Experimental investigation into material removal mechanisms in High Speed Wire EDM
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ORIGINAL ARTICLE
Experimental investigation into material removal mechanisms in High Speed Wire EDM Kai Oßwald 1
&
Lukas Brandl 1 & Ingo Lochmahr 2
Received: 29 June 2020 / Revised: 21 September 2020 / Accepted: 15 October 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract High Speed Wire EDM (HSWEDM) is characterized by high relative velocities between its electrodes which appear in almost no other field of electrical discharge machining (EDM). Also, it previously has been described as a hybrid process. Consequently, material removal mechanisms show significant differences compared with other EDM processes. In this research, single discharge craters of HSWEDM processes were examined, and their geometrical features were associated with the underlying parameters. Discharge crater geometries on the workpiece electrode (anode) could be investigated by measurements whilst those on the wire electrode (cathode) were calculated. Results show that the high wire velocity leads to moving foot points on both electrodes. Pulse duration and the type of working medium influence the generation of discharge craters and thus their geometry and the modes of material removal. Static discharges and anodic dissolution could also be identified as material removal mechanisms and characterized in their geometrical properties. However, they are of secondary importance. Keywords Electrical discharge machining . EDM . High speed wire EDM . HSWEDM . Material removal mechanism
Abbreviations DC Discharge crater FP Foot point HSWEDM High Speed Wire Electrical Discharge Machining W Wire WE Wire electrode WP Workpiece List of Symbols di Diameters li Lengths n Number of samples s working gap te Discharge duration ti Pulse duration t0 Pulse interval time vw Wire velocity
* Kai Oßwald [email protected] 1
Institute for Materials and Material Technologies, Pforzheim University, Tiefenbronner Str. 65, 75175 Pforzheim, Germany
2
National Instruments Germany GmbH, Ganghoferstraße 70b, 80339 Munich, Germany
Δx ΔxFP
Relative movement of electrode during discharge duration te Deformation of plasma channel
1 Introduction High Speed Wire Electrical Discharge Machining (HSWEDM) has been described as a hybrid machining process in which different types of electric pulses lead to material removal [1]. In addition, a number of other features mark its difference to conventional wire EDM. The wire speed is typically set to 10–12 m/s and the (molybdenum) wire is continuously wound back and forth between two spools. The high wire speed is improving flushing significantly. Consequently, the workpiece is usually not submerged in working medium. In order to enable the hybrid process to take place, specific working media were developed that typically have conductivity values around 3 mS/cm. The pulse duration is commonly set to values between 20 and 50 μs and thus longer than in conventional wire EDM processes [2]. Recent publications on HSWEDM deal with aspects concerning the working medium [3, 4], phenomena in the working gap
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