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Research Papers

Elastohydrodynamic Lubrication Modeling of Hydrodynamic Nanopolishing Process

[+] Author and Article Information
Rinku Mittal

Department of Mechanical Engineering,  Indian Institute of Technology Bombay, Powai, Mumbai 400076, Indiarinkumittal@gmail.com

Ramesh K. Singh

Department of Mechanical Engineering,  Indian Institute of Technology Bombay, Powai, Mumbai 400076, Indiaramesh@me.iitb.ac.in

Suhas S. Joshi

Department of Mechanical Engineering,  Indian Institute of Technology Bombay, Powai, Mumbai 400076, Indiassjoshi@iitb.ac.in

J. Manuf. Sci. Eng 134(4), 041001 (Jun 27, 2012) (11 pages) doi:10.1115/1.4006769 History: Received September 23, 2010; Revised March 02, 2012; Published June 26, 2012; Online June 27, 2012

Nanopolishing processes are used in medical, industrial, telecommunication, optics, and military fields. Hydrodynamic polishing (HDP) is one of the prominent nanopolishing methods in creating nanopolished surfaces on hard and profiled surfaces, where rigid tool-based methods like diamond turning, grinding, and honing have many limitations. This work is focused on modeling of hydrodynamic polishing method. In this method, a film of abrasive suspension is formed between the work-piece surface and a rotating soft tool, which helps in nanopolishing. The past experimental research gives an insight into the process but the process has not been explicitly modeled. Consequently, besides experimental characterization, a numerical/mathematical model of hydrodynamic polishing process is important. This paper presents a model of the HDP process which takes into account the polishing process variables, such as, contact load, spindle speed, tool and work-piece material properties/geometry, and abrasive suspension properties. The response of the model is the pressure distribution and the abrasive film thickness in the polishing zone. To model the elastohydrodynamic process encountered in HDP, the pressure and the film thickness profiles of lubricated isothermal point contacts have been evaluated using the multilevel multi-integration (MLMI) scheme coded in C programming language. Finally, load, tool stiffness, speed, and particle concentration in the suspension have been implicitly correlated to the surface roughness (SR) to evolve a semi-empirical model for surface roughness as a function of mean film thickness and mean pressure. Empirical models for mean film thickness and mean pressure have also been developed as a function of process variables. These models have been developed from a Taguchi L27 orthogonal array wherein the mean pressure/film thickness values have been determined from the model and the average surface roughness values have been measured experimentally. It has been observed that the load does not affect the surface roughness significantly and mean pressure does not change with the change in abrasive size and spindle speed. Abrasive particle concentration has been found to be the most important parameter and it affects the surface roughness significantly.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Overall modeling approach for development of semi-empirical model

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Figure 2

Schematic of the HDP process [7]

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Figure 3

Experimental setup for the study of HDP process [7]

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Figure 4

Viscosity variation with shear rate for abrasive sizes of 0.05, 0.3, and 1 μm

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Figure 5

Flow diagram of full multigrid process

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Figure 6

Computational domain for point contact EHL in hydrodynamic polishing

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Figure 7

(a) Pressure distribution in point contact EHL and (b) film thickness in point contact EHL

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Figure 8

Pressure and film thickness profile in point contact EHL at centerline (y = 0)

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Figure 9

Pressure distribution on thin film (a) case 1 and (b) case 2

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Figure 10

Simulated and measured mean pressure values

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Figure 11

Sensitivity analysis for force

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Figure 12

Sensitivity analysis for radius

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Figure 13

Logic for selection of interactions

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Figure 14

Scanning electron micrographs: (a) unpolished surface and (b) polished surface; white light interferometery images: (c) unpolished surface and (d) polished surface

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Figure 15

Main effect plots for load (a) pressure; (b) thickness; and (c) roughness

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Figure 16

Main effect plots for abrasive size (a) pressure; (b) thickness; and (c) roughness

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Figure 17

Main effect plots for stiffness (a) pressure; (b) thickness; and (c) roughness

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Figure 18

Main effect plots for spindle speed (a) pressure; (b) thickness; and (c) roughness

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Figure 19

Comparison of EHL and regression models for (a) mean film pressure and (b) mean film thickness

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Figure 20

Predicted and measured surface roughness values

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