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外 文 翻 译Reducing Automotive Engine Speed Fluctuation at Idle单元制造和组装工艺系别：机电工程系专业名称：机械设计制造及其自动化学生姓名：何石学号：06090525指导教师姓名、职称：王博 讲师完成日期 2012年12月30日摘要现在有很多种制造工艺能够把原材料加工成零件，然而如果把这些工艺过程分解为基本加工方法，就会发现只剩下一些单元工艺过程，这些单元工艺过程能够构成了最复杂的制造系统。这一章节将详细的介绍这些单元工艺过程，使一个由其他专业人员组成的集成产品和工艺设计团队中的一个经过训练的专业设计工程师能对关于制造过程的基本方面有很好的了解。而且本节介绍的知识将帮助那些希望从更专业的制造手册、相关出版物及工具目录中获取进一步资料的个人。 考虑到制造工艺对工件结构的影响，可以分为以下五个单元工艺过程： 材料去除工艺通过一种可控制且确定的方式改变材料的质量来获得工件的几何形状，例如铣削、车削、电火花加工、抛光。 变形工艺在不改变工件质量和成分的前提下，通过塑性变形来改变工件的形状，例如滚压、锻造、印花。 初步成形工艺通过大量的成形材料来形成工件的几何形状，例如铸造、注射成型、金属模铸造和粉末成型。 结构改变工艺在不改变工件初始形状的前提下，改变工件的显微结构、特性或者外表形貌，例如热处理和表面硬化。 连接和装配工艺把小的工件组合在一起来获得期望的形状、结构和特性。这种工艺有两种基本类型：（1）利用机械能、化学能或热能把工件连接在一起（例如焊接和扩散连接）（2）完全的机械连接（例如铆接、热压装配和传统装配）1、单元工艺过程的选择 每个制造出来的工件都有确定的几何形状且要满足一系列要求，包括以下方面： (1)形状和尺寸 (2)物料清单 (3)精度和公差 (4)物理特性（包括机械特性） (5)产品质量 (6)制造成本在满足这些要求下，通常有多种方法可用来生产特定的零件，这就需要权衡比较不同的方法。2、单元工艺过程的控制和自动化每个单元工艺过程在某些方面必须是可以控制的。对更高精度、速度和制造生产率的要求促进了自动化融入到基本工艺中，这个过程包括零部件设计细节翻译到机器指令以及单元工艺过程自生的运作并作为整个生产环境的一个子系统。这一章节关于计算机辅助设计/计算机辅助制造（CAD/CAM）方面将讨论CAD文件的建立和储存以及它们在CAM中的使用中所设计的技术。对精度的要求不断在变化，如下图(2-1)。对日益严格的公差的要求促进了设计和制造工艺的不断改进。图2-1精密加工领域现代机床的控制强调两个方面：自适应控制和信息交流。对于自适应控制，控制者必须调整控制增益使整个系统在有动态干扰的情况下处于或接近于最佳状态。扩大的信息交流将基本工艺控制者搜集的数据和生产制造的其它部分联系了起来。关于生产时间和零件生产数量的数据存储在一个可以访问的数据库中且可以通过库存控制和质量监测来使用，这个数据库可以被用于生产调度，以避免冗余数据库的问题和成本。 在一个工厂，包含两个或更多数控机床的制造系统可能会使用一个独立的能控制几台机床或整个车间的大型计算机，该系统通常被称为分布式数控（DNC）。 现在很多工厂都采用柔性制造系统（FMS）一种对DNC改进的系统。一个FMS包括一些数控单元工艺过程（不仅仅是机床），这些数控单元工艺过程通过一个自动物料处理系统连接起来，并且用工业机器人来实现有柔性要求的各种任务，例如装卸单元工艺过程中的队列。这些系统采用一个计算机作为系统的主控制器，且每个单元工艺工程都用计算机来指示下一步的任务。FMS的特点包括： （1）能高自动化地生产各种各样的零部件；（2）减少了生产时间且降低了库存； （3）提高了生产效率； （4）降低了生产成本； （5）能较快的适应产品及生产水平的改变；3、单元工艺过程 接下来将讨论一些单元工艺过程，许多例子将介绍本手册使用者经常会碰到的金属材料的工艺过程。然而，其它材料也可以用本章节所讨论的单元工艺过程来加工，可能需要适当的改变。 这一章节也将讨论机械装配和物料搬运过程。机械装配的时间平均占机械制造时间的一半，且可以通过改善工艺过程来提高机械装配过程的自动化和柔性化。物料搬运过程使不同工艺过程间建立了联系，物料搬运系统能保证不同工艺过程和装配工序所需的物料能在准确的时间内到达适当的位置。 这一章节结尾将通过一个案例研究来说明如何理解不同的单元工艺过程用于做出工程决策。材料去除工艺（1）传统加工 钻孔、铰孔、拉孔、镗孔、车削、铣削、磨削、刨削（2）特种加工 电火花加工、电化学加工、激光加工、喷射加工、超声波加工相变工艺 砂型铸造和熔模铸造结构改变工艺 正火和激光表面硬化变形工艺 模锻和轧压成形整合工艺过程 高分子化合物聚合和金属焊接机械装配工艺物料搬运过程案例研究4、材料去除工艺 这些工艺过程就是通过机械、电、激光或化学方法来加工得到期望的形状和表面特性。工件材料包括陶瓷、聚合物、复合材料以及金属，金属中尤其是目前最常见的铁和钢合金。通过其它工艺过程也能够提高工件的表面粗糙度和尺寸精度，例如锻造。加工过程是许多制造系统必不可少的一部分。 加工过程在制造过程中是重要的，其原因如下：（1）精度高 加工过程能获得较准确的几何轮廓、较高的尺寸精度和表面粗糙度，而这些通常是不能通过其它工艺过程获得的。例如砂型铸造的表面粗糙度为400-800in（10-20m），锻造的为200-400in（5-10m），压力铸造的为80-200in（2-5m）。超精密加工（超精加工、研磨、金刚石车削）的表面粗糙度能达到0.4in（0.01m）或更高 。在铸造中获得的尺寸精度的1-3%（公差与尺寸的比值）取决于热膨胀系数，金属锻造中的0.05-0.3%取决于弹性刚度，而在加工中这个值是0.001%。 （2）柔性化 最终加工产品的的形状是可以通过编程获得的，因此在相同的机床上可以加工许多不同的零件，而且基本上所有形状的零件都可以加工出来。在加工过程中，产品的轮廓是由刀具所走的路线形成的，而与刀具的形状无关。与此相反，在铸造、成型和锻造过程中需要专用工具来形成产品的几何轮廓，这限制了产品的柔性化。 （3）经济性 选择合适的工艺过程来加工小批量和大批量产品时，其成本相对较低。 在传统加工中，在刀具和工件相接处的地方起主要作用的物理机制是工件的塑性变形或工件的可控断裂，工件上的切削力是由比工件更硬的刀具的切削刃作用在工件上产生的。然而，许多新材料要么比传统切削刀具硬，要么就不能承受传统加工过程中的大切削力。特种加工能通过热、化学、电化学和机械（具有高冲击速度）间的相互作用来加工由那些高硬度、高强度的材料构成的精密的零件。 机械的切削加工性是根据刀具寿命、切削功率要求和工件最终表面粗糙度来定义的。迄今为止，还不能用一个基本关系式来描述这三个因素之间的关系，因此，机械切削加工性是根据经验测试决定的。4.1工艺过程的选择 加工机床可以分为以下两大类：（1）通过旋转运动形成表面的机床（2）通过直线运动形成平面或轮廓表面的机床 加工设备和加工过程的选择主要取决于以下几个因素： （1）工件的大小 （2）工件的轮廓（3）加工设备的能力（主轴转速、进给量、功率大小） （4）尺寸精度 （5）工序数量 （6）要求的表面条件和产品质量 例如，下图描述了不同的传统单元加工工艺过程所能达到的公差等级，这些数据能帮助你在符合产品要求的前提下选择合适的加工工艺。图4-1加工过程的容差与三维数据4.2传统加工 传统加工过程是通过塑性变形来去除工件材料的，这个过程需要工件和刀具直接接触并且要通过工件和刀具之间的相对运动产生的剪切应力来形成切屑，这就需要刀具比工件更硬，以避免刀具的磨损。这儿讨论的单元工艺过程是经常会碰到的工艺过程中具有代表性的，章节最后的参考资料中有关于单元加工工艺更详尽的描述。 传统加工中的运动学 在传统加工过程中，工件表面形状是由刀具和工件之间的相对运动形成的，相对运动包括主运动和进给运动两个基本运动。主运动是由机床产生，能使工件和刀具产生相对运动。