关 键 词：

齿轮泵 设计 装配 仿真 毕业设计

资源描述：

齿轮泵设计与装配仿真毕业设计,齿轮泵,设计,装配,仿真,毕业设计

内容简介：

河南理工大学万方科技学院本科毕业设计（论文）中期检查表指导教师： 张小明 职称： 所在院（系）： 机械系 教研室（研究室）： 题 目齿轮泵设计与装配仿真学生姓名杨成龙专业班级机设4班 学号0828080085一、选题质量：（主要从以下四个方面填写：1、选题是否符合专业培养目标，能否体现综合训练要求；2、题目难易程度；3、题目工作量；4、题目与生产、科研、经济、社会、文化及实验室建设等实际的结合程度）1选题涉及对齿轮泵的整体研究与参数设计以及装配仿真，符合专业培养目标，能够体现综合训练的要求。充分发挥学生的自主能力，紧密结合机械方面的知识，在设计中对所学的知识综合的加以运用，可以综合体现学生的知识掌握程度以及设计水平。培养学生运用所学知识进行生产实践以及解决实际问题的能力，为以后工作打下坚实的基础。2题目难易适中，要求学生有独立绘图的能力，以及能够使用计算机辅助绘图的能力。对学生的专业素质要求较高。3题目工作量较大，需要进行主要零件的的设计计算与校核，并要求绘制装配图。 4选题不但能够紧密结合实际，也在所学习专业知识的范围内，对以后的工作学习都有很大的帮助，齿轮泵设计已经有国家标准，因此设计内容有实例可参照，但是需要有自己独到的理解。二、开题报告完成情况：开题报告已如期按要求完成。对选择的题目进行了目的和意义的分析，并且通过网络和部分技术书籍，对国内外齿轮泵的研究进行了概述，初步建立了齿轮泵设计的整体框架，开题报告最后，从零件设计校核到最后装配仿真的实现，对设计工作进行了明确的分工，这些不仅有利于自己的设计环节，也有利于指导老师对我进度进行掌握，从而使本设计在合理合适的时间内完成。三、阶段性成果：1通过老师的指导帮助，对齿轮泵设计过程有了一定的认识，对其工作原理也有进一步的了解，并搜集了大量的资料，为设计的顺利进行做好了准备。2已如期按要求完成开题报告。3对于齿轮泵的一些零件的设计已经开始设计与校核，部分零件图开始绘制，并开始进行设计说明书的书写。四、存在主要问题：在设计过程中，不能很好的运用所学的知识，理论知识认知深度不够，不能很好的理论结合实际。局部结构设计思路不够清晰，有些盲目，有些文献的引用及查找不是很到位，设计不够连贯，系统性不强。对于一些已经标准化的零部件不能很好的结合设计实例选用。绘图能力不足，绘图有点慢，不能很好的运用计算机辅助制图。对于一些专业用语理解不够，资料的查找还有欠缺，数据的计算，公式的选用以及运用上还有一定的不足。五、指导教师对学生在毕业实习中，劳动、学习纪律及毕业设计（论文）进展等方面的评语指导教师： （签名） 年 月 日3河南理工大学万方科技学院本科毕业设计（论文）开题报告题目名称齿轮泵设计与装配仿真学生姓名杨成龙专业班级08机械设计4班学号0828080085一、 选题的目的和意义：齿轮泵是液压传动系统中常用的液压元件，在结构上可分为外啮合齿轮泵和内啮合齿轮泵两大类。齿轮泵结构简单、尺寸小、重量轻、制造维护方便、自吸能力强、工作可靠、对油液污染不敏感等优点，但是还存在流量和压力脉动大、噪声大、排量不可调节等缺点。它被广泛应用于各种低压系统中。随着齿轮泵在结构上的不断完善，它也被广泛应用于中高压系统中，因此研究齿轮泵对农业和工业均有重要的意义。随着CAX(CAD/CAE/CAM)技术的发展，3D技术在齿轮泵设计过程中发挥着越来越重要的作用。Pro/ENGINEER进行齿轮泵设计设计和运动分析，进行虚拟装配和动态仿真，利用这种方法可以及早发现设计中的缺陷，降低产品开发成本，缩短设计周期，可以大大提高产品设计的效率。本此课程设计是对自己大学学习的一次总结。通过本次课程设计，要学会独立查找与应用相关资料，并能够独立完成设计内容，培养认真严谨的学习态度，独立运用Pro/E和CAD绘制相关零件图以及装配图，加强自身综合运用所学专业知识和基本技能，独立分析和解决问题，开展试验研究、技术经济分析、撰写科技论文和技术报告等方面的能力。通过对齿轮泵的设计与分析，了解齿轮泵的原理以及各个零部件，了解其研究现状，在完成设计的同时更深入的思考，分析问题找出解决方案。在设计过程中要认真细致，反复校核。通过这次课程设计熟练应用自己的专业知识以及基本技能。二、 国内外研究综述：齿轮泵结构简单、加工方便、重量轻、有较强的自吸能力，因此被广泛应用，主要缺点是压力不平衡、噪声大、轴承寿命短。流量脉动大。国内外有关齿轮泵的研究主要集中在（1）齿轮参数及泵体结构的优化设计（2）困油冲击及卸荷措施（3）齿轮泵噪声控制（4）泄漏问题（5）齿轮泵的变量方法研究（6）齿轮泵间隙优化及补偿技术（7）轮齿表面涂覆技术（8）齿轮泵的寿命及其影响因素（9）齿轮泵高压化途径而提高工作压力所带来的问题是：轴承寿命大大缩短；泵泄漏加剧容积效率下降。产生这两个问题的根本原因在于齿轮上不平衡的径向液压力。目前针对这两个问题所进行的研究是：对齿轮泵的径向间隙进行补偿；减小齿轮泵的径向液压力，如优化齿轮参数，缩小牌也扣尺寸等；提高轴承承载能力。但这些方法都不能从根本上解决问题。因此对齿轮泵的研发和设计在各国都尤为重要。三、 毕业设计（论文）所用的主要技术与方法： 收集齿轮泵的相关资料，阅读参考文献。根据所给的设计参数对齿轮进行反复的计算，对齿轮、壳体、齿轮轴、轴承等进行计算，进行选材以及强度校核，最终绘制出零件图。利用Pro/E进行齿轮泵的整体造型装配以及运动分析，利用CAD绘制出齿轮泵的重要零件图。根据零件的设计过程进行总结，撰写毕业论文。四、 主要参考文献与资料获得情况：1.许贤良、王传礼. 液压传动. 北京：国防工业出版社，2006.92.邓乐、王裕清. 液压传动. 北京：北京邮电大学出版社，2010.43.任济生、唐道武、马克新. 机械设计机械设计基础课程设计. 徐州：中国矿业大学，2008.84.濮良贵、纪名刚. 机械设计. 北京：高等教育出版社，2006.55.刘鸿文. 材料力学. 北京：高等教育出版社，2004.16.哈尔滨工业大学理论力学教研室. 理论力学. 北京：高等教育出版社，2002.87.宁涛、王飞、岳荣刚. 中文版Pro/ENGINEER Wildfire 4.0基础教程. 北京：清华大学出版社，2008.38.薛焱. 中文版AutoCAD 2010基础教程. 北京：清华大学出版社，2010.10五、 毕业设计（论文）进度安排（按周说明） 第1-2周 进行毕业实习第3-6周 选择毕业设计课题，并着手查找收集相关资料及文献，确定论文题目完成毕业实习报告以及开题报告。第7-8周 开始毕业设计，进行齿轮泵零件设计计算以及校。第9-10周 完成齿轮泵的Pro/E造型以及装备，绘制零件图及装配图。第11-15周 完成毕业论文。第16周 准备答辩，参加毕业答辩。六、 指导教师审批意见： 指导教师： （签名）年 月 日 3河南理工大学万方科技学院本科毕业论文附录：外文资料与中文翻译外文资料：Rolling Contact BearingsThe concern of a machine designer with ball and roller bearings is fivefold as follows:(a) life in relation to load; (b) stiffness,ie.deflections under load; (c) friction; (d) wear; (e) noise. For moderate loads and speeds the correct selection of a standard bearing on the basis of a load rating will become important where loads are high, although this is usually of less magnitude than that of the shafts or other components associated with the bearing. Where speeds are high special cooling arrangements become necessary which may increase frictional drag. Wear is primarily associated with the introduction of contaminants, and sealing arrangements must be chosen with regard to the hostility of the environment.Because the high quality and low price of ball and roller bearing depends on quantity production, the task of the machine designer becomes one of selection rather than design. Rolling-contact bearings are generally made with steel which is through-hardened to about 900HV, although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600HV. It is not surprising that, owing to the high stresses involved, a predominant form of failure should be metal fatigue, and a good deal of work is based on accept values of life and it is general practice in bearing industry to define