Lubricant free forming with tailored tribological conditions

第一阶段和第二阶段的结果表明，在干拉深过程中的直接接触导致强烈的工具和板表面之间的相互作用。使用传统工具时，无润滑深冲会导致成形力增加、局部磨损发生以及取决于板材的裂纹形式的失效。这促使表面改性的发展，减少摩擦和磨损，从而有助于控制材料流动。作为第一和第二项目阶段的方法，开发了无定形碳基涂层和激光表面改性，并分析了它们的摩擦学行为。通过ta-C和a-C：H涂层减少摩擦和磨损，同时应用基于激光的热处理和微结构化来控制深冲工艺中的材料流动。为了实现矩形件的干式拉深，对压边保持器和凹模进行了表面修正。在干燥条件下，与使用无涂层工具拉制的杯形件相比，ta-C涂层的应用降低了钢和铝合金杯形件的成形力并提高了表面质量。这说明了在本研究项目中所选择的措施的帮助下，干式拉深的可行性。然而，目前尚不清楚如何开发的修改在长滑动距离的摩擦学行为的变化。因此，第三个项目阶段的主要目标是调查在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。关于涂层工艺，涂层设计和沉积参数将被调整以改善涂层的磨损行为。此外，还将开发和分析基于激光的热处理、微结构化和平滑化措施。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它们远离接触区。与接触应力和剪应力的增加有关的薄板特性也将被研究。这将证明所选择的措施是否能够在广泛的应用中实现干式深冲。

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.