进给运动是附加在主运动上且能使切削持续进行的运动，进给运动也需要一部分能量。这两个运动一般情况下同时进行且运动方向正交。 虽然对车削、铣削、钻削和磨削功能的定义没有特别显著的区别，但是加工工艺方面的专家已经给有特定功能的组合或相关机器配置的工艺过程规定了专用术语。可以根据切削刃的基本类型将经常使用的金属切削刀具分为三类：单刃切削刀具、多刃切削刀具和砂轮。 动态稳定性和振动 在选择机床时需要考虑机床的振动稳定性。在金属切削过程中，刀具可能是以一定的振幅和频率来加工工件的，这会引起切削力的过多变化，从而导致零件表面质量不好以及会降低刀具的寿命。 切削中的强迫振动是由回转零件旋转不平衡、传动机构的缺陷以及多刃切削中的断续切削中产生的周期性干扰力所引起的。自激振动往往发生在提高切削速度的时候，自激振动也称为颤振。所有的自激振动是由在切削过程中机架和驱动系统间的负反馈回路产生的。机床的传递函数，在刚度和阻尼方面的特性，对整个反馈系统的稳定性起关键的作用。在切削刀具和工件间测量的大多数机床的静刚度大约为100000 lb-ft/in，当机床静刚度达到1000000 lb-ft/in时性能很好，当其静刚度为10000lb-ft/in时，机床性能不佳，但这种刚度的小型机床仍能用于低成本产品的生产。 机床的基本部件 先进的机床设计和制造理念消除了不同类型机床间的差别。50年前，大多数机床只有一种功能，如钻孔或车削，而且只能单机操作。自动换刀装置和数控系统（CNC）的出现使车床成为了车削中心，铣床成为了加工中心，这些多工艺过程的加工中心具有很多加工功能，例如车削、铣削、钻孔、镗孔和磨削。 机床床身支撑着主轴箱和工作台，在选择机床床身的材料时应考虑材料的硬度、耐磨性、热膨胀系数、抗振性、抗腐蚀性以及成本。 工作台或主轴箱安装在导轨上，每种类型的导轨上都有一个沿床身轨道滑动的滑板，在这个滑板上面安装工作台或主轴。矩形导轨是最原始和最简单的导轨，由于接触面积大，具有刚度高、抗振性好等特性，而且能够承受大切削力和冲击载荷。由于导轨上静摩擦系数和动摩擦系数的不同，矩形滑板要经历粘滑运动，这种情况下会产生定位和进给运动的误差。直线导轨也包括一个尾座和滑板，只是直线导轨采用了能消除粘滑的滚动轴承。直线导轨质量轻而且操作时摩擦力小，因而能用较少的能量实现较快的定位，然而由于其表面接触面积不大，导轨的刚度不够高。 导轨上的滑板是由液压装置、齿轮齿条机构或丝杠带动的。液压活塞成本低、动力强，但难于维护且精度较低，加工过程中产生的热量会降低加工精度。电动齿轮齿条机构易于维护且用于大范围的运动，但精度不高且操作时消耗很多能量。电动丝杠是使用最普遍的，包括成本较低的一般丝杠和高精度的滚珠丝杠两种。滚珠丝杠间隙小，非常适合刀具轨迹连续的数控机床，然而受限于滚珠和丝杠间的接触面积，滚珠丝杠的刚度不够高。 电动机是大多数机床的主要动力源，提供主轴旋转、滑板移动以及一些辅助运动所需的动力。大多数电动机采用220V或440V的三相交流电。在调速时实现大的扭矩是机床和电动机设计过程中的所追求的目标。在最近几年，主轴转速提高得很快，例如5年前主轴转速接近1600 rpm，而现在的主轴转速能达到12,000 rpm或更高，然而高的转速使振动加剧，这会给机械传动带来一定的困难。随着电动机设计技术和控制技术的提高，现在也能实现快速调整电动机转速和转矩。对于大多数高速和低扭矩机床来说，那些具有超过三速变速系统的机械系统已经是不必要的了，电主轴的额定功率大概在3.7-112kW之间，平均能达到37Kw,而定位马达的转矩大概在0.2-115Nm之间。 由于扭矩是由主轴传递给刀具的，因此主轴的旋转精度对于机床来说非常重要。影响主轴旋转精度的主要因素有：轴承类型及其布置形式、润滑和冷却条件。6UnitUnitUnitUnit ManufacturingManufacturingManufacturingManufacturing andandandand AssemblyAssemblyAssemblyAssembly ProcessesProcessesProcessesProcessesThere are a bewildering number of manufacturing processes able to impart physical shape andstructure to a workpiece. However, if these processes are broken down into their basicelements and then examined for commonality, only a few fundamental processes remain.These are the building blocks, or unit processes, from which even the most complicatedmanufacturing system is constructed. This section describes these unit processes in sufficientdetail that a technically trained person, such as a design engineer serving as a member of anintegrated product and process design team comprised of members from other specialties,could become generally knowledgeable regarding the essential aspects of manufacturingprocesses. Also, the information presented in this section will aid such an individualinpursuing further information from more specialized manufacturing handbooks, publications,and equipment/tool catalogs.Considering the effect that a manufacturing process has on workpiece configuration andstructure, the following five general types of unit manufacturing process can be identified.Material removal processesGeometry is generated by changing the mass of theincoming material in a controlled and well-defined manner, e.g., milling, turning,electrodischarge machining, and polishing.Deformation processes The shape of a solid workpiece is altered by plastic deformationwithoutchanging its mass or composition, e.g., rolling, forging, and stamping.Primary shaping processesA well-defined geometry is established by bulk formingmaterial that initially had no shape, e.g., casting, injection molding, die casting, andconsolidation of powders.Structure-change processes The