基于UG的铣床夹具的虚拟设计及运动仿真【中心距45的齿轮油泵夹具】
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中心距45的齿轮油泵夹具
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英文原文Basic Machining OperationsMachining tools have evolved from the early foot powered lathe Egyptians and John Wilkinsons boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and 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 from of a severely deformed chip. The chip is waste product that is workpiece in the from of a severely deformed 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 the machine surface depends on the shape of the tool and its path during the machining opration. Most machine operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and 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 on the machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface of uniformly varying diameter is called taper turning. If the tool point travels in a path of varying radius, a contoured surface like that of 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 surface 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 hole the workpiece steady and reciprocate the tool across , it is 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 work piece may be in any of the three coordinate directions.Basic Machine ToolsMachine tools are used to part of a specified geometetrical shape and precise size by removing metal from a ductile material in the form chips. The latter are a waste product and vary from long continuous ribbons of a disposal point of view, to easily handed well-broken chips resulting from cast iron. Machine tools perform five basic metal-remove processes: 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 mollify drilled holes and are related to drilling; hobbling and gear cutting are fundamentally milling operations; hack sawing and broaching are a from 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. 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 large, as in heavy turning operations, or extremely small, as in lapping or superfinishing operations where only the high spots of a surface are removed.A machining tool performs three major functions: 1. it rigidly supports the workpice or its holder and the cutting tool; 2. it provides relative motion between the workpice and the cutting tool; 3. it provides a range of feeds and speeds usually ranging from 4 to32 choices in each case.Speed and Feeds in Machining Speeds, feeds, and depth pf 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 depths of cut, feed, and cutting speed are machine setting 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 centersThe basic operations operations performed on an engine lathe are illustrated in fig. 11-3. those operations performed on external surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and tapping, the operations on internal surfaces are also performed by a single point cutting tool.All machining operate, 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 end 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 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 collet 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 result 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 the driver plate mounted on the spindle nose. One end of the workpiece is machined; then the workpiece can be turned around in the lathe to machine to 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 remove 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 chicks.While very large diameter workpiece 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.BoringThe objective of boring a hole in a lathe is:1、To enlarge the hole 2、To machine the hole to the desired diameter3、To accurately