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Prof. Kim's Research
Fatigue Improvement Process Development and Analysis in Automotive and Aerospace applications
In the automotive industry, resistance spot welding (RSW), or spot-welding, has been and continues to be an important process in body structure assembly. Fatigue is a frequent cause of failure in sheet steel joined by spot welds and resistance spot welds are prominent sites for origination of defects and cracks. Even though there is a great amount of interest in achieving high durability and fatigue resistance for resistance spot-welded sheets, there is no open literature in regards to developing a process to improve the fatigue strength of RSW low carbon steel joints. In order to improve fatigue strength of low carbon steel and aluminum RSWs, a post-weld cold working process has been recently introduced. The cold working process generates uniform and consistent large zones of compressive residual stresses in resistance spot-welded low carbon steel structures using a specially designed indentation device. To achieve the proper magnitude of compressive residual stresses, indenting process parameters have been developed for a range of sheet thicknesses and weld sizes. This innovative technology can minimize the cost needed to improve the fatigue life of the resistance spot weld in metal structures.
Micro-Electircal-Discharge-Machining of Advanced Engineering Materials
Machining of materials on micrometer or nanometer scales is considered to be a key future technology. Aside from the well-known lithographic processes used in the fabrication of micro-electro mechanical system (MEMS) devices, micromachining technologies play an increasing role in the miniaturization of complete machines ranging from biological and medical applications to electro-mechanical sensors and actuators. Currently, research in micromachining focuses only on semiconductor or metal fabrications. Micromachining technology using photolithography on silicon substrate is without a doubt the best known because it is one of the key processes to fabricate micro-structures in industry. However, there are some limitations in this process due to its quasi-three-dimensional structure, its low aspect ratio, and limitation of the working material. Micro- Electrical Discharge Machining (micro-EDM) is a new technology and has established itself as one of the major alternatives to the conventional methods for machining difficult-to-cut materials and/or generating complex contours. Micro-EDM can offer the possibility of making three-dimensional structures in micro- or nano- scales.
Traditional manufacturing of advanced engineering materials
Today, advanced engineering materials such as composites are being used extensively in the aerospace industry as well as other types of industries due to their advantages including better durability, reduced maintenance requirements and increased potential for future developments. The machining processes of composites are essential to finish the majority of the post-mold manufactured composite parts. Even though importance of composite materials is emerging recently, very limited studies on machining of composite materials were reported. The field of manufacturing processes of composite materials and their performances is the focus of this research.
Nontraditional machining of engineering materials
As new advanced engineering materials are introduced, new machining processes that are technologically and economically viable, are also being developed correspondingly. Abrasive waterjet (AWJ) machining is one of them. In the AWJ machining, workpiece material is removed by the action of high speed water mixed with abrasive particles. A widely used aircraft structural titanium alloy (Ti6Al4V) was machined with abrasive waterjet (AWJ) to investigate its machinabilty under varying cutting conditions. Machinability was evaluated in terms of kerf geometry, cut surface quality, and microstructural integrity. Quality of the machined surface, and microstructure features were examined using surface profilometry, scanning electron microscopy, and EDX-Ray analysis.
Since electrical discharge machining (EDM) is first applied in machining more than five decades ago, it is widely applied for machining of any electrically conductive materials today. EDM of Metal Matrix Composites (MMC) is a complex phenomenon where many scientific areas of engineering and technology are involved in its theory and practice. An analysis of the effect of EDM conditions on machining performance and hole quality for metal matrix composites has been done. This study may be used to assist the process design and quality control in EDM machining of metal matrix composites for a broad range of future products applications.
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