[Psychology] Mechanical Assemblies Phần 8 potx

386 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" (a) For parts that can be grasped and manipulated with one bare hand Symmetry (S = a + p) S < 360° 360° < S < 540° 540° < S < 720° S = 720° Code 0 1 2 3 No handling difficulties Thickness > 2 mm Size > 15 mm 0 1.13 1.5 1.8 1.95 6 mm < size < 15 mm 1 1.43 1.8 2.1 2.25 < 2 mm Size > 6 mm 2 1.69 2.06 2.36 2.51 Part nests or tangles Thickness > 2 mm Size > 1 5 mm 3 1.84 2.25 2.57 2.73 6 mm < size < 15 mm 4 2.17 2.57 2.9 3.06 <2mm Size > 6 mm 5 2.45 3 3.18 3.34 (b) For parts that can be lifted with one hand but require two hands to manage FIGURE 15-1. Selected Manual Handling Times in Seconds. Parts (a) and (b) are mutually exclusive. Both apply to small parts within easy reach, that are no smaller than 6 mm, do not stick together, and are not fragile or sharp. Symmetry is measured by summing angles a and /}; a is the number of degrees required to rotate the part about an axis normal to the insertion axis in order to return it to an identical configuration, and f> is the same with respect to an axis about the insertion axis. The code to be assigned is the combination of the row and column headings in italics. For example, a part coded "12" has handling time 2.06 sec. (Courtesy of Boothroyd Dewhurst, Inc. Copyright © 1999.) table appears in Figure 15-1. Each code is accompanied by an estimated handling time in seconds, ranging from 1.13 seconds to 5.6 seconds. These times were developed over a period of years by means of experiments and are applicable to small parts. 4 Individual companies have also developed their own time estimates. Boothroyd also pro- vides guidelines for scaling the times for larger parts. The assembly conditions that affect assembly time are listed in Table 15-5. A portion of the manual insertion time table appears in Figure 15-2. There are 24 code numbers with insertion times that range from 1.5 seconds to 10.7 seconds. As with the numbers in Figure 15-1, these 4 MIT students who have used these times for handling and assembly report that they are accurate within about 10%. However, it is important to recall the information cited above that it takes 1,000 to 3,000 trials to become really proficient at an assembly task, whereas the MIT student data are based on ten or twenty practice runs at most. TABLE 15-4. Part Features that Affect Manual Handling Nesting, tangling, fragility Need to use two hands or more than one person Need to use tools Size, thickness, and weight Flexibility, slipperiness, stickiness Need for mechanical or optical magnification assistance Degree of symmetry of the part Source: [Boothroyd, Dewhurst, and Knight]. times apply to small parts and must be scaled up for larger ones. For example, a person assembling cell phones might install several complex-shaped metal shields over a circuit board to block radio-frequency interference during a cycle time of 15 seconds or less. By contrast, on an automobile final assembly line, station times are typically 45 to 60 seconds, during which one large item like a seat, roof, hood, or battery might be obtained and installed. Sometimes, two Code 4 a < 180° Size > 15 mm 0 4.1 6 < Size < 15 mm 1 4.5 a = 360° Size > 6 mm 2 5.6 15.D. TRADITIONAL DFM/DFA (DFx IN THE SMALL) 387 people work together to handle the larger items. Often there is no time to install and tighten fasteners, so another person does this at the next station. In support of the time estimates in these tables, [Boothroyd, Dewhurst, and Knight] presents several detailed explanations for the sources of the estimates, including empirical formulas and graphs. These include: • The influence of symmetry or asymmetry on the time a person needs to orient something correctly starting TABLE 15-5. Conditions that Affect Manual Insertion Time Whether the part is secured immediately or after other operations Accessibility of the insertion region Ability to see the insertion region Ease of aligning and positioning the part A tool is needed Whether the part stays put after being placed or whether the assembler must hold it until other parts or fasteners are installed Simplicity of the insertion operation Source: [Boothroyd, Dewhurst, and Knight]. (a) Part inserted but not secured immediately, or secured by snap fit (b) Part inserted and secured immediately by power screwdriver. Note: add 2.9 seconds to get power tool. (c) Separate operation times for solid parts already in place FIGURE 15-2. Selected Manual Insertion Times (Courtesy of Boothroyd Dewhurst, Inc. Copyright © 1999.) Parts (a) and (b) are mutually exclusive, while Part (c) contains times that are added to times in the other two