Enhanced magnetic properties in Nd-Fe-B magnets prepared by spark plasma sintering via die-upsetting process

The magnetic properties and microstructure of Nd-Fe-B magnets prepared by spark plasma sintering with different die-upsetting processes were investigated. The results showed that the optimum magnetic properties of die-upset Nd-Fe-B magnets were obtained at 680 ℃ when the die-upset level was 60%, and the degree of magnetic alignment was 0.84. The microstructures showed that the coarse grains oc-curred predominantly within certain areas, and abnormal grain growth was not observed within the major areas of well-aligned grains. There existed many small spherical grains, which stacked together and were not aligned during die upsetting when the deformation temperature was 650 ℃. These small spherical grains grew up, and were aligned when the deformation temperature increased from 650 to 680 ℃, which could improve the crystallographic alignment of die-upset Nd-Fe-B magnets.

Quasi-periodic layer structure of die-upset NdFeB magnets

Isotropic magnets were prepared from melt-spun powders at different hot pressing temperatures from 550 to 700 ℃, then upset into fully dense anisotropic magnets at the same die-upsetting temperature of 850 ℃. Die-upset magnets had the characteristics of inhomogeneous microstructure, including well-aligned grains structure and nonaligned grains layers transverse to press direction, which was quasi-periodic layer structure with a total length of 5-15 μm. Nonaligned grains layers were mainly made of large grains and had higher Nd content. To clearly understand the formation of layer structure, the microstructure of isotropic precursors with different hot pressing temperatures and their subsequent die-upset magnets was investigated. A new interpretation for the formation of layer structure was proposed in this paper： the layer structure was correlated to the original ribbon interface which was divided into three types based on the contact forms. Because of the incomplete contact of neighboring ribbons, concentration of stress occurred in the contacted points and the Nd-rich phase was squeezed into interspaces at high temperature under stress. Due to the release of interfacial energy and the fluidity of enough Nd-rich liquid phases, the nonaligned layers with large grains formed both in hot compaction and subsequent hot deformation process. The layer structure affected the magnetic properties of die-upset magnets. With increase of the hot pressing temperature, the nonaligned grains layers became thicker, and the magnetic performance of die-upset magnets decreased. It was necessary to reduce the thickness of large grains layers for the preparation of high-performance die-upset magnets.

Enhanced mechanical properties in die-upset Nd-Fe-B magnets via die-upsetting process

The mechanical properties of die-upset Nd-Fe-B magnets produced at different die-upset processes were investigated. The results showed that the optimum comprehensive mechanical properties of die-upset Nd-Fe-B magnets were obtained at the deformation temperature of 680 ℃. The anisotropy of Vickers hardness was more obvious at the die-upset level of 55%, and the Vickers hardness measured parallel to the c-axis was significantly lower than that perpendicular to the c-axis. The fracture toughness measured parallel to the c-axis first increased, and then decreased with increase in die-upset level. The maximum fracture toughness of Nd-Fe-B magnets was obtained at the die-upset level of 60%. The microstmcture showed that the width of defect layers and the average size of large grains increased, and the layered structure of die-upset Nd-Fe-B magnets was obviously different with increase in the die-upset level.

铣刨齿钢体冷挤压成形工艺与模具设计分析

针对铣刨齿钢体需要多工序成形的特点,从工艺方案制定、冷挤压工艺参数选择、模具结构设计等方面对铣刨齿钢体成形质量的影响因素进行分析,主要对铣刨齿钢体进行正挤压和镦法兰两工序成形模具结构分析,研究了退火热处理工艺对35MnB钢挤压工艺性能的影响。试验结果表明,当35MnB钢组织球化等级为5、6级时,可以进行连续冷挤压成形,即正挤压后不需要中间热处理即可进行镦法兰工序成形;当球化组织等级为3、4级时,正挤压后,需要增加中间退火工序,才可以进行镦法兰工序,否则会引起法兰端面开裂现象。本文工艺在两挤压工序之间不需要进行热处理工序即可保持挤压件主体的金属流线完整。

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直齿圆柱齿轮浮动凹模冷闭式镦挤成形数值模拟分析

结合齿轮浮动凹模锻造和分流锻造技术,提出了一模两击式直齿轮冷闭式镦挤新技术,即先进行环形坯料带活动芯轴的镦挤预锻,后进行无芯轴空心分流终锻的两步成形工艺。并通过DEFORM—3D数值模拟分析和比较,验证了该技术能解决成形力过大和齿形充不满等缺陷,是适用于直齿圆柱齿轮精锻的有效工艺方案。

Ga对HDDR磁粉热变形磁体磁性能和微观结构的影响

利用HDDR工艺制备出Nd32FebalBGax(x=0.0、0.2%、0.4%、0.6%、0.8%(质量分数))磁粉,并且对HDDR磁粉进行热压/热变形处理制备出全密度各向异性磁体。研究了热变形温度和Ga含量对Nd-Fe-B热变形磁体磁性能的影响,观测了不同Ga含量热变形磁体的微观结构,探讨了微量元素Ga的添加对用HDDR磁粉制备的热变形磁体微观结构和磁性能的影响机制。研究发现,Ga的添加能够明显减小热变形磁体的主相晶粒尺寸,改善磁体的微观织构,并可以同时提高热变形磁体的剩磁和矫顽力。当Ga含量为0.6%(质量分数)时,热变形磁体的磁能积达到最大值228.3kJ/m3。