microstructure, properties, or appearance of theworkpiece araltered without changing the original shape of the workpiece, e.g., heat treatmentand surface hardening.Joining and assembly processes Smaller objects are put together to achieve a desiredgeometry structure, and/or property. There are two general types: (1) consolidation processeswhich usemechanical, chemical, or thermal energy to bond the objects (e.g., welding anddiffusion bonding) and (2) strictly mechanical joining (e.g., riveting, shrink fitting, andconventional assembly).UnitUnitUnitUnit ProcessProcessProcessProcess SelectionSelectionSelectionSelectionEach component being manufactured has a well-defined geometry and a set of requirementsthat it must meet. These typically include:Shape and sizeBill-of-materialAccuracy and tolerancesAppearance and surface finishPhysical (including mechanical) propertiesProduction quantityCost of manufactureIn order to satisfy these criteria, more than one solution is usually possible and trade-offanalyses should be conducted to compare the different approaches that could be used toproduce a particular part.ControlControlControlControl andandandand AutomationAutomationAutomationAutomation ofofofof UnitUnitUnitUnit ProcessesProcessesProcessesProcessesEvery unit process must be controlled or directed in some way. The need for improvedaccuracy, speed,and manufacturing productivity has spurred the incorporation of automationinto unit processes regarding both the translation of part design details into machineinstructions, and the operation of the unit process itself and as a subsystem of the overallproductionenvironment.Thesectionofthischapteroncomputer-aideddesign/computer-aided manufacturing (CAD/CAM) discusses the technology involved increating and storing CAD files and their use in CAM. The expectations of precision arecontinuing to change,as indicated in Figure 13.2.1. This drive for ever-tighter tolerances ishelping spur interest in continual improvements in design and manufacturing processes.FIGURE 2.1 Precision machining domains.Modern machine tool controls are emphasizing two areas: adaptive control andcommunication. For adaptive control the controller must adapt its control gains so that theoverall system remains at or near communication links the data the optimal condition in spiteof varying process dynamics. Expanded collected by a unit process controller to othersegments of the manufacturing operation. Data regarding production time and quantity ofparts produced can be stored in an accessible database for use by inventory control andquality monitoring. This same database can then be used by production schedulers to avoidproblems and costs associated with redundant databases.At the factory level, machining operations employing two or more numerically controlled(NC)machine tools may use a separate mainframe computer that controls several machinetools or an entire shop. The system is often referred to as distributed numerical control(DNC).Today many factories are implementing fiexible manufacturing systems (FMS), anevolution of DNC.An FMS consists of several NC unit processes (not necessarily onlymachine tools) which are interconnected by an automated materials handling system andwhich employ industrial robots for a variety of tasks requiring fiexibility, such asloading/unloading the unit process queues. A single computer serves as master controller forthe