the load capacity of the bearing as that value below which 90 percent of a batch will exceed life of one million revolutions.Notwithstanding the fact that responsibility for basic design of ball and roller bearings rests with the bearing manufacturer, the machine designer must form a correct appreciation of the duty to be performed by the bearing and be concerned not only with bearing selection but with the conditions for correct installation.The fit of the bearing races onto the shaft or onto the housings is of critical importance because of their combined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit. Inadequate interference can induce serious trouble from fretting corrosion. The inner race is frequently located axially by against a shoulder. A radius at this point is essential for the avoidance of stress concentration and ball races are provided with a radius or chamfer to follow space for this.Where life is not the determining factor in design, it is usual to determine maximum loading by the amount to which a bearing will deflect under load. Thus the concept of static load-carrying capacity is understood to mean the load that can be applied to a bearing, which is either stationary or subject to slight swiveling motions, without impairing its running qualities for subsequent rotational motion. This has been determined by practical experience as the load which when applied to a bearing result in a total deformation of 0.0025mm for a ball 25mm in diameter.The successful functioning of many bearings depends upon providing them with adequate protection against their environment, and in some circumstances the environment must be protected from lubricants or products of deterioration of the bearing design. Moreover, seals which are applied to moving parts for any purpose are of interest to iridologists because they are components of bearing systems and can only be designed satisfactorily on basis of the appropriate bearing theory.Notwithstanding their importance, the amount of research effort that has been devoted to the understanding of the behavior of seals has been small when compared with that devoted to other aspects of bearing technology.LathesLathes are widely used in industry to produce all kinds of machined parts. Some are general purpose machines, and others are used to perform highly specialized operations.Engine lathesEngine lathes, of course, are general-purpose machine used in production and maintenance shop all over the world. Sized ranger from small bench models to huge heavy duty pieces of equipment. Many of the larger lathes come equipped with attachments not commonly found in the ordinary shop, such as automatic shop for the carriage.Tracer or Duplicating LathesThe tracer or duplicating lathe is designed o produce irregularly shaped parts automatically. The basic operation of this lathe is as fallows. A template of either a flat or three-dimensional shape is placed in a holder. A guide or pointer then moves along this shape and its movement controls that of the cutting tool. The duplication may include a square or tapered shoulder, grooves, tapers, and contours. Work such as motor shafts, spindles, pistons, rods, car axles, turbine shafts, and a variety of other objects can be turned using this type of lathe.Turret LathesWhen machining a complex work piece on a general-purpose lathe, a great deal of time is spent changing and adjusting the several tools that are needed to complete the work. One of the first adaptations of the engine lathe which made it suitable to mass production was the addition of multi-tool in place of the tailstock. Although most turrets have six stations, some have as many as eight.High-production turret lathes are very complicated machines with a wide variety of power accessories. The principal feature of all turret lathes, however, is that the tools can perform a consecutive serial of operations in proper sequence. Once the tools have been set and adjusted, little skill is requiring running out duplicate parts.Automatic Screw MachineScrew machines are similar in construction to turret lathes, except that their heads are designed to hold and feed long bars of stock. Otherwise, there is little different between them. Both are designed for multiple