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Research Papers: Other (Seals, Manufacturing)

Tribological Characterization of Machining at Very Small Contact Areas

[+] Author and Article Information
Michael R. Lovell1

Department of Industrial Engineering, University of Pittsburgh, Pittsburgh, PA 15261mlovell@pitt.edu

P. Cohen

Marcus Department of Industrial and Manufacturing Engineering, Penn State University, University Park, PA 16802

Pradeep L. Menezes, R. Shankar

Department of Industrial Engineering, University of Pittsburgh, Pittsburgh, PA 15261

1

Corresponding author.

J. Tribol 131(4), 042201 (Sep 23, 2009) (7 pages) doi:10.1115/1.3195038 History: Received October 17, 2007; Revised May 06, 2009; Published September 23, 2009

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of 105mm2. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor τk were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Three models of asperity deformation

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Figure 2

Semi-orthogonal cutting of a tube with controlled contact tool

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Figure 3

Microstructure of 70/30 brass specimens: (a) annealed at 732°C for 1 h and (b) nonannealed

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Figure 4

Comparison of friction coefficient versus shear factor curves for (a) micromachining 70/30 brass and (b) pin-on-disk results for aluminum 1100 at velocity of 5 mm/s (5)

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Figure 5

Effect of material on the relationship between friction and shear factor

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Figure 6

Variation in the shear stress with the coefficient of friction. The resolved shear stress value is found to be a constant that is independent of the coefficient of friction.

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Figure 7

Variation in friction coefficient versus friction force. Note that the data collapse to a single universal distribution that is independent of the hardness value.

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Figure 8

Effect of shear factor on coefficient of friction for machining of brass. Shown are the separable impacts of contact length (or area) and work yield strength.

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