Electrochemical machining passivation

Electrochemical machining is a recent innovation, the practice dating back less than twenty-five years. Much of the driving force for its development has come from the aerospace industry with its requirement to machine very hard alloys (e.g. those based on Ti and Fe/Co/Ni/Cr) to produce components able to perform a function reUably but also having minimum weight this specification often leads to components of very complex shape. The alloys which must be employed cause problems in conventional machining because of the low rate of metal removal and the short tool life. Electrochemical machining is, however, based on different properties of the metal independent of its hardness and it is only necessary to find an electrolyte where the alloy will dissolve anodically without passivation when the rate of metal removal may be estimated from Faraday s law. 

Electrochemical machining (ECM) relies upon a high local current density and control of the anodic dissolution such that passivation (Chapter 10) does not... 

In electrochemical grinding, the mechanical removal of both the passive anodic film and the metal proceeds concurrently with the anodic dissolution. In this method, normally electrolytes, in which the metal dissolution is localized only on the areas of abrasive depassivation, are used. This enhances the machining accuracy in relation to the ECM. As compared with mechanical grinding, the combined method is characterized by a significantly lower tool wear and a high productivity. 

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