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.