Computer- Integrated Manufacturing Systems 0 This chapter describes how computer systems and communications networks affect product development and manufacturing through the integration of all of their activities. 0 The chapter begins by explaining the principles of manned and untended man- ufacturing cells and their features, and how cells can be integrated into flexible manufacturing systems. ° The new concept of holonic manufacturing and its applications are reviewed. ° ]ust-in-time production, lean manufacturing, and communication systems are then described. ° The chapter ends with a discussion of artificial intelligence and expert systems as applied to manufacturing. 39.l Introduction This chapter focuses on the computer integration of manufacturing activities. Integration means that manufacturing processes, operations, and their management are treated as a system. A major advantage of such an approach is that machines, tooling, and manufacturing operations now acquire a built-in flexibility, called flexible manufacturing. As a result, the system is capable of rapidly responding to changes in product types and fluctuating demands, as well as ensuring on-time deliv- ery of products to the customer. Failure of on-time delivery in a highly competitive global environment can upset management plans and production schedules and, consequently, can have major adverse effects on a company’s operations. This chapter describes the key elements that enable the execution of the func- tions necessary to achieve flexible manufacturing. The chapter begins with cellular manufacturing, which is the basic unit of flexibility in the production of goods. It shows that manufacturing cells can be broadened into flexible manufacturing sys- tems, with major implications for the production capabilities of an operation. Holonic manufacturing is then described, which is a new concept of how manufac- turing units can be organized to achieve higher efficiency in operations. The important concept of just-in-time production is examined, in which parts are produced “just in time” to be made into subassemblies, assemblies, and final products. This method eliminates the need for inventories (which can be a major 39.| Introduction l||7 39.2 Cellular Manufacturing l||8 39.3 Flexible Manufacturing Systems IIZO 39.4 Holonic Manufacturing I|22 39.5 just-in-time Production |l24 39.6 LeanManufacturing l|25 39.7 Communications Networks in Manufacturing I|27 39.8 Artificial Intelligence IIZ9 39.9 Economic Considerations |132 EXAMPLES: 39.I Manufacturing Cells in a Small Machine Shop III9 39.2 Flexible Manufacturing Systems in Large and Small Companies I |22 l|l7
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CHAPTER
Computer-IntegratedManufacturingSystems
0 This chapter describes how computer systems and communications networksaffect product development and manufacturing through the integration of allof their activities.
0 The chapter begins by explaining the principles of manned and untended man-ufacturing cells and their features, and how cells can be integrated into flexiblemanufacturing systems.
° The new concept of holonic manufacturing and its applications are reviewed.
° ]ust-in-time production, lean manufacturing, and communication systems arethen described.
° The chapter ends with a discussion of artificial intelligence and expert systemsas applied to manufacturing.
39.l Introduction
This chapter focuses on the computer integration of manufacturing activities.Integration means that manufacturing processes, operations, and their managementare treated as a system. A major advantage of such an approach is that machines,tooling, and manufacturing operations now acquire a built-in flexibility, calledflexible manufacturing. As a result, the system is capable of rapidly responding tochanges in product types and fluctuating demands, as well as ensuring on-time deliv-ery of products to the customer. Failure of on-time delivery in a highly competitiveglobal environment can upset management plans and production schedules and,consequently, can have major adverse effects on a company’s operations.
This chapter describes the key elements that enable the execution of the func-tions necessary to achieve flexible manufacturing. The chapter begins with cellularmanufacturing, which is the basic unit of flexibility in the production of goods. Itshows that manufacturing cells can be broadened into flexible manufacturing sys-tems, with major implications for the production capabilities of an operation.Holonic manufacturing is then described, which is a new concept of how manufac-turing units can be organized to achieve higher efficiency in operations.
The important concept of just-in-time production is examined, in which partsare produced “just in time” to be made into subassemblies, assemblies, and finalproducts. This method eliminates the need for inventories (which can be a major
39.| Introduction l||739.2 Cellular
Manufacturing l||839.3 Flexible Manufacturing
Systems IIZO
39.4 HolonicManufacturing I|22
39.5 just-in-timeProduction |l24
39.6 LeanManufacturing l|2539.7 Communications
Networks in
Manufacturing I|2739.8 Artificial
Intelligence IIZ939.9 Economic
Considerations |132
EXAMPLES:
39.I Manufacturing Cellsin a Small MachineShop III9
39.2 Flexible ManufacturingSystems in Large and SmallCompanies I |22
l|l7
Chapter 39 Computer-Integrated Manufacturing Systems
financial burden on a company), as well as significantly saving on space and storagefacilities. Because of the necessity for and extensive use of computer controls, hard-ware, and software in all the activities just outlined, the planning and effective imple-mentation of communication networks constitute a critical component of the overalloperation. The chapter concludes with a review of artihcial intelligence, which con-sists of expert systems, natural-language processing, machine vision, artificial neuralnetworks, and fuzzy logic.
39.2 Cellular Manufacturing
A manufacturing cell is a small unit consisting of one or more workstations. A
workstation usually contains either one machine (called a single-machine cell) orseveral machines (called a group-machine cell), with each machine performing a dif-ferent operation on a part. The machines can be modified, retooled, and regroupedfor different product lines within the same family of parts.
Cellular manufacturing has been utilized primarily in machining, finishing,and sheet-metal-forming operations. The machine tools commonly used in the cellsare lathes, milling machines, drills, grinders, and electrical-discharge machines; forsheet forming, the equipment typically consists of shearing, punching, bending, andother forming machines. The equipment may include special-purpose machines andCNC machines. Automated inspection and testing equipment also are generally apart of this cell.
The capabilities of cellular manufacturing typically involve the following oper-ations:
° Loading and unloading raw materials and workpieces at workstations.° Changing tools at workstations.° Transferring workpieces and tooling between workstations.° Scheduling and controlling the total operation in the cell.
In attended (manned) machining cells, raw materials and parts can be movedand transferred manually by the operator (unless the parts are too heavy or themovements are too hazardous) or by an industrial robot located centrally in the cell.
Flexible Manufacturing Cells. Recall that, in view of rapid changes in market de-mand and the need for more product variety in smaller quantities, flexibility in manu-facturing operations is highly desirable. Manufacturing cells can be made flexible byusing CNC machines and machining centers (Section 252) and by means of industri-al robots or other mechanized systems for handling materials and parts in variousstages of completion (Section 37.6). An example of an attended flexible manufactur-ing cell (FMC) that involves machining operations is illustrated in Fig. 39.1. Note thatan automated guided vehicle moves parts between machines and inspection stations;machining centers fitted with automatic tool changers and tool magazines have anability to perform a wide variety of operations. (See Section 25.2.)
A computer-controlled inspection station with a coordinate-measuring ma-chine can similarly inspect dimensions on a wide variety of parts. Thus, the organi-zation of these machines into a cell can allow the successful manufacture of verydifferent parts. With computer integration, a manufacturing cell can produce partsin batch sizes as small as one part, with negligible delay between parts. (The actualdelay is the time required to download new machining instructions.)
Section 39.2 Cellular Manufacturing
Horizontal milling Direction of partwithin cell/»
Lathes
Workerpositions
Vertical millingmachines
Finalmcoming *___ inspection
raw material Raw Finishedt t
material par carCart Completed part
FIGURE 39.l Schematic illustration of a manned flexible manufacturing cell, showingvarious machine tools and an inspection station. Source: After ]T. Black.
Flexible manufacturing cells are usually unattended or unmanned; their designand operation are thus more exacting than those for other cells. The selection of ma-chines and industrial robots, including the types and capabilities of end effectors andtheir control systems, is critical to the proper functioning of the FMC. The likeli-hood of a significant change in demand for part families should be consideredduring the design of the cell, in order to ensure that the equipment involved has thenecessary flexibility and capacity. As with other flexible manufacturing systems(described in Section 393), the cost of FMCS is very high. However, this disadvan-tage is outweighed by increased productivity (at least for batch production), flexibil-ity, and controllability.
Cell Design. Because of the unique features of manufacturing cells, their designand placement requires efficient layout and-organization of the plant and the con-sideration of product flow lines. The machines may be arranged along a line or in aU-shape, an L-shape, or a loop. Selecting the best machine and material-handlingequipment arrangement also involves taking into account such factors as the pro-duction rate, the type of product, and its shape, size, and weight. The cost of flexi-ble cells can be high, but this disadvantage is outweighed by increased productivity,flexibility, and controllability.
EXAMPLE 39.1 Manufacturing Cells in a Small Machine Shop
What follows is an actual example of the applicationof the manufacturing-cell concept in a small shop.Company A has only 10 employees, 11 milling ma-chines, and 11 machining centers. The machines areset up in cells (milling cells and turning cells). The ma-chines in the cells are arranged so as to allow an opera-tor to machine a part in the most efficient and precisemanner. Each cell allows the operator to monitor theperformance of the machines in the cell,
Gver 1200 different product lots have beenproduced over the years, with quantities rangingfrom 1 part to as many as 35,000 parts of the samedesign. The parts are inspected as they are produced.Each employee in the shop is involved in the pro-gramming and the running of the machines and inthe in-process inspection of parts.
III9
I 20 Chapter 39 Computer-Integrated Manufacturing Systems
39.3 Flexible Manufacturing Systems
A flexible manufacturing system (FMS) integrates all of the major elements of pro-duction into a highly automated system (Fig 39.2). First utilized in the late 1960s, anFMS consists of (a) a number of manufacturing cells, each containing an industrialrobot serving several CNC machines and (b) an automated material-handling system.All of these are interfaced with a central computer. Different computer instructionscan be downloaded for each successive part passing through a particular worksta-tion. The system can handle a variety of part conjqgurations and produce them in anyorder. A general view of an FMS installation in a plant is shown in Fig. 39.3.
An FMS is capable of optimizing each step of the total operation. These stepsmay involve (a) one or more processes and operations, such as machining, grinding,cutting, forming, powder metallurgy, heat treating, and finishing, (b) the handling ofraw materials, (c) measurement and inspection, and (d) assembly. The most commonapplications of FMS to date have been in machining and assembly operations.
An FMS can be regarded as a system that combines the benefits of two systems:(1) the highly productive, but inflexible, transfer lines and (2) job-shop production,which can produce large product variety on stand-alone machines, but is inefficient.(See also Fig. 37.2.) The relative characteristics of transfer lines and FMS are shownin Table 39.1. Note that with an FMS, the time required for a changeover to a differ-ent part is very short. The quick response to product and market-demand variationsis a major attribute of FMS.
Compared with conventional manufacturing systems, FMS have the followingmajor benefits:
° Parts can be produced in any order, in batch sizes as small as one, and at alower unit cost.
° Direct labor and inventories are reduced or eliminated.
Coordinate-measuring machine
Machining center Ei:""`i.
Machining _L #fancenter gc -- i
TOO' f`3?r§*‘ ‘ii iiii magazine ~ /-\G\/
ii j path ri `,
Pallet stations
FIGURE 39.2 A schematic illustration of a flexible manufacturing system, showing machin-ing centers, a measuring and inspection station, and automated guided vehicles. Source: AfterJT. Black.
° The lead times required for productchanges are shorter.
° Because the system is self-correcting,production is more reliable and productquality is uniform.
Elements of FMS. The basic elements of aflexible manufacturing system are (a) worksta-tions and cells, (b) automated handling andtransport of materials and parts, and (c) con-trol systems. The Workstations are arrangedto yield the greatest efficiency in productionwith an orderly flow of materials and parts inprogress through the system.
The types of machines in Workstationsdepend on the type of production. For example,for machining operations, they usually consistof a variety of 3- to 5-axis machining centers,CNC lathes, milling machines, drill presses, andgrinders. Also included are various other piecesof equipment, such as that for automated in-spection (including coordinate-measuring ma-chines), assembly, and cleaning. Other types ofmanufacturing operations suitable for FMS are
Section 39.3 Flexible Manufacturing Systems I |2l
FIGURE 39.3 A general view of a flexible manufacturing system ina plant, showing several machining centers and automated guidedvehicles moving along the white line in the aisle. Source: Courtesy ofCincinnati Milacron, Inc.
sheet-metal forming, punching and shearing, and forging. FMS also may incorporatefurnaces, various machines, trimming presses, heat-treating facilities, and cleaningequipment.
Because of the flexibility of FMS, material-handling systems are very impor-tant. These systems are controlled by a central computer, and their operations areperformed by automated guided vehicles, conveyors, and various transfer mecha-nisms. FMS are capable of transporting raw materials, blanks, and parts in variousstages of completion to any machine, in random order, and at any time. Prismaticparts usually are moved on specially designed pallets. Parts having rotational sym-metry, such as those used in turning operations, usually are moved by robots andvarious mechanical devices.
Scheduling. Because FMS are a major capital investment, efficient machine uti-lization is essential. Machines must not stand idle; consequently, proper schedulingand process planning are crucial. Scheduling for FMS is dynamic, unlike that in job
TABLE 39.|
Comparison of General Characteristics of Transfer Lines andFlexible Manufacturing Systems (FMS)
Characteristic Transfer line FMS
Part variety Few InfiniteLot size >10O 1-50Part-changing time Long Very shortTool change Manual AutomaticAdaptive control Difficult AvailableInventory High LowProduction during breakdown None Partialjustification for capital expenditure Simple Difficult
I 22 Chapter 39 Computer-Integrated Manufacturing Systems
3
shops, where a relatively rigid schedule is followed to perform a set of operations.The scheduling system in flexible manufacturing specifies the types of operations tobe performed on each part and identifies the machines or manufacturing cells onwhich these operations are to take place. Dynamic scheduling is capable of respond-ing to quick changes in product type; thus, it is responsive to real-time decisions.
Because of the flexibility of FMS, no setup time is wasted in switching be-tween manufacturing operations. However, the characteristics, performance, andreliability of each unit in the system must be monitored to ensure that parts are ofacceptable quality and dimensional accuracy before they move on to the nextworkstation.
Economic justification of FMS. FMS installations are very capital intensive, cost-ing millions of dollars. Consequently, a thorough cost-benefit analysis must be con-ducted before any final decision is made. This analysis must include such factors asthe costs of capital, energy, materials, and labor; the expected markets for the prod-ucts to be manufactured; and any anticipated fluctuations in market demand andproduct type. An additional important consideration is the time and effort requiredfor installing and debugging the system.
As can be seen in Fig. 37.2, the most effective FMS applications are in medium-quantity batch production. When a variety of parts is to be produced, FMS is
suitable for production quantities typically of 15,000 to 35 ,000 aggregate parts peryear. For individual parts with the same configuration, production may reach100,000 parts per year. In contrast, high-volume, low-variety parts production is
best obtained from transfer machines (dedicated equipment). Finally, low-volume,high-variety parts production can best be done on conventional standard machinery(with or without numerical control) or by machining centers (Chapter 25).
EXAMPLE 39.2 Flexible Manufacturing Systems in Large and Small Companies
Because of the advantages of FMS technology, manymanufacturers have long considered implementing a
large-scale system in their facilities. However; afterdetailed review, and on the basis of the experience ofother companies, many companies decide on smaller,simpler, modular, and less expensive systems that aremore cost effective. These systems include flexiblemanufacturing cells (the cost of which would be onthe order of a few hundred thousand dollars), stand-alone machining centers, and various CNC machinetools that are easier to control than an FMS.
When FMS became an established alternative,the expectations were high, and in some cases exten-sive computerization led to much confusion andinefficiency in company operations. Particularly forsmaller companies, important considerations include
not only the fact that a large capital investment andmajor hardware and software acquisitions are neces-sary, but also the fact that the efficient operation of a
large FMS requires the extensive training of person-nel. Often, the surprising result is found that an FMSleads to a manufacturing enterprise that is less lean(see Section 39.6).
There are several examples of the successfuland economically viable implementation of an FMSin a large company. The results of a survey of 20such operating systems in the United States indicatedsignificant improvements over previous methods.Some systems are now capable of economically pro-ducing lot sizes of even one part. In spite of the highcost, the system has paid for itself in a number ofcompanies.
39.4 Holonic Manufacturing
Holonic manufacturing is a new concept describing a unique organization of manu-facturing units. The word holonic is from the Greek /volos (meaning “whole ”) and thesuffix on (meaning “a part of”). Thus, each component in a holonic manufacturing
Section 39.4 Holonic Manufactunng I 23
system (at the same time) is an independent entity (or u/hole) and a subservient part ofa hierarchical organization. We describe this system here because of its potential ben-eficial impact on computer-integrated manufacturing operations.
