【作者】 李丽；

【导师】 张建华；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2005， 博士

【摘要】 烧结NdFeB永磁体材料是由稀土族元素和过渡族金属元素形成的以金属间化合物为基的永磁材料,综合了稀土元素的高磁晶各向异性和铁族元素高居里温度的优点,具有磁能积高、性价比好、体积小、质量轻等优异特点,因而获得广泛的应用。其缺点是容易腐蚀,目前常采用向合金中添加微量元素和采用防护涂层两种方法来提高它的抗腐蚀性能。烧结NdFeB永磁体材料的制造工艺决定了在制模和烧结过程中无法保证工件所要求的形状和尺寸精度,烧结成型后须进行精密成型加工。但它属于典型的硬脆材料,加工比较困难。目前国内外对NdFeB永磁体材料加工方法和加工机理的研究很少。本文在综合分析硬脆材料加工方法的基础上,对NdFeB永磁体材料加工方法和加工机理进行了系统的研究。具体内容如下: 在NdFeB永磁体材料力学性能测试的基础上,分析了其超声波加工机理并进行了实验研究,得出了加工参数与加工效果之间的关系,并对加工表面形貌进行了分析研究。 深入研究了工具附以旋转的超声波加工新方法,磨料循环液通过旋转的工具进入加工区域,确保磨料顺利进入加工区域并均匀分布在加工表面上,可提高加工效率、减小工具磨损、改善加工质量和降低加工成本。尤其适用于较大面积工件的加工。材料去除机理包括超声空化、磨粒的直接机械锤击、冲击、磨蚀作用,几种去除机理的组合有利于提高材料去除率。建立了材料去除模型,所建模型与静载荷、振幅、磨粒尺寸、转速、频率、磨料浓度等参数有关,以数值计算的方法分析了材料去除率与各项参数之间的关系。设计了旋转式超声波加工装置并进行了实验研究,实验结果与所建去除模型的分析结论相一致。 深入研究了烧结NdFeB永磁体材料电火花加工的材料去除机理,发现其材料去除机理包括熔化、气化、热裂、热剥落或整体颗粒去除。实验研究了峰值电流、脉冲宽度和脉冲间隔对材料去除率、表面粗糙度及电极损耗的影响规律。加工后更多还原

【Abstract】 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.更多还原