MECHANICS OF CHIP FORMATION AND ITS EFFECT ON THE SURFACE INTEGRITY OF HARDENED STEELS
Abstract
The cutting of hardened steels has become possible due to the development of cubic boron nitride tools and the improvement of ceramic tools. However, the mechanism involved in the cutting of hardened steels is not clear, and the surface characteristics of a machined surface have not been systematically investigated. The purpose of this investigation is to clarify these problems, and to help improve production efficiency and assure the quality of parts produced. A series of cutting experiments were conducted to study the mechanism of cutting hardened steel, and the chips produced were examined using the scanning electron microscope and the optical microscope. Next, the surface structure was examined by reflection electron diffraction method. Then the effects of cutting conditions and the hardness of steels were experimentally investigated. An analytical model based on the Merwin and Johnson method was developed to calculate the stress cycle of material elements during cutting and the residual stresses after cutting. Reflection electron diffraction study revealed the existence of austenite in the white layer of the machined surface together with the untempered martensite. Residual stresses near the machined surface of hardened steels are compressive, and they change to tensile stresses as the hardness decreases. Adiabatic shear was observed when AISI 4340 steel with hardness over HRC 50 was machined. The model developed was able to explain the reversal of residual stresses due to the mechanical deformation caused by a cutting tool.
Degree
Ph.D.
Subject Area
Industrial engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.