper aims at developing a numerical model for examining and simulating the dynamic keyhole establishment process, which will be a key in developing an effective control technology for DSAW. The model is used to determine the geometrical shape of the keyhole and the weld pool, and the temperature distribution in the workpiece. Quantitative information on the establishment of the keyhole in DSAW, such as the transient development of the keyhole and the weld pool, the increase rate of the depth of the surface depression, the time interval from full penetration to the keyhole establishment, the minimum span of the weld pool for describing the conditions required to complete the keyhole establishment, and variation of the overflow height of the weld pool surface on the plasma arc welding side, has been obtained through numerical analysis. The DSAWexperiments show that the predicted weld cross-section is in agreement with the measured one. The results lay a foundation for guiding the further development of the DSAW process and its effective control.

The correlation of the heat flux on the anode surface with the plasma properties at the free-fall edge was developed. By using the models of the tungsten inert gas (TIG) welding arc and the anode boundary layer, the heat transfer contributions to the anode heat flux in TIG welding were analyzed. The percentages of the electron flow contribution and the convection contribution were determined. The results show that the energy carried by the electrons constitutes most of the heat on the anode surface. 2001 Elsevier Science B.V. All rights reserved.

Establishing the correlation between transient behaviors of surface deformation of weld pools and workpiece penetration information, and quantitatively analyzing the surface deformation at top and bottom surfaces at the moment when the pool is penetrated and their dynamic responses to welding process parameters will provide many basic data for the realization of topside vision-based penetration control in gas tungsten arc welding (GTAW). A transient numerical model is developed to investigate the dynamic behaviors of full-penetrated GTAW weld pools in this paper. A whole and comprehensive scheme is used in which many factors such as moving arc, 3-D fluid and heat flow fields, transient state, full-penetrated weld pool and surface deformation at both top and bottom surfaces are considered. The transient developments of 3-D surface deformation and shape of weld pool during the period from partial penetration to full penetration are predicted. The simulated results show that the curves of ratios of the maximum depression to the length and width at top surface of weld pool at different times clearly indicate the basic information of penetration. So the relation of the ratios versus time can be used as an indicator to judge whether the weld pool is penetrated.

A mathematical model has been developed to describe the transient heat and fluid flow fields in gas tungsten arc welding (GTAW). The transient development and diminution of the weld pool at two periods after the arc ignites and extinguishes are analysed quantitatively. The data for the weld pool configurations under different welding conditions from the transient state to the quasi-steady state are obtained. The time for the weld pool shape to reach the quasi-steady state and the time for the weld pool to solidify completely are predicted. GTAWexperiments show that the predictions of the weld pool shape based on the model are in agreement with the measured values. The numerical results of the dynamic development and diminution of weld pool configurations could be used to correlate the transient characteristics of weld pool behaviour with the occurrence of weld formation defects.

The profile of the free surface deformation of a weld pool gives information about the extent of penetration depth, and weld bead apperance. Calculating the surface deformation of the weld pool is of great significance to the task of welding process modeling and simulation. Two nonlinear partial differential equations for describing both front- and back-side deformation of weld pool surfaces are derived in detail to make the physical terms and the sign of Lagrange multiplier in two equations be with one accord. Under some practical welding conditions, the secant method is used to determine the value of Lagrange multiplier, and the coupled equations are numerically solved to calculate both front and back free surfaces’ deformation of full-penetrated three-dimensional weld pools. The influence of the welding current on the surface depression of weld pool is examined. It shows that the predicted weld pool deformation is in agreement with the measurements

The common commercial charge coupled device (CCD) camera is combined with a composite light filter to form a vision sensing system of low cost. It can capture the whole image of a weld pool clearly during constant-current gas tungsten arc welding (GTAW). Based on the imageprocessing algorithm, the edges of the weld pool under di erent welding conditions can be extracted. Calibration is made to obtain the weld pool geometry in real size. The measured results are useful for developing a welding process control system and verifying the mathematical models of weld pool behaviours.

A real-time monitoring system is developed for detecting abnormal conditions in robotic gas metal arc welding. The butt-joint test pieces with cut gap are used to intentionally introduce the step disturbance of welding conditions. During the welding process, the welding voltage and current signals are sampled and processed on-line to extract the characteristic information reflecting the process quality. After 1st statistical processing, it is found that seven statistical parameters (the mean, standard deviation, variance, and kurtosis of welding voltage; the mean, variance, and kurtosis of welding current) show variations during the step disturbance. Through 2nd statistical processing of the means of the welding voltage for subgroups of continuous measurement, the statistical control chart is obtained, and SPC (statistical process control) -based on-line identifying method is developed. Ten robotic welding experiments are conducted to verify the real-time monitoring system. It is found that the correct identification rate for normal and abnormal welding conditions are 100% and 95%, respectively.

This paper introduces a fuzzy logic system that is able to recognize common disturbances during automatic gas metal arc welding (GMAW) using measured welding voltage and current signals. A statistical method was employed to process the captured transient raw data, and the probability density distributions (PDDs) and the class frequency distributions (CFDs) were obtained. Based on the processed data (PDD values of welding voltage and current and CFD values of the short-circuiting time), the system automatically generates fuzzy rules and membership functions of linguistic variables, conducts inference and defuzzification, and completes the evaluation process without further expert knowledge.

Double-sided arc welding (DSAW) is a novel arc process developed at the University of Kentucky in which the workpiece is disconnected from the power supply and the two torches are used to establish two arcs on the both sides of the workpiece to close the current loop. As a result, the welding current is forced to flow through the workpiece along the thickness direction. This configuration and current flow direction improve the concentration of the arc energy distribution and provide a mechanism to guide the arc into the keyhole. Hence, DSAW process is capable of achieving deep narrow penetration and symmetrical welds. However, despite the progress in process development, there is a lack of a clear understanding of the physical processes and phenomena occurring in the weldment. In this study, a numerical model is developed to compute the temperature field and history in double-sided arc weldment. Using this numerical model, the temperature distributions and profiles at different cross-sections and along different lines of interest have been computed and compared with the results in regular plasma arc welding. It was found that DSAW process has advantages in obtaining deep narrow penetration, in producing symmetrical hour glass-shaped welds, in reducing the sensitization zone, in lowering the temperature gradient along the thickness, thus lowering the thermal distortion and residual stress, and in decreasing the sensitization duration.