Holonic organizational systems have been studied since the 19605, and thereare a number of examples in biological systems. Three fundamental observationsabout these systems are the following:
I. Complex systems will evolve from simple systems much more rapidly if thereare stable intermediate forms than if there are none. Also, stable and complexsystems require a hierarchical system for their evolution.
2. Holons are simultaneously self-contained wholes of their subordinated partsand dependent parts of other systems. Holons are autonomous and self-reliant units that have a degree of independence and can handle contingencieswithout asking higher levels in the hierarchical system for instructions. At thesame time, holons are subject to control from multiple sources of higher sys-tem levels.
3. A /oolarchy consists of (a) autonomous wholes in charge of their parts and(b) dependent parts controlled by higher levels of a hierarchy. Holarchies arecoordinated according to their local environment.
In biological systems, hierarchies have the characteristics of (a) stability in the faceof disturbances, (b) optimum use of available resources, and (c) a high level of flex-ibility when their environment changes.
A manufacturing holon is an autonomous and cooperative building block of amanufacturing system for the production, storage, and transfer of objects or infor-mation. It consists of a control part and an optional physical-processing part. Forexample, a holon can be a combination of a CNC milling machine and an operatorinteracting via a suitable interface. A holon can also consist of other holons thatprovide the necessary processing, information, and human interfaces to the outsideworld, such as a group of manufacturing cells. Holarchies can be created and dis-solved dynamically, depending on the current needs of the particular manufacturingprocess.
A holonic-systems view of the manufacturing operation is one of creating aworking manufacturing environment from the bottom up. Maximum flexibility canbe achieved by providing intelligence within holons to both (a) support all produc-tion and control functions required to complete production tasks and (b) managethe underlying equipment and systems. The manufacturing system can dynamicallyreconfigure into operational hierarchies to optimally produce the desired products,with holons or elements being added or removed as needed.
Holarc/Jical manufacturing systems rely on fast and effective communicationbetween holons, as opposed to traditional hierarchical control, Where individualprocessing power is essential. A large number of specific arrangements and softwarealgorithms have been proposed for holarchical systems, but a detailed description ofthese is beyond the scope of this bool<. However, the general sequence of events canbe outlined as follows:
I. A factory consists of a number of resource holons, available as separate entitiesin a resource pool. For example, available holons may consist of (a) a CNCmilling machine and operator, (b) a CNC grinder and operator, or (c) a CNClathe and operator.
2. Upon receipt of an order or a directive from higher levels in the factory hierar-chical structure, an order holon is formed and begins communicating andnegotiating with the available resource holons.
I 24 Chapter 39 Computer-Integrated Manufacturing Systems
3. The negotiations lead to a self-organized grouping of resource holons, whichare assigned on the basis of product requirements, resource holon availability,and customer requirements. For example, a given product may require a CNClathe, a CNC grinder, and an automated inspection station to organize it intoa production holon.
4. In case of breakdown, the unavailability of a particular machine, or changingcustomer requirements, other holons from the resource pool can be added or
subtracted as needed, allowing a reorganization of the production holon. Pro-
duction bottlenecks can be identified and eliminated through communicationand negotiation between the holons in the resource pool.
Step 4 has been referred to as plug and play, a term borrowed from the com-
puter industry, where hardware components seamlessly integrate into a system.
39.5 just-in-time Production
The just-in-time (]IT) production concept originated in the United States, but wasfirst implemented on a large scale in 1953 at the Toyota Motor Company in ]apanto eliminate waste of materials, machines, capital, manpower, and inventorythroughout the manufacturing system. The ]IT concept has the following goals:
° Receive supplies just in time to be used.° Produce parts just in time to be made into subassemblies.° Produce subassemblies just in time to be assembled into finished products.° Produce and deliver finished products just in time to be sold.
In traditional manufacturing, the parts are made in batches, placed in inventory,and used whenever necessary. This approach is known as a push system, meaningthat parts are made according to a schedule and are placed in inventory, to be used
whenever they are needed. In contrast, ]IT is a pull system, meaning that parts areproduced to order and the production is matched with demand for the final assem-bly of products.
There are no stockpiles and the ideal production quantity is one. ]IT is also
called zero inventory, stoc/cless production, and demand scheduling. Moreover,parts are inspected as they are manufactured and are used within a short time. Inthis way, a worker maintains continuous production control, immediately identify-ing defective parts and reducing process variation to produce quality products.
Implementation of the ]IT concept requires that all aspects of manufacturingoperations be monitored and reviewed so that all of those operations and resourceswhich do not add value are eliminated. This approach emphasizes (a) pride and ded-
ication in producing high-quality products, (b) the elimination of idle resources, and(c) teamwork among workers, engineers, and management to quickly solve anyproblems that arise during production or assembly.
The ability to detect production problems as the parts are being made has
been likened to what happens to the level of water (representing inventory levels) in
a lake covering a bed of boulders (representing production problems). When the
water level is high (analogous to the high inventories associated with push produc-tion), the boulders are not exposed. By contrast, when the level is low (analogousto the low inventories associated with pull production), the boulders are exposedand can be identified and removed. This analogy indicates that high inventorylevels can mask quality and production problems with parts that are already madeand stockpiled.
Section 39.6 Lean Manufacturing I 25
The ]IT concept requires the timely delivery of all supplies and parts from out-side sources and from other divisions of a company; thus, it significantly reduces oreliminates in-plant inventory. Suppliers are expected to deliver-often on a dailybasis-preinspected goods as they are needed for production and assembly. This ap-proach requires reliable suppliers, close cooperation and trust between the companyand its vendors, and a reliable system of transportation. Also important for smootheroperation is a reduction in the number of its suppliers. In one example, an AppleComputer plant reduced the number of its suppliers from 300 to 70.
Advantages of _|lT. Summarized here are the major advantages of just-in-timeproduction:
0 Low inventory carrying costs.° Fast detection of defects in the production or the delivery of supplies and,
hence, low scrap loss.° Reduced inspection and reworking of parts.° High-quality products made at low cost.
Although there can be significant variations in performance, just-in-time pro-duction has resulted in reductions of 20 to 40% in product cost, 60 to 80% in in-ventory, up to 90% in rejection rates, 90% in lead times, and 50% in scrap, rework,and warranty costs. Increases of 30 to 50% in direct-labor productivity and of 60%in indirect-labor productivity also have been attained.
Kanban. The implementation of ]IT in japan involved kanban, meaning “visiblerecord.” These records originally consisted of two types of cards (called kanbans,now largely replaced by bar-coded plastic tags and other devices):
0 The production card, which authorizes the production of one container or cartof identical, specified parts at a workstation.
° The conveyance cara' or rnoz/e card, which authorizes the transfer of one con-tainer or cart of parts from a particular workstation to the workstation wherethe parts will be used.
The cards contain information on the type of part, the location where the card wasissued, the part number, and the number of items in the container. The number ofcontainers in circulation at any time is completely controlled and can be scheduledas desired for maximum production efficiency.
39.6 Lean Manufacturing
In a modern manufacturing environment, companies must be responsive to theneeds of the customers and their specific requirements and to fluctuating globalmarket demands. At the same time, to ensure competitiveness, the manufacturingenterprise must be conducted with a minimum amount of wasted resources. This re-alization has lead to lean production or lean manufacturing strategies.
Lean manufacturing involves the following steps:
I. Identify value. The critical starting point for lean thinking is a recognition ofvalue, which can be done only by a customer or by considering a customer’sproduct. (See also Section 40.9.1.) The goal of any organization is to producea product that a customer wants, at a desired price, capability, location, time,
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2.
3.
4.
Integrated Manufacturing Systems
volume, etc. Providing the wrong good or service produces waste, even if it is
provided efficiently. It is important to identify all of a manufacturer’s activitiesfrom the viewpoint of the customer and optimize processes to maximize addedvalue. This viewpoint is critically important because it helps identify whetheror not an activity:
a. Clearly adds value.
b. Adds no value, but cannot be avoided.
c. Adds no value, but can be avoided.
Identify value streams. The value stream is the set of all actions required tobring a product to fruition, including
a. Product design and development tasks, involving all actions from concept,to detailed design, to production launch;
b. Information management tasks, involving order taking, a detailed schedule,and delivery;
c. Physical production tasks, by means of which raw materials progress toa finished product in the hands of the customer.
It has often been noted that no one person can be accurately described asa manufacturer of cars, boats, or airplanes. Organizations or systems createthese products, and systems can become large and unwieldy, with tasks that donot create value. By identifying value streams, those tasks can be identified andeliminated.
Make the value stream flow. It has been noted that flow is easiest to achieve in
mass production, but it is more difficult for small-lot production. Productionin batches should be avoided, so just-in-time approaches (Section 39.5) areessential. The solution in such cases is to use manufacturing cells (Section 392),where minimum time and effort are required to switch from one product toanother and a product being manufactured encounters continuous flow.
In addition to just~in-time approaches, establishing product flow throughfactories requires the following:
° Eliminating waiting time. Waiting time may be caused by unbalancedworkloads, unplanned maintenance, or quality problems. Therefore, theefficiency of workers must be maximized at all times.
Q Eliminating unnecessary processes and steps, because they representcosts.
° Minimizing or eliminating product transportation, because it representsan activity that adds no value. This waste can be either eliminated, by,
for example, forming machining cells, or minimized, with, for instance,better plant layouts.
° Performing time and motion studies to identify inefficient workers orunnecessary product motions.
° Eliminating part defects.
Establish pull. Pull-type and push-type systems are described in Section 39.5. Ithas been observed that once value streams are flowing, significant savings aregained in terms of inventory reduction, as well as product development, orderprocessing, and physical production. Indeed, 90% reductions in physicalproduction have been noted in some cases. Under these circumstances, it is
possible to establish pull manufacturing, where products are produced uponorder by a customer, and not in batches that ultimately are unwanted and donot create value.
Section 39.7 Communications Networks in Manufacturing I 27
5. Achieve perfection. As described in Section 36.1, /aaizen is used to signify con-tinuous improvement, and clearly, there is a need for continuous improvementin all organizations. With lean manufacturing approaches, it has been foundthat continuous improvement can be accelerated, so that production withoutwaste is possible. Moreover, upon the adoption of lean manufacturing prin-ciples, firms encounter an initial benefit, referred to as kaika/eu, or “radicalimprovement.”
39.7 Communications Networks in Manufacturing
In order to maintain a high level of coordination and efficiency of operation in inte-grated manufacturing, an extensive, high-speed, and interactive communicationsnetwork is essential. The local area network (LAN) is a hardware-and-software sys-tem in which logically related groups of machines and equipment communicate witheach other. A LAN links these groups to each other, bringing different phases ofmanufacturing into a unified operation.
A LAN can be very large and complex, linking hundreds or even thousands ofmachines and devices in several buildings. Various network layouts (Fig. 39.4) offiber-optic or copper cables are typically used, over distances ranging from a fewmeters to as much as 32 km; for longer distances, wide area networks (WANS) areused. Different types of networks can be linked or integrated through “gateways”and “bridges,” often with the use of secure file transfer protocols (FTPs) overInternet connections. A number of advanced network protocols, including ip V6 andInternet2, are under development, but have not yet been applied to manufacturing.Controlling access to the network is important; otherwise collisions can occur whenseveral workstations are transmitting simultaneously. Continuous scanning of thetransmitting medium is essential.
A carrier-sense multipleaccess with collision detection (CSMA/CD) system was de-veloped in the 1970s and implemented in Ethernet, which is now the industry standard.Other access-control methods are the token ring and to/een bus-in each of which a
Ex a|[ij T Ei] T T BUSE/ station I I I I
[11] El [Il El II] EIlj User station
(a) Star (b) Ring (c) Bus
FIGURE 39.4 Three basic types of topology for a local area network (LAN). (a) The startopology is suitable for situations that are not subject to frequent configuration changes. Allmessages pass through a central station. Telephone systems in office buildings usually havethis type of topology. (b) In the ring topology, all individual user stations are connected in acontinuous ring. The message is forwarded from one station to the next until it reaches itsassigned destination. Although the wiring is relatively simple, the failure of one station shutsdown the entire network. (c) In the bus topology, all stations have independent access to thebus. This system is reliable and is easier than the other two to service. Because its arrangementis similar to the layout of the machines in the factory, its installation is relatively easy, and itcan be rearranged when the machines are rearranged.
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token (special message) is passed from device to device. Only the device that has thetoken is allowed to transmit, while all of the other devices only receive.
Conventional LANs require the routing of wires, often through masonry wallsor other permanent structures, and require computers and machinery to remain sta-tionary. Wireless local area networks (WLANS) allow equipment such as mobile teststands or data-collection devices (e.g., bar-code readers) to easily maintain a networkconnection. A communication standard (IEEE 802.11) currently defines frequenciesand specifications of signals, and two radio-frequency methods and one infraredmethod for WLANS. Although wireless networks are slower than those which arehardwired, their flexibility makes them desirable, especially in situations where slowtasks, such as machine monitoring, are the main application.
Personal area networks (PANS) are used for electronic devices, such as cellulartelephones and personal data assistants, but are not as widespread for manufactur-ing applications. PANs are based on communications standards (such as Bluetooth,IrDA, and HomeRF) and are designed to allow data and voice communication overshort distances. For example, a short-range Bluetooth device will allow communica-tion over a 10-m distance. PANs are undergoing major changes, and communica-tions standards are continually being refined.
Communications Standards. Typically, one manufacturing cell is built with ma-
chines and equipment purchased from one vendor, another cell with machinespurchased from another vendor, and a third purchased from yet another vendor. As
a result, a variety of programmable devices are involved and are driven by severalcomputers and microprocessors purchased at various times from different vendorsand having various capacities and levels of sophistication.
Each cell’s computers have their own specifications and proprietary standards,and they typically cannot communicate with others beyond the cell, unless they all
are equipped with custom-built interfaces. This situation created islands of automa-tion; in some cases, up to 50% of the cost of automation was related to overcomingdifficulties in the communications between individual manufacturing cells and otherparts of the organization.
The existence of automated cells that could function independently from eachother (i.e., without a common base for information transfer) led to the need for a
communications standard to improve both communications and the efficiency ofcomputer-integrated manufacturing. The first step toward standardization began in1980. After considerable effort, and on the basis of existing national and interna-tional standards, a set of communications standards known as the manufacturingautomation protocol (MAP) was developed.
The International Organization for Standardization (ISO)/Open SystemInterconnect (OSI) reference model is accepted worldwide. The ISO/OSI model hasa hierarchical structure in which communication between two users is divided intoseven layers (Fig. 39.5). Each layer has a special task:
° Data transmission, by mechanical and electronic means° Error detection and correction° Correct transmission of the message° Control of the dialog between users° Translation of the message into a common syntax° Verification that the data transferred has been understood.
The operation of this system is complex. Basically, each standard-sized chunkof message or data to be transmitted from User A to User B moves sequentiallythrough the successive layers at A’s end from Layer 7 to Layer 1. More information
Section 39.8 Art|f|c|aI Intelligence I |29
Master control Data Manufacturingsystem network center
Z ` < - < > < >
< > *T1> <-> -> -- -> T T End system Intermediate End system
User A system User B
FIGURE 39.5 The ISO/OSI reference model for open communication. Source: After U.Rembold.
is added to the original message as it travels through each layer. The completepacket is transmitted through the physical communications medium to User B andthen moves through the layers (from 1 to 7) at B’s end. The transmission takes placethrough coaxial cable, fiber-optic cable, microwaves, and similar devices.
Communication protocols have been extended to office automation as well,with the development of technical and office protocol (TOP), which is based on theISO/OSI reference model. In this way, total communication (MAP/TOP) is estab-lished among the factory floor and offices at all levels of an organization. A commonpractice is the use of Internet tools (hardware, software, and protocols) within a com-pany to link all departments and functions into a self-contained and fully compatibleIntranet. Several tools for implementing this link are available commercially; they areinexpensive and are easy to install, integrate, and use.
39.8 Artificial Intelligence
Artificial intelligence (AI) is that part of computer science which is concerned withsystems that exhibit some characteristics usually associated with intelligence inhuman behavior, such as learning, reasoning, problem solving, recognizing patterns,and understanding language. The goal of AI is to simulate such human behaviors onthe computer. The art of bringing relevant principles and tools of AI to bear on dif-ficult application problems is known as knowledge engineering.