locate the position of the hole 4、To obtain a smooth surface finish in the holeThe motion of the boring tool is parallel to the axis of the lathe when the carriage is moved in the longitudinal direction and the work piece revolves about the axis of the lathe. When these two motions are combined to bore a hole, it will be concentric with the axis of rotation of the lathe. The position of the hole can be accurately located by holding the work piece in the lathe so that the axis about which the hole is to be machined coincides with the axis of rotation of the lathe. When the boring operation is done in the same setup of the work that is used to turn and face it, practically perfect concentricity and perpendicularity can be achieved.The boring tool is held in a boring bar which is fed through the hole by carriage. Variations of this design are used, depending on the job to be done. The lead angle used, if any, should always be small. Also, the nose radius of the boring tool must not be too large. The cutting speed used for boring can be equal to the speed for turning. However, when the spindle speed of the lathe is calculated, the finished, or largest, bore diameter should be used. The feed rate for boring is usually somewhat less than for turning to compensate for the rigidity of the boring bar.The boring operation is generally performed in two steps; namely, rough boring and finish boring. The objective of the rough-boring operation is to remove the excess metal rapidly and efficiently, and the objective of the finish-boring operation is to obtain the desired size, surface finish, and location of the hole. The size of the hole is obtained by using the trial-cut procedure. The diameter of the hole can be measured with inside calipers and outside micrometer calipers. Basic Measuring Instrument, or inside micrometer calipers can be used to measure the diameter directly.Cored holes and drilled holes are sometimes eccentric with respect to the rotation of the lathe. When the boring tool enters the work, the boring bar will take a deeper cut on one side of the hole than on the other, and will deflect more when taking this deeper cut, with the result that the bored hole will not be concentric with the rotation of the work. This effect is corrected by taking several cuts through the hole using a shallow depth of cut. Each succeeding shallow cut causes the resulting hole to be more concentric than it was with the previous cut. Before the finale, finish cut is taken, the hole should be concentric with the rotation of the work in order to make certain that the finished hole will be accurately located.Shoulders, grooves, contours, tapers, and threads are also bored inside of holes. Internal grooves are cut using a tool that is similar to external grooving tool. The procedure for boring internal shoulder is very similar to the procedure for turning shoulders. Larger shoulders are faced with the boring tool positioned with the nose leading, and using the cross slide to feed the tool. Internal contours can be machined using a tracing attachment on a lathe. The tracing attachment is mounted on the cross slide and the stylus follows the outline of the master profile plate. This causes the cutting tool to move in a path corresponding to the profile of the profile plate. Thus, the profile on the master profile plate is reproduced inside the bore. The master profile plate is accurately mounted on a special slide which can be precisely in two directions, in order to align the cutting tool in the correct relationship to the work. This lathe has cam-lock type of spindle nose which permits it to take a cut when rotating in either direction. Normal turning cuts are taken with the spindle rotating