Formability Predictions in Stamping and Process Parameter Optimization Based on the Inverse Approach Code Fast_Stamp
A simplified (one step) method 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. In the present paper we recall the main finite element formulation aspects, for an efficient estimation of the large elastoplastic strains encountered in deep drawing operations. The capabilities of the code Fast_Stamp include: fixed (imposed) initial blank, bending effects due to tool curvatures, blankholder restraining forces (including drawbeads). Considerations of bending and unbending during forming stages can improve the IA regarding stresses distribution. In this case satisfactory estimation of springback can result. Since 1996 we also developed “math based” optimization algorithms and strategies. The cost functions and constraints are mainly expressed to reduce or control the thickness changes, the localized necking, the wrinkling tendency, the springback after forming. The design variables are describing the ...
Optimization of drawbead restraining forces and drawbead design in sheet metal forming process
Abstract This paper presents an optimization procedure of drawbead restraining forces in order to improve the sheet metal formability in deep drawing process. A simplified finite element method called inverse approach (IA) has been developed for sheet forming analysis with the consideration of the drawbead restraining forces. This IA is combined with a mathematical programming algorithm to optimize the restraining forces and then to design the drawbeads. The obtained optimization procedure is very efficient due to the simplified assumptions of the IA and the analytical sensitivity analysis. The Square cup of Numisheet’93 and the Renault Twingo dashpot cup are presented to demonstrate the usefulness of the proposed optimization procedure for industrial applications. Verifications of the obtained results have been carried out using a precise incremental commercial code OPTRISTM based on explicit dynamic approach to show the effectiveness of our approach.
Hapten inhibition of passive antidextran dextran anaphylaxis in guinea pigs. Role of molecular size in anaphylactogenicity and precipitability of dextran fractions.
High titred antidextran antisera have been raised in rabbits by prolonged immunization with soluble conjugates between isomaltose oligosaccharides or dextran mw 4,400 and bovine serum albumin in complete Freund’s adjuvant. Guinea pigs sensitized with such antisera exhibited anaphylactic shock on i.v. challenge with fractions of hydrolyzed B512 dextran. The severity of anaphylaxis depended on the amount of sensitizing antibody and the dose and molecular size of the challenging dextran fraction. In maximally sensitized animals, fractions of mw 3,600 or larger were anaphylactogenic and smaller molecular size fractions were nonanaphylactogenic. In submaximally sensitized animals, dextran fractions of mw 10,500 or less were foundnonanaphylactogenic. In addition, nonanaphylactogenic dextran fractions produced desensitization, i.e. protection from anaphylaxis due to subsequent or simultaneous injection of more high molecular and anaphylactogenic dextran fractions. When the molar ratio in a mixture of nonanaphylactogenic/anaphylactogenic fractions was about 7.6, protection was complete with reduction of mortality from 100 to 0%. A molar ratio of 1.9, corresponding to a 13-percent by weight admixture of nonanaphylactogenic dextran, still significantly reduced mortality from 100 to 50%. From the ability to form precipitates with antidextrans and to elicit anaphylaxis in sensitized guinea pigs, and from the absence of these properties, the approximate molecular size range of bivalent and monovalent dextran B512 fractions was found to correspond to mw 3,600 and mw 1,430, respectively. The practical applicability of hapten inhibition is discussed.