An investigation into the influence of inter-component assembly gaps upon the geometry of tack welded annular structures

Large accurate annular weldments are important to a number of heavy industries, such as power generation and civil aero-engine. This research examines the interaction between small assembly gaps and the Preliminary Welding Process (PWP), colloquially known as tack welding. This study has identified two fundamental weld distortion geometries prevalent within ring structures; the quantised saddle and the quantised conic, both a consequence of the small assembly gaps. Furthermore, physical weld trials and finite element modelling, in both simple two plate assemblies and full ring assemblies have shown that volumetric weld shrinkage is the principle thermal-mechanical mechanism driving the identified distortions, so careful placement of the initial welds to avoid assembly gaps can yield a 19× reduction in out-of-plane distortions in the final weldment.