tables when required. Times in Part (a) apply to small parts where there is no resistance to insertion. No access or vision difficulties Obstructed access or restricted vision Obstructed access and restricted vision Code 0 1 2 Secured by separate operation or part No holding down required Easy to align 0 1.5 3.7 5.9 Not easy to align / 3.0 5.2 7.4 Holding down required Easy to align 2 2.6 4.8 7.0 Not easy to align 3 5.2 7.4 9.6 Secured right away by snap fit Easy to align 4 1.8 4.0 7.7 Not easy to align 5 3.3 5.5 7.7 No access or vision difficulties Restricted vision only Obstructed access only Code 3 4 5 Easy to align 0 3.6 6.3 9.0 Not easy to align / 5.3 8.0 10.7 388 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" from a random orientation (time rises approximately linearly regardless of detailed part cross-sectional shape from a base of 1.5 seconds to a peak of 2.7 seconds as the required number of degrees of rotation rises) • The influence of part size and thickness (size greater than about 15 mm does not impose any handling time penalty, while thickness greater than 2 mm does not cause any handling time penalty; these conclusions obviously do not apply to parts the size of car seats) • The influence of part weight (for small parts, the time rises linearly with weight, and a part weigh- ing 20 pounds imposes a penalty of 0.5 seconds plus any additional time associated with walking) • The influence of clearance ratio (see Chapter 10) on insertion time (time penalty is inversely proportional to the log of the clearance ratio and ranges from 0.2 to 0.5 seconds depending on whether there is a chamfer or not) In addition to the time estimates provided in [Boothroyd, Dewhurst, and Knight], one can use standard time handbooks such as [Zandin]. These handbooks use standard work actions like "reach," "grasp," and so on, without taking the design of the part or the assembly operation into account. However, they contain data that applies to larger parts, walking time, and time to position equipment to aid assembly. These time estimates do not take account of variations due to fatigue or time of day. In many factories, assembly line workers can adjust the speed of the line during the day as long as they make the total number of assemblies required by the end of the day. This approach is satisfac- tory for a line that feeds a warehouse but not for one that feeds another line unless additional measures are taken to ensure that the downstream processes receive assemblies when they need them. Several general guidelines are also offered: • Avoid connections, or make them short and direct. Items like pipes that join different parts or assemblies could be made shorter, straighter, or even eliminated if the parts were closer to each other or otherwise better arranged. A guideline like this can run into conflicts if the parts in question must be replaced for maintenance or are subject to design revision or customer options. Conflict can also arise if the parts must be kept separate in order to allow cooling air to pass between them or to reduce the effect of radio- frequency interference, for example. • Provide plenty of space to get at the parts and their fasteners during assembly. This guideline often conflicts with the need to make products small even as they become more complex. Car engine compart- ments, cell phones, and cameras are typical examples. In such cases, assemblers need tools, magni- fiers, dexterity, and extra time. • Avoid adjustments. Adjustments take time, hence the guideline. Sometimes, as discussed in Chapter 6, it is not economical to make parts of sufficient accuracy to avoid adjustments. In other cases, the customer makes the adjustments in the normal course of using the product. The user of a sewing machine adjusts thread tension to accommodate different thread materials with different coefficients of friction. • Use kinematic design principles. As noted in Chap- ter 4, overconstraint makes the assembly strategy operator-dependent and thus makes both time and quality operator-dependent. [Redford and Chal] notes that the classification method, while not explaining in detail what to do if a part or operation takes longer than desired, nevertheless places it in the table next to other classification possibilities that are better or worse. Thus the engineer can see what kinds of improvements might be made in a given case: Would the part be better if it was thicker, had a chamfer, didn't tangle, was a little more symmetric, and so on? How much time will that save? And so on. [Boothroyd, Dewhurst, and Knight] notes that design changes for ease of assembly, like those that reduce part count (discussed below) cannot be made without know- ing their impact on the cost of making the part. Thus [Boothroyd, Dewhurst, and Knight] also contains chapters on design for sheet metal, injection molding, machin- ing, and other manufacturing processes, as well as robot assembly. The information in the tables for handling and insertion times is encapsulated in software available from Boothroyd Dewhurst, Inc., Kingston, Rhode Island. 