Study On The Three-Dimensional Reconstruction For Weld Pool In Pulsed Twin Arc Welding Of Aluminum

A new sensing technology was presented based on binocular vision for three-dimensional reconstruction of weld pool surface in pulsed twin arc welding of aluminum in this study. After analyzing the difficulty of sensing weld pool of aluminum in GMAW process and the structure of the torch, the visual sensing system for clear weld pool acquisition has been set up and the best sensing orientation, two cameras placed symmetrically after the top of the weld pool to get synchronous image with the angle of 30 degrees and distance of 57mm between two camera axes.A three-dimensional reconstruction method, based on the theory of stereo vision, is used in the reconstruction of weld pool surface. Some breakthroughs has been made in synchronous acquisition of pool image, camera calibration and image distortion correction, three-dimensional reconstruction based-on feature points matching. The three-dimensional reconstruction software, consists of pool image synchronization acquisition module, camera calibration module and three-dimensional reconstruction module, has been programmed with the function of three-dimensional reconstruction of an object, weld pool width measurement, three-dimensional reconstruction of the weld pool surface.To verify this method, the three-dimensional shape of a nut has been firstly reconstructed and the error between calculated and physical size is about 2%. Then it is applied to the measurement of the weld pool width under different welding speeds, the average error between calculated and real weld width is less than 3.5%. And the continuous measurement of the weld width under a fixed welding speed has been accomplished; the average error is less than 3%. Finally this method is used to reconstruct weld pool surface at the last moment of welding and in normal welding process separately and three-dimensional weld pool surfaces have been obtained, including weld pool profiles, arc profiles and contours of the main features.From the three-dimensional shape of pool surface, we can see the surface of the weld pool is rough instead of flat. During the welding process, the area below arc is concave under the force of droplet impact and arc pressure. In the rear of the pool the surface is raised along with the fill of molten metal. In the reconstructed shape, the distribution of the weld depth accords with its actual situation, that is, the depth of the weld pool is continuously reduced and its maximum is located in the arc zone and its minimum is in the rear of the weld pool.The binocular-vision based method is feasible in the three-dimensional reconstruction of weld pool surface, which helps to understand fluid flow behavior and observe width and penetration in the welding process. Research on weld pool surface reconstruction has great research significance and practical value for real-time sensing and control of weld pool.