Enhancing formability in hydromechanical deep drawing process adding a shallow drawbead to the blank holder

• We proposed a new method so as to increase the limiting drawing ratio (LDR) of AA5754-O in the hydromechanical deep drawing (HDD) process.
• In this method, a shallow drawbead was added to the blank holder to increase the LDR.
• This drawbead provides strain hardening of a large region on the flange region of the sheet.
• The LDR of the AA5754-O was enhanced from 2.65 to 2.787 by adding a shallow drawbead to the blank holder.
• Analysis of variance (ANOVA) shows that adding a drawbead to the holder is one of the most influencing factors.

In this paper, a new method was proposed in order to enhance the limiting drawing ratio (LDR) of AA5754-O in the hydromechanical deep drawing process (HDD). In the proposed method, a shallow drawbead was added to the blank holder to increase LDR so as to provide strain hardening of a large region on the flange of the sheet material in addition to pre-bulging process which affects particularly only the initial stage but not the later ongoing process. So the LDR of the AA5754-O was increased from 2.65 to 2.787 by enlarging the region of strain hardening in the flange and partially reducing wrinkling tendency due to occurred tensile stresses using the convenient pressure and blank holder force profiles. The importance levels and their convenient values for height of drawbead, pre-bulge height and pressure, surface roughness of the punch were determined with analysis of variance (ANOVA) is a statistical method. ANOVA analysis illustrated that adding a shallow drawbead to the blank holder is the most effective factor between the investigated factors for the HDD process. While the effects of the pre-bulging pressure and pre-bulging height were determined as quite small, the surface roughness of the punch was found unimportant compared to the effect of the shallow drawbead. The highest LDR value was obtained with 1 mm drawbead height, 5 mm pre-bulging height, 10 MPa pre-bulging pressure and 2.8 μm surface roughness of the punch.

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