Tribological Investigation of Deep-Drawing Processes Using Servo Presses

Abstract

Deep-drawing is one of the most important processes for the economic production of sheet metal parts, especially for high quantities. The forming forces during the process are a limiting factor for the producible shapes. A particular importance is associated with the tribology, because the percentage of friction forces on the total forces is relatively high. The friction between sheet metal and tool is influenced by several factors, such as surface characteristics of the work piece and the tool, lubrication conditions and process parameters, like the contact pressure and the sliding speed. Controlling these parameters will expand the process window for deep-drawing. Lately, servo presses provide the possibility of controlling the process speed in dependency of the process progress. The subject of this paper is the tribological investigation of deep-drawing processes. The friction coefficient decreases with an increasing sliding speed. Investigating this correlation and utilizing it for the application with modern servo technology for industrial use is the main objective of the presented research works. First of all the dependency of the friction coefficient on the sliding speed is investigated by the use of the strip drawing tests, which allows the control of every parameter independently. The dependencies are implemented in a FEM-simulation, evaluating the potential for real deep-drawing processes. Deep-drawing experiments are then used to validate the results of the simulation with a speed-dependent friction coefficient as well as for the verification of the force reduction due to the influencing of process speed. In the end, the numerical simulated results in comparisons to the experimental measured results are discussed.