tooling, and both have adaptations for identical work. Originally, the turret lathe was designed as a chucking lathe for machining small casting, forgings, and irregularly shaped work pieces.The first screw machines were designed to feed bar stock and wire used in making small screw parts. Today, however, the turret lathe is frequently used with a collect attachment, and the automatic screw machine can be equipped with a chuck to hold castings.The single-spindle automatic screw machine, as its name implies, machines work on only one bar of stock at a time. A bar 16 to 20 feet long is feed through the headstock spindle and is held firmly by a collect. The machining operations are done by cutting tools mounted on the cross slide. When the machine is in operation, the spindle and the stock are rotated at selected speeds for different operations. If required, rapid reversal of spindle direction is also possible.In the single-spindle automatic screw machine, a specific length of stock is automatically fed through the spindle to a machining area. At this point, the turret and cross slide move into position and automatically perform whatever operations are required. After the machined piece is cut off, stock is again fed into the machining area and the entire cycle is repeated.Multiple-spindle automatic screw machines have from four to eight spindles located around a spindle carrier. Long bars of stock, supported at the rear of the machine, pass though these hollow spindles and are gripped by collects. With the single spindle machines, the turret indexes around the spindle. When one tool on the turret is working, the others are not. With a multiple spindle machine, however, the spindle itself index. Thus the bars of stock are carried to the various end working and side working tools. Each tool operates in only one position, but tolls operate simultaneously. Therefore, four to eight work pieces can be machined at the same time.Vertical Turret LathesA vertical turret is basically a turret lathe that has been stood on its headstock end. It is designed to perform a variety of turning operations. It consists of a turret, a revolving table, and a side head with a square turret for holding additional tools. Operations performed by any of the tools mounted on the turret or side head can be controlled through the use of stops.Machining CentersMany of todays more sophisticated lathes are called machining centers since they are capable of performing, in addition to the normal turning operations, certain milling and drilling operations. Basically, a machining center can be thought of as being a combination turret lathe and milling machine. Additional features are sometimes included by the versatility of their machines.Numerical ControlOne of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools were manually operated and controlled. Among the many limitations associated with manual control machine tools, perhaps none is more prominent than limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader.Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:1. Electrical discharge machining.2. Laser cutting.3. Electron beam welding.Numerical control has also made machines tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes.Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in early 1950s with funding provided by the USAir force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectively.However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is straight lines making up the steps, the smoother is the curve. Each line segment in the steps had to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. This instructional program was written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.A major problem wads the fragility of the punched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each programmed instruction had to be return through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems.The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problem of NC associated with punched paper and plastic tape.The development of a concept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend o a host computer. When the lost computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control.The development