Research Papers

Experimental Results on Lamellar-Type Solid Lubricants in Enhancing Minimum Quantity Lubrication Machining

[+] Author and Article Information
Trung Kien Nguyen

Machining Technology Department,
School of Mechanical Engineering,
Hanoi University of Science and Technology,
No. 1 DaiCoViet Road,
Hanoi, Vietnam

Kyung-Hee Park

Korea Institute of Industrial Technology,
35-3, Hongcheon-ri, Ipjang-myeon, Seobuk-gu,
Cheonan-si 331-825, Chungcheongnam-do,
South Korea

Patrick Y. Kwon

Department of Mechanical Engineering,
Michigan State University,
East Lansing 48824, MI
e-mail: pkwon@egr.msu.edu

1Corresponding author.

Manuscript received October 19, 2015; final manuscript received June 17, 2016; published online September 19, 2016. Editor: Y. Lawrence Yao.

J. Manuf. Sci. Eng 138(10), 101011 (Sep 19, 2016) (12 pages) Paper No: MANU-15-1522; doi: 10.1115/1.4033995 History: Received October 19, 2015; Revised June 17, 2016

This paper studies the effect of various lamellar-type solid lubricants (graphite and hBN) that can be mixed into a lubricant to potentially improve the machinability of minimum quantity lubrication (MQL) machining. To examine this, the solid lubricants are classified into particles and platelets based on their aspect ratios as well as their respective sizes. In particular, the particles are classified into microparticles and nanoparticles based on their dimensions (average radius), while the platelets were classified, based on their average thickness, into two types: the “microplatelets” if the thickness is typically up to few tens of microns and the “nanoplatelets” if the thickness is well below a tenth of a micron (even down to few nanometers). Our previous work has shown that the mixture of an extremely small amount (about 0.1 wt. %) of the graphitic nanoplatelets and vegetable oil immensely enhanced the machinability of MQL machining. In this paper, many lubricants, each mixed with a particular variety of nano- or micro-platelets or one type of nanoparticles, were studied to reveal the effect of each solid lubricant on MQL machining. Prior to the MQL machining experiment, the tribological test was conducted to show that the nanoplatelets are overall more effective than the microplatelets and nanoparticles in minimizing wear despite of no significant difference in friction compared to pure vegetable oil. Consequently, the MQL ball-milling experiment was conducted with AISI 1045 steel yielding a similar trend. Surprisingly, the oil mixtures with the microplatelets increased flank wear, even compared to the pure oil lubricant when the tools with the smooth surface were used. Thus, the nanoscale thickness of these platelets is a critical requirement for the solid lubricants in enhancing the MQL machining process. However, maintaining the nanoscale thickness is not critical with the tools with the rough surfaces in enhancing the MQL process. Therefore, it is concluded that finding an optimum solid lubricant depends on not only the characteristics (material as well as morphology) of solid lubricants but also the characteristic of tool surface.

Copyright © 2016 by ASME
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Fig. 1

Pitch and Yaw angle of the nozzle in end-ball milling

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Fig. 2

SEM surface images of tool surfaces and roughness (Rz) parameters: (a) tool A at 1000×, (b) tool B at 1000 x, and (c) roughness in relation to grinding marks

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Fig. 3

SEM micrographs to reveal the shape and diameter of micro- and nano-platelets (*from ACS Material website1): (a) GrapP10*, (b) graphite, (c) xGnP (M5), (d) hBN5, and (e) hBN300

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Fig. 4

SEM Micrographs revealing the thickness of nano- and microplatelets graphite and hBN5: (a) xGnP M5, (b) microplatelets graphite, and (c) hBN5

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Fig. 5

The configuration of tribological tests

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Fig. 6

The work material in relation to the milling inserts

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Fig. 7

Experimental setup for MQL ball milling (a) and the minimum pitch angle (b)

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Fig. 8

The stability of the mixtures with 0.1 wt. % micro- and nano-platelets after 72 h

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Fig. 9

Wetting angle (degree) of lubricants on tool A surface (left angle, right angle) at room temperature

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Fig. 10

Friction coefficients as a function of the sliding speed on tool A: (a) 2.5 cm/s and (b) 4.0 cm/s

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Fig. 11

Wear track under various lubricant conditions on tool A (normal load: 10 N, speed: 2.5 cm/s)

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Fig. 12

Relative scale of microplatelets (hBN5) and nanoplatelets (xGnP M5) in the valleys of tool surfaces: (a) microplatelets hBN5 and (b) nanoplatelets xGnP

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Fig. 13

Flank Wear at 3500 rpm after each cutting layer layers with tool A (missing data: tool chipping)

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Fig. 14

Wear track and friction under various lubricant conditions with tool B (load: 10 N, speed: 2.5 cm/s): (a) depth of wear track, (b) width of wear track, and (c) friction coefficients of the mixture with hBN platelets

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Fig. 15

Flank wear at 3500 rpm after each cutting layer layers with tool B

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Fig. 16

Flank wear under various yaw angles tested with the lubricant mixed with 0.1 wt. % of xGnP M5 (missing data: tool chipping)

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Fig. 17

Top view of MQL experiment: the distribution of lubricant at two extreme cases: (a) the best case with θ = −30 deg and (b) the worst case with θ = 120 deg




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