Next-generation electrical discharge machining

电火花加工（EDM）是一种精密的材料去除工艺，它利用刀具和工件电极之间受控的快速电火花放电产生的热量。直到最近，电火花加工中材料去除的热性质限制了其在制造安全关键部件（如飞机发动机部件）中的应用。然而，与先进的固态发电机技术相关的电火花加工机床的最新进展，为电火花加工成为航空航天工业的主要产品铺平了道路，甚至取代了拉削等工艺，用于加工涡轮盘中的杉树叶片保持槽。随着热导率下降的航空航天材料的出现，电火花加工在未来几年将得到更广泛的应用，由于切削刀具的能量分配更高，加速了刀具的磨损，这使得它们极难切削。尽管取得了重大进展，但电火花加工在很大程度上仍然受到切削工艺的低材料去除率以及重铸材料和微裂纹的表面完整性问题的限制。有趣的是，这些问题在电火花加工中是相互关联的，在单次放电规模下的材料去除机制的背景下。熔融材料的去除目前被理解为由于放电后电介质蒸发所产生的气泡的内爆，据估计，由于弹射力不足，不到20%的熔融材料被去除。其余的材料被重铸回工作面上；这不仅使该工艺在材料去除方面效率极低，而且还严重影响了加工表面的完整性，因为熔融材料的快速凝固和收缩会产生微裂纹。因此，喷射效率的提高将提高去除率，同时产生更好的表面质量。目前，工艺和发电机技术的各个方面都处于如此复杂的发展阶段，因此有必要对工艺获得额外的基本物理见解，并仔细研究开箱即用的激进思想，以进一步提高电火花加工性能。在此背景下，本研究的长期目标是在越来越高的空间和时间分辨率下，从根本上研究电火花加工中材料去除的机制，以提高材料喷射效率。在短期内，该研究寻求开发新的工艺概念，并追求以科学为基础的创新方法，以同时大幅提高机加工表面的去除率和质量。

Electrical discharge machining (EDM) is a precision material removal process that utilizes the heat generated from controlled, rapid electrical spark discharges struck between the tool and workpiece electrodes. Until recently, the thermal nature of material removal in EDM has limited its application in the manufacture of safety-critical components like those in an aircraft engine. Recent advances in EDM machine tools to do with advanced solid-state generator technologies have however paved the way for EDM to emerge as a staple in the aerospace industry, to the extent that it is even displacing processes like broaching, in the machining of fir-tree blade retention slots in turbine disks. EDM is poised for an even more widespread application in the coming years with the advent of aerospace materials of declining thermal conductivity, which renders them extremely difficult to cut, due to the higher energy partition to the cutting tool that accelerates tool wear. Significant progress notwithstanding, EDM continues to be largely limited by a low material removal rate relative to cutting processes, and surface integrity issues referring to recast material and micro-cracks. Interestingly, these issues are interrelated in EDM, in the context of the mechanism of material removal at the scale of a single discharge. The removal of molten material is presently understood to be due to the implosion of the gas bubble that is manifest from the evaporation of the dielectric fluid following a discharge, and it is estimated that less than 20% of the molten material is removed, due to insufficient ejection forces. The rest of the material is recast back on the work surface; not only does this render the process highly inefficient in terms of material removal, it also severely affects the integrity of the machined surface, because of the micro-cracks that result from rapid solidification and shrinkage of the molten material. An improvement in the ejection efficiency would therefore bring about an increase in the removal rate and concurrently yield a better surface quality. Currently, aspects of process and generator technology are at such a sophisticated stage of development that it is imperative to gain additional fundamental physical insights into the process, and peruse outside-the-box radical ideas, to further enhance EDM performance. In this context, the long-term objective of the proposed work is to investigate the mechanism of material removal in EDM at increasingly higher spatial and temporal resolutions and in fundamental terms, with the objective of increasing the material ejection efficiency. In the short-term, the research seeks to develop novel process concepts, and pursue science-based innovative approaches to bring about a simultaneous and substantial enhancement in both the removal rate and the quality of the machined surface.