Electrochemical machining is a process that has the potential to machine complex full-form shapes at high production rates. The economic utilisation of this process, however, has been impeded by the iterative trial and error approach that is often required to generate process specifications for any one machining set-up. This approach arises due to the incompleteness of models used to describe the complex physical, chemical and hydrodynamic parameter interdependencies. Such interdependence results in non-ideal effects that distort the transfer geometry between the tool shape and the required workpiece form. In this thesis a semi-empirical characterisation strategy, aimed at mapping out parameter interdependence through a single characterisation trial is proposed. This approach has been realised through the development of a segmented tooling assembly that enables the probing of spatial parameters sensitivities and through the development of distributed gap measurement system. The combined use of these systems, in the form of the characterisation cell assembly, has enabled detail parameter mappings to be carried out within a procedure taking only a few minutes to complete. The concept of the C-function expression is introduced as a means of representing parameter independence generated by the characterisation trials. This expression represents non-ideal effects as a spatial series, descretized along intervals of flow path length, with coefficients representing the sensitivity of gap size to primary process variables. Characterisation trials have been carried out using both titanium and nickel based alloys machined using chloride and nitrate based electrolytes. The method has also been applied to an analysis of one of the recently developed titanium aluminide alloys. These trials have identified a range of parameter interdependencies. Most significantly these have included an observation of the previously unknown phenomenon which has been termed electrochemical hysteresis, and a range of spatial characteristics in the dependencies between current density, flow velocity and gap size. The use of the C-function as a means of representing these characteristics is demonstrated by extrapolating planar characterisation data to shape prediction for a 2-D double-cosine profile.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643269 |
| Date | January 2001 |
| Creators | Clifton, David |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13433 |
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