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Research Papers: Applications

Determination of a Dimensionless Equation for Shear Friction Factor in Cold Forging

[+] Author and Article Information
K. H. Jung

Forming Technology Research and Development Group,
KITECH,
Gaetbeol-ro 156 (Songdo-dong),
Yeonsu-gu,
Incheon, 406-840, Korea

Y. T. Im

Fellow ASME
Department of Mechanical Engineering,
KAIST, 335, Gwahakro,
Yuseong-gu,
Daejeon, 305-701, Korea
e-mail: ytim@kaist.ac.kr

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received October 14, 2012; final manuscript received January 2, 2013; published online March 28, 2013. Assoc. Editor: George R. Nikas.

J. Tribol 135(3), 031102 (Mar 28, 2013) (9 pages) Paper No: TRIB-12-1177; doi: 10.1115/1.4023856 History: Received October 14, 2012; Revised January 02, 2013

In cold bulk forming processes, a constant shear friction model is widely used to apply friction. However, it is not easy to predict the shear friction factor since frictional behavior is highly nonlinear and is dependent upon a number of processing variables, such as the hardness of the material, lubricity, sliding velocity, surface contact conditions, and the environment, etc. This paper presents a dimensionless equation that predicts the shear friction factor at the counter punch interface mfd that was empirically determined by dimensional analysis, using the tip test results available in the literature as a function of selected process variables, such as the yield strength and initial specimen's radius of the deforming material, hardness, and surface roughness of the deforming material and the counter punch, viscosity of the lubricant, and deformation speed. To verify the determined equation, a new set of experiments were carried out for specimens made of AL7075-O. The prediction of the shear friction factor at the punch interface was also achieved by simply dividing the dimensionless equation by the x ratio defined by x = mfd/mfp, which is dependent on the hardening exponent of the deforming material based on previous studies. The predicted mfd and mfp were found to be reasonable owing to comparisons with the experimental data obtained for AL7075–O in this study. These results will be beneficial in scientifically assessing the effect of the processing parameters on the friction, individually and economically selecting the lubrication condition for cold bulk forming for practical applications.

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References

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Figures

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Fig. 1

Schematic description of the tip test used in the experiment

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Fig. 2

Stress-strain curves of AL7075 obtained by the compression test

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Fig. 3

Comparison of the load and stroke curves for the tip test for AL7075-O with a deformation speed of 0.1 mm/s between the experiment and simulation for (a) the smooth, and (b) rough counter punch

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Fig. 4

Linear regression model (δ = α = β = γ = 1 in Eq. (11)) between the shear friction factor at the counter punch and the experimental data available in the literature [12-15]

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Fig. 5

Dimensionless equation for the shear friction factor at the counter punch determined by the present investigation

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Fig. 6

Effect of the viscosity of the lubricant on the shear friction factor mfd

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Fig. 7

Effect of the process variables on the friction owing to (a)-(c) the hardness of the deforming material, and (d)-(f) the deformation speed

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Fig. 8

Comparison of the mfd values of AL7075-O between the experiment and Eq. (13)

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Fig. 9

Distributions of the residuals according to the type of lubricants: (a) the VG series, (b) corn oil, and (c) grease

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Fig. 10

Comparison of the empirically determined mfp for (a) x < 1 (smooth counter punch), and (b) x > 1 (intermediate and rough counter punch) with the experimental data available in the literature [12-15]

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