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A Method of D-Type Weld Seam Extraction Based on Point Clouds

Identification of the seam to be welded in automatic welding is an important challenge, especially on a complex 3D surface. At present, most studies on weld extraction are for butt joints and fillet joints. Few studies focus on D-type welds, which connect to pipelines or pressure vessels. In this paper, a method of identification and extraction of pipeline joint welds based on 3D point clouds is proposed. First, the problem that the surface of pipe fittings cannot be effectively stitched owing to lack of markings is solved by putting marker points on the surface to allow accurate splicing of the point cloud. Second, according to the contour feature information of the workpiece, a processing method for D-type welding seams is proposed. Finally, a boundary extraction algorithm based on the point cloud normal is used to obtain the point cloud of the weld. The experimental results show that this method can effectively extract the weld. The running time for the point cloud weld extraction method is less than half that of the existing methods. The accuracy of the proposed method is improved in all three directions: by 28.2% in the X direction, 19.1% in the Y direction and 16.0% in the Z direction. Moreover, this method is convenient for transforming weld coordinates to robot-based coordinates for the automatic welding of spatially complex welds.