Artificial intelligence has a major effect on the design, automation, and overalleconomics of the manufacturing operation, largely because of advances in computermemory expansion (VLSI chip design; Chapter 28) and decreasing costs. Artificialintelligence packages costing as much as a few thousand dollars have been devel-oped, many of which can be run on personal computers. Thus, AI has become acces-sible to office desks and shop floors.
I |30 Chapter 39 Computer-Integrated Manufacturing Systems
FIGURE 39.6 Basic structure of an expert system. Theknowledge base consists of knowledge rules (general informa-tion about the problem) and inference rules (the way conclu-sions are reached). The results may be communicated to theuser through the natural-language interface.
Expert Systems. An expert system (ES), also called aknowledge-based system, generally is defined as anintelligent computer program that has the capabilityto solve difficult real-life problems by the use ofknowledge-based and inferential procedures (Fig. 39.6).The goal of an expert system is to conduct an intellec-tually demanding task in the way that a human expertwould.
The field of knowledge required to perform thetask in question is called the domain of the expert sys-tem. Expert systems utilize a knowledge base contain-ing facts, data, definitions, and assumptions. They alsohave the capability of adopting a heuristic approach-that is, making good judgments on the basis of dis-covery and revelation and making high-probabilityguesses, just as a human expert would. The knowledgebase is expressed in computer code, usually in the formof if-then rules, and can generate a series of questions.The mechanism for using these rules to solve problemsis called an inference engine. Expert systems can com-municate with other computer software packages.
To construct expert systems for solving the com-plex design and manufacturing problems one encoun-
ters in real life, one needs (a) a great deal of knowledge and (b) a mechanism formanipulating that knowledge to create solutions. Because of the difficulty involvedin accurately modeling the many years of experience of an expert or a team of ex-perts, and because of the complex inductive reasoning and decision-making capa-bilities of humans (including the capability to learn from mistakes), developingknowledge-based systems requires considerable time and effort.
Expert systems operate on a real-time basis, and their short reaction times pro-vide rapid responses to problems. The programming languages most commonly usedfor these applications are C+ +, ]ava, and Prolog; other languages also are available.An important development is expert-system software shells or environments, alsocalled framework systems. These software packages are essentially expert-system out-lines that allow a person to write specific applications to suit special needs. Writingthese programs requires considerable experience and time.
Several expert systems have been developed that utilize computers with vari-ous capabilities and for such specialized applications as the following:
° Problem diagnosis in various types of machines and equipment, and the deter-mination of corrective actions
° Modeling and simulation of production facilities° Computer-aided design, process planning, and production scheduling° Management of a company’s manufacturing strategy.
Natural-language Processing. Traditionally, retrieving information from a data-base in computer memory has required the utilization of computer programmers totranslate questions in natural language into “queries” in some machine language.Natural-language interfaces with database systems are in various stages of develop-ment. These interfaces allow a user to obtain information by entering English or otherlanguage commands in the form of simple, typed questions.
Software shells are available, and they are used in such applications as sched-uling material flow in manufacturing and analyzing information in databases.
Section 39.8 Artificial intelligence I l3|
Speech orformatted input ¢..,,____h‘ Camera
iacquisition , - e ~ee so ,L 5; K~°W'@°Q@. pmbiem Camera ~
Q base i S0|\/ef Control i , , t i f Y, QV1 Reasoning E program . ..___ Q li’ J 'ggi ,(~;f_~.ec :,,_,,>g,;,;§@;~,;;:_',;<_,\,4(,;;;` U 1 1 g r
(Expert system) . S r Part
FIGURE 39.7 Expert system as applied to an industrial robot guided by machine vision.
Significant progress continually is being made on computer software that will havespeech synthesis and recognition (voice recognition) capabilities, in order to elimi-nate the need to type commands on keyboards.
Machine Vision. The basic features of machine vision were described in Sec-tion 37.7.1. Computers and software, implementing artificial intelligence, are com-bined with cameras and other optical sensors (Fig. 39.7). These machines then performsuch operations as inspecting, identifying, and sorting parts, as well as guiding robots(intelligent robots; Section 37.6.2)-operations that otherwise would require humanintervention.
Artificial Neural Networks. Although computers are much faster than the humanbrain at performing sequential tasks, humans are much better at pattern-based tasksthat can be performed with parallel processing, such as recognizing features (onfaces and in voices, even under noisy conditions), assessing situations quickly, andadjusting to new and dynamic conditions. These advantages also are due partly tothe ability of humans to use all senses (sight, hearing, smell, taste, and touch) simul-taneously (called data fusion) and in real time. The branch of AI called artificial neu-ral netu/or/es (ANN) attempts to gain some of these capabilities through computerimitation of the way that data are processed by the human brain.
The human brain has about 100 billion linked neurons (cells that are the fun-damental functional units of nerve tissue) and more than a thousand times thatmany connections. Each neuron performs exactly one simple task: It receives inputsignals from a fixed set of neurons, and when those input signals are related in acertain way (specific to that particular neuron), it generates an electrochemical out-put signal that goes to a fixed set of neurons. It now is believed that human learningis accomplished by changes in the strengths of these signal connections betweenneurons.
Artificial neural networks are used in such applications as noise reduction (intelephones), speech recognition, and process control. For example, they can be usedfor predicting the surface finish of a workpiece obtained by end milling on the basisof input parameters such as cutting force, torque, acoustic emission, and spindle ac-celeration. Although still controversial, the opinion of many is that true artificial in-telligence will evolve only through advances in ANN.
Fuzzy Logic. An element of AI having important applications in control systemsand pattern recognition is fuzzy logic, also called fuzzy models. Introduced in 1965and based on the observation that people can make good decisions on the basis of
I 32 Chapter 39 Computer-Integrated Manufacturing Systems
imprecise and nonnumeric information, fuzzy models are mathematical means ofrepresenting vagueness and imprecise information--hence the term “fuzzy.”
These models have the ability to recognize, represent, manipulate, interpret,and utilize data and information that are vague or lack precision. Fuzzy models dealwith reasoning and decision making at a level higher than neural networks. Typical
linguistic examples are the words: few, very, more or less, small, medium, extremely,and almost all.
Fuzzy technologies and devices have been developed (and successfully applied)in areas such as robotics and motion control, image processing and machine vision,machine learning, and the design of intelligent systems. Some applications are in
(a) the automatic transmission in automobiles; (b) a washing machine that automat-ically adjusts the washing cycle for load size, type of fabric, and amount of dirt; and(c) a helicopter that obeys vocal commands to go forward, up, left, and right, and tohover and land.
39.9 Economic Considerations
The economic considerations in implementing the various computer-integrated activ-
ities described in this chapter are critical in view of the many complexities and the
high costs involved. Flexible manufacturing system installations are very capital in-
tensive; consequently, a thorough cost-benefit analysis must be conducted before a
final decision is made. This analysis should include such factors as the following:
° The cost of capital, energy, materials, and labor.° Expected markets for the products to be produced.° Anticipated fluctuations in market demand and in the type of product.° The time and effort required for installing and debugging the system.
Typically, an FMS system can take two to five years to install and at least six
months to debug. Although FMS requires few, if any, machine operators, the personnelin charge of the total operation must be trained and highly skilled. These personnel in-
clude manufacturing engineers, computer programmers, and maintenance engineers.The most effective FMS applications have been in medium-volume batch production.When a variety of parts is to be produced, FMS is suitable for production volumes of
15,000 to 35,000 aggregate parts per year. For individual parts that are of the sameconfiguration, production may reach 100,000 units per year. In contrast, high-volume,low-variety parts production is best obtained from transfer machines (dedicatedequipment, Section 37.2.4). Low-volume, high-variety parts production can bestbe done on conventional standard machinery (with or without NC) or by machiningcenters (Section 25.2).
SUMMARY
° Integrated manufacturing systems are implemented to various degrees to opti-mize operations, improve product quality, and reduce costs.
° Computer-integrated manufacturing systems have become the most importantmeans of improving productivity, responding to changing market demands, andenhancing the control of manufacturing and management functions. With the ex-
tensive use of computers and the rapid developments in sophisticated software,many aspects of manufacturing-including product designs, their analysis, andtheir simulation-are now highly detailed and thorough.
Bibliography I |33
° Advances in holonic manufacturing, just-in-time production, and communica-tions networks are all essential elements in improving productivity.
° Lean manufacturing is intended to identify and eliminate waste, leading to im-rovements in roduct ualit customer satisfaction and decreasin roduct cost.P P fl Y» » g P
° Artificial intelligence continues to create new opportunities in all aspects of man-ufacturing engineering and technology.
° Economic considerations in the design and implementation of computer-integratedmanufacturing systems, especially flexible manufacturing systems, are particularlycrucial because of the major capital expenditures required.
Rehg, ].A., Computer-Integrated Manufacturing, PrenticeHall, 1994.l, Introduction to Robotics in CIM Systems, 3rd ed.,Prentice Hall, 1997.
Russell, S., and Norvig, P., Artificial Intelligence: A ModernApproach, 2nd ed., Prentice-Hall, 2002.
Shingo, S., A Study of the Toyota Production System,Productivity Press, 1989.
Singh, N., and Rajamani, D., Cellular Manufacturing Systems:Design, Planning and Control, Chapman Sc Hall, 1996.
Vajpayee, S.I<., Principles of Computer-Integrated Manu-facturing, Prentice Hall, 1998.
I |34 Chapter 39 Computer-Integrated Manufacturing
REVIEW QUESTIONS
Systems
39.I. What is a manufacturing cell? Why was it developed?
39.2. Describe the basic principle of flexible manufacturingsystems.
39.3. Why is a flexible manufacturing system capable of
producing a wide range of lot sizes?
39.4. What are the benefits of just-in-time production? Whyis it called a pull system?
39.5. Explain the function of a local area network.
QUALITATIVE PROBLEMS
39.l2. In what ways have computers had an impact on
manufacturing? Explain.
39.l3. What advantages are there in viewing manufacturingas a system? What are the components of a manufacturingsystem?
39.l4. Discuss the benefits of computer-integrated manu-facturing operations.
39.15. Why is just-in-time production required in lean man-ufacturing?
39.l6. Would machining centers be suitable in just-in-timeproduction? Explain.
SYNTHESIS, DESIGN, AND PRO]ECTS
39.6. What are the advantages of a communications standard?
39.7. What are the differences between ring and star net-works?
39.8. Describe your understanding of holonic manufacturing.
39.9. What is Kanban? Explain.
39.l0. What is lean manufacturing?
39.lI. Describe the elements of artificial intelligence. Is
machine vision a part of it? Explain.
39.l7. Give an example of a push system and of a pullsystem. Indicate the fundamental difference between the twomethods.
39.l8. ls there a minimum to the number of machines in a
manufacturing cell? Explain.
39.|9. Are robots always a component of a FMC? Explain.
39.20. Are there any disadvantages to zero inventory?Explain.
39.2 I. Give examples in manufacturing processes and oper-
ations in which artificial intelligence could be effective.
39.22. Think of a product line for a commonly used house-hold item and design a manufacturing cell for making it.
Describe the features of the machines and equipment involved.
39.23. What types of (a) products and (b) productionmachines would not be suitable for FMC? What design or
manufacturing features make them unsuitable? Explain withexamples.
39.24. Describe your opinions concerning the voice-recognition capabilities of future machines and controls.
39.25. Can a factory ever be completely untended? Explain.
39.26. Assume that you own a manufacturing company andthat you are aware that you have not taken full advantage of
the technological advances in manufacturing. However, nowyou would like to do so, and you have the necessary capital.Describe how you would go about analyzing your company’sneeds and how you would plan to implement these technolo-gies. Consider technical as well as human aspects.
39.27. How would you describe the benefits of FMS to an
older worker in a manufacturing facility whose experiencehas been running only simple machine tools?
39.28. Artificial neural networks are particularly usefulwhere problems are ill defined and the data are vague. Giveexamples in manufacturing where artificial neural networkscan be useful.
39.29.gence systems ultimately will be able to replace the humanbrain. Do you agree? Explain.
39.30.tive. For example, observe the following closely, and identify,eliminate (when possible), or optimize the steps that producewaste in (a) preparing breakfast for a group of eight, (b) wash-ing clothes or cars, (c) using internet browsing software, and(d) studying for an exam, writing a report, or writing a termpaper.
It has been suggested by some that artificial intelli-
Evaluate a process from a lean-production perspec-
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Product Design and
in a CompetitiveEnvironment
CHA
' Manufacturing high-quality products at the lowest possible cost is critical in aglobal economy.
° This chapter discusses the many interrelated factors in product design, develop-ment, and manufacturing.
° The chapter begins with a discussion of product design and life-cycle consider-ations in design and manufacturing.
° Material and process selection, together with their effects on design and manu-facturing, are then described, followed by a discussion of the important factorsinvolved in the costs associated with a product.
° Finally, the principle of value analysis is described, along with a discussion ofhow it can help optimize manufacturing operations and minimize product cost.
40.l Introduction
In an increasingly competitive global marketplace, manufacturing high-qualityproducts at the lowest possible cost requires an understanding of the often complexrelationships among numerous factors. It was indicated throughout this text that
I. Product design and selection of materials and manufacturing processes are in-terrelated, and
2. Designs are periodically modified to,
a. Improve product performance,
b. Strive for zero-based rejection and waste,c. Make products easier and faster to manufacture,d. Consider new materials and processes that are continually being developed.
Because of the increasing variety of materials and manufacturing processesnow available, the task of producing a high-quality product by selecting the bestmaterials and the best processes, and at the same time minimizing costs, continuesto be a major challenge, as well as an opportunity. The term world class is widelyused to indicate high levels of product quality, signifying the fact that products mustmeet international standards and be marketable and acceptable worldwide. Recallalso that world-class status, like product quality, is not a fixed target for a company
4040.I Introduction I |3540.2 Product Design I |3640.3 Product Quality and Life
Expectancy I |3940.4 Life-cycle Assessment and
SustainableManufacturing I |40
40.5 Material Selection forProducts I |42
40.6 MaterialSubstitution I |46
40.1 Manufacturing ProcessCapabilities I |48
40.8 Process Selection I |5240.9 Manufacturing Costs and
Cost Reduction I |56
EXAMPLES:
40.| An Application of Designfor Manufacturing andAssembly I |39
40.2 SustainableManufacturing in theProduction of NikeAthletic Shoes I |42
40.3 Effect of WorkpieceHardness on Cost inDrilling I |46
40.4 Material Substitution inCommon Products I |48
40.5 Material Changesbetween C-SA andC-5B Military CargoAircraft I |48
40.6 Process Substitution inMaking CommonProducts I |54
40.7 Process Selection inMaking a SimplePart I |54
40.8 Manufacturing a Sheet-metal Part by DifferentMethods I |55
CASE STUDY:
40.| Automobile Tires: FromCradle-to-grave toCradle-to-cradle I |4|
|l35
l 36 Chapter 40 Product Design and Process Selection in a Competitive Environment
to reach, but rather a moi/ing target, rising to higher and higher levels as time passes(also known as continued improvement).
Although the selection of materials for products traditionally has requiredmuch experience, several databases and expert systems are now available that greatlyfacilitate the selection process that is aimed at meeting specific requirements. Also, in
reviewing the materials used in existing products (from simple hand tools to automo-biles and aircraft), there are numerous opportunities for the substitution of materialsfor improved performance and, especially, cost savings.
In the production phase, it is imperative that the capabilities of manufacturingprocesses be properly assessed as an essential guide to the ultimate selection of an
appropriate process or sequence of processes. As described throughout this book,there usually is more than one method of manufacturing a product, its components,and its subassemblies.
Increasingly important are the life-cycle assessment and life-cycle engineeringof products, services, and systems, particularly regarding their potentially adverseimpact on the environment. The major emphasis now is on sustainable manufactur-ing, with the purpose of reducing or eliminating any and all adverse effects of man-ufacturing on the environment, while still allowing a company to be profitable.
Although the economics of individual manufacturing processes has been de-
scribed throughout the book, this chapter takes a broader view and summarizes the
important overall manufacturing cost factors. It also introduces cost-reductionmethods, including value analysis, which is a powerful tool to evaluate the cost ofeach manufacturing step relative to its contribution to a product’s value.
