Square Cup Forming of Locally Solution-Treated Aluminum Alloy Sheets by Hydromechanical Forming Method

The combination of the hydromechanical deep drawing method and the partially softened blank method was investigated to improve the press formability of aluminum alloy sheets. The strength distribution was previously endowed to an aluminum alloy sheet by partial heat treatment, and then the deep drawing was performed by applying hydraulic pressure against the punch during forming. This combined method was applied to the deep drawing of square cups of A6061 sheets and forming tests were conducted on circular blanks of various diameters to investigate the forming limits. While the conventional deep drawing method could form blanks up to 70 mm in diameter, a diameter of up to 90 mm could be achieved by the hydromechanical deep drawing with partially softened blanks. The effect of the partially softened region on the formability was investigated to clarify the optimal region for forming the maximum diameter. The effect of the hydraulic pressure in the hydromechanical deep drawing process was also investigated. The forming limit was improved by increasing the hydraulic pressure, and when the hydraulic pressure was 20 MPa, it was possible to form a blank of 100 mm. The mechanism for improving formability was clarified by studying the punch load force and thickness distribution.