The weld pool surface provides important information for understanding arc welding processes. In this study, a novel vision sensor is proposed to measure the three-dimensional shape of the free weld pool surface. A pulsed laser is projected on to the weld pool through a specific grid. Specular reflection from the pool surface is sensed using a high shutter speed camera. The three-dimensional weld pool surface shape is clearly shown by the specular reflection. To determine the shape of the pool surface, an image processing technology has been developed to extract the skeleton of the specular reflection from the acquired image. The imaging principle is analysed to determine the correlation between the reflection and the weld pool surface. If the weld pool surface is known, the corresponding specular reflection can be directly calculated using the imaging model which is derived based on the reflection law. However, no explicit models can be obtained to determine the weld pool surface using the reflection and sensor parameters. To solve this difficulty, an iterative algorithm is proposed. The weld pool surface can now be calculated in 1 second from the specular reflection of the weld pool surface. A higher calculation speed is currently being pursued.
Keyhole plasma arc welding achieves much deeper penetration than do all other existing arc welding processes. Because of its ability to penetrate thicker material, the control of the keyhole in plasma arc welding becomes critical. From an analysis of the physical process, a sensor to detect the state of the keyhole for keyhole process control has been proposed and developed. This sensor measures the electrical effect of the plasma cloud generated during keyhole plasma arc welding. It is found that the plasma cloud, which rapidly decreases to zero upon establishment of the fully penetrated keyhole, can be used to detect the state of the keyhole reliably. The effectiveness of the proposed sensor for detecting the keyhole state has been verified during pulse keyhole plasma arc welding.
The gas tungsten arc welding process is an uncertain nonlinear multivariable system. In order to control the welding process, the nonlinear dynamic relationship between the weld pool geometry reflecting the weld quality and the welding parameters must be developed. A three-dimensional numerical model is developed to investigate the dynamic characteristics of the weld pool geometry when the welding current and welding speed undergo a step-change. Under the welding conditions employed in this research, the transformation periods are about 4 s for a 20 A down step-change of welding current, and about 2 s for a 20 mm min −1 up step-change of welding speed, respectively. At the initial stage during the step-change of welding current and welding speed, the responses of weld pool geometry are quicker, but they slow down subsequently until the weld pool reaches a new quasi-steady state. Welding experiments were conducted to verify the simulation results. It was found that the predicted weld pool geometries agree with the measured ones.
Full penetration welding is widely used in metal joining, but it has been ignored in previous convective numerical models. In addition to the ree surface on top of the pool, an additional free surface appears on the bottom of the workpiece. I t can be shown that the top sur J ace, temperature distribution and fluid flow field in the weld pool are all coupled with the pooh bottom surface. This complicates the numerical process and therefore no convective models have previously been developed for fully penetrated weld pools. I n order to improve the numerical solution for the fully penetrated weld pool, a three-dimensional model is proposed. Free top and bottom pool sugaces have been included. The electromagnetic force, buo ancy force and surface tension gradient (Marangoni) are the three driving that the depression of the top surjiace contains abundant information about the full penetration state as specijied by the back-side bead width.forces for weld pool convection. Welding parameters are c K anged in order to analyse their efects on weld pool geometry. It is found NOTATION
The abrasive waterjet nozzle is one of the most critical parts that influences the technical and economical pe$ormance of an abrasive waterjet system. In order to control the uniformity of cutting results in milling and cutting, it is necessary to devise
a sensing system that can sense on-line the nozzle wear. This paper presents an on-line technique for monitoring the nozzle wear which is based on monitoring the acoustic signals generated by the abrasive waterjet. The autoregressive moving average (ARMA) spectra are used to estimate the nozzle wear. It has been shown that the A R M A spectra can reveal more features of the nozzle wear than the conventional fast Fourier tranSform (FFT) method. It was found that the amplitude of the spectra and the frequency of the spectra peaks of A R M A models have a high sensitivity to a small variation of the nozzle exit geometry. A method based on on-line acoustic signals is proposed for identification of the nozzle inside diameter.of abrasive waterjet cutting
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