Abstract: Micro-detonation of striking arc machining is a newly developed special machining technology for engineering ceramics and its energy output is by plasma jet. For there are intense light and heat while machining, it is very difficult to observe the plasma jet. By means of high speed photography and spectroscopic diagnosis, the external morphology and internal physical state of plasma jet are studied. The external appearance of plasma jet and material removal process of Si3N4 and Al2O3 are observed by using high speed photography. The observation finds that the diameter of jet increases with the increase of electric current and the diameter of ablation pit in single pulse machining expands gradually with machining time. The shape of ablation pit seems like a spherical cap. Combined with the propertiesy of materials, it can be inferred that the Si3N4 decomposes and Al2O3 melts during machining. For spectral analysis of the plasma jet, hydrogen atomic tracing method is employed and Hα spectral line is chosen. Results of analysis show that the electron density of plasma, which is obtained by Stark broadening method, is in the range of 1016 to 1017 cm–3 and reaches the condition of local thermodynamics balance. The influence regularity of machining parameters to electron density is analyzed.

Key words: Engineering ceramics, High speed photography, Micro-detonation of striking arc machining, Plasma jet, Spectroscopic analysis