of the microprocessor allowed for the development of programmable logic controllers (PNC) and microcomputer. These two technologies allowed for the development of computer numerical control (CNC). With CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed off-line and download at the individual machine tool. CNC solved the problems associated with downtime of the host computer, but it introduced another known as data management. The same program might be loaded on ten different being solved by local area networks that connect microcomputer for better data management.CNC machine tool feed motion systemsCNC machine tool feed motion systems, especially to the outline of the control of movement into the system, must be addressed to the movement into the position and velocity at the same time the realization of two aspects of automatic control, as compared with the general machine tools, require more feed system high positioning accuracy and good dynamic response. A typical closed-loop control of CNC machine tool feed system, usually by comparing the location of amplification unit, drive unit, mechanical transmission components, such as feedback and testing of several parts. Here as mechanical gear-driven source refers to the movement of the rotary table into a linear motion of the entire mechanical transmission chain, including the deceleration device, turning the lead screw nut becomes mobile and vice-oriented components and so on. To ensure that the CNC machine tool feed drive system, precision, sensitivity and stability, the design of the mechanical parts of the general requirement is to eliminate the gap, reducing friction, reducing the movement of inertia to improve the transmission accuracy and stiffness. In addition, the feeding system load changes in the larger, demanding response characteristics, so for the stiffness, inertia matching the requirements is very high. Linear Roller GuidesIn order to meet these requirements, the use of CNC machine tools in general low-friction transmission vice, such as anti-friction sliding rail, rail rolling and hydrostatic guide ways, ball screws, etc.; transmission components to ensure accuracy, the use of pre-rational, the form of a reasonable support to enhance the stiffness of transmission; deceleration than the best choice to improve the resolution of machine tools and systems converted to the driveshaft on the reduction of inertia; as far as possible the elimination of drive space and reduce dead-zone inverse error and improve displacement precision.Linear Roller Guides outstanding advantage is seamless, and can impose pre-compression. By the rail body, the slider, ball, cage, end caps and so on. Also known as linear rolling guide unit. Use a fixed guide body without moving parts, the slider fixed on the moving parts. When the slider moves along the rail body, ball and slider in the guide of the arc between the straight and through the rolling bed cover of Rolling Road, from the work load to non-work load, and then rolling back work load, constant circulation, so as to guide and move the slider between the rolling into a ball.Limits and TolerancesThe breakage of the machine spare parts, generally always from the surface layer beginning of .The function of the product, particularly its credibility and durable, is decided by the quantity of spare parts surface layer to a large extent. Purpose that studies the machine to process the surface quantity be for control the machine process medium various craft factor to process the surface quantity influence of regulation, in order to make use of these regulations to control to process the process, end attain to improve the surface quantity, the exaltation product use the function of purpose .The machine processes the surface quantity to use the influence of the function to the machine(A) The surface quantity to bear to whet the sexual influence 1. Rough degree of surface to bear to whet the sexual influenceA just process vice-of two contact surfaces of good friction, the first stage is rough only in the surface of the peak department contact, the actual contact area is much smaller than theoretical contact area, in contact with each other the peak of the units have very great stress, to produce actual contact