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XXX附录一整个组件的评价原则1：整体元件数量应尽量减少。装配效率的第一项措施是基于数量的组件或子组件中使用的产品。零件计数评价估计的最小数目的组件可能与比较设计评价评估这个最小。这一方针的措施估计是这样：A.发现元件的理论上的最小数目。检查是否真的应该分开的元件设计的每对相邻的部件。包括诸如螺栓，螺母紧固，并在这交流计数夹。假设没有生产或材料的局限性：（1）组件必须分开，如果设计的机械操作。例如，组件必须滑动或相对于彼此旋转必须单独的组件。然而，如果相对运动很小，则弹性可以建成的标志的需要。这是很容易完成的塑料部件采用弹性铰链，薄片耐疲劳的材料，作为一一铰的自由度。（2）组件必须是否必须由不同的材料，例如是分开的，当一个组件的电或热绝缘体和另一个，相邻的组件是一个导体。（3）组件必须分开如果组装或拆卸是不可能的。（注：最后一句话是“不可能的，”而不是“不方便”。）因此，每对相邻部件的检查发现，如果他们绝对需要单独的组件。如果他们不这样做，那么理论上他们可以组合成一个组件。回顾整个产品的这种方式，我们开发的组件的理论上的最小数目。该座椅框架具有至少一个组件。在重新设计的框架组件的实际数目（图11.12）四。B.寻找潜在的改进。对任何产品，我们可以计算出其潜在的改善：实际的数量。潜在的改善=（组件理论上的最小值-组件的数量）/组件的实际数目C.率工作表上的产品（图11.10）。如果潜在的改善小于10%，目前的设计是优秀的。如果改进潜力为11至20%，目前的设计是很好的。如果改进潜力为20至40%，目前的设计是好的。如果改进潜力为40至60%，目前的设计是公平的。如果改良潜力大于60%，目前的设计很差。图11.12中的座椅框架的改进潜力（41）/ 4 = 75%。在这种情况下，设计很差，但量太低，使用一种方法来进一步减少组件数量。作为一个产品的重新设计，跟踪实际的改进：实际的改进组件的数量=(在最初的设计组件的数量-重新设计在初始设计的组件数量)/在最初设计组件的数量在30的范围内的组件的数量，典型的改进60%是通过重新设计产品以减少元件数量实现。把这一方针的角度来看，它与早期阶段的设计过程比较。在本文的设计理念，产品的功能分解为细尽可能的概念发展的基础（7章）。然后我们用形态发展的每个功能的想法。这会导致不良的设计，可以尽量减少组件的数量。考虑普通指甲钳的设计（图11.13）。如果假定所有的功能都是独立的，每个函数生成conceptsare，那么结果，如图11.14中看到的，是一场灾难。注意每个函数映射到一个或多个接口。在另一个极端，DFA哲学会导致图11.15所示的产品。图11.13普通指甲钳。指甲钳与图11.14 for each函数的一个接口。开源开发模式：设计（KarlUlrichT。斯隆商学院，麻省理工学院在这里，在组装的产品的评价，该指南鼓励块-尽可能多的功能为每个组件。这种设计理念，不过，也有问题。模具成本（模具或模具）的形状所造成的最小的元件数量可高，这里没有考虑成本。此外，对复杂零件的公差可能更为关键，和制造业的变化可能会影响许多功能，现在加上。原则2：使单独的紧固件的最小使用。减少元件数量的方法之一是尽量减少单独的紧固件的使用。这是明智的每一件会增加成本和降低强度，有很多原因。图11.15指甲钳一个工件。首先，每个紧固件使用一个组件来处理，并可能有多于一个的与之配套的螺母，螺栓的情况下平垫圈，止动垫圈。的组件处理的每个实例需要时间，典型地10秒每件。第二，紧固件的总成本是成本的COM组件本身以及采购，成本核算，盘点，及质量控制。第三，紧固件应力集中；他们是设计中潜在的结构失效点。出于所有这些原因，最好是消除尽可能多的紧固件的设计。这是更方便的进行大批量的产品，其成分可以扣合在一起，比体积小的产品或产品部件利用许多股票。另外一点，应考虑在评估一个设计是如何使用紧固件已标准化。一个很好的例子，部分标准化的事实是，几乎所有的大众甲壳虫，在上世纪70年代流行的汽车，可以是固定的一套螺丝刀和一个13毫米扳手。最后，如果组件固定在一起，必须拆开维修保养，使用捕获的紧固件（紧固件保持松散连接的一个组成部分，即使解开）。许多品种的捕获的紧固件是可用的，所有的设计使其不会错位的装配或维修时。还有的单独的紧固件数量设计质量没有一般的规则。由于工作表是两设计相对比较，一个绝对的评价是不必要的。显然，优秀的设计会有几个单独的紧固件，和那些确实有将标准和可能的捕获。可怜的设计，另一方面，需要许多不同的紧固件装配。如果超过1/3的产品组件的紧固件，组合逻辑应该被质疑。 悬臂卡 （a）矮小的卡扣耳：很短的弯曲长度可以导致破损。 (b) 扭扣 运动部件卡 (c)图11.16按扣设计图11.16和图11.17显示减少Fas数量听众的一些想法。在注射成型的塑料设计，摆脱紧固件最好的方法是通过使用适合的卡。一个典型的悬臂卡在图11.16a显示时的重要考虑因素。设计的照片在插入过程中载荷和坐着时。在插入过程中，卡的行为像一个悬臂梁弯曲的插入位移量。主应力在法是在梁的根部因此弯曲。因此，它是低在这一点上的应力集中和确保卡可以弯曲没有足够接近的材料的弹性极限的重要（图11.16b）。坐着的时候，卡的主要载荷是力F0，力部件保持在一起。它可以导致破碎的抓脸，剪的抓捕失败，与卡体的拉伸破坏。（这里。想力流） (a) (b) 图11.17单扣件的例子。 此外，设计必须考虑到解开扣子。如果设备是永远分开来维修，然后再考虑功能，允许一个工具或手指弯曲折断而F0 = 0。附加单元配置图11.16c所示。注意：每一个特点可以插入另一个以坐在负载。另一种方法来减少数量的紧固件是只使用一个紧固件和销，钩，或帮助联系其他部件干涉。图11.17中的例子显示出这个主意的塑料和金属板材中的应用。原则3：设计一个用于定位其他组件库组件产品。该指南鼓励使用一个单一的基础上所有其他部件组装。图11.18中的基地提供一致的组件的位置，基础安装，运输，定位，和强度。理想的设计是建立像一层蛋糕，每个组件或组件堆叠在另一个。没有这个基础建设上，组件可以包括许多组件，每个都有自己的固定和运输需求和最后的组装需要大量的重新定位和夹具。一个单一的基础部分使用了装配线的长度缩短了2倍 。 图11.18仪表总成与大多数的这些措施，没有绝对的标准，确定挖掘的一个优秀的产品和一个贫穷的人。记住，工作表上的评级是相对的。准则4：不需要重新定位在装配基地。如果自动装配设备，如机器人或特别设计的组件放置机中使用的组件，这座被精确定位是很重要的。较大的产品，可能是费时和昂贵的重新定位。一个优秀的设计不需要重新定位的基础。一个产品需要超过两重新定位产品被认为是穷人。原则5：使装配序列的有效。如果有N个组成部分进行组装，有潜在的N！（n的阶乘）不同的可能的序列组装。在现实中，一些组件必须组装之前别人；因此可能的装配序列数通常远小于N！。一个有效的装配序列是一个提供装配用最少的步骤。避免元器件损坏的风险。避免尴尬，不稳定，或在装配过程中的产品和装配人员和机械条件不稳定的位置。避免产生许多断开组件是后来加入的。因为即使是一个小小的设计变化可以在装配序列改变可用的选择，这是考虑到序列的效率在设计的重要。这里描述的技术将通过一个简单的例子证明，一个圆珠笔组装（图11.19）。步骤1：列出所有的组件和过程在装配过程中。开始一个布局或产品的装配图和账单的材料。对于笔组件的所有组件都在图11.19中列出的。在某些产品中，被组装的部件包括部件和生产过程为例，该组件被称为“墨”在圆珠笔包括过程实际上把墨水管。此外，一些产品在装配过程中，需要测试。这些测试也应该包括作为组件。最后，紧固件应集中与他们举行组件。步骤2：列表组件在该图中，节点代表部件和链接代表的联系。连接图可以有回路。