system, and each process may utilize a computer to direct the lower-order tasks.Advantages of FMS include: A wide range of parts can be produced with a high degree of automation Overall production lead times are shortened and inventory levels reduced Productivity of production employees is increased Production cost is reduced The system can easily adapt to changes in products and production levelsUnitUnitUnitUnit ProcessesProcessesProcessesProcessesIn the following discussion, a number of unit processes are discussed, organized by the effectthat they have on workpiece configuration and structure. Many of the examples deal withprocessing of metals since that is the most likely material which users of this handbook willencounter. However, other materials are readily processed with the unit processes describedin this chapter, albeit with suitable modifications or variations.Mechanical assembly and material handling are also discussed in this section. On average,mechanical assembly accounts for half of the manufacturing time, and processes have beendeveloped to improve the automation and fiexibility of this very difficult task. Materialhandling provides the integrating link between the different processes material-handlingsystems ensure that the required material arrive at the proper place at the right time for thevarious unit processes and assembly operations.The section ends with a case study that demonstrates how understanding of the differentunit processes can be used to make engineering decisions.Material removal (machining) processesTraditional machiningDrill and reamingTurning and boringPlaning and shapingMillingBroachingGrindingMortalityNontraditional machiningElectrical discharge machiningElectrical chemical machiningLaser beam machiningJet machining (water and abrasive)Ultrasonic machiningPhase-change processesGreen sand castingInvestment castingStructure-change processesNormalizing steelLaser surface hardeningDeformation processesDie forgingPress-brake formingConsolidation processesPolymer composite consolidationShielded metal-arc weldingMechanical assemblyMaterial handlingCase study: Manufacturing and inspection of precision recirculating ballscrewsMaterialMaterialMaterialMaterial RemovalRemovalRemovalRemoval ProcessesProcessesProcessesProcessesThese processes, also known as machining, remove material by mechanical, electrical, laser,or chemical means to generate the desired shape and/or surface characteristic. Workpiecematerials span the spectrum of metals, ceramics, polymers, and composites, but metals, andparticularly iron and steel alloys, are by far the most common. Machining can also improvethe tolerances and finish of workpieces previously shaped by other processes, such as forging.Machining is an essential element of many manufacturing systems.Machining is important in manufacturing becauseIt is precise. Machining is capable of creating geometric configurations, tolerances, andsurface finishes that are often unobtainable by other methods. For example, generallyachievable surfaceroughness for sand casting is 400 to 800 in. (10 to 20m), for forging 200to 400 in. (5 to 10 m), and for die casting 80 to 200 in. (2 to 5 m). Ultraprecisionmachining (i.e., super-finishing, lapping, diamond turning) can produce a surface finish of0.4in (0.01 m) or better. The achievable dimensional accuracy in casting is 1 to 3% (ratioof tolerance to dimension) depending