The importance of oxygen in dry machining of metal on a lathe

Abstract

Experiments have been made during machining operations carried out in a vacuum chamber. It is found that vapours and gases can influence the cutting, and that oxygen is particularly effective in reducing cutting forces and improving surface finish. This observation is supported by cutting and friction tests on an ordinary lathe, with jets of oxygen or nitrogen directed at the tool-chip interface. It is concluded that the action of oxygen is primarily to restrict the formation of an adherent built-up nose of metal on the tool, which may reach a large size during vacuum machining. Calculation of the rate of collision of oxygen molecules with the fresh chip surface suggests that there is not time for formation of a monatomic layer on the undersurface of the chip before it leaves the tool face contact, so the adsorption on the tool itself is likely to be the more important factor. The effectiveness of a lubricating film on the tool face was demonstrated by coating the tool with MoS2, which prevented the build-up, in vacuo, until the coating wore away.