4202拖拉机后桥两侧面钻孔机床总体设计【机械毕业设计全套资料+已通过答辩】
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附件 1：外文资料翻译译文 机械设计 摘要： 机器是由机械装置 和 其它组件组成 的。 它是 一种 用来转换 或 传递能量的装置 ， 例如：发动机、涡轮机、车辆、起重机、印刷机、洗衣机、照相机和摄影机等。许多原则和设计方法 不但 适用于机器的设计，也适用于非机器的 设计 。术语中的“机械装置设计” 的含义要比“机械设计”的含义更为广泛一些，机械装置设计包 括机械设计。在分析运动及设计结构时，要把 产品 外型以及 以 后的保养也要考虑在机械设计中。在机械工程领域中，以及其它工程领域中，所有这些都需要机械设备，比如：开关、凸轮、阀门、船舶以及搅拌 机等。 关键词 ： 设计流程 设计规则 机械设计 设计流程 设计开始 之前就要 想到 机器的 实际性，现存的机器需要在耐用性、效率、重量、速度，或者成本上得到改善。新的机器必需具 有以前机器 所 能 执行的功能。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不 要 受 到任何 约束。即使产生了许多不切实际的想法，也会在设计的早期，即 在 绘制图纸之前被改正掉。只有这样，才不致于 阻断 创新的思路。通常 ,还 要提出几套设计方案，然后 加以 比较。 很有可能在这个计划最后 决定中 ,使用 了 某些不在计划 之内的 一些 设想 。 一般的当外型特点和组件部分 的尺寸特点分析得透彻时，就可以全面的 设计和分析。 接着 还要客观的分析机器性能的优越性，以及它的安全 、 重量、耐用性 ，并且 竞争力的成本 也要考虑在 分析结果 之内 。每一个至关重要的部分要优化它的比例和尺寸，同时也要保持与其它组成部分相协调。 也要 选择原材料和处理原材料 的 方法。通过力学原 理 来分析和实现这些重要的特性，如那些静态反应的能量和摩擦力的最佳利用，像动力惯性、加速动力和能量；包括弹性材料的强度、应力和刚度等材料的物理特性，以及流体润滑和驱动器的流体力学。设计的过程是重复和合作的过程，无论是正式或非正式的进行，对设 计者来说每个阶段都很重要。 最后，以图样为设计的标准，并建立将来的模型。如果它的测试是符合事先要求的，则再将对初步设计进行某些修改，使它能够在制造成本上有所降低。产品的设计需要不断探索和发展。许多方案必须被研究、试验、完善，然后决定使用还是放弃。虽然每个工程学问题的内容是独特的，但是设计师可以按照类似的步骤来解决问题。 产品的责任诉讼迫使设计人员和公司在选择材料时，采用最好的程序。在材料过程中，五个最常见的问题为：（ a）不了解或者不会使用关于材料应用方面的最新最好的信息资料； (b)未能预见和考虑材料的合理用 途（如有可能，设计人员还应进一步预测和考虑由于产品使用方法不当造成的后果。在近年来的许多产品责任诉讼案件中，由于错误地使用产品而受到伤害的原告控告生产厂家，并且赢得判决）；(c)所使用的材料的数据不全或是有些数据不确定，尤其是当其性能数据 长期不更新 ； (d)质量控制方法不适当和未经验证； (e)由一些完全不称职的人员选择材料。 通过对上述五个问题的分析，可以得出这些问题是没有充分理由 而 存在的结论。对这些问题的研究分析可以为避免这些问题的出现 而 指明方向。尽管采用最好的材料选择方法也不能避免发生产品责任诉讼，设计人 员和工业界按照适当的程序进行材料选择，可以大大减少诉讼的数量。 从以上的讨论可以看出，选择材料的人们应该对材料的性质，特点和加工方法有一个全面而基本的了解。 在随后生产和售后服务的几年中，要接受新观念的变化，或者由试验和经验为基础，进一步分析并改进。 一些设计规则 在本节中，建议要运用创造性的态度来替代和改进。也许会创造出更实用、更经济、更耐用的产品。 为了激发创造性思维，下列是设计和分析的建议规则。前六个规则对设计者来说特别适用。 1. 要有 创造性 的 利用所需 要 的物理性质 和 控制过程。 2. 认识负载产生的影响及其意义 。 3. 预测没有想到的负载。 4. 创造出对载荷更为有利的条件。 5. 提供良好的应力分布和最小的刚度条件。 6. 运用最简单的方程来优化体积和面积。 7. 选择组合材料。 8. 仔细选择所备的原料和不可缺少的组件。 9. 调整有效的设计方案，以适应生产过程和降低成本。 10. 规定好准确的位置条件为了使组件安装时不干涉。 机械设计包括一下内容： 1. 对设计过程、设计所需要公式以及安全系数进行介绍。 2. 回顾材料特性、静态和动态载荷分析，包括梁、振动和冲击载荷。 3. 回顾应力的基本规律和失效分析。 4. 介绍静态失效理论和静态载荷下机械断裂分析。 5. 介绍疲劳失效理论并强调在 压力条件下接近高循环的疲劳设计，这通常用在旋转机械的设计中。 6. 深入探讨机械磨损机理、表面接触应力和表面疲劳现象。 7. 使用疲劳分析技术校核轴的设计。 8. 讨论润滑油膜与滚动轴承的理论和应用。 9. 深入介绍直齿圆柱齿轮的动力学、设计和应力分析，并简单介绍斜齿轮、锥齿轮和涡轮有关方面的问题。 10. 讨论弹簧设计、螺杆等紧固件的设计，包括传动螺杆和预紧固件。 11. 介绍盘式和鼓式离合器以及制动器的设计和技术说明。 机械设计 一台完整机器的设计是一个复杂的过程。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制 图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。 任何产品在设计时第一步就是选择产品每个部分的构成材料。许多的材料被今天的设计师所使用。对产品的功能，它的外观、材料的成本、制造的成本作出必要的选择是十分重要的。对材料的特性必须事先作出仔细的评估。 仔细精确的计算是必要的，以确保设计的有效性。在任何失败的情况下，最好知道在最初设计中有有缺陷的部件。计算（图纸尺寸）检查是非常重要的。一个小数点的位置放错，就可以导致一个本可以完成的项目失败。设计工作的各个方面都应该检查和复查。 计算机是一 种 工具，它 能够 帮助机械设计师减轻繁琐的计算，并对现有数据提供进一步的分析。互动系统基于计算机的能力，已经使计算机辅助设计（ 计算机辅助制造（ 为 了 可能。心理学家经常谈论如何使人们适应他们所操作的机器。设计人员的基本职责是努力使机器来适应人们。这并不是一项容易的工作，因为实际上并不存在着一个对所有人来说都是最优的操作范围和操作过程。另一个重要问题，设计工程师必须能够同其他有关人员进行交流和磋商。在开始阶段，设计人员必须就初步设计同管理人员进行交流和磋商，并得到批准。这一般是通过口头讨论，草图和 文字材料进行的。 如前所诉，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小 数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就使用原来的方法。因此，设计人员必须要有耐心，因为 所花费的时间和努力并不能保证带来成功。一个全新的设计，要求屏弃许多陈旧的，为人们所熟知的方法。由于许多人墨守成规，这样做并不是一件容易的事。一位机械设计师应该不断地探索改进现有的产品的方法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺 陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新方法。 附件 2：外文原文 （复印件） A is a of of of to to is in a to in in of in as of as a in or be to a by as or or n to to of if in in of is to up of in in a of in as or a be a of be be by of as of of of of of of of of be by of in a be by a or is a or to of an be or of is to in In of a) t or to (b) to as to In in of (c) of or of is (d) is (e) by to is to of to be to on of to to a a be If it to be in at a of is to as or as n it is a to to of To 1. A of of 2. 3. 4. 5. 6. to 7. a of 8. 9. a to 10. of in 1. an to 2. 3. of 4. on to is in of 5. of 6. 7. . a to of a to 9. 10. 11. of he of a is a is a in in so on of in of is to is to be to s of of of in a A of of a. be to to of a In of it is to in of is of of an of be is a to to of on of to s is to is an to to in is be to on In to to on on is is If is to on to on in a do of as is on a to to is is to in a On be on if a to A to is to is to to to A of is an A of in it 潍坊学院本科毕业设计任务书 课题名称： 650拖拉机后桥两侧面钻孔机床 总体 设计 课题类别： 工 程 设 计 专 业： 机械设计制造及其自动化 年 级： 2008级 指导教师： 杨 祖 效 学生姓名： 张 忠 刚 2012年 3 月 6 日 一、 课题条件： 1、 被加工零件： 650拖拉机 后桥 零件图 2、产品生产纲领： 60000台 /年。 3、最低主轴高度 4、组合机床设计手册、组合机床通用零部件图册及产品样本等技术资料。 