40.2 Product Design
Those aspects which are relevant to design for manufacture and assembly (DFMA),as well as to competitive manufacturing, have been highlighted throughout variouschapters of this text. Several guidelines for the selection of materials and manufac-turing processes are given in the references listed in Table 40.1. Major advances arecontinually being made in design for manufacture and assembly, for which a num-ber of software packages are now available. Although their use requires consider-able training, these advances greatly help designers develop high-quality productswith fewer components, thus reducing production time and assembly and, conse-quently, reducing product cost.
Product Design Considerations. In addition to the design guidelines we have givenregarding individual manufacturing processes, there are general product design con-siderations. (See also robust design, Section 36.5.1.) Designers often muSt check andverify whether they have addressed considerations such as the following:
° Have all alternative designs been thoroughly investigated?° Can the design be simplified and the number of its components minimized
without adversely affecting its intended functions and performance?° Can the design be made smaller and lighter?° Are there unnecessary features in the product or some of its components, and
if so, can they be eliminated or combined with other features?° Have modular design and building-block concepts been considered for a family of
similar products and for servicing and repair, upgrading, and installing options?° Are the specified dimensional tolerances and surface finish unnecessarily tight,
thereby significantly increasing product cost, and if so, can they be relaxed with-out any adverse effects?
TABLE 40.I
Section 40.2 Product Design I |37
References bo Various Topics in This Book (Page numbers are in parentheses)
Material PropertiesTables 2.1 (57), 2.2 (59), 2.3 (62), and Figs. 2.4, 2.6, 2.7,
joining processes: Various sections in Chapters 30-32Machining: Sections in Chapters 23-24Polymers processing: Section 19.15Powder metallurgy: Section 17.6Sheet-metal forming: Section 16.13
Section 26.9 and Fig. 26.35Section 27.1 1
Section 31.8Section 32.7Section 37.1 1
Section 39.9Table 40.6 (1157) and Section 40.9
° Will the product be difficult or excessively time consuming to assemble and disas-semble for maintenance, servicing, or recycling of some or all of its components?
° 1s the use of fasteners minimized, including their quantity and variety?° Have environmental considerations been taken into account and incorporated
into product design and material and process selection?
I 38 Chapter 40 Product Design and Process Selection in a Competitive Environment
° Have green design and life-cycle engineering principles been applied, includingrecycling and cradle-to-cradle considerations?
° Can any of the design activities be outsourced?
40.2.I Product Design and Quantity of Materials
Depending on the particular product, the cost of materials can become a significantportion of the total cost. Although material costs cannot be reduced below the often-fluctuating market level, reductions can be made in the quantity of the materials usedin each of the components of a product. The wide use of available techniques, such as
minimum-weight design; design optimization; and computer-aided design, manufac-turing, and assembly, as well as the availability of vast resources on materials andtheir characteristics, have greatly facilitated design analysis, material selection andprocess, and overall optimization.
Significant reductions in the quantity of materials purchased can be achieved by
reducing the component’s volume or using materials with higher strength-to-weightor stiffness-to-weight ratios. The latter can be attained by improving and optimizingthe product design and by selecting different cross sections, such as those having a
high moment of inertia (such as I-beams and channels) or by using tubular or hollowcomponents instead of solid bars.
Implementing such design changes may, however, present significant challengesin manufacturing. Consider, for example, the following:
a. Casting or molding thin cross sections can present difficulties in die andmold filling and in meeting specified dimensional accuracy and surface finish(Section 122).
b. Forging of thin sections requires high forces, due to friction, and especially inhot forging, due to rapid chilling of tin regions (Section 14.3).
c. Impact extrusion of thin-walled parts can be difficult, especially when highdimensional accuracy and symmetry are required (Section 15 .4.1).
d. The formability of sheet metal may be reduced as sheet thickness decreases; italso can lead to buckling of the part under the high compressive stresses devel-oped in the plane of the sheet during forming (Section 16.3).
e. Machining and grinding of thin workpieces may lead to part distortion, poordimensional accuracy, and vibration and chatter (Section 26.5); consequently,advanced machining processes have to be considered (Chapter 27).
f. Welding thin sheets or slender structures can cause significant distortion due tothermal gradients developed during welding (Section 3O.10).
Conversely, making parts with thick cross sections can have their own adverseeffects. Consider, for example, the following:
a. In processes such as die casting (Section 11.4.5 ) and injection molding (Sec-
tion 19.3), the production rate can become slower because of the increasedcycle time required to allow sufficient time for the thicker regions to coolbefore removing the part from the mold.
b. Porosity can develop in thicker regions of castings, unless controlled (Fig. 10.14).
c. The bendability of sheet metals decreases as their thickness increases (Sec-
tion 16.5 ).
d. In powder metallurgy, there can be significant variations in density and, hence,properties, throughout parts with varying thicknesses (Section 17.6).
e. Welding thick sections can present problems in the quality of the welded joint(Section 30.9).
Section 40.3 Product Quality and Life Expectancy I 39
f. In die-cast parts, thinner sections will have a higher strength per unit thickness(because of the smaller grain size developed), compared with thicker sections(Section 11.4.5).
g. Processing plastic parts requires increased cycle times as their thickness orvolume increases; this is because of the longer time required for the parts tocool sufficiently to be removed from the molds (Chapter 19).
EXAMPLE 40.l An Application of Design for Manufacturing and Assembly
The redesign of the pilot’s instrument panel for a
military helicopter, built by McDonnell~Douglas, wasconsidered with a view toward reducing the numberof parts in the panel (and thus also its weight) andthe time required for its fabrication and assembly.The components of the panel consisted of sheetmetal, extrusions, and rivets.
Using DFMA software and analyzing the panelin detail, it was estimated that the redesign would leadto the following changes: (a) the number of parts, from
74 down to 9; (b) the panel Weight, from 3.00 kg to2.74 kg; (c) fabrication time, from 305 hrs to 20 hrs;(d) assembly time, from 149 hrs to 8 hours; and(e) total production time, from 697 hrs to 181 hrs. Italso was estimated that, as a result of design modifica-tions, cost savings would be 74%. Un the basis ofthese results, other components of the instrumentpanel were subjected to such analysis as well, resultingin similar savings.
40.3 Product Quality and Life Expectancy
Product quality and the techniques involved in quality assurance and control aredescribed in detail in Chapter 36. Recall that the word quality is difficult to defineprecisely, partly because it includes not only well-defined technical characteristics,but also human, and hence subjective, opinions. Generally, however, a high-qualityproduct is considered to have at least the following characteristics:
0 It satisfies the needs and expectations of the customer.° It has a pleasing appearance and handles well.° It has high reliability and functions safely over its intended life.° It is compatible with and responsive to the customer’s capabilities and working
environment.° Installation, maintenance, and future improvements are easy to perform and at
low cost.
A major priority in product quality is the concept of continuous improvement, as
exemplified by the japanese term kaizen, meaning never-ending improvement. Note,however, that the level of quality a manufacturer chooses to impart to a particular prod-uct depends on the particular market for which the product is intended. For example,low-quality, low-cost products have their own market niche, including what are com-monly referred to as dollar stores. Conversely, there always is a market for high-quality,expensive products, such as a Rolls-Royce automobile, a gold and diamond-studdedwristwatch, high-performance sports equipment, and a high-precision machine tool.
40.3.l Return on Quality
In implementing quality into products, it is important to understand the concept ofreturn on quality (ROQ), because of the following considerations:
° Quality must be viewed as an investment, because of its major influence oncustomer satisfaction.
I |40 Chapter 40 Product Design and Process Selection in a Competitive Environment
° An incremental improvement in quality vis-a-vis the additional costs involvedmust be carefully investigated.
0 There must be a certain limit on how much should be spent on qualityimprovements.
° Because quality can be rather subjective, all changes to be made must becritically evaluated.
Although customer satisfaction is a qualitative factor and is difficult to include incalculations, satisfaction is increased and customers are more likely to be retained(and become repeat customers) when there are no defects in products.
On the one hand, high-quality products do not necessarily cost more. Forexample, in industries making computer chips and computer hardware, the ROQis minimized while the aim is to approach zero defects. (See also six sigma,Section 36.7.2.) On the other hand, there are other products, such as ordinarydoor hinges, water faucets, and hubcaps, for which the additional cost involved in
eliminating the final few defects can be unnecessarily high. It also is important toconsider the fact that the relative costs involved in identifying and repairing de-fects in products grow by orders of magnitude, in accordance with the rule of ten,as shown in Table 1.5.
Life Expectancy of Products. The average life expectancies of products are givenin Tables 1.4 and 36.1. As expected, life expectancies within each group of productscan vary significantly; the variations will depend on the materials and productionprocesses employed.
Life-cycle assessment (LCA) is defined, according to the ISO 14000 standard(Section 36.6.3), as “a systematic set of procedures for compiling and examining theinputs and outputs of materials and energy, and the associated environmental im-pacts or burdens directly attributable to the functioning of a product, process, orservice system throughout its entire life cycle.” The life cycle involves consecutiveand interlinked stages of a product or a service, from the very beginning to its dis-posal or recycling, and includes the following:
a. Extraction of natural resources.
b. Processing of raw materials.
c. Manufacturing of products.
d. Transportation and distribution of the product to the customer.
e. Use, maintenance, and reuse of the product.
f. Recovery, recycling, and reuse of the components of the product, or else theirdisposal, including metalworking fluids, cleaning solvents, and various liquidsused in heat-treating and plating processes.
All of these factors are basically applicable to any type of product. Recall thateach type of product has its own metallic and nonmetallic materials, processed intoindividual components and assembled; thus, each product has its own life cycle.Moreover, la) some products, particularly those made of paper, cardboard, inexpen-sive plastic, and glass, are intentionally made to be disposable, but nonetheless arerecyclable, and (b) numerous other products are completely reusable.
Section 40.4 Life-cycle Assessment and Sustainable Manufacturing I |4l
Life-cycle Engineering. The major aim of life-cycle engineering (LCE) is toconsider reusing and recycling the components of a product, beginning with theearliest stage: product design. Life-cycle engineering is also called green designor green engineering. The considerations involved include environmental factors,optimization, and numerous technical factors regarding each component of aproduct.
Although life-cycle analysis and engineering are comprehensive and powerfultools, their implementation can be challenging, time consuming, and costly, largelybecause of uncertainties (regarding materials, processes, long-term effects, costs, etc.)in the input data and the time required to collect reliable data to properly assess theoften complex interrelationships among all the components of the whole system.Various software is being developed to expedite these analyses, particularly for thechemical and process industries, because of the higher potential for environmentaland ecological damage in their operation. Examples of such software includeFeaturePlan and Teamcenter, which runs in a ProEngineer environment.
Cradle-to-cradle Production. In examining the importance of product life-cycleconsiderations, the principles of cradle-to-grave and cradle-to-cradle productionwere described in some detail in Section 1.4. The case study that follows illustratesan application of this type of production.
CASE STUDY 40.l Automobile Tires: From Cradle-to-grave to Cradle-to-cradle
Automobiles, buses, trucks, tractors, and motorcyclesare pervasive in modern society. They are dependedon for personal transport as well as for commerce,and they bring products to markets that are accessibleto consumers.
One major environmental concern associatedwith such vehicles is caused by the need to periodicallypurchase new tires. Even though tires have surpris-ingly high wear resistance, they eventually (after about65,000 km to 100,000 km) are not suited for furthersafe operation on vehicles. Traditionally, tires havebeen removed and replaced with new ones, with thediscarded tires typically dumped in landfills. Thispractice has now become an environmental hazard asthe number of discarded tires continues to grow. Eachyear in the United States, there are around 300 milliontires discarded, mostly in landfills.
The traditional model of manufacturing a tireand taking into account its use and disposal is a classicexample of cradle-to-grave production. However, tiresdo not fit into the biological recycling paradigm, be-cause they do not readily break down into nutrientsfor organisms and thus take several decades to decom-pose in landfills. Although tires are flammable, theircombustion produces harmful gases and particulates,
making incineration an unviable option for disposal.As a result, the traditional life cycle has led to an accu-mulation of discarded tires.
The product life cycle for tires is being trans-formed by PermaLife products into a cradle-to-cradlemodel. The company takes discarded tires and pro-cesses them as follows:
° In a cryogenic freezing operation, the tire is sep-arated into its major components: rubber, andsteel and fiber reinforcement. The rubber is
subjected to a temperature below its glass-transition temperature (Section 7.2.3), which,for the type of rubber tires are made of, is
-11S°C. The steel and fiber reinforcements inthe tire are not significantly affected by thisoperation. At -115°C, the rubber becomesvery brittle, and when processed in a hammermill (shown in Fig. 17.6c), it shatters into mil-lions of small pieces.
° The rubber, in the form of small particles, is theneasily separated from the fiber or fiber mesh andthe steel reinforcements, which are then recycledseparately from the rubber.
° Colors can be added to the granulated material.
I |42 Chapter 40 Product Design and Process Selection in a Competitive Environment
The resulting artificial mulch, referred to by itstrade name of Permalife Softstuffm, has successfullybeen used as a playground material, for landscaping,and as a support material beneath artificial turf widelyused in sports stadiums around the world. From a
functional standpoint, this material can be tailored tothe particular application: (a) For playgrounds, a softmaterial can be developed with a large-size granule toprevent injury in the case of a child falling, While alsomaking its ingestion unlikely. (b) For professionalathletic competitions, the material can be made stiffer,so that the likelihood of injury is low While athleticperformance is optimized.
The major advantages of this material are asfollows:
° The material will not cause splinters or attractinsects (as opposed to natural wood mulch).
° Maintenance is less costly and more environ-mentally friendly, as opposed to natural grasssurfaces, which require fertilizer and mainte-nance for optimum performance.
° The material does not stain, as opposed to Woodor grass surfaces.
Source: Courtesy of M. Sergia and N. Menonna,Permalife, Inc.
Sustainable Manufacturing. As is now universally acknowledged, the natural re-sources on this Earth are limited, thus necessitating conservation of both materialsand energy. The concept of sustainable manufacturing emphasizes the need for con-serving resources, particularly through proper maintenance and reuse. While prof-itability is important to an organization, sustainable manufacturing is meant to meetpurposes such as (a) increasing the life cycle of products, (b) eliminating harm to theenvironment and the ecosystem, and (c) ensuring our collective Well-being, especiallythat of future generations.
EXAMPLE 40.2 Sustainable Manufacturing in the Production of Nike Athletic Shoes
Among numerousexamples from industry, the produc-tion of Nike shoes indicates the benefits of sustainablemanufacturing. These athletic shoes are assembledwith the use of adhesives. Up to around 1990, the ad-hesives used contained petroleum-based solvents,which pose health hazards to humans and contributeto petrochemical smog. The company cooperated withchemical suppliers to successfully develop a Water-based adhesive technology, now used in the majorityof shoe-assembly operations. As a result, solvent use inall manufacturing processes in Nike’s subcontractedfacilities in Asia has been greatly reduced.
Regarding another component of the shoe, therubber outsoles are made by a process that results in
significant amounts of extra rubber around the pe-riphery of the sole (called flashing, similar to the flashshown in Fig. 14.5d). With about 40 factories usingthousands of molds and producing over a million out-soles a day, flashing constitutes the largest chunk ofwaste in manufacturing the shoes. In order to reducethis waste, the company developed a technology thatgrinds the flashing into 500-um rubber powder,which is then added back into the rubber mixtureneeded to make the outsole. With this approach,waste was reduced by 40%. Moreover, it was foundthat the mixed rubber had better abrasion resistanceand durability, and its overall performance was higherthan the best premium rubber.
40.5 Material Selection for Products
ln selecting materials for a product, it is essential to have a clear understanding ofthe functional requirements for each of its individual components. The general crite-ria for selecting materials were described in Section l.5 of the General Introduction;this section will discuss them in more specific detail.
General Properties of Materials. Mechanical properties (Chapter 2) includestrength, toughness, ductility, stiffness, hardness, and resistance to fatigue, creep, and
Section 40.5 Material
impact. Physical properties (Chapter 3) include density, melting point, specific heat,thermal and electrical conductivity, thermal expansion, and magnetic properties.Chemical properties of primary concern in manufacturing are susceptibility to oxi-dation and corrosion and to the various surface-treatment processes described inChapter 34.