with the surface area of plastic deformation, deformation and peak between the Department of shear failure, causing serious wear.Parts wear may generally be divided into three stages, the initial stage of wear and tear, and normal wear and tear all of a sudden intense phase of stage wear.Parts of the surface roughness of the surface wear big impact. In general the smaller the value of surface roughness, wear better. However, surface roughness value is too small, lubricants difficult to store, contact between the adhesive-prone elements, wear it to increase. Therefore, the surface roughness of a best value, the value and parts of the work related to increased work load, the initial wear increased, the best rough surface is also increased.2. Cold working hardening the surface of the wear resistance Processing the Cold Work hardening the surface of the friction surface layer of metal micro hardness increase, it will generally improve the wear resistance. Cold Working but not a higher degree of hardening, wear resistance for the better, because too much will lead to hardening of the Cold Working excessive loose organization of metal, even a crack and peeling off the surface of the metal, declined to wear resistance.(B)The surface quality of the impact of fatigue strengthMetal hand alternating loads of fatigue after the damage occurred in parts often Chilled layer below the surface and, therefore parts of the surface quality of fatigue very influential.1. Surface roughness on the impact of fatigue strengthIn alternating load, the surface roughness of the Au-site easily lead to stress concentration, a fatigue crack, the higher the value of surface roughness, surface traces of Yu Shen Wen, Wen at the end of the radius smaller, anti-fatigue damage at the end of the more capacity worse.2. Residual stress, fatigue Cold Work hardening of the impact Residual stress on the impact of large parts fatigue. Surface layer of residual stress fatigue crack will expand and accelerate the fatigue damage the surface layer and the residual stress can prevent fatigue crack growth, delaying the formation of fatigue damage.(C)The surface quality of the corrosion resistance of the impactParts of the corrosion resistance to a large extent depend on the surface roughness. The higher the value of surface roughness, Au Valley accumulates on the more corrosive substances. Corrosion resistance of the worse.Surface layer of residual stress will produce stress corrosion cracking, lower parts of the wear-resistance, and the residual stress is to prevent stress corrosion cracking.(D) The surface quality with qualityRough surface will affect the value of the size of the co-ordination with the surface quality. The gap with rough value will increase wear and tear, increased space, with the requirements of the destruction of nature. For Fit, the assembly part of the process of convex surface-crowded peak times, the actual reduction of the surplus and reduce the support of the connection between the strength.DimensioningThe design of a machine includes many factors other than those of determining the loads and stresses and selecting the proper materials. Before construction or manufacture can begin, it is necessary to have complete assembly and detail drawings to convey all necessary information to the shop men. The designer frequently is called upon to check the drawings before they are sent to the shop. Much experience and familiarity with manufacturing processes are needed before one can become conversant with all phases of production drawings.Drawings should be carefully checked to see that the dimensioning is done in a manner that will be most convenient and understandable to the production departments. It is obvious that a drawing should be made in such a way that it has one and only one interpretation. In particular, shop personnel should not be required to make trigonometric or other involved calculations before the production machines can be set up.Dimensioning is an involved subject and long experience is required for its mastery.Tolerances must be placed on the dimensions of a drawing to limit the permissible variations in size because it is impossible to manufacture a part exactly to a given dimension. Although small tolerances