Study On Machining Technology And Mechanisms Of NdFeB Magnetic Material

Sintered NdFeB permanent magnetic material is a kind of metallic compound composed of rare earth elements and transition element. Combining the advantages of both rare earth element and iron element, it has many good properties such as high remanence, good ratio of price to performance and low density. It is widely used in many fields. But it is easy to rust in many conditions and there are two methods to protect it from rusting at present. One is to append microelement in this metallic compound, the other is to use protection coat.The production of NdFeB sintered magnetic material makes that it is hard to ensure the required shape and dimension precision of workpiece, so it should be shape machined after sintering. As a kind of typical difficult-to-machine material, very few detailed report of machining technology or mechanism of sintered NdFeB material is available either at home or abroad. There is no report of combined machining of NdFeB material. Machining technologies and mechanisms for NdFeB material have been studied systematically on the basis of analysis of machining methods for hard and brittle materials. The research contents are as follows:Ultrasonic machining mechanism of NdFeB material is analyzed and experiments were carried out. The relationship between machining parameters and machining quality is studied and the machining surface is also analyzed.A new kind of machining technology named ultrasonic machining aided tool rotary motion is proposed. Abrasive grains enter the machining area through two holes in the rotary tool. So abrasive grains can easily reach the machining area and distribute equably. This method can improve machining efficiency, reduce tool wear, improvemachining quality and reduce cost. Its removal mechanisms include ultrasonic cavitation, mechanical abrasion by direct hammering of abrasive particles and grinding. So material removal rate is improved. Material removal model is developed on the basis of static load, amplitude, grit size, rotary speed, frequency and density of grit liquid. Ultrasonic machining aided tool rotary motion equipment was designed and experiments were carried out on it. Results indicate that it is in accordance with the model data. This new kind of technology is an effective method to machine NdFeB magnetic material with high MRR.Removal mechanisms for NdFeB material is provided on the basis of large EDM experiments. The mechanisms could be classified as vaporization melt, thermal spalling and detachment of grain. The effects of peak current, pulse-on-time and pulse-off-time on material removal rate, surface roughness and relative tool waste were studied. The machined surface is classified into three layers: recast layer, heat affected layer and matrix. The thickness of recast layer and heat affected layer is changing as the discharge energy changes. It is found that a layer of non-crystal alloy is formed after EDM which could improve the rust resistance of NdFeB material. So EDM can not only machine the material but also protect the machining surface from erosion.In order to improve the machining rate of EDM for NdFeB material, considering the effect of ultrasonic vibration on medium, EDM aided tool ultrasonic vibration method is analyzed and experiments were carried out on an a set of refitted equipment, the effect of peak current and pulse-on-time on material removal rate and surface roughness were studied. Compared with EDM, recast of liquid alloy on the machining surface is reduced due to the effect of ultrasonic vibration, which results in the shift of discharge location and good machining condition. So machining efficiency is improved, recast layer becomes thinner and less micro cracks display on the workpiece surface.In order to solve the hole machining problem of NdFeB material, stepped electrode is applied in EDM. This new type tool increases the roomage for debris and decreasesthe possibility of twice discharge. So machining efficiency increases and tool corrosion rate decreases. The machining precision is better than cylindrical electrode.Machining mechanism of ultrasonic abrasive and powder mixed EDM combined machining is studied thoroughly. Tool vibrates with high frequency and revolves simultaneously. Material removal mechanisms were analyzed and experiments were carried out on self-designed equipment. Results indicate that it could achieve higher material removal rate, but tool wear rate is higher.The simulation system for NdFeB material is developed using Visual Basic language. This simulation system can predict machining quality and optimize machining parameters of several machining methods. Simulation indicates that predicted and optimized data errors could be controlled in a small range.