(Dr. Shreyes Melkote, advisor)

"Modeling and Verification of Cutting Tool Temperatures in Rotary Tool Turning of Hardened Steel"

Abstract

The chip formation process in machining is accompanied by heat generation. The heat generated influences both the workpiece physical properties as well as the cutting tool. High temperatures accelerate tool wear and thermal softening which are not desirable because they alter the accuracy of the machined surface and tool life.

Many studies have been done to lower the heat generated in cutting. A first approach is to use a cutting fluid but its effectiveness is limited by its ability to penetrate between the tool and the chip. A second approach is to remove the heat generated through a cooling cycle as in interrupted cutting. The idea is either to translate a wide tool to the side as it moves forward relative to the workpiece, which allows the dissipation throughout the body of the tool or to use a cutting edge in the form of a disk that rotates about its principal axis. The latter, known as a rotary tool, provides a rest period for the cutting edge, thus enabling the edge to be cooled and a continuously fresh portion of the edge to be engaged with the workpiece. The rotary tool can be either driven by an external power source or self-propelled.

This thesis focuses on the self-propelled rotary tool (SPRT) process for machining of difficult-to-machine material such as bearing steels, where tool life is of particular concern. Since the cutting temperatures are known to influence tool life significantly, the first task in this investigation involved developing a model to analyze heat transfer and temperature distribution in the cutting tool during SPRT turning of the hardened 52100 steel (58 HRC). Both rotary and equivalent fixed tool processes are compared in terms of cutting tool temperatures generated. The model is based on the moving heat source theory of conduction and employs the Finite Element Method (FEM) for its solution. The model is experimentally verified through measurement of the cutting temperature distribution using an Infra-Red imaging camera under different cutting conditions. Predicted and measured temperatures show good overall agreement when they are measured along the cutting edge and measured temperatures are up to 50°C lower in rotary tool cutting than in fixed tool cutting under the same conditions.