例如，笔可以有按钮，支撑管的端部，创建接口6，管和按钮之间的联系（如图11.20中虚线和假定不在本例的其余部分存在）。 帽 头 体 管 按钮 图11.19 圆珠笔组装按钮6 2 1 3 4 头 管按钮 图11.20 圆珠笔的组装图步骤3：选择一个基准组件。基座组件应在连接图的一端或是一个大的组成部分。它应该是组件，需要最少的组件，允许组件从最少的方向。为圆珠笔，选项有盖，按钮，或身体。盖需要在管头组件，因此是一个贫穷的候选人。人体需要的组件从两个方向。按钮可能是最好的基地的一部分，但是很难把握。无论是身体和按钮需要进一步研究。步骤4：递归添加下一个组件。使用连接图作为指导基地添加组件。它是意识到价格的教材重要；例如，管必须在头在墨水安装。这是列出所有的优先级在开始这一步有用。为圆珠笔，其优先级连接3必须先连接4。连接1必须先连接5。步骤5：确定组件。组件可以制成，有一个安全的连接部件，可以重新定位而不崩溃，并与其他部件的简单连接。子组件只应该在简化过程中使用。为笔，头，管，和油墨形成一个组件，简化装配。有许多潜在的装配序列的圆珠笔。一个是开发使用所描述的程序是 2，4， 3，1，5 或按钮，身体，头，管，墨水，帽第一序列列表连接，第二组件，在组件的顺序。括号内表示组件。这里给出的方法在评价装配顺序和确定的序列的设计变化的影响是非常有用的。它还装配序列的有效措施。如果所有的连接都是按逻辑顺序，无组件生成，并没有尴尬的连接，然后是额定效率高；如果连接序列无法完成，组件，或尴尬的连接是必要的，那么效率低和生成一个连接图之间的联系。为圆珠笔的连接图如图11.20所示。 附录二11.3.1 Evaluation of the Overall AssemblyGuideline 1: Overall Component Count Should Be Minimized. The first measure of assembly efficiency is based on the number of components or sub- assemblies used in the product. The part count is evaluated by estimating the minimum number of components possible and comparing the design being eval- uated to this minimum. The measure for this guideline is estimated in this way:a. Find the Theoretical Minimum Number of Components. Examine each pair of adjacent components in the design to see if they really should be separate components. Include fastening components such as bolts, nuts, and clips in this ac- counting. Assuming no production or material limitations: (1) Components must be separate if the design is to operate mechanically. For example, components that must slide or rotate relatively to each other must be separate components. However, if the relative motion is small, then elasticity can be built into the de- sign to meet the need. This is readily accomplished in plastic components by using elastic hinges, thin sections of fatigue-resistant material that act as a one degree-of-freedom joint. (2) Components must be separate if they must be made of different materials, for example, when one component is an electric or thermal insulator and another, adjacent component is a conductor. (3) Components must be separate if assembly or disassembly is impossible. (Note that the last word is “impossible,” not “inconvenient.”)Thus, each pair of adjacent components is examined to find if they absolutely need to be separate components. If they do not, then theoretically they can be combined into one component. After reviewing the entire product this way, we develop the theoretical minimum number of components. The seat frame has a minimum of one component. The actual number of components in the redesigned frame (Fig. 11.12) is four.b. Find the Improvement Potential. To rate any product, we can calculate its improvement potential:2 Improvement potential =Actual number of componentsc. Rate the Product on the Worksheet (Fig. 11.10). If the improvement potential is less than 10%, the current design isoutstanding. If the improvement potential is 11 to 20%, the current design is very good. If the improvement potential is 20 to 40%, the current design is good. If the improvement potential is 40 to 60%, the current design is fair. If the improvement potential is greater than 60%, the current design is poor.The improvement potential of the seat frame in Figure 11.12 is (4 1) / 4 = 75%. In this case, design is poor, but the volume is too low to use a method to further reduce