자기연마와 전해연마의 복합공정에서 가공메커니즘 규명과 응용

Abstract

Magnetic abrasive polishing was widely used for making a fine surface in a variety of industrial products. Fundamentally, this method can be applied for ferrous workpiece materials since the non-ferrous material has little magnetic flux density. Nowadays, nevertheless, the materials for most products are changing from metal to non-metal, because of reducing the weight of products and showing the excellent properties in comparison to a conventional product. The new material adoption like this makes the magnetic abrasive polishing difficult to finish that material. Thus, the development of a new polishing method for the non-ferrous materials is necessary. In this study, an efficient hybrid machining system combined with electro polishing and magnetic abrasive polishing was developed, and then this system was used for polishing and deburring of a micro-channel. New abrasives, which were mixed with carbon nanotube (CNT) and cobalt (Co) particles, were applied for this hybrid system. The carbon nanotube has an excellent wear resistance as a polishing abrasive but it is non-magnetic matter which is impossible to be used as the polishing abrasives in the hybrid machining. Therefore, to add this non-magnetic material to the magnetic property, metal based cobalt which has good magnetic property was molten by a plasma melting process. From this study, fundamental nature for the carbon nanotube itself as the polishing abrasive was characterized by simulation and experimentation. The suitable electrolyte for the hybrid machining with the CNT particles was selected by checking the chemical reaction with the polishing particles. The basic components for the hybrid machining system were designed and assembled such as a power supply, inductor and electro-magnet array table. Acoustic emission technique was applied to monitor the uniform surface roughness and neural network method of the input variables from the acoustic emission signal parameters was adopted for predicting the surface roughness after the hybrid machining. A circulation unit for the hybrid machining system was newly designed for maintaining uniform concentration of the CNT particles and easily scattering the CNT particles into the electrolyte. The machined small sized chip was filtered by a magnetic filter unit and this kind of filter unit was essential for the hybrid machining system. As a case study, the micro channels for the separate plate of a fuel cell were polished and a burr occurred at the corner of the micro channel was removed. After experiments, the response surface models for burr height and surface roughness were developed and confirmed by the additional verification test. The dominant parameters for the hybrid machining process were determined and the optimal conditions for producing the good surface quality were selected by the design of experimental method. Finally, it was indicated by this study that the developed hybrid machining process combined with the electro polishing and the magnetic abrasive polishing was one of practically applicable methods for producing a high quality surface of precision products.