| 摘要 |
PURPOSE:To improve the mechanical strength of a main surface by dividing bulging forming of the main surface into plural times, and also extruding the position of a punch gradually to a position which is near a knockout, and forming a titled mask. CONSTITUTION:In the first step, a punch 24 is projected in the direction of a knockout 25 of the lower part, and bulging is slightly applied to the main surface of a flat mask. Subsequently, the punch 24 is drawn up as a whole or by several mm., and thereafter, the punch 24 is projected again in the direction of the knockout 25 as the second step. The punch 24 bulges to a position which is nearer the knockout 25 than that of the first step. After drawing up the punch 24, the same step is performed and a main surface 20 having a prescribed curved surface is obtained. When it is returned to its original state by applying stresses Y1, Y2, etc. by the first step, the second step, etc., a working hardening phenomenon is promoted and the yield point strength is raized, therefore, a tough mask is obtained. |
