Lubricant-free tribology concepts for cold extrusion by interaction-reduced surfaces

The currently most effective approach for reduction of friction and wear in cold forging is the application of lubricants. Scope of the present study is the design and realization of a surface modification concept for form ing tools to enable the cold extrusion of aluminum in absence of lubricants. By quantum-mechanical guided design of wear resisting layers with reduced interaction, minimization of adhesion as the main wear mechanism is aspired. Through smoothing of roughness peaks and topography homogenization the laser assisted surface modification of the tools systematically aims at minimization of abrasive wear and thus less wear particles that act as nuclei for adhesive processes. Evaluation of the developed structures and layers is carried out on a newly designed torsion-tribometer, which enables the free scaling of contact stress and slide path combined with a certain amount of surface expansion. The report first gives an insight into the current state of the art, analyses the load case during cold extrusion and derives suitable tribological experiments for the characterization of adequate surface modifications. Subsequently, laser polishing and structuring processes are presented and, based on a quantum mechanical calculation of the interaction between tool and workpiece (aluminum), a possible solution concept by the use of self-assembling monolayers is presented. Finally, the methods are combined and their influence on adhesive wear is highlighted in tribological tests.