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Abstract

A description of the term “machinability” is given, and it is shown that the behaviour of the metal being machined, called “true machinability”, and also the conduct of the tool, known as “cutability”, are separate and distinct factors in the metal cutting process. The action of cutting-fluids is shown to be a modifying factor.

Recent work at one laboratory in the field of “true machinability” is described, and includes the effects on this property of hardness, rate of work hardening, microstructure, manganese segregations, and the size of lead globules. The effects on surface finish of speed in turning and some aspects of interest which arise under conditions of intermittent cutting, such as shaping, are included.

Under new work on “cutability” is mentioned the modifying effect on that factor of surface austenite, produced by grinding, and metallic segregations, as shown by micro-radiography. A general description is given of the properties and performance of milling cutters produced by a casting process. Developments in the field of cutting-fluids are noted.

Future trends in the developments of all the important fields of machinability are especially discussed, in view of the present alloy shortage. The use of ceramic materials and low tungsten and molybdenum high-speed steels as cutting-tool materials is mentioned, and also the application of new cutting techniques such as the “hot spot” and electrolytic/electro-erosion methods. Suggestions are made for improvements in both machining stock and cutting-fluids.

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Recent Developments in the Machinability of Steel

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