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Research Papers

Experimental Assessment of High Temperature Formability of Boron Steel Sheet Manufactured With a Spring Compound Bending Die

[+] Author and Article Information
Yang Li

Precision Manufacturing System Division,  Pusan National University, Pusan 609-735, Korea

Yong-Phil Jeon

Precision Manufacturing System Division,  Pusan National University, Pusan 609-735, Koreaypjeon@pusan.ac.kr

Chung-Gil Kang1

Engineering Research Center for Net Shape and Die Manufacturing (ERC/NSDM) and School of Mechanical Engineering,  Pusan National University, Pusan 609-735, Koreacgkang@pusan.ac.kr

1

Corresponding author.

J. Eng. Mater. Technol 134(2), 021019 (Mar 27, 2012) (8 pages) doi:10.1115/1.4006227 History: Received September 08, 2011; Revised February 21, 2012; Accepted February 23, 2012; Published March 27, 2012; Online March 27, 2012

Bending behavior occurs in the hot press forming process, resulting in many cases of failure during forming. To address the problem of cracking and improve the formability and mechanical properties of boron steel sheets in the bending process, an experiment has been carried out by using a spring compound bending die. Also, a comparison has been made between the traditional U-bending die and the spring compound bending die with regard to formability. The influence of the parameters for hot press forming such as the heating temperature, punch speed, and die radii on the mechanical properties and microstructure was analyzed by tension testing and metallographic observations.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Photograph of the experimental apparatus for two kinds of bending die. (a) U-bending die and (b) spring U-bending die.

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Figure 2

Steps in traditional bending and spring bending. (a) U-bending die and (b) spring U-bending die.

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Figure 3

Details of the gap spring for the spring compound bending die circled in Fig. 2

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Figure 4

Comparison of the formability for different bending die sets

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Figure 5

Punch load variation for the traditional U-bending die. (a) Blank holder force = 10 kN and (b) blank holder force = 6 kN.

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Figure 6

Relationship between the punch load and the blank holding force for the traditional U-bending die

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Figure 7

Punch load variation under the spring U-bending die (Rd  = 2 mm). (a) Vp  = 6 mm/s; (b) Vp  = 12.5 mm/s; (c) Vp  = 25 mm/s.

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Figure 8

Punch load variation under the spring U-bending die (Rd  = 11 mm). (a) Vp  = 6 mm/s; (b) Vp  = 12.5 mm/s; (c) Vp  = 25 mm/s.

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Figure 9

Ultimate punch load for bending

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Figure 10

Evolution of the blank temperature with regard to the side temperature (ST) and central temperature (CT) for traditional U-bending at Bf  = 10 kN and Vp  = 10 mm/s. (a) Side temperature; (b) central temperature.

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Figure 11

Temperature variation of different parts during punching for the low friction die. (a) Temperature variation of the side part; (b) temperature variation of the central part.

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Figure 12

Positions for checking the mechanical properties

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Figure 16

Comparison of the elongation for positions A and B shown in Fig. 1 (a) Position A and (b) position B.

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Figure 15

Comparison of the ultimate tensile strength for positions A and B shown in Fig. 1 (a) Position A and (b) position B.

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Figure 14

Microstructure of different positions according to different experimental conditions

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Figure 13

Hardness at the measured positions shown in Fig. 1

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