It may be possible to improve superplastic forgability of titanium alloys by conducting cold predeformation such as cold rolling. Superplasfic forgtng processes were carried out with cold-rolled titanium alloy to shape the middle of a wristwatch case, and compared to the results of the rigid plastic finite element method. The finite element analysis (FEA) of wristwatch cases can be simplified by making three-dimensional shapes approximate axisymmetric models. As a result, it was inferred that the deformed condition and the dimensions of the preform can be determined effectively because the deformation state of the material with which dies are filled and the distribution of the stress generated in each part of the wristwatch case can be predicted by FEA. To be specific, it was discovered that damage to the die may arise around the root of flashes and the distance between dies at the stroke point where the upper die touches the preform should be as short as possible to fill the dies with material quickly.
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