give higher quality work and a better operating mechanism, the cost of manufacture increases rapidly as the tolerances are reduced, as indicated by the typical curve of Fig 14.1. It is therefore important that the tolerances be specified at the largest values that the operating or functional considerations permit.Tolerances may be either unilateral or bilateral. In unilateral dimensioning, one tolerance is zero, and all the variations are given by the other tolerance. In bilateral dimensioning, a mean dimension is used which extends to the midpoint of the tolerance zone with equal plus and minus variations extending each way from this dimension.The development of production processes for large-volume manufacture at low cost has been largely dependent upon interchangeability of component parts. Thus the designer must determine both the proper tolerances for the individual parts; the manner of placing tolerances on drawings depends somewhat on the kind of product or type of manufacturing process. If the tolerance on a dimension is not specifically stated, the drawing should contain a blanket note which gives the value of the tolerance for such dimensions. However, some companies do not use blanket notes on the supposition that if each dimension is considered individually, wider tolerance than those called for in the note could probably be specified. In any event it is very important that a drawing be free from ambiguities and be subject only to a single interpretation.Dimension and ToleranceIn dimensioning a drawing, the numbers placed in the dimension lines represent dimension that are only approximate and do not represent any degree of accuracy unless so stated by the designer. To specify a degree of accuracy, it is necessary to add tolerance figures to the dimension. Tolerance is the amount of variation permitted in the part or the total variation allowed in a given dimension. A shaft might have a nominal size of 2.5 in. (63.5mm), but for practical reasons this figure could not be maintained in manufacturing without great cost. Hence, a certain tolerance would be added and , if a variation of 0.003 in.(0.08mm) could be permitted, the dimension would be stated 2.5000.003(63.50.008mm).Dimensions given close tolerances mean that the part must fit properly with some other part. Both must be given tolerances in keeping with the allowance desired, the manufacturing processes available, and the minimum cost of production and assembly that will maximize profit. Generally speaking, the cost of a part goes up as the tolerance is decreased. If a part has several or more surfaces to be machined, the cost can be excessive when little deviation is allowed from the nominal size.Allowance, which is sometimes confused with tolerance, has an altogether different meaning.It is the minimum clearance space intended between mating parts and represents the condition of tightest permissible fit. If a shaft, size 1.498, is to fit a hole of size 1.500, the minimum size hole is 1.500 and the maximum size shaft is 1.498. Thus the allowance is 0.002 and the maximum clearance is 0.008 as based on the minimum shaft size and maximum hole dimension.Tolerances may be either unilateral or bilateral. Unilateral tolerance means that any variation is made in only one direction from the nominal or basic dimension. Referring to the previous example, the hole is dimensioned 1.500, which represents a unilateral tolerance. If the dimensions were given as 1.5000.003, the tolerance would be bilateral; That is, it would vary both over and under the nominal dimension. The unilateral system permits changing the tolerance while still retaining the same allowance or type of fit. With the bilateral system, this is not possible without also changing the nominal size dimension of one or both of the two mating parts. In mass production, where mating parts must be interchangeable, unilateral tolerances are customary. To have an interference or fore fit between mating parts, the tolerances must be such as to create a zero or negative allowance.Tolerances Limits and FitsThe drawing must be a true and complete statement of the designers expressed in such a way that the part is convenient to manufacture. Every dimension necessary to define the product