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The simplified (one step) method also called “inverse approach”(IA) for the numerical analysis of the stamping process has been continuously developed by the authors since the end of the eighties (1, 2, 3, 4). In the present paper we recall the main finite element formulation aspects of a robust IA analysis code, called FAST_STAMP, for an efficient estimation of the large elastoplastic strains (in particular the thickness strains) encountered in deep drawing operations. Our results will be presented and compared with others, obtained either from experiments or from incremental codes such as ABAQUS or STAMPACK. The presentation includes “math based” optimization algorithms and strategies for process parameter design. The cost functions and constraints are mainly express to reduce or control the thickness changes, the localized necking, the wrinkling tendency, the springback effects after forming. The design variables are describing the shape of the blank and the tools, the restraining forces due to drawbeads, material properties such as anisotropy coefficient and hardening exponent. Results will be presented to show the actual capabilities of the coupled analysis and optimization strategy with application to the design of stamping parameters. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Treatment of contact between a sheet and tools is one of the most difficult problems to deal with in finite-element simulations of sheet forming processes. In order to obtain more accurate tool models without increasing the number of elements, this paper describes a new formulation for contact problems using interpolation proposed by Nagata for tool surfaces. A contact search algorithm between sheet nodes and the interpolated tool surfaces was developed and was introduced into the static-explicit elastoplastic finite-element method code STAMP3D. Simulations of a square cup deep drawing process with a very coarsely discretized punch model were carried out. The simulated results showed that the proposed algorithm gave the proper drawn shape, demonstrating the validity of the proposed algorithm. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The design of addendum surfaces in sheet forming process is very important for the product quality, but it is very time-consuming and needs tedious trial-error corrections. In this paper, we propose a methodology to automatically generate the addendum surfaces and then to optimize them using a forming modelling solver. The surfaces’ parameters are taken as design variables and modified in course of optimization. The finite element mesh is created on the initial addendum surfaces and mapped onto the modified surfaces without remeshing operation. The Feasible Sequential Quadratic Programming (FSQP) is adopted as our algorithm of optimization. Two objective functions are used: the first one is the thickness function to minimize the thickness variation on the workpiece ; the second one is the appearance function aiming to avoid the scratching defects on the external surfaces of panels. The FSQP is combined with our “Inverse Approach” or “One Step Approach” which is a very fast forming solver. This leads to a very efficient optimization procedure. The present methodology is applied to a square box. The addendum surfaces are characterised by four geometrical variables. The influence of optimization criteria is studied and discussed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]