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Research Papers: Hydrodynamic Lubrication

Computational Fluid Dynamics Analysis of a Machine Hammer Peened Surface Structure for Lubricated Sliding Contacts

[+] Author and Article Information
D. Trauth

Laboratory for Machine Tools
and Production Engineering WZL,
Department of Grinding and Forming,
RWTH Aachen University,
Steinbachstr. 19,
Aachen 52074, Germany
e-mail: D.Trauth@wzl.rwth-aachen.de

F. Klocke

Laboratory for Machine Tools and Production Engineering WZL,
RWTH Aachen University,
Steinbachstr. 19,
Aachen 52074, Germany

M. Terhorst, P. Mattfeld

Laboratory for Machine Tools and Production Engineering WZL,
Department of Grinding and Forming,
RWTH Aachen University,
Steinbachstr. 19,
Aachen 52074, Germany

1Corresponding author.

2Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Professor of Manufacturing Technology, director of the Chair of Manufacturing Technology, co-director of the Laboratory for Machine Tools and Production Engineering WZL of RWTH Aachen University, and Head of the Fraunhofer Institute for Production Technology IPT in Aachen, Germany.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received April 28, 2015; final manuscript received October 11, 2015; published online November 9, 2015. Assoc. Editor: Daniel Nélias.

J. Tribol 138(2), 021704 (Nov 09, 2015) (10 pages) Paper No: TRIB-15-1139; doi: 10.1115/1.4031782 History: Received April 28, 2015; Revised October 11, 2015

Machine hammer peening (MHP) is an incremental surface finishing process. It enables both surface smoothing and texturing. Compared to well-established surface texturing processes, MHP has the advantage of simultaneous induction of strain hardening and compressive residual stresses. Both texturing and surface layer modification are very beneficial in case of mixed-boundary lubrication. MHP has been only recently developed. Therefore, the influence of surface textures manufactured by MHP on tribological interactions is unknown and lacks fundamental investigations. In this work, hydrodynamics of MHP textures is investigated by means of a three-dimensional (3D) computational fluid dynamics (CFD) analysis. The analyzed MHP textures have already been experimentally used to reduce friction in strip drawing tests. Using CFD analysis, an optimal arrangement of multiple elliptically shaped surface structures for maximizing the fluid pressure and the load-bearing capacity is determined. Furthermore, a correlation between the determined process parameters and the lubrication properties is presented. Because of significantly high hydrostatic pressures, cavitation is neglected in this work. Additionally, the effect of structure pileups is neglected in this study. Within the range of parameters investigated, it was found that an arrangement of surface textures by MHP should be transversally overlapping and clearly separated longitudinally. High structure depths, lubricant viscosities, and sliding velocities further improve the load-bearing capacity as well as small fluid-film thicknesses.

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References

Figures

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Fig. 1

Illustration of the approach pursued in this work

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Fig. 2

Illustration of contact mechanics of MHP (a) and an exemplary surface structure (b). The structure parameterized in (c). Legend: f = MHP frequency (Hz), v  = machine feed rate (m/min), lp = line pitch (mm), a = indentation distance (mm), d = head diameter (mm), F = impact force (N), Ra = surface roughness (μm), σi = equivalent stresses in the inner surface layer (MPa), 2rp1 = structure length (μm), 2rp2 = structure width (μm), hp = structure height (μm), 2r1 = cell length (μm), and 2r2 = cell width(μm).

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Fig. 3

Illustration of the slider bearing geometry (a) and validation of the CFD model (b). Legend: U = velocity of the sliding plate (mm/s), h = height of the slider bearing geometry (mm), v = velocity profile (mm/s), and p = pressure profile (MPa).

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Fig. 4

Discretization analysis (a) to obtain the best results. (b) The computation time and numerical deviation from the analytic solutions are given.

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Fig. 5

Visualization of different velocity profiles along the structure length L. Entering the structure, the profile shape changes from concave (a) to linear (b) to convex (c) in the structure center. Exiting the structure, the fluid flow changes back over a linear transition (d) to a concave profile (e) leading to a symmetrical situation.

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Fig. 6

Visualization of the resulting (a) as well as the transversal fluid flow (b). The velocity of the transversal fluid flow is approximately ten times lower than that of the resulting flow vector.

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Fig. 7

Illustration of selected 3D fluid pressures (a) and analysis of the influence of the gap height on the transversal fluid pressure profile (b)

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Fig. 8

Illustration of selected 3D fluid pressures regarding varying geometry parameters (a) and analysis of the corresponding transversal fluid pressure profiles (b)

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Fig. 9

Investigation of the impact of overlapping and nonoverlapping structure arrangements on the fluid pressure (a) and the transversal fluid pressure profile (b)

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Fig. 10

Load-bearing capacity of transversely arranged structures: table data (a) and graphical illustration (b). Legend: 2r2 = level of transversal overlap, p¯ = averaged fluid pressure (MPa), and ∫ p(y)dy = load-bearing capacity (MPa mm).

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Fig. 11

Analysis of the impact of touching (a) and overlapping (b) structures on the longitudinal fluid pressure

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Fig. 12

Combined investigation of longitudinally and transversely mixed structures on the fluid pressure (a), nonoverlapping (b), touching (c), and overlapping (d) structures is discussed

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Fig. 13

Comparison of the approximated structure geometry with experimental data (a) and analysis of the resulting fluid pressure profiles longitudinal to the sliding direction (b)

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Fig. 14

Recommendation of an optimized surface structure for hydrodynamic applications using MHP as surface finishing process. (a) The overall arrangement is qualitatively shown, while (b) shows the parameter of one single structure, and in (c) indicators at the tribological parameters are given.

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