Investigation of Effects of Strip Metals and Relative Sliding Speeds on Friction Coefficients by Reversible Strip Friction Tests

Friction at the interface between strips and dies is an important factor influencing the formability of strip or sheet forming. In this study, the frictional behaviors of strips at variant speeds were investigated using a self-developed strip friction test machine with a dual tension mechanism. This friction test machine, stretching a strip around a cylindrical friction wheel, was used to investigate the effects of various parameters, including sliding speeds, contact angles, strip materials, and lubrication conditions on friction coefficients at the strip-die interface. The friction coefficients at the strip-die interface were calculated from the drawing forces at the strip on both ends and the contact angle between the strip and die. A series of friction tests using carbon steel, aluminum alloy, and brass strips as the test piece were conducted. From the friction test results, it is known that the friction coefficients can be reduced greatly with lubricants on the friction wheel surface and the friction coefficients are influenced by the strip roughness, contact area, relative speeds between the strip and die, etc. The friction coefficients obtained under various friction conditions can be applied to servo deep drawing or servo draw-bending processes with variant speeds and directions.