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Research Papers

Preform Design for Tube Hydroforming Based on Wrinkle Formation

[+] Author and Article Information
Chen Yang, Gracious Ngaile

Department of Mechanical and Aerospace Engineering,  North Carolina State University, Raleigh, NC 27695

J. Manuf. Sci. Eng 133(6), 061014 (Dec 09, 2011) (11 pages) doi:10.1115/1.4005118 History: Received April 19, 2011; Accepted August 18, 2011; Published December 09, 2011; Online December 09, 2011

A two-stage preforming process based on wrinkle formation is developed for the tube hydroforming process to accumulate material in the forming zone, thus reducing the thinning rate and improving the formability. In preforming stage one, the wrinkle onset is triggered with limited axial compression. In preforming stage two, the wrinkle grows stably and uniformly to a certain height. Then, the preformed wrinkles are flattened to conform to the die shape in the final tube hydroforming process. An analytical model based on bifurcation analysis and postbuckling analysis of the elastic-plastic circular cylinder under axial compression and internal pressure is used to study the wrinkle evolution characteristics in tube hydroforming. The analytical results offer valuable guidance to the process design of the two-stage preforming process. To validate this methodology, preform die sets for two axisymmetric parts were designed and tube hydroforming experiments were carried out on SS 304 tubing. Through this methodology, an expansion rate of 71% was achieved.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Crushing process

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Figure 2

Expanded forming window

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Figure 3

Scheme for THF preform design

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Figure 5

Strain–stress curve of SS-304 tube

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Figure 6

(a) Half wave length from analytical model (b) half wave length from FEA

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Figure 7

Critical strain versus internal pressure

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Figure 8

Wrinkle development with die constraints

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Figure 9

Wrinkle height from analytical model and FEA

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Figure 10

Axial stress versus axial compression under different pressures

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Figure 11

(a) Nonaxisymmetric wrinkle (b) localized wrinkle [16]

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Figure 12

Free wrinkle growth and constrained wrinkle growth in the die

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Figure 13

The end bulge and die of the preforming stage

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Figure 14

Preforming and bulging die

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Figure 15

Wrinkle evolution and formed part

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Figure 16

The thinning distribution on the bulged part

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Figure 17

Preforming and bulging die

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Figure 18

Wrinkle evolution and formed part

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Figure 19

Thinning rate and expansion rate distribution

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Figure 20

150-t hydroforming press and forming die

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Figure 21

Loading path of hydroforming the bulge

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Figure 22

(a) Wrinkle formation in preforming stage (b) bulged part

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Figure 23

Thinning rate comparison between experiment and FEA

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Figure 24

Loading path of hydroforming the part with varying cross section

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Figure 25

(a) Wrinkle formation in preforming stage (b) formed part

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Figure 26

Wrinkled tube and its size

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