The forming tools of multilevel parts may be simplified by choosing shelf dies. To support the axial force on the flanged section of the die, some corresponding support is needed on the interior of the ring as well. Going ahead with a consolidated research line, stress and strain states of shelf (or “shouldered”) dies, with fixed filling height, have been numerically analyzed by FEM. After previous study of two-diameter shrink-fitting surface, connected by a transversal ring, the effects of a conical shrink-fitting surface have been investigated. Also in this case, to assess stress distribution and strain pattern, on the nucleus and on the ring, no analytical calculation method is available, whereas the usual empirical approach sometimes leads to disappointing and expensive operating failures. The shelf geometry depends on part shape and compression ratio on the inner of the nucleus, but may be variable on the common surface nucleus/ring. In this investigation, the common profile between the outer shoulder of the nucleus and the inner shoulder of the shrink-fitting ring has been assumed conical, with various angles. The FEM analysis, based on two-level parts with different relative extension of flange and different heights, covers different die geometries. The effects of relative interferences have been also investigated, for typical nucleus materials, such as HSS from powder or hard metal (10% Co). The results confirm unpleasant experiences: also in case of conical shrink-fitting surfaces, the stress levels on compaction of flanged parts are too high to be compensated by pre-stressing through shrink fitting. Within the investigated range of compact shapes, independently of interference, unacceptable tensile stresses frequently appear on the critical regions of the nucleus. The presence of radiuses reduces the stress levels, but does not always consent to reach safe enough values. The effect of common semi-angle is modest. The influences of compact profile dimensions on the pattern of stress distribution and deformation of the inner die profile are assessed. The proposed FEM results to design shelf-type dies with conical shrink-fitting dies should contribute to avoid any risk of failure on metal powder compaction to get flanged shapes with the lowest number of punches.

Compaction Shelf Dies with Conical Shrink-fitting Surface: FEM Analysis of Stress and Deformation Behaviour

ARMENTANI, ENRICO;CRICRI, GABRIELE;ESPOSITO, RENATO
2010

Abstract

The forming tools of multilevel parts may be simplified by choosing shelf dies. To support the axial force on the flanged section of the die, some corresponding support is needed on the interior of the ring as well. Going ahead with a consolidated research line, stress and strain states of shelf (or “shouldered”) dies, with fixed filling height, have been numerically analyzed by FEM. After previous study of two-diameter shrink-fitting surface, connected by a transversal ring, the effects of a conical shrink-fitting surface have been investigated. Also in this case, to assess stress distribution and strain pattern, on the nucleus and on the ring, no analytical calculation method is available, whereas the usual empirical approach sometimes leads to disappointing and expensive operating failures. The shelf geometry depends on part shape and compression ratio on the inner of the nucleus, but may be variable on the common surface nucleus/ring. In this investigation, the common profile between the outer shoulder of the nucleus and the inner shoulder of the shrink-fitting ring has been assumed conical, with various angles. The FEM analysis, based on two-level parts with different relative extension of flange and different heights, covers different die geometries. The effects of relative interferences have been also investigated, for typical nucleus materials, such as HSS from powder or hard metal (10% Co). The results confirm unpleasant experiences: also in case of conical shrink-fitting surfaces, the stress levels on compaction of flanged parts are too high to be compensated by pre-stressing through shrink fitting. Within the investigated range of compact shapes, independently of interference, unacceptable tensile stresses frequently appear on the critical regions of the nucleus. The presence of radiuses reduces the stress levels, but does not always consent to reach safe enough values. The effect of common semi-angle is modest. The influences of compact profile dimensions on the pattern of stress distribution and deformation of the inner die profile are assessed. The proposed FEM results to design shelf-type dies with conical shrink-fitting dies should contribute to avoid any risk of failure on metal powder compaction to get flanged shapes with the lowest number of punches.
9781899072149
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/372612
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