A mathematical model using the finite-difference method has been propo
sed in this work to examine the plastic deformation behavior of the sh
eet during blow-forming in a conical closed die. In the formulation of
this mathematical model, nonuniform thinning in the free bulged regio
n and the contact condition including the sticking and sliding frictio
n modes between the sheet and die are considered. Effects of various f
orming parameters such as the die entry radius, friction coefficient,
inclined angle of the die, etc., upon the optimized pressurization pro
file, forming time and the thickness distribution of products were dis
cussed systematically. Furthermore, experiments on superplastic blow-f
orming in a conical closed die were carried out using 8090 Al-Li sheet
s. It is found that the theoretical predictions agree with experimenta
l results. The thickness distributions of the SPF-ed product obtained
with different friction coefficients along the die entry, sidewall and
bottom are closer to the experimental data than those obtained with a
constant friction coefficient. (C) 1998 Elsevier Science Ltd. All rig
hts reserved.