高速电弧放电加工技术基础研究

The challenge of efficient machining of high-temperature alloy has been a bottleneck of air turbine engine manufacturing for many decades in China. An originally invented technology so called "high speed arc discharge machining" is proposed to perform a high- efficiency and low-cost machining of the difficult-to-cut materials such as nickel based high-temperature alloys. During this machining process, the arc plasma column in between the electrode and workpiece, is broken periodically by high velocity water based working fluid which is exerted with multi-hole inner flushing. This mechanism is referred to as "Hydrodynamic Force Induced Arc Breaking". By utilizing the extremely high density energy field which is supplied by the high current arcing, the difficult-to-cut materials can be removed much more efficiently than any other processing methods. In order to disclose the sealed mechanisms, solve the scientific puzzle and discover the machining characteristics of this innovative machining method, following fundamental researches will be conducted with the help of observations, experiments and numerical analysis. 1) Observation and analysis of the formation and evolvement of arc plasma; 2) The mechanism of the polarity effect that happens during arc discharge machining; 3) Experimental investigation into the influence of the core technical factors and essential parameters on the performance of the high speed arc discharge machining; 4) Feasibility validation for the high speed arc discharge machining of typical high temperature alloy parts with complex geometry. The achievements of this project will help to lay down the foundation of this new academic area and take the advantage of early development.

高温合金等难切削材料的高效加工难题已成为长期制约我国航空发动机研制与生产的重大瓶颈。本项目提出一种源头创新的"高速电弧放电加工方法"。通过利用大电流电弧放电提供能量密度很高的特种能场，采用水基工作液介质，施加高速多孔内冲液，形成独特的流体动力断弧作用，成功地实现了高温合金等难切削材料的高效加工。本项目将针对这一新技术的未知机理、科学问题以及加工特性等开展系统深入的基础研究，以期对这一新技术获得系统、科学的认知，为形成高速电弧放电加工技术体系提供理论依据。采取观测、实验及数值模拟等方法重点研究：1)高速电弧放电加工中等离子体弧柱形成与演变过程；2)等离子弧柱对阳极高效蚀除但对阴极蚀除很少的极性效应机理；3)各核心技术要素对高速电弧放电加工工艺性能的影响规律；4)典型高温合金复杂曲面零件的加工适用性验证。所获得的研究成果将有助于我国在这一新的学术方向及其产业应用方面争取先发优势。

研究工作针对电弧放电加工的高效材料去除机理和利用高速电弧放电实现航空航天难切削材料的高效加工等科学问题及相关工程应用问题而开展了全面、系统的研究并取得了显著的成果。在机理方面，首先验证了流体动力断弧机制的存在及其在高速电弧放电加工中的重要作用，观测和分析电弧放电通道在流体动力断弧机制下形态变化的过程和放电加工蚀除颗粒从熔池内排出的过程，并测量和分析了出电弧放电通道的温度特征并采用双线法对放电通道温度进行了测量。推导出放电通道在击穿放电之后的扩张阶段的半径表达式，发现放电通道扩张阶段的传热时间累积效应。建立了考虑时间累积效应的热分析模型和高速电弧放电加工的“先扩张后偏移”材料蚀除模型，拟合了流体动力断弧机制下尾状放电痕的形成，并且从能量利用效率的观点解释了高速电弧放电加工能够获得较大的材料去除效率的原因。.在机理研究成果的基础上，针对航空航天典型难切削材料，特别是高温合金、钛合金和碳化硅铝基复合材料等进行了系统的电弧放电加工工艺特性研究，并研究了极性效应对加工性能的影响。加工效率较传统电火花加工提高了20-30倍，加工高温合金的效率较传统铣削加工提高1倍以上，而加工表面的热损伤与传统电火花加工接近，对后续精加工不产生不良影响。对于开敞型腔及叶盘类零件的加工需求和高速电弧放电加工的特点，提出了高速电弧放电侧铣加工工艺。针对复杂形状的闭式涡轮叶盘的高效加工需求，结合高速电弧放电加工，提出了新型的叠片电极形式，并进行了理论及实验研究，实现了闭式形状的沉入式高效BEAM加工。为解决高速电弧放电加工效率高，但加工精度有限的问题，提出了高速电弧放电加工表面质量改进的组合加工方法，使其具有高效、低成本和较好表面质量的特点。实现了多件航空航天应用背景样件的加工，为高速电弧放电加工技术迈向工业应用奠定了基础。