5、绘图工 具及绘图条件 6、计算机 二、毕业设计主要内容： 1、组合机床主轴箱总体方案设计 2、主轴箱总图设计 3、零件图设计 4、撰写设计说明书（不少于 8000字） 5、外文资料翻译 (不少于中文 3000字 ) 三、计划进度： 1、调研、收集阅读资料 1周 2、总体方案设计 3周 3、主轴箱总图及零件图设计 4周 4、撰写设计说明书 2周 5、答辩准备 1周 6、毕业设计答辩 1周 四、主要参考文献： 1大连组合机床研究所 M械工业出版社， 1956. 2大连组合机床研究所 M械工业出版社， 1963. 3金振华 M械工业出版社， 1993. 4李庆余 ,张佳 M械工业出版社， 5谢家瀛 一版） M械工业出版社， 6大连组合机床研究所编 M. 北京：机械工业出版社， 1975. 7沈阳大学等编 上海：上海科学技术出版社， 1985 8许晓旸 重庆 ： 重庆大学出版社 M， 9谈武宗 J导教师 杨祖效 教研室主任 2012年 3 月 6 日 年 月 日 Journal of Materials Processing TechnologyJournal of Materials Processing Technology 128（2002）7-18：15101515Elsevier Science B.V.Knowledge model as an integral way to reuse the knowledge for fixture design processCharles W. BeardsleyAbstract:The fixture design is considered a complex process that demands the knowledge of different areas, such as geometry, tolerances, dimensions, processes and manufacturing resources. Nowadays, the fixture design process is o-riented to automated systems based on knowledge models. These models describe the characteristics and relationships of the physical elements together withthe inference processes that allow carrying out the activity of fixture design. With the employment of the knowledge models, besides the automation, it ispossible to systematize and structure the knowledge of the fixture design process.With the use of specific methodologies, as the knowledge template, it ispossible to reuse the knowledge represented in a model, for its use in a different design process. The knowledge template represents a pattern that defines the common entities and inference processes to use in the design process .In this work, with the use of knowledge template we propose the reuse of the knowledge described in the design process of fixtures for machining to other types of fixtures uses like inspection, assembly or welding. 2005 Elsevier B.V. All rights reserved.Keywords: Knowledge model; Knowledge template; Fixture designPage 91. IntroductionThe continuous challenge that involves the knowledge representation hasoriented to many different research groups to develop methodologies that describe stages for capture and representation of the knowledge in design and manufacturing systems 13. This has allowed to define knowledge models as a tool that helps us to clarify the structure of intensive knowledge and information-processing tasks. In this sense, a knowledge model provides a specification of the data and inference processes required by the system of study 4. A first approach in the development of knowledge models applied to machining fixtures design process has been proposed by Hunter 5.During the last decade, the use of modelling techniques has allowed usto represent the fixture design process employed in some manufacturing operations, such as machining, assembly and inspection, etc. 6. Due to the complexity and the wide scope of the fixture design process, different researchgroups have been focused in the analysis of specific activities of this process,such as fixture configuration, tolerance analyses, stability and accessibility.A great number of investigations has taken in consideration the way inwhich represent the knowledge used in the fixture design process. These researches are focused in the documentation of the design parameters, the structuring of the information of the fixture and the description of the fixture elements used in fixture design 2,7. On the other hand, the implementation of the knowledge used in the fixture design can be classified regarding the artificial intelligence technique(AI) used 8,9 and on the automation level of t-he design system2.However, whatever it is the artificial intelligence technique used and the automation level of this type of systems, the process of knowledge modelling in the fixture design is important for several reasons: the need to specify the concepts used in the fixture design; to establish the relationships amongdifferent knowledge groups; to develop knowledge based systems (KBS), and finally, to provide a conceptual base for reusing the knowledge. In this sense, the entities and structures defined in a knowledge model for design process of machining fixtures can be partially reused to develop new models for fixture design process, as the inspection or assembly fixture. The entities and structures reused has been defined using the method of knowledge template4.The work presented is a detailed proposition of the knowledge model for machining fixture design and the definition of the knowledge groups that can be reused in the