Research Papers

Analytical Model for the Characterization of the Guiding Zone Tribotest for Tube Hydroforming

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

Department of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Raleigh, NC 27695

J. Manuf. Sci. Eng 131(2), 021008 (Mar 18, 2009) (11 pages) doi:10.1115/1.3090888 History: Received June 25, 2008; Revised December 31, 2008; Published March 18, 2009

Common part failures in tube hydroforming include wrinkling, premature fracture, and unacceptable part surface quality. Some of these failures are attributed to the inability to optimize tribological conditions. There has been an increasing demand for the development of effective lubricants for tube hydroforming due to widespread application of this process. This paper presents an analytical model of the guiding zone tribotest commonly used to evaluate lubricant performance for tube hydroforming. Through a mechanistic approach, a closed-form solution for the field variables contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress can be computed. The analytical model was validated by the finite element method. In addition to determining friction coefficient, the expression for local state of stress and strain on the tube provides an opportunity for in-depth study of the behavior of lubricant and associated lubrication mechanisms. The model can aid as a quick tool for iterating geometric variables in the design of a guiding zone, which is an integral part of tube hydroforming tooling.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

(a) Friction zone in THF; (b) typical THF tooling

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Figure 2

Variants of guiding zone tribotests

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Figure 3

Scheme of guiding zone tribotest

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Figure 4

Stresses acting on the element: (a) r-θ plane and (b) r-z plane

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Figure 5

Stress state of tube covered by sections I and II

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Figure 6

Relationship between f and λ

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Figure 7

Stress state of tube fully covered by section II

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Figure 8

Schematic of FEA model for the guiding zone test

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Figure 9

Influence of interface friction on contact pressure, effective stress, and effective strain distribution

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Figure 10

Coordinate systems of tube

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Figure 11

Friction hill envelope for THF guiding zone

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Figure 12

Variation of maximum Rp with Lo/Do ratio for various friction conditions

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Figure 13

Evolution of friction hill envelop and maximum contact pressure for a tubular material with K=500 MPa, n=0.3, and a forming pressure of 60 MPa

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Figure 14

Characteristic curve of Eq. 16



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