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

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.

It is a key issue to establish an appropriate model of the heat source in the simulation of the keyhole plasma arc welding (PAW). It requires that the model account for the keyhole effect and have the characteristic of volumetric distribution along the direction of the plate thickness. For available heat source models, neither Gaussian nor double ellipsoidal modes of heat source is applicable to keyhole PAW process. With considering the force of the high speed plasma jet and the associated strong momentum, a modified three-dimensional conical heat source model is proposed as the basis for the numerical analysis of temperature fields in keyhole PAW process. Further, a new heat source model for quasi-steady state temperature field in keyhole PAW is developed to consider the “bugle-like” configuration of keyhole and the decay of heat intensity distribution of the plasma arc along the direction of the workpiece thickness. Based on this heat source model, finite-element analysis of temperature profile in keyhole PAW is conducted and the weld geometry is determined. The results show that the predicted location and locus of the melt-line in the PAW weld cross section are in good agreement with experimental measurements.