Abstract
The historical background of electro-erosion technique is briefly outlined and the difference between spark and arc*** discharges is defined. The underlying principle of the relaxation-type spark circuit as employed in industrial machines is explained, and development trends are discussed. The various factors bearing upon the efficiency of spark-erosion operations are enumerated. The mechanical features of a typical spark-erosion machine are described, and the range of machining operations for which spark cutting machines can be designed, is outlined. Typical samples of work produced on a commercial unit are described and illustrated, and the properties of spark-machined surfaces are discussed.

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