Mesh-based tool path calculations for tubular joints

Morten Lind,Pål Ystgaard

doi:10.1177/1687814020933383

Abstract

Manufacturing of large steel tube structures is faced with excessive welding, fit-up and rework times in tube joints, due to various types of deviation from nominal shape of the tubes. This article presents a procedure and geometry calculus for generating cutting and welding paths based on measured geometries. The procedure poses the two measured meshes as per construction specification and invokes a mesh intersection procedure to get the mesh intersection path; performs an optional smoothing; interpolates the smoothed path to a specified angular resolution; estimates the two surface normal vectors and the two surface tangents in the plane spanned by the normals at each interpolation point; calculates the cutting tool and welding tool approach directions for obtaining the specified welding groove geometry at each interpolation point; and finally stores all the data parameterized by the interpolation angle. Illustrations of results with both synthetic, representative meshes and meshes obtained from scanning of actual tubes at the shop-floor at a manufacturer are presented. The reference implementation for the developed software tool is based on Python and uses the mesh modeller from the 3D creation suite Blender as platform.

Highlights

Large steel tube structures, such as offshore jackets, are truss geometries composed of legs of larger diameter and braces of smaller diameter tubes; these are names of the offshore jacket terminology.[1]
Many executions of the software have been performed on synthetic meshes generated with a broad variety of deformations, noise levels and geometric resolutions
As long as these deformations and noise levels stay within limits that leave the topology of the meshes wellformed and their relative pose maintains a single, closed intersection curve, the software have always produced correct results

Summary

Introduction

Large steel tube structures, such as offshore jackets, are truss geometries composed of legs of larger diameter and braces of smaller diameter tubes; these are names of the offshore jacket terminology.[1]. Zero order correction to the nominal geometry, obtained by measurement and fitting the radius of the tubes, can be trivially incorporated when specifying a cutting task to the path generation software.

Results

Conclusion