Browsing by Author "Ko, Wing F."
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Item The Mechanics of Material Removal Mechanisms in the Machining of Ceramics(1994) Zhang, G.M.; Satish, K.G.; Ko, Wing F.; ISRThis paper presents a study on the mechanics of material removal for ceramic materials by observing single-point turning process of aluminum oxide (Al2O3). On-line cutting force measurement is performed and the surface integrity is characterized off-line by examining the surface texture. A theoretical analysis of fracture mechanics provides a comprehensive understanding of the chip formation process, and a model describing the material removal mechanisms is discussed. Based on the model, a systematic investigation of the chip fragments formed during machining is performed.Item Study of the Formation of Macro-and-Micro-Cracks during Machining of Ceramics(1993) Zhang, G.M.; Anand, Davinder K.; Ghosh, Subrata; Ko, Wing F.; ISRThis paper presents an experimental study on the formation of macro- and micro- cracks formed during the machining of ceramic materials. Aluminum oxide (Al2O3) was used as the testing material and polycrystalline diamond tipped carbide inserts were used for material removal. The cutting force was recorded during machining and surface finish was measured after machining. an environmental SEM was used to obtain high-magnification images of macro- and microcracks induced by machining. With the assistance of a computer-based vision system, qualification of fracture surfaces with respect to crack nucleation, growth, and cleavage was attempted. Results from this research provide an insight into the prevailing mechanisms of material removal during the machining of ceramics, and suggest the development of crack- controlled machining technologies.Item Submerged Precision Machining of Ceramic Material(1995) Zhang, G.M.; Ko, Wing F.; Ng, S.; ISRThe brittle nature of ceramics makes them difficult to machine. This paper presents a study to explore a new method to machine ceramic material. The method is based on the stress-corrosion- cracking behavior of ceramic material under certain aggressive environments. An apparatus is designed to create a machining environment where workpiece and cutting tool are submerged in a bath filled with cutting fluids. Observations on the surface texture formed during machining have been made to investigate the effectiveness of submerged machining on quality and efficiency of the machining operation. The obtained results strongly suggest that the chemo-mechanical interactions occurred during machining have great influence on the stress distribution produced in the ceramic material being machined, thus have direct effects on crack initiation and propagation. By controlling the machining parameters, higher material removal rate with less surface damage can be achieved, showing the potential of submerged machining as an innovative technology for machining ceramic material.Item A Systems Engineering Approach to Design a Smart Tool Post Structure(1995) Ko, Wing F.; Zhang, G.M.; ISRPrecision machining has received more and more industry-wide attention as dimensional accuracy becomes a significant measure of quality in a product. The key in achieving today's quality requirement is, therefore, precision of a machine tool. Since the invention of the first CNC machine tool in the 1960s, machine tool research has entered an almost stagnant stage. There are numerous reasons for the slow progress, and the lack of system- wide studies of the machine tool performance is one of them.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.