15.D.2. The Hitachi Assembleability Evaluation Method The Hitachi Assembleability Evaluation Method (AEM) belongs to a class of "points off" methods ([Miyakawa, 15.D. TRADITIONAL DFM/DFA (DFx IN THE SMALL) 389 Ohashi, and Iwata]). In these methods, the "perfect" part or assembly operation gets the maximum score, usually one hundred, and each element of difficulty is assigned a penalty. There are twenty different operational circum- stances, each with its own penalty. Each circumstance is accompanied by a simple icon for identification, permit- ting the method to be applied easily with little training. The AEM is part of a larger suite of tools including the Pro- ducibility Evaluation Method (PEM, [Miyakawa, Ohashi, Inoshita, and Shigemura]), the Assembly Reliability Eval- uation Method (AREM, described below), and the Recy- clability Evaluation Method (REM). The method is applied manually or with the aid of com- mercially available software. When a part or operation is fully evaluated, all the penalties are added up and sub- tracted from one hundred. If the score is less than some cut- off value, say eighty, the operation or part is to be subjected to analysis to improve its score. The penalties and time estimates have been refined based on the experience of the entire Hitachi corporation, which makes a wide range of consumer and industrial goods such as camcorders, televi- sion sets, microwave ovens, automobile components, and nuclear power stations. All the evaluations are based on comparing the current design to a base design that is either "ideal" or represents the previous design of the same or a similar product. Because of the depth of the underlying dataset and the ratio technique of evaluation, the method is especially useful for designing the next in a series of similar products over a period of years. Repeated use of the method on the same product line relentlessly drives out low scoring operations. The evaluation takes place in two stages. First, each operation is evaluated, yielding an evaluation score £, for each operation. If several operations are required on one part, an average score E is calculated. The score for the entire product is either the sum of all the individual part scores or the average of the part scores. In either case, it is possible that an assembly with fewer parts will have a higher score simply because fewer penalties are available to reduce it. In this case, the method clearly states, "reduction in part count is preferable to better score." However, the method does not include a systematic way of identify- ing which parts might be eliminated. Examples of the penalties and use of the method appear in Figure 15-3 and Figure 15-4. 15.D.3. The Hitachi Assembly Reliability Method (AREM) The Hitachi Assembly Reliability Evaluation Method ([Suzuki, Ohashi, Asano, and Miyakawa]) extends the AEM beyond cost and time into the domain of assembly success and product reliability. The impetus for this method arises from several trends: the rise in product liability suits, the introduction of new product and process technologies resulting in production uncertainties and long ramp-up times, shorter product development time resulting in design mistakes, and the degree to which out- sourcing makes a manufacturer dependent for quality on the work of other companies. The method has proven useful for products that must achieve very high reliability, products that change drastically from one model or version to the next, complex products, ones that are assembled at multiple sites around the world, and products containing many parts and subassemblies from suppliers. The basic logic of the method is shown in Figure 15-5. The method is similar in style to the AEM in the sense that each operation is evaluated and compared to a standard, resulting in a penalty. In addition, the method contains a scale factor called the basic shop fault rate, based on data from a given factory, that permits the failure rate at that factory to be estimated based on the product's design. FIGURE 15-3. Examples of AEM Symbols and Penalty Scores. ([Miyakawa, Ohashi, and Iwata]. Hitachi, Ltd. Used by permission.) 