Improving low carbon steel chip breakability by cryogenic chip cooling

Abstract

This paper presents a cryogenic machining approach to improve the chip breakability for cutting AISI1008 low carbon steel, a typical ductile material. A cryogen delivery system supplies liquid nitrogen (LN2) coolant specifically to chip faces in a properly scaled jet instead of flooding the general cutting zone. The concept for this cooling approach is to locally and selectively bring the chip temperature down to the embrittlement temperature of the workpiece material while minimizing the cooling effect on the primary shear plane, which can otherwise cause increased cutting resistance. The embrittlement temperature was determined to be between −50 and −120°C from standard material tensile and impact tests. A finite element (FE) simulation was performed to predict the chip temperature under various cutting conditions. The numerical results and cutting tests performed on turning operations are used to explain the varied chip breaking improvements for a given range of feeds and cutting speeds.