자기입자가공과 펄스 전기화학 폴리싱을 이용한 하이브리드 공정의 가공특성 연구

Abstract

With the recent upgrading of industry, products are becoming smaller and more complex in shape. At the same time, high dimensional accuracy and high quality of material are required. The quality of the product surface in the current trend is one of the key attributes of modern manufacturing. To respond to the various shapes and high quality required by high-tech industries, in the field of ultra-precision machining, use non-traditional machining methods(MAF, ECP, EDM, PCM, etc.) that are different from conventional machining methods, or use hybrid machining that combines two or more already used processing methods to enhance the quality of processed products, or improve the quality of processed products, and composites. In this study, among non-traditional machining methods, MAF(Magnetic abrasive finishing) and ECP(Electrochemical polishing) were used to obtain high quality surfaces. MAF is a machining method that reduces surface roughness by flattening the surface by rotating a magnet with magnetic particles attached to it, or by rotating a workpiece, such as a pipe, between the magnet and the magnetic particles. The ECP uses electrochemical reactions to melt the surface of the workpiece, smoothing it out, lowering the surface roughness. It also removes impurities from the surface and produces a stable oxide film to increase corrosion resistance. ECP is non-contact machining, so it has the advantage of being applied to complex shapes, and has glossy features. The purpose of hybrid machining for processing surfaces is to obtain high quality surfaces, reduce processing time by reducing the number of processes, or use different process energy to lower processing costs, and to machining difficult to cut material easily. The types of hybrid machining can be divided into Assisted hybrid machining and Combined hybrid machining, controlled application of process mechanisms, depending on the material removal area. In this paper, a non-traditional machining method, noting that MAF is applicable to various shapes and is accessible by simple devices, Based on the existing method of fusion electrochemical machining in hybrid machining to increase efficiency, PECP, which can be applied to various shapes that are advantages of MAF, can be fused in various ways and analyzed hybrid machining characteristics. Equipment for observing and measuring machined surfaces is optical microscopy and AFM. The AFM measurement method is focused on the table and the CCD camera first checks the surface. The measurement conditions were determined by 30μm×30μm as the reference range, and the surface measured by AFM was analyzed through XEI program, and the local surface was checked for smoothness as well as whether Ra, Rz, and points were removed based on the cross-sectional line. MAF and PECP cross-processing is an experiment to check the effect of each process on each other. Process and compare and analyze MAF, PECP and PECP, MAF in two order. The first control group is the surface of STS304 plate before machining, the second control group is the surface of STS304 plate with only MAF, and the third control group is the surface of STS304 plate with only PECP. The first comparator measures a large point shape, with a Ra value of 40 to 60. The second control analysis analyzed the vertical force applied by magnetic particles on the surface and found that it represented a value similar to the theoretical formula. And the higher the frequency, wet processing the better the result surface. The third comparator analyzed the result surface over time and identified the surface by polishing time. The first group of experiments is the PECP machining characteristic after MAF machining and the purpose is to identify the effect of PECP on the surface of MAF. As a result of the experiment, if PECP is applied to a surface that has been MAF, defects will be filled faster than those that only PECP has. The second group is MAF processing after PECP. The purpose of this experiment is to conduct MAF on the surface of advancing PECP, to determine how MAF affects the surface of PECP. The results of the experiment showed that particle processing on already smoothed surfaces through PECP was different from normal particle processing mechanisms, and the result surface was measured with AFM, which showed good result surfaces in a short period of time with small-sized magnetic particles mixed with large abrasive particles. Micro-pit caused by PECP was also removed by particle processing. But the scratch marks from particle processing must remain on the surface, so it is not appropriate to finish with MAF. The first method of hybrid machining of MAF and PECP(Combined hybrid machining). Two or more processes simultaneously contribute to material removal, and both processes affect the same processing area. It is known that the cross-process simultaneous hybrid processing method shows improved material removal rate and surface integrity. The experimental device was constructed by matching the processing areas of the two processes, and the results showed that large Pits were generated on the surface regardless of current density, and Ra value of surface roughness was higher than that of the pre-process surface. The machining depth is 22μm at 0.4A/cm2, 23μm at 0.6A/cm2 and 31μm at 0.8A/cm2, and 1.43 to 1.83 times deeper than the surface where only PECP was processed. As a result, the combined hybrid processing method of cross-processes has shown that the material removal rate has improved but the surface quality has decreased. This seems to increase the material removal rate as PECP electrochemical reaction helps MAF particle processing. However, observing the magnetic particles used in processing, it appears that MAF interferes with the electrochemical reactions of the PECP, resulting in poor surface solubility, and a stable oxide layer because mechanical machining removes the formation of the oxide layer. Therefore, for simultaneous hybrid processing of cross-processes, matching the processing area has an adverse effect on surface quality, so a convergence method that can have a positive effect on each other, such as basic characteristics of cross-process processing, is needed without MAF and PECP interfering with each other. The second method of converging MAF and PECP is cross-process sequential hybrid processing. This experimental device is designed to repeat MAF and PECP during the entire machining process, based on the results obtained from the high quality surface, if MAF and PECP are carried out on the surface where PECP has been performed on the surface where MAF and PECP have been cross-processed. First, the characteristics of PECP and MAF were identified according to rotation because the workpiece rotates, and the faster the rotation speed, the better the electrochemical reaction occurred, and the slurry was eliminated from the magnetic particle processing. Thus, the optimal RPM is set at 0.5, with no slurry being eliminated, and experiments were conducted on other influencing factors. The first experiment involved sequential hybrid processing experiments that differed in the size of abrasive particles. The experimental results showed that the conditions using 3~5μm abrasive particles showed lower Ra and Rz values than the result surface using 0.5μm and 1.5μm abrasive particles, and the Ra values were 9.5nm to correspond the research target surface roughness. The second experiment analyzed the result surface according to the sequential hybrid processing time and confirmed through the image analysis program that the number of defects on the surface increases as the processing time increases. The results confirmed that the optimum PECP time tends to be the same as the optimum hybrid machining time. And as shown in the cross processing, MAF is not able to remove the micro-pit from the PECP, and it is judged that the last process in sequential hybrid processing is PECP. Therefore, it is considered appropriate to use abrasive particles larger than MAF to remove micro-pit by using small abrasive particles to help flatten the surface.