1、英文资料 Limits and Tolerances The breakage of the machine spare parts ,generally always from the surface layer beginning of .The function of the product ,particularly its credibility and durable ,be decided by the quantity of spare parts surface layer to a large extent. Purpose that studies the machine
2、 to process the surface quantity be for control the machine process medium various craft factor to process the surface quantity influence of regulation, in order to make use of these regulations to control to process the process, end attain to improve the surface quantity, the exaltation product use
3、 the function of purpose . The machine processes the surface quantity to use the influence of the function to the machine (A) The surface quantity to bear to whet the sexual influence 1.Rough degree of surface to bear to whet the sexual influence A just process vice-of two contact surfaces of good f
4、riction, the first stage is rough only in the surface of the peak department contact ,the actual contact area is much smaller than theoretical contact area, in contact with each other the peak of the units have very great stress, to produce actual contact with the surface area of plastic deformation
5、, deformation and peak between the Department of shear failure, causing serious wear. Parts wear may generally be divided into three stages, the initial stage of wear and tear, normal wear and tear all of a sudden intense phase of stage wear. Parts of the surface roughness of the surface wear big im
6、pact. In general the smaller the value of surface roughness, wear better. However, surface roughness value is too small, lubricants difficult to store, contact between the adhesive-prone elements, wear it to increase. Therefore, the surface roughness of a best value, the value and parts of the work
7、related to increased work load, the initial wear increased, the best rough surface is also increased. 2.Cold Working hardening the surface of the wear resistance Processing the Cold Work hardening the surface of the friction surface layer of metal microhardness increase, it will generally improve th
8、e wear resistance. Cold Working but not a higher degree of hardening, wear resistance for the better, because too much will lead to hardening of the Cold Working excessive loose organization of metal, even a crack and peeling off the surface of the metal, declined to wear resistance. (B)The surface
9、quality of the impact of fatigue strength Metal hand alternating loads of fatigue after the damage occurred in parts often Chilled layer below the surface and, therefore parts of the surface quality of fatigue very influential. 1. Surface roughness on the impact of fatigue strength In alternating lo
10、ad, the surface roughness of the Au-site easily lead to stress concentration, a fatigue crack, the higher the value of surface roughness, surface traces of Yu Shen Wen, Wen at the end of the radius smaller, anti-fatigue damage at the end of the more capacity Worse. 2. Residual stress, fatigue Cold W
11、ork hardening of the impact Residual stress on the impact of large parts fatigue. Surface layer of residual stress fatigue crack will expand and accelerate the fatigue damage the surface layer and the residual stress can prevent fatigue crack growth, delaying the formation of fatigue damage. (C)The
12、surface quality of the corrosion resistance of the impact Parts of the corrosion resistance to a large extent depends on the surface roughness. The higher the value of surface roughness, Au Valley accumulate on the more corrosive substances. Corrosion resistance of the more worse. Surface layer of r
13、esidual stress will produce stress corrosion cracking, lower parts of the wear-resistance, and the residual stress is to prevent stress corrosion cracking. (D) The surface quality with quality Rough surface will affect the value of the size of the co-ordination with the surface quality. The gap with
14、 rough value will increase wear and tear, increased space, with the requirements of the destruction of nature. For Fit, the assembly part of the process of convex surface-crowded peak times, the actual reduction of the surplus and reduce the support of the connection between the strength. Dimensioni
15、ng The design of a machine includes many factors other than those of determining the loads and stresses and selecting the proper materials. Before construction or manufacture can begin, it is necessary to have complete assembly and detail drawings to convey all necessary information to the shop men.
16、 The designer frequently is called upon to check the drawings before they are sent to the shop. Much experience and familiarity with manufacturing processes are needed before one can become conversant with all phases of production drawings. Drawings should be carefully checked to see that the dimens
17、ioning is done in a manner that will be most convenient and understandable to the production departments. It is obvious that a drawing should be made in such a way that it has one and only one interpretation. In particular, shop personnel should not be required to make trigonometric or other involve
18、d calculations before the production machines can be set up. Dimensioning is an involved subject and long experience is required for its mastery. Tolerances must be placed on the dimensions of a drawing to limit the permissible variations in size because it is impossible to manufacture a part exactl
19、y to a given dimension. Although small tolerances give higher quality work and a better operating mechanism, the cost of manufacture increases rapidly as the tolerances are reduced, as indicated by the typical curve of Fig 14.1. It is therefore important that the tolerances be specified at the large
20、st values that the operating or functional considerations permit. Tolerances may be either unilateral or bilateral. In unilateral dimensioning, one tolerance is zero, and all the variations are given by the other tolerance. In bilateral dimensioning, a mean dimension is used which extends to the mid
21、point of the tolerance zone with equal plus and minus variations extending each way from this dimension. The development of production processes for large-volume manufacture at low cost has been largely dependent upon interchangeability of component parts. Thus the designer must determine both the p
22、roper tolerances for the individual parts, The manner of placing tolerances on drawings depends somewhat on the kind of product or type of manufacturing process. If the tolerance on a dimension is not specifically stated, the drawing should contain a blanket note which gives the value of the toleran
23、ce for such dimensions. However, some companies do not use blanket notes on the supposition that if each dimension is considered individually, wider tolerance than those called for in the note could probably be specified. In any event it is very important that a drawing be free from ambiguities and be subject only to a single interpretation. Dimension and Tolerance
