Comparison of Tensile Testing Flow Stress to Orthogonal Plate Machining Flow Stress in FCC, BCC, and HCP Materials at Various Levels of Hardness Using a Videographic Quick Stop Device

Abstract

Basic and advanced metal cutting research has been an ongoing effort since Cocquilhat’s early work directed towards measuring the work required to remove a given volume of material when drilling in the year 1851. Over the 150+ years since his experiments, one of the persistent issues in metal cutting has been how best to determine the flow stress in a metal undergoing cutting. In all the many models proposed since then, the flow stress of metal flowing in front of a cutting tool has not proven to be the same as the flow stress of metal undergoing a tensile pull. This paper examines the flow stress phenomenon using an improved Videographic Quick Stop equipment at Auburn University. The orthogonal machining plates and tensile specimens were all cut from the same stock. Tensile testing of the stock was performed immediately prior to the machining of the plates in a standard MTS load frame to allow actual metal cutting experiments to be performed and compared to actual load frame data from the same stock. Machining was conducted in a specially modified Cincinnati Horizontal Milling machine using an improved Videographic Quick Stop Device (VQSD) to capture the geometry of the cutting formation simultaneously with the forces in the X, Y and Z-axes using a standard Kistler force plate dynamometer. Utilizing the VQSD greatly increases the number of replicates available for statistical analysis by the metal cutting researcher. This allows for comprehensive multivariate analysis of the data with high confidence (> 95%) in the meaning of the results obtained, along with for powerful regression. The results of the data collection and statistical analysis are then used to populate the various historical models predicting the flow stress in metal cutting. The results indicate that one model is superior to all the other models in predicting the flow stress as predicted by the accompanying tensile test data. Further improvements in this model may lead to instantaneous tensile strength measurement when metal cutting with the need for load frames. This in turn would allow optimization of cutting conditions to match material conditions, resulting in a better product and longer-lived tools.