Lubricant-free tribology concepts for cold extrusion by interaction-reduced coatings and structures

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In cold extrusion processes, lubricants are used to decrease friction and wear. Within the SPP 1676 the research consortium was able to advance the fundamental research knowledge in the field of dry extrusion of aluminum. Machines and devices were developed to realize different surface modifications and to test them in process-oriented tribological tests. The combination of laser structuring by remelting and subsequent functionalization with self-assembled monolayers (SAM) showed a significant reduction of adhered aluminum and transferred friction forces under dry conditions. Within the third project phase the efficacy of surface modifications fashioned by laser structuring by remelting as well as by functionalization will be further advanced and their application in extrusion processes will be enabled by designing die geometries in consideration of the tolerable tool loads.The approach of modifying the surface topography with laser radiation will be supplemented by the control of the chemical composition of the remelted surface layer by controlling the composition of the process gas atmosphere. Based on these surface modifications the influence on wear as well as on the achievable area-coverage of the functionalization is researched.The functionalization will be supported by adhesion layers in order to increase area-coverage, while plasma treatments after SAM-deposition will be investigated to enable cross-linking of SAM-molecules. This will improve the mechanical stability of methyl-terminated SAM on die surfaces and prevent the direct interaction between the oxidized tool-steel surface and aluminum, which leads to aluminum-adhesion usually observed in lubricant-free aluminum forming.The developed surface modifications will be evaluated by trials on a compression-torsion-tribometer and on a lab-scale cold extrusion test bench. Moreover, forming stage sequences are investigated with the aim of realizing high global strains by reducing die loads on the modified surfaces.By transferring the fundamental research knowledge gained to real die geometries and extrusion processes the consortium aims at an application-oriented conclusion of the project.