Study on the Technique of Magnetic Abrasive Finishing in Mould Surface

　　Study on the Technique of Magnetic Abrasive Finishing in Mould Surface
　　Recently, advanced technologies in manufacturing industry demand the production of much more precise and efficient parts. However, tradition machining involving a single process cannot satisfy the present demand for both quality and high efficiency simultaneously. The surface quality is determined by surface roughness and the tress state of the surface. The available traditional and advanced finishing processes alone are still incapable of producing desired surface characteristics on complex Block neodymium magnet geometries, and in exercising in-process control on finishing action. Thus, a magnetic abrasive finishing process would meet the demand represents the current trend in the field of manufacturing. The magnetic abrasive finishing (MAF) process has intrinsically superior finishing characteristics, especially of complex shapes. A mixture of the iron grain and aluminum oxide abrasive yielded a superior effect on the surface finish and material remove rate. Traditional fine finishing operations such as grinding, lapping, or honing employ a rigid tool that subjects the work piece to substantial normal stresses which may cause micro cracks resulting in reduced strength and reliability of the machined part.
　　A relatively new fine finishing method, magnetic abrasive finishing (MAF) is an advanced finishing method, the method was originally introduced in the Soviet Union, with further fundamental research in various countries including Japan. Nowadays, the study of the magnetic field assisted finishing processes is being conducted at industrial levels around the world.Magnetic abrasive finishing (MAF) is an advanced finishing process in which the cutting force is primarily controlled by the magnetic field. It minimizes the possibility of micro cracks on the surface of the work piece, particularly in hard brittle material, due to controlled low forces acting on abrasive particles. This process is able to produce surface roughness of nanometer range on flat surfaces as well as internal and external cylindrical surfaces. Via MAF, the initial surface roughness of 0.25μm Ra can be improved easily to 0.05μm Ra within a few minutes. And produces neither a deteriorated layer nor micro-cracks on the finished surface. The MAF process offers many advantages, such as self-sharpening, self-adaptability, controllability, and the finishing tools require neither compensation nor dressing. Magnetic abrasive finishing (MAF) is a processing technology using magnetic abrasive brush formed by magnetic abrasive grain (MAG) under magnetic field to finish surface of work piece. The surface is finished by the shearing of the peaks resulting in circular lays formed by the rotation of the FMAB. In magnetic abrasive finishing (MAF) process, magnetic force plays a dominant role in the formation of flexible magnetic abrasive brush (FMAB) and developing abrasive pressure. In order to produce the magnetic force, the magnetic fields used in MAF include permanent magnetic field and electromagnetic field.In the magnetic abrasive finishing (MAF) process, magnetic field is generated using an electromagnetic. Current in the ranges of 0-10A is passed through the copper coil wound in the form of a solenoid.
　　The magnetic field generated within the magnetic core passes through the magnetic head. Magnetic abrasive is introduced in the gap between the magnetic heads, i.e., between the N and the S poles. Due to the presence of the magnetic field, the abrasive align in the direction of the field and the magnetic powders will be arranged like brushes and the strength and stiffness of the magnetic brushes can be controlled by the electric current supplied. Shinmura et al. have studied basic principles of the MAF Ball Neodymium Magnets process and concluded that the stock removal and surface finish value (Ra) increase as the magnetic abrasive particle diameter“D”increases. In order to achieve smooth surface and remove surface damage, the ferromagnetic particle diameter mast be chosen as a compromise of material removal rate and resulting surface finishing. In the fifth chapter gets the optimal diameter“D”of the magnetic abrasive particle by the finishing tests. Kim et al. have modeled and simulated the MAF process and concluded that the magnetic flux density in the air-gap is affected greatly by the length of the air-gap; magnetic flux density increases as the air-gap length decreases. In addition to magnetic flux density, this paper has studied flat surface finishing of steel work piece and concluded that rotating speed of magnetic pole, magnetic abrasive mesh and finishing time etc are the parameters which significantly influence the change in surface finish value (Ra).Most of the previous research work has been focused on the finishing characteristics and mechanism from a macroscopic point of view using the surface roughness profiles as the measure. However, those approaches do not adequately characterize the behavior of abrasive cutting edges acting against the surface during the removal process. This paper examines the acting forces, magnetic field set, magnetic abrasive grains and experiments by which provides a fundamental understanding of the process characteristic about MAF.This paper makes theory and test data analyses about MAF as the discussing focus. The main contribution of this dissertation is briefly presented as follow:In chapter 2, this paper deals with the theoretical investigations of the MAF process about the magnetic force. To analyze the finishing process, a force transducer has been designed and fabricated to measure forces acting during MAF.A microcosmic model of the process is developed to analyze the mechanism of the material removal and forces on the work piece surface.
　　A theoretical model for material removal is also proposed accounting for micro cutting by considering a uniform surface profile without statistical distribution.In chapter 1,the dissertation introduces the background and the internal and overseas development survey of the research, the summarize about the technique of the MAF and application foreground of this research are discussed.In chapter 3, this dissertation discuss the design of the magnetic field set a copper coil, wound in the form of a solenoid, is used for the generation of the magnetic field in the core. the alloy of aluminum is used as the magnetic core material. Magnetic heads are designed such that the stronger magnetic field is concentrated surrounding the air gap with minimal leakage between the magnetic heads and the magnetic core.In chapter 4, this dissertation analyzed grinding mechanism and effect of magnetic abrasive grain in the magnetic abrasive finishing. Magnetic abrasives grains (MAG) were abrasive tool of magnetic abrasive technique. Some preparation technique of MAG is introduced. Blinding and sinter techniques are emphasesly introduced. In some situations, it is proved that magnetic abrasive grains are produced by blinding technique can replace the magnetic abrasive grains are produced by sinter technique by experiments in this study.In chapter 5, the test analyzing of MAF. There are many main effect factors on MAF, such as Magnetic Flux Density, Rotating Speed of Tool Magnetic Pole, Grain Diameter of Magnetic Abrasive, neodymium prices Finishing Time, Working Gap and Feed Speed of Machine and so on. Based on a series of experiments, to get the effect law of the diverse factors on finishing quality and efficiency, this dissertation explore and study these factors which have important contribution on the finishing quality. Process parameters were provided to the popularization and application of MAF technology.In chapter 6,the conclusion and expectation.