Effect of workpiece pre-straining on tribological performance of surface coatings in sheet metal forming

The material condition of a workpiece changes as it is formed. Typically, the workpiece hardens and undergoes geometrical and topographical changes. In progressive forming, where workpieces are formed in multiple steps, this means that the workpiece in subsequent steps is different from the as-received material. In this work, strip reduction of an as-received strip and of a pre-strained strip are compared. EN1.4404 stainless steel is pre-strained by bending-under-tension. This leads to changes in the material condition and the surface topography of the strip. Two different coatings are tested in a strip-reduction test to evaluate the effect of these changes to the workpiece state on the tribological performance of the tool coatings. A coating that performed poorly when used to reduce the as-received material exhibited an improved performance when used to reduce the pre-strained material.