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

Abstract

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.

Evaluación de la fuerza de doblado y de fricción en el conformado de chapa de acero inoxidable AISI 304 DDQ mediante ensayos de doblado en condiciones multiaxiales de embutición

“…La presión aparente tiene una influencia directa en los procesos de fricción en general. Queda demostrado que las presiones en el radio de entrada a la matriz pueden alcanzar valores elevados con rotura de película lubricante y paso de régimen de lubricación mixto a lubricación límite e, incluso, a la rotura de capa adsorbida en este último régimen con adhesiones en el deslizamiento [17] . Por tanto, los resultados obtenidos demuestran que el radio de doblado actúa como variable importante en la fricción del proceso de doblado, en tanto que el ángulo de doblado es una variable menos significativa.…”

“…Las funciones analíticas se ajustan mejor a los valores obtenidos para aceros con bajo coeficiente de endurecimiento [14] . Por tanto, el análisis efectuado demuestra que la formulación analítica requiere establecer correcciones en función del coeficiente de endurecimiento del material, cuestión ésta que afecta no solo a procesos de doblado bajo tensión sino a otros procedimientos de doblado [17] .…”

Adhesion Mechanism of Galvannealed Steel Sheet during Flat Sliding Test Studied by Microscopic Analysis of Die Surfaces

“…[1][2][3][4][5][6][7][8] The adhesion between the coated materials and die material occurring on the contact areas has been considered to be the main cause of friction resistance. From the macroscopic point of view, the adhesion is evaluated by the stick-slip behavior on the friction -stroke (distance) curve recorded during sliding tests.…”

“…From the macroscopic point of view, the adhesion is evaluated by the stick-slip behavior on the friction -stroke (distance) curve recorded during sliding tests. 7) However, the mechanism of adhesion of Zn-based coating has been rarely discussed and has not been fully understood especially from the microscopic point of view.…”

“…2,3,[5][6][7][8][9] In these papers the real contact surface areas or pits have been evaluated and discussed in the terms of sliding conditions and friction properties. For example, the friction forces of the contact area were correlated to the adhesion force 6) and the concave pits were considered to play a role in supplying the lubricant to the sliding interface.…”