the number of components.As a product is redesigned, keep track of the actual improvement:Actual improvement.Number of components.in initial design.Number of components. in redesign=Number of components in initial designTypical improvement in the number of components in the range of 30 to 60% is realized by redesigning the product in order to reduce the component count.To put this guideline in perspective, compare it with earlier phases of the design process. In the design philosophy of this text, the functionality of the product is broken down as finely as possible as a basis for the development of concepts (Chap. 7). We then used a morphology for developing ideas for each function. This can lead to poor designs, as can the effort to minimize the number of components. Consider the design of the common nail clipper (Fig. 11.13). If the assumption is made that all the functions are independent and that conceptsFigure 11.13 Common nail clipper.Figure 11.14 Nail clipper with one interface for each function. (Source: Design developed by Karl T. Ulrich, Sloan School of Management, Massachusetts Institute of Technology.)are generated for each function, then the result, as seen in Fig. 11.14, is a disaster. Note that each function is mapped to one or more interface. At the other extreme, the DFA philosophy leads to the product shown in Fig. 11.15.Here, in evaluating the product for assembly, this guideline encourages lump- ing as many functions as possible into each component. This design philosophy, however, also has its problems. The cost of tooling (molds or dies) for the shapes that result from a minimized component count can be highand that cost is not taken into account here. Additionally, tolerances on complex components may be more critical, and manufacturing variations might affect many functions that are now coupled.Guideline 2: Make Minimum Use of Separate Fasteners. One way to reduce the component count is to minimize the use of separate fasteners. This is advisableEvery fastener adds costs and reduces strength.Figure 11.15 A one-piece nail clipper.for many reasons. First, each fastener used is one more component to handle, and there may be many more than one in the case of a bolt with its accompanying nut, flat washer, and lock washer. Each instance of component handling takes time, typ- ically 10 sec per fastener. Second, the total cost for fasteners is the cost of the com- ponents themselves as well as the cost of purchasing, inventorying, accounting for, and quality-controlling them. Third, fasteners are stress concentrators; they are points of potential structural failure in the design. For all these reasons, it is best to eliminate as many fasteners as possible from the design. This is more easily done on high-volume products, for which components can be designed to snap together, than on low-volume products or products utilizing many stock components.An additional point that should be considered in evaluating a design is how well the use of fasteners has been standardized. A good example of part standard- ization is the fact that almost everything on the Volkswagen Beetle, a car popular in the 1970s, can be fixed with a set of screwdrivers and a 13-mm wrench.Finally, if the components fastened together must be taken apart for mainte- nance, use