Lubricant permeation from micro oil pits under intimate contact condition

In the situation of serious tool-workpiece contact when a smooth surface is desired in metalforming, the lubricant is either enclosed within the micro pits or infiltrates the contact plateaus region. The evolution of surface topography and the interfacial shear stress is accordingly altered. A quantitative analysis has been developed based on a series of compression-sliding tests and three-dimensional measurements of workpiece surface. It is found that the lubricant in the oil pits seeps into the contact region under the present experimental conditions. The fractional area of oil pit is a linear function of the average surface separation. The deformation of the oil pits is in the mode of "centripetal flow" where the opening of the pit is diminished while the depth of the oil pit is basically kept constant during the deformation. The specific permeation flux, which is defined as the nondimensional permeation flux per unit relative sliding speed and width of oil pit is an important index for the tendency of permeation. The variation of the specific permeation flux reveals that the lubricant permeation increases with sliding speed and average surface separation. After adopting the permeation model, it is Sound that the slipping between tool surface and permeating lubricant might exist. The average film thickness of the infiltrating oil increases with increasing sliding velocity and less serious asperity contact.