Bendability and forming behaviour of high strength steel in U bending operation

Conference proceedings article

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Author list: Kaewtatip P., Prasitkhetkhan N., Khantachawana A., Premanond V., Hato R., Sresomreong B., Koga N.

Publisher: Hindawi

Publication year: 2008

Start page: 295

End page: 300

Number of pages: 6

eISSN: 1745-4557

URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84899761822&partnerID=40&md5=e7075ffc4c9ef1106d60b6611e6a062c

Languages: English-Great Britain (EN-GB)

Abstract

In this work, the bendability and forming behaviour of high strength steels in U bending were studied. The sheet materials used in the experiments are (JIS) SAPH440 (thickness 2 mm), SPFH590 (thickness 2 mm) and SPFC780Y (thickness 1.2 mm). Firstly, minimum bend radius of each material was investigated. Next, the experiments to compare three different methods of minimizing springback were carried out. The first method is, so called; bottoming that is the reduction of sheet thickness at the bottom of the workpiece or at bended angle by 10%. The second one is bottom overbending, i.e., the method to overbend the workpiece at bottom by 6o. For this method, the punch having a concave bottom surface and the bottom pad having corresponded convex upper surface have been used. The last one is flange overbending, i.e., the method to overbend the flange of workpiece by 6o. This can be done by using the punch having side relief angle (taper punch). The punches and dies edge radii are 5 mm. The clearance between punch and die are determined to be the same as material thickness. Two kinds of sheet layouts were experimented, i.e., the sheets were placed in order that their rolling directions were (1) parallel and (2) perpendicular to the bend line. The results revealed that the springback angle increased with the strength of sheet material. The bottom and flange overbending methods are more effective to reduce springback than bottoming method. In addition, for bottoming method, the force required was about 8 times higher than conventional bending force.

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