captured fasteners (fasteners that remain loosely attached to a compo- nent even when unfastened). Many varieties of captured fasteners are available, all designed so that they will not be misplaced during assembly or maintenance.There are no general rules for the quality of a design in terms of the number of separate fasteners. Since the worksheet is just a relative comparison between two designs, an absolute evaluation is not necessary. Obviously, an outstanding design will have few separate fasteners, and those it does have will be standardized and possibly captured. Poor designs, on the other hand, require many different fasteners to assemble. If more than one-third of the components in a product are fasteners, the assembly logic should be questioned.Figures 11.16 and 11.17 show some ideas for reducing the number of fas- teners. In designing with injection-molded plastics, the best way to get rid of fasteners is through the use of snap fits. A typical cantilever snap is shown in Fig. 11.16a. Important considerations when designing snaps are the loads during insertion and when seated. During insertion, the snap acts like a cantilever beam flexed by the amount of the insertion displacement. The major stress during in- sertion is therefore bending at the root of the beam. Thus, it is important to have CatchBendingF0TensionShearInsertion displacementCantilever snap (a)Undersized snap-fit lugs: Too short a bending length can cause breakage.Properly sized snap-fit lugs: Longer lugs reduce stress.(b)PlateTwistTabC-clipChamfered surfaceBarbsSnapsTwist snapMoving parts snap(c)Figure 11.16 Snap-fastener design.low stress concentrations at that point and to be sure that the snap can flex enough without approaching the elastic limit of the material (Fig. 11.16b). When seated, the snaps main load is the force F0, the force holding the components together. It can cause crushing on the face of the catch, shear failure of the catch, and tensile failure of the snap body. (Think of the force flow here.)Mold-in pinsHook under(a)(b)Figure 11.17 Single fastener examples.Additionally, design consideration must be given to unsnapping. If the device is ever to come apart for maintenance, then consider features that allow a tool or a finger to flex the snap while F0 = 0. Additional snap configurations are shown in Fig. 11.16c. Note that each has one feature that flexes during insertion and another that takes the seated load.Another way to reduce the number of fasteners is to use only one fastener and either pins, hooks, or other interference to help connect the components. The examples in Fig. 11.17 show both plastic and sheet-metal applications of this idea.Guideline 3: Design the Product with a Base Component for Locating Other Components. This guideline encourages the use of a single base on which all the other components are assembled. The base in Fig. 11.18 provides a foundation for consistent component location, fixturing, transport, orientation, and strength. The ideal design would be built like a layer cake, with each component or subassembly stacking on top of another one. Without this base to build on, assembly may consist of work on many subassemblies, each with its own fixturing and transport needs and final assembly requiring extensive repositioning and fixturing. The