Compensation of welding shrinkage in ship production by integrating computer-aided design and computer-aided engineering in a design for assembly technique

Abstract

Welding is the primary joining process in ship production and inherently causes shrinkage and angular distortion that degrade the dimensional quality (adherence to tolerance specifications) of ship blocks during assembly. Considering that intermediate products of low quality are not scrapped but must be reworked, the productivity of each workstation greatly depends on the dimensional quality of these intermediate products. One of the major ''design for assembly'' methodologies to control welding shrinkage in shipbuilding is a shrinkage compensation design. This allows the artificial redesign of nominally shaped pieces of plate, to include optimal expansion values that accommodate welding shrinkage. This minimizes the amount of reworking caused by degraded dimensional quality. This research presents a new shrinkage compensation design methodology and technique combining computer-aided design with computer-aided engineering, which overcomes the shortcomings of the empirical approach used until now. An optimization procedure is proposed, by which to find the best shrinkage compensation design shape on the basis of the object function, which would minimize total rework cost (due to shrinkage) predicted for the next block-to-block assembly. The proposed design scheme was successfully applied to shipyard production design and was found to enhance the dimensional quality, as well as the productivity, of shipbuilding.