390 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" FIGURE 15-4. Assembleability Eval- uation and Improvement Examples. ([Miyakawa, Ohashi, and Iwata]. Hitachi, Ltd. Used by permission.) FIGURE 15-5. Hitachi Assembly Relia- bility Evaluation Method. (Hitachi, Ltd. Used by permission.) On this basis, one can decide either to improve the product or to improve the factory in order to increase the score. The basic assumption behind the method is that if the assembly reliability is low, either the product is at fault (resulting in a product structure penalty) or there is some variation in the assembly process (resulting in an operational variance penalty). Product structure factors that influence assembly faults include dimensional variation, flexibility or fragility of parts, lack of sufficient access to the assembly point, too much force needed to ensure complete insertion, and so on. Operational variance factors include not positioning a part accurately enough, applying too much force or not enough force, not driving screws all the way in, cutting a wire, and so on. These factors are to some extent represented in the Boothroyd handling time and insertion time tables but are associated with time rather than failure to perform the assembly correctly. In addition, other kinds of mistakes are 15.D. TRADITIONAL DFM/DFA (DFx IN THE SMALL) 391 FIGURE 15-6. The Westinghouse DFA Calculator. The calculator is a rotary slide rule. It consists of a large disk with a slightly smaller disk and a transparent cursor on each side. The smaller disks can be rotated independently of the large disk and the cursors. Difficulty starts at zero and accumulates as the topics marked A, B, C, and so on, are addressed in turn. (Reprinted from [Sturges] with permission from Elsevier Science.) possible, as discussed in Chapter 16. The most frequent of these are using the wrong part and using a damaged part. No DFA method deals directly with these issues, although general guidelines include warnings about help- ing the operator to distinguish between similar parts. 15.D.4. The Westinghouse DFA Calculator Sturges developed a rotary calculator at Westinghouse for estimating handling and insertion difficulty (Figure 15-6). On one side the user calculates a handling difficulty index that is interpreted as seconds required. On the other side the same kind of calculation is done to estimate assembly time. Factors such as part shape, symmetry, size of features to be grasped or mated with, direction of insertion, clearance, and fastening method are assessed and added up by repositioning the disks and the cursor. 15.D.5. The Toyota Ergonomic Evaluation Method Most DFA methods are designed to evaluate assembly of small parts. In the auto industry, final assembly of the product involves relatively large and heavy parts. Here, ergonomics, the science of large-scale human work and motion, is applicable. Toyota has determined that the product of the weight of a part and the time it must be sup- ported by a worker is a good indicator of physical stress ([Niimi and Matsudaira]). In addition, the worker's pos- ture is important: standing, slightly bending, or bending deeply are each more stressful than the one before for the same weight and duration. Thus Toyota has developed a stress evaluator called TVAL (Toyota Verification of As- sembly Line) to prioritize assembly operations for improvement to reduce physical stress. The form of TVAL is where d\,di, and d^ are constants and t and W are the time and part weight, respectively. For example, installing a lightweight grommet onto a car door requires standing for 30 seconds and has a TVAL of about 25. By contrast, installing a rear combination lamp involves bending for- ward deeply for over 60 seconds and has a TVAL of 42. Before TVAL was applied to a section of assembly line, TVALs ranged from 30 to 48. After redesigning the worst stations, TVALs range from 22 to 35. 15.D.6. Sony DFA Methods Sony has a unique way of involving its engineers in the DFA process. The engineers must prepare exploded view drawings of all concepts. This forces consideration of assembly even before detailed design begins. This is illustrated in Figure 15-7. A DFA analysis is done on the concept, based on the exploded view, using Sony's own DFA software. The DFA score is included with other criteria in judging the merit of each concept. 5 5 This process was explained to the author during two visits to Sony in 1991. Next Page 392 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" FIGURE 15-7. Exploded View Drawing of Sony Walkman Chassis. Drawings like this are made by design engineers for every design concept. (Used by permission of Sony FA.) 15.E. DFx IN THE LARGE DFx in the large deals with issues that require consideration of the product as a whole, rather than individual parts in isolation, and likely will require consideration of the context in the factory, supply chain, distribution chain, and the rest of the product's life cycle. We take up such issues here. Our focus will be on (a) product structure and its relation to product simplification and (b) design for disassembly, repair, and recycling. 