機(jī)械專(zhuān)業(yè)畢業(yè)設(shè)計(jì)外文翻譯--極限與誤差-全文預(yù)覽
【正文】 示軸。軸表給出基本尺寸在 500mm 以上和“通用的軸和孔”分成兩個(gè)表 “一般用途”和“精密 機(jī)械和鐘表”。 規(guī)定了 20 種標(biāo)準(zhǔn)公差等級(jí)，即 IT01， IT0， IT1118，它們是在 500mm 以內(nèi)硬性劃分的每一段（例如 03， 36， 610，? ? ,400500mm）的基本尺寸都對(duì)應(yīng)有不同的標(biāo)準(zhǔn)公差數(shù)值。任一給定基本尺寸，公差范圍和偏差被標(biāo)準(zhǔn)化根據(jù)零偏差，這個(gè)零偏差稱(chēng)為零線。每個(gè)零件有一個(gè)極限尺寸，上下偏差從基本尺寸分開(kāi)，大小和符號(hào)是極限尺寸減去基本獲得的。如名義尺寸 30mm公差帶 ?? 極限尺寸 。公差變化依賴制造機(jī)器的精度，加工過(guò)程和尺寸大小。一般，如一個(gè)公差被標(biāo)注的尺寸數(shù)字的旁邊。 影響零件功能的尺寸必須總是明確的給出不能留下另外的尺寸。 除絕對(duì)需要的尺寸之外，不應(yīng)該再有更多的尺寸，而在任一方向上，只能在一個(gè)尺寸上注上特殊要求。為了在配合零件有過(guò)盈或受力配合，公差必須產(chǎn)生一個(gè)零或負(fù)的允差。如果尺寸標(biāo)注為 177。因此最大允差為 和最大間隙為 ，在最小軸和最大孔尺寸的基礎(chǔ)上。如果一個(gè)零件有幾個(gè)或多個(gè)面要生產(chǎn)，當(dāng)要求小的偏差生產(chǎn)成本將急劇上升。 。公差是在某一零件上被允許的變化量或在尺寸上總的變化量。然而一些生產(chǎn)者并不用綜合注釋假定每個(gè)尺寸是單獨(dú)的被考慮的可能會(huì)規(guī)定出注釋中要求的更寬的公差。 工藝制造流 程發(fā)展大批量制造低成本依靠零部件的互換性。雖然小的公差產(chǎn)生高質(zhì)量的產(chǎn)品和機(jī)器，但是隨公差的減小制造成本快速增加，正如圖典型曲線所示，因此公差的確定在能保證產(chǎn)品質(zhì)量或功能下取最大值。非常明顯圖紙應(yīng)在有一種且只有一種解釋的方式下標(biāo)注。裝配或制造之前必須完成裝配圖和零件圖的繪制以便傳遞所有必要的信息給車(chē)間的工人。表面粗糙度值愈大，則凹谷中聚積腐蝕性物質(zhì)就愈多。 在交變載荷作用下，表面粗糙度的凹谷部位容易引起應(yīng)力集中，產(chǎn)生疲勞裂紋，表面粗糙度值愈大，表面的紋痕愈深，紋底半徑愈小，抗疲勞破壞底能力就愈差。因此，接觸面的粗糙度有一個(gè)最佳值，其值與零件的工作情況有關(guān)，工作載荷加大時(shí)，初期磨損量增大，表面粗糙最佳也加大。 零件磨損一般可分為三個(gè)階段，初期磨損階段、正常磨損階段忽然劇烈磨損階段。 that is , it would vary both over and under the nominal dimension. The unilateral system permits changing the tolerance while still retaining the same allowance or type of fit. With the bilateral system, this is not possible without also changing the nominal size dimension of one or both of the two mating parts. In mass production, where mating parts must be interchangeable, unilateral tolerances are customary. To have an interference or fore fit between mating parts, the tolerances must be such as to create a zero or negative allowance. Tolerances Limits and Fits The drawing must be a true and plete statement of the designer’s expressed in such a way that the part is convenient to manufacture. Every dimension necessary to define the product must be stated once and repeated in different views. Dimensions relating to one particular feature, such as the position and size of hole, where possible, appear on the same view. There should be no more dimensions than are absolutely necessary, and no feature should be located by more than one dimension in any direction. It may be necessary occasionally to give an auxiliary dimension for reference, possibly for inspection. When this is so, the dimension should be enclosed in a bracket and marked for reference. Such dimensions are not governed by general tolerances. Dimensions that affect the function of the part should always be specified and not left as the sum or other dimensions. If this is not done, the total permissible variation on that dimension will form the sum or difference of the other dimensions and their tolerance, and this with result in these tolerances having to be made unnecessarily tight. The overall dimension should always appear. All dimensions must be governed by the general tolerance on the drawing unless otherwise stated. Usually, such a tolerance will be governed by the magnitude of the dimension. Specific tolerances must always be stated on dimensions affecting or interchangeability. A system of tolerances is necessary to allow for the variations in accuracy that are bound to occur during manufacture, and still provide for interchangeability and correct function of the part. A tolerance is the difference in a dimension in order to allow for unavoidable imperfections in workmanship. The tolerance range will depend on the accuracy of the manufacturing organization, the machining process and the magnitude of the dimension. The greater the tolerance range is disposed on both sides of the nominal dimension. A unilateral tolerance is one where the tolerance zone is on one side only o
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