Lubricant free forming with tailored tribological conditions

第一阶段和第二阶段的研究结果表明，干拉深过程中的直接接触导致了刀具和板料表面之间的强烈相互作用。使用传统的工具，无润滑剂的深拉深会导致成形力增加，局部磨损和裂纹形式的失效，这取决于板材的材料。这激发了表面改性的发展，减少摩擦和磨损，从而有助于控制材料流动。作为项目第一和第二阶段的研究方向，非晶碳基涂层和激光表面改性的摩擦学性能得到了发展和分析。通过ta-C和a- c:H涂层可以减少摩擦和磨损，同时采用激光热处理和显微组织来控制深拉深过程中的材料流动。为了实现矩形杯的干拉深，在压边架和模具上进行了有前途的表面改性。在干燥条件下，与未涂覆的工具相比，ta-C涂层的应用降低了钢和铝合金杯的成形力，提高了杯的表面质量。通过本课题所选择的措施，论证了干拉深的可行性。然而，目前尚不清楚所开发的改性材料在长滑动距离下的摩擦学行为如何变化。因此，项目第三阶段的主要目标是研究不同载荷条件下表面改性的磨合和磨损行为。这些知识将用于提高耐磨性。在涂层工艺方面，将调整涂层设计和沉积参数，以改善涂层的磨损性能。此外，将开发和分析基于激光的热处理、显微组织和光滑措施。涂层表面的热处理可以降低临界残余应力，同时微观结构能够收集磨损颗粒并使其远离接触区。与增加接触和剪切应力相关的具有挑战性的薄片性能也将进行研究。这将证明所选择的措施是否能够在广泛的应用中实现干深拉深。

The results of the first and the second project phase show that the direct contact during dry deep drawing leads to intensive interactions between tool and sheet surface. With conventional tools, lubricant-free deep drawing causes increasing forming forces, local wear occurrence and failure in form of cracks depending on the sheet material. This motivates the development of surface modifications which reduce friction as well as wear and thus, help to control the material flow. As approach in the first and second project phases, amorphous carbon based coatings and laser based surface modifications have been developed and analyzed regarding their tribological behavior. Reduction of friction and wear is achieved by ta-C and a-C:H coatings while a laser based heat treatment and microstructuring are applied to control the material flow in the deep drawing process. Promising surface modifications have been applied on blank holder and die in order to realize a dry deep drawing of rectangular cups. Under dry conditions, the application of ta-C coatings leads to a reduced forming force and increased surface quality of the cups for steel and aluminum alloys in comparison to cups drawn with uncoated tools. This demonstrates the feasibility of dry deep drawing with the help of the measures chosen in this research project. However, it is not clear how the tribological behavior of the developed modifications changes at long sliding distances. Thus, the main objective of the third project phase is the investigation of run-in and wear behavior of the surface modifications under varied load conditions. This knowledge will be used in order to increase the wear resistance. Regarding the coating process, coating designs and deposition parameters will be adapted to improve the wear behavior of the coatings. In addition, laser based measures in terms of heat treatment, microstructuring and smoothing will be developed and analyzed. A heat treatment of coated surfaces could reduce critical residual stresses while microstructures are able to collect wear particles and keep them away from the contact zone. Challenging sheet properties which are associated with increasing contact and shear stresses will be investigated as well. This will prove whether the selected measures enable dry deep drawing for a broad range of applications.