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Title: Micro electrical discharge machining : axis-symmetric component manufacture and surface integrity
Author: Rees, Andrew
ISNI:       0000 0004 2752 0831
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2011
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The development of micro engineering is highly dependent on the machining processes that support it. Micro Electrical Discharge Machining (uEDM) is one of the key enabling technologies for the fabrication of micro tools and micro components. The capabilities of this machining technology have to be studied to determine the process capabilities and constraints. The present work investigates factors that influence the process of uEDM and the components that can be produced by applying this technology. Chapter 2 reviews the current state of the art in this field. In addition, different aspects related to the process capabilities are discussed, especially, the factors that affect the quality of electrodes produced on-the-machine, surface roughness optimisation/prediction and the effect of material micro structure on resultant surface integrity. In Chapter 3 factors affecting the quality of electrodes produced on the machine through the process of Wire Electro-Discharge Grinding (WEDG) are investigated. The effects that electrode material, machining strategy and machine accuracy have on the electrode re-generation are studied. Then, in Chapter 4, the effects of process parameters on the resulting surface finish after performing WEDG are investigated in order to identify an optimum processing window. In addition, a method for predicting the resulting surface finish is proposed. In Chapter 5 a comparative study is carried out to investigate the effects of material microstructure refinement on the resulting surface integrity of samples machined by Micro Wire Electrical Discharge Machining (uWEDM). In particular, the process- material interactions on the resulting micro hardness, phase content changes, Heat Affected Zone (HAZ), surface roughness, micro cracks, recast layers formation, Material Removal Rate (MRR) and element spectrum after both rough and finishing uWEDM cuts are studied. Finally, in Chapter 6 the main contributions to knowledge as a result of the carried out research are presented. They can be summarised as follows: The choice of electrode material used when applying the process of WEDG has a significant effect on achievable aspect ratio and surface roughness. The application of specially developed dressing strategies has a major impact on the quality of the electrode. Due to the inherent process errors related to machine accuracy and repeatability of the WEDG process, specialised "adaptive control" systems need to be developed and implemented to increase the process accuracy. Technological parameters that are optimised for conventional juWEDM are not directly applicable for use with the WEDG process as they do not provide comparable results in respect to surface finish. The application of inductive learning algorithms is a simple and cost-effective method for identifying patterns in the process behaviour and thus to create models for on-the-machine prediction of the surface roughness. Material microstructure refinement does not only provide superior mechanical properties to workpiece materials but also leads to favourable machining "footprints" during uWEDM machining and a lower surface roughness. Surface contamination due to the alloying of the tool electrode with the workpiece material is always present regardless of material microstructure, and thus can limit the application areas of this technology.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available