分离叉零件机械加工工艺及工装夹具设计【铣R15圆弧面】【铣内侧面】【说明书+CAD】
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湖南科技大学 2015 届毕业设计(论文)开题报告题 目分 离 叉 工 艺 及 夹 具 设 计作者姓名刘鑫鑫学号1103010509所学专业机械设计制造及其自动化1、 研究的意义,同类研究工作国内外现状、存在问题(列出主要参考文献)研究的意义:随着全球制造产业的区域转移整个制造行业竞争的加剧,导致机械加工生产单位都面临提高生产效率的问题。而在机加过程中作为装夹工件的工艺装备的夹具,在提高生产效率方面有其显著的优势。特别是在在切削过程中,配以适当的加工辅助工具。(如夹具)等有力于提高企业生产效率,使得许多复杂零件的加工成为可能,常规零件加工的质量进一步提升,并降低劳动强度,在保证产品质量加工精度的同时批量生产,从而降低生产成本,从而夹具的使用在某种长度上提高实际生产企业的效益。因而对夹具知识的认识和学习,在今天显的尤为更重要起来。结合目前实际生产,常常发现仅用通用夹具不能满足生产要求,用通用夹具装夹工件生产效率低劳动强度大,加工质量不高,而且往往需要增加划线工序,而专门设计的铣床夹具,主要包括夹具的定位方案、夹紧方案、对刀方案,夹具体与定位键的设计及加工精度等方面的分析。可以有效的减少工件的加工基本时间和辅助时间,大大提高了劳动生产力,从而可以有效地减轻工人的劳动强度和增加劳动效率。不论是传统制造,还是现代制造系统,夹具都是十分重要的。因此,好的夹具设计可以提高产品劳动生产率,保证和提高加工精度,降低生产成本等,还可以扩大机床的使用范围,从而使产品在保证精度的前提下提高效率,降低成本。国内外现状: 近些年来,随着数控机床、加工中心、柔性制造单元、柔性制造系统等现代化加工设备的广泛应用,使传统的机械加工的制造方法发生了重大变革,人们对夹具的功能已经从过去的装夹、定位、引导刀具定位为装夹、定位。而数字化的设备加工功能的扩大化,已经将夹具的引导刀具的功能完全替代,给今后夹具的快速定位、快速装夹提出了更高的要求。目前国内外已开始将夹具设计和数字化、现代化加工技术相结合,研究和推广KBV夹具,即基于知识的工程。把知识、技能、经验、原理、规范等结合到三维CAD系统中,使得设计人员只要输入工程参数或应用要求,系统就能依据相关的知识,推理构造出符合特定要求的工程设计结果KBV夹具。我国对分离叉类不规则零件的加工处于效率低,加工成本高的阶段,大批量生产正逐渐成为现代机械制造业新的生产模式,在这种模式中,要求加工机床和夹具装备具有更好的柔性,以缩短准备时间,降低生产成本,所以手动夹紧的方式已经过时,气动,液压夹紧夹具正是适应这一生产模式的工装准备。国外为了适应这一生产模式,也把柔性制造系统作为开发新产品的有效手段。存在的问题:制造业是国民经济的基础,随着以计算机技术为主导的现状科学技术的迅速发展,以时间驱动为特征的市场竞争,产品更新换代的加快,商品需求的多样化等,是制造业面临着巨大的挑战。在现阶段分离叉零件的加工还没有达到现代自动化的加工水平,它的加工工艺还需要人工画线的加工方法来保证精度,而对工件的装夹也是通过人工的方法进行的。参考文献:甘永立.几何公差与测量.上海:上海科技出版社,2004张福润,徐鸿木主编.机械制造技术基础.武汉:华中科技出版社,20002、 研究目标、内容和拟解决的关键问题(根据任务要求进一步具体化)本设计是分离叉工艺规程及一些工序的专用夹具设计;分离叉内侧面铣夹具的主要加工表面是平面及孔,因此主要研究内容为基准的选择,加工工艺和零件主要部位的专用夹具的设计工件定位是否正确,定位精度是否满足要求,工件夹紧是否可靠等。工件在夹具中的定位精度,主要与定位基准是否与工序基准重合,定位基准与定位元件的配合状况等诸多因素有关,可以提高夹具的制造精度,减少配合间隙;夹紧必须可靠,但夹紧力不可过大,以免工件或夹具产生过大变形,可采用多点夹紧或在工件刚性薄弱部位安放适当的辅助支撑。3、 特色与创新之处工件在夹具中的正确定位,是通过工件上的定位基准与夹具上的定位元件相接触而实现的,只需要找正便可将工件夹紧;通过对夹具上的对刀位置,即可保证工件加工表面相对于刀具的正确位置;装夹基本上不受人工技术水平的影响,能比较容易和稳定地保证加工精度;装夹迅速,方便,能减轻劳动强度,显著地减少辅助时间,提高劳动生产率。