Characterization of the application behavior of self-lubricating powder pressing tools

金属粉末成型最常用的方法是模内双面压制。由该压制工艺产生的生坯的性能，如生坯密度，对于烧结件的最终密度以及抗拉强度和疲劳强度等机械性能是必不可少的。一般而言，绿色特性取决于材料和工艺的特定因素。例如，挤压过程中摩擦的减少对可压缩性有积极的影响。通常，为了减少摩擦，用过的粉末通过向粉末中加入少量的润滑剂(蜡)，然后将其混合来进行“润滑”。另一种方法是模具润滑，其中在每次冲压操作之前，借助喷嘴将稀薄的润滑剂施加到模具壁上。这带来了各种优势，例如更高的生坯密度和烧结密度，更低的密度梯度，以及取消脱蜡过程。然而，这种润滑方法的应用并不广泛。这主要是由于额外的工作，如额外的工艺步骤，但也存在生产复杂几何图形的问题。一种非常有希望的方法来抵消这些缺点，同时受益于模具润滑的优点是应用自润滑涂层。因此，本项目的目的是验证自润滑涂层在金属粉末模压成型中的适用性，以直接改善生坯或间接改善烧结性能。研究采用两种涂层和一种钢粉(含和不含润滑剂/蜡)。为此，进行了粉末的表征和工具的设计。除了压缩压力对所产生的相对密度的影响外，还通过压制调查确定了不同润滑策略与生坯强度之间的相关性。为了解释结果，在压制过程中记录了力分布，并将其与材料特性相关联。然后，对坯件进行烧结，以显示所研究的润滑策略对最终材料性能的影响。为此，创建了显微照片，并确定了密度和硬度分布。通过分析作为润滑策略的函数确定的特征值(密度、硬度、压下力和顶出力)，应该强调自润滑模具涂层的潜力。最后，所获得的知识应该转移到复杂的部件几何，包括材料属性的比较研究。

The most frequently used process for shaping of metal powders is the double-sided pressing in dies. The properties of the green compact resulting from this pressing process, such as the green density, are essential for the final density of the sintered component and thus for the mechanical properties, like tensile strength and fatigue strength. In general, green properties are dependent on material- and process-specific factors. For instance, the reduction of friction during pressing has a positive effect on compressibility. Usually, in order to reduce friction the used powders are “lubricated” by adding a lubricant (wax) to the powder in small amounts and subsequently mixing it. An alternative method is the die lubrication, where a thin lubricant is applied to the die wall by means of a nozzle prior to each pressing operation. This leads to various advantages, such as higher green and sintered densities, lower density gradients and the elimination of the dewaxing process. However, the application of this lubrication method is not widely used. The reasons for this are mainly the extra efforts, such as the additional process step, but also problems with the production of complex geometries.A highly promising approach to counteract these disadvantages while at the same time benefiting from the advantages of a die lubrication is the application of self-lubricating coatings. Consequently, the aim of the project is to validate the suitability of self-lubricating coatings in die pressing of metal powders to directly improve the green or indirectly improve the sintered properties.The investigations are carried out with two coatings and a steel powder (with and without lubricant/wax). For this purpose the characterization of the powder and the tool design are carried out. Besides the influence of the compression pressure on the resulting relative density, the dependencies between the different lubrication strategies and the green strengths are determined via pressing investigations. In order to interpret the results, the force profiles are recorded during pressing and correlated with the material characteristics. After that, the green parts are sintered in order to show the influences of the investigated lubrication strategies on the final material properties. For this, micrographs are created and density and hardness distributions are determined. By analyzing the determined characteristic values (density, hardness, pressing and ejection forces) as a function of the lubrication strategy, the potentials of self-lubricating die coatings should be emphasized. Finally, the acquired knowledge should be transferred to complex component geometry, including a comparative study of the material properties.