粉末冶金是什么.doc

粉末冶金是什么? 粉末冶金（Powder Metallurgy)是制取金属粉末，及采用成形和烧结工艺将金属粉末（或金属粉末与非金属粉末的混合物）制成材料和制品的工艺技术。它是冶金和材料科学的一个重要分支学科。粉末冶金有历史2500年前 块炼铁锻造法制造铁器20世纪初 制取难熔金属。1909年制造电灯钨丝，推动了粉末冶金的发展；1923年粉末冶金硬质合金的出现被誉为机械加工中的革命。30年代 成功制取含油轴承。粉末冶金铁基机械零件的发展，充分发挥了粉末冶金少切削甚至无切削的优点。40年代 金属陶瓷、弥散强化等材料 60年代 粉末冶金高速钢，粉末高温合金应用80年代 汽车领域应用迅速发展粉末冶金的特点节材，节能 低环境污染较好的尺寸精度较好的表面状态接近最终形状 降低产品制造成本产品一致性好特殊的多合金组织多孔性组织复杂的形状适合大批量生产经济性节能：粉末成形所需压力远低于锻造、辊轧等传统制程；烧结温度又低于主成分熔点。故耗费之能源远低于铸造、机械加工等其它制程。省材：粉末冶金法的材料利用率高达95%以上，远高于其它制程。例如机械加工法的材料利用率平均仅有4050%之间。省时：在自动化生产在线，成形一个生胚的时间可低至0.5秒；而每一成品所耗费的平均烧结时间亦可低至数秒钟。其时间成本远低于其它制程。精度：粉末冶金产品的尺寸精度极高，在一般用途中，几乎无须后续加工性质上某些具有独特性质或显微组织的产品，除粉末冶金制程外，无法以其它制程获得。例如：多孔材料：过滤器、含油轴承、透气钢等复合材料：弥散强化或纤维强化复合材料合金系统：大部分合金系统均有固溶限，超过此一限度，其铸造组织会产生共晶、共析、或金属间化合物等偏析现象，形成不均匀的组织结构；而某些元素间即使在熔融状态下也不互溶，故不可能以铸造法制造。粉末冶金法的特性却使其可轻易调配出任意比例且组织均匀的合金材质(因其制程中未达熔点)。特殊性上有些材料虽可能以其它方法制作，在实作上却有相当的困难度，例如：高熔点金属：钨(3380)、钼(2615)、陶瓷等高熔点材料很难熔化铸造。活性金属：钛、钽等金属在熔融状态下的活性极高，易氧化或侵蚀坩埚，铸造上有相当大的困难。故多以粉末冶金法制造。粉末冶金选用准则1 零件尺寸粉末冶金零件的大小受限制于粉末的压缩性与成形压机吨位。对于一般钢的粉末冶金材料，可制备下列规格的零件： 投影表面面积小于32 000ram2； 直径小于175mm或不大于300ram(对于有大孔的零件)； 最大长度为150ram，最小长度为15ram； 长度对直径的最大比率为5：1；长度与壁厚之比的最大值为8。 倘若产品设计使用的是非铁金属材料，则投影面积可增大502 零件形状 零件的几何形状必须适合在垂直方向进行单轴向压制动作(见零件图例)。根切、凹人或螺纹一般都是在后续加工中成形或切削加工。零件的横断面变化大时，需要成形压机中的模具有各种不同动作。这些限制零件只能有5个台面，但是，通过模具设计，在零件长度方向(台面)上增加小的变动是可能的(见具体说明复杂形状粉末冶金零件设计的MPIF设计手册)。零件长度大于254mm 时，密度从顶面(密度最高)到中间处(密度较低)将有所不同。3 零件数量 鉴于使用的专用模具是“硬件”，应该讨论生产定货单的数量的成本与可行性数量。4 力学物理性能要求为有助于大多数产品应用选择合适的材料，标准35提供了范围广阔的设计性能。中等密度钢的牌号(64-69gcm3)一般可替代铸铁或普碳钢；高密度的牌号(7074gem3)一般可替代韧性铸铁和热处理的钢；粉末锻造与无孔隙材料系统一般可替代高性能钢。倘若零件设计的关键性能要求超出了标准中列出的标准值，则应将这些要求详细说明在工程图上。为了选择性能与成本及可行性二者都最佳的材料，和粉末冶金零件生产商讨论零件的应用是最重要的。为了避免产生概念不清或误解，买方与生产方都应在制造粉末冶金零件之前，就下列条件达成协议：最小强度值，牌号选择，化学组成，验收试验，标准性能值及制造工艺，因为这些都可能影响零件应用。 5 零件用途零件的技术规范或图纸应尽量提供零件的附加资料，提供组装图有利于较充分地了解零件应用。对于选择材料与生产工艺，下列问题是最重要的： 零件将用于流体压力条件下；要求必须密封不渗漏吗? 零件必须防止被腐蚀，要求的程度如何? 零件要切削加工的表面是哪些?公差如何? 零件需要哪一种热处理? 零件是用于高冲击载荷应用吗? 零件是用于磨损应用，磨损面是哪个表面? 表面粗糙度是一个重要设计特性；哪些表面有此性能要求?如何测量? 零件是用于磁性应用吗? 零件是用于高于室温的环境吗? 零件不得有哪一种毛边?角半径的大小? 零件需要焊接吗? 对零件的使用性能，有关键部位的要求吗? 需要特殊包装吗7粉末冶金应用领域粉末冶金制品的应用范围十分广泛，从普通机械制造到精密仪器；从五金工具到大型机械；从电子工业到电机制造；从民用工业到军事工业；从一般技术到尖端高技术，均能见到粉末冶金工艺的身影粉末冶金产品的应用各种机械制品多孔材料硬质合金生产耐高温制品优质工具钢磁性材料、触头材料摩擦材料各种领域的金属粉末金属陶瓷与特种陶瓷 What is powder metallurgy?Powder metallurgy is the technology which made from metal powder,through compacting and sintering process to make powder metal(or metal powder with mixture of non-metal powder) into material and products.It is a very important subdiscipline of metallurgy and material science.Powder metallurgy history2500 years,iron block(solid reduction method) forging method to make iron implements.The early of 20th. Century,make refractory metal.In 1909, making tungsten wire for bulbs promotes the development of powder metallurgy.In 1923,the emergence of powder metallurgy hard alloy is praised as the revolution of machining.30s,successful make out oil bushing.The development of powder metallurgy iron machinery parts,give full play to the advantage of powder metallurgy which requires less machining or even without machining40s,metal ceramic and dispersion-strengthened material.60s,powder metallurgy HSS and the application of powder superalloy.80s,booming development in auto industry.Features of powder metallurgyMaterial and energy savingLow pollutionGood dimensional accuracyGood surface conditionClose final shapeLower production costGood product consistencySpecial organization of many alloysPorous organizationComplex shapeSuitable mass productionEconomy aspectEnergy saving:The pressure requirement of powder metallurgy is greatly lower than forging,rolling etc. Traditional process;sintering temperature is also lower than main composition melting point.So the cost of energy is much lower than forging,CNC and other process.Material saving:the material usage of powder metallurgy is up to above 95%,much higher than other process,such as CNC,which material usage is approx between 40%-50%.Time saving:In automatic production line,the time of forming a blank only needs 0.5 seconds;and the average sintering time of each products also lower to a few seconds.The time cost is much lower than other process.Precision:The size of powder metallurgy products achieves high accuracy,in general process,no need further machining process.PropertySome products with special properties or microscopic structure,can only be made by powder metallurgy,other process will not be able to achieve .For example:Porous material:filter,oil bushing,porous steel etc.Composite