- 學位論文
微放電加工效率與能力提昇之研究
Studies on Improvements for Efficiency and Capability of Micro-EDM Process
摘要
本研究針對電容式微放電電源成功開發了一新型之伺服進給策略。此策略主要採階層式架構，具有粗調節與細調節兩個階層。粗調節部分使用傳統之平均電壓法作為參考訊號，再利用以波形分類為基礎之微放電加工線上監視系統作為細調節控制進給速率之參考依據，細調節部分採用比例控制法，將極間維持在穩定狀況，以提昇放電效率；之後使用直徑300μm之電極進行微放電穿孔與盲孔加工實驗。在厚度1.2mm之鋁合金薄片穿孔加工中，證明使用此系統進行控制，可將傳統定速進給法之加工速率自1.83μm/s提昇至3.72μm/s，約為2倍；形狀精度方面可將孔錐度從3.6°抑制至2.7°；在鋁合金盲孔加工中實際加工深寬比亦可自5提昇至10，為2倍；進給深度為1.5mm時，加工速率可自2.66μm/s提昇至4.31μm/s，為1.6倍；在不銹鋼盲孔加工中可提昇加工深寬比自4.6至8.8，約為1.9倍；進給深度為1.5mm時，加工速率可自0.45μm/s提昇至0.58μm/s，為1.27倍。 另外，本研究針對傳統電容式放電電源之缺點進行了改善，設置一電晶體開關於電容式電路之放電迴路中，並配置適當開關頻率，使電容可在充滿電之狀態下進行放電而不受極間狀態影響，進而提昇放電效率。在定深度鋁合金盲孔加工實驗中證實了此新型電源較傳統之電容式電源在鑽削至深寬比4.6時，時間從1262秒減至837秒（效率提昇34%）。此外，本研究亦針對此新型電源發展比例控制策略，並使用直徑300μm之電極進行微放電穿孔與盲孔實驗。實驗結果顯示，在厚度1.2mm之鋁合金穿孔實驗中，孔錐度可抑制在0.63°；在加工效率方面，在進給深度1.5mm時加工速率可從1.83μm/s提昇至4.36μm/s，約為純電容式放電定速進給策略之2.4倍；在鋁合金盲孔加工中，相較純電容式定速進給策略可將加工深寬比自5提昇至12，為2.4倍；進給深度為1.5mm時，加工速率可自2.66μm/s提昇至4.29μm/s，約為1.6倍；在不銹鋼盲孔加工中亦可將加工深寬比自4.6提昇至10，為2.14倍；進給深度為1.5mm時，加工速率可自0.45μm/s提昇至0.83μm/s，為1.82倍。
並列摘要
In this study, a pulse discrimination method of the RC circuit was taken to develop a servo control system of micro-EDM. The main structure of the controlling strategy is a hierarchical type control method composed by coarse and fine control. Average voltage across the resistance Vr, which is usually a control index in conventional Micro-EDM process, is taken properly as a reference signal for coarse controlling purpose. The pulse discriminating system which is an innovative monitor for Micro-EDM was employed in this paper. The composition of pulse type can be analyzed and taken as an index of gap deterioration for fine control, which is based on the proportional control method. During the process, feed rate would be adjusted to a proper speed to maintain a good gap distance for normal discharging. In the experiments of micro-EDM through holes drilling with an electrode of 300μm diameter and a 6061 aluminum alloy specimen, which is 1.2mm thick, the drilling velocity can be enhanced from 1.83μm/s to 3.72μm/s, which is 2 times faster comparing with RC constant feed strategy. The taper angle can be reduced from 3.6° to 2.7°. In blind holes drilling, the aspect ratio can be increased from 5 to 10 and from 4.6 to 8.8 on a block of 6061 aluminum alloy and SUS304 stainless steel, which is 2 and 1.9 times deeper than RC constant feed strategy, respectively. The drilling velocity can be increased from 2.66μm/s to 4.31μm/s and from 0.45μm/s to 0.58μm/s on a block of 6061 aluminum alloy and SUS304 stainless steel, which is 1.6 and 1.27 times faster than RC constant feed strategy, respectively. In the other way, a transistor has been put into the discharge part of the RC circuit, instead of the charging part, to improve the efficiency in this study. Under a proper switching frequency, the capacitance can be fully charged without the influence of gap condition and the performance can be enhanced accordingly. In blind holes drilling experiment, this new transistor-RC circuit performs 34% better than a traditional RC circuit, which takes 837 and 1262 seconds, respectively, when drilling aspect ratio is at 4.6. The proportional control strategy has also been developed with this new power circuit, and an electrode of 300μm diameter was adopted in both through and blind holes drilling experiments. The taper angle can be reduced to 0.63° in through holes drilling, and the drilling velocity can be enhanced from 1.83μm/s to 4.36μm/s, which is 2.4 times faster comparing with RC constant feed strategy. In blind holes drilling, the aspect ratio can be increased from 5 to 12 and from 4.6 to 10 on a block of 6061 aluminum alloy and SUS304 stainless steel, which is 2.4 and 2.14 times deeper than RC constant feed strategy, respectively. The drilling velocity can be increased from 2.66μm/s to 4.29μm/s and from 0.45μm/s to 0.83μm/s on a block of 6061 aluminum alloy and SUS304 stainless steel, which is 1.6 and 1.82 times faster than RC constant feed strategy, respectively.