Abstract: In-reactor maintenance of nuclear power plant components was typically performed by immersion in boric acid solution. In order to verify the feasibility of the EDM in boric acid solution, 2200 mg/L boric acid solution was used as the discharge medium for processing experiments. DOE were adopted to explore the effects of processing parameters on material removal rate, inlet diameter of hole, surface quality and electrode loss in boric acid environment, the small hole forming was realized under optimal electrical parameters, and the size accuracy of small holes and the distribution law of recast layer were analyzed. The results show that the discharge process of boric acid solution as the working medium is intense and produces a lot of bubbles. The bubble-assisted discharge and the mechanism of promoting chip removal may improve the material removal rate of EDM in boric acid solution. Under the optimal parameters of peak current I=24 A, pulse width Ton=20 μs and interpulse Toff=20 μs, the thickness of recast layer on the pore surface is small and there is no crack. Boric acid solution is suitable as the working medium of EDM. The research results may provide theoretical support for EDM of in-reactor parts maintenance in nuclear power plants.

Key words: boric acid solution, mechanism of electric discharge machining（EDM）, bubble, design of experiment(DOE), recast layer

摘要： 核电厂堆内零部件在线维修需要浸没在硼酸溶液中实施，为验证硼酸溶液中电火花加工（EDM）的可行性，以2200 mg/L的硼酸溶液为放电介质进行加工实验。采用实验设计（DOE）探究硼酸环境下工艺参数对材料去除率、通孔的入口直径、表面质量以及电极损耗的影响规律，在最优电参数下实现小孔成形加工，并分析小孔尺寸精度和再铸层分布规律。研究结果表明：硼酸溶液作为工作介质的放电过程剧烈且产生大量气泡，气泡辅助放电和促进排屑机理可以提高硼酸溶液中电火花加工的材料去除率；在峰值电流I=24 A、脉宽Ton=20 μs和脉间Toff=20 μs的最优参数下，小孔表面再铸层厚度较小且无裂纹；硼酸溶液适合作为电火花加工的工作介质。研究结果可为核电厂堆内零部件在线维修的电火花加工提供理论支撑。

关键词: 硼酸溶液, 电火花加工机理, 气泡, 实验设计, 再铸层