超塑性Zn-Al合金を用いた薄板材の板厚/直径比のきわめて小さいエンボス成形

抄録

In order to reduce the assembling processes in manufacturing small, thin and precise parts, superplastic embossing method with the continuous supply of discs was newly developed. Using the Zn-21.5% Al-0.5% Cu-0.01%Mg alloy (SPZ) sheet, the stacked disc block of a disc specimen in thickness of 0.4 to 1.0mm, in the thickness/diameter ratio of 0.013 to 0.03 and two dummy discs in the thickness of 1.0mm were superplastically forged at 523K. A forged specimen and dummy discs were easily separated and these are discharged from the die after embossing. The configuration of embossed products was dependent on the superplastic forming conditions of temperature, punch speed and load. Under the optimum condition, highly accurate embossed-projection with sharp and lackless corner and without draft angle was obtained. Equivalent strain at the top corner of the projection was lager than 1.4. In the heavily deformed portion of the embossed discs with the equivalent strain of 1.0, the aspect ratio of grain changed from the initial value of 1.8 to 1.2 after superplastic embossing. The present method can be applied to form a precision part of watch dial.