The following considerations are significant in the selection of materials forvarious products:
° Do the materials selected have the appropriate manufacturing characteristics?° Can some of the materials be replaced by others that are less expensive?° Do the materials under consideration have properties that meet minimum
requirements and specifications?° Are the ravv materials (also called stock) specified available in standard shapes,
dimensions, tolerances, and surface characteristics?° ls the supplier of the materials reliable? Can the materials be delivered in the re-
quired quantities vvithin the required time frame? Are there likely to be significantprice increases or fluctuations?
° Does the material present any environmental hazards or concerns?
Material selection has become easier and faster because of the increasing avail-ability of extensive computer databases that provide greater accessibility and accuracy.In order to facilitate the selection of materials, expert-system software (called smartdatabases, Section 39.8) has been developed. With the proper input of product designand functional requirements, these systems are capable of identifying appropriatematerials for a specific application, just as an expert or a team of experts Would.
Shapes of Commercially Available Materials. After selecting appropriate materials,the next step is to determine the shapes and the sizes in which these materials areavailable commercially (Table 40.2). Depending on the type of material (metal, poly-mer, ceramic, etc.) materials generally are available as castings, extrusions, forgings,powder metals, drawn rod and Wire, and rolled bars, plates, sheets, and foil.
Purchasing materials in shapes that require the least amount of additional pro-cessing obviously is an important economic consideration. Also relevant are suchcharacteristics as surface finish and quality, dimensional tolerances, straightness, andflatness. (See, e.g., Figs. 27.4, 23.13, and 23.14, and Table 11.2.) The better and the
TABLE 40.2
Shapes nf Commercially Available Materials
Material Available as
Aluminum B, F, I, P, S, T, WCeramics B, p, s, TCopper and brass B, f, I, P, s, T, WElastomers b, P, TGlass B, P, s, T, WGraphite B, P, s, T, WMagnesium B, I, P, S, T, W
Plastics B, f, P, T, W
Precious metals B, F, I, P, t, WSteels and stainless steels B, I, P, S, T, Wzine F, 1, P, W
Note: B I bar and rod; F = foil;I I ingots; P = plateand sheet; S = structural shapes; T = tubing; W = wire.Lowercase letters indicate limited availability.
Selection for Products I |43
l 44 Chapter 40 Product Design and Process Selection in a Competitive Environment
more consistent these characteristics are, the less additional processing will be re-
quired. Note, for example, that if we want to produce simple shafts with good dimen-sional accuracy, roundness, straightness, and surface finish, then we could purchaseround bars that are first turned or drawn and then centerless-ground (Fig. 2622) tothe dimensions specified. Unless the facilities in a plant have the capability of produc-ing round bars economically, it generally is cheaper to purchase them. lf we need tomake a stepped shaft (i.e., a shaft having different diameters along its length, as
shown in Fig. IV.3), we could purchase a round bar with a diameter at least equal tothe largest diameter of the stepped shaft and then turn it on a lathe or process it by
some other means in order to reduce its diameter.Each manufacturing operation produces parts that have specific shapes, surface
finishes, and dimensional accuracies. Consider the following examples:
° Castings generally have lower dimensional accuracy and a poorer surface finish
than parts made by cold forging, cold extrusion, or powder metallurgy.° Hot-rolled or hot-drawn products generally have a rougher surface finish and
larger dimensional tolerances than cold-rolled or cold-drawn products.° Extrusions have smaller cross-sectional tolerances than parts made by roll
forming of sheet metal.° Round bars machined on a lathe have a rougher surface finish than similar
bars that are ground.° The wall thickness of welded tubing is generally more uniform than that of seam-
less tubing, which is typically produced by the Mannesmann process (Fig. 13.1 8).
Manufacturing Characteristics of Materials. Manufacturing characteristics of
materials generally include castability, workability, formability, machinability, weld-ability, and hardenability by heat treatment. Raw materials have to be formed,shaped, machined, ground, fabricated, or heat treated into individual componentshaving specific shapes and dimensions; consequently, a knowledge of their manufac-turing characteristics is essential.
Recall that the quality of the raw material can greatly influence its manufac-turing properties. The following are typical examples (see also individual processes):
0 A bar with a longitudinal seam, or lap, will develop cracks during simpleupsetting and heading operations.
° Round rods with internal defects such as hard inclusions will crack duringfurther processing.
0 Porous castings will develop a poor surface finish when subsequently machined.° Parts that are nonuniformly heat treated and cold-drawn bars that are not
properly stress relieved will distort during subsequent processing.° Incoming stock that has variations in composition and microstructure cannot
be heat treated or machined consistently and uniformly.° Sheet-metal stock having variations in its cold-worked conditions will exhibit
different degrees of springback during bending and other forming operationsbecause of differences in yield stress.
° If prelubricated sheet-metal blanks are supplied with nonuniform lubricantthickness and distribution, their formability, surface finish, and overall qualityin subsequent stamping operations will be adversely affected.
Reliability of Material Supplies. There are several factors that influence the relia-bility of material supplies: shortages, strikes, geopolitical factors, and the reluctanceof suppliers to produce materials in a particular shape or quality. Even though rawmaterials may generally be available throughout a country as a whole, they may notreadily be available at a particular plant’s location.
Section 40.5 Material Selection for Products I 45
Recycling Considerations. Recycling may be relatively simple for products suchscrap metal, plastic bottles, etc.; it often requires that individual components of aproduct be taken apart and separated. Also, obviously, if much effort and time has tobe expended in doing so, recycling may become prohibitively expensive. Some generalguidelines to facilitate the process during the life cycle of a product are as follows:
° Reduce the number of parts and types of materials in products.° Reduce the variety of product models.' Use a modular design to facilitate disassembly.° For plastic parts, use single types of polymers as much as possible.° Mark plastic parts for ease of identification, as is done with plastic food con-
tainers and bottles (See Section 7.8).° Avoid using coatings, paints, and plating; instead, use molded-in colors in
plastic parts.° Avoid using adhesives, rivets, and other permanent joining methods in assem-
bly; instead, use fasteners, especially snap-in fasteners.
As an example of this type of approach to recycling, one manufacturer of laser-jetprinters reduced the number of parts in a cartridge by 32% and the variety of plasticmaterials by 55%.
Cost of Materials and Processing. Because of its processing history, the unit costof a raw material (typically, cost per unit weight) depends not only on the materialitself, but also on its shape, size, and condition. For example, because more opera-tions are involved in the production of thin wire than in that of round rod, the unitcost of the thin wire is much higher. Similarly, powder metals generally are moreexpensive than bulk metals. Furthermore, the cost of materials typically decreases as
the quantity purchased increases. Likewise, certain segments of industry (such asautomotive companies) purchase materials in very large quantities; the larger thequantity, the lower is the cost per unit weight (bulk discount).
Table 6.1 shows the cost per unit volume relative to that of carbon steel. Thebenefit of cost per volume can be seen by the following simple example: In thedesign of a steel cantilevered rectangular beam supporting a certain load at its end,a maximum deflection is specified. Using equations from handbooks, and assumingthat the weight of the beam can be neglected, we can determine an appropriatecross section of the beam. Since all dimensions are now known, the volume of thebeam can be calculated; then the cost of the beam can be determined by multiply-ing the volume by the cost of the material per unit volume. Note, on the otherhand, if the cost is given per unit weight, we first have to calculate the weight of thebeam and then determine the cost.
The cost of a particular material is subject to fluctuations caused by factors as
simple as supply and demand or as complex as geopolitics. If a product is no longer costcompetitive, alternative and less costly materials may have to be selected. For example,(a) the copper shortage in the 1940s led the U.S. government to mint pennies from zinc-plated steel, (b) when the price of copper increased substantially during the 19605, elec-trical wiring in homes was switched to aluminum; however, this substitution led to theredesign of terminals of switches and outlets in order to avoid excessive heating at thejunctions, because aluminum has a higher contact resistance than copper.
Scrap. When scrap is produced during manufacturing, as in sheet-metal fabricating,forging, and machining (Table 40.3), the value of the scrap is deducted from the ma-terial’s cost in order to obtain the net material cost. As expected, the value of thescrap depends on the type of metal and on the demand for it; typically, it is between
I I46 Chapter 40 Product Design and Process Selection in a Competitive Environment
TABLE 40.3
Approximate Percentages of Scrap Pruduced in Various Manufacturing Processes
Process Scrap (%) Process Scrap (%)
Machining 10-60 Permanent-mold casting 10
Hot forging 20-25 Powder metallurgy <5Sheet-metal forming 10-25 Rolling < 1
Hot extrusion 15
10 and 40% of the original cost of the material. Note that, in machining, scrap canbe very high, whereas operations such as rolling, ring rolling, and powder metallurgy(all of which are net- or near-net-shape processes) produce the least scrap.
EXAMPLE 40.3 Effect of Workpiece Hardness on Cost in Drilling
Gear blanks forged from 8617 alloy steel and havinga hardness range from 149 to 156 HB required thedrilling of a hole 75 mm in diameter in the hub. Theblanks were drilled with a standard helix drill. Afteronly 10 pieces, however, the drill became dull, temper-atures increased excessively, and the drilled holes haddeveloped a tough internal surface finish. In order toimprove machinability and reduce galling, the hardness
of the gear blanks was increased to range from 217 to241 HB by heating them to 840°C and then quenchingthem in oil. When blanks at this hardness level weredrilled, galling was reduced, surface finish was im-proved, drill life increased to 50 pieces, and the cost ofdrilling was reduced by 80%.
Source: ASM International.
40.6 Material Substitution
There is hardly a product on the global market today for which the substitution ofmaterials has not played a major role in helping companies maintain their competi-tive positions. Automobile and aircraft manufacturing are typical examples of majorindustries in which the substitution of materials is an ongoing activity; a similartrend is evident in sporting goods and numerous other products.
Although new products continually appear on the market, the majority of thedesign and manufacturing activities is concerned with improving existing products.There are several reasons for substituting materials in existing products:
l. Reduce the costs of materials and processing.
2. Improve manufacturing, assembly, and installation, and allow conversion toautomated assembly.
3. Improve the performance of the product, such as by reducing its weight and by
improving resistance to wear, fatigue, and corrosion.
4. Increase stiffness-to-weight and strength-to-weight ratios.
5. Reduce the need for maintenance and repair.
6. Reduce vulnerability to the unreliability of the supply of materials.
7. Improve compliance with legislation and regulations prohibiting the use of
certain materials.
Section 40.6 Material Substitution l 47
8. Improve robustness to reduce variations in performance or environmental sen-sitivity of the product.
9. Increase the ease of recycling for environmental reasons.
Substitution of Materials in the Automobile lndustry. The automobile is a goodexample of the effective substitution of materials in order to achieve one or more ofthe objectives outlined previously. Some examples of material substitution in auto-mobiles are as follows:
° Certain components of the metal body replaced with plastic or reinforced-plastic parts.
° Metal bumpers, gears, pumps, fuel tanks, housings, covers, clamps, and vari-ous other components replaced With plastics or composites.
° Carbon-steel chassis pillars replaced by TRIP or TWIP steels (see Section 5.5.6).° Metallic engine components replaced with ceramic and composites parts.° All-metal driveshafts replaced with composite-material driveshafts.° Cast-iron engine blocks changed to cast-aluminum, forged crankshafts to cast
crankshafts, and forged connecting rods to cast, powder-metallurgy, or com-posite-material connecting rods.
° Leather seats in automobiles in some luxury cars (including Mercedes) cannow be replaced (offered as an option) With synthetic materials in response toconcerns raised by advocacy groups.
Because the automobile industry is a major consumer of both metallic and non-metallic materials, there is constant competition among suppliers, particularly insteel, aluminum, and plastics. Industry engineers and management continually areinvestigating the relative advantages and limitations of these principal materials intheir applications, recycling and other environmental considerations, and relativecosts and benefits (in particular).
Substitution of Materials in the Aircraftand Aerospace Industries ! FRP structure
° Conventional aluminum alloys (par- Ummm FRP'Ta|ummum honeycomb %ticularly 2000 and 7000 series) are l--_-3 A'Um'fiUm honeycomb *F/gi'beingreplacedvvith aluminum-lithium lil Mela|'t°'meta| / Ialloys, titanium alloys, polymer- lil Tlt3nlUm'I'3Ced 0009)/Comb % Ireinforced composites, and glass- £9 % 'llllfliil'
reinforced aluminum because of the Q .\"higher strength-to-Weight ratios of ° % thesematerials.(See Example 9.-4.) K ’ X) y , J
» Forged parts are being replaced with , ` . ; wipowder-metallurgy parts that are QV ) /manufactured with better control of . 1 Qimpurities and microstructure; the Q# /QKOX; § ||||||II|v
powder-metallurgy parts also re- ¢ ‘high quire less machining and produce ff N less scrap of expensive materials. ," \‘,( A
A Illlf/ »o Advanced composite materials and 1 /I ),honeycomb structures are replacing /If G9 $1 Qtraditional aluminum airframe com- QQ .gfponents (Fig. 40.1), and metal-matrix i""'i ' ‘§'composites are replacing some of the21lL11T1iH\lfI1 éifld IIIHHIUH1 iH SfI‘LlCfl1lT3l FIGURE 40.I Advanced materials in the Lockheed C-SA transport aircraftcomponents. Note; FRP 2 fiber-reinforced plastic.
I |48 Chapter 40 Product Design and Process Selection in a Competitive Environment
EXAMPLE 40.4 Material Substitution in Common Products
In the following list, the commonly available products d. Cast-iron vs. aluminum lawn chair:can be made of either set of materials mentioned:
a. Metal vs. wooden baseball bat.
b. Metal vs. reinforced-plastic or wood handle fora hammer.
c. Plastic vs. metal intake manifold.
e. Plastic vs. sheet-metal light-switch plate.
These products are given as typical examples, and onthe basis of the topics covered in various chaptersthroughout this book, the choice of materials can bereviewed with regard to their respective advantagesand limitations.
EXAMPLE 40.5 Material Changes between C-SA and C-SB Military Cargo Aircraft
Table 40.4 shows the changes made in materials for Source: After H.B. Allison, Lockheed-Georgia.various components of the two aircraft listed and thereasons for the changes.
TABLE 40.4
Material Changes from C-SA to C-SB Military Cargo Aircraft
Item C-SA Material C-SB Material Reason for change
Process capability is the ability of a particular manufacturing process to produce,under controlled production conditions, defect-free parts within certain limits of pre-cision. (See also Section 36.8.2.) The capabilities of several manufacturing processesregarding their dimensional limits are shown in Fig. 40.2. Note, for instance, thatsand casting (Section 11.2.1) cannot produce thin parts, whereas cold rolling(Section 133) is a process capable of producing very thin materials, as evidenced by
a product such as aluminum foil.Equally important as to overall dimensions are the capabilities of various
processes to meet stringent dimensional tolerance and surface-finish requirements, asshown in Fig. 40.3. Note, for example, how sand casting is at the extreme oppositecorner of microfabrication (Chapters 28 and 29). The importance of emphasizing theterm “under controlled conditions” can be appreciated when one views the size of theenvelopes in the figure. Note, for instance, the large envelope for machining and finish-ing operations, with boundaries that span three orders of magnitude. Thus, if a turning
Section 40.7 Manufacturing Process Capabilities I 49
1 0
9 _ ___;§, My &¢5\G6“ ,,,,. S“(\Q'g 8 - h ,<\<>°”E it as ' ?' 5 Forging <St@e'l ifV 7 _ jr 5 PW +I (5\.9e\\(D 5'0“g<1> 6 ~ @\\ 03
LE 5 -
8\ N\Q)~
Cas\if\Q i/‘~‘~ C351 "Om4 - Pm
Z Foigmgk ent (Stee\)~ die Casting (Cu)_ im
3 \as\e<-mo\d»‘nf-iermosetting POIVWGVS DIG CHSUHQ (AD
-5 2 _ P Die casting (Zn)E A* I Hot rolling
1 - /'hermoplastic polymers Cold rolling
50 100 150 200 250 300Minimum dimension of web w (mm)
FIGURE 40.2 Manufacturing process capabilities for minimum part dimensions. Source: After].A. Schey.
operation is carried out on an old lathe using inappropriate tools and processingparameters, then the tolerances and surface finish will, of course, be poor.
