FORMABILITY ANALYSIS OF TAILORED BLANKS IN SINGLE POINT INCREMENTAL FORMING

In this thesis, formability of monolithic and tailored blanks made of metallic and
polymer sheets in single point incremental forming (SPIF) is investigated through
prediction of forming limit curves (FLC), incremental sheet forming (ISF) tests and
metallurgical characterizations of the incrementally formed blanks. Two aluminium
alloy sheets namely AA5083 and AA7075, and polycarbonate sheet were used to study
single point incremental formability (SPIFability) of tailored blanks. Initially
formability of aluminium alloy AA5083-sheet in SPIF is investigated through FLCs
and maximum formable wall angle considering different forming parameters and
conditions. Theoretical FLCs for SPIF predicted by deformation instability method
(DIM) were found to be higher than the experimental ones determined by ISF tests.
SPIF was found to give 60-80% higher formability compared to that for conventional
forming in terms of limit strains for varying strain paths in case of AA5083 sheet. The
maximum formable wall angle was improved for lower step depth but not significantly
increased for higher forming speed. The SPIFability was seen to get further improved
at elevated temperature compared to that at room temperature. Microstructure studies
revealed grain refinement in the deformed sheet by SPIF forming, and microhardness
values in the deformed sheets were observed to increase for incrementally formed parts
compared to that of the as received sheet. SPIFability of friction stir tailor welded
blanks (FS-TWB) made of dissimilar aluminium alloy sheets namely AA5083 and
AA7075 in SPIF are investigated using FLCs and ISF tests at both room temperature
and elevated temperature. Initially FS-TWBs were made with optimal process
parameters such as tool shoulder diameter, welding speed, and tool rotational speed
maximizing ultimate tensile strength and percentage elongation determined through
experiments and response surface methodology. A combination of lower rotational
speed, higher weld speed and a moderate tool shoulder diameter was found to produce
optimal weld quality within the considered ranges of the input parameters. FLCs and
maximum formable wall angle for FS-TWBs with optimal weld quality were
determined using DIM and ISF tests. Formability was observed to be lower for FSTWBs
compared to both base sheet materials in SPIF, and it was increased in case of
heat-assisted SPIF. FLCs were determined for the tailor laminated blanks (TLBs) made
of AA5083 and PC sheets and compared with that of the base sheets. Formability of
AA5083/PC and AA5083/PC/ AA5083 laminated blanks was seen to be higher than
PC and AA5083 sheets for plane strain case. Optical macrographs of the cross-sections
of the incrementally formed TLBs showed a sharp decrease in the thickness
distribution compared to that for the monolithic sheets. It was seen that failures like
bump structure, delamination and tearing could be reduced in SPIF of TLBs employing
discontinuous tool-path instead of the conventional continuous tool path.