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本科毕业设计(论文)题目 多功能焊台设计 学院名称 机械与汽车工程学院 专业班级 机械（高职）082 学生姓名 王金超 导师姓名 范维华 2012年 6 月 3 日 1 山东轻工业学院毕业设计（论文）中期进展报告表学院机械与汽车工程学院专业班级机械（高职）08-2学生姓名 王金超学号200801014066导师姓名范维华设计（论文）题目多功能焊台设计根据题目和设计任务书的要求，在老师的指导下，前段时间主要完成了开题报告、英文翻译、实习报告的工作，并查阅了与题目相关的资料，初步拟订了设计方案，并在各种方案中相互比较各自的优缺点，从而确定了最终的设计方案。根据设计题目的要求，在原有的数据基础上要对支撑架一些部位进行改进设计。并且绘制零件图和装配图。在此期间主要完成支撑架的设计。并且根据支撑架结构把所设计的装配图基本用计算机绘制完成，但还有一些细节的地方还没有具体绘制完成，对于零件间的联接地方表达的还不是很清楚，还需继续完善，并开始绘制零件图的工作。以后的时间主要详细完成装配图、绘制零件图、编写设计说明书等具体的东西，尽量在最早的时间里完成自己的设计。需要做的工作还有很多，时间又很紧，需要我们时刻都不能松懈！在设计过程中，对于自己的疑问和错误在老师和同学的帮助下，基本上都得到了解决。同时，在绘制装配图的时候一些尺寸不能随便定，要根据发动机底壳的尺寸来确定整体的尺寸值，才能得到合理的装配图。在后面的时间里，将根据自己和老师的进度要求，最快最好的完成各项工作。 2012年5月15日指导教师评价意见1设计（论文）进展情况评价 （基本完成计划、部分完成计划、没有完成计划）2学生工作态度情况评价 （认真、一般、较差）3已完成设计（论文）质量评价 （较好、一般、较差）4设计（论文）不足之处及改进意见 指导教师签字： 年 月 日注：每名学生填写一份，并由指导教师填写意见、签字后，返还学生归档 Limits and Tolerances Dimensioning 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. 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 dimensioning 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 involved 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 exactly 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 Fig14.1. It is therefore important that the tolerances be specified at the largest 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 midpoint 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 proper tolerances for the individual parts, and the correct amount of clearance or interference to permit assembly with the mating 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 tolerance for such dimensions.However, some companies do not use blanket notes on the supposition that if each dimension is considered individually, wider tolerances 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 In dimensioning a drawing, the numbers placed in the dimension lines represent dimension that are only approximate and do not represent any degree of accuracy unless so stated by the designer.To specify a degree of accuracy, it is necessary to add tolerance figures to the dimension. Tolerance is the amount of variation permitted in the part or the total variation allowed in a given dimension. A shaft might have a nominal size of 2.5in.(63.5mm), but for practical reasons this figure could not be maintained in manufacturing without great cost. Hence, a certain tolerance would be added and, if a variation of0.003in.(0.08mm) could be permitted, the dimension would be stated 2.5000.003(63.50.08mm). Dimensions given close tolerances mean that the part must fit properly with some other part. Both must be given tolerances in keeping with the allowance desired, the manufacturing processes available, and the minimum cost of production and assembly that will maximize profit. Generally speaking, the cost of a part goes up as the tolerance is decreased. If a part has several or more surfaces to be machined, the cost can be excessive when little deviation is allowed from the nominal size. Allowance, which is sometimes confused with tolerance, has an altogether different meaning. It is the minimum clearance space intended between mating parts and represents the condition of tightest permissible fit. If a shaft, size 1.498-0.003, is to fit a hole of size 1.500+0.003, the minimum