Multivariate Analysis of Orthogonal Tube Cutting Forces With 3-D Tool Wear Analysis of AISI 1020 Alloy Steel Using Cold Compressed Air Versus Liquid Nitrogen as Metal Working Fluids

Abstract

The growing cost associated with insurance, handling and disposing of conventional metal working fluids (oil and water based) continues to drive a need for alternative metal working fluids. An orthogonal tube turning machining experiment on AISI 1020 alloy steel was conducted to study the performance of High Speed Steel (HSS) tool inserts and carbide tool inserts utilizing cold compressed air and liquid nitrogen environments as the metal working fluid of choice The use of both high speed steel and carbide inserts allowed for direct comparison of geometrically identical inserts in customized tool holders that were used to present the tools with the geometrically identical tool rake angle alpha. Tool holder stiffness was therefore common to all tool rake angles compared. AISI 1020 steel 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 commercial steel. 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” at different tool rake angles of 0°, 7° and 15°, with no chip breaker installed in the tool. 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. Surprisingly, the inexpensive, simple cold compressed air produced less wear than the more expensive liquid nitrogen for all cutting factor level combinations.