inspection fixture design process, using the knowledge template method. Fig. 1 presents a general view of the contents of this ex Fig. 1. The structure of the work. planation.2. Present state of fixture design process knowledge modellingThe fixture concept arises from the need to establish a physical connection between part, and tool, and part and machine-tool. This connection should fulfil some requirements for support the machining operation to carry out. The mainly functionality of the fixture is to support, locate and clamp the part to the machine tool. However, in order to interpreting correctly the needed knowledge for develop the fixture design process, it is necessary to define the basic information related with this process according to the classification exposed in Table 1.All this information has been represented in models that describe the entities, attributes and relationships between each knowledge group in the fixture design process. The definition of these models can be carried out using methodologies that describe the activities to capture, represent and reuse the knowledge of a design system, for example MOKA and CommonKADS.The MOKA methodology is based on the definition of two models.These models allow to capture and to structure the knowledge of a system. The first model, uses a group of forms (ICARE: Illustrations, Constraints, Activities, Rules,Entities) that allow to capture and to represent the knowledge in a semistructured way; the second model allows to represent knowledge ina structured way, using the extension of UML 10.The CommonKADS methodology proposes the use of tools and techniques to carry out the capture and representation of the knowledge. In the case of reusing knowledge, CommonKADS proposes the use of the knowledgetemplate: a knowledge template is a piece of a knowledge model, in which the data and reasoning processes can be employed in the development of other applications 3.3. Methodology for development a knowledge model: structural modelThe methodology proposed for development of a knowledge model includes the realization of two stages. The first stage represents the knowledgeof the objects like part geometry, machining process, functional and detailed fixture design,and fixture resources (see Table 1). The second stage describesthe inference process (design and interpretation rules) needed to obtain a firstsolution for the machining fixture. These two stages allow to describe the structural model and behaviour model of the objects that compose the knowledge model for machining fixtures. This work is focused mainly in the descriptionof the structural model for machining fixture design process. Table 1Knowledge group for machining fixtureKnowledge group CharacteristicsPart geometry Geometry: holes, slots, etc.DimensionsTolerancesMachining process Type of machining process Machining phase and sub phaseMachining operationFunctional and detailed Methodology of designfixture design process Design rulesInterpretation rulesDesign constrainsFixture resources Type of fixture (modular, general, or dedicated)(functional elements Type of fixture elements (support, locate, clamp)and commercial elements) Type of machine tool (vertical milling machine, horizontal milling machine, etc.)The proposed structural model contains a general structure of the knowledge groups related with the fixture design process. The description of theaspects related with the knowledge groups are presented in Table 1. Fig. 2 shows the general structure of the knowledge groups for machining fixture design process. Due to the complexity of the fixture design process, the fixture design cannot be considered as an independent process with respect to the manufacturing process. In this sense, the information of the manufacturing process isdirectly represented in the fixture design process. In a similarway, the resources involved in the manufacturing process have a narrow relationship with the fixture resources, in terms of machine tools and commercial elements of fixture. The definition of each knowledge groups (see Table 1) has taken intoconsideration the attributes and necessary operations to represent the knowledge relative to these knowledge groups. The applications of these models are presented in the following sections.Fig. 2. Structural model for machining fixture.4. Knowledge template modelIn this section, we describe those pieces of the knowledge model thatcan be reused in other applications using the method of knowledge template.From a conceptual point of view, a knowledge template describes a piece of the knowledge model in which the inference and the knowledge tasks are defined with the objective of reuse this knowledge in other similar applications. In this sense, it is necessary to distinguish among the analytic and the synthetic tasks. The analytic tasks define the classification of the objects involvFig. 