Design of a pulse power supply unit for micro-ECM

Electrochemical micro-machining (μECM) requires a particular pulse power supply unit (PSU) to be developed in order to achieve desired machining performance. This paper summarises the development of a pulse PSU meeting the requirements of μECM. The pulse power supply provides tens of nanosecond pulse duration, positive and negative bias voltages and a polarity switching functionality. It fulfils the needs for tool preparation with reversed pulsed ECM on the machine. Moreover, the PSU is equipped with an ultrafast overcurrent protection which prevents the tool electrode from being damaged in case of short circuits. The developed pulse PSU was used to fabricate micro-tools out of 170 μm WC-Co alloy shafts via micro-electrochemical turning and drill deep holes via μECM in a disk made of 18NiCr6. The electrolyte used for both processes was a mixture of sulphuric acid and NaNO3 aqueous solutions.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMP-ICT-FoF-285614

Design of an electrochemical micromachining machine

Electrochemical micromachining (μECM) is a non-conventional machining process based on the phenomenon of electrolysis. μECM became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications including microfluidics systems, stress-free drilled holes in automotive and aerospace manufacturing with complex shapes, etc. This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has three axes of motion (X, Y, Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2-nm resolution encoders for ultra precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. This machine features two process control algorithms: fuzzy logic control and adaptive feed rate. A self-developed pulse generator has been mounted and interfaced with the machine and a wire ECM grinding device has been added. The pulse generator has the possibility to reverse the pulse polarity for on-line tool fabrication.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMPICT- FoF-285614)

The effect of high frequency and duty cycle in electrochemical microdrilling

Pulse electrochemical micromachining possesses attractive features compared to conventional electrochemical machining processes based on a continuous current because it allows instantaneous electrochemical reaction by applying ultrashort voltage pulses. This study focuses on effects of applied frequency and duty cycle in electrochemical microdrilling on nickel plate. During microtool fabrication, tungsten micro-shafts are electrochemically etched to make two desired cylindrical microtools of different lengths and diameters to investigate the effects of pulsed frequency and duty cycle on electrochemical micromachining. The shape and size of the fabricated microholes, machining time, actual material removal rate (MRR(act)) and the number of short circuits are considered as response factors. Shapes of micro-drilled holes are measured and compared to tool geometry. As for both short and long microtools, MRR(act) and machining time respectively decreased and increased with an increase in applied frequency. But the MRR(act) and machining time respectively increased and decreases with an increase in duty cycles. Experimental data reveals that there is a strong correlation among the shape and size of the microhole fabricated with applied frequency and duty cycle during microdrilling. However, MRR(act) was found to be much higher for short tool than a long tool