عنوان مقاله
مدلسازی دهانه شعاعی تشکیل شده توسط انحلال مواد در حفاری micro-EDM وmicro-ECM همزمان با استفاده از آب یون زدوده
فهرست مطالب
مقدمه
تحلیل تئوری
نتایج شبیه سازی
تائید آزمایشی
نتیجه گیری
بخشی از مقاله
اثر فاصله دهانه
شکل 4a داده های شبیه سازی شده چگالی جریان را برای فاصله دهانه اولیه مختلف در حین یک دوره پالس نشان میدهد. فرکانس پالس و نسبت کار بترتیب در 500 kHz و 0.3 ثابت می گردد. می توان مشاهده کرد که چگالی جریان می توان برای دهانه 5-𝜇𝑚 به مقدار اوج خود برسد. این بدین معناست که لایه دوگانه فرض می شود که بطور کامل شارژ شده است. بر عکس، برای فاصله دهانه بالاتر مشاهده می گردد ، که چگالی جریان کاهش داده می شود و حتی نمی تواند به مقدار اوج خود هم برسد.
کلمات کلیدی:
Modeling of radial gap formed by material dissolution in simultaneous micro-EDM and micro-ECM drilling using deionized water Minh Dang Nguyen n , Mustafizur Rahman, Yoke San Wong National University of Singapore, Department of Mechanical Engineering, 9 Engineering Drive 1, 117576, Singapore article info Article history: Received 27 July 2012 Received in revised form 5 December 2012 Accepted 10 December 2012 Available online 25 December 2012 Keywords: Micro-EDM Micro-ECM Deionized water Short pulses Modeling Radial gap abstract For enhancing the surface finish of micro-holes, micro-EDM and micro-ECM have been combined in a unique hybrid machining process by using low-resistivity deionized water as bi-characteristic fluid. The affected material layer generated by electric sparks is further dissolved from machined surface owing to the effect of electrochemical reaction. To maintain the dimensional accuracy of micro-holes, short voltage pulses are applied to localize the material dissolution zone and thus the thickness of further removed material layer is of prime importance in deciding the final dimension of micro-holes. This study presents the modeling of radial gap distance in simultaneous micro-EDM and micro-ECM drilling by predicting the thickness of material layer further dissolved by electrochemical reaction. The analytical approach incorporating the double-layer theory, the Butler–Volmer equation and the Faraday’s law of electrolysis is used to simulate the radial gap distance for different pulse parameters. The simulation data is then verified with the experimental results. It is observed that the applied pulse parameters directly affect the final dimension of obtained micro-holes. The effectiveness of short voltage pulses in localizing the material dissolution zone is found to be in accordance with the doublelayer charging characteristic. When the pulse duration is too short, the material dissolution is negligible and SEDCM has no effect on improving the inner surface of micro-hole. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Owing to the remarkable advantage which is negligible cutting force, micro-electric discharge machining (micro-EDM) is a preferable process for machining micro-shapes [1,2]. However, microEDM still has some disadvantages which stem from its own material removal mechanism. Because the material is removed through melting and vaporization, the machined surface is made up with thermally damaged layers [3,4]. The uppermost layer, which has been known as the white layer or recast layer, has high residual stress and may contain micro-cracks. Beneath this recast layer are the other heat affected zones which undergo material structure alteration. In addition, the texture of generated surface is characterized by the overlapping of numerous discharge craters which usually associates with high irregularities [5]. The enhancement of surface generated by micro-EDM is thus highly desirable. For improving the surface integrity of machined shapes, electrochemical micromachining (micro-ECM) has been combined as a sequential process after micro-EDM. Because the material removal mechanism is based on the ionic dissolution, the surface generated by micro-ECM is relatively smooth and free of residual stress as well as micro-crack [6]. This approach has also been studied in several researches [7–10]. The results from these studies demonstrate that ECM could be used as an effective method to reduce the roughness of surfaces generated by EDM. For small-size products and micro-scale applications, the solution with significantly low conductivity such as deionized water has been used as a weak electrolyte in enhancing the surface finish of micro-shapes by microECM. The lateral surface integrity of micro-pin and micro-hole has been reported to be enhanced by some researchers [11,12]. Although such low conductivity solution has been used to moderate dissolution rate, the stray material dissolution is a challenging issue for micro-machining. It is realized that when being exposed to long dissolution time or using significantly low resistivity deionized water, the machined shapes is distorted due to the excessive material removal by electrochemical reaction [12,13]. Recently, the EDMed surface of micro-shapes has also been improved by performing micro-ECM right after micro-EDM [14]. Although they are carried out in the same machine tool, the machining fluid needs to be changed from dielectric fluid to electrolyte and different power supply is also required for micro-ECM. In that scenario, micro-EDM and micro-ECM have been combined in a unique machining process, known as simultaneous micro-EDM and micro-ECM (SEDCM), to produce micro-shapes with better surface integrity [15,16]. In this method, low-resistivity
