FORMABILITY ANALYSIS OF TAILORED BLANKS IN SINGLE POINT INCREMENTAL FORMING
Creators: name: KUMAR, GAUTAM
Publisher: name: Zenodo
Year: 2021
Subjects: Single Point Incemental Forming, Friction Stir Welding, Forming Limit Curve, Formability, Laminated Sheet, AA5083 Sheet, AA7075 Sheet, Polymeric Sheet

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