| 摘要 |
PURPOSE:To obtain an excellent curved surface of shadow mask without causing hole spread and breakage by using a press die formed to have its curved surface different from that of a knockout so that the stepped differences between the die and the knockout at the corners and the central part of a long side are different from each other at the time of bulging a shadow mask. CONSTITUTION:The peripheral edge part of a flat-mask metallic thin sheet 5 consisting of a perforated rectangular main surface and its peripheral part is held by a blank holder 1 and a die 2. The main surface is bulged into a prescribed curved surface by lowering a punch 3 with the aids of the punch 3 and a knockout 4. Further, a skirt part is formed by extruding the punch 3 into the die 2. At that time, a die 8 is formed so as to make the working rate at each part uniform and the stepped difference between the knockout 4 and the die 8 at the corner parts (l1) and the central parts (l) of long and short sides different from each other in conformity with the design of a shadow mask. |
