Abstract
Micro EDM is a known nonconventional process for the machining of hard to cut materials. Due to its ablating nature based on melting and evaporation through heat induced by electrical discharges it is independent of hardness, toughness or brittleness of the workpiece. Because of these benefits, EDM is widely used in tool- and mould making; micro-EDM with its much lower discharge energies has been successfully applied to micromachining of high-accuracy parts. The precision manufacturing of high aspect ratio micro geometries such as deep micro bores relies on stable process conditions in the discharge gap. Its minimisation – precondition for minimal feature size and highest accuracy – limits the effectiveness of conventional flushing techniques, leading to a higher fraction of unwanted discharge states (open and short circuit), lower process speed and geometrical errors. New hybrid technology approaches such as ultrasonic or low frequency superposition significantly raise process stability and speed. Another restriction to EDM, the exclusive machinability of electrically conductive materials, is overcome by the application of the assisting electrode method that enables a micro-ED-machining of nonconductive zirconium oxide ceramics. This paper presents the current status of investigation into the micro-EDM process with ultrasonic vibration assistance – directly applied to the workpiece and indirectly applied high-intensity ultrasonic to the dielectric – in metallic materials as well as into the machining of electrically nonconductive ceramic materials. Using ultrasonically aided micro-EDM, the process speed can be raised by up to 40%, enabling bores of less than 90μm in diameter with aspect ratios >40 for metallic materials. The modified setup using the assisting electrode principle allows for machining of aspect ratio >5 for nonconductive ceramic materials, leading to new possibilities for the design and manufacture of complex, high-accuracy micro parts in high-performance engineering materials.
Highlights
Electro discharge machining (EDM) is a known and widely used nonconventional machining process for hard to cut materials because of its ability to function independently of the hardness, brittleness or toughness of the workpiece
More and more high-tech materials such as ceramics are being used for micro parts; this presents an opportunity to apply μEDM in that emerging material area
A standard μEDM machine tool was used for the experiments (Sarix T1-T4) and was modified to comply with the special requirements of μEDM of nonconductive ceramics
Summary
Electro discharge machining (EDM) is a known and widely used nonconventional machining process for hard to cut materials because of its ability to function independently of the hardness, brittleness or toughness of the workpiece. The noncontact nature of the process results in a nearly force-free machining, allowing the usage of soft, easy to machine electrode materials even when shaping very hard workpieces. The discharge gap width is commonly regulated based on the mean gap voltage (ue) that delivers different levels for the normal, short or open circuit state Depending on this and a set target value, the electrode is fed or withdrawn (feed s) (Fig. 3). In μEDM, gap widths of wGP ≤ 10 μm are common The combination of these factors leads to large difficulties in efficient flushing and new approaches have to be taken to ensure stable process conditions. One option is the direct vibration of the workpiece, which can be considered a high frequency version of the flushing by lifting principle
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