In the sections that follow, we describe important aspects of process capabilitiesas they relate to manufacturing processes and production operations.
Dimensional Tolerances and Surface Finish. The dimensional tolerances and sur-face finish produced are particularly important in subsequent assembly operations(because of possible difficulties in fitting the parts together for assembly) and in theproper operation of machines and instruments (because their performance can affecttolerances and finish). The dimensional tolerance and surface finish typically obtainedby various manufacturing processes are illustrated qualitatively in Fig. 40.3.
Closer tolerances and better surface finish can be achieved by subsequent addi-tional finishing operations (Section 26.7), but at higher cost, as shown in Fig. 40.4.Also, the finer the surface finish required, the longer is the manufacturing time(Fig. 40.5 ). In the machining of aircraft structural members made of titanium alloys,it has been observed that as much as 60% of the cost of machining may be expendedin the final machining pass in order to maintain proper tolerances and surface finish.Thus, unless otherwise required, and with appropriate technical and economic justi-fication, parts should be made with as rough a surface finish and as wide a dimen-sional tolerance as functionally and aesthetically will be acceptable.
Production Quantity. Depending on the type of product, the production quantity(also known as lot size) varies widely. For example, bearings, bolts, spark plugs, plas-tic containers, tires, automobiles, and lawn mowers are produced in very large quan-tities, whereas jet engines, diesel engines, locomotives, and medical equipment areproduced in limited quantities. Production quantity also plays a significant role inprocess and equipment selection. In fact, an entire manufacturing discipline (calledeconomic order quantity) is devoted to mathematically determining the optimumproduction quantity.
I |50 Chapter 40 Product Design and Process Selection in a Competitive Environment
FIGURE 40.3 A plot of achievable tolerance versus surface roughness for assortedmanufacturing operations. The dashed lines indicate cost factors, where an increase in
precision corresponding to the separation of two neighboring lines gives an increase in costfor a given process (within a factor of two). Source: l\/LF. Ashby, Materials Selection in Design,Butterworth-Heineman, 1999.
17 Production Rate. An important factor in manufacturingprocess selection is the production rate, defined as the number ofpieces to be produced per unit of time, such as per hour, per day,
Q 11 or per year. The production rate obviously can be increased by2), using multiple equipment and highly automated machines.
ug Recall that processes such as die casting, powder metallurgy, deepE 5 drawing, wire drawing, and roll forming are high-production-
3 rate operations. By contrast, sand casting, conventional and elec-§ trochemical machining, metal spinning, superplastic forming,
adhesive and diffusion bondin , and the rocessin of reinforced0 0 25 0 5 0 75 g p gplastics generally are relatively slow operations.
Tolerance (mm)
Lead Time. Lead time generally is defined as the length oftime between the receipt of an order for a product and its de-FIGURE 40.4 Dependence of manufacturing cost
on dimensional tolerances. livery to the customer at a specified time. The selection of a
manufacturing process and operation is greatlyinfluenced by the time required to start produc-tion. Depending on the die’s shape complexity,size, and material, the lead time for suchprocesses as forging, extrusion, die casting, rollforming, and sheet-metal forming can range
production requirements in a very short time.Recall that machining centers, flexible manu-facturing cells, and flexible manufacturing sys-tems are all capable of responding rapidly andeffectively to product changes and to produc-tion quantities. (See also rapid prototyping,Chapter 20.)
6
Section 40.7 Manufacturing Process Capabilities I Sl
FIGURE 40.5 Relative production time as a function of surface finishproduced by various manufacturing processes. (See also Fig. 26.35 )
Robustness of Manufacturing Processes and Machinery. Robustness was de-scribed in Section 36.5 .1 as characterizing a design, a process, or a system that con-tinues to function within acceptable parameters despite variabilities in itsenvironment. In order to appreciate the importance of robustness in manufacturingprocesses, let’s briefly consider a situation in which a simple plastic gear is beingproduced by injection molding (Section 19.3), but significant and unpredictablevariations in quality arise as the gears are being produced. There are several well-understood variables and parameters in the injection molding of plastics, includingthe effects of ravv-material (such as pellets) quality, speed, and temperatures withinthe system; all these are independent variables; hence, they can be controlled.
However, there are certain other variables, called noise, that are largely be-yond the control of the operator. Among these are ambient-temperature and humid-ity variations in the plant throughout the day, dust in the air entering the plant froman open door (and thus possibly contaminating the pellets being fed into the hop-pers of the injection-molding machine), and variability in the performance of indi-vidual operators during different shifts. Obviously, these variables are difficult orimpossible to control precisely.
In order to obtain or sustain good product quality, it is necessary to understandthe effects, if any, of each element of noise in the operation. For example, (a) Whyand how does the ambient temperature affect the quality and surface characteristicsof the molded gears? (b) Why and how does the dust coating on a pellet affect its be-havior in the molding machine? (c) How different are the performances of differentoperators during different shifts, and Why are they different? and (d) Are there inher-ent variations in machine performance during the day and, if so, how and Why?
Such an investigation will make it possible to establish new operating parame-ters so that variations in, say, ambient temperature and the plant environment donot affect gear quality adversely. Note that these considerations are equally valid forany manufacturing operation, although some (such as bulk-deformation processes)are less sensitive to noise than others (especially microelectronics manufacturing).
I 52 Chapter 40 Product Design and Process Selection in a Competitive Environment
40.8 Process Selection
Process selection is intimately related to the characteristics of the materials to be
processed, as shown in Table 40.5.
Characteristics and Properties of the Workpiece Materials. Recall that some
materials can be processed at room temperature, whereas others require elevatedtemperatures-and hence furnaces, appropriate tooling, and various controls. Some
materials are easy to work with because they are soft and ductile. Other materials,such as those which are hard, brittle, and abrasive, require special processing tech-
nologies and equipment.Materials have different manufacturing characteristics, such as castability,
forgeability, workability, machinability, and weldability. Note from Table 40.5 thatfew materials have favorable characteristics in all of these relevant categories. For
example, a material that is castable or forgeable may later present difficulties in sub-
sequent processes, such as machining, grinding, and finishing, that may be requiredfor an acceptable surface finish and dimensional accuracy.
Materials have different responses to the rate of deformation (strain-rate sen-
sitivity, Sections 2.2.7 and 7.3) to which they are subjected. Thus, the speed at whicha particular machine is operated can affect product quality, including the develop-
ment of external and internal defects. Impact extrusion or drop forging, for exam-
ple, may not be appropriate for materials with high strain-rate sensitivity, whereassuch materials will perform well in a hydraulic press or in direct extrusion.
Geometric Features of the Part. Features such as part shape, size, and thickness,
dimensional tolerances, and surface-finish requirements greatly influence the selec-
tion of a process or processes, as described throughout this chapter and variousother chapters in the book.
Production Rate and Quantity. These requirements dictate process selection by
way of the productivity of a process, machine, or system. (See Section 40.7.)
Process Selection Considerations. The factors involved in process selection are
summarized by the following questions:
l. Are some or all of the parts or components that are needed commerciallyavailable as standard items?
2. Which components of the product have to be manufactured in the plant?3. Is the tooling that is required available in the plant? If not, can it be purchased
as a standard item?4. Can group technology be implemented for parts with similar geometric and
manufacturing attributes?5. Have all alternative manufacturing processes been investigated?6. Are the methods selected economical for the type of material, the part shape to
be produced, and the required production rate?7. Can the requirements for dimensional tolerances, surface finish, and product
quality be met consistently, or can they be relaxed?8. Can the part be produced to final dimensions without requiring additional
processing or finishing operations?9. Are all processing parameters optimized?
IO. Is scrap produced, and if so, is it minimized? What is the value of the scrap?
I l. Have all the automation and computer-control possibilities been explored forall phases of the total manufacturing cycle?
IZ. Are all in-line, automated inspection techniques and quality control being
l |54 Chapter 40 Product Design and Process Selection in a Competitive Environment
EXAMPLE 40.6 Process Substitution in Making Common Products
The following list gives some typical choices that canbe made in process selection for the products listed:
a. Forged vs. cast crankshaft.
b. Forged vs. powder-metallurgy connecting rod.
¢:. Sheet metal vs. Cast hubcap.
d. Machining vs. precision forming of a large gear.
e. Forging vs. powder-metallurgy production of a
spur gear:
f. Thread rolling vs. machining a threaded fastener.
g. Casting vs. stamping a metal frying pan.
h. Formed aluminum tubing vs. cast iron for out-door furniture.
i. Welding vs. mechanical fastening of machine~tool structures.
EXAMPLE 40.7 Process Selection in Making a Simple
You are asked to produce the simple axisymmetricpart shown in Fig. 40.6a; it is 125 mm long, and itslarge and small diameters are, respectively, 38 mm and25 mm. Assume that this part must be made of metalbecause of functional requirements such as strength,stiffness, hardness, wear resistance, and resistance toelevated temperatures.
Which manufacturing process would youchoose, and how would you organize the productionfacilities to manufacture a cost-competitive, high-qualityproduct? Recall that, as much as possible, parts shouldbe produced at or near their final shape (net- or near-net-shape manufacturing), under an approach thatlargely eliminates much secondary processing and thusreduces the total manufacturing time and cost. Becauseit is relatively simple, this part can be manufactured by
(a) casting or powder metallurgy, (b) forging, or upset-ting, (c) extrusion, (d) machining, or le) joinin twoseparate pieces together.
Before After
" ' " e(3) (D) (Cl
Part
For net-shape production, the two suitableprocesses are casting and powder metallurgy; each ofthese two processes has its own characteristics, needfor specific tooling, labor skill, and costs. The partcan also be made by cold, warm, or hot forming. Onemethod is upsetting (heading, Fig. 1411) a 25-mmround bar in a suitable die to form the larger end.Another possibility is partial direct extrusion of a 38-mm diameter bar to reduce its diameter to 25 mm.Note that each of these processes produces little or nomaterial waste, an important factor in green manu-facuring.
The part also can be made by machining a
38-mm-diameter bar stock to reduce the lower sec-tion to 25 mm. Machining this part will require muchmore time than forming it, and a considerable amountof material inevitably will be wasted as metal chips(Table 4O.3). However, unlike net-shape processes,which generally require special dies, machining
2 Joined (dl (9)
FIGURE 40.6 Various methods of making a simple part: (a) casting or powdermetallurgy, (b) forging or upsetting, (c) extrusion, (d) machining, and (e) joiningtwo pieces.
involves no special tooling, and this operation can becarried out easily on a CNC lathe at high rates. Notethat, alternatively, the part can be made in two sepa-rate pieces and then joined by welding, brazing, oradhesive bonding.
After these initial considerations, it appears thatif only a few parts are needed, machining this part is
the most economical method. For a high production
Section 40.8 Process Selection I |55
quantity and rate, producing the part by a headingoperation or by cold extrusion (a variation of closed-die forging, Section 15.4) would be an appropriatechoice. Finally, note that if, for some technical reason,the top and bottom portions of the part must be madeof different materials, the part can be made in twopieces, and joining them would be the most appropri-ate choice.
EXAMPLE 40.8 Manufacturing a Sheet~metal Part by Different Methods
A simple, dish-shaped part can be formed from sheetmetal by placing a round, flat piece of sheet metal be-tween a pair of male and female dies in a press and thenclosing the dies by applying a vertical force (Fig. 4O.7a).Parts like this typically are formed in such manner athigh production rates; the method is generally knownas stamping or presswor/Qing.
Assume now that the size of the part is verylarge, say, 2. m in diameter and that the lot size is only50 parts. We now have to reexamine the total opera-tion. Is it economical to manufacture a set of dies 2 rn
in diameter (which would be very costly; see Section14.7) when the total production quantity is very low?Are presses available with sufficient capacity to ac-commodate such large dies? Are there alternativemethods of manufacturing this part? Does the parthave to be made in one piece?
This part also can be made by welding smallerpieces of sheet metal, formed by other methods, asdescribed in Chapter 16. (Note that large municipalwater tanks and ships are made by this method.)Would a part manufactured by welding be acceptablefor its intended purpose in the environment in whichit will be used? Will it have the required properties
and the desired shape after welding, or will it requireadditional processing?
The part also can be made by explosive forming,as shown in Fig. 40.7b. Because of the nature of theprocess, the deformation of the material in explosiveforming takes place at a very high rate. Consequently,a series of questions has to be asked regarding thisprocess (Section 16.1 1 ):
a. ls the material capable of undergoing deforma-tion at high rates without fracture or any detri-mental effect on the final properties of theformed part?
b. Can the dimensional tolerances and surfacefinish be held within acceptable limits?
c. ls the life of the die sufficiently long, given thatthe die is subjected to the very high transientpressures generated in explosive forming?
d. Can this operation be performed in a manufac-turing plant within city limits, or should it becarried out in open country?
e. Although explosive forming has the advantageof requiring only one die, is the operationeconomical? Upper W are Expnsive
Sheet ?€¥~T{f §§ l Water "‘”a Lower die Vacuum line
(fi) (b)
FIGURE 40.1 Two methods of making a dish-shaped sheet-metal part: (a) pressworking using a male and female die and(b) explosive forming using one die only.
I 56 Chapter 40 Product Design and Process Selection in a Competitive Environment
40.9 Manufacturing Costs and Cost Reduction
The total cost of a product generally consists of material costs, tooling costs, fixedcosts, variable costs, direct-labor costs, and indirect-labor costs. As a general guide
to the costs involved, see the sections on the economics of each chapter concerningindividual groups of manufacturing processes and operations: Part II (casting),Part III (rolling, forging, extrusion, drawing, sheet-metal working, powder metallur-gy, ceramics, polymer processing); Part IV (machining, abrasive processing, ad-vanced machining); and Part VI (welding and various joining processes).
Depending on the particular company and the type of products made, differentmethods of cost accounting may be used, with methodologies of accounting proce-dures that can be complex and even controversial. Moreover, because of the manytechnical and operational factors involved, calculating individual cost factors cor-rectly can be challenging, time consuming, and not always reliable.
Costing Systems, also called cost justification, typically include the followingconsiderations: (a) intangible benefits of quality improvements and inventory reduc-tion, (b) life-cycle costs, (c) machine usage, (d) cost of purchasing machinery com-pared with that of leasing it, (e) financial risks involved in implementing highlyautomated systems, and (f) new technologies and their impact on products.Additionally, the costs to a manufacturer that are attributed directly to product lia-
bility continue to be a matter of major concern, and every product now has a built-in added cost to cover possible product liability claims. It has been estimated thatliability suits against car manufacturers in the United States add about $5 00 to theindirect cost of an automobile, and 20% of the price we pay for a ladder is attrib-uted to potential product liability costs.
Materials Costs. Some cost data on materials are given in various tables through-out this book, as also listed in Table 40.1. Because of the different operations requiredin producing raw materials, their costs depend not only on the type of material (fer-
rous, nonferrous, nonmetallic, etc.), but also on its processing history (ingot, powder,drawn rod, extrusion), as well as its size, shape, and surface characteristics. For ex-ample, per unit weight, (a) drawn round bars are less expensive than bars that are
ground to close tolerances and a fine surface finish, (b) square bars are more expen-sive than round bars, (c) cold-rolled plate is more expensive than hot-rolled plate,(d) thin wire is more expensive than thick wire, and (e) hot-rolled bars are much lessexpensive than metal powders of the same type.
Tooling Costs. Costs are involved in making the tools, dies, molds, patterns, and spe-cial jigs and fixtures required for manufacturing a product. Tooling costs can be veryhigh, but they can be justified in high-volume production, such as automotive applica-tions, where die costs can be on the order of $2 million. The expected life of tools and die,and their obsolescence because of product changes, also are important considerations.
Tooling costs are greatly influenced by the production process selected. Forexample, (a) the tooling cost of die casting is higher than that of sand casting; (b) thetooling cost of machining or grinding is much lower than that of powder metallurgy,forging, or extrusion; (c) carbide tools are more expensive than high-speed steel tools,
but their life is longer; (d) if a part is to be manufactured by spinning, the tooling cost
of conventional spinning is much lower than that of shear spinning; and (e) toolingfor rubber-forming processes is less expensive than that of the die sets (male andfemale) used for the deep drawing and stamping of sheet metals.
Fixed Costs. These costs include electric power, fuel, taxes on real estate, rent, in-
surance, and capital (including depreciation and interest). The company has to meet
Section 40.9 Manufacturing Costs and Cost Reduction I |57
fixed costs regardless of whether or not it has made a particular product; thus, fixedcosts are not sensitive to production volume.
