Systematization of heat straightening process of stiffened plate by surface flattening

Heat straightening of welding-induced distortion, which has mostly relied on shipyard experience, was systemized for computation. The process of geometrically flattening a curved surface with fixed edges was formulated step by step based on thermal forming mechanisms. The proposed algorithm divides the measured surface into patches, connects them with virtual springs, and optimally arranges the patches on a plane in a direction that minimizes the potential energy within the weld lines. The overlaps between the geometrically calculated patches become the amount to shrink. The relationship between spot heating distance, curvature, and shrinkage was investigated through experiments and thermal elastic-plastic analysis to convert shrinkages into process parameters. It showed that the plastic shrinkage increases as the spot heating distance narrows, but the rate decreases. Also, the plastic shrinkage keeps constant regardless of the curvature, whereas the total shrinkage decreases as the curvature decreases. For validation of the proposed methodology, flame straightening experiments were carried out. It has been shown that the case using the plastic shrinkage produced fewer heating spots with higher efficiency than that using the total shrinkage.