Wear, tool-electrode

Table 6.1 Tool-Electrode Wear for Gravity-Feed Drilling [76]...

Note that the drilling evolution shown in Fig. 7.8 is also affected by the wear of the tool-electrode. However, the amount of tool-electrode wear during one minute of drilling is below a few micrometres (see [76] and Table 6.1). 

As more OH radicals are present in the case of an active anode than for an active cathode, chemical etching is also more important. Consequently, the surfaces are smoother than those obtained by cathodic machining [63,120]. However, when using anodic polarisation, the tool-electrode will be anodically dissolved resulting in high tool wear. 

To date very little is known about tool wear. The two major causes of tool wear are chemical etching and anodic dissolution. The discharge activity at the tool-electrode may also cause some tool wear, but to date this has never been quantified. Based on the author s personal experience, tool wear is not a serious problem, and even after machining with the same tool-electrode (stainless steel) for several hours, no significant tool-wear could be measured. 

With the alternative ECM technique, hard metals can be shaped electrolytically and the rate of machining does not depend on their hardness. Moreover the tool-electrode used in the process does not wear, and therefore soft metals can be used as tools to form shapes on harder workpieces, unlike oonventioned practice. The bases of ECM will first be described in the paper. Then some unsolved research problems will be discussed. Industrial applications, which illustrate how the process is used in practice, will be investigated. 

Chromium carbide is important in powder preparations designed for thermal spray apphcations of corrosion and wear-resistant coatings on tool and machine parts. Lower carbon carbides of chromium are important in hardfacing tods and electrodes for weld-apphed ovedays on machine wear surfaces. However, these carbides are usually formed in situ from Cr and C in the rod and not added as preformed carbides. The properties of Ci2C2 are hsted in Table 2. 

Electrodes for electric discharge machining are partially coated with pyrolytic boron nitride in order to prevent undesirable electric discharge between the electrode and a workpiece [330]. A boron nitride layer is used to prevent bonding of a conductive material, applied for indicating wear, to hard tool ceramics [331]. Equipment for applying pyrolytic boron nitride layers has been described [332], and also for applying boron nitride as protective sheets for immersion pyrometers for molten metals [333]. 

The fourth column shows the mass lost by the tool (blade, disc, nozzle, electrode) related to the section cut (coefficient of tool wear). The mass of secondary solid waste related to the section cut is found, for each trial configuration, by adding the relevant lines in columns 3 and 4. 

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