厚壁管闭式镦粗有限元分析及实验研究

为解决厚壁管在单向加压的普通液压机上进行闭式镦粗后壁厚不均的问题 ,本文提出了一种浮动凹模芯模闭式镦粗法。首先 ,介绍了该工艺的成形过程及模具结构 ;其次 ,采用刚塑性有限元法对新工艺和传统工艺进行了有限元模拟 ,比较模拟结果发现新工艺可明显地提高管件壁厚的均匀性 ;最后 ,对该工艺及传统工艺进行了试验研究 ,试验结果和模拟结果吻合良好。

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本文根据锥形模膛镦锻变形特点，分析了大长径比坯料镦锻变形的三个过程，导出了这些过程中变形瞬态的数学模型，提出了在平面弯曲和空间螺旋弯曲情况下，能进行稳定镦锻的原始坯料长径比ψ０，并绘出了相应的ψ－φ临界曲线，所得出的三条镦锻限制曲线，为设计模具提供了理论依据。结合实验研究，提出了设计大长径比坯料镦锻模膛的工艺参数。利用本文的结果，设计的抽油杆锻模，在生产中取得了满意的效果。

高钨镦块材料的组织与性能

电镦发动机气门用镦块材料要求具有高的高温硬度，同时保持一定的韧性和可加工性。所研制的Ｗ２５２，Ｗ２３２高钨合金镦块在８００℃时，ＨＶ值分别为１５０和１６９，其使用寿命比ＣｕＷ８０镦块提高２０倍以上。用于生产排气门时，其成品率由５７．８％提高到９８．２％以上。

异形抽油杆镦锻模具设计

为了满足石油工业对抽油杆的批量要求,通过理论分析和实验研究,设计了一种异形抽油杆,并制定了Φ28.5mm抽油杆的镦锻成形工艺,同时设计出了一套结构简单、使用方便、寿命高的成形模具。该抽油杆具有节省材料,安装方便的优点。使用该工艺加工抽油杆的材料利用率高,生产效率高,精度高,使用寿命长。具有显著的社会效益和经济效益,对批量生产该异类形抽油杆,具有推广价值。

阶梯轴冷挤镦成形工艺及模具设计

以汽车变速箱二轴锻件为例,介绍了在通用液压机上采用开式冷挤压与闭式冷镦相结合的成形方法锻制阶梯轴的一种多工步冷锻工艺。讨论了制订锻件图中各工艺参数的确定原则、坯料制备、工步选定和设备的选择;给出了各冷锻工步的锻件工序图和模具装配图,介绍了模具的工作过程与模具材料的选择。该工艺及模具经生产实践验证,具有很好的经济效益,可供同类锻件开发冷锻工艺时参考。

空心抽油杆镦锻工艺的实验研究

通过对空心抽油杆镦锻工艺中金属流动特征的分析和实验研究 ,解决了空心抽油杆中部压方成形等无规则可循的难题。提出了避免空心抽油杆在镦锻过程中产生内壁凹陷、折叠、难充满的有效措施。在制订镦锻工艺时 ,采用倒装结构的凹模 ,减小了金属在模腔中的流动阻力 ,制订了36mm空心抽油杆镦锻成形工艺。

Cr12MoV钢冷镦凹模断裂分析

分析了材料为Cr12MoV的标准件冷镦凹模断裂原因,发现主要是由于淬火温度过高和回火不够充分所致,通过选择适当的淬火温度并进行充分回火,可以延长模具的使用寿命。

Φ88·9×6·45油管端部镦锻模具设计

通过理论和实验研究,分析了油管局部镦锻的变形特点,并针对Φ88.9×6.45这种油管,在考虑镦锻设备和保证锻件质量的前提下,制定了该油管的镦锻工艺,并设计了相应的模具。

钢管管端加厚模具的设计及应用

介绍了钢管管端加厚主要变形工具(夹紧模、加厚模、冲头)的尺寸设计方法,提出了加厚模具的材料要求,分析了加厚模具的常见损坏方式,给出了提高加厚模具使用寿命的具体措施。实际应用结果表明:该管端加厚模具设计方法具有较好的应用价值,所开发的产品完全满足用户需求。

系列化拉条镦头模设计

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12V240曲轴弯曲镦锻成形模具结构设计的改进

采用有限元方法模拟了 1 2V2 4 0曲轴的成形过程 ,分析了曲线成形规律和模膛充不满缺陷产生的原因 ,并据此提出改进模具结构设计方案 。

加厚油管管端成形工艺研究

针对加厚油管的管端成形,提出"闭式聚料、开式成形"的镦锻工艺,并应用有限元分析软件Deform-3D对73mm×5.51mm的加厚油管管端成形过程进行模拟,得到其变形规律。设计适合此工艺的模具,并在实际生产中推广使用。该工艺使生产效率提高,模具寿命加长,具有优越性。

温镦挤模具磨损失效分析

对失效的H13温锻模具钢进行了分析,发现模具钢硬度、晶粒大小、合金元素含量基本符合标准。高温摩擦磨损实验及磨损形貌观测表明,模具磨损的主要形式为黏着磨损,氧化磨损和磨粒磨损。运用DEFORM-3D软件模拟分析了模具硬度和毛坯温度等工艺参数对模具磨损的影响,结果与实际磨损状况基本吻合。这可为延长模具寿命提供帮助。