Development of an electrochemical micromachining (μECM) machine

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.Electrochemical machining (ECM) and especially electrochemical micromachining (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 such as microfluidics systems and stressfree drilled holes in the automotive and aerospace sectors. Electrochemical machining is considered as a non-conventional machining process based on the phenomenon of electrolysis. This process requires maintaining a small gap - the interelectrode gap (IEG) - between the anode (workpiece) and the cathode (tool-electrode) in order to achieve acceptable machining results (i.e. accuracy, high aspect ratio with appropriate material removal rate and efficiency). This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has 3 axes of motion (X, Y and 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 2nmresolution 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. A pulse power supply unit (PSU) and a special control algorithm have been implemented. The pulse power supply provides not only ultra-short pulses (50ns), but also plus and minus biases as well as a polarity switching functionality. It fulfils the requirements of tool preparation with reversed ECM on the machine. Moreover, the PSU is equipped with an ultrafast over current protection which prevents the tool-electrode from being damaged in case of short-circuits. Two different process control algorithms were made: one is fuzzy logic based and the other is adapting the feed rate according to the position and time at which short-circuits were detected. The developed machine is capable of drilling micro holes in hard-to-machine materials but also machine micro-styli and micro-needles for the metrology (micro CMM) and medical sectors. This work also presents drilling trials performed with the machine with an orbiting tool. Machining experiments were also carried out using electrolytes made of a combination of HCl and NaNO aqueous solutions. The developed machine was used to fabricate micro tools out of 170μm WC-Co alloy shafts via micro electrochemical turning and drill deep holes via μECM in disks made of 18NiCr6 alloy. Results suggest that this process can be used for industrial applications for hard-to-machine materials. The author also suggests that the developed machine can be used to manufacture micro-probes and micro-tools for metrology and micro-manufacturing purposes.Brunel University European Commissio

Hybrid micro-machining processes : a review

Micro-machining has attracted great attention as micro-components/products such as micro-displays, micro-sensors, micro-batteries, etc. are becoming established in all major areas of our daily life and can already been found across the broad spectrum of application areas especially in sectors such as automotive, aerospace, photonics, renewable energy and medical instruments. These micro-components/products are usually made of multi-materials (may include hard-to-machine materials) and possess complex shaped micro-structures but demand sub-micron machining accuracy. A number of micro-machining processes is therefore, needed to deliver such components/products. The paper reviews recent development of hybrid micro-machining processes which involve integration of various micro-machining processes with the purpose of improving machinability, geometrical accuracy, tool life, surface integrity, machining rate and reducing the process forces. Hybrid micro-machining processes are classified in two major categories namely, assisted and combined hybrid micro-machining techniques. The machining capability, advantages and disadvantages of the state-of-the-art hybrid micro-machining processes are characterized and assessed. Some case studies on integration of hybrid micro-machining with other micro-machining and assisted techniques are also introduced. Possible future efforts and developments in the field of hybrid micro-machining processes are also discussed

Micro-Electro Discharge Machining: Principles, Recent Advancements and Applications

Micro electrical discharge machining (micro-EDM) is a thermo-electric and contactless process most suited for micro-manufacturing and high-precision machining, especially when difficult-to-cut materials, such as super alloys, composites, and electro conductive ceramics, are processed. Many industrial domains exploit this technology to fabricate highly demanding components, such as high-aspect-ratio micro holes for fuel injectors, high-precision molds, and biomedical parts.Moreover, the continuous trend towards miniaturization and high precision functional components boosted the development of control strategies and optimization methodologies specifically suited to address the challenges in micro- and nano-scale fabrication.This Special Issue showcases 12 research papers and a review article focusing on novel methodological developments on several aspects of micro electrical discharge machining: machinability studies of hard materials (TiNi shape memory alloys, Si3N4–TiN ceramic composite, ZrB2-based ceramics reinforced with SiC fibers and whiskers, tungsten-cemented carbide, Ti-6Al-4V alloy, duplex stainless steel, and cubic boron nitride), process optimization adopting different dielectrics or electrodes, characterization of mechanical performance of processed surface, process analysis, and optimization via discharge pulse-type discrimination, hybrid processes, fabrication of molds for inflatable soft microactuators, and implementation of low-cost desktop micro-EDM system