15.E.1. Product Structure Product structure involves many of the issues normally associated with product architecture, but the focus is on the structure more than on its influence on architecture issues. That is, one reads about products that are built in stacks or in arrays, or about consolidating parts, in the context of simplifying assembly rather than about "integrality" or "modularity." Nevertheless, one of the first books to deal with design for assembly, [Andreasen et al.], clearly recognizes the close connection, not only between DFA and product structure, but between these two topics and the larger issue of product development processes them- selves. Early consideration of assembleability inevitably turns to opportunities for restructuring the product, and this cannot be done except early in the design process. A design process that does not permit early consideration of assembly issues will therefore be a very different process from one that does, and the resulting product will be different as well. Furthermore, the differences will extend beyond the local issue of assembleability. 15.E.1 .a. Styles of Product Structure and their Influence on Ease of Assembly Several architectural styles have been identified in assemblies. These are the stack and the array. Examples of these are shown in Figure 15-8. In general, arrays present the fewest constraints on the assembly process. Printed circuit boards are the most ob- vious example. These are usually made by high speed machines that select parts from feeders each of which Previous Page 15.E. DFx IN THE LARGE 393 FIGURE 15-8. Examples of Stack and Array Product Structures. Both stacks and arrays come in two generic varieties: the parts are mostly the same or mostly different. ([Redford and Chal]. Copyright © Alan Redford. Used by permission.) presents one part (100K resistor, a particular integrated circuit, etc.) Because this product structure is so simple, the assembly sequence can be optimized to suit selection and insertion of the different kinds of parts. The factors involved include how far the insertion head has to travel to get each kind of part, how many of each kind are needed, how close together on the board they are, and so on. Opti- mization algorithms have been developed to find the best insertion sequence. The main justification for a stack architecture is that gravity aids the insertion process. If locating features are provided, a part will stay put once it is placed. In Fig- ure 15-8, two types of stacks are shown, namely, those with identical parts and those with different parts. In the former case, there are ample opportunities for alternate assembly sequences, such as preparing a separate subassembly comprising the stack of the identical disks. When the parts are quite different, as suggested by the illustration, their individual properties and mating features may create assembly sequence constraints. Most products are combinations of the generic structures illustrated above. [Kondoleon] conducted a survey of a dozen varied products, including consumer and industrial items, noting which assembly operations were needed and the directions along which they occurred. The results appear in Figure 15-9 and Figure 15-10. They show that there are two dominant insertion operations and two dominant directions. The implication is that these products appear to have a major axis of insertion and perhaps of operation as well. Perpendicular to this axis is the direction in which fasteners are installed. These observations probably reflect the Cartesian nature of the architectures of the machine tools used to make the parts. 15.E.1.b. Simplification Methods As noted earlier in this chapter, a major effort of DFA is product simplification. Simpler products have fewer parts, which means fewer assembly operations, workstations, factory space, and workers. In addition, each part represents design effort and overhead. Whether simpler/fewer always means less expensive is a separate issue discussed below. While most researchers and practitioners of DFA un- derstand the desirability of reducing the number of parts, only the Boothroyd method presents a systematic approach to doing this. The idea is to subject each part to three criteria that might justify its inclusion in the product, and eliminate any part that fails the criteria. 