VAPOUR LUBRICATION IN FRICTION AND LO W-SPEED METAL CUTTING

An experimental study of metal cutting in a vacuum and of the influence of atmospheric gases and lubricating vapours is described. A lathe equipped with a vacuum chamber is used with a calibrated tool-bar. Experiments have been conducted with mild steel, copper, and aluminium. Oxygen is shown to have a strong influence on the cutting of mild steel, and it is suggested that this is attributable to the reduction of adhesion between tool and chip, especially to the limitation of the size of the built-up edge. The cutting force is thereby greatly diminished. Copper and aluminium do not show built-up edge formation, and it is found that the cutting force in vacuum does not differ greatly from that in air. This is explained on the supposition that a relatively strong adsorbed oxygen layer on the free chip surface impedes dislocation movement at the shear plane, and counteracts the effect of reduced adhesion at the tool face. The results suggest that the cutting force for aluminium at low speeds with 18 " rake tool is actually slightly higher in air than in vacuum. This explanation is supported by high-temperature cutting results on copper and a test with degassed and oxygen-saturated cutting fluid