4、 拟采取的研究方法、步骤、技术路线文献资料法:通过各种途径,翻阅大量文献资料,扩展自己知识,掌握一定的专业理论,为毕业设计打下理论基础;数据分析法:通过一定的数据,分析存在的现象情况,对结果作出定量和定性分析,说明现象存在的条件及可能性:案例分析法:通过具体的实例,来说明论证自己得出的结论,这样可以更形象客观的来论证论文的观点;资料引证法:通过对大量资料的阅读,掌握,引用其中有用的内容来论证论文的观点。拟定工艺路线:表示零件的加工顺序及加工方法,分出工序,安装或工件及工步等,并选择各工序所使用的机床,刀具,夹具及量具等。步骤及技术路线:制订工艺规程、确定加工余量、工艺尺寸计算、工时定额计算、定位误差分析等。在整个设计中也是非常重要的,通过这些设计,不仅让我们更为全面地了解零件的加工过程、加工尺寸的确定,而且让我们知道工艺路线和加工余量的确定,必须与工厂实际的机床相适应。工序的划分和定位基准的选择,在开始的时候,要认真分析零件图,了解分离叉的结构特点和技术要求。加工表面的粗糙度、平行度、垂直度,注意零件各孔系自身精度(同轴度,圆度,粗糙度等)和它们的相互位置精度,采用AutoCAD软件绘制零件图,一方面可以使我们对其零件有进一步了解与认识,另一方面可以增强我们对AutoCAD软件的熟悉和运用。工序的划分确定加工顺序和工序内容,安排工艺的加重和分散程度,划分工序阶段,与生产纲领有密切联系,具体可以根据生产类型,零件的结构特点,技术要求和机床设备。定位基准的选择根据粗基准的选择原则:遵循基准同意,基准重合。夹具设计要确定工件定位是否正确,定位精度是否满足要求,工件夹紧是否可靠等等。工件在夹具中的定位精度,主要是定位基准是否与工序基准重合,定位基准与定位元件的配合状况等因素有关,可提高夹具的制造精度,减少配合间隙,就能提高夹具在机床上的定位精度,夹具中出现过的定位时,可通过撤销多余定位元件,使多余定位元件失去限制重复自由度的能力,增加定位元件与定位基准的配合间隙等办法来解决,夹紧必须可靠,但夹紧力不可过大,一面工件或夹具产生过大变形,可采用多点夹紧或在工件刚性薄弱部位安放适当的辅助支撑,夹具的设计必须要保证夹具的定位准确的机构合理,考虑夹具的定位误差和安装误差。我们将通过对工件与夹具的认真分析,结合一些夹具的具体设计事例,查阅相关的夹具设计资料,联系在工厂看到的一些加工的夹具来解决这些问题。5、 拟使用的主要设计、分析软件及仪器设备设计,分析软件:Auto CAD,proe仪器设备:机床,刀具,夹具等6、参考文献陈宏钧.实用金属切削手册【M】.北京:机械工业出版社,2005杨黎明.机床夹具设计手册【M】.国防工业出版社,2003王力行.专用机床夹具安装精度分析【J】.装备制造技术,2008赵生虎.夹具的优化设计及经济性分析研究【J】.煤矿机械.2006赵家齐.机床制造工艺学课程设计指导书【M】.第二版,北京:机械工业出版社,2008注:1、开题报告是本科生毕业设计(论文)的一个重要组成部分。学生应根据毕业设计(论文)任务书的要求和文献调研结果,在开始撰写论文之前写出开题报告。2、参考文献按下列格式(A为期刊,B为专著)A:序号、作者(外文姓前名后,名缩写,不加缩写点,3人以上作者只写前3人,后用“等”代替。)、题名、期刊名(外文可缩写,不加缩写点)年份、卷号(期号):起止页码。B:序号、作者、书名、版次、(初版不写)、出版地、出版单位、出版时间、页码。3、表中各项可加附页。3 英文原文Cutting process and fixture designMachine 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 over sized 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 work price 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 de
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