JFE No. 17 2007 8 p. 52 58 PRB Development of a New Bending Method PRB for High Strength Steel Tube and Application of High Strength Steel Tubes for Automotive Parts SUZUKI Koji TOYODA Shunsuke SATO Akio UENO Yukikazu OKADA Masao JFE JFE JFE JFE PRB 780 MPa 780 MPa Abstract: JFE Steel has developed a new bending method (PRB) for thin-walled high strength steel tubes without a mandrel and a wiper in collaboration with Toyota Motor Corp. and Taiyo Corp. JFE Steel also developed the 780 MPa class electric-resistance-welded tubes (ERW tubes) for automotive suspension parts, and contributed to the realization of the development of the arm parts applying 780 MPa class ERW tubes. By eliminating the mandrel and the wiper, which wear out eventually and require long adjusting time, in the rotary draw bender, this new bending method enables the bending of the thin-walled high strength steel tube in high productivity as well as enabling the bending of the thin-walled high strength steel tube with irregular shape. 1. 1 THF 2007 4 19 2 3 THF 590 MPa 3 R 4 PRB Bending Method with Slight Reduction of Diameter by Push with Pressure Die and Rotation of Bending Die 52
R R/D R D 2.0 R 2. R 2.1 2.1.1 Fig. 1 R 1940 5 1950 6 1960 7 1980 CNC 8 Photo 1 R t/d 4 390 MPa R/D 4.5 R/D 1 R 9 390 MPa R CNC Cramping Fig. 1 Tube Mandrel Pressure Bending Wiper Booster Cylinder Schematic diagram of rotary draw bending (a) 2 Ball type mandrel (b) Wiper Photo 1 Tools for rotary draw bending Changing ratio of thickness (%) Fig. 2 30 20 10 0 10 Inside of bend 20 30 Clemp Outside of bend 100 50 0 30 60 90 50 100 Distance Bending angle ( ) Distance Wall thickness distribution of high tensile steel tubes in rotary draw bending (TS780 MPa electric resistance welded steel pipe, OD70 WT2.6 mm, R/D 2.05) 2.1.2 R 9 780 MPa 4 Fig. 2 10 1 R 2 3 2.2 R R/ 2.0 2.2.1 Fig. 3 1960 Frantz 11 12 2.2.2 1980 53 JFE No. 17 2007 8
Fixed bending Tube 3. PRB Fig. 3 Clamp q Rotary pressure Schematic diagram of compression bending qtube, wspherical bearing, ebending, rguide cylinder Fig. 4 w e r Schematic diagram of push through bendig 3.1 PRB 17 19 3.2 PRB MOS Fig. 4 13 φ114.3 mm CNC R R/D 2.0 R 14 2.2.3 15 Fig. 5 16 T/D 5 10 R/D 4.3 3 R 3 3.2.1 PRB Fig. 6 PRB Bending Inroad of bending into the pipe Pipe Pressure Pressing before bennding Slight reduction in diameter Fig. 5 Schematic diagram of bend-rolling process Fig. 6 Principle of PRB method JFE No. 17 2007 8 54
Tube Bending Cramping Pressure Wrinkles No wrinkles Fig. 7 Cylinder Cylinder Schematic diagram of PRB method Photo 2 Appearance of bent tube by rotary draw bending and PRB method 10 20 3 7 10 PRB PRB Fig. 7 Fig. 1 3.2.2 PRB Photo 2 Fig. 8 70.0 mm 2.6 mm 780 MPa JIS 12A YS 757 MPa TS 803 MPa EL 17 R140 mm R/D 2.0 90 Changing ratio of thickness (%) Fig. 8 30 20 10 0 10 Inside of bend PRB method 20 Rotary draw bend Outside of bend 30 100 50 0 30 60 90 50 100 Distance Bending angle ( ) Distance Longitudinal thickness distribution of bent tube 2 Photo 2 PRB PRB Fig. 8 Photo 2 PRB 20 30 PRB 45 PRB PRB 780 MPa Table 1 90 R/D 2.0 PRB 55 JFE No. 17 2007 8
Table 1 Spring back angle of bent tube by PRB method and rotary draw bending Grade: 780 MPa class Applied tube Size: OD70 WT2.6 mm Bending angle ( ) 90 90 Bending radius of central axis 140 140 Mandrel and wiper Pressure force by booster Pressure force by pressure Ellipticity (%) 20 10 0 PRB method Rotary draw bending 10 None None 15 tf (147 kn) Cross section shape 3 ball-mandrel and wiper 10 tf (98 kn) None 3.2.3 PRB PRB R 1 1 R 2 3 3 4 5 2 Fig. 9 ξ 1 ξ H W OD 20 100 50 0 30 60 90 50 100 Distance Fig. 9 Bending angle ( ) Ellipticity of bent tube Distance ξ (H W)/OD 1 4. PRB 4.1 780 MPa 780 MPa 20 21 R/D 2.0 10 2 3 PRB 3 7 THF Fig. 10 Fatigue endurance Toughness Tube formability Low C ( 0.2) Low alloy (Si 1.0) Homogeneous microstructure (Ferrite Bainite) Property constancy Paintability Concept of material design about 780 MPa class electric resistance welded tube JFE No. 17 2007 8 56
Table 2 Merits by applying 780 MPa class ERW tube to automotive part bent by PRB method Items Press formed part (Steel sheet) Bent and hydraulic formed part (ERW tube) Total number of production process (Forming and welding) 100% 28% 72% Number of assembled parts 100% 71% 29% Weight/One part 100% 82% 18% Cost/One part 100% 74% 26% Merits Photo 3 Automotive part applied PRB method and 780 MPa class ERW tube Si Fig. 10 1 2 3 22 PRB Photo 3 780 MPa 4.2 17 4.2.1 780 MPa 780 MPa PRB φ70 t 2.6 mm Photo 3 Table 2 72 4.2.2 590 MPa 3 Photo 4 PRB 3 590 MPa φ65 t3.8 mm Photo 4 5. Automotive part applied PRB method and 590 MPa class ERW tube PRB R 3 590 780 MPa PRB 780 MPa R THF 1 CAMP-ISIJ 2003 vol. 16 p. 1158 2 2005-07 vol. 46 no. 534 p. 560 3 2005-07 vol. 46 no. 534 p. 552 4 H16 2004 p. 291 292 5 Schubert, Paul B. Pipe and Tube Bending, The Industrial Press. 1953. 57 JFE No. 17 2007 8
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