on the thermal expansion coefficient and in metalforming it is 0.05 to 0.30% depending on the elastic stiffness, but in machining the achievabletolerance can be 0.001%It is fiexible. The shape of the final machined product is programmed and therefore manydifferent parts can be made on the same machine tool and just about any arbitrary shape canbe machined.In machining, the product contour is created by the path, rather than the shape,of the cutter. By contrast, casting, molding, and forming processes require dedicated tools foreach product geometry, thus restricting their fiexibility.It can be economical. Small lots and large quantities of parts can be relatively inexpensivelyproduced if matched to the proper machining process.ProcessProcessProcessProcess SelectionSelectionSelectionSelectionMachine tools can be grouped into two broad categories:Those that generate surfaces of rotationThose that generate flat or contoured surfaces by linear motionSelection of equipment and machining procedures depends largely on these considerations: Size of workpieceConfiguration of workpiece Equipment capacity (speed, feed, horsepower range) Dimensional accuracyNumber of operations Required surface condition and product qualityFor example, Figure 13.2.2 graphically indicates the various tolerance levels that can betypically achieved for common machining unit processes as a function of the size of theworkpiece. Such data can help in identifying candidate unit processes that are capable ofmeeting product requirements.FIGURE 4.1Tolerance vs. dimensional data for machining processes.TraditionalTraditionalTraditionalTraditional MachiningMachiningMachiningMachiningTraditional machining processes remove material from a workpiece through plasticdeformation. The process requires direct mechanical contact between the tool and workpieceand uses relative motion between the tool and the workpiece to develop the shear forcesnecessary to form machining chips. The tool must be harder than the workpiece to avoidexcessive tool wear. The unit processes described here are a representative sample of thetypes most likely to be encountered. The reference list at the end of the section should beconsulted for more detailed information on the unit processes discussed below,plus those that are not included here.Process Kinematics in Traditional Machining. In all traditional machining processes, thesurface is created by providing suitable relative motion between the cutting tool and theworkpiece. There are two basic components of relative motion: primary motion and feedmotion. Primary motion is the main motion provided by a machine tool to cause relativemotion between the tool and workpiece. The feed motion, or the secondary motion, is amotion that, when added to the primary motion, leads to a repeated or continuous chipremoval. It usually absorbs a small proportion of the total power required to perform amachining operation. The two motion components often take place simultaneouslyinorthogonal directions.The functional definitions of turning, milling, drilling, and grinding are not distinctivelydifferent, but machining process specialists have developed terminology peculiar to a givencombination of functions or machine configurations. Commonly used metal-cutting machinetools, however, can be divided into three groups depending upon the basic type of cutter used:single-point tools, multipoint