394 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" FIGURE 15-9. Census of Assembly Operations and Their Directions. The conclusions to be drawn from these data must be tempered by the fact that they were gathered in the middle 1970s. Product design methods and product materials have changed greatly since that time but no study comparable to this has been repeated since. ([Kondoleon]) FIGURE 15-10. Summary Census of Assembly Operations. ([Kondoleon]) 15.E. DFx IN THE LARGE 395 The three criteria are as follows ([Boothroyd, Dewhurst, and Knight]): 1. During operation of the product, does the part move relative to all other parts already assembled? Small motions that could be accommodated by flex hinges integral to the parts are not counted. 2. Must the part be of a different material or be isolated from all other parts already assembled? 3. Must the part be separate from all other parts already assembled because otherwise the assembly or disassembly of other separate parts would be impossible? Unless at least one of these questions can be answered "yes" for a part, that part theoretically can be combined with another part or eliminated entirely. This criterion is applied ruthlessly using main product functions as the focus. Thus, for example, all separate fasteners are automatically flagged as theoretically unnecessary. The effect of part consolidation on part cost is evaluated separately using DFx in the small. It is not expected that the theoretically unnecessary parts will really be eliminated because other criteria for performance or manufacturability might be affected. The purpose of the exercise is to focus atten- tion on necessity. The assembly efficiency metric is calculated as follows: (theoretical minimum Assembly _ number of parts) efficiency ~~ * 3 sec/part (15-2) estimated assembly time including all parts In this metric, an assembly time of 3 seconds per part is assumed, based on an ideal assembly time for a small part that presents no difficulties in handling, orienting, and in- serting. Thus the numerator represents an ideal minimum assembly time for a relatively simple manually assembled product that contains only those parts that survive the three questions listed above. The denominator represents the actual assembly time of the current or modified design. Typical products that are ripe for part count reduction often have assembly efficiencies on the order of 5% to 10% while efficiencies after reduction analysis or redesign are typically on the order of 25%. An assembly efficiency of or near 100% is unlikely to be achieved in practice. This finding implies that other valid reasons beyond those listed in the three questions above intervene to prevent parts from being eliminated. Considering the issues raised in Chapters 12 and 14, this should be no surprise. FIGURE 15-11. Plastic Injection Molded Part. This part goes into a domestic hot water heating system and has dozens of features on it. It is about 1.5" high. Its mold clearly took a long time to develop. It utilizes "hollow core" molding, which involves folding and moving mold core parts. Such a part will not be economical unless it is made in very large quantities. (Poschmann Industrie-Plastic GmbH & Co KG. Photo by the author.) Some of the products used as part-count-reduction examples in the DFA literature may appear ridiculous at first sight. These typically are rich in threaded fasteners, including washers and nuts. Each screw/washer/nut set counts as three parts that are automatically eliminated, driving down the assembly efficiency. As Boothroyd points out, some of these products look like model shop prototypes that were put directly into production without any attempt to design them for production efficiency. Anecdotally, fasteners seem to account for low assembly efficiency in many cases. 6 Eliminating them is thus an easy way to boost the score. The pros and cons of mod- ifying or eliminating fasteners are discussed later in this chapter. Today, many products exhibit evidence of careful at- tention to structure and part consolidation. As reflected in the examples in Section 15.F, even quite modest consumer products contain injection molded or stamped parts of high quality, exquisite tolerances, and complex features. See Figure 15-11 for a picture of one such part. This is the result of recent progress in development of stamping methods as well as of new polymer materials having high strength, low shrinkage, and high-dimensional stability over time. Examples include the casings of electric drills 6 Ken Swift, University of Hull, personal communication. [...]... 0.00 6.35 0.00 3.34 1.95 2.45 0.00 1.95 2. 