Institute for Systems Research

This thesis processes a new method of measuring wheel wear using a duplication pattern of the grinding wheel. Plunge-grinding experiments on sintered silicon nitride (SSN) and sintered reaction-bonded silicon nitride (SRBSN) were conducted using a horizontal-spindle surface grinder with diamond-grit, resin-bond peripheral wheels. To gain a better understanding of the wear process, grinding forces were measured using a computer-based data-acquisition system. Stylus profilometry served to measure the volumetric wheel wear and to measure the surface roughness of the ground silicon nitride for the purpose of characterizing the effect of wheel wear on the grinding performance. Major contributions of this thesis research include development of a method for measuring wear of diamond grinding wheels, and identification of the interrelation between the rate of wheel wear and the two machining parameters (namely, downfeed and wheel speed used in the investigation).

Using a systems engineering approach, a computer-based surface integrity assessment methodology is formulated. It combines the most recently developed image processing technology with computer graphics while incorporating the principles of fracture mechanics. Microhardness testing is used to study material properties related to machining. Four types of material selected are human enamel, Dicor-MGC, HCC Dentine, and HCC Enamel. Three- dimensional visualization of the surface impressions is achieved using an environmental scanning electron microscope and an atomic force microscope. Machining experiments are conducted to study the surface integrity, including surface finish, micro- cracking, and edge chipping. Analytical investigation correlates these surface responses to the machining parameters, such as spindle speed, feed rate, and the depth of cut, to seek a parametric region in which quality of machined ceramic components can be ensured. Surface integrity performance indices such as surface roughness, cavity density, and chip aspect ratio are proposed to quantify such evaluations.

Major contributions of this thesis research include the development of the combined SEM- AFM stereophotography method. The high resolution achieved with this method ensures coverage of rich information on the surface texture formed during machining. Specific findings of this thesis research include the identification of micro-mechanics of fracture occurred during the material removal process, and a good understanding of possible influences of the microstructures on the machining performance.