tools, or abrasive grits.Dynamic Stability and Chatter. One of the important considerations in selecting a machinetool is its vibrational stability. In metal cutting, there is a possibility for the cutter to move inand out of the workpiece at frequency and amplitude that cause excessive variations of thecutting force, resulting in poor surface quality and reduced life of the cutting tool.Forced vibrations during cutting are associated with periodic forces resulting from theunbalance of rotating parts, from errors of accuracy in some driving components, or simplyfrom the intermittent engagement of workpiece with multipoint cutters.Self-excited vibrationsoccur under conditions generally associated with an increase in machining rate. Thesevibrations are often referred to as chatter. All types of chatter are caused by feedback loopwithin the machine tool structure between the cutting aprocess and the machine frame anddrive system. The transfer function of the machine tool, in terms of the stiffness and dampingcharacteristics, plays a critical role in the stability of the overall feedback system. The staticstiffness of most machine tools, as measured between the cutting tool and the workpiece tendsto be aroundlb-ft/in. A stiffness oflb-ft/in. is exceptionally good, while stiffnessoflb-ft/in, is poor but perhaps acceptable for low-cost production utilizing smallmachine tools.Basic Machine Tool Components. Advances in machine-tool design and fabricationphilosophy are quickly eliminating the differences between machine types. Fifty years ago,most machine tools performed a single function such as drilling or turning, and operatedstrictly stand-alone. The addition of automatic turrets, tool-changers, and computerizednumerical control (CNC) systems allowed lathes to become turning centers and millingmachines to become machining centers. These multiprocess centers can perform a range ofstandard machining functions: turning, milling, boring, drilling, and grinding.The machine tool frame supports all the active and passive components of the toolspindles, table and controls. Factors governing the choice of frame materials are: resistanceto deformation (hardness),resistance to impact and fracture (toughness), limited expansionunder heat (coefficient of thermal expansion), high absorption of vibrations (damping),resistance to shop-floor environment (corrosion resistance), and low cost.Guide ways carry the workpiece table or spindles. Each type of way consists of a slidemoving along a track in the frame. The slide carries the workpiece table or a spindle. Theoldest and simplest way is the box way. As a result of its large contact area, it has highstiffness, good damping characteristics, and high resistance to cutting forces and shock loads.Box slides can experience stick-slip motion as a result of the difference between dynamic andstatic friction coefficients in the ways. This condition introduces positioning and feed motionerrors. A linear way also consists of a rail and a slide, but it uses a rolling- element bearing,eliminating stick-slip. Linear ways are lighter in weight and operate with less friction, so theycan be positioned faster with less energy. However, they are less robust because of the limitedsurface contact area.Slides are moved by hydraulics, rack-and-pinion systems, or screws. Hydraulic pisto
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