Control of the deterioration of deep drawing limit by hydraulic counterpressure for 1050-H24 aluminum sheets

摘要

Influence of hydraulic counterpressure on the deep drawability of an aluminum work hardening sheet, and the forming method for improving deep drawing limit are examined. When a 1050-H24 aluminum sheet is formed by hydraulic counterpressure deep drawing, the limiting drawing ratio decreases compared with one formed by the conventional deep drawing. This is caused by inverse bulging deformation generated between a punch and a die due to hydraulic counterpressure. The radial strain caused by the inverse bulging deformation concentrates on the punch profile radius, which causes the local decrease of sheet thickness. For this reason, it is impossible to encourage material inflow into the die from a flange part. For relieving locally concentrated strain caused by inverse bulging deformation, material inflow into the die from the flange part is necessary. For this purpose, a method to push the flange edge by radial pressure drawing is effective. In addition, for suppressing the inverse bulging deformation generated under high liquid pressure, a method to reduce a blank holder profile radius and restraining by the metallic mold is effective.