Research Papers

A Study on Warm Hydroforming of Al and Mg Sheet Materials: Mechanism and Proper Temperature Conditions

[+] Author and Article Information
Ho Choi

Materials Research Team, Advanced Technology Center, R & D Division, Hyundai Motor Company and Kia Motors Corporation, Gyung-Gi, 445–706, South Korea

Muammer Koç

NSFI/UCR Center for Precision Forming (CPF), and Department of Mechanical Engineering, Virginia Commonwealth University (VCU), Richmond, VA 23284-3015

Jun Ni

Department of Mechanical Engineering, and S.M. Wu Manufacturing Research Center, University of Michigan, Ann Arbor, MI 48109-2136

J. Manuf. Sci. Eng 130(4), 041007 (Jul 10, 2008) (14 pages) doi:10.1115/1.2951945 History: Received February 16, 2007; Revised November 11, 2007; Published July 10, 2008

Hydroforming of lightweight materials at elevated temperature is a relatively new process with promises of increased formability at low internal pressure levels. In this study, the mechanism of warm hydroforming processes is presented in terms of its formability by comparison with warm forming, and cold hydroforming processes. Additionally, a strategy is proposed to control process parameters, such as temperature, hydraulic pressure, blank holder force, and forming speed. As a part of this strategy, the proper temperature condition is determined by adaptive-isothermal finite element analysis (FEA) and a design of experiment (DOE) approach. The adaptive-isothermal FEA determines the temperature levels of the blank material, which is selectively heated, by checking position of the blank material and adopting temperature level of the neighboring tooling. The proposed adaptive-isothermal FEA/DOE approach leads to the optimal temperature condition in a warm hydroforming system accurately and rapidly as opposed to costly and lengthy experimental trial and errors and/or fully coupled thermo-mechanical simulations. Other process parameters are also optimized in a continued study (Choi, 2007, “Determination of Optimal Loading Profiles in Warm Hydroforming of Lightweight Materials  ,” J. Mater. Process. Techn., 190(1–3), pp. 230–242.).

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Potential benefits and comparison of warm hydroforming with conventional stamping process

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Figure 2

Process control strategy for the warm hydroforming

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Figure 3

Determination of proper temperature levels and strain rates for a part of lightweight materials; (a) a simple cup part, (b) temperature dependent flow curves (17), and (c) strain rate dependent flow curves (17)

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Figure 4

Warm hydroforming simulation model: (a) FE model for Case 1, (b) simulation conditions (20)

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Figure 5

Boundary conditions for hydraulic pressure (user subroutine): (a) checking material position and contact with the die corner; (b) pressure profile used in the simulations as reported in (4)

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Figure 6

Results of FE model (1) validation for LDR: (a) implicit scheme, (b) explicit scheme for warm deep drawing (DD) and hydro-mechanical deep drawing (HMD) cases (for process condition, please refer to Fig. 4)

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Figure 7

Warm hydroforming simulation model based on [8]: (a) FE Model 2; (b) simulation conditions

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Figure 8

Comparison of equivalent strain (e¯) at the top of the dome: (a) with different fluid temperatures. (b) with different punch temperatures (for process condition, please refer to Fig. 7)

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Figure 9

Temperature (a) and stress (b) distributions on the blank material in warm hydroforming, warm forming, and cold hydroforming processes

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Figure 10

Comparison of temperature (a) and (b), strain (c) and (d), and thickness (e) distribution on the blank in warm hydroforming, warm forming, and cold hydroforming processes

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Figure 11

Comparison of minor-major strain distribution on the blank at each stage of warm hydroforming, warm forming, and cold hydroforming

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Figure 12

Three different thermal models at low Peclet number (Pe<1): (a) isothermal approach (11), (b) adaptive-isothermal approach (checking material position and assigning neighboring tooling temperature to blank temperature), and (c) fully coupled thermomechanical approach

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Figure 13

Flow chart and associated algorithm for the adaptive-isothermal approach

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Figure 14

Energy balance on the die corner and definition of Peclet number

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Figure 15

Comparison of response surfaces with three different methodologies: (a) isothermal FEA/DOE, (b) adaptive-isothermal FEA/DOE, and (c) fully coupled thermomechanical FEA/DOE. Tp=punch temperature, Tf=flange temp., Tdc=die corner and fluid temp.

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Figure 16

Comparisons of optimal temperature distributions and analysis of variance (ANOVA) for the three approaches in warm hydroforming: (a) optimal temperature distribution. (b) ANOVA of three approaches

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Figure 17

Comparison of the part depth predictions and corresponding calculation time by the three different approaches. Adaptive-isothermal FEA/DOE approach offers accurate predictions with much reduced time compared to other approaches.

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Figure 18

Comparisons of (a) temperature, (b) strain, and (c) thickness for the warm hydroforming process with different temperature conditions




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