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

自润滑粉末压制工具的应用行为表征

• 批准号: 403432892
• 负责人: Professor Dr.-Ing. Bernd-Arno Behrens
• 金额: --
• 依托单位: Institut für Umformtechnik und Umformmaschinen (IFUM)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/403432892?language=en
• 关键词: Characterization; application; behavior; self; lubricating

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.

最常用的金属粉末成型工艺是在模具中进行双面压制。由该压制过程产生的绿色压坯的性质，例如绿色密度，对于烧结部件的最终密度是必不可少的，并且因此对于机械性质，例如拉伸强度和疲劳强度是必不可少的。一般来说，绿色特性取决于材料和工艺的特定因素。例如，在压制过程中摩擦的减少对压缩性具有积极影响。通常，为了减少摩擦，使用过的粉末通过向粉末中加入少量润滑剂（蜡）并随后混合来“润滑”。另一种方法是模具润滑，在每次压制操作之前，通过喷嘴将薄润滑剂施加到模具壁上。这导致各种优点，例如较高的绿色和烧结密度、较低的密度梯度和消除脱蜡过程。然而，这种润滑方法的应用并不广泛。其原因主要是额外的努力，如额外的工艺步骤，但也与复杂的几何形状的生产问题。一个非常有前途的方法来抵消这些缺点，同时受益于模具润滑的优点是自润滑涂层的应用。因此，该项目的目的是验证自润滑涂层在金属粉末模压中的适用性，以直接改善绿色或间接改善烧结性能。为此，进行粉末的表征和工具设计。除了压缩压力对所得相对密度的影响之外，通过压制调查确定不同润滑策略与绿色强度之间的依赖性。为了解释结果，在压制过程中记录力分布，并将其与材料特性相关联。之后，烧结绿色零件，以显示所研究的润滑策略对最终材料性能的影响。为此，创建显微照片并确定密度和硬度分布。通过分析所确定的特征值（密度、硬度、压力和顶出力）作为润滑策略的函数，应强调自润滑模具涂层的潜力。最后，所获得的知识应转移到复杂的部件几何形状，包括材料特性的比较研究。