must be stated once and repeated in different views. Dimensions relating to one particular feature, such as the position and size of hole, where possible, appear on the same view.There should be no more dimensions than are absolutely necessary, and no feature should be located by more than one dimension in any direction. It may be necessary occasionally to give an auxiliary dimension for reference, possibly for inspection. When this is so, the dimension should be enclosed in a bracket and marked for reference. Such dimensions are not governed by general tolerances.Dimensions that affect the function of the part should always be specified and not left as the sum or other dimensions. If this is not done, the total permissible variation on that dimension will form the sum or difference of the other dimensions and their tolerance, and this with result in these tolerances having to be made unnecessarily tight. The overall dimension should always appear.All dimensions must be governed by the general tolerance on the drawing unless otherwise stated. Usually, such a tolerance will be governed by the magnitude of the dimension. Specific tolerances must always be stated on dimensions affecting or interchangeability. A system of tolerances is necessary to allow for the variations in accuracy that are bound to occur during manufacture, and still provide for interchangeability and correct function of the part.A tolerance is the difference in a dimension in order to allow for unavoidable imperfections in workmanship. The tolerance range will depend on the accuracy of the manufacturing organization, the machining process and the magnitude of the dimension. The greater the tolerance range is disposed on both sides of the nominal dimension. A unilateral tolerance is one where the tolerance zone is on one side only of the nominal dimension, in which case the nominal dimension may from one of the limits.Limits are the extreme dimensions of the tolerance zone. For example, nominal dimension 30mm tolerance limits Fits depend on the relationship between the tolerance zones of two mating parts, and may be broadly classified into a clearance fit with positive allowance, a transition fit where the allowance may be either positive or negative (clearance or interference) , an interference fit where the allowance is always negative.Type of Limits and FitsThe ISO system of Limits and Fits, widely used in a number of leading metric countries, is considerably more complex than the ANSI system.In this system, each part has a basic size. Each limit of part, high and sign being obtained by subtracting the basic size form the limit in question. The difference between the two limits of size of a part is called the tolerance, an absolute without sign.There are three classes of fits: 1) clearance fits, 2) transition fits (the assembly may have either clearance or interference), and 3) interference fits.Either a shaft-basis system or a hole-basis system may be used. For any given basic size, a range of tolerance and deviations may be specified with respect to be line of zero deviation, called the zero line. The tolerance is a function of the basic size and is designated by a number symbol, called the grade-thus the tolerance grade. The position of the tolerance with respect to the zero line also a function of the basic size-is indicated by a letter symbol(or two letter), a capital letter for holes and a lowercase letter for shafts. Thus the specification for a hole and shaft having a basic size of 45mm might be45H8/g7. Twenty standard grades of tolerance are provided, called IT 01,IT 0 ,IT 1-18, providing numerical values for each nominal diameter, in arbitrary steps up to 500mm (for example 0-3,3-6,6-10, 400-500mm). The value of the tolerance unit, I, for grades 5-16 isWhere is in microns and D in millimeters.Standard shaft and whole deviations similarly are provided by sets of formulas, however, for practical, both tolerances and deviations are provided in three sets of rather complex tables. Additional tables gives the values for basic sizes above 500mm and for “Commonly Used Shafts and Holes” in two categories -“General Purpose” and “Fine Mechanisms and Horology”.中文翻译：滚动轴承对于球轴承和滚子轴承，一个机械设计人员应该考虑下面五个方面：（a)寿命与载荷关系；（b）刚度，也就是在载荷作用下的变形；（c）摩擦；（d）磨损；（e）噪声。