3. Knowledge tasks based on the structural model.ed in the fixture design process. The synthetic tasks have relationship with the reasoning way procedure from which a fixture solution is obtained.Using these two types of tasks, a first approach has been established to define the knowledge groups that can be classified under the analytic and synthetic tasks. Fig. 3 shows the objects of the structural model that describe the analytic and synthetic tasks of the machining fixture design process.The division of these two tasks allows to set in a first level the knowledge groups, that it objects and attributes that can be employed in the development of new applications. Also, this separation allows us to identify those knowledge groups that describe inference procedures in the design process,as the functional fixture design and the detailed fixture design. This section presentsthe definition of the tasks of the knowledge model classified under theconcept of analytic and synthetic tasks that can be reused in other applications.4.1. Analytic task definitionThe entities (or classes) defined under this category can be classified regarding the level of dependence level that present the objects involved in the machining fixture design. The first level defines those knowledge groups that are not consequence of the fixture design process, as geometry, dimensions and tolerances of the part. In this level, the entities that compose these knowledge groups can be totally reused in their structure, relationships and attributes. Fig. 4 shows an example of the knowledge group of geometry that can be reused in other applications.Fig. 4. Knowledge template for part entity (analytic task).The second level describes those entities that present a similar structure and relationships in the fixture design process(fixture functions and commercial elements for machining fixtures). In this level, can be reused only a portion of the structure and relationships that are not conditioned by the fixture design process.The third level describes those entities that present a complete dependence to the fixture design process. In this level, cannot be reused the knowledge previously defined (structures, relationships and attributes), due to dependence of the process developed.4.2. Synthetic task definitionThe definition of the synthetic tasks involves the identification of those objects linked with the inference procedure carried out in the fixture design process. In this type of tasks, it cannot have a total reutilization of the knowledge, because the inference process carried out using a group of production rules that depend of the type of process executed.Under this classification, the knowledge group of functional design establish the functional solution of the fixture definition: the supporting surfaces,locating and clamping of the part. The definition of these surfaces is depending to the manufacturing process developed. This last characteristic makes thatthe functional design possesses depend of the machining processes developedduring the manufacturing of the part. In this sense, the sharing knowledge ofthis group is limited to the definition of the surfaces and supporting points,locating, clamping for machining fixture and to selection of the functional elements. However, the knowledge group of functional elements can be reusedFig. 