Cutting Forces With 3-D Tool Wear Analysis in Orthogonal Tube Machining of 6061-T6 Aluminum Alloy With Uncoated Carbide Tool Inserts Using Cold Compressed Air Versus Liquid Nitrogen as Metal Working Fluids

Metal working fluids remain in common use throughout many industries where metal cutting is necessary. Optimizing the use of a metal working fluid must balance environmental needs, production needs and economic needs. An orthogonal tube turning machining experiment on 6061-T6 aluminum alloy was conducted to study the performance of uncoated carbide tool inserts utilizing cold compressed air and liquid nitrogen environments as the metal working fluid of choice. The tool inserts selected for this study did not have any chip breaker and studied at 3 different rake angles of 0°, 7° and 15°. Aluminum alloy 6061-T6 was used because of its commercially dominant availability and usage. Cold cryogenic cooling was selected because of its growing usage in high performance machining applications. The use of cold compressed air has been much less studied in the machining of metals than in the machining of plastics and composites where it is quite commonly used. The comparisons between these two methods represent the first published values comparing the current extremes of gaseous metal working fluid applications in a commercially dominant aluminum alloy. This statistically designed experiment produced a large amount of comparative data that focused on the wear of the tools in two different cutting environments allowing for multivariate analysis of variance and regressive curve fitting. The orthogonal tube turning was set up on a conventional two axis HAAS TL-2 CNC tool room lathe. Forces were collected utilizing a standard Kistler force dynamometer to record the force data in X, Y and Z axes. Two levels of uncut chip thickness, 0.002” and 0.004” per revolution were maintained with a constant feed and depth of cut of 0.125”. Tool rake angles and depth of cuts were selected to ensure maximum statistical power / decisiveness of the experiment. The experiment was carried out for duration of 1 minute while the force data was collected for the entire duration of cut. New tool insert was used for each factor level combination. The traditional force analysis results are provided for an orthogonal tube turning experiment. In addition, all tools were analyzed for 3-dimensional rake face wear using an innovative Keyence white light microscope in conjunction with a Dektak surface profilometer. Although cutting forces were statistically the same, the inexpensive, simple cold compressed air produced less rake wear than the more expensive liquid nitrogen for all cutting factor level combinations. There was no measureable benefit in using the more expensive liquid nitrogen system.