Method to improve solid lubricant film tribological performance and adhesion to hot forming material
According to one embodiment, a film of solid lubricant particles is applied to metal workpieces, which are then subjected to a controlled humid environment for predetermined times and temperatures. Following the exposure to humidity, the lubricated metal workpieces are heated for a hot forming operation. The humidification of the lubricated workpiece increases the adhesion of solid lubricant films to the metal workpieces, thereby improving the tribological performance of the workpieces during subsequent hot forming operations.
1. A method of increasing the adhesion of a lubricant to at least one metal workpiece for subsequent hot forming of the metal workpiece, the method comprising:
applying lubricant particles dispersed in a liquid carrier to a surface of at least one metal workpiece and removing the liquid carrier to form a lubricant film over the metal workpiece surface, wherein the lubricant film consists of particles of at least one of boron nitride, graphite, WS 2 , or MoS 2 , and wherein the lubricant film of the particles has a predetermined thickness of up to about 100 micrometers;
positioning the metal workpiece in a humidified air chamber;
exposing the metal workpiece in the chamber to a predetermined level of relative humidity of about 50 percent to about 100 percent, for a predetermined humidification period of time of at least one day, and at a predetermined humidification temperature, comprising selecting the predetermined level of humidity, humidification time, and temperature to increase the adhesion of the lubricant film of the particles to the metal workpiece;
removing the metal workpiece from the chamber; and thereafter
heating the metal workpiece for a hot forming operation on the lubricated surface of the metal workpiece.
2. A method as set forth in claim 1 wherein the predetermined humidification temperature is about 25° C. to about 60° C.
3. A method as set forth in claim 1 wherein the predetermined level of relative humidity is about 80 percent to about 100 percent.
4. A method as set forth in claim 1 wherein the predetermined humidification period of time is about 1 day to about 10 days.
5. A method as set forth in claim 1 wherein the liquid carrier comprises at least one of water or alcohol.
6. A method as set forth in claim 1 wherein the dispersion of lubricant particles in the liquid carrier comprises a surfactant or dispersant, and following removal of the liquid carrier, the lubricant film of particles further consists of the surfactant or dispersant.
7. A method as set forth in claim 1 wherein the particles have an average diameter of about five micrometers.
8. A method as set forth in claim 1 wherein the lubricant film has a thickness of about 5 to about 9 micrometers.
9. A method as set forth in claim 1 wherein the lubricant film has a thickness of about 12 to about 17 micrometers.
10. A method as set forth in claim 1 wherein the metal workpiece comprises aluminum alloy 5083.
11. A method as set forth in claim 1 wherein the metal workpiece comprises one of an aluminum alloy, magnesium alloy, or titanium alloy.
12. A method as set forth in claim 1 wherein the metal workpiece is a metal sheet.
13. A method as set forth in claim 12 wherein the hot forming operation comprises heating the metal sheet, stretching at least a portion of the metal sheet so that one side of the sheet is brought into contact with a shaping surface by applying a working gas pressure to the opposite side of the sheet, and wherein the stretching is accomplished by continually increasing the working gas pressure to a final stretching pressure.