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

在冷挤压过程中，润滑剂用于减少摩擦和磨损。在spp1676研究联盟能够推进在铝干挤压领域的基础研究知识。为了实现不同的表面修饰并在面向过程的摩擦学测试中进行测试，开发了机器和设备。在干燥条件下，通过重熔激光结构和随后的自组装单层（SAM）功能化相结合，显著减少了粘附铝和转移的摩擦力。在第三个项目阶段，通过重熔和功能化的激光结构形成的表面修饰的效果将进一步提高，并且通过考虑可容忍的工具负载设计模具几何形状，将使其在挤压过程中的应用成为可能。用激光辐射改变表面形貌的方法将辅以通过控制工艺气体气氛的组成来控制重熔表面层的化学成分。在此基础上，研究了这些表面改性对磨损的影响以及对功能化可实现的覆盖面积的影响。粘附层将支持功能化，以增加面积覆盖，而在sam沉积后的等离子体处理将被研究，以实现sam分子的交联。这将提高甲基端接的SAM在模具表面的机械稳定性，并防止氧化的工具钢表面与铝之间的直接相互作用，从而导致铝粘附，通常在无润滑剂的铝成形中观察到。开发的表面修改将通过压缩-扭转-摩擦计和实验室规模的冷挤压试验台进行试验来评估。此外，研究了成形阶段顺序，目的是通过减少改性表面上的模具载荷来实现高整体应变。通过将获得的基础研究知识转移到实际的模具几何形状和挤压过程中，该联盟的目标是得出一个面向应用的项目结论。

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.