The fundamental forming properties and the behaviour are experimentally studied on the free forming of circular aluminum sheets (A1100-O, 1/2H) clamped at their periphery and formed by the direct method usually acting the impulsive pressure on the blank. The pressure distributions obtained are generally highest at the centre and lower for the periphery. In this forming, the relations among the polar deflection
h of blanks formed, the mean forming velocity
vh during forming at the pole, the die diamter
d (35-70 mm) and the material thickness
t0 (0.6-1.0 mm) are approximately found as follows :
h is proportional to
d0.5 and
t0-1, and
vh is to
d-0.5 and
t0-0.5 at each charged energy
Wc, and material, and the ratio
h/
vh (total forming time τ
f) is constant at each
d,
t0 and material independently to
h or
Wc. Therefore in this method,
vh cannot be controlled for forming at
h and is more increased as larger deformation resistance of blanks for forming as the same
h. The strain inclinations from the centre to the periphery of blanks formed are smaller in O than in 1/2H, and larger than those of the hydrostatical method in O, but smaller in 1/2H at the same
h.
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