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An Experimental Simulation of Drawing Characteristics of a Dual-Phase Steel

Proceedings article published in 2009 by Haydar Livatyali, Mehmet Firat, M. Fatih Önhon, Gökhan Doğan, Burak Gürler
This paper is available in a repository.
This paper is available in a repository.

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Preprint: policy unknown
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Postprint: policy unknown
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Abstract

The sheet drawing characteristics of a dual-phase steel (DP 600) through a round-type drawbead are determined experimentally using a specially-designed drawbead tester. For this purpose, the strip drawing tests are conducted with strips cut from 1 mm thickness blanks. The strip geometries, thickness strains, pulling forces and clamping forces are measured after the drawing through a round-type drawbead of 5 mm bead and shoulder radius. The drawbead force parameters and thinning strains are calculated. The experiments are repeated with conventional draw-quality sheets (DC06) of the same thickness for the purpose of establishing a benchmark database. A comparison of calculated drawing characteristics between two types of steels indicates the significant differences in terms of drawbead force parameters. In addition, analysis of experimental data demonstrated bead penetration, clamping force and material flow stress as the dominant factors on drawbead restraint force and blank thinning deformation for both materials. 1 INTRODUCTION A common attribute of most stamping processes is the need for the regulating the blankholder restraint force during the stretch-drawing in accord with the irregular part boundaries [1]. This may be done by adopting addendum surfaces to the actual part geometry, but usually, application of drawbeads may also be required to achieve a highly controlled and robust deformation processing [2,3]. This has been a well established practice mostly with the draw-quality low strength steel automotive sheets [4,5]. Market constraints for reduced weight vehicles with lower fuel consumption obligate stamping methods engineer to extend this practice to deformation processing of relatively newer high-strength steels such as dual-phase steels (DP). DP steels are advanced high-strength steels which are low alloyed and heat treated to contain both a ferritic and martensitic phases for extra strength [6-9]. They feature a soft ferrite microstructure; with a matrix containing islands of martensite in the secondary phase where increasing proportion of martensite increase the tensile strength. It performs a low yield strength-to-tensile strength ratio, high tensile strength and high work hardening rate [7]. This is the key feature of increasing use of DP-steels in automotive structures for thinner gages. The high strength and workhardening characteristics of DP-steels, however, may lead to high press-tonnages which were usually not practical issue with conventional steels. The required press forces increases considerably in forming with drawbeads on the blank holder particularly when thicker than 1 mm. Since decades of experience on drawbead design focused on mild steel grades; therefore, a deeper understanding of the drawbead behavior of DP steel is needed.