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Research Papers

# An Experimental Study on Robustness and Process Capability of the Warm Hydroforming Process

[+] Author and Article Information
Muammer Koç1

NSF IUCRC Center for Precision Forming (CPF), Virginia Commonwealth University, Richmond, VA 23284; Instanbul Sehir University, Istanbul 34662, Turkeykoc.muammer@gmail.com

Ali Agcayazi

NSF IUCRC Center for Precision Forming (CPF), Virginia Commonwealth University, Richmond, VA 23284

John Carsley

General Motors R&D, Warren, MI 48090

1

Corresponding author.

J. Manuf. Sci. Eng 133(2), 021008 (Mar 14, 2011) (13 pages) doi:10.1115/1.4003619 History: Received August 26, 2010; Revised January 11, 2011; Published March 14, 2011; Online March 14, 2011

## Abstract

The warm sheet hydroforming process was investigated to determine the optimal process conditions of temperature, pressure, and pressurization rate for maximum formability of AA5754-O using an experimental stretch forming die shape. The optimal process conditions were evaluated to determine the robustness and process capability based on physical measurement of formed parts including thickness strain, cavity fill ratio, and radius of curvature. For the simple die shape investigated, a temperature of $268°C$, a pressure of 25 MPa, and a pressurization rate of 0.22 MPa/s provided the most balanced combination of uniform thickness strain with the greatest cavity fill ratio and sharpest radius. Temperature had a greater effect on measured properties than either pressure or pressurization rate, although the effect of pressure increased as temperature decreased. The procedures demonstrated in this experimental study could be used to optimize process parameters for robust operation of production applications for more complex automotive body panels fabricated by the warm hydroforming process.

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## Figures

Figure 1

Variables affecting the part formability, part quality, and process robustness in warm hydroforming

Figure 2

Warm hydroforming experimental setup and die insert type for phase 1 screening experiments in which a die insert with a flat top surface and a depth of 11.5 mm was used

Figure 3

Comparison of thickness distribution a for phase 1 screening experiments. Thickness values were compared for both profiles A and B (cross sections A-A and B-B). For both profiles, locations 6 and 8 (transition radii) demonstrated the minimum thickness measurements (i.e., largest thinning) for all pressure and temperature conditions.

Figure 4

Comparison of CFR for phase 1 screening experiments to reveal a narrow range of process parameters (i.e., temperature and pressure). CFR values were compared for profiles A and B (cross sections A-A and B-B).

Figure 5

(a) Die insert type for phase 2 process robustness and phase 3 process capability experiments in which a die insert with a grooved top surface and a depth of 16.5 mm was used. (b) Sample hydroformed parts indicating the thickness, radii, and flatness measurement locations.

Figure 6

Response surfaces for (a) thickness (t, mm) and (b) cavity filling ratio (CFR, %) as a function of experimental factors including pressure, temperature, and pressurization rate at nominal hold values (i.e., T:260°C, P: 25 MPa, and PR: 0.22 MPa/s)

Figure 7

Response surfaces for (a) corner radii (R1, mm) and (b) flatness (mm) as a function of experimental factors including pressure, temperature, and pressurization rate at nominal hold values (i.e., T:260°C, P: 25 MPa, and PR: 0.22 MPa/s)

Figure 8

Optimal process conditions to achieve maximum thickness, maximum cavity filling ratio, minimum radius, and minimum flatness deviation (i.e., T:268°C, P: 25 MPa, and PR: 0.22 MPa/s)

Figure 9

Summary of thickness measurements: (a) total variation of thickness measurement at locations 1–10 along profile A, (b) variation of thickness measurements at locations 6 and 8 along profile A for each experiment, and (c) process capability analysis based on thickness measurements at location 6

Figure 10

(a) Cavity filling variation in each experiment and (b) process capability analysis of CFR calculations based on measurements along profile A on the warm hydroformed AA5754 parts

Figure 11

Radii measurements (R1, R2, and R3) for the 30-process capability experiments. (a) Variation of radii in each experiment and a total variation of radii measurements. (b) Process capability analysis of measurements for radius R3.

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