THE ACTION OF GASEOUS LUBRICANTS IN THE ORTHOGONAL MACHINING OF AN ALUMINUM-ALLOY BY TITANIUM NITRIDE COATED TOOLS

Specimens of an aluminium alloy have been machined at low speeds (up to 0.1 m s-1) with both conventional high speed steel and titanium nitride coated tools under controlled atmospheres. In the presence of CCl4 vapour, TiN coated tools gave lower cutting forces and superior surface finishes. Although ethanol vapour also acted as an effective cutting lubricant, it produced little difference in behaviour between the two tool materials. Measurements of tool forces and observations on the degree of material transfer and pick-up suggest that the effectiveness of TiN coatings involves not only their direct frictional interaction with the material of the workpiece but also the interaction with any cutting lubricant: the coating may play a role by changing the wettability of the tool surface by reaction products formed at the interface between the chip and the tool.