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Research Papers: Mixed and Boundary Lubrication

Electrogalvanized Low Carbon Steel Adhesion Tendency in Friction Processes Under Mixed Lubrication Regime

[+] Author and Article Information
V. Miguel1

Department of Mechanical Engineering, Industrial Engineering School of Albacete, University of Castilla-La Mancha, 02071 Albacete, Spainvalentin.miguel@uclm.es

J. Coello, A. Calatayud, A. Martínez

Regional Development Institute: Material Science and Engineering, University of Castilla-La Mancha, 02071 Albacete, Spain

M. C. Manjabacas

Department of Mechanical Engineering, Industrial Engineering School of Albacete, University of Castilla-La Mancha, 02071 Albacete, Spain

C. Ferrer

Department of Mechanical and Materials Science, Polytechnic University of Valencia, 46022 Valencia, Spain

1

Corresponding author.

J. Tribol 133(1), 012101 (Dec 21, 2010) (9 pages) doi:10.1115/1.4003114 History: Received March 22, 2010; Revised November 18, 2010; Published December 21, 2010; Online December 21, 2010

Although some authors work at times with large flat dies and evaluate friction under more realistic conditions than usual, pressure is not totally controlled. In any case, cohesive friction does not appear to have been well studied in literature, but pressure and sliding velocity may provide useful information about preventing the cohesive phenomenon in sheet stamping processes. In this work, the coefficient of friction (COF) for DC-05 electrogalvanized steel is experimentally evaluated under lubrication regime by flat face dies. These tests are also considered to reproduce friction conditions in the die-sheet-blankholder system at some stages of the deep drawing process. High pressure condition in a flat friction system can also be considered for studying the friction behavior in the die radius. This work investigates the influence of contact pressure and sliding velocity of the sheet on the COF value. Adhesion tendency during sliding is also evaluated. Sheets were lubricated with a prelube type mineral oil and different lubricant film thicknesses are present on the sheet as a result of the draining off time effect, an aspect that will be evaluated later. Although sliding velocity has almost no influence on the COF value, pressure has an influence that may be expressed by a potential mathematical function. The COF value tends to be constant for high enough pressure values. This behavior may be explained, in part, from the viewpoint of zinc acting as a typical soft metallic lubricant. Sliding velocity is the most important variable from the adhesion phenomenon point of view, which appears more frequently for low velocity values. The draining off time, which some research works consider fixes the initial lubrication conditions in friction tests, has no significant effect when a mineral oil, typically used as a prelube, is selected as a lubricant. The authors found that pressure is the most important variable for the COF value. Velocity is the determining factor for the adhesion phenomenon in friction processes under mixed lubrication.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Flat friction test scheme

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Figure 2

Width of the friction band on the sheet after the flat friction test. (a) Friction is uniform in only one band. (b) Friction is observed in two different bands.

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Figure 3

Different friction force-stroke registers for electrogalvanized steel. (a) Typical behavior relating to nonadhesion condition. (b) Register with a stick-slip effect.

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Figure 4

Electrogalvanized coating. (a) After a friction test done with a pressure of 6 MPa and a velocity of 100 mm/min. (b) As the received strip material.

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Figure 5

COF values versus velocity for the different draining off times

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Figure 6

Average COF values for two different velocities (100 mm/min and 1750 mm/min) and three draining off times

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Figure 8

COF related apparent pressure correlations for the 100 mm/min and 1750 mm/min velocities for 0 h draining off time

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Figure 9

COF related apparent pressure correlations for the 100 mm/min and 1750 mm/min velocities for 24 h draining off time

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Figure 10

COF versus velocity for an apparent pressure of 3.4 MPa and a draining off time of 0 h

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Figure 11

COF for two velocity values and two draining off times. Influence of apparent pressure on the COF value.

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Figure 12

Mapping velocity-pressure with the adhesion phenomenon

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Figure 13

SEM micrographs of electrogalvanized steel surfaces. (a) Reception state. (b) After sliding at 0.9 MPa and 1750 mm/min. (c) After sliding at 9.6 MPa and 100 mm/min.

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Figure 14

Friction force registers for the tests done under high apparent pressure conditions

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Figure 15

COF values versus pressure for bare sheets and comparisons with electrogalvanized (EG) sheets

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Figure 16

SEM micrographs of a friction sample at high pressure (90 MPa). (a) Surface showing friction and frictionless areas after testing. (b) Detail of friction area.

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