Analysis of discharge-dependent surface integrity of cemented carbide forming dies machined by sinking EDM and its influence on the tribological characteristics and the resulting fatigue behavior

硬质合金由于具有很高的耐磨性和抗压强度，在金属成形中作为工具材料的潜力越来越大。它们的特点是与钢相比硬度增加，同时与陶瓷相比弯曲强度增加。在这种情况下，弯曲强度是工具设计的基本材料参数，因为弯曲应力通常是关键的失效原因。然而，硬质金属作为金属成形中的活性元件的工具材料的进一步推广受到高材料成本和特别是高加工成本的影响。由于电火花加工不依赖于材料的机械性能，是硬质合金成形模具加工的关键技术。然而，机加工硬质合金刀具通常显示出低于预期的韧性。其中一个原因是缺乏工艺知识，无法使刀具表面特别适应要求轮廓。另一方面，现有技术和先前工作中呈现的结果表明，通过在整个工艺链中进行适当的工艺设计，最终部件强度可以得到显著提高。该项目的目标是科学和结构化地分析电火花加工的放电相关表面完整性对由硬质合金材料制成的部件的摩擦学和机械行为的影响。在前一个研究阶段，提出了几个问题，并应在随后的研究期间回答。应使用全析因实验设计来创建模型，该模型可以物理地解释表面完整性对工艺能量的依赖性。该模型的普遍适用性应在第二台机床上进行验证。摩擦学材料行为的描述模型显示出非线性，需要在额外的实验中进行研究。另一个尚未科学描述的影响是在加工硬质合金时发生的几何形状偏差。应通过改变电极材料和加工参数来收集有关这种影响原因的信息。为了证明电火花加工对硬质合金加工的适用性，应检查几个后续处理步骤。这些研究结果可用于设计和制造多种硬质合金冷成形模具，并将在实际条件下进行测试。最后，应该从两个研究阶段的所有发现中创建一个模型。这应用于为用户、机床和材料制造商提供建议。

Cemented carbides have a growing potential as a tool material in metal forming because of their great resistance to wear and high compressive strength. They are characterized by an increased hardness compared to steels and simultaneously increased bending strength compared to ceramics. The flexural strength in this context is an essential material parameter for tool design, as bending stresses are often critical failure reasons. The further spread of hard metals as a tool material for active elements in metal forming are however conflicted by high material- and particularly high processing costs. Due to its independence from mechanical material properties, Electrical Discharge Machining (EDM) is a key technology for the machining of cemented carbide forming dies. However, machined carbide tools often show a toughness that remains below expectations. One reason for this is the lack of process knowledge to adapt the tool surfaces specifically to the requirement profile. On the other hand, the results presented in the state of the art and the previous work show that the final component strength can be specifically and significantly increased through adequate process design within the entire process chain. The objective of the project involves the scientific and structured analysis of the influence of discharge-dependent surface integrity of EDM (Sinking EDM) on the resulting tribological and mechanical behaviour of components made from cemented carbide materials.In the previous research phase, several issues were raised and should be answered over the course of this subsequent research period. A full factorial experimental design should be used to create a model that can physically explain the dependence of surface integrity from the process energy. The general applicability of the model should be verified on a second machine tool. The description model of the tribological material behaviour has shown non-linearities that need to be investigated during additional experiments. Another effect that has not yet been scientifically described, is the geometrical shape deviation occurring upon machining of cemented carbide. Information on the cause of this effect should be gathered by varying the electrode material and the machining parameters. In order to show the applicability of EDM for the machining of cemented carbides, several subsequent treatment steps should be examined. These findings should be used to design and manufacture multiple cold forming dies from cemented carbide, which are going to be tested under realistic conditions. Finally a model should be created from all the findings made in both research periods. This should be used to derive recommendations for users, machine tool and material manufacturers.