5. Knowledge template for functional elements entity.in other applications, due to the functional elements can be employed in multiple domains in the fixture design process. Fig. 5 shows an example of the knowledge template for functional elements used in the fixture design process.In the detailed design occur similar situations to those of the functional design. In this case, the detailed design depends on the fixture functional design through a correspondence between functional and commercial elements.The knowledge group for fixture elements can be partially reused to define anew group of fixture elements. For it, we must use the structure, relationships and entities defined for the following categories, base, support, locate, clampand auxiliary elements.Table 2Initial information for fixture machiningInformation CharacteristicsInitial geometr Final geometry Machining operations Face milling Side millingDrillingManufacturing resources Vertical milling machineFixture resources Modular fixture elements5. Application of the knowledge modelIn the next two sections, we present the application of the knowledge model for machining and inspection fixture design. These models taking into consideration two different parts, because we wish express the potentiality of the use of knowledge template.The implementation of the structuralmodel,discussed in Section 3, isbased on the instantiation of each attribute defined defined in the knowledge groups that compose this model. The instantiation is defined as the assignment of a concrete value for a specific attribute. For it, the initial conditions are exposed for the application of the knowledge model, which include the description of the initial geometry, final geometry, lists of machiningoperations,machine-tool and fixture resources. Table 2 shows the initial information for the application of the knowledge model for machining fixture.Mechanical Engineeringupon the principles of mechanics, such as those of static for reaction forces and for the optimum utiliza- tion of friction; of dynamics for inertia, acceleration, and energy; of elasticity and strength of materials for stress and deflection; of physical behavior of materials; and of fluid mechanics for lubrication and hydrodynamic drives. The analyses may be made by the same engineer who conceived the arrange- ment of mechanisms, or, in a large company, they may be made by a separate analysis division or research group. As a result of the analyses, new arrangements and new dimensions may be required. Design is a reiterative and cooperative process, whether done formally or informally, and the analyst can contribute to phases other than his own.Finally, a design based upon function and reli- ability will be completed, and a prototype may be built. If its tests are satisfactory, and if the device is to be produced in quantity, the initial design will undergo certain modifications that enable it to be manufactured in quantity at a lower cost. During subsequent years of manufacture and service, the design is likely to undergo changes as new ideas are conceived or as further analyses based upon tests and experience indicate alterations. Sales appeal, customer satisfaction, and manufacturing cost are all related to design, and ability in design is intimately involved in the success of an engineering venture.Some Rules for DesignIn this section it is suggested that, applied with a creative attitude, analyses can lead to important improvements and to the conception and perfec- tion of alternate, perhaps more functional, eco- nomical, and durable products. The creative phase need not be an initial and separate one. Although he may not be responsible for the whole design, an analyst can contribute more than the numerically correct answer to a problem that he is asked to solvemore than the values of stress, dimensions, or limitations of operation. He can take the broader view that the specifications or the arrangements may be improved. Since he will become familiarwith the device and its conditions of operation be- fore or during his analysis, he is in a good position to conceive of alternatives. It is better that he suggest a change in shape that will eliminate a moment or a stress concentration than to allow construction of a mechanism with heavy sections and excessive dynamic loads. It is better that he scrap his fine analysis, rather than that he later see the mechanism scrapped.To stimulate creative thought, the following rules are suggested for the designer and analyst. The first six rules are particularly applicable for the analyst, although he may become involved with all ten rules.1. Apply ingenuity to utilize desired physical properties and to control undesired ones.2. Recognize functional loads and their significance.3.Anticipateunintentional loads.4. Devise more favorable load- ing conditions.5. Provide for favorable stress distribution and stiffness with minimum weight.6. Use basic equations to proportion and opti- mize