New Methodologies in the field of micromanufacturing

Manufacturing processes are continually improving and updating with a view towards enhancing productivity. With the rapid development of technology, the demand for miniature, lightweight and advanced products is increasing. To compensate these emerging global trends towards the miniaturization of products, the electrochemical micromachining (µECM) is a promising technique. The µECM utilizes high frequency pulses for micron to nano-scale dissolution process that can be driven by with or without feedback control systems. This thesis includes the activities performed during the last three years, as the development of electrochemical micromachining workcell, fabrication of microtools, parametric effects analysis, and fabrication of various microproducts on some noble materials. During microtool fabrication, tungsten micro shafts of 0.38 mm are electrochemically etched to fabricate the desired cylindrical tools with or without conical tips. In the fabrication of microtool, electrolyte concentrations are varied in the range to 0.08–2.0 M KOH for the applied potential differences of 3–15 V AC and different etching time. The microtool fabrication process has been monitored by measuring the size, shape and overall tool geometry. These prefabricated microtools are used in the fabrication of various microdrilling and micromilling processes, especially in the fabrication of single hole micronozzles, multiple hole micronozzles array and microhole fabrication on vitrectomy needles. A mathematical model has been developed for the analysis of material removal rate (MRR) based on pulsed electrical power applied in µECM. The parametric effects of the process are studied on applied potentials, electrolyte temperature, applied frequency and its duty cycle, the dimension of microtools. For the parametric effect analysis, material removal rate, machining time, the number of short circuits, the shape and size of the fabricated microproducts are considered as response factors. The proper experimental parameters, the relationship between the parameters and the distribution of metal removal are established from the experiments worked out. The experimental micromachining tests show that MRR increases with the increase in applied potential, duty cycle, the electrolyte temperature, and microtool diameter, whereas MRR decreases with baseline potential in a certain range, applied frequency, and tool length. Machining time shows the opposite trend of MRR for all the parameters except microtool diameter. It increases with increasing microtool diameter. The microtool feed rate also has a significant effect on the dimension of fabricated microproducts. The waveforms generated during machining are analyzed; an in-process monitoring and control process has also been developed based on the waveforms. The result shows that the shape of the waveform and its corresponding values are in good agreement with the MRR, machining time and on the dimension of fabricated microholes. The proposed monitoring technique could be employed as a predictive tool in electrochemical processing. Finally, the microtools fabricated have been used for fabricating micronozzles and micropockets on nickel plates, microholes on high grade stainless steel to realize the practical applications of microdrilling process

Simultaneous Micro-EDM and Micro-ECM in Low-resistivity Deionized Water

Ph.DDOCTOR OF PHILOSOPH

Electro-Discharge Machining of Ceramics: A Review

Conventional machining techniques of ceramics such as milling, drilling, and turning experience high cutting forces as well as extensive tool wear. Nevertheless, non-contact processes such as laser machining and electro-discharge machining (EDM) remain suitable options for machining ceramics materials, which are considered as extremely brittle and hard-to-machine. Considering the importance of ceramic machining, this paper attempts to provide an insight into the state of the art of the EDM process, types of ceramics materials and their applications, as well as the machining techniques involved. This study also presents a concise literature review of experimental and theoretical research studies conducted on the EDM of ceramics. Finally, a section summarizing the major challenges, proposed solutions, and suggestions for future research directions has been included at the end of the paper

Electrochemical micromachining: An Introduction

Copyright © 2016 The Author(s). Electrochemical machining (ECM) is a relatively new technique, only being introduced as a commercial technique within the last 70 years (1). A lot of research was conducted in the 1960s and 1970s but research on electrical discharge machining (EDM) around the same time slowed ECM research (2). The main influence for the development of ECM came from the aerospace industry where very hard alloys were required to be machined without leaving a defective layer in order to produce a component which would behave reliably (3). ECM was primarily used for the production of gas turbine blades (2) or to machine materials into complex shapes that would be difficult to machine using conventional machining methods (4). Tool wear is high and the metal removal rate is slow when machining hard materials with conventional machining methods such as milling. This increases the cost of the machining process overall and this method creates a defective layer on the machined surface (3). Whereas with ECM there is virtually no tool wear even when machining hard materials and it does not leave a defective layer on the machined surface. This paper reviews the application of electrochemical machining with regards to micro-manufacturing and present state of the art micro ECM considering different machined materials, electrolytes and conditions used.The research reported in this article was supported by the European Commission within the project ‘Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)’ (FP7-2011-NMP-ICT-FoF-285614)

Quality assessment and improvement on spark assisted chemical engraving gravity feed micro-drilling

This thesis presents an investigation on the gravity feed micro-drilling spark assisted chemical engraving (GFMD-SACE). The competitive advantage of the GFMD-SACE process is its combined simplicity and low-cost with high aspect ratio and smooth surface finish. As long as these values are well-preserved and intensified, this process will take a share in the market of micro-fabrication. The main objective of this study is to establish a systematic approach of the improvement in GFMD-SACE by minimizing initially different variabilities in the process. The methodology is to observe in details the process by adapting the six sigma procedures to determine the major error states and their root causes. To this end, the process initial documentations are created such that it keeps the door wide open for continuous improvement. Based on the initial evaluation, an improved process is recommended on the tool electrode thermal and material properties, electrolyte levels and the use of pulse voltage. Compared to the traditional process, the improvement procedure shows less variability and more capability to achieve high quality in micro-drillin

Micro-EDM Process for Tool-based Compound Micromachining

Ph.DDOCTOR OF PHILOSOPH