counterclockwise. The boring cut is taken with the spindle revolving in a clockwise direction, or “backwards”. This permit the boring cut to be taken on the “back side” of the bore which is easier to see from the operators position front of the lathe. This should not be done on lathes having a threaded spindle nose because the cutting force will tend to unscrew the chuck.MillingMilling is a machining process for removing material by relative motion between a workpiece and a rotating cutter having multiple cutting edges. In some applications, the workpiece is held stationary while the rotating cutter is moved past it and a given feed rate (traversed). In other applications, both the workpiece and cutter are moved in relation to each other and in relation to the milling machine. More frequently, however, the workpiece is advanced at a relatively low rate of movement or feed to a milling cutter rotating at a comparatively high speed, with the cuter axis remaining in a fixed position, a characteristic feature of the milling process is that each milling cutter tooth takes its share of the stock in the form of small individual chips. Milling operations are performed on many different machines.Since both the workpiece and cutter can be moved relative to one another, independently or in combination, a wide variety of operations can be performed by milling. Applications include the production of flat or contoured surfaces, slots, grooves, recesses, threads, and other configurations. Milling is one of the most universal, yet complicated machining methods. The process has more variations in the kinds of machines used, workpiece movements, and types of tooling than any other basic machining method. Important advantages of removing material by means of milling include high stock removal rates, the capability of producing relatively smooth surface finishes, and the wide variety if cutting tools that are available. Cutting edges of the tools can be shaped to form any complex surface.The major milling methods are peripheral and face milling; in addition, a number of related methods exist that are variations of these two methods, depending upon the type of workpiece or cutter. Peripheral Milling On peripheral milling, sometimes called slab milling, the milled surface generated by teeth or inserts located in the periphery of the cutter body is generally in a plane parallel to the cutter axis. Milling operations with form-relieved and formed profile cutters are included in this class. The cross section of the milled surface corresponds to the outline or contour of the milling cutter or combination of cutters used. Peripheral milling operations are usually performed on milling machines with the spindle positioned horizontally, however, they can also be performed with end mills on vertiasl-spindle machines. The milling cutters are mounted on an arbor which is generally supported at the outer end for increased rigidity, particularly when, because of the conditions of the setup, the cutter or cutters are located at some distance from the nose of the spindle. Peripheral milling should generally not be done if the peripheral milling should generally not be done if the part can be face milled.Face Milling Face milling is done on both horizontal and vertical milling machines. The milled surface resulting from the combined action of cutting edges located on the periphery and face of the cutter is generally at right angles to the cutter axis. The milled surface is flat, with no relation to the contour of the teeth, except when milling is done to a shoulder. Generally, face milling should be applied wherever and whenever possible.Chip thickness in conventional (up) face milling varies from a minimum at the entrance