dimensions.7. Choose materials for a combina- tion of properties.8. Select carefully, between stock:and integral components.9. Modify a functional design to fit the manu- facturing process and reduce cost.10. Provide for accurate location and nonin- terference of parts in assembly.Machine DesignThe complete design of a machine is a complex process. The designer must have a good back- ground in such fields as statics, kinematics, dy- namics, and strength of materials, and in addition, be familiar with the fabricating materials and proc- esses. The designer must be able to assemble all the relevant facts, and make calculations, sketches, and drawings to convey manufacturing informationto the shop.One of the first steps in the design of any product is to select the material from which each part is to be made. Numerous materials are avail- able to todays designers. The function of the prod- uct, its appearance, the cost of the material, and the cost of fabrication are important in making a selec- tion. A careful evaluation of the properties of a. ma- terial must be made prior to any calculations.Careful calculations are necessary to ensure the validity of a design. Calculations never appear on drawings, but are filed away for several reasons. In case of any part failures, it is desirable to know what was done in originally designing the defective components. Also, an experience file can result from having calculations from past projects. When a similar design is needed, past records are of great help.The checking of calculations (and drawing di- mensions) is of utmost importance. The misplace- ment of one decimal point can ruin an otherwise acceptable project. For example, if one were to de- sign a bracket to support 100 lb when it should have been figured for 1,000 lb, failure would surely be forthcoming. All aspects of design work should be checked and rechecked.The computer is a tool helpful to mechanical designers to lighten tedious calculations, and pro- vide extended analysis of available data. Interactive systems, based on computer capabilities, have made possible the concepts of computer aided de- sign (CAD) and computer-aided manufacturing (CAM). Through such systems, it is possible for one to transmit conceptual ideas to punched tapes for numerical machine control without having formal working drawings.Laboratory tests, models, and prototypes help considerably in machine design. Laboratories fur- nish much of the information needed to establish basic concepts; however, they can also be used to gain some idea of how a product will perform in the field.Finally, a successful designer does all he can to keep up to date. New materials and productionmethods appear daily. Drafting and design person- nel may lose their usefulness by not being versed in modern methods and materials. A good designer reads technical periodicals constantly to keep abreast of new developments.Engineering TolerancingIntroductionA solid is defined by its surface boundaries. Designers typically specify a components nominal dimensions such that it fulfils its requirements. In reality, components cannot be made repeatedly to nominal dimensions, due to surface irregularities and the intrinsic surface roughness. Some variability in dimensions must be allowed to ensure manufac- ture is possible. However, the variability permitted must not be so great that the performance of the assembled parts is impaired. The allowed variability on the individual component dimensions is called the tolerance.The term tolerance applies not only to the ac- ceptable range of component dimensions produced by manufacturing techniques, but also to the output of machines or processes, For example, the power produced by a given type of internal combustion engine varies from one engine to another. In prac- tice, the variability is usually found to be modeled by a frequency distribution curve, for example the normal distribution (also called the Gaussian distri- bution). One of the tasks of the designer is to spec- ify a dimension on a component and the allowable variability on this value that will give acceptable performance.Component TolerancesControl of dimensions is necessary in order to ensure assembly and interchangeability of com- ponents. Tolerances are specified on critical di- mensions that affect clearances and interference fits. One method of specifying tolerances are to state the nominal dimension followed by the per- missible variation, 50 a dimension could be stated as 40.000 0. 