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The line array roll set (LARS) process is an effective metal forming process used to manufacture doubly curved metal plates. This study describes process optimization of forming steps that can be used to form a twisted shape. In the incremental forming of a twisted shape using the LARS process, a defect near the edge of the formed shape was observed. A plate was subjected bending and twisting simultaneously by the roll sets as part of this process; therefore, it was assumed that the edge defect resulted from the excessive longitudinal strain near the edge region of the plate. To obtain a desired shape with more precision and to minimize any possible defect, the process of forming the desired shape should be systematically and accurately designed. To obtain the optimized design and to ensure that the maximum longitudinal strain is under the limit of the critical value, an iteration scheme is used for the optimization. Edge profiles of deformed shapes for both a non-optimized design and an optimized design were compared. From the comparison, it was found that the optimized design can minimize the number of forming steps by decreasing the edge wave caused by excessive edge stretching.

In this study, we performed laser cleaning using a Q-switching fiber laser to remove the shop-primer paint and the oxide layer. An analysis of the surface cleaned by laser was carried out at various energy densities. The results showed that the oxide layer on the steel surface was not removed at a relatively low energy density, whereas the base metal was damaged under excessive energy density. We confirmed that it was essential to select an appropriate energy density for efficiently removing only the paint and the oxide layer without damaging the base metal in laser cleaning.