1、MachiningTurningThe engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered.The engine lathe has been replaced in to
2、days production shops by a wide variety of automatic lathes such as automatic tracer lathes, turret lathes, and automatic screw machines. All the advantages of single-point tooling for maximum metal removal, and the use of form tools for finish and accuracy, are now at the designers fingertips with
3、production speeds on a par with the fastest processing equipment on the scene today.Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled o
4、perator. In redesigning an experimental part for production, economical tolerances should be used.Turret Lathes Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately and rapidly. Applying this criterion for establishing the production q
5、ualification of a specific method, the turret lathe merits a high rating.In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations.A
6、utomatic Screw Machines Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has
7、long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important part in the economy of the parts machined on the automatic screw machine. Quantities less than 1000 parts may be more economical to
8、 set up on the turret lathe than on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities.Automatic Tracer Lathes Since surface roughness depends greatly upon material turned
9、, tooling, and feeds and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances.In some cases, tolerances of 0.05mm are held in continuous production using but one cut. Groove width can be held to 0.125mm on some parts. Bore
10、s and single-point finishes can be held to 0.125mm. On high-production runs where maximum output is desirable, a minimum tolerance of 0.125mm is economical on both diameter and length of turn.Milling With the exceptions of turning and drilling, milling is undoubtedly the most widely used method of r
11、emoving metal. Well suited and readily adapted to the economical production of any quantity of parts, the almost unlimited versatility of the milling process merits the attention and consideration of designers seriously concerned with the manufacture of their product.As in any other process, parts t
12、hat have to be milled should be designed with economical tolerances that can be achieved in production milling. If the part is designed with tolerance finer than necessary, additional operations will have to be added to achieve these tolerances-and this will increase the cost of the part.Grinding Gr
13、inding is one of the most widely used methods of finishing parts to extremely close tolerances and fine surface finishes. Currently, there are grinders for almost every type of grinding operation. Particular design features of a part dictate to a large the type of grinding machine required. Where pr
14、ocessing costs are excessive, parts redesigned to utilize a less expensive, higher output grinding method may be well worthwhile. For example, wherever possible the production economy of centerless grinding should be taken advantage of by proper design consideration.Although grinding is usually cons
15、idered a finishing operation, it is often employed as a complete machining process on work which can be ground down from rough condition without being turned or otherwise machined. Thus many types of forgings and other parts are finished completely with the grinding wheel at appreciable savings of t
16、ime and expense.Classes of grinding machines include the following: cylindrical grinders, centerless grinders, shafts, and similar parts are ground on cylindrical machines either of the common-center type or the centerless machine.Thread grinders are used for grinding precision threads for thread ga
17、ges, and threads on precision parts where the concentricity between the diameter of the shaft and the pitch diameter of the thread must be held to close tolerances.The internal grinders are used for grinding of precision holes, cylinder bores, and similar operations where bores of all kinds are to b
18、e finished.The surface grinders are for finishing all kinds of flat work, or work with plain surfaces which may be operated upon either by the edge of a wheel or by the face of a grinding wheel. These machines may have reciprocating or rotating tables.机 械 加 工车削普通车床作为最早的金属切削机床中的以种，目前仍然有许多有用的和为人们所需要的特
19、性。现在，这些机床主要用在规模较小的工厂中，进行小批量的生产，而不是进行大批量的生产。在现代的生产车间中，普通车床已经被种类繁多的自动车床所取代，诸如自动仿形车床，六角车床和自动螺丝车床。现在，设计人员已经熟知先利用单刃刀具除去大量的金属余量，然后利用成型刀具获得表面光洁度和精度这种加工方法的优点。这种加工方法的生产速度与现在工厂中使用的最快的加工设备的速度相等。普通车床的加工偏差主要依赖于操作者的技术熟练程度。设计工程师应该认真地确定由熟练工人在普通车床上加工的试验零件的公差。在把试验零件重新设计为生产零件时，应该选用经济的公差。六角车床 对生产加工设备来说，目前比过去更着重评价其是否具有精
20、确地和快速的重复加工能力。应用这个标准来评价具体的加工方法，六角车床可以获得较高的质量评定。在小批量的零件（100200 件）设计加工方法是，采用六角车床是最经济的。为了在六角车床上获得尽可能小的公差值，设计人员应该尽量将加工工序的数目减至最少。自动螺丝车床 自动螺丝车床通常被分为以下几种类型：单轴自动、多轴自动、和自动夹紧车床。自动螺丝车床最初是被用来对螺钉和类似的带有螺纹的零件进行自动化和快速加工的。但是，这种车床的用途早就超过了这个狭窄的范围。现在，它在许多种类的精密零件的大批量生产中起着重要的作用。如果工件的数量少于 1000 件，在六角车床上进行加工比在自动螺丝车床上加工要经济得多。
21、如果计算出最小经济批量，并且针对工件批量正确地选择机床，就回降低零件的加工成本。自动仿形车床 因为零件的表面粗糙度在很大程度上取决于工件材料、刀具、进给量和切削速度，采用自动仿形车床加工所得到的最小公差不一定是最经济的公差。在某些情况下，在恋雪生产过程中，至进行一次切削时的公差可以达到0.05mm。对于某些零件，槽宽的公差可以达到0.125mm。在希望获得最大产量的大批量生产中，进行直径和长度的车削时的最小公差值为0.125mm 是经济的。铣削除了车削和钻削，铣削无疑是应用最广泛的金属切削方法。铣削非常适合于而且也易于应用在任何数量的零件的经济生产中。在产品制造过程中，许许多多种类的铣削加工时
22、之得人员认真考虑和选择的。与其他种类的加工一样，对于进行铣削加工的零件，其公差应该被设计成铣削生产所能达到的经济公差。如果零件的公差设计得比需要的要小，就需要增加额外的工序，以获得这些公差这将增加零件的成本。磨削磨削是一种应用最广泛的零件精加工方法，用来获得非常小的公差和非常高的表面光洁度。目前，几乎存在着合适于各种磨削工序的磨床。零件的设计特征在很大程度上决定了需要采用的磨床的种类。当加工成本太高时，就值得对零件进行重新设计，使其能够通过采用既便宜有具有高生产效率的磨削方法加工出来。例如，在有可能的时候，可以通过对零件的适当设计，尽量用无心磨削加工，以获取经济效益。尽管通常认为磨削适用于精加
23、工工序，对于那些合适于采用磨削来完成粗、精加工工序的工件，也经常采用磨削方法完成全部加工，而不采用车削或者其他加工方法。磨床有以下几种类型：外圆磨床、无心磨床、内圆磨床、平面磨床和工具磨床。外圆磨床和无心磨床是用来磨削圆柱形工件或者圆锥形工件的。因此，花键轴、轴和其他类似的零件时采用普通的外圆磨床，或者采用无心磨床进行加工的。螺纹磨床又来磨削螺纹量规上的精密螺纹和用来磨削螺纹的中径与轴的同心度公差很小的精密零件上的螺纹。内圆磨床用来磨削精密的孔，汽缸孔以及各种类似的，需要进行精加工的孔。平面磨床用来对各种平面工件，或者带有平面的工件进行精加工。可以采用砂轮的边或者砂轮的端面进行磨削。这类机床上装有往复式工作台或者回转工作台。
