unit3.ppt

1、Dimensional control,王建辉,dimensional a.尺度的，尺寸的 dimensional chain 尺寸链 dimensional control mating n.配合，交配 the mating of parts 零件的配合 mating parts 配合零件 bench n.钳工台，工作台，长凳 Thisbenchis made of elm. 这条长凳是榆木制的。 The final work was done at the bench. 最后的工作是在钳工台上完成的,fitter n.装配工，钳工 George is a pipefitter. 乔治是一名

2、管道技工。 scrape n 随着时间的推移 Tolerance n.容忍，宽容；公差，容许偏差 Beyond Tolerance 难以忍受 tolerance system 公差制 The magnitude of the tolerance depends upon the type of operation involved.,Virtually ad事实上，实际上 He was virtually a prisoner. 他实际上是个囚犯。 It is virtually impossible to manufacture a part without error. Proclaim

3、v.宣告（布），声明，显示 The government has proclaimed a new law. 政府已公布了一项新法令。 Proclaim it to be perfect His accent proclaimed that he was a southerner. 他的口音表明他是南方人。,draughtsman n.绘图员，起草人 The draughtsman rapidly blocked out his idea. 制图员很快地把他的计划画出草图。 machinist n.机械工，机械师 A good machinist. 熟练的机械师 preference n.偏爱

4、，优先选择 have a preference for 偏爱. preference shares; 优先股,unilateral a.单方面的，单方面做出的；单边的 a unilateral decision 单方面的决定 .They cancelled the contract unilateral. 他们单方面地取消了该合同。 unilateral limits 单边极限 bilateral a.有两边的，双边的 a bilateral trade deal. 双边贸易协定。 bilateral limits 双边极限,datum n. 数据，资料 nomimal diameter 公称

5、直径 International Organization for Standardization(ISO) 国际标准化组织,Part Passage A,在早期的工程（问题）中，配合零件获得的方法是，首先尽可能把一个零件加工到所需尺寸，再将与它配合的零件加工到接近所需尺寸，不断将这两个零件进行试配，再进一步加工直至获得所需配合的尺寸。,In the early days of engineering, the mating of parts was achieved by machining one part as nearly as possible to the required siz

6、e, 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.,Part Passage A,If it was inconvenient to offer one part to the other part during machining, the final work was done at the bench by

7、a fitter, who scraped the mating parts until the desired fit was obtained, the fitter therefore being a “fitter” in the literal sense. It was obvious that the two parts would have to remain together, and in the event of one having to be replaced, the fitting would have to be done all over again.,假若在

8、加工中不便于将一个零件与另一个零件进行试配，那么最后的工作是由钳工在钳工台上完成，钳工刮削配合零件直至达到所需配合，所以“钳工”一词在英文中的意思为“装配者”。显然，两个配合件应该总在一起（工作），当其中任意一个需要替换时，所有的适配刮削工作又要从头重做。,Part Passage A,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 fi

9、tting operations.,这时，我们期望能够买到已损坏零件的替用品，而无需进行刮削或其他钳工操作就能正常工作。 当一个零件从货架上拿来就可以替换同样材料规格的另一个零件时，就说这个零件是可以互换的。,When one part can be used “off the shelf” to replace another of the same dimension and material specification, the part is said to be interchangeable.,Part Passage A,具有可互换性的配件体系不必进行高成本的刮削操作，因而降低了

10、生产的成本。当要换掉磨损的零件时，零件的可互换性对客户而言也是很有益处的。然而，可互换体系要求配件的尺寸必须规格化，还必须考虑因为加工操作的不足之处引起的尺寸变化。,A system of interchangeability usually lowers the production costs, as there is no need for an expensive “fiddling” operation, and it also benefits the customers in the event of the need to replace worn parts. It also

11、, however, demands that the dimensions of mating parts be specified, and that dimensional variations, due to machine and operator shortcomings, be taken into account.,Part Passage A,Some form of inspection must be introduced to ensure that the manufacture is controlled; this is particularly importan

12、t, because dimensional errors may not be revealed until some time has elapsed, and often many miles from the place where the machining was done.,必须采取某种形式的检测方法来确保对加工的控制。这一点特别重要。因为尺寸误差有时可能要过一段时间才会发现，而此时往往却已远离加工的地方。,Part Passage A,Tolerance and limits of size Since it is accepted that it is virtually i

13、mpossible to manufacture a part without error, or in the rare event of a part being without error，to be able to proclaim it to be perfect ( because the measuring instruments are subject to errors), it is necessary to indicate the maximum errors permitted. ,1.公差与极限尺寸 大家知道，事实上零件不可能毫无误差地制造出来，或者说没有误差的零件

14、是非常罕见的，要说明尺寸的准确性（因为测量仪器必然有误差），就有必要指出最大允许误差,Part Passage A,The draughtsman must indicate the largest and smallest sizes that can be permitted without the part functioning incorrectly. The extreme dimensions are called the limits of size, and the difference between them is called the tolerance.,绘图人员必须

15、标明零件正常工作时的最大允许尺寸和最小允许尺寸。这些尺寸的机制就称作极限尺寸，它们之间的差值称为公差。,Part Passage A,公差的大小取决于所涉及的加工操作的类型、机械工的技能、机床的精确度以及零件的尺寸。对于给定级别的公差，实际公差必须随着尺寸增大而增大。为使加工成本最小，公差应尽可能取大。,The magnitude of the tolerance depends upon the type of operation involved, the skill of the machinist, the accuracy of the machine, and the size o

16、f the part. For a given grade of tolerance, the actual tolerance must be increased with size. The tolerance should be as large as possible, to keep the cost to a minimum.,Part Passage A,在图上标注公差时，许用公差主要由所用操作的类型决定，但也必须考虑本国的优先级。下面用例子来说明用到的一些标注方法。 （1）单边极限。单边极限通常用在两个面之间的距离、孔径或轴径被指定的情况下。,The method of ind

17、icating, on a drawing, the permitted tolerance depends mainly upon the type of operation involved, but local preference must also be taken into account. The following examples will illustrate some of the methods used. 1.Unilateral limits. These are usually used when the distance between two faces, o

18、r the diameter of a hole or shaft is specified.,Part Passage A,比如，当直径要圆整时，机械工更愿意向最大允许尺寸圆整。这样，当他加工到所得直径尺寸略大于最大允许尺寸时，还可以在整个公差范围内再切一次，而知道不会因此使产品报废。,For example, when a diameter is being ground, the machinist would prefer to aim at the largest size permitted, so that, in the event of his reaching a diam

19、eter that is just a little larger than the maximum size permitted, he can take another cut, knowing that he can use up the whole of the tolerance before the job is rejected.,Part Passage A,A draughtsman might dimension a nominal 75-0.012 mm diameter shaft as D75.Similarly, a nominal 75mm hole might be dimensioned as D75-0.012, the same reasoning applies as for shafts. 2.Bilateral limits. These are usually applied when, for example, the position of a hole is speci