对于中等载荷和转速，根据额定负荷选择一个标准轴承，通常都可以保证其具有令人满意的工作性能。当载荷较大时，轴承零件的变形，尽管它通常小于轴和其他与轴承一起工作的零部件的变形，将会变的重要起来。在转速高的场合需要专门的冷却装置，而这可能会增大摩擦阻力。磨损主要是由于污染物的进入引起的，必须选用密封装置以防止周围环境的不良影响。因为大批量生产这种方式决定了球轴承和滚子轴承不但质量高，而且价格低，因而机器设计人员的任务是选择而不是设计轴承。滚动接触轴承通常是采用硬度约为900HV、整体淬火的钢来制造。但在许多机构上不使用专门的套圈，而将相互作用的表面淬硬到大约600HV。滚动轴承由于工作中会产生高的应力，其主要失效形式是金属疲劳，这一点并不奇怪，目前正在进行大量的工作以求改进这种轴承的可靠性。轴承设计可以基于人们所接受的寿命值来进行。在轴承行业中，通常将轴承的承载能力定义为这样的值，即所承担的载荷小于这个值时，一批轴承中将会有90%的轴承具有超过一百万转的寿命。尽管球轴承和滚子轴承的基本设计责任在轴承制造厂家，机器设计人员必须对轴承所完成的任务做出正确的评价，不仅要考虑轴承的选择，而且换药考虑轴承的正确安装条件。轴承圈套与轴或轴承座的配合非常重要，因为它们之间的配合不仅应该保证所余要的过盈量，而且也应该保证轴承的内部间隙。不正确的过盈量会产生微动腐蚀从而导致严重的故障。内圈通常是通过靠紧在轴肩上进行轴向定位的。轴肩处的圆弧半径主要是为了避免应力集中。在轴承内圈上加工出一个圆弧或者倒角，用来提供容纳轴肩处圆弧半径的空间。在使用寿命不是设计中的决定因素的场合，通常根据轴承受载荷时产生的变形量来确定其最大载荷。因而，“静态承受能力”这个概念可以理解为对处于静止状态的或进行缓慢转动的轴承所能够施加的载荷。这个载荷对轴承的随后进行旋转运动时的质量没有不利影响。按照时间经验确定，静态载荷能力是这这样一个载荷，当它作用在轴承上时，滚动体与滚到在任何一个接触点处的总变形量不超过滚动体直径的0.01%。这相当于直径为25mm的球产生0.0025mm的永久变形。只有将轴承与周围环境适当地隔开，许多轴承才能成功地实现它们的功用。在某些情况下，必须保护环境，使其不受到润滑剂和轴承表面磨损生成物的污染。轴承设计的一个重要组成部分是使密封装置起到应有的作用，此外，对摩擦学研究人员来说，为了任何目的而应用于运动零部件上的密封装置都是他们感兴趣的。因为密封装置是轴承的一部分，只有根据适当的轴承理论才能设计出令人满意的密封系统。虽然它们很重要，与轴承其他方面的研究工作相比，在密封装置的研究方面所做的工作还是比较少的。车床车床是工业生产生活中被广泛用来加工各种类型的机械零件。一些车床是通用机床，而另一些车床则被用来完成某些专门工序的加工任务。普通车床普通车床是全世界的生产车间和维修车间里广泛使用的通用机床。它的尺寸范围很广，从小型的台式车床到巨大的重型车床。许多大型的车床装配在普通车间中通常看不到得附件，例如，滑板的自动挡块。靠模车床或仿形车床靠模车床或仿形车床被设计用来对形状不规则的零件进行自动加工。这种车床的基本操作如下：在夹持装置上安装平面或立体形状的样板，然后，导向触头或指针沿着它的外形移动。从而控制切削刀具的运动。仿形加工可以包括方形或锥形轴承肩、各种槽、锥体和轮廓。像电动机的轴、主轴、活塞、杆件、汽车轴、汽轮机轴和其他很多种类的工件都可以采用这种车床来进行切削加工。转塔车床在通用车床上加工一个复杂的工件时，在更换和调整加工时所用的一些刀具上要花费很多时间。对普通车床的早期改装工作之一是增加一个可以安装多把刀具的转塔来代替尾架，使它能够更好地适应大批量生产的需要。虽然大多数转塔有六个工位，但有些转塔有八个工位。高生产率的转塔车床是装有许多动力附件的非常复杂的机器。然而，所有转塔车床的主要特点是刀具能按适当顺序完成一系列的加工工序。一旦这些刀具被安装调整好后，只需要很低的技术就可车削加工很多相同的零件。自动螺丝车床螺丝车床在结构上与转塔车床类似，不同之处是螺丝车床的主轴头部能被设计用来夹持和送进长棒料。除此之外，它们之间几乎没有什么差别。这两种车床都用于多刀具切削，都适合加工同样的工件。最初，为转塔车床设计的用途和卡盘车床的用途一样，也是用来加工小型铸件、锻件和形状不规则的零件。早期的螺丝车床通过棒料和线材的选送，制造小的螺丝零件。时至今日，转塔车床上经常使用夹头附件，而自动螺丝车床上则可通过安装卡盘来夹持铸件。单轴自动螺丝车床，顾名思义，一次仅能加工一根棒料。一根16至20英尺长的棒料可以通过主轴箱中的主轴孔送进，并用夹头将其夹紧。机械加工工序是由装在转塔和横刀架上的刀具完成的。当机床工作时，主轴和棒料按照每道工序所选择的转速旋转。如果需要时也可以使主轴快速反转。在单轴自动螺丝车床上，棒料的一段规定好的长度穿过主轴自动送到加工区。在这里，转塔和横刀架进入加工位置并自动完成所需的任何加工工作。当加工好的零件被切断后，棒料再次被送入加工区，并重复整个循环。多轴自动螺丝床在主轴鼓周围装有4到8根主轴。在机床尾部支撑着的长棒料穿过这些空心主轴，通过夹头进行夹紧。在单轴车床上，转塔围绕主轴转位。当转塔丝杠的一个刀具工作时，其他的刀具不工作。然而，在多轴自动车床上，主轴自己转位。因此，几根棒料被传送到各个不同的端面加工和侧面加工的刀具位置处。每把刀具仅在一个位置工作，但是所有的刀具都能同时工作。因此，在同一时间内加工4到8个工件。立式转塔车床立式转塔车床基本上就是将其从床头箱一端向下面立起来的一台转塔车床。它被设计用来完成各种各样的切削工作。它由一个转塔，一个旋转工作台和一个侧面溜板组成的。在侧面溜板上装有可以安装几把刀具的正方形刀架。由安装在转塔或侧面溜板上的任何刀具完成的加工工序都可通过使用挡块来加以控制。加工中心当前，许多技术更为先进的车床叫做加工中心。因为，它们除了完成常规的车削工作之外，还可以完成某些铣削、钻削工作。加工中心基本上可以认为是转塔车床和铣床的组合体。有时，制造厂商为了增加机床的多用性，还会增加一些其他的性能。数字控制先进制造技术中的一个最基本的概念是数字控制（NC）。在数控技术出现之前，所有的机床都是人工操纵和控制的。在与人工控制的机床有关的很多局限性中，操作者的技能大概是最突出的问题。在采用人工控制时，产品的质量直接与操作者的技能有关。数字控制代表了从人工控制机床走出来的第一步。数字控制依托着着采用预先录制的，存储的符号指令，控制机床和其他制造系统。一个数控技师的工作部是去操纵机床，而是编写能够发出机床操作指令的程序。对于一台数控机床，其上必须装有一个被称为阅读机的界面装置，用来接受和解释编程指令。发展数控技术是为了克服人类操作者的局限性。而且她确实完成了这项工作。数字控制的机器比人工控制的机器的精度更高、生产的零件的一致性更好、生产的速度更快、而且长期的工艺设备成本更低。数控技术的发展导致制造工艺中的其他几项新发明的产生：电火花加工技术，激光切削，电子束焊接。数字控制使得机床比它们采用人工操纵的前辈们的用途更为广泛。一台数控机床可以自动生产很多种类的零件，每个零件都可以有不同的和复杂的加工过程。数控可使生产厂家承担那些对于采用人工控制的机床和工艺来说，在经济上是不划算的产品的生产任务。与许多先进技术一样，数控诞生于麻省理工学院的实验室中。数控这个概念是20世纪50年代初在美国空军的资助下提出来的。在其最初的阶段，数控机床可以经济和有效的进行直线切割。然而，曲线轨迹成为机床加工的一个问题，在编程时应采用一系列的水平与竖直的台阶来生成曲线。构成台阶的每个线段越短，曲线就越光滑。台阶中的每个线段都必须经过计算。在这个问题的促使下，于1959年诞生了自动编程工具（APT）语言。这是一个专门适用于数控的编程语言，使用类似于英语的语句来定义零件的几何形状，描述切削刀具的形状和规定必要的运动。APT语言的研究和发展是数控技术进一步发展过程中的一大进步。最初的数控系统与今天应用的数控系统是有很大的差别的。在那时的机床中，只有硬线逻辑线路。指令程序写在穿孔纸带上（它后来被塑料磁带取代），采用带阅读机将写在纸带或磁带上的指令给机器翻译出来。所有这些共同构成了机床数字控制方面的巨大进步。然而，在数控发展的这个阶段中还存在着许多问题。一个主要问题是穿孔纸带的易损坏性。在机械加工过程中，载有编程指令信息的纸带断裂和被撕坏事常见的事情。在机床上每加工一个零件，都需要将载有编程指令的纸带放入阅读机中重新运行一次。因此，这个问题变的很严重。如果需要制造100个某种零件，则应该将纸带分别通过阅读机100次。易损坏的纸带显然不能承受严酷的车间环境和这种重复使用。这就导致了一种专门的塑料磁带的研制。在纸带上通过采用一系列的小孔来载有编程指令，而在塑料带上通过采用一系列的磁点来载有编程指令。塑料带的强度比纸带要高的多，这就可以解决常见的撕坏和断裂问题。然而，它依然存在着两个问题。其中最重要的一个问题是，对输入带中的指令进行修改时非常困难的，或者是根本不可能。即使对指令程序进行微小的调整。也必须中断加工，制造一条新带。而且带通过阅读机的次数还必须与需要加工的零件的个数相同。幸运的是，计算机技术的实际应用很快解决了数控技术中与穿孔纸带和塑料纸带有关的问题。在形成直接数字控制（DNC)这个概念后，可以不再采用纸带或塑料带作为编程指令的载体，这样就解决了与之有关的问题。在直接数字控制中，几台机床通过数据传输线路连接到一台主计算机上。操纵这些机床所需要的程序都存储在这台主计算机中。当需要时，通过数据传输线路提供给每台机床。直接数字控制是在穿孔纸带和塑料带基础上的一大进步。然而，它也有着与其他依赖于主计算机的技术一样的局限性。当主计算机出现故障时，由其控制的所有机床都将停止工作。这个问题促使了计算机数字控制技术的产生。微处理器的发展为可编程逻辑控制器和微型计算机的发展做好了准备。这两种技术为计算机数控（CNC）的发展打下了基础。采用了CNC技术后，每台机床上都有一个可编程逻辑控制器或微机对其进行数字控制。这可以使得程序被输入和存储在每台机器内部。它还可以在机床以外编制程序，并且将其下载到每台机床中。计算机数控主要解