Capital Costs. These costs represent machinery, tooling, equipment, and investmentin buildings and land. As can be seen in Table 40.6 the cost of machines and systemscan vary widely, depending on numerous factors. In view of the generally high equip-ment costs (particularly those involving transfer lines and flexible-manufacturing
TABLE 40.6
Relative Costs for Machinery and Equipment
Automatic screw machine M-HBoring mill, horizontal M-HBroaching M-HDeep drawing M-HDie casting M-HDrilling L-MElectrical-discharge machining L-MElectron-beam welding M-HExtruder, polymer L-MExtrusion press M-HFlexible manufacturing cell and system H-VHForging M-HFused deposition modeling L
Note: L = low; M 2 medium; H = high; VH = very high.Costs vary greatly, depending on size, capacity, options,and level of automation and computer controls. See alsothe sections on economics in various chapters.
I 58 Chapter 40 Product Design and Process Selection in a Competitive Environment
cells and systems), high production quantities and rates are essential to justify suchlarge expenditures, as well as to keep product costs at or below the all-importantcompetitive level. Lower unit costs (cost per piece) can be achieved by continuousproduction, involving around-the-clock operation (as long as demand warrants it).Equipment maintenance also is essential to ensure high productivity. Any break-down of machinery leading to downtime can be very costly, by as much as thou-sands of dollars per hour.
Direct-labor Costs. Direct-labor costs are for labor that is directly involved inmanufacturing products (also known as productive labor). These costs include thecosts of all labor, from the time raw materials are first handled by the worker to thetime when the product is manufactured, a period generally referred to as floor-to-floor time. Direct-labor costs are calculated by multiplying the labor rate (the hourlywage, including benefits) by the amount of time that the worker spends producingthe particular part.
The time required for producing a part depends not only on its specified size,shape, dimensional accuracy, and surface finish, but also on the workpiece materialitself. The cutting speeds for machining high-temperature alloys, for example, arelower than those for machining aluminum or plain-carbon steels. Consequently, thecost of machining aerospace materials is much higher than that of machining morecommon alloys, such as those of aluminum and steel.
Labor costs in manufacturing and assembly vary greatly from country to coun-try (see Table L4 in the General Introduction). It is not surprising that most of theproducts one purchases today are either made or assembled in countries where laborcosts are low. On the other hand, firms located in countries with high labor ratestend to emphasize high value-added manufacturing tasks or high automation levels,so the labor component of the cost is significantly reduced.
For labor-intensive industries, such as machine building, steelmaking, petro-chemicals, and chemical processing, manufacturers generally consider moving pro-duction to countries with a lower labor rate, a practice known as outsourcing. Whilethis approach can be financially attractive, the cost savings anticipated may not al-ways be realized, because of the following hidden costs associated with outsourcing:
° International shipping is far more involved and time consuming than domesticshipping. For example, it takes roughly four to six weeks for a container shipto bring a product from China to the United States or Europe, an interval thatcontinues to increase because of important homeland security issues.
° Lengthy shipping times indicate that the benefits of just-in-time manufacturingapproaches (Section 39.5 ) and their associated cost savings may not be realized.Also, because of the long shipping times, schedules are rigid, design modifica-tions cannot be made easily, and companies cannot readily address changes inthe market or in demand. Thus, companies that outsource can lose agility andmay have difficulties in following lean-manufacturing approaches.
° Legal systems are not as well established in countries with lower labor rates asthey are in other countries. Procedures that are common in the United Statesand the European Union, such as accounting audits, protection of patenteddesigns and intellectual property, and conflict resolution, are more difficult toenforce or obtain in other countries.
° Because payments typically are expected on the basis of units completed, prod-uct defect rates can be significant.
° There are various other hidden costs, such as increased paperwork and docu-mentation, lower productivity from existing employees because of lowermorale, and difficulties in communication.
Section 40.9 Manufacturing Costs and Cost Reduction I |59
Indirect-labor Costs. These costs are generated in the servicing of the total manufac-turing operation. They generally consist of the costs of such activities as supervision,maintenance, quality control, repair, engineering, research, and sales, as well as thecost of office staff. Because they do not contribute directly to the production of fin-ished parts, or they are not chargeable to a specific product, these costs are referred toas the overhead or burden rate, and are charged proportionally to all products. Thepersonnel involved in these activities are categorized as nonproductive labor.
Manufacturing Costs and Production Quantity. One of the most significant fac-tors in manufacturing costs is the production quantity. Obviously, a large produc-tion quantity requires high production rates, which, in turn, require the use ofmass-production techniques that involve special machinery (dedicated machinery)and employ proportionally less direct labor. At the other extreme, a smaller produc-tion quantity usually means a larger direct-labor involvement.
Small-batch production usually involves general-purpose machines, such aslathes, milling machines, and hydraulic presses. The equipment is versatile, andparts with different shapes and sizes can be produced by appropriate changes in thetooling. However, direct-labor costs are high because these machines usually areoperated by skilled labor.
In medium-batch production, the quantities are larger and general-purposemachines are equipped with various jigs and fixtures, or they can be computer con-trolled. To further reduce labor costs, machining centers and flexible-manufacturingsystems are important alternatives. Generally, for quantities of 100,000 or more, themachines are designed for specific purposes, and they perform a variety of specificoperations with very little direct labor involved.
Cost Reduction. Cost reduction requires a study of how the costs described previ-ously are interrelated, using relative costs as an important parameter. As we haveseen, the unit cost of a product can vary widely. For example, some parts may bemade from expensive materials, but require very little processing-as in the case ofminted gold coins. Consequently, the cost of materials relative to that of direct laboris high.
By contrast, some products may require several complex and expensive pro-duction steps to process relatively inexpensive materials, such as carbon steels. Forexample, an electric motor is made of relatively inexpensive materials, yet severaldifferent manufacturing operations are involved in the making of the housing, rotor,bearings, brushes, and various other components. Unless highly automated, assem-bly operations for such products can become a significant portion of the overall cost(Section 37.9).
A typical breakdown of the costs in modern manufacturing is as follows:
Design 5 %Material 50%Manufacturing
Direct Labor 15%Overhead 30%
In the 1960s, labor accounted for as much as 40% of the production cost; today, it canbe as low as 5%, depending on the type of product and level of automation. In theforegoing breakdown, note the very small contribution of the design phase, yet the de-sign phase generally has the largest influence on the quality and success of a productin the marketplace. The various opportunities for cost reduction have been discussed
I 60 Chapter 40 Product Design and Process Selection in a Competitive Environment
in a number of chapters throughout this book. Among these opportunities are thefollowing:
' Simplifying both part design and the number of subassemblies required.° Reducing the amount of materials used.° Specifying broader dimensional tolerances and allowing rougher surface finish° Using less expensive materials.° Investigating alternative methods of manufacturing.' Using more efficient machinery, systems, and equipment.
The introduction of more automated systems and the adoption of up-to-datetechnology in a manufacturing facility is an obvious means of reducing some costs.However, this approach must be undertaken with due care and only after a thor-ough cost-benefit analysis, which requires reliable input data and a considerationof the technical as well as the human factors involved. Advanced technologies,which can be very costly to implement, should be implemented only after a com-plete analysis of the more obvious cost factors, known as return on investment(ROI).
40.9.l Value Analysis
Manufacturing adds value to materials as they become discrete products and are
marketed. Because this value is added in individual stages during the creation of the
product, the utilization of value analysis (also called value engineering, value control,and value management) is important. Value analysis is a system that evaluates eachstep in design, material and process selection, and operations in order to manufacturea product that performs all of its intended functions and does so at the lowest possi-ble cost.
A monetary value is established for each of two product attributes: (a) usevalue, reflecting the functions of the product, and (b) esteem or prestige value,reflecting the attractiveness of the product that makes its ownership desirable. Thevalue ofa product is then defined as
Product function and performanceValue = _ (40.1)
Product cost
Thus, the goal of value analysis is to obtain maximum performance per unit cost.Value analysis generally consists of the following six phases:
l. Information phase: to gather data and determine costs.
2. Analysis phase: to define functions and identify problems as well as opportunities.
3. Creativity phase: to seek ideas in order to respond to problems and opportuni-ties without judging the value of each idea.
4. Evaluation phase: to select the ideas to be developed and identify the costsinvolved.
5. Implementation phase: to present facts, costs, and values to the company man-agement; to develop a plan and to motivate positive action, all in order to obtaina commitment of the resources necessary to accomplish the task.
6. Review phase: to reexamine the overall value-analysis process in order tomake necessary adjustments.
Value analysis is an important and all-encompassing interdisciplinary activity,usually coordinated by a value engineer and conducted jointly by designers,
manufacturing engineers, and quality-control, purchasing, and marketing personneland managers. In order for value analysis to be effective, it must have the full supportof a company’s top management. The implementation of value analysis in manufac-turing can result in such benefits as (a) significant cost reduction, (b) reduced leadtimes, (c) better product quality and performance, (d) a reduced time for manufactur-ing the product, and (e) reduced product weight and size.
An example of product weight reduction is the development of the antilockbraking system (ABS) for automotive applications. In 1989, the typical weight of aBosch brand system was 6.2 kg. In 2001, its weight was 1.8 kg, a reduction of 70%,which also helped reduce the weight of the automobile. Note that, considering thefunction of the product and the fact that weight is related to the product’s volume, re-ducing the size indicates that the ratio of surface area to volume increases.
SUMMARY
° Regardless of how well a product meets design specifications and quality stan-dards, it also must meet economic criteria in order to be competitive in the domes-tic and global marketplace. Several guidelines have been established for designingproducts for economic production.
° Important considerations in product design and manufacturing include manufac-turing characteristics of materials, product life expectancy, life-cycle engineering,and an awareness of minimizing any potential harm to our environment and theecosystem.
° Substitution of materials, modification of product design, and relaxing of dimen-sional tolerance and surface finish requirements are important methods of costreduction.
° The total cost of a product includes several elements, such as the costs of materi-als, tooling, capital, labor, and overhead. Material costs can be reduced throughcareful selection without compromising design and service requirements, func-tions, specifications, or standards for good product quality.
° Labor costs generally are becoming an increasingly smaller percentage of pro-duction costs in highly industrialized countries, but to counteract lower wages indeveloping countries, labor costs can be reduced further through highly auto-
Key Terms l I6
mated and computer-controlled manufacturing operations.
I |62 Chapter 40 Product Design and Process Selection in a Competitive Environment
BIBLIOGRAPHY
Anderson, D.M., Design for Manufacturability Sc ConcurrentEngineering, CIM Press, 2003.
Ashby, M.F., Materials Selection in Mechanical Design, 3rd ed.,Pergamon, 2005.
ASM Handbook, Vol. 20: Materials Selection and Design,ASM International, 1997.
Billatos, S., and Basaly, N., Green Technology and Design forthe Environment, Taylor 85 Francis, 1997.
Boothroyd, G., Dewhurst, P., and Knight, W, Product Designfor Manufacture and Assembly, 2nd ed., Dekker, 2001.
Bralla, ].G., Design for Manufacturability Handbook, 2nd ed.,McGraw-Hill, 1999.
Cha, ]., jardim-Goncalves, R., and Steiger-Garcao, A.,
Concurrent Engineering, Taylor Sc Francis, 2003.Dettmer, WH., Breaking the Constraints to World-Class
Performance, ASQ Quality Press, 1998.Dorrf, R.C., and Kusiak, A. (eds.), Handbook of Design,
Manufacturing and Automation, Wiley, 1995.Giudice, F., La Rosa, G., and Risitano, A., Product Design for
the Environment, CRC Press, 2006.Harper, C.A. (ed.), Handbook of Materials for Product
Design, McGraw-Hill, 2001.Hartley, ].R., and Okamoto, S., Concurrent Engineering:
Shortening Lead Times, Raising Quality, and LoweringCosts, Productivity Press, 1998.
REVIEW QUESTIONS
Hundai, M. (ed.), Mechanical Life Cycle Handbook, CRCPress, 2001.
Madu, C. (ed.), Handbook of Environmentally ConsciousManufacturing, Springer, 2001.
Magrab, E.B., Integrated Product and Process Design andDevelopment: The Product Realization Process, CRCPress, 1997.
Mangonon, P.C., The Principles of Materials Selection forDesign, Prentice Hall, 1999.
McDonough, W., and Braungart, M., Cradle to Cradle:Rethinking the Way We Make Things, North PointPress, 2002.
Poli, C., Design for Manufacturing: A Structured Approach,Butterworth-Heinemann, 2001.
Shina, S.G. (ed.), Successful Implementation of ConcurrentEngineering Products and Processes, Wiley, 1997.
Stoll, H.W., Product Design Methods and Practices, Dekker,1999.
Swift, K.G., and Booker, ].D., Process Selection: From Designto Manufacture, 2nd ed., Butterworth-Heinemann,2003.
Wenzel, H., and Hauschild, M., Environmental Assessmentof Products, Vol. 2, Springer, 1997.
Wenzel, H., Hauschild, M., and Alting, L., EnvironmentalAssessment of Products, Vol. 1, Springer, 2003.
40.l. Explain what is meant by “manufacturing properties”of materials.
40.2. Why is material substitution an important aspect ofmanufacturing engineering?
40.3. What factors are involved in the selection of manufac-turing processes? Explain why they are important.
40.4. How is production quantity significant in processselection? Explain.
40.5. List and describe the major costs involved in manu-facturing.
40.6. Explain the difference between direct-labor cost andindirect-labor cost.
40.7. Describe your understanding of the following terms:la) life expectancy, (b) life-cycle engineering, (c) sustainablemanufacturing, and (d) green manufacturing.
40.8. Is there a significant difference bewteen cradle-to-grave and cradle-to-cradle production? Explain.
40.9. How would you define value? Explain.
40.I0. What is the meaning and significance of the term“return on investment”? Explain.
QUALITATIVE PROBLEMS
40.l I. Describe the major considerations involved in select-ing materials for products.
40.l2. What is meant by manufacturing process capabili-ties? Select four different manufacturing processes and de-scribe their capabilities.
40.l3. Comment on the magnitude and range of scrapshown in Table 40.3 and the reasons for the variations.
40.|4. Explain why the value of the scrap produced in a
manufacturing process depends on the type of material andprocesses involved.
40.|5. Describe your observations concerning the informa-tion given in Table 6.1 and the reasons for those observations.
40.l6. Other than the size of the machine, what factors areinvolved in the range of prices in each machine categoryshown in Table 40.6? Explain.
40.I7. Explain how the high cost of some of the machinerylisted in Table 40.6 can be justified.
40.I8. On the basis of the topics covered in this book, ex-plain the reasons for the relative positions of the curvesshown in Fig. 40.2.
40.|9. What factors are involved in the shape of the curveshown in Fig. 40.4? Explain.
40.20. Describe the problems that may have to be faced inreducing the quantity of materials in products. Give someexamples.
40.2l. Explain the reasons that there is a strong desire inindustry to practice near-net-shape manufacturing.
Synthesis, Design, and Projects I |63
40.22. State and explain your thoughts concerning cradle-to-cradle manufacturing.40.23. List and explain the advantages and disadvantagesof outsourcing manufacturing activities to countries with lowlabor costs.
SYNTHESIS, DESIGN, AND PROJECTS
40.24. As you can see, Table 40.5 lists only metals and theiralloys. On the basis of the information given in various chap-ters in this book and in other sources, prepare a similar tablefor nonmetallic materials, including ceramics, plastics, rein-forced plastics, and both metal-matrix and ceramic-matrixcomposite materials.
40.25. Is it always desirable to purchase stock that is closeto the final dimensions of a part to be manufactured? Explainwhy or why not and give some examples.
40.26. What course of action would you take if the supply ofa raw material selected for a product line becomes unreliable?Explain.
40.27. Estimate the position of the curves for the followingprocesses in Fig. 40.5 : (a) centerless grinding, (b) electrochem-ical machining, (c) chemical milling, and (d) extrusion.40.28. Review Fig. 1.3 in the General Introduction and presentyour own thoughts concerning the two flowcharts. Would youwant to make any modifications, and if so, what would they be?