size hole is 1.500 and the maximum size shaft is 1.498. Thus the allowance is 0.002 and the maximum clearance is 0.008 as based on the minimum shaft size and maximum hole dimension. Tolerances may be either unilateral or bilateral. Unilateral tolerance means that any variation is made in only one direction from the nominal or basic dimension. Referring to the previous example, the hole is dimensioned 1.500+0.003, which represents a unilateral tolerance. If the dimensions were given as 1.5000.003, the tolerance would be bilateral; 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 force 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 complete statement of the designers requirements expressed in such a way that the part is convenient to manufacture.Every dimension necessary to define the product must be stated once only and not repeated in different views. Dimensions relating to one particular feature, such as the position and size of a hole, should, 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 difference of 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 tolerances, and this will 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 function 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 organisation, the machining process and the magnitude of the dimension. The greater the tolerance range, the cheaper the manufacturing process. A bilateral tolerance is one where 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 of the nominal dimension, in which case the nominal dimension may form one of the limits. Limits are the extreme dimensions of the tolerance zone. For example, nominal dimension 30mm tolerance +30.025+30.000 limits 30.02530.000 Fits depend on the relationship between the tolerance zones of two mating parts, and may be broadly classified into a clearance fit with positive allowance, a transition fit where the allowance may be either positive or negative (clearance or interference), an interference fit where the allowance is always negative.Type of Limits and Fits The ISO System of Limits and Fits, widely used in a number of leading metric countries, is considerably more complex than the ANSI system. In this system, each part has a basic size. Each limit of size of a part, high and low, is defined by its deviation from the basic size, the magnitude and sign being obtained by subtracting the basic size from the limit in question. The difference between the two limits of size of a part is called the tolerance, an absolute amount without sign. There are three classes of fits: 1) clearance fits, 2) transition fits (the assembly may have either clearance or interference), and 3) interference fits. Either a shaft-basis system or a hole-basis system may be used. For any given basic size, a range of tolerances and deviations may be specified with respect to the line of zero deviation, called the zero line. The tolerance is a function of the basic size and is designated by a number symbol, called the gradethus the tolerance grade.The position of the tolerance with respect to the zero line also a function of the basic sizeis indicated by a letter symbol (or two letters), a capital letter for holes and a lowercase letter for shafts. Thus the specification for a hole and shaft having a basic