An experimental work on the superplastic bulge forming of machined sheets is presented in this study. Unlike the previously employed incremental-iterative method, a reverse deformation model was used to estimate the initial thickness distribution of the machined sheets from which a constant final thickness can be obtained when the shape of the bulged sheet is hemisphere. The reverse deformation modci was obtained by modifying previously-known models, which were based on the axisymmetric membrane and the incremental strain theory.Bulge forming experiments were conducted on machined sheets of Al alloy, A5083, at about 530°C under constant pressure control mode. The result of this simulation to estimate the final constant thickness distribution agreed well with the experiment, and confirmed that the reverse deformation model can be successfully applied in optimizing the thickness distribution of the starting sheets in order to obtain the desired final thickness distribution of the free bulged hemispherical product.

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The endless hot rolling concept was introduced to meet the demand for diverse hot-rolled steel sheet products produced by a process that is cost-effective compared with the conventional batch-type process. Endless rolling involves joining the head and tail ends of two bars after rough rolling. A new solid-state joining technology was proposed to instantaneously obtain a joint with high integrity using relatively simple equipment. In this report, we present the mechanism of super deformation joining (hereinafter referred to as "SDJ") and discuss results of our evaluation of the characteristics of joints to rolling. Super deformation by shearing creates new uncontaminated joint surfaces, and a large upsetting force at the completion of joining promotes metal bonding. SDJ was applied to the joining machine of POSCO POHANG #2HOT, and the use of endless hot rolling in commercial production was started in Jan. 2007. #2HOT is now producing approximately a hundred thousand tons of coils every month by endless hot rolling owing to the stabilization of operation.