A precision ultrafine w-EDM (wire electrical discharge machining) technique specifically for machining intricate parts and structures is developed in this paper. A thumb-sized and versatile w-EDM device equipped with a complete control system for wire tension (ultrafine tungsten wire of 13 µm diameter) is designed and employed for the study of ultrafine w-EDM. The tension of the wire electrode is controlled by magnetic repulsive force to steady the wire during machining. Ultrafine wire cutting can be conducted in vertical-, horizontal- or slantwise-wire arrangements. Via some experiments, optimal machining conditions including discharge capacitance, feed rate, wire tension and the appropriate design for the w-EDM device are obtained. Two miniature samples including a micro of Taipei's landmark 101 building and a micro relay are fabricated and the feasibility of the proposed approach is verified. It is confirmed that the ultrafine w-EDM technique using an ultrafine tungsten wire of 13 µm was realized successfully.
This study presents the development of a drilling technique for an innovative tabletop drilling machine that combines micro-EDM with drilling to fabricate micro-holes in diamond-tool. The mechanisms designs of double V-shaped bearings and double spindles which provide a precision clamping and vertical alignment for diamond-tool and micro-tube are devised to enable to machine a co-centric micro-hole for micro-tool. A diamond-tool, made with copper-based sintered alloy, is drilled by using the developed technique of co-centric micro-hole EDM-drilling into a hollow shaft which can create equilibrium of drilling forces, prevent a drilling squeezing to be occurred and enable to offer a temporary storing space for drilling chips. Relative experiments including the determinations of drilling ratio and discharge capacitance are carried out via this established machine. Experimental results show that excellent geometric and dimensional accuracy of micro-holes on the diamond-tool can be achieved.
In this study on-machine measurement-assisted techniques are utilized in combination with micro-EDM to successfully machine intricate micro-parts. Two measurement approaches, automatic optical inspection (AOI) and critical contact measurement (CCM), are used on a previously built machine tool. AOI acquires the image from the contour of the machined workpiece and further processes the image to determine the finish allowance. CCM measures on-line the consumption of the microelectrode to create an accurate compensation rate. These two non-contact measurement techniques facilitate on-machine error detection and re-machining during micro-EDM. Significant work efficiency and preservation of machining accuracy are gained by having the workpiece and tool remain in place throughout machining procedures. A micro-probe with a diameter of 30 µm and a micro 3D engraving mold on a small tungsten steel ball are perfectly fabricated and verified, respectively.
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