The Kinetics of Gas-Phase Lubrication in the Orthogonal Machining of an Aluminium Alloy

Tetrachloromethane (carbon tetrachloride) has been used as a model gas-phase lubricant to investigate the kinetics of lubrication in the low-speed orthogonal machining of a precipitation-hardened aluminium alloy, in a controlled low-pressure environment. The dependence of cutting force on lubricant gas pressure, feed (that is depth of cut in these experiments), cutting speed and interfacial temperature was investigated. The results are not consistent with previous theories of vapour-phase lubrication in which transport of the lubricant molecules is assumed to control the reaction rate. A new model is proposed involving activated chemisorption of the lubricant at the tool-chip interface. The predictions of this model are in good agreement with the experimental observations and an activation energy of 18.4 kJ/mol has been derived for the relevant reaction.