Studies on Improvements for Efficiency and Capability of Micro-EDM Process
Date Issued
2010
Date
2010
Author(s)
Chang, Ting-Yen
Abstract
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.
Subjects
RC circuit
pulse discriminating
hierarchical control
transistor-RC circuit
Type
thesis
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