In case of actual line heating process in the shipyard, the various weaving motions of gas torch moving along the target heating line have been adopted. By adopting weaving motions, it is possible to keep the maximum temperature under melting point and also to maintain the constant heating velocity through rhythmical motion of workers. In this study, an approach to determine the optimal heating conditions of line heating with weaving motions was presented, and some examples were introduced. The maximum angular distortion per unit hour was adopted as an objective function. SUMT algorithm is applied as an optimization tool. To get the optimal heating conditions, equivalent load method based on inherent strain was used. This study also deals with the process of deriving the optimal heating conditions for the specified thickness, heat flux with various torch speeds and weaving breadths as variables. The results of calculated optimal weaving heating conditions were well corresponded to the manufacturing standard.
The inherent strain method has been used as one of the most efficient analysis method to predict the plate forming deformation by line-heating (Jang, Ko and Seo, 1997). Inherent strain method is an approach to calculate the deformation by elastic equivalent forces which is obtained by integration of inherent (irrecoverable) strain in the HAZ region. Due to its accuracy and efficiency, the inherent strain method will be able to substitute thermal elasto-plastic 3-D FEM analysis which requires much more computing time.
It is very important to properly assume the inherent strain region for the precise prediction of plate deformation by line heating. There have been several methods to assume the inherent strain region. Recently, an improved method considering phase transformation effect of steel has been developed (Jang, Ha and Ko, 2003).