| CPC B32B 37/182 (2013.01) [B32B 3/08 (2013.01); B32B 3/30 (2013.01); B32B 7/022 (2019.01); B32B 15/043 (2013.01); B32B 15/08 (2013.01); B32B 15/20 (2013.01); B32B 37/24 (2013.01); B32B 38/0012 (2013.01); C25D 11/04 (2013.01); B32B 2037/243 (2013.01); B32B 2038/002 (2013.01); B32B 2307/54 (2013.01); B32B 2307/7376 (2023.05); B32B 2311/24 (2013.01); B32B 2457/00 (2013.01)] | 12 Claims |

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1. A method for producing an outer shell, comprising steps of:
a) stacking a second plate on a first plate, the second plate having an accommodation space therein that is recessed toward the first plate;
b) disposing a filling material in the accommodation space of the second plate;
c) after step b), stacking a third plate on the second plate so as to cover the filling material and to form a composite structure; and
d) after step c), stamping the composite structure such that a peripheral portion of the composite structure is bent, thereby forming the outer shell,
wherein, in step b), a weight of the filling material is lower than a weight of the first plate, a weight of the second plate, and a weight of the third plate, or rigidity of the filling material is higher than rigidity of the first plate, rigidity of the second plate, and rigidity of the third plate.
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