Rubber Forming Processes of Thin Sheets
In the last decade flexible media have been increasingly utilized in sheet metal drawing processes in order to reduce the tooling cost and to improve the product quality. In the present paper an axisymmetric deep drawing process of thin steel sheets is ta
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A. Custro, L. Fratini and S. Lo Casto University of Palermo, Palermo, Italy
KEY WORDS: Sheet Metal Drawing, Rubber Forming, Numerical Simulations
ABSTRACT: In the last decade flexible media have been increasingly utilized in sheet metal drawing processes in order to reduce the tooling cost and to improve the product quality. In the present paper an axisymmetric deep drawing process of thin steel sheets is taken into account: in particular a flexible pad is utilized in order to simplify the tooling set. The process mechanics is investigated through numerical simulations and experimental tests with the aim to find out a proper set of operative parameters allowing the stamping of sound components and to highlight the particular deformation path of the drawing cup. The comparison between the numerical predictions and the experimental verification has shown a very good overlapping.
1. INTRODUCTION Nowadays the competitive arena of the metal-working industry requires innovation, high qualitative products and low costs. In this way, in order to get up to date, modern companies have to aim to high flexibility, to new product design and to processes research. In particular the latter should be focused either on the optimization of the classic metal forming processes or on the development of innovative forming operations and procedures aimed to the improving of the forming Iimits and to the reduction of the production stages. Published in: E. Kuljanic (Ed.) Adl'anced Manufacturing Systemsand Technology, CISM Coursesand Lectures No. 406, Springer Verlag, Wien New York, 1999.
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A. Custro, L. Fratini and S. Lo
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As far as sheet metal stamping is regarded, in the last decades innovative solutions have been introduced such as tailored blanks, Iaser forming or flexible media as forming tools (1]. Pointing the attention on such flexible tools, the hydroforming or acquadraw processes have tobe mentioned [2][3][4][5][6], in which fluid counter pressure is utilized as female die. The stamping process is developed fulfilling the die cavity with an uncompressible fluid (generally water or oil); as the blank enters the die, the hydraulic pressure increases and acts on the drawing component, flowing out beneath the blank and the die: in this way a sort of dynamic equilibrium between the blankholder pressure and the fluid one is established. As a consequence an increase in the friction at the punch workpiece interface is obtained and subsequently a reduction in the axial stresses is observed. Since the limiting drawing ratio is strongly affected by the reached Ievel of axial stresses during the deep drawing process, hydroforming processes allow higher drawing ratios or, more generally, increased forming Iimits. Furthermore, it should be observed that in the sheet metal processes one of the most important targets is the reduction of thinning phenomena; in hydroforming processes a more uniform thickness along the drawn cup is obtained due to the hydrostatic pressure acting on the external surface of the blank. On the other band
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