size of 45 mm might be 45H8/g7. Twenty standard grades of tolerances are provided, called IT01, IT0, IT118, providing numerical values for each nominal diameter, in arbitrary steps up to 500mm (for example 03, 36,610, ., 400500 mm). The value of the tolerance unit, i, for grades 516 is i=0.453D +0.001D Where i is in microns and D in millimeters. Standard shaft and hole deviations similarly are provided by sets of formulas, however, for practical application, both tolerances and deviations are provided in three sets of rather complex tables. Additional tables give the values for basic sizes above 500 mm and for “Commonly Used Shafts and Holes” in two categories“General Purpose” and “Fine Mechanisms and Horology”.标注尺寸机械设计除了计算载荷和应力、选择合适的材料外，还包括许多其它因素。在建造或制造开始前，完成装配图和零件图以把必要信息传达给车间工人是必须的。在送往车间前设计者常常被召集来检查图纸。而在精通生产图纸的所有情况之前，需要有许多经验并熟悉制造工艺。图纸必须仔细检查其尺寸是否按生产部门最方便易懂的方式标注。很明显图纸应该只有唯一的解释。 尺寸标注是一项复杂的工作，要掌握它需要有丰富的经验。尤其是不能要求车间工人在生产机械安排前进行三角或其它复杂的计算。由于要把零件加工到正好为给定尺寸是不可能的，因此图纸的尺寸必须加上公差以限制其可允许的变化。虽然较小公差能得到较高加工质量和较好操作机构，但随着公差的减小制造成本会迅速增加，因此公差被定为从操作或功能考虑允许的最大值是重要的。公差既可以是单向的也可以是双向的。单向标注有一公差为零，所有变化都由另一公差给定。而双向标注则采用一平均尺寸，它将公差带中点从该尺寸双向扩展为相等的正负变化范围。大规模低成本制造生产工艺的发展很大程度取决于组成零件的互换性。因此设计者必须确定单个零件的合适公差以及配合零件装配允许的正确间隙或过盈量。在图纸上标注公差的方法相当程度上依赖于产品的性质或制造工艺的类型。如果尺寸公差没有特别注明，图纸应该包含一个给出这些尺寸公差值的普遍适用注释。然而有些公司不采用普遍适用注释，假定每个尺寸是单独被考虑的，可能会规定出比注释中要求的更宽的公差。在任何情况下图纸不模棱两可并只服从于单一的解释是十分重要的。尺寸和公差在图纸标注尺寸时，除非设计者有意标明，注在尺寸线上的数字代表的尺寸仅仅是近似的，并不代表任何精度等级。为了详细标明精度等级，有必要在尺寸上增加公差数字。公差是零件允许的变动量或给定尺寸允许的总变动。一根轴可能的名义尺寸为2.5in.(63.5mm)，但由于实际原因不用大成本是不能在制造中保持这个数字的，因此要增加确定的公差。如果允许有0.003in.(0.08mm)的变化，则此尺寸可表达为2.5000.003(63.50.08mm)。 具有紧密公差的尺寸表示该零件必须恰当地与某些其它零件配合。所采用的制造工艺和使利润最大化的最小生产及装配成本都要求给定公差以保持所需允差。一般而言，零件的成本随着公差的减小而上升。如果一个零件有若干或较多表面要机加工，且几乎不允许偏离名义尺寸，则成本会超过正常合理的界限。允差，有时会跟公差混淆，但其具有完全不同的含义。它是配合零件之间最小的预期间隙空间，代表着允许的最紧配合条件。如果一根尺寸为1.498-0.003的轴与尺寸为1.500+0.003的孔配合，孔的最小尺寸为1.500而轴的最大尺寸为1.498。这样允差就是0.002，而由最小轴尺寸和最大孔尺寸形成的最大间隙为0.008。公差可以是单向的也可以是双向的。单向公差意味着任何变动都是只从名义或基本尺寸出发向一个方向变动的。引用前例，孔的尺寸标注为1.500+0.003，它表示了一个单向公差。如果尺寸标为1.5000.003，就是双向公差；即它可以在名义尺寸之上或之下变化。单向体系允许在依然保留相同允差或配合类型的情况下改变公差。而双向体系在不同时改变一个或两个配合零件名义尺寸的情况下，这是不可能做到的。大规模生产中配合零件必须能互换，单向公差是经常遇到的。为了使配合零件之间具有过盈或强制配合，公差必须产生零或负允差。公差、极限和配合图纸必须按方便制造零件的方式将设计者的要求真实和完整地表达出来。对每一描述产品所需的尺寸都只须标注一次而不必在不同的视图中重复。有关同一特性的尺寸，诸如孔的位置和大小，如果可能应出现在同一视图上除绝对需要的尺寸外，不应该有更多的尺寸；而在任意方向上，只能在一个尺寸上标注特性要求。偶尔也可能为了检查而必须给出供参考的辅助尺寸。在这种情况下，尺寸应该用括号括起来，以便参考。这样的尺寸不受通用公差控制。影响零件功能的尺寸总是应该标注的而不要留作其它尺寸的和或差。如果不是这样，那尺寸允许的总的变化将形成其它尺寸及它们的公差的和或差，这会导致这些公差不得不定得过紧。总尺寸一般应该标注。除非另行说明，所有尺寸都必须受图上的通用公差控制。一般这样的公差受到尺寸量值的控制。在影响功能或互换性的尺寸上必须标注专门的公差。为了允许在制造过程中必然会发生的精度变化，并提供零件的互换性和正确功能，一个公差系统是必需的。公差是为了允许工艺上不可避免缺陷而存在的尺寸上的不同。公差范围取决于制造机构的精度、机加工过程和尺寸的量值。公差范围越大，则制造过程的成本就越低。双向公差是在公称尺寸两侧都有公差带的公差。单向公差是仅在公称尺寸一侧有公差带的公差，在这种情况下公称尺寸成了两个极限中的一个。极限是公差带的极限尺寸。例如公称尺寸30毫米 公差 极限配合取决于两配合零件公差带之间的关系，并且可以概括地分为具有正允差的间隙配合，允差可以是正或负的过渡配合和总是负允差的过盈配合。极限和配合的类型 在一些最主要采用公制的国家中广泛使用的ISO的极限和配合系统，比ANSI的极限和配合系统要复杂得多。在这个系统中，每个零件都有基本尺寸。零件尺寸的每一极限，不管大小，都通过对基本尺寸的偏差来定义；其量值和符号由正被讨论的极限减去基本尺寸得到。零件尺寸的两个极限之差称为公差，这是一个没有符号的绝对量值。存在三种配合：1)间隙配合，2)过渡配合(装配后可以有间隙或过盈)，和3)过盈配合。在一些最主要采用公制的国家中广泛使用的ISO的极限和配合系统，比ANSI的极限和配合系统要复杂得多。在这个系统中，每个零件都有基本尺寸。零件尺寸的每一极限，不管大小，都通过对基本尺寸的偏差来定义；其量值和符号由正被讨论的极限减去基本尺寸得到。零件尺寸的两个极限之差称为公差，这是一个没有符号的绝对量值。基轴制或基孔制均可采用。对任何给定的基本尺寸，公差范围和偏差可以相对于被称为零线的零偏差线来确定。公差是基本尺寸的函数 并通过一个被称为等级的数字符号标明即公差等级。公差相对于零线的位置同样为基本尺寸的函数通过一个或两个字母符号表达，大写字母表示孔而小写字母表示轴。这样基本尺寸为45毫米的一个孔和轴配合规格可