Institute for Systems Research

In this thesis study, research efforts have been devoted to identifying, key links related to information acquisition, manipulation, and transformation so as to prepare the data essential for constructing physical models of the objects under investigation. Specifically, a Surveyor 3000 laser scanner located at the National Zoological Park is used for digitization of objects. Three software systems, namely, DataSculpt (developed by Laser Design), Magics RP (developed by Materialise), and Maestro (developed by 3D Systems), are employed to convert and assemble imaging data files into a single .stl file, recognizable by most CAD systems. A stereolithography apparatus, SLA-250/40, is used for rapid prototyping of physical models with high sophistication and accuracy.

Unique contributions of this thesis effort include the successful realization of a Homunculus facial skull constructed from only four existing fossil fragments in the world, and a reverse engineering approach to generate physical duplicates from an existing component, i.e., a distributor used in pick-up trucks.

This thesis presents a combined analytical and experimental study with focus on optimizing the machining performance of a type of newly developed dental material. It is called DICOR/MGC, where MGC stands for machinable glass ceramic. The study starts from analyzing their microstructural characteristics to searching for the machining conditions that provide satisfactory performance in terms of surface finish and acceptable flexural strength. To gain a better understanding of the material removal mechanism(s), a dynamometer is designed to perform an on-line recording of the cutting force generated during machining. Method of using an environmental scanning electron microscope is employed to examine the machined surface texture and identify the machining induced cracking. Two major contributions of this thesis study are (1) the fundamental understanding of the relationships among the material microstructures, the machining parameters, and the material preparation on surface integrity of dental ceramics, and (2) the development of an architecture for searching machining conditions that optimize the machining performance of dental ceramics.

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).

A vision system, in which optical devices are employed, is designed and built to implement the surface finish assessment using fractal geometry. The developed prototype serves as a testbed for this thesis research. The testbed employs a CCD (Charged Coupled Device) camera to capture the image of a machined surface. A computer software tool is developed and implemented to process the image data and extract information characterizing the surface condition by using the proposed fractal geometry approach. The system provides 3-D visualization of surface topography and displays numerical values of the surface characterization indices including the fractal dimension and the lacunarity for the purpose of performing diagnostics. Special efforts have been made to investigate effects of the reflectivity of part material on the optical area-based surface characterization technique. Significant findings include the effectiveness of using light filters in image data acquisition and the utilization of light filters to facilitate the system calibration for machining a variety of materials through compensation.

The research presented in this thesis focuses on improving machining accuracy using a systems engineering approach. A conventional lathe during machining is taken under consideration as a machining system. The tool post is identified as a critical component in the machining system to achieve the defined machining accuracy. Smart material made actuators are used to design a new tool post structure that is capable of carrying out an active vibration control during machining.

In this thesis research, the fabrication of the designed tool post is completed. Results obtained from the initial tests strongly demonstrate its capability to attenuate tool vibration during machining in an active and intelligent way. Thus, the smart tool post system fulfills the design objective of achieving microscopic level machining precision on a low-cost conventional machine tool platform. Suggestions on the actuator specifications are made for further improvement on vibration compensation.