and exit of the cutter tooth to a maximum along the horizontal diameter. The milled surface is characterized by tooth and revolution marks, as in the case of peripheral milling cutters. The prominence of these marks is controlled by the accuracy of grinding the face cutting edge of the teeth, or by the accuracy of the body/insert combination in indexable cutters and of mounting the cutter so that it runs true on the machine spindle. It is also controlled by the rigidity of the machine and workpiece itself. When the length of the face cutting edge is less than the feed per revolution (or the amount the work has moved in one revolution of the cutter), a series of roughly circular grooves or ridges results on the milled surface. Similar marking is produced by the trailing teeth drag on the milled surface of the work. This is known as heel drag.In face milling, it is important to select a cutter with a diameter suited to the proposed width of cut if best results are to be obtained. Cuts equal in width to the full cutter diameter should be avoided, if possible, since the thin chip section at entry of the teeth results in accelerated tooth wear abrasion plus a tendency for the chip to weld or stick to the tooth or insert and be carried around and recut. This is detrimental to surface finish. A good ratio of cutter diameter to the width of the workpiece or proposed path of cut is 5:3.中文译文基本的加工工序切削，镗削和铣削机床是从早期的埃及人的脚踏动力车床和约翰.威尔金森的镗床发展而来的。它们用于为工件和刀具两者提供刚性支撑并且可以精确控制它们的相对位置和相对速度。一般来说，在金属切削中用一个磨尖的楔形工具以紧凑螺纹形的切屑形式从有韧性工件表面上去除一条很窄的金属。切屑是废弃的产品，与其工件相比，它相当短但是比未切削的部分厚度有相对的增加。机器表面的几何形状取决于刀具的形状以及加工过程中刀具的路径。不同的加工工序生产出不同几何形状的部件。如果一个粗糙的柱形工件绕中心轴旋转而且刀具穿透工件表面并沿与旋转中心平行的方向前进，就会产生一个旋转面，这道工序叫车削。如果以类似的方式加工一根空心管的内部，则这道工序就叫镗削。制造一个直径均匀变化的锥形外表面叫做锥体车削。如果刀具尖端以一条半径可变的路径前进，就可以制造出象保龄球杆那种仿形表面；如果工件足够短而且支撑具有足够的刚性，仿形表面可以通过用一个垂直于旋转轴的仿形刀具来制造。短的锥面或柱面也可以仿形切削。常常需要的是平坦的或平的表面。它们可以通过径向车削或端面车削来完成，其中刀具尖端沿垂直于旋转轴的方向运动。在其他情况下，更方便的是固定工件不动，以一系列直线方式往复运动刀具横过工件，在每次切削行程前具有一定横向进给量。这种龙门刨削和牛头刨削是在刨床上进行的。大一些的工件很容易保持刀具固定不动，而像龙门刨削那样在其下面拉动工件，再每次往复进给刀具。仿形面可以通过使用仿形刀具来制造。也可以使用多刃刀具。钻削使用两刃刀具，深度可达钻头直径的5-10倍。不管是钻头转动还是工件转动，切削刃与工件之间的相对运动都是一个重要因素。在铣削作业中，有许多切削刃的旋转铣刀与工件相接合，这种工件相对铣刀运动缓慢。根据铣刀的几何形状和进给的方式，可以加工出平面和仿形面。可以使用水平或垂直旋转轴，工件可以沿三个坐标方向中的任意一个进给。基本的机床机床用于以切屑的形式从韧性材料上去除金属来加工特殊几何形状和精密尺寸的部件。切屑是废品，其变化形状从像钢这样的韧性材料的长的连续带状屑到铸铁形成的易于处理、彻底断掉的切屑，从处理的观点来讲，不想要长的连续带状屑。机床完成5种基本的金属切削工艺：车削、刨削、钻削、铣削和磨削。其他所有金属切削工艺都是这5种基本工艺的变形。例如：镗削是内部车削；铰削、锥体车削和平底锪孔则修改钻孔，与钻削有关；滚齿与切齿是基本铣削作业；弓锯削和拉削是铣削和磨削的一种形式；而研磨、超精加工、抛光和磨光是磨削和研磨切削作业的各种变化形式。因此，仅有4种使用专用可控几何形状的刀具基本机床：1、车床，2、刨床，3、钻床，4、铣床。磨削工艺形成碎屑，但是磨粒的几何形状不可控制。不同加工工艺切削的材料的数量和速度却不相同。可能极大，如大型车削作业；或者极小，如磨削和超精加工作业，只有表面高出的点被去除。机床完成3种主要功能：1、刚性支撑工件或工件夹具以及切削刀具；2、提供工件与切削刀具之间的相对运动；3、提供了一定范围的速度进给，通常每种有4-32种选择。切削速度和进给切削速度、进给量和切削深度是切削加工的3个主要变量，其他变量还有工件和工具材料、冷却剂以及切削刀具的几何形状。金属切削的速率和加工所需的功率就决定于这些变量。切削深度、进给量和切削速度是任何金属切削作业中必须都建立的变量。它们都影响切削力、功率和对金属切削的速率。可以通过把它们与留声机的唱针和唱片相比较给出定义。切削速度（V）由任意时刻唱片表面相对于拾音器支臂内部的唱针的速度来表示；进给量由唱针每圈径向向内的前进量或者由两个相邻槽的位置差来表示。切削深度是唱针进入的量或者是槽的深度。切削那些在外表面上用单刃刀具完成的工序叫车削。除钻削、铰削和锥体车削外，在内表面的作业也由单刃刀具完成。包括车削和镗削在内的所有加工工序都可以分为粗加工、精加工和半精加工。粗加工工序的目的是尽可能迅速且高效地去除大量的材料，在工件上只留下少量的材料给精加工工序。精加工工序用以获得工件最终的大小、形状和表面粗糙度。有时，在精加工工序前进行半精加工作业以便在工件上留下少的、预定的和均匀量的原材料供精加工去除。通常，较长的工件是在一个或两个车床顶尖的支撑下进行的。用于安装车床顶尖的锥形孔叫做顶尖孔，它是在工件的端部钻出的通常沿着柱形部件的轴心。与尾架邻近的工件端部总是由尾架顶尖支撑，而挨着主轴箱的一端则由主轴箱顶尖支撑或装在卡盘内。工件的主轴箱一端可以装在一个四爪卡盘或套爪卡盘内。这种方法牢固地夹持工件并且把功率平稳地传送到工件上；由卡盘提供的额外支撑减少了车削作业时发生震动的倾向。如果仔细地将工件精确的固定在卡盘上，用这种方法将获得精密的结果。通过将工件支撑在两个顶尖之间可以获得非常精确的结果。一个车床夹头夹在工件上；然后由安装在主轴前端的拨盘一起带动。先加工工件的一端，然后可以在车床上将工件掉头加工另一端。工件上的顶尖孔是用作精确定位面以及承受工件重量和抵抗车削力的支撑面。在工件被拆下后，顶尖孔可以精确地将其装回机床。工件千万不要同时通过卡盘和顶尖安装在主轴箱一端。虽然这样似乎是一种快捷方法，但是这样做使得工件受力不均匀，顶尖的对正作用不能维持，而且爪的压力可能损坏顶尖孔、车床顶尖甚至车床主轴。几乎被独自用在大量生产工件上的补偿或浮动爪式卡盘是上述的一个例外。这些卡盘是自动偏心夹紧卡盘不能起到普通三爪或四爪卡盘同样的作用。直径非常大的工件虽然有时安装在两个顶尖上，但是最好用花盘把它们固定在主轴箱端以获得流畅
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