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Fig. 3 a Preforming depth versus minimum thickness. b Preforming depth versus S/N ratio for
T min
It is observed from Fig. 4 that thinning band appears near clamped edge in SPIF
process as described by Young and Jeswiet [22]. It is seen in the thickness profiles of
preformed sheet that preforming causes plastic deformation at the tool-sheet contact
area and bending deformation surrounding the plastic deformation. Small amount of
stretching results in small amount of plastic deformation. The deformation results
in improvement in the thickness at thinning band as seen from thickness profiles of
conical frustum. As the amount of stretching increases from 10 to 14 mm, considerable improvement in thickness reduction at thinning band is observed. But an
increase in preforming depth leads to more thickness reduction near the apex of
conical frustum. Further increase in preforming depth from 14 to 18 mm shows
no signs of thinning band near clamped edge. Instead, large amount of thickness
Fig. 4 Thickness profiles of conical frustum formed using SPIF and HISF process at different
preforming depth