Short Communication An experimental analysis of drawing characteristics of a dual-phase steel through a round drawbead Haydar Livatyali a , Mehmet Firat b, * , Burak Gurler c , Murat Ozsoy b a Istanbul Technical University, Faculty of Mechanical Engineering, Istanbul, Turkey b The University of Sakarya, Department of Mechanical Engineering, Adapazari, Turkey c Ford Turkey, Tool and Die, Kocaeli, Turkey article info Article history: Received 12 June 2009 Accepted 22 August 2009 Available online 27 August 2009 abstract The sheet drawing characteristics of a dual-phase steel (DP600) through a round drawbead are deter- mined experimentally using strip drawing tests. For this purpose, a drawbead simulator is designed and integrated with a standard tensile testing machine. Drawing tests are conducted with steel strips cut from 1 mm thickness blanks. The strip geometries, thickness strains, pulling forces and clamping forces are measured during drawing through a round drawbead of 5 mm bead and shoulder radius. The drawbead force parameters and thinning strains are determined from measurements. The experi- ments 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. The results of experimental analyzes for both steel types can employed as model input curves for equiv- alent drawbead models in FE process simulations. Ó 2009 Elsevier Ltd. All rights reserved. 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 re- quired to achieve a highly controlled and robust deformation pro- cessing [2,3]. This approach 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, however, obligate stamping methods engineer to extend this practice to deformation processing of relatively new- er high-strength steels such as dual-phase steels (DP). DP steels are advanced high-strength steels which are low alloyed and heat trea- ted to contain both a ferritic and martensitic phases for extra strength [6–8]. 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 [6,7]. This is the key design feature of DP-steels in automotive structures and of increasing use in thinner gages. The high strength and workhar- dening characteristics of DP-steels, however, may lead to high press-tonnages which were usually not practical issue with con- ventional 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 de- sign focused on mild steel grades; therefore, a deeper understand- ing of the drawbead behavior of DP steel is needed. Drawbeads generate a stable tensile force opposite to the sheet drawing direction by introducing a series of local bending, straiten- ing and reverse bending deformation on the sheet [9]. The design and selection of drawbead elements in stretch-draw dies for DP- steels necessitates the determination of sheet drawing characteris- tics in terms of drawbead restraint force (DBRF) and drawbead nor- mal force (DBNF) as the baseline parameters. In addition, the effect of bead penetration on these force parameters should also be qual- ified to achieve an economic stamping process [10]. The reduction of binder force and thus press tonnage as well as reduced adden- dum surface and blank size, furthermore, requires an accurate determination of sheet drawing characteristics including thinning and formability [8,9,11]. An exploration of recent literature, never- theless, presents a rather limited number of studies on DP-steels [6,8,11] and indicates the need for experimental determination of drawing characteristics with a particular emphasis on drawbead applications. 0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.08.030 * Corresponding author. Tel.: +90 264 295 5451; fax: +90 264 295 5450. E-mail address: firat@sakarya.edu.tr (M. Firat). Materials and Design 31 (2010) 1639–1643 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes