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双头钻扩铰专机设计-专机总体及主轴箱设计【8张图纸】【优秀】

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摘要

组合机床是一种高效专用机床，有特定的使用条件。在确定设计机床前，应该进行具体的经济技术分析。加工同一个机械产品的零件，通常会有很多种工艺方案，不同的方案会有不同的经济效果，影响技术经济的因素有很多，有时技术指标先进的方案，经济指标不一定优越。因此，需要对技术、经济指标作综合评价，选出优化方案进行经济效果评价，如果满意即可决定。

本课题是双头钻扩铰专机设计。其来源于惠发特精密机械有限公司。在设计中，通过研究被加工零件的特点，对相关数据进行计算，对相关部件进行选择，从而确定机床的总体布局。并绘制出被加工零件工序图，加工示意图，机床联系尺寸图和生产率计算卡。在此基础上拟定了主轴箱的传动路线，设计了轴的结构，进行了皮带轮及轴等相关零件的强度，刚度校核，并绘制出主轴箱装配图。该机床对零件的两端孔同时进行加工，加工的工艺性好，工件装夹方便。采用滚珠丝杠导轨实现刀具进给。工件采用V形块定位，液压夹紧，一次装夹完成不仅保证了孔的加工精度，而且还提高了加工效率，降低了工人的劳动强度。

关键词：双头钻扩铰专机；组合机床；主轴箱

摘要III

AbstractIV

目录V

1 绪论1

1.1 惠发特精密机械有限公司简介1

1.2 本设计任务简介1

1.3本设计应达到的要求1

2 机床总体设计2

2.1 工艺方案制定2

2.1.1 工件和加工部位的主要要求2

2.1.2 拟定工艺路线2

2.1.3 二种工艺线路的比较与确定及其各分析其优缺点6

2.1.4 安装与夹紧方案的比较与确定，包括定位、夹紧、夹紧部位、形式等7

2.1.5 刀具、辅具的确定8

2.1.6 工序8

2.1.7 工序的集中与分散9

2.1.8 确定加工工艺路线9

2.1.9 加工工序卡片10

2.2 专机总体设计11

2.2.1 确定专机的驱动方式，切削力，切削功率、电动机选择等计算13

2.2.2 基本参数（尺寸）设计17

2.2.3 传动系统设计17

2.2.4三图一卡的设计19

3 主轴箱的设计27

3.1 主轴箱及其卸荷机构27

3.2 主轴的结构型式28

3.2.1 主轴的构造28

3.3 主轴的轴承选用29

3.3.1 几种轴承的比较29

3.3.2 轴承的安装与定位30

3.4 主轴刚度计算30

3.5 轴承寿命计算31

3.6 电机的安装33

3.7 两主轴箱等高与共线调节33

4 其他设计34

4.1 夹具34

4.2 进给系统34

4.3 液压原理34

4.4 冷却系统35

5 附件设计部分（床身部件）36

5.1 对床身部件的具体要求36

5.2 选择床身部件的材料、毛胚制造方式36

5.2.1 铸造加工工艺36

5.2.2 焊接加工工艺36

5.3 对床身部件与其他部件联系的方式确定36

5.3.1 床身与其余部件的整体布局36

5.3.2 导轨安装36

5.3.3 排屑及冷却液回流37

5.3.4 起吊问题37

5.4 床身部件加工工艺方案及工艺路线确定37

5.4.1 加工工艺方案的比较与确定37

5.4.2 加工工艺路线39

5.5 技术要求说明39

6 结论与展望41

致谢42

参考文献43

　　　1 绪论

1.1 惠发特精密机械有限公司简介

无锡惠发特精密机械有限公司位于无锡市惠山区堰桥镇工业园，公司生产工艺先进，设备齐全，技术力量雄厚。专门从事各种系列型号液压机的生产，其各项性能指标均已达到国外同类产品的水平。

公司全体员工秉承“追求卓越品质，满足客户需求”的经营理念，不断强化质量管理，坚持跟踪服务，已通过了ISO9001：2000国际质量体系认证，为各种内燃机、电机电器、汽车、摩托车、粉末冶金、轴承等良好组配创造了条件。同时还生产专用组合机床、数控专用组合机床及三棍轮、二棍轮精密校直机。

1.2 本设计任务简介

本设计是从事专业机床设计，包括总体设计、进给系统、床身部件、液压系统、主轴箱设计。

课题来源于无锡市惠发特精密机械有限公司。本课题系机动车减震器缸筒加工的专用机床设计，对于摩托车及其这一类机动车的减震器缸筒加工均有一定得参考价值，在减震器行业技术更新中起相当的作用。

此次毕业设计任务要求机床功能得到进一步的完善，能够提高零件的加工精度和加工效率，能够降低加工成本。该零件属摩托车减震器用，其材料为铸铝，要求单班制生产，年产量5万件。限于水平和经验，不完善之处，敬请批评指正。

1.3本设计应达到的要求

1. 对缸体加工工艺（经简化）方案的简要分析比较。

2. 完成本工序的工序图，加工示意图，机床总图及床身部件图。

3. 设计说明书一份，要求对机床的总体设计部分详细分析说明，并包括必要的计算，文字简洁通顺，重要公式数据应注明出处。

4. 对制造厂家调研，了解其对质量、成本要求，所设计的专机要结合厂方具体生产条件。2 机床总体设计

2.1 工艺方案制定

　　　机械加工工艺规程是规定产品或零部件机械加工工艺过程和操作方法的工艺文件。生产规模的大小，工艺水平的高低以及解决各种工艺问题的方法和手段都要通过机械加工工艺规程来体现。因此，机械加工工艺规程设计是一项重要而又严肃的工作。为能具体确切地说明工艺过程，一般将机械加工工艺过程分为工序、安装、工位、工步、走刀。

　　　工艺方案制定正确与否，将决定机床能否达到“体积小，重量轻，结构简单，使用方便，效率高，质量好”的要求，这是设计最重要的一步。

　　　为使工艺方案制定的合理、先进，必须认真分析被加工的零件图纸，深入现场全面了解被加工零件的结构特点，加工部位，尺寸精度，表面粗糙度和技术要求，定位夹紧方式工艺方法和加工过程所采用的刀具，辅具，切屑用量。分析其优缺点，总结设计，制造，使用单位和操作者的丰富的实践经验，以求理论紧密联系实际，从而确定零件在组合机床上完整的工艺（工序）内容及方法，从而决定刀具种类，结构型式，数量及切屑用量等。

　　　根据选定的工艺方案确定机床的配置形式，并制定出影响机床总体布局和技术性能的主要部件结构方案。既要考虑能实现工艺方案，以确保零件的加工精度，技术要求及生产率；又要考虑机床的操作方便可靠，易于维修，且冷却，排屑情况良好。

　　　对于同一个零件的加工，可能会有各种不同的工艺方案和机床配置方案，在最后决定采取哪种方案时，决不能草率，要全面地看问题，综合分析各方面的情况，进行多种对比，选择最佳方案。

2.1.1 工件和加工部位的主要要求

　　　被加工零件为棒状铝合金：

　　　牌号：代号：ZL104 铸造方法：金属型

　　　热处理：淬火+人工时效

　　　力学性能：抗拉强度/：145 伸长率δ5(%)：2

　　　　　　　　布氏硬度HBS(5/250/30)：70

　　　铸铝合金应具有良好的铸造性能，其成分应接近共晶点。

　　　双孔加工：左端 Ф14.5，表面粗糙度Ra=6.3微米

　　　右端阶梯孔最大Ф43，最小Ф35，表面粗糙度Ra=6.3微米

　　　其他技术要求见零件图，要求年产量为5万件，单班制生产。实物图如图2.1。

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双头钻扩铰专机设计-专机总体及主轴箱设计.gif

内容简介：: 英文原文Basic Machining Operations and Cutting TechnologyMachine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinsons boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface of a ductile workpiece in the form of a severely deformed chip. The chip is a waste product that is considerably shorter than the workpiece from which it came but with a corresponding increase in thickness of the uncut chip. The geometrical shape of workpiece depends on the shape of the tool and its path during the machining operation. Most machining operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and the tool penetrates beneath its surface and travels parallel to the center of rotation, a surface of revolution is produced, and the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface uniformly varying diameter is called taper turning, if the tool point travels in a path of varying radius, a contoured surface like that of a bowling pin can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be contour formed. Flat or plane surfaces are frequently required. They can be generated by radial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the workpiece steady and reciprocate the tool across it in a series of straight-line cuts with a crosswise feed increment before each cutting stroke. This operation is called planning and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the workpiece under it as in planning. The tool is fed at each reciprocation. Contoured surfaces can be produced by using shaped tools. Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10 times the drill diameter. Whether the drill turns or the workpiece rotates, relative motion between the cutting edge and the workpiece is the important factor. In milling operations a rotary cutter with a number of cutting edges engages the workpiece. Which moves slowly with respect to the cutter. Plane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of rotation may be used, and the feed of the workpiece may be in any of the three coordinate directions. Basic Machine Tools Machine tools are used to produce a part of a specified geometrical shape and precise I size by removing metal from a ductile material in the form of chips. The latter are a waste product and vary from long continuous ribbons of a ductile material such as steel, which are undesirable from a disposal point of view, to easily handled well-broken chips resulting from cast iron. Machine tools perform five basic metal-removal processes: I turning, planning, drilling, milling, and grinding. All other metal-removal processes are modifications of these five basic processes. For example, boring is internal turning; reaming, tapping, and counter boring modify drilled holes and are related to drilling; bobbing and gear cutting are fundamentally milling operations; hack sawing and broaching are a form of planning and honing; lapping, super finishing. Polishing and buffing are variants of grinding or abrasive removal operations. Therefore, there are only four types of basic machine tools, which use cutting tools of specific controllable geometry: 1. lathes, 2. planers, 3. drilling machines, and 4. milling machines. The grinding process forms chips, but the geometry of the abrasive grain is uncontrollable. The amount and rate of material removed by the various machining processes may be I large, as in heavy turning operations, or extremely small, as in lapping or super finishing operations where only the high spots of a surface are removed. A machine tool performs three major functions: 1. it rigidly supports the workpiece or its holder and the cutting tool; 2. it provides relative motion between the workpiece and the cutting tool; 3. it provides a range of feeds and speeds usually ranging from 4 to 32 choices in each case. Speed and Feeds in Machining Speeds, feeds, and depth of cut are the three major variables for economical machining. Other variables are the work and tool materials, coolant and geometry of the cutting tool. The rate of metal removal and power required for machining depend upon these variables. The depth of cut, feed, and cutting speed are machine settings that must be established in any metal-cutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by comparing them to the needle and record of a phonograph. The cutting speed (V) is represented by the velocity of- the record surface relative to the needle in the tone arm at any instant. Feed is represented by the advance of the needle radially inward per revolution, or is the difference in position between two adjacent grooves. The depth of cut is the penetration of the needle into the record or the depth of the grooves. Turning on Lathe Centers The basic operations performed on an engine lathe are illustrated. Those operations performed on external surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and lapping, the operations on internal surfaces are also performed by a single point cutting tool. All machining operations, including turning and boring, can be classified as roughing, finishing, or semi-finishing. The objective of a roughing operation is to remove the bulk of the material as rapidly and as efficiently as possible, while leaving a small amount of material on the work-piece for the finishing operation. Finishing operations are performed to obtain the final size, shape, and surface finish on the workpiece. Sometimes a semi-finishing operation will precede the finishing operation to leave a small predetermined and uniform amount of stock on the work-piece to be removed by the finishing operation. Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit the lathe centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the tailstock is always supported by a tailstock center, while the end near the headstock may be supported by a headstock center or held in a chuck. The headstock end of the workpiece may be held in a four-jaw chuck, or in a type chuck. This method holds the workpiece firmly and transfers the power to the workpiece smoothly; the additional support to the workpiece provided by the chuck lessens the tendency for chatter to occur when cutting. Precise results can be obtained with this method if care is taken to hold the workpiece accurately in the chuck. Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver plate mounted on the spindle nose. One end of the Workpiece is mecained;then the workpiece can be turned around in the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece and to resist the cutting forces. After the workpiece has been removed from the lathe for any reason, the center holes will accurately align the workpiece back in the lathe or in another lathe, or in a cylindrical grinding machine. The workpiece must never be held at the headstock end by both a chuck and a lathe center. While at first thought this seems like a quick method of aligning the workpiece in the chuck, this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center. The alignment provided by the center will not be maintained and the pressure of the jaws may damage the center hole, the lathe center, and perhaps even the lathe spindle. Compensating or floating jaw chucks used almost exclusively on high production work provide an exception to the statements made above. These chucks are really work drivers and cannot be used for the same purpose as ordinary three or four-jaw chucks. While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission; moreover, large lathe dogs that are adequate to transmit the power not generally available, although they can be made as a special. Faceplate jaws are like chuck jaws except that they are mounted on a faceplate, which has less overhang from the spindle bearings than a large chuck would have. Introduction of Machining Machining as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported workpiece. Low setup cost for small Quantities. Machining has two applications in manufacturing. For casting, forging, and press working, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may he produced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining; to start with nearly any form of raw material, so tong as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore .machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or press working if a high quantity were to be produced. Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process. On the other hand, many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are seldom produced by any means other than machining and small holes in press worked parts may be machined following the press working operations. Primary Cutting Parameters The basic tool-work relationship in cutting is adequately described by means of four factors: tool geometry, cutting speed, feed, and depth of cut. The cutting tool must be made of an appropriate material; it must be strong, tough, hard, and wear resistant. The tool s geometry characterized by planes and angles, must be correct for each cutting operation. Cutting speed is the rate at which the work surface passes by the cutting edge. It may be expressed in feet per minute. For efficient machining the cutting speed must be of a magnitude appropriate to the particular work-tool combination. In general, the harder the work material, the slower the speed. Feed is the rate at which the cutting tool advances into the workpiece. Where the workpiece or the tool rotates, feed is measured in inches per revolution. When the tool or the work reciprocates, feed is measured in inches per stroke, Generally, feed varies inversely with cutting speed for otherwise similar conditions. The depth of cut, measured inches is the distance the tool is set into the work. It is the width of the chip in turning or the thickness of the chip in a rectilinear cut. In roughing operations, the depth of cut can be larger than for finishing operations. The Effect of Changes in Cutting Parameters on Cutting Temperatures In metal cutting operations heat is generated in the primary and secondary deformation zones and these results in a complex temperature distribution throughout the tool, workpiece and chip. A typical set of isotherms is shown in figure where it can be seen that, as could be expected, there is a very large temperature gradient throughout the width of the chip as the workpiece material is sheared in primary deformation and there is a further large temperature in the chip adjacent to the face as the chip is sheared in secondary deformation. This leads to a maximum cutting temperature a short distance up the face from the cutting edge and a small distance into the chip. Since virtually all the work done in metal cutting is converted into heat, it could be expected that factors which increase the power consumed per unit volume of metal removed will increase the cutting temperature. Thus an increase in the rake angle, all other parameters remaining constant, will reduce the power per unit volume of metal removed and the cutting temperatures will reduce. When considering increase in unreformed chip thickness and cutting speed the situation is more complex. An increase in undeformed chip thickness tends to be a scale effect where the amounts of heat which pass to the workpiece, the tool and chip remain in fixed proportions and the changes in cutting temperature tend to be small. Increase in cutting speed; however, reduce the amount of heat which passes into the workpiece and this increase the temperature rise of the chip m primary deformation. Further, the secondary deformation zone tends to be smaller and this has the effect of increasing the temperatures in this zone. Other changes in cutting parameters have virtually no effect on the power consumed per unit volume of metal removed and consequently have virtually no effect on the cutting temperatures. Since it has been shown that even small changes in cutting temperature have a significant effect on tool wear rate it is appropriate to indicate how cutting temperatures can be assessed from cutting data. The most direct and accurate method for measuring temperatures in high -speed-steel cutting tools is that of Wright &. Trent which also yields detailed information on temperature distributions in high-speed-steel cutting tools. The technique is based on the metallographic examination of sectioned high-speed-steel tools which relates microstructure changes to thermal history. Trent has described measurements of cutting temperatures and temperature distributions for high-speed-steel tools when machining a wide range of workpiece materials. This technique has been further developed by using scanning electron microscopy to study fine-scale microstructure changes arising from over tempering of the tempered martens tic matrix of various high-speed-steels. This technique has also been used to study temperature distributions in both high-speed -steel single point turning tools and twist drills. Wears of Cutting Tool Discounting brittle fracture and edge chipping, which have already been dealt with, tool wear is basically of three types. Flank wear, crater wear, and notch wear. Flank wear occurs on both the major and the minor cutting edges. On the major cutting edge, which is responsible for bulk metal removal, these results in increased cutting forces and higher temperatures which if left unchecked can lead to vibration of the tool and workpiece and a condition where efficient cutting can no longer take place. On the minor cutting edge, which determines workpiece size and surface finish, flank wear can result in an oversized product which has poor surface finish. Under most practical cutting conditions, the tool will fail due to major flank wear before the minor flank wear is sufficiently large to result in the manufacture of an unacceptable component. Because of the stress distribution on the tool face, the frictional stress in the region of sliding contact between the chip and the face is at a maximum at the start of the sliding contact region and is zero at the end. Thus abrasive wear takes place in this region with more wear taking place adjacent to the seizure region than adjacent to the point at which the chip loses contact with the face. This result in localized pitting of the tool face some distance up the face which is usually referred to as catering and which normally has a section in the form of a circular arc. In many respects and for practical cutting conditions, crater wear is a less severe form of wear than flank wear and consequently flank wear is a more common tool failure criterion. However, since various authors have shown that the temperature on the face increases more rapidly with increasing cutting speed than the temperature on the flank, and since the rate of wear of any type is significantly affected by changes in temperature, crater wear usually occurs at high cutting speeds. At the end of the major flank wear land where the tool is in contact with the uncut workpiece surface it is common for the flank wear to be more pronounced than along the rest of the wear land. This is because of localised effects such as a hardened layer on the uncut surface caused by work hardening introduced by a previous cut, an oxide scale, and localised high temperatures resulting from the edge effect. This localised wear is usually referred to as notch wear and occasionally is very severe. Although the presence of the notch will not significantly affect the cutting properties of the tool, the notch is often relatively deep and if cutting were to continue there would be a good chance that the tool would fracture. If any form of progressive wear allowed to continue, dramatically and the tool would fail catastrophically, i. e. the tool would be no longer capable of cutting and, at best, the workpiece would be scrapped whilst, at worst, damage could be caused to the machine tool. For carbide cutting tools and for all types of wear, the tool is said to have reached the end of its useful life long before the onset of catastrophic failure. For high-speed-steel cutting tools, however, where the wear tends to be non-uniform it has been found that the most meaningful and reproducible results can be obtained when the wear is allowed to continue to the onset of catastrophic failure even though, of course, in practice a cutting time far less than that to failure would be used. The onset of catastrophic failure is characterized by one of several phenomena, the most common being a sudden increase in cutting force, the presence of burnished rings on the workpiece, and a significant increase in the noise level. Mechanism of Surface Finish Production There are basically five mechanisms which contribute to the production of a surface which have been machined. These are:(l) The basic geometry of the cutting process. In, for example, single point turning the tool will advance a constant distance axially per revolution of the workpiecc and the resultant surface will have on it, when viewed perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut. (2) The efficiency of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a surface which contains hard built-up-edge fragments which will result in a degradation of the surface finish. It can also be demonstrated that cutting under adverse conditions such as apply when using large feeds small rake angles and low cutting speeds, besides producing conditions which lead to unstable built-up-edge production, the cutting process itself can become unstable and instead of continuous shear occurring in the shear zone, tearing takes place, discontinuous chips of uneven thickness are produced, and the resultant surface is poor. This situation is particularly noticeable when machining very ductile materials such as copper and aluminum. (3) The stability of the machine tool. Under some combinations of cutting conditions; workpiece size, method of clamping ,and cutting tool rigidity relative to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions this vibration will reach and maintain steady amplitude whilst under other conditions the vibration will built up and unless cutting is stopped considerable damage to both the cutting tool and workpiece may occur. This phenomenon is known as chatter and in axial turning is characterized by long pitch helical bands on the workpiece surface and short pitch undulations on the transient machined surface. (4)The effectiveness of removing swarf. In discontinuous chip production machining, such as milling or turning of brittle materials, it is expected that the chip (swarf) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not influence the cut surface in any way. However, when continuous chip production is evident, unless steps are taken to control the swarf it is likely that it will impinge on the cut surface and mark it. Inevitably, this marking besides looking. (5)The effective clearance angle on the cutting tool. For certain geometries of minor cutting edge relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting edge. This can produce a good surface finish but, of course, it is strictly a combination of metal cutting and metal forming and is not to be recommended as a practical cutting method. However, due to cutting tool wear, these conditions occasionally arise and lead to a marked change in the surface characteristics. Limits and Tolerances Machine parts are manufactured so they are interchangeable. In other words, each part of a machine or mechanism is made to a certain size and shape so will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that will fit the mating part in the correct way. It is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools become worn. A slight variation from the exact size is always allowed. The amount of this variation depends on the kind of part being manufactured. For examples part might be made 6 in. long with a variation allowed of 0.003 (three-thousandths) in. above and below this size. Therefore, the part could be 5.997 to 6.003 in. and still be the correct size. These are known as the limits. The difference between upper and lower limits is called the tolerance. A tolerance is the total permissible variation in the size of a part. The basic size is that size from which limits of size arc derived by the application of allowances and tolerances. Sometimes the limit is allowed in only one direction. This is known as unilateral tolerance.Unilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is shown in only one direction from the nominal size. Unilateral tolerancing allow the changing of tolerance on a hole or shaft without seriously affecting the fit.When the tolerance is in both directions from the basic size it is known as a bilateral tolerance (plus and minus). Bilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is split and is shown on either side of the nominal size. Limit dimensioning is a system of dimensioning where only the maximum and minimum dimensions arc shown. Thus, the tolerance is the difference between these two dimensions. Surface Finishing and Dimensional Control Products that have been completed to their proper shape and size frequently require some type of surface finishing to enable them to satisfactorily fulfill their function. In some cases, it is necessary to improve the physical properties of the surface material for resistance to penetration or abrasion. In many manufacturing processes, the product surface is left with dirt .chips, grease, or other harmful material upon it. Assemblies that are made of different materials, or from the same materials processed in different manners, may require some special surface treatment to provide uniformity of appearance. Surface finishing may sometimes become an intermediate step processing. For instance, cleaning and polishing are usually essential before any kind of plating process. Some of the cleaning procedures are also used for improving surface smoothness on mating parts and for removing burrs and sharp corners, which might be harmful in later use. Another important need for surface finishing is for corrosion protection in a variety of: environments. The type of protection procedure will depend largely upon the anticipated exposure, with due consideration to the material being protected and the economic factors involved. Satisfying the above objectives necessitates the use of main surface-finishing methods that involve chemical change of the surface mechanical work affecting surface properties, cleaning by a variety of methods, and the application of protective coatings, organic and metallic. In the early days of engineering, the mating of parts was achieved by machining one part as nearly as possible to the required size, machining the mating part nearly to size, and then completing its machining, continually offering the other part to it, until the desired relationship was obtained. If it was inconvenient to offer one part to the other part during machining, the final work was done at the bench by a fitter, who scraped the mating parts until the desired fit was obtained, the fitter therefore being a fitter in the literal sense. J It is obvious that the two parts would have to remain together, and m the event of one having to be replaced, the fitting would have to be done all over again. In these days, we expect to be able to purchase a replacement for a broken part, and for it to function correctly without the need for scraping and other fitting operations.When one part can be used off the shelf to replace another of the same dimension and material specification, the parts are said to be interchangeable. A system of interchangeability usually lowers the production costs as there is no need for an expensive, fiddling operation, and it benefits the customer in the event of the need to replace worn parts. Automatic Fixture Design Traditional synchronous grippers for assembly equipment move parts to the gripper centre-line, assuring that the parts will be in a known position after they arc picked from a conveyor or nest. However, in some applications, forcing the part to the centre-line may damage cither the part or equipment. When the part is delicate and a small collision can result in scrap, when its location is fixed by a machine spindle or mould, or when tolerances are tight, it is preferable to make a gripper comply with the position of the part, rather than the other way around. For these tasks, Zaytran Inc. Of Elyria, Ohio, has created the GPN series of non- synchronous, compliant grippers. Because the force and synchronizations systems of the grippers are independent, the synchronization system can be replaced by a precision slide system without affecting gripper force. Gripper sizes range from 51b gripping force and 0.2 in. stroke to 40Glb gripping force and 6in stroke. Grippers Production is characterized by batch-size becoming smaller and smaller and greater variety of products. Assembly, being the last production step, is particularly vulnerable to changes in schedules, batch-sizes, and product design. This situation is forcing many companies to put more effort into extensive rationalization and automation of assembly that was previouslyextensive rationalization and automation of assembly that was previously the case. Although the development of flexible fixtures fell quickly behind the development of flexible handling systems such as industrial robots, there are, nonetheless promising attempts to increase the flexibility of fixtures. The fact that fixtures are the essential product - specific investment of a production system intensifies the economic necessity to make the fixture system more flexible. Fixtures can be divided according to their flexibility into special fixtures, group fixtures, modular fixtures and highly flexible fixtures. Flexible fixtures are characterized by their high adaptability to different workpieces, and by low change-over time and expenditure. There are several steps required to generate a fixture, in which a workpiece is fixed for a production task. The first step is to define the necessary position of the workpiece in the fixture, based on the unmachined or base pan, and the working features. Following this, a combination of stability planes must be selected. These stability planes constitute the fixture configuration in which the workpiece is fixed in the defined position, all the forces or torques are compensated, and the necessary access to the working features is ensured. Finally, the necessary positions of moveable or modular fixture elements must be calculated- adjusted, or assembled, so that the workpiece is firmly fixed in the fixture. Through such a procedure the planning and documentation of the configuration and assembly of fixture can be automated.The configuration task is to generate a combination of stability planes, such that fixture forces in these planes will result in workpiece and fixture stability. This task can be accomplished conventionally, interactively or in a nearly fully automated manner. The advantages of an interactive or automated configuration determination are a systematic fixture design process, a reduction of necessary designers, a shortening of lead time and better match to the working conditions. In short, a significant enhancement of fixture productivity and economy can be achieved.中文译文基本加工工序和切削技术机床是从早期的埃及人的脚踏动力车和约翰威尔金森的镗床发展而来的。它们为工件和刀具提供刚性支撑并可以精确控制它们的相对位置和相对速度。基本上讲，金属切削是指一个磨尖的锲形工具从有韧性的工件表面上去除一条很窄的金属。切屑是被废弃的产品，与其它工件相比切屑较短，但对于未切削部分的厚度有一定的增加。工件表面的几何形状取决于刀具的形状以及加工操作过程中刀具的路径。大多数加工工序产生不同几何形状的零件。如果一个粗糙的工件在中心轴上转动并且刀具平行于旋转中心切入工件表面，一个旋转表面就产生了，这种操作称为车削。如果一个空心的管子以同样的方式在内表面加工，这种操作称为镗孔。当均匀地改变直径时便产生了一个圆锥形的外表面，这称为锥度车削。如果刀具接触点以改变半径的方式运动，那么一个外轮廓像球的工件便产生了；或者如果工件足够的短并且支撑是十分刚硬的，那么成型刀具相对于旋转轴正常进给的一个外表面便可产生，短锥形或圆柱形的表面也可形成。平坦的表面是经常需要的，它们可以由刀具接触点相对于旋转轴的径向车削产生。在刨削时对于较大的工件更容易将刀具固定并将工件置于刀具下面。刀具可以往复地进给。成形面可以通过成型刀具加工产生。多刃刀具也能使用。使用双刃槽钻钻深度是钻孔直径5-10倍的孔。不管是钻头旋转还是工件旋转，切削刃与工件之间的相对运动是一个重要因数。在铣削时一个带有许多切削刃的旋转刀具与工件接触，工件相对刀具慢慢运动。平的或成形面根据刀具的几何形状和进给方式可能产生。可以产生横向或纵向轴旋转并且可以在任何三个坐标方向上进给。基本机床机床通过从塑性材料上去除屑片来产生出具有特别几何形状和精确尺寸的零件。后者是废弃物，是由塑性材料如钢的长而不断的带状物变化而来，从处理的角度来看，那是没有用处的。很容易处理不好由铸铁产生的破裂的屑片。机床执行五种基本的去除金属的过程：车削，刨削，钻孔，铣削。所有其他的去除金属的过程都是由这五个基本程序修改而来的，举例来说，镗孔是内部车削；铰孔，攻丝和扩孔是进一步加工钻过的孔；齿轮加工是基于铣削操作的。抛光和打磨是磨削和去除磨料工序的变形。因此，只有四种基本类型的机床，使用特别可控制几何形状的切削工具1.车床，2.钻床，3.铣床，4.磨床。磨削过程形成了屑片，但磨粒的几何形状是不可控制的。通过各种加工工序去除材料的数量和速度是巨大的，正如在大型车削加工，或者是极小的如研磨和超精密加工中只有面的高点被除掉。一台机床履行三大职能：1.它支撑工件或夹具和刀具2.它为工件和刀具提供相对运动3.在每一种情况下提供一系列的进给量和一般可达4-32种的速度选择。加工速度和进给速度，进给量和切削深度是经济加工的三大变量。其他的量数是攻丝和刀具材料，冷却剂和刀具的几何形状，去除金属的速度和所需要的功率依赖于这些变量。切削深度，进给量和切削速度是任何一个金属加工工序中必须建立的机械参量。它们都影响去除金属的力，功率和速度。切削速度可以定义为在旋转一周时速度记录面相对任何瞬间呈辐射状扩散的针，或是两个相邻沟槽的距离。切削深度是进入的深度和沟槽的深度。在车床中心的车削在机动车床上完成的基本操作已被介绍了。那些用单点刀具在外表面的操作称为车削。除了钻孔，铰孔，研磨内部表面的操作也是由单点刀具完成的。所有的加工工序包括车削，镗孔可以被归类为粗加工，精加工或半精加工。精加工是尽可能快而有效的去除大量材料，而工件上留下的一小部分材料用于精加工。精加工为工件获得最后尺寸，形状和表面精度。有时，半精加工为精加工留下预定的一定量的材料，它是先于精加工的。一般来说，较长的工件同时被一个或两个车床中心支撑。锥形孔，所谓的中心孔，两端被钻的工件适于车床中心-通常沿着圆柱形工件的轴线。工件接近为架的那端通常由尾架中心支撑，在靠近主轴承的那端由主轴承中心支撑或由爪盘夹紧。这种方法可以牢固的加紧工件并且能顺利地将力传给工件；由卡盘对工件提供的辅助支撑减少切削时发生的颤振趋势，如果能小心准确地采用卡盘支撑工件的方法，则可以得到精确的结果。在两个中心之间支撑工件可以得到非常精确的结果。工件的一端已被加工，那么工件便可车削了。在车床上加工另一端，中心孔充当精确定位面和承载工件重量和抵制切削力的支撑面。当工件由于任何一原因从车床上移除后，中心孔将准确地使工件回到这个车床上或另一个车床上或一个圆柱磨床上。工件不允许被卡盘和车床中心夹在主轴承上。然而首先想到的是一个快速调整卡盘上工件的方法，但这是不允许的因为在由卡盘夹持的同时也由车床中心支撑是不可能的。由车床中心提供的调整将不能持续并且爪盘的压力会损坏中心孔和车床中心，甚至是车床主轴。浮动的爪盘为上述陈述提供了一个例外，它几乎完全使用在高生产工作上，这些卡盘是真正的工作驱动者并且不为同样的目的如普通的三爪，四爪卡盘使用。而大直径的工件有时装在两个中心，它们最好有由面板夹持在主轴承尾部来顺利得到能量转换；许多车床夹头并不能足量的转换能量，虽然可以作为特殊的能量转换。机械加工介绍作为产生形状的一种方法，机械加工是所有制造过程中最普遍使用的而且是最重要的方法。机械加工过程是一个产生形状的过程，在这过程中，驱动装置使工件上的一些材料以切屑的形式被去除。尽管在某些场合，工件无支承情况下，使用移动式装备来实现加工，但大多数的机械加工是通过既支承工件又支承刀具的装备来完成。小批量，低成本。机械加工在制造业上有两个应用。是铸造，锻造和压力工作，产生每一个特殊形状，甚至一个零件，几乎总有较高的模具成本。焊接的形状很大程度上取决于原材料。通过利用总成本高但没有特殊模具的设备，加工是有可能的；从几乎任何形式的原材料开始，只要外部尺寸足够大，由任意材料设计形状。因此加工是首选的方法，当生产一个或几个零件甚至在大批量生产时，零件的设计在逻辑上导致铸造，锻造或冲压制品。高精度，表面精度。机械加工的第二个应用是基于可能的高精度和表面精度的。如果在其他工序中大批量生产，很多低量零件会产生出低的但可接受的公差。另一方面，许多零件由一些大变形过程产生一般的形状，并且只在具有很高精度的选定面加工。举例来说，内线流程是很少产生任何方式以外的其他机械加工并且紧接着压力操作后零件上的小洞可能被加工。主要的切削参数在切削时基本工具工作的关系充分描述的方法有4个因素：刀具几何形状，切削速度和切削深度。刀具必须由适当的材料做成；它必须有一定的强度，粗糙度，硬度和抗疲劳度。刀具几何形状由面和角度描述，对每一种切削操作都是正确的。切削速度是指切削刃通过工作面的速度，它已每分钟通过的英尺数表示。对于加工效率，切削速度相对于特殊工作组合必须具有适当规模。一般来讲，工件越硬，速度越小。进给是刀具进入工件的速率。当工件或刀具旋转时，进给量的单位是英寸每转。当刀具或工件往复移动时，进给量的单位是英寸没次，总的来说，在其他相似情况下进给量与切削速度成反比。切削速度用英寸表示，是刀具进入工件的距离表示的，它是指车削时屑片的宽度或是直线切削时屑片的厚度。粗加工时切削深度比精加工的切削深度大。切削参数的改变对切削温度的影响在金属切削作业中热量产生于主要和第二变形区而这些结果导致了复杂温度遍布于刀具，工件和屑片。一个典型的等温先如图所示，它可以看出正如预测的，当工件材料经历主要变形，被减切时，有一个非常大温度梯度遍布于屑片的整个宽度。当第二变形区的屑片还有一小段距离就达到了最大温度。因为几乎所有的工作都以金属切削转化为热量而完成，可以预测去除每一单位体积的金属所增加的能量消耗将会提高切削温

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