40.29. Over the years, numerous consumer products (suchas rotary-dial telephones, analog radio tuners, turntables, andvacuum tubes) have become obsolete or nearly so, whilemany new products have entered the market. Make two lists:a comprehensive list of obsolete products that you can thinkof and a list of new products. Comment on the reasons forthe changes you observe.
40.30. List and discuss the different manufacturing methodsand systems that have enabled the manufacture of new
products. (These products and systems are known as enablingtechnologies).
40.3 I. Select three different products, and make a survey ofthe changes in their prices over the past 10 years. Discuss thepossible reasons for the changes.
40.32. Describe your own thoughts concerning the replace-ment of aluminum beverage cans with cans made of steel.
40.33. Select three different products commonly found inhomes. State your opinions on (a) what materials were used ineach product, (b) why those particular materials were chosen,(c) how the products were manufactured, and (d) why thoseparticular processes were used.
40.34. Comment on the differences, if any, among the de-signs, materials, and processing and assembly methods usedfor making products such as hand tools and ladders for pro-fessional use and those for consumer use.
40.35. The cross section of a jet engine is shown in Fig. 6.1.On the basis of the topics covered in this book, select anythree individual components of such an engine and describethe materials and processes that you would use in makingthem in quantities of, say, 1000.40.36. Inspect some products around your home, and de-scribe how you would go about taking them completely apartquickly and recycling their components. Comment on their de-sign regarding the ease with which they can be disassembled.40.37. What products do you know of that would be verydifficult to disassemble for recycling purposes? Explain.
LIST OF TABLESGeneral Introdugtign 6.10 Properties and Typical Applications of Selected Wrought
Approximate Number of Parts in Products 2
Historical Development of Materials, Tools, andManufacturing Processes 3
General Manufacturing Characteristics of VariousMaterials 16
Average Life Expectancy of Various Products 30Relative Cost of Repair at Various Stages of ProductDevelopment and Sale 30Typical Cost Breakdown in Manufacturing 33
Approximate Relative Hourly Compensation for Workersin Manufacturing 34
Part I Fundamentals of Materials: Behaviorand Manufacturing Properties
Grain Sizes 48Homologous Temperature Ranges for Various Processes 52Relative Mechanical Properties of Various Materials atRoom Temperature 57Mechanical Properties of Various Materials at RoomTemperature 59
Typical Values for K and n for Metals at RoomTemperature 62Typical Ranges of Strain and Deformation Rate inManufacturing Processes 65Physical Properties of Selected Materials at RoomTemperature 89
Physical Properties of Materials 90
Outline of Heat-treatment Processes for SurfaceHardening 120Applications for Selected Carbon and Alloy SteelsTypical Mechanical Properties of Selected Carbon andAlloy Steels 139Mechanical Properties of Selected Advanced High-strengthSteels 141AISI Designations for High-strength Sheet Steel 141Mechanical Properties and Typical Applications of SelectedAnnealed Stainless Steels at Room Temperature 144Basic Types of Tool and Die Steels 145Processing and Service Characteristics of Common Tooland Die Steels 146Typical Tool and Die Materials for Metalworking 147Approximate Cost-per-unit-volume for Wrought Metalsand Plastics Relative to the Cost of Carbon Steel 152General Characteristics of Nonferrous Metals andAlloys 152Properties of Selected Aluminum Alloys at RoomTemperature 153Manufacturing Characteristics and Typical Applications ofSelected Wrought Aluminum Alloys 154Properties and Typical Forms of Selected WroughtMagnesium Alloys 157Properties and Typical Applications of Selected WroughtCopper and Brasses 159Properties and Typical Applications of Selected WroughtBronzes 159Properties and Typical Applications of Selected NickelAlloys 160Properties and Typical Applications of SelectedNickel-based Superalloys at 870"C (1600"F) 161
137
7.1
7.2
7.37.48.18.2
8.39.1
9.29.39.4
Titanium Alloys at Various Temperatures 162Range of Mechanical Properties for Various EngineeringPlastics at Room Temperature 172Glass-transition and Melting Temperatures of SomePolymers 180General Recommendations for Plastic Products 186Trade Names for Thermoplastic Polymers 186Types and General Characteristics of Ceramics 199Properties of Various Ceramics at RoomTemperature 202Properties of Various Glasses 206Types and General Characteristics of CompositeMaterials 218Typical Properties of Reinforcing Fibers 220Metal-matrix Composite Materials and Applications 228Summary of Fiber and Material Properties for anAutomotive Brake Caliper 229
Part II Metal-Casting Processes and Equipment10.1 Volumetric Solidification Contraction or Expansion for
Various Cast Metals 24811.1 Summary of Casting Processes 25911.2 General Characteristics of Casting Processes 26111.3 Properties and Typical Applications of Some Common
Die-casting Alloys 28112.1 Normal Shrinkage Allowance for Some Metals Cast in
Sand Molds 29712.2 Typical Applications for Castings and Casting
Characteristics 30412.3 Properties and Typical Applications of Cast Irons 30412.4 Mechanical Properties of Gray Cast Irons 30512.5 Properties and Typical Applications of Nonferrous
Cast Alloys 30512.6 General Cost Characteristics of Casting Processes 308
Part III Forming and Shaping Processes and EquipmentIII.1 General Characteristics of Forming and Shaping
Processes 31514.1 General Characteristics of Forging Processes 33714.2 Range of k Values for Eq. (14.2) 34114.3 Forgeability of Metals 34814.4 Typical Speed Ranges of Forging Equipment 35314.5 Comparison of Suspension Upright Designs for the Lotus
Elise Automobile 35715.1 Typical Extrusion Temperature Ranges for Various Metals
and Alloys 36516.1 General Characteristics of Sheet-metal Forming
Processes 38316.2 Important Metal Characteristics for Sheet~forming
Operations 39216.3 Minimum Bend Radius for Various Metals at Room
Temperature 39816.4 Typical Ranges of Average Normal Anisotropy, Ravg, for
Various Sheet Metals 40917.1 Compacting Pressures for Various Powders 44717.2 Sintering Temperature and Time for Various Metals 45317.3 Mechanical Properties of Selected PM Materials 45517.4 Comparison of Mechanical Properties of Some Wrought
and Equivalent PM Metals 455 _
I |78 List of Tables
17.5
17.618.1
19.1
19.2
20.1
20.2
Mechanical Property Comparisons for Ti-6AL-4V TitaniumAlloy 456Forged and PM Titanium Parts and Cost Savings 461General Characteristics of Ceramics Processing 466General Characteristics of Forming and Shaping Processesfor Plastics and Composite Materials 485Comparative Production Characteristics of VariousMolding Methods 521Characteristics of Additive Rapid-prototypingTechnologies 528Mechanical Properties of Selected Materials for RapidPrototyping 529
Part IV Machining Processes and Machine Tools21.121.2
21.3
21.4
22.122.222.3
22.4
22.5
23.1
23.223.323.423.5
23.6
23.723.8
23.923.1023.11
23.1224.1
24.224.326.1
26.2
26.3
Factors Influencing Machining Operations 559Approximate Range of Energy Requirements in CuttingOperations 571Ranges of n Values for the Taylor Eq. (21.20a) for VariousTool Materials 575Allowable Average Wear Land for Cutting Tools in VariousMachining Operations 577General Characteristics of Tool Materials 593General Characteristics of Cutting-tool Materials 5 94General Operating Characteristics of Cutting-toolMaterials 594ISO Classification of Carbide Cutting Tools Accordingto Use 599Classification of Tungsten Carbides According to
Machining Applications 600General Characteristics of Machining Processes and TypicalDimensional Tolerances 617General Recommendations for Tool Angles in Turning 619Summary of Turning Parameters and Formulas 621General Recommendations for Turning Operations 622General Recommendations for Cutting Fluids for
Machining 625Typical Capacities and Maximum Workpiece Dimensionsfor Machine Tools 627Table 635Typical Production Rates for Various MachiningOperations 635General Troubleshooting Guide for Turning Operations 638
General Capabilities of Drilling and Boring Operations 644General Recommendations for Speeds and Feeds in
Drilling 649General Troubleshooting Guide for Drilling Operations 650Summary of Peripheral Milling Parameters andFormulas 663General Recommendations for Milling Operations 670General Troubleshooting Guide for Milling Operations 670Ranges of Knoop Hardness for Various Materials andAbrasives 721
Approximate Specific-energy Requirements for Surface
Grinding 729Typical Ranges of Speeds and Feeds for AbrasiveProcesses 735
26.4
26.527.1
27.227.3
Part V
General Characteristics of Abrasive Machining Processesand Machines 736General Recommendations for Grinding Fluids 743General Characteristics of Advanced MachiningProcesses 761
General Applications of Lasers in Manufacturing 775Satellite Classification 782
Micromanufacturing and Fabricationof Microelectronic Devices
28.1 General Characteristics of Lithography Techniques 801
28.2 General Characteristics of Silicon Etching Operations 80928.3 Comparison of Etch Rates for Selected Etchants and Target
Materials 81029.1 Comparison of Micromold Manufacturing Techniques 84729.2 Comparison of Properties of Permanent-magnet
Materials 84729.3 Comparison of Nanoscale Manufacturing Techniques 856
Part VI Joining Processes and EquipmentV1.1 Comparison of Various joining Methods 86430.1 General Characteristics of Fusion-welding Processes 86630.2 Approximate Specific Energies Required to Melt a Unit
Volume of Commonly Welded Metals 871
30.3 Designations for Mild-steel Coated Electrodes 87932.1 Typical Filler Metals for Brazing Various Metals and
Alloys 92432.2 Types of Solders and Their Applications 92632.3 Typical Properties and Characteristics of Chemically
Reactive Structural Adhesives 931
32.4 General Characteristics of Adhesives 932
Part VII Surface Technology34.1 Ceramic Coatings for High-temperature Applications 989
Part VIII Common Aspects of Manufacturing36.1 Average Life Expectancy of Some Products 102236.2 Deming’s 14 Points 102436.3 Constants for Control Charts 1035
Part IX Manufacturing in a Competitive Environment37.1 History of the Automation of Manufacturing
Processes 105337.2 Approximate Annual Production Quantities 105639.1 Comparison of General Characteristics of Transfer Lines
and Flexible Manufacturing Systems (FMS) 112140.1 References to Various Topics in This Book 113740.2 Shapes of Commercially Available Materials 114340.3 Approximate Percentages of Scrap Produced in Various
Manufacturing Processes 114640.4 Material Changes from C-5A to C-5B Military Cargo
Aircraft 114840.5 General Characteristics of Manufacturing Processes for
Various Metals and Alloys 115340.6 Relative Costs for Machinery and Equipment 1157
References To Various Topics I |79
REFERENCES TO VARIOUS TOPICS(Page Numbers are in Parentheses)
Material PropertiesTables 2.1 (57), 2.2 (59), 2.3 (62), and Figs. 2.4, 2.6, 2.7, 2.8,
2.15, 2.16, 2.17, 2.29Tables 3.1 (89), 3.2 (90), and Figs. 3.1, 3.2, 3.3Tables 5.2 (139), 5.4 (141), and 5.5 (144)Tables 6.3 through 6.10 (153-162)Tables 7.1 (172), 7.2 (180), 7.3 (186)
1 hp 1 746W = 550 ft~lb/s1 l<W = 1.34 hp I 3413 BTU/hr°F = 9/5 °C + 32°C = 5/9 (°F - 32)K = °C + 273.15
778 ft-lb
I |80 List Of Examples
1.1
1.2
1.3
1.4
1.5
1.12.12.23.15.1
5.26.17.17.2
7.38.18.28.39.1
9.29.39.4
10.1
10.211.1
12,113.114.115.115.215.316.116.2
17.117.2
18.1
19.119.219.3
19.4
20.120.220.320.420.521.121.2
21.322.122.223.123.2
LIST OF EXAMPLES
Incandescent Light Bulbs 6
Baseball Bats 17
U.S. Pennies 17
Saltshaker and Pepper Mill 26Mold for Making Sunglasses Frames 28
Number of Grains in the Ball of a Ballpoint Pen 49Calculation of Ultimate Tensile Strength 63
Calculation of Modulus of Resilience from Hardness 72
Selection of Materials for Coins 96Advanced High-strength Steels in Automobiles 142Stainless Steels in Automobiles 145An All-aluminum Automobile 156
Dental and Medical Bone Cement 177Use of Electrically Conducting Polymers in RechargeableBatteries 183Materials for a Refrigerator Door Liner 189
Ceramic Knives 199Ceramic Gun Barrels 204Ceramic Ball and Roller Bearings 205Calculation of Stiffness of a Composite and LoadSupported by Fibers 225Composite Military Helmets and Body Armor 226Aluminum-matrix Composite Brake Calipers 228Composites in the Aircraft Industry 230Solidification Times for Various Shapes 248Casting of Aluminum Automotive Pistons 252Investment~cast Superalloy Components for GasTurbines 274Illustrations of Poor and Good Casting Designs 300Calculation of Roll Force and Torque in Flat Rolling 320Calculation of Forging Force in Upsetting 339Calculation of Force in Hot Extrusion 363Manufacture of Aluminum Heat Sinks 368Cold-extruded Part 369Calculation of Punch Force 385Tailor-welded Sheet Metal for AutomotiveApplications 388Hot Isostatic Pressing of a Valve Lifter 449Mobile Phone Components Produced through MetalInjection Molding 450Dimensional Changes During the Shaping of CeramicComponents 472Blown Film 491Force Required in Injection Molding 498Polymer Automotive-body Panels Shaped by VariousProcesses 514Metal-matrix Composite Brake Rotors and CylinderLiners 5 18
Functional Rapid Prototyping 526Coffeemaker Design 534Production of Second Life® Avatars 537Fuselage Fitting for Helicopters 538Casting of Plumbing Fixtures 547Relative Energies in Cutting 571Increasing Tool Life by Reducing the CuttingSpeed 5 77Effect of Cutting Speed on Material Removal 578Alloying Elements in High-speed Steel Cutting Tools 596Effects of Cutting Fluids on Machining 608Material-removal Rate and Cutting Force in Turning 625Typical Parts Made on CNC Turning Machine Tools 633
Machining of Complex Shapes 633Material-removal Rate and Torque in Drilling 648Material-removal Rate, Power, Torque, and Cutting Timein Slab Milling 664Material-removal Rate, Power Required, and Cutting Timein Face Milling 667Broaching Internal Splines 678Machining Outer Bearing Races on a Turning Center 700Forces in Surface Grinding 729Action of a Grinding Wheel 733Cycle Patterns in Cylindrical Grinding 739Grinding versus Hard Turning 742Belt Grinding of Turbine Nozzle Vanes 746Combining Laser Cutting and Punching of Sheet Metal 776Moore’s Law 806Comparison of Wet and Dry Etching 815Processing of a p-type Region in n-type Silicon 817Surface Micromachining of a Hinge 836Operation and Fabrication Sequence for a Thermal Ink-jetPrinter 843Production of Rare-earth Magnets 847Welding Speed for Different Materials 871Laser Welding of Razor Blades 881Weld Design Selection 896Roll Bonding of the U.S. Quarter 901
Heat Generated in Spot Welding 908
Resistance Welding vs. Laser-beam Welding in theCan-making Industry 912Diffusion-bonding Applications 915Soldering of Components onto a Printed CircuitBoard 929Determination of the Coefficient of Friction 960Repair of a Worn Turbine-engine Shaft by ThermalSpraying 979Applications of Laser Surface Engineering 983Ceramic Coatings for High-temperature Applications 989Length Measurements throughout History 999Coordinate-measuring Machine for Car Bodies 1010Production of Polymer Tubing 1027Increasing Quality without Increasing the Cost of a
Product 1028Calculation of Control Limits and Standard Deviation 1037Historical Origin of Numerical Control 1061Special Applications of Sensors 1080Simulation of Plant-scale Manufacturing 1107Manufacturing Cells in a Small Machine Shop 1119Flexible Manufacturing Systems in Large and SmallCompanies 1122An Application of Design for Manufacturing andAssembly 1139Sustainable Manufacturing in the Production of NikeAthletic Shoes 1142Effect of Workpiece Hardness on Cost in Drilling 1146Material Substitution in Common Products 1148Material Changes between C-5A and C-5B Military CargoAircraft 1148Process Substitution in Making CommonProducts 1154Process Selection in Making a Simple Part 1154Manufacturing a Sheet-metal Part by DifferentMethods 1155