Improvement of stretch flangeability of ultra high strength steel sheet by smoothing of sheared edge

Effects of Testing Method on Stretch-Flangeability of Dual-Phase 980/1180 Steel Grades

“…Stretch-flangeability, measured by hole expansion testing (HET), is a measure of formability that has been used to characterize the performance of materials during forming of sheets with holes. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] HET can be performed with conical [4][5][6][7][8] and flatbottom punches, 4,9-13 as well as different hole preparation methods (for example, sheared or machined). 4,[14][15][16] Studies have shown that materials tested with a conical punch generally have a higher hole expansion ratio (HER) than the same material tested with a flat-bottom punch.…”

Fatigue Strength of High Strength Steel Sheets Joined by Hemming Process

“…For the high strength steel sheets, the dimensional accuracy of formed products deteriorates due to large springback and die deflection, and the formability is small. Mori et al [3] improved the expansion of a hole of a punched ultra-high strength steel sheet by smoothing fracture surface of the sheared edge using a conical punch. Abe et al [4] developed a gradually contacting punch to increase the stretch flangeability of the ultra-high strength steel sheets.…”

Punching process including thickening of hole edge for improvement of fatigue strength of ultra-high strength steel sheet

“…Kim et al [8] have developed a burr-free punching process consisting of mechanical half piercing and hydro counter punching. Mori et al [9] have smoothed the fracture surface of the sheared edge using the conical punch to improve the hole expansion ratio of the punched ultra-high strength steel sheet. Mori et al [10] have improved a sheared edge of ultra-high strength steel sheets in slight clearance punching with a punch having a small round edge.…”