use of a single base component has shortened the length of some assembly lines by a factor of 2. As with most of these measures, there are no absolute standards for deter- mining an outstanding product and a poor one. Keep in mind that the rating on the worksheet is relative.Guideline 4: Do Not Require the Base to Be Repositioned During Assembly. If automatic assembly equipment such as robots or specially designed component placement machines are used during assembly, it is important that the base be positioned precisely. On larger products, repositioning may be time-consuming and costly. An outstanding design would require no repositioning of the base. A product requiring more than two repositionings is considered poor.Guideline 5: Make the Assembly Sequence Efficient. If there are N compo- nents to be assembled, there are potentially N! (N factorial) different possible sequences to assemble them. In reality, some components must be assembled prior to others; thus the number of possible assembly sequences is usually much less than N!. An efficient assembly sequence is one that Affords assembly with the fewest steps. Avoids risk of damaging components. Avoids awkward, unstable, or conditionally unstable positions for the product and the assembly personnel and machinery during assembly. Avoids creating many disconnected subassemblies to be joined later. Since even a minor design change can alter the available choices in assembly sequence, it is important to consider the efficiency of the sequence during design. The technique described here will be demonstrated through a simple example, the assembly of a ballpoint pen (Fig. 11.19).Step 1: List All the Components and Processes Involved in the Assembly Process. Begin with a layout or assembly drawing of the product and a bill of materials. All components for the pen assembly are listed in Fig. 11.19. In some products, the components to be assembled include subassemblies and processesfor example, the component called “ink” in the ballpoint pen includes the process of actually putting the ink in the tube. Additionally, some products require testing during the assembly process. These tests should also be included as components. Finally, fasteners should be lumped with the component they hold in place.Step 2: List the Connections Between Components and Generate a Connections Diagram. The connection diagram for the ballpoint pen is shown in Fig. 11.20.BodyTubeButtonCapHeadInkCapInkHeadBodyTubeButtonFigure 11.19 Ballpoint pen assembly.Button62Body134HeadTubeInk5CapFigure 11.20 Connection diagram for a ballpoint pen.In this diagram, the nodes represent the components and the links represent the connections. Connection diagrams can have loops. For example, the pen may have the button supporting the end of the tube, creating interface 6, a link between the tube and the button (shown as a dashed line in Fig. 11.20 and assumed not to exist throughout the remainder of this example).Step 3: Select a Base Component. The base component should be at one end of the connection diagram or be a large component. It should be the component that requires the least subassembly and allows assembly from the fewest directions. For the ballpoint pen, the options are the cap, the button, or
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