material:dispersion strengthened or fibre reinforced composite materialAlloy system:Most of alloy system has solvus,exceed this solvus,the forging organization will produce eutectic,eutectoid and intermetallic compounds and segregation,forming uneven organization structure;However,some elements are not miscible,even under melting condition,so it is impossible to be made out by forging.The properties of powder metallurgy can easily mix out any proportions and homogeneous organization of alloy material.ParticularitySome material may able to use other process to make,but there is difficulty in practice.For example:High melting point metal:Tungsten(3380),molybdenum(2615),ceramic and other high melting point material which are difficult to be made by forging.Reactive metals:The activation of Titanium,tantalum etc.is very high under molten condition,easily oxidizing or crucible erosion,it causes great difficulty in forging,therefore,most of them are made by powder metallurgy.The standard of choosing powder metallurgyProducts sizeThe size of powder metallurgy parts is limited by the compressibility of powder and tons of compacting machine.For normal steel powder metallurgy material,can create following spec.of parts:Projection surface area lower than 32 000ram2Diameter less than 170mm or max 300ram(for parts with big hole)Maxlength 150ram,minlength 1.5ramThe max ratio between length and diameter is 5:1;the max ratio between length and wall thickness is 8If the design of products are using non-iron metal material,the projection area can increase 50%2. Products shapeThe products geometry must be suitable to make uniaxial press in in vertical.direction.Undercut,recess or thread are normally finished by post process or machining.When the cross section of parts changes a lot,it requires the tooling on molding machine has various action.These limited components can only have 5 flats,but,through tooling design,adding small alteration in the length of parts direction is possible.When the length of parts are longer than 25.4mm,the density will be different from top(max density) to middle(relatively low).3. Products quantityConsidering the special tooling is “hardware”,so it is necessary to discuss the purchase order quantity or MOQ.4. Mechanics/Physical property requirementsIn order to help most of products to choose suitable material,spec.35 provides widely design performance.The number of medium-density steel(64-69gcm3) can replace cast iron or plain carbon steel;high-density brand(7074gem3) can replace toughness ductile iron or heat-treated iron;powder forging and non-porous material can replace high-performance steel.If the key property of products design must be beyond the standard value of standard,then these requirements must be listed on the drawing.In order to choose the best material in performance,cost and feasibility,it is very important to discuss the application of products with customer,In order to avoid concepts unclear or misunderstanding,customer and supplier should reach an agreement before producing powder metallurgy products.like min strength,brand of material,chemical composition,inspection test,standard property value and producing tech,as these factors will influence the function of products.5. Products usageThe products tech.spec. or drawing should provide additional information as clear as possible,also provide assembling picture to supplier to let them fully understand the application of products.For choosing material and producing process,following questions are very important:When products work under fluid pressure,are they required sealed and no leakage?When products are required to prevent erosion,whats the standard?Which area are required machining?Whats the tolerance?What kind of heat treatment required?Are the products used in high-impact load?If the products require anti-wear function,which face requires?Surface roughness is a very important design,which face requires this?And how to measure?Are the products used in magnetic applications?Are the products used in high temperature environment ?What kind of burrs does the product not allowed to have?Fillet radius size?Does the product require welding?For the usage function of product,does it has requirement for critical location?Does product require special package?Powder metallurgy application fieldPowder metallurgy is widely used many different fields,we can see powder metallurgy from no