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RISS 인기검색어
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- 저자 : Jiangwen Liu (검색결과 2 건)
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Junfeng He,Zhongning Guo,Haishan Lian,Junjie Wang,Xiaolei Chen,Jiangwen Liu 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.1
Traditional micromilling leaves burrs and has a high surface roughness in the workpiece, which compromises the microstructural machining quality. Electrophoresis-assisted ultrasonic micromilling machining (EUMM) is proposed to solve this problem. An electrophoresis assisted electric field is applied to attract abrasive particles into the machining gap. Combined with the ultrasonic vibrations of the workpiece, the impact and grinding effect of these abrasive particles in the machining gap removes burrs that are generated during machining and reduces the surface roughness of the microstructure. Micro channels were generated for this study to verify the proposed method. The experimental results show that the EUMM significantly reduces burr formation during microchannel milling. The EUMM also decreases the surface roughness (Ra); the bottom roughness using the EUMM (0.33 µm) is lower than that with either the ultrasonic micromilling (UMM) or traditional micromilling. The EUMM also improves the sidewall roughness since the grinding and particle impacts significantly smooth the sidewalls. The particles during EUMM ensure a low surface roughness of 0.34 µm for the vertical sidewalls. Furthermore, the EUMM has a lesser effect on the width of the micro channels; as the spindle speed increases, the microchannel width only increases from 486 to 498 µm.
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Zhixiang Zou,Xiaoyu Zhang,Kangcheung Chan,Tai-Man Yue,Zhongning Guo,Can Weng,Jiangwen Liu 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.6
Micro-electrical discharge machining (micro-EDM) has an issue of uneven tool electrode wear that seriously affects the micro-hole accuracy. However, the mechanism of uneven tool electrode wear remains unclear. In this study, the uneven tool electrode wear mechanism has been studied both theoretically and experimentally. It was first discovered that the ultrafine debris particles produced by the EDM spark play a critical role in uneven tool electrode wear. A theoretical model was established to reveal the movement and the distribution of the debris by employing Einstein’s tea leaf paradox i.e., classic secondary flow theory and the electrophoretic theory. According to this model, when the polarity is positive, the ultrafine debris aggregates gradually and adheres onto the bottom of the micro-hole, thereby a debris layer of a parabolic profile is formed progressively. This dynamic debris layer shields the material to be removed by the EDM spark. As a result, the tip of the tool electrode is unevenly worn into a conical concavity shape. Conversely, under negative polarity, the tip of the tool electrode is unevenly worn into a conical shape. A set of experiments was performed to verify the model and the results agreed well with the predicted phenomena. Subsequently, a novel approach is proposed to eliminate the uneven tool electrode wear by reversing pulse polarity in a repetitive manner. Using this method, uneven tool electrode wear can be avoided and high accuracy micro-holes without the features of a cone and/or conical concavity can be obtained.
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