Tribo-Characteristics of Stainless Steel Sheets in Iterative Processes of Sheet Metal Forming

The present authors have developed a tribo-simulator for the long-term iterative processes of sheet metal forming. A sheet metal blank wrapped around a mandrel with a rubber sheet can be deformed by the steel ball as a tool to make spiral grooves on the metal sheet, and the frictional force, normal pressure, and temperature on the steel ball can be measured. The tribo-simulator could realize a total sliding length of 7.2 m and an iterative number of 40 under the sliding speed of about 300800 mm/s. Friction coefficients and temperature can be measured during all the iterative processes. Some tribological tests of different sheets of stainless steel lubricated with various kinds of mineral oil with different viscosities and a solid wax film coating-type lubricant were carried out. As a result, the variation in friction coefficient changed significantly depending on the lubricants and sheets used. The friction coefficient and temperature increment increased markedly after certain iterative processes with galling when using lower-viscosity mineral oil and no lubricant. On the other hand, the friction coefficient and the temperature increment showed approximately low constant values without galling when using the highest-viscosity mineral oil and the solid wax lubricant. The friction coefficient and the temperature increment were approximately constant without galling when using medium-viscosity mineral oil with some extreme-pressure additives. Two different sheets of stainless steel SUS 304 (Japan Industrial Standard) showed different tribological characteristics in spite of the fact that they were the same type of austenite stainless steel.