Lubricant free forming with tailored tribological conditions

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Within lubricant free forming an intensive interaction of workpiece and tool surface occurs. The aim of this research project is the realization of dry forming processes by developing and applying innovative tribological systems. The challenges of dry forming such as increased friction accompanied by increased wear are met by tool based surface modifications in a tailored tool approach. In the first period of the project forming of steel sheets is investigated in a lubricant-free deep drawing process. In order to test the transferability of derived correlations to other workpiece material classes also an aluminum alloy is tested. In basic experiments under laboratory conditions the fundamental understanding of lubricant free forming is generated by the analysis and description of the occurring tribological effects. At the same time the test results serve as input values for the simulation based design of the segmented tool for manufacturing the demonstrator cup. In the FE simulation tribological relevant tool areas are identified. Subsequently, required surface properties for each tool segment are derived in an inverse approach. The requirements represent the targets for the development of tailored surface modifications. In order to guarantee reasonable wear resistance the suitability of DLC coating systems for lubricant free deep drawing is assessed. In some tool areas lubricant free forming requires an extraordinary high wear resistance of the coatings. In this regard the laser induced heat treatment of DLC coatings is investigated for the local enhancement of wear resistance. Furthermore, for the purpose of controlling the material flow tool based surface structures will be developed and applied by laser ablation. While developing the surface coatings and structures the frictional and wear behavior of the different modification types are investigated by carrying out model tests under laboratory conditions. In particular, the influences of the factors tool material, surface structure and coating on the tool behavior are quantified. For determination of the limits of dry forming process the interactions of tool behavior and occurring process loads are investigated in the laboratory tests. The derived correlations between the process loads, the surface modifications and the resulting tool behavior are used for the local adjustment of the tribological conditions within the lubricant free model process. In order to validate these correlations the friction and wear behavior of the segmented tool is determined in the deep drawing process for the investigated steel and aluminum grade. The results of the first period of the project represent the basis for qualification of tailored tribological systems for the application in lubricant free forming processes.