Numerical Simulation Research Of Sheet Metal Incremental Formability

Sheet metal single point incremental forming(SPIF)is a rapid flexible forming technology which can form arbitrarily complex-shape parts without specific dies and more suit for aerospace, automotive, and civil areas of low-volume, diverse, complex sheet metal parts.Based on the experiments and finite element numerical simulations, mainly research the forming mechanism, forming limit, forming defects which are all related to the formability in SPIF. Get some useful conclusions which will have a great significance for the follow-up study and the widespread application of SPIF.Firstly of all, describe the specific method and course of numerical simulation in SPIF: present the die-less single point incremental forming process, the mechanical model and the detail parameter settings in numerical simulation; indicate the generation method of numerical simulation tool path which is proposed to use the forward and inverse way avoiding the occurrence of distortion at the bottom of the workpiece. Secondly, carry out the study of incremental forming mechanism, focusing on the analysis of stress-strain state and thickness distribution law: the deforming elements are in a plane stress state; deformation elements are in the plane strain state when using straight forming path, but the strain state tend to two-pull strain state when using annular forming path; the workpiece thickness distribution follows the cosine rule. Thirdly, study the forming limit of SPIF: Based on finite element numerical simulations, applying Oyane ductile rupture criteria to predict the forming limit of sheet LY12 (M) with the thickness of 1.5mm effectively, when the integral value I=4, the predict rupture starting point and the forming limit curve are more consistent with the experimental results; due to the "partial, alternate, small increments" deformation characteristics, small deformation accumulate to large deformation, achieve a uniform deformation mandatorily, so SPIF get a higher forming limit; besides, the value of the tool radius divided the sheet thickness r/t。has a great influence on the sheet forming limit in SPIF: when the value is too small, the sheet is easy to rupture due to the local stress concentration; when the value is too large, forming limit is also low just as traditional bulge forming; Therefore, for a certain thickness sheet, you must select a appropriate value .Finally, list some forming defects(wrinkling, springback, forming indentation, bottom inward convex, shape variation, forming micro-cracks) in SPIF and give the detail reasons and reasonable measures to deal with.