98 2. 98 2. 98 1.95 0.00 4.10 2. 98 1.13 0.00 00 00 98 98 08 98 12 98 44 12 12 98 02 39 39 39 00 98 00 39 00 98 1.50 1.50 9.00 9.00 6.50 9.00 5.00 9.00 8. 50 5.00 5.00 9.00 2.50 8. 00 8. 00 8. 00 1.50 9.00 1.50 8. 00 1.50 9.00 5.26 2.63 9.00 9.00 10.60 9.00 22.70 9.00 11 .84 6.95 7.45 9.00 4.45 10. 98 10. 98 10. 98 3.45 9.00 5.60 10. 98 2.63 9.00 267.25 Min 4.4542 $0.021 $0.011... Cost 2 3 2 30 04 30 1.95 2. 18 1.95 30 38 30 2.00 6.50 2.00 7.90 26.04 7.90 $0.032 $0.105 $0.032 2 1 1 1 1 1 36 30 30 30 33 30 3.06 1.95 1.95 1.95 2.51 1.95 40 30 30 30 00 30 4.50 2.00 2.00 2.00 1.50 2.00 15.12 3.95 3.95 3.95 4.01 3.95 $0.061 $0.016 $0.016 $0.016 $0.016 $0.016 2 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 00 00 00 00 80 00 88 00 38 30 08 00 30 09 09 09 30 00 80 09 00 00 1.13 1.13 0.00... $0.014 720 180 720 720 540 720 180 720 720 360 720 720 360 360 1 1 l 1 1 1 1 1 1 1 1 1 30 1.95 30 30 1.95 95 :> .85 95 88 95 95 50 95 95 13 13 00 21 00 00 00 34 00 06 03 19 06 19 92 00 1.5 6.5 1.5 1.5 1.5 6 1.5 5.5 3.5 10 5.5 10 5 1.5 3.45 9.01 3.45 3.45 4.35 7.95 3. 38 7.45 5.45 11.50 7.45 11.95 30.65 2.63 Time 115.57 $0.014 $0.036 $0.014 $0.014 $0.0 18 $0.032 $0.014 $0.030 $0.022 $0.047 $0.030 $0.0 48 $0.124... handle (plastic) Self-tapping screws (2) Staples Part Alpha Beta 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 360 360 360 180 180 180 360 360 360 360 360 360 360 360 360 360 360 360 360 360 360 360 180 360 360 360 90 0 0 0 0 0 0 360 360 360 360 360 360 360 360 360 360 360 360 360 360 360 360 0 360 360 0 180 Note: Alpha and Beta are summed to determine the total reorientation restrictions... no 3, pp 3 18- 3 38, 1997 [Harper and Rosen] Harper, B., and Rosen, D W., "ComputerAided Design for Product De- & Remanufacture," Proceedings of the 19 98 ASME Design Engineering Technical Conferences, Atlanta, GA, paper no DETC 98/ CIE-5695, September 19 98 [Hayes-Roth, Waterman, and Lenat] Hayes-Roth, E, Waterman, D A., and Lenat, D B., editors, Building Expert Systems, London: Addison-Wesley, 1 983 [Hinckley]... beginning with 0 is of nominal size and weight, can be grasped without tools, and can be maneuvered with one hand Part symmetry is < 360° Easy to grasp with thickness > 2 mm and size > 15 mm 04 08 09 30 36 38 80 88 Easy to grasp with thickness < 2 mm and size < 6 mm Difficult to grasp with thickness < 2 mm and size > 6 mm Difficult to grasp with thickness < 2 mm and size < 6 mm Each part beginning with... 7.45 9.00 4.45 10. 98 10. 98 10. 98 3.45 9.00 5.60 10. 98 2.63 9.00 267.25 Min 4.4542 $0.021 $0.011 $0.036 $0.036 $0.043 $0.036 $0.092 $0.036 $0.0 48 $0.0 28 $0.030 $0.036 $0.0 18 $0.044 $0.044 $0.044 $0.014 $0.036 $0.023 $0.044 $0.011 $0.036 Cost $1. 083 Cost/hr $14. 58 Note: The codes in this table correspond to an earlier version of the Boothroyd method and thus do not match the codes in Figure 15-1 and Figure... Design for Assembly," B S thesis, MIT Mechanical Engineering Department, May 2001 [Coulter, Mclntosh, Bras, and Rosen] Coulter, S L., Mclntosh, M W., Bras, B., and Rosen, D W., "Identification of Limiting Factors for Improving Design Modularity," Proceedings of the 19 98 ASME Design Engineering Technical Conferences, Atlanta, GA, paper no DETC 98/ DTM-5659, September 19 98 [Esawi and Ashby] Esawi, A M K.,... bolts were replaced by a feature on Total assembly time Minimum number of parts Theoretical assembly time Assembly efficiency 57 27 2.11 8 8(11, 12, 18, 20,21,23,24,25) 12 (all fasteners plus half the others; note functional risk in eliminating some of them) 267.25 15 45 16 .84 % Note: This analysis rigorously applies the Boothroyd analysis and eliminates all fasteners plus a few other parts with the understanding... locators in the fixture FIGURE 15- 28 Clamp for Holding the Assembly in the Fixture in Figure 15-27 15.F .8 Assembly Aids in Fixture • Grease is added to the area where the anvil slides along subassembly 1 • Subassembly 4, the staple gun delivery subassembly, is created using Parts 13-19 and joining them using the following sequence: Part 14 to 16, Part 17, Part 15, Part 13, Part 18, Part 19 • Install subassembly . mm 0 1.13 1.5 1 .8 1.95 6 mm < size < 15 mm 1 1.43 1 .8 2.1 2.25 < 2 mm Size > 6 mm 2 1.69 2.06 2.36 2.51 Part nests or tangles Thickness > 2 mm Size > 1 5 mm 3 1 .84 2.25 2.57 2.73 6. only Obstructed access only Code 3 4 5 Easy to align 0 3.6 6.3 9.0 Not easy to align / 5.3 8. 0 10.7 388 15 DESIGN FOR ASSEMBLY AND OTHER "ILITIES" from a random orientation (time . align / 3.0 5.2 7.4 Holding down required Easy to align 2 2.6 4 .8 7.0 Not easy to align 3 5.2 7.4 9.6 Secured right away by snap fit Easy to align 4 1 .8 4.0 7.7 Not easy to align 5 3.3 5.5 7.7 No access