003mm. This means that the dimen- sion should be machined so that it is between 39-0 000997 and 40. 003mm. Where the variation can vary either side of the nominal dimension, the tolerance is called a bilateral tolerance. For a unilateral tol- erance, one tolerance is zero, e.g. 40. 000 +0.006 .Most organizations have general tolerances that apply to dimensions when an explicit dimension is not specified on a drawing. For machined dimen- sions a general tolerance may be 0. 5mm. So a dimension specified as 15.0mm may range between14.5mm and 15.5mm. Other general tolerances can be applied to features such as angles, drilled and punched holes, castings, forgings, weld beads and fillets.When specifying a tolerance for a component, reference can be made to previous drawings or general engineering practice. Tolerances are typi- cally specified in bands as defined in British or ISO standards. For a given tolerance, e. g. H7 /s6, a set of numerical values is available from a correspond- ing chart for the size of component under consid- eration. The section following gives specific exam- ples of this for a shaft or cylindrical spigot fitting into a hole.Standard Fits for Holes and ShaftsA standard engineering task is to determine tolerances for a cylindrical component, e. g. a shaft, fitting or rotating inside a corresponding cylindrical component or hole. The tightness of fit will depend on the application. For example, a gear located on to a shaft would require a tight interference fit, where the diameter of the shaft is actually slightly greater than the inside diameter of the gear hub in order to be able to transmit the desired torque, alternatively, the diameter of a journal bearing must be greater than the diameter of the shaft to allow rotation. Given that it is not economically possible to manu- facture components to exact dimensions, some variability in sizes of both the shaft and hole dimen- sion must be specified. However, the range of vari- ability should not be so large that the operation of the assembly is impaired. Rather than having an infinite variety of tolerance dimensions that could be speeded, national and international standards havebeen produced defining bands of tolerances, ex- amples of which are listed e.g. Hll/cll. To turn this information into actual dimensions corresponding tables exist, defining the tolerance levels for the size of dimension under consideration. In order to use this information the following list and give definitions used in conventional tolerancing. Usually the de- based systern is used, as this results in a reduction in the variety of drill, reamer, brooch and gauge tooling required within a company.Size: a number expressing in a particular unit the numerical value of a dimension.Actual size: the size of a part as obtained by measurement.Limits of size: the maximum and minimum sizes permitted for a feature.Maximum limit of size: the greater of the two limits of size.Minimum limit of size: the smaller of the two limits of size.Basic size: the size by reference to which the limits of size are fixed.Deviation: the algebraic difference between a size and the corresponding basic size.Actual deviation: the algebraic difference be- tween the actual size and the corresponding basic size.Upper deviation: the algebraic difference the maximum limit of size and the corresponding basic size.Lower duration: the algebraic difference be- tween the minimum limit of size and the corre- sponding basic size.Tolerance: the difference between the maxi- mum limit of size and the minimum limit of size.Shaft: the term used by convention to designate all external features of a part. Hole: the term used by convention to designate all internal features of a part.Conceptual design is the generation of solu- tions to meet the specified requirements. Concep- tual design can represent the sum of all subsystems and component parts which go on to make up the whole system. Ion and Smith describe conceptualdesign as an iterative process comprising a series of generative and evaluative stages which converge to the preferred solution. At each stage of iteration the concepts are defined in greater detail, allowing more thorough evaluation.It is important to generate as many concepts and ideas as poss
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