1、附录1机械英语文章翻译机械英语文章翻译3附录1机械英语文章翻译_机械英语文章翻译3附录1 英文翻译 Dimensional Control In the early days of engineer, the mating of parts was achieved by machining one part as nearly as possible to the required size, machining the mating part nearly to size, and then completing its machining, continually offering th
2、e other part to it, until thedesired relationship was obtained. If it was inconvenient to offer one part to the other part during machining, the final work was done at the bench by a fitter, who scraped the mating parts until the desired fit was obtained, the fitter therefore being a fitter in the l
3、iteral sense. It is obvious that the two parts would have to be done all over again. 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 fitting operations. When one part can be used off the shelf t
4、o replace another of the same dimension and material specification, the parts are said to be to be interchangeable. A system of interchangeability usually lowers the production costs, as there is no need for an expensive fiddling operation, and it also benefits the customer in the event of the need
5、to replace worn parts. It also, however, demands that the dimension of mating parts be specified, and that dimensional variations, due to machine and operator shortcomings, be taken into account. Some form of inspection must be introduced to ensure that the manufacture is controlled; this is particu
6、larly important, because dimensional errors may not be revealed until some time has elapsed, and often many miles from the place where the machining was done. 1. Tolerance and Limits of size Since it is accepted that it is virtually impossible to manufacture a part without error, or in the rare even
7、t 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. The draughtsman must indicate the largest and smallest sizes that the limits of size, and the difference betwe
8、en them is called the tolerance, the actual tolerance must be increased with size. The tolerance should be as large as possible, to keep the cost to a minimum.The method of indicating, on a drawing, the permitted tolerance depends mainly upon the type of operation involved, but local preference must
9、 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, or the diameter of a hole or shaft id specified. For example, when a diameter is being ground, the machinist would prefer t
10、o aim at the largest size permitted, so that, in the event of his reaching a diameter 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. A draughtsman might dimension a nominal 75-0.
11、012 mm diameter shaft as D75. Similarly, a nominal 75mm hole might 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 specified. The machine operator may position he hole nearer the datum or
12、 further from the datum than intended, he must aim between the limits of position, so that the maximum error can be made without causing the part to be rejected. The center distance between two holes would therefore be specified as, for example, 100+0.02mm. 2. Fits are concerned with the relationshi
13、p between two parts. Consider a shaft and a hole combination: if the shaft is larger than the hole, the condition is said to be of interference; and if smaller than the hole, the condition is said to be of clearance. The interference may be such that the two parts can be assembled only by shrinking,
14、 or it may be very slight, so that the parts can be assembled by hand-operated press. Similarly, the clearance can be slight, so that the shaft can rotate easily in the hole, or be large, so that there is ample clearance for bolts to pass through.In order that the precise condition is ensured, the l
15、imits of size of both the shaft and the hole must be stipulated. (1) Classes of fit. These are classified as follows.Clearance fit. When the limits of size of both the hole and the shaft are such that the shaft is always smaller than the hole, the fit id said to be a clearance fit.Interference fit.
16、When the limits of size of both the hole and the shaft are such that the shaft is always larger than the hole, the fit id said to be a interference fit.Transition fit. When the limits of size of both the hole and the shaft are such that the condition may be clearance or interference, the fit id said
17、 to be a transition fit. (2) Hole-based system and Shaft-based system. In order to obtain a range of degrees of clearance, and degrees of interference, it is necessary to use a wide variation of hole sizes and shaft sizes. For example, a manufacturing company could be making a number of parts, all o
18、f a nominal 25-mm diameter, but which are all slightly different in actual limits of size, to suit the actual fit required of each pair of parts. This situation could mean that a large number of drills, reamers, gauges, etc. were required.It is logical that, to reduce this number, a standard hole co
19、uld be used for each nominal size, and the variation of fit e obtained by making the mating shaft smaller or larger than the hole. This is known as a hole-based system. Alternatively, a standard shaft could be used for each nominal size, and the variation of fit is obtained by making the mating hole
20、 larger or smaller, as required. This is known as a shaft-based system. a hole-based system is usually preferred, because it standardizes fixed size equipment such as reamer and plug gauges; but a shaft-based system is usually also provided, because sometimes it is more convenient to employ a common
21、 shaft to which a number of components is assembled, each with a different fit, and sometimes it is convenient to use bar stock without further machining. 3. Systems of limits and fits It is convenient to establish a standardized system of limits and fits, not only to eliminate the need for the drau
22、ghtsman to determine the limits each time an assembly is detailed, but also to standardize the tools and gauges required. A system of limits and fits should cater for a wide range of nominal sizes. To satisfy the various needs of industry, and should cater for a wide range of quality of work. The sy
23、stem should, if possible, be tabulated, to save the user the trouble of having to calculate the limits of size to suit of the class of fit, the quality of the work, and the size of the part. 4. British Standard 4500: 1969, ISO limits and fits This standard replace BS 4500 is essentially a revision o
24、f BS 1961 to bring the British Standard into line with the latest recommendations of the International Organization for Standardization (ISO). The system refers to holes and shafts, but these terms do not only apply to cylindrical parts but can equally well be applied to the space contained by. Or c
25、ontaining, two parallel faces or tangent planes. The system is tabulated,and covers sizes up to 3150mm. The Numerical Controls development The first electronic computer in the world emerged in 1946, this indicates the mankind has created the tool that can strengthen and replace the mental labour par
26、tly . It, and mankind those that create to strengthen tool of manual labor compare among agriculture, industrial society, the qualitative leap has arisen , has established the foundation that the mankind enters the information-intensive society . 6 years later, namely in 1952, the technology of the
27、computer was applied to the lathe , the first numerical control lathe has emerged in U.S.A. From then on, the traditional lathe had produced the change of the quality. In nearly half a century, the numerical control system went through two stages and six generations development The numerical control
28、 lathe is regarded as the integrated typical products of electromechanics, play an enormous role among mechanical manufacturing industry , solve structure complicated , accurate , batch little , changeable processing problem of part in the modern machine-building well, and can stabilize the processi
29、ng quality of the products , improve production efficiency by a large margin . But seen from situation which enterprises face at present, because the numerical control lathe price is relatively expensive, ambassadors enterprises are unable to do what one wants very much to do to relatively make the
30、investment once only. Our country can yet be regarded as a kind of better good plan to the numerical control transformation of the ordinary lathe as the lathe big country . This text proposes to the domestic enterprises current situation at present the economic numerical control of the simple and ea
31、sy type transforms the thinking and design method for technical staff of numerical controls reference.Numerical control transformation mean to ordinary lathe some position make certain transformation generally, match the numerical control device, thus make the lathe have working ability of numerical
32、 control, its purpose is for improving machining accuracy of the old equipment and production efficiency, adapt to many variety and production , short run of part , can make industrial grade can process the high-quality part too than low worker at the same time, reduce investment of technological tr
33、ansformation of the equipment ,etc. Price performance on all these for improving been for lathe than,namely last mechanical performance and the working ability not higher with less money. So transform ordinary lathe as numerical control lathe whether one improve numerical control effective way of rate. Generally speaking, carry on the tran
