The production of hollow-ware by deep drawing and bulge forming.

Results of a study of the production of hollow-ware by
deep-drawing and bulge forming are presented. Axisyrnrnetrical
and asymmetrical shapes were successfully produced from soft
aluminium flat blanks in one stroke of a punch. The process
consists of drawing, ironing and bulging inside a closed die
cavity. The constituent operations are studied individually.
In deep drawing without a blank-holder, an approach to
convex type die design is presented. The investigation
evaluates the effect of die profile geometry on the drawing
performance. Three dies of the second degree spiral type,one
near to the tractrix shape and the other two with larger
radius of curvature, are considered. The materials tested
include mild steel, stainless steel, soft aluminium and brass.
The drawing process through tractrix, exponential spiral,
second degree spiral and conical type dies is analysed using
a numerical solution formulated earlier and the theoretical
results on the punch load and the strain development are compared
with the experimental results. Good correlation is
obtained on the development of strains. The theoretical
prediction of the punch load is reasonably good except for
mild steel which is highly anisotropic. It is shown that by
modifying the die profile, the 'punch load can be significantly
reduced. The reductions predicted by theory are in
good agreement with experiment which means that optimum die
design for minimum load is possible.
In ironing of cups, using soft aluminium blanks, it was
found that punch speeds in the range 7-45 rom/sec have
negligible effect on the drawing load. The ironing load
decreases slightly as the speed increases in this range.
The reduction is more significant with higher degrees of
ironing. Measurement of ironed cup wall thickness showed
that thickness variations are attributed to planar anisotropy
of the blank and geometrical errors in tooling.
Free bulge forming is used as a simplified approach to
closed die forming. The bulge profile modes under different
loading conditions of internal pressure and axial force, the
effect of the unsupported cup length and the effect of the
cup wall thickness on the bulge ratio were investigated using
a specially designed test rig. For bulging of as deep-drawn
cups, the bulge ratio increases with increase of cup wall
thickness, and it decreases with increase of length. For
bulging of annealed cups the length effect is negligible and
the bulge ratio increases slightly with increase of cup wall
thickness.
The procedure used in producing different hollow-ware.
shapes is described together with typical failure examples.
The thickness reduction and bulge ratio distributions are
shown and comparison is made between annealed and as deep-drawn
cups.