21st Century Manufacturing Episode 13 ppsx

8.7.8.1 Boothroyd and Dewhurst Method The Boothroyd and Dewhurst evaluation method assigns scores to the followingtasks: • Parts count: this is simply counted, and where possible design

• Have screws and other fasteners been minimized and reduced to snap fits?

• Can everything be duneinallautomatic assembly machine?

• Can a base part, base plate, or central axle be used, to which everything elsecan be assembled? This helps to orient everything toward a central assemblytheme

• Are subassemblies modular?

• Has group technology been used for the next part in the assembly process?

• Is the greatest value-adding task performed last? This is an important point incase something is damaged at the last minute

• Has the required assembly dexterity been minimized?

8.7.7 Design Checklist for Welding, Brazing, Soldering,

con-"micromelting/casting" needs to be done in a protective atmosphere; otherwise, theoxygen in the air forms local oxide deposits that damage the metallurgical integritythis atmosphere as it decomposes in the heat, thereby generating a covering shield

of inert gases

Brazing and soldering: A filler material is locally melted with a "soldering iron" (forsoldered joints) or a flame (for a brazing operation) and made to flow between thebut when the filler material resolidifies, a solid-state bond is created between eachsurface and the filler material The filler material may be conventional electricalsolder (tin-lead alloys) or brazing compound (silver or copper alloys) Brazing gives

a higher strength than soldering

Gluing methods: Epoxy resins and acrylic glues provide a chemical bond between thetwo surfaces to be joined Clean surfaces devoid of grease and as much oxide as pos-sible are the ideal conditions Nevertheless, the bonds created are significantly lowerare often susceptible over time to the ultraviolet rays in natural light.Jt is unwise todepend on a glued joint for long-term service

During CAD, designers aim to create component geometries that enhance thestructural integrity of a formed joint Figure 8.20 shows some recommended jointstream manufacturing," the accessibility of a manually operated welding torch or

"spot-welding robot" should be considered For example, on an automobile assemblyline, the welding operations inside a car's trunk are done in tight quarters The orig-

Not recommended Recommended

Flgure 8.20 An example of designguides for soldering anrt hn17ing

processes (from Design Manufacturability Handbook edited by

1 G Bralla, © 1998 Reprinted bypermission of the McGraw-HillCompanies.)

inal designer, the process planners, and the Iixturing engineers aU playa role inmaking the process easy or hard to execute, which in turn affects the resulting quality

is a main recommendation

8.7.8 Formal Methods of Scoring Assemblies

Formal schemes are now being used by corporations-Chrysler and Compaq are twonotables-in a variety of industries to quantify the preceding lists as much as pos-sible Obviously, the best practices for all companies should increasingly includethese assembly evaluations

8.7.8.1 Boothroyd and Dewhurst Method

The Boothroyd and Dewhurst evaluation method assigns scores to the followingtasks:

• Parts count: this is simply counted, and where possible design changes are

made to reduce the number of parts

• Symmetry: axial symmetry is preferred and given the highest ranking.

• Size of parts: medium-sized parts that can be picked up easily by humans are

given the highest ranking Small read-write heads would be given a lowranking because they require stereomicroscopes and tweezers for assembly

Heavy parts that might need hoists or human amplifiers to pick them up wouldalso get a low ranking.

• Shapes: smooth shapes that avoid tangling are given a high ranking

• Quanta of difficulty: finally, additional penalties are given to parts that are in

any way awkward, slippery, or easily damaged One way of calculating thisranking is to measure the time and level of skill needed to complete the task

8.7.8.2 Xerox Corporation

The Xerox scoring method is similar to that of Boothroyd and Dewhurst tive scores are given in the following areas:

Quantita-• Parts count (as before)

• Direction of assembly motion (as shown in Figure 8.19)

• Flxturing needs at each setup

• Fastening methods, with snap fits preferred over screws or joining methods8.7.9Maintaining a System Perspeetiv& Closing Thoughts

In the design and prototyping of the ST Microelectronics' 'IouctsChtptv (the casestudy in Chapter 2) several DFMlDFA strategies were employed For example, snapaluminum molds more expensive to machine and more expensive to operate because

of the undercuts needed Thus, as a word of caution, the design team should certainlylook at the "big picture." For the first run of 200 parts, it might not be worth the cost

of the snap fit But for millions of production parts, the extra time taken to machinethe molds and also to operate the cores for the undercuts during molding will prob-ably payoff in "downstream assembly costs."

This section concludes with an interesting success story (Prentice, 1997) from

an extended "learning organization." During the redesign of a rather ordinaryportable stereo, the question arose, What size should the outside plastic casing be?analysis, a great benefit was gained by adjusting the size so that a certain number ofadjusting the size of an individual stereo it was possible to fit a greater number intowhat because the perfect tightness of fit prevented the cargo from shifting andbecoming damaged It is perhaps unusual to be able to adjust a design based on aconstraint so far away in the logistical chain, but the example does challenge an indi-vidual design engineer to think as broadly as possible in a learning organization.8.8 MANAGEMENT OF TECHNOLOGY

8.8.1 Integrated Product and Process Design

Economic pressures, particularly related to the quality of manufactured goods andtime-to-market, are forcing designers to think not only in terms ofproduct design butalso in terms ofintegrated product and process design and, finaUy,in terms of deter-

As a result of these three high-level needs, there is nowan even greater needfur comprehensive models-c-of the type introduced in Chapters 7 and 8-that pre-dict material behavior during a manufacturing process, the stresses and/or tempera-tures on associated tooling, and the final product integrity The overall goal is toenrich a CAD/CAM environment with:

• Physically accurate finite element analyses (PEA) and visualizations of themanufacturing process

• Access to process planning modules that allow detailed cost estimatesFor the polymer materials and moldmaking that have been the focus of this chapter,CAD/CAM-related URLs are given in Section 8.12

8.8.2 Databases and Expert Systems

In addition to the FEA methods in manufacturing, expert systems(Barr and baum, 1981) continue to be valuable Expert systems formulate solutions to manu-facturing concerns that cannot be solved directly with quantitative analysis Since theearly 1980s they have been useful in a wide variety of scheduling problems (seeAdiga, 1993) Expertise is gathered by the formal questioning and recording processknown asknowledge engineering.In this approach, engineers work with factory-floorpersonnel to compile records, taperecordings, and videotapes These build up a qual-itative model of the approaches needed for problem solving,

Feigen-When carried out within a learning organization (see Chapter 2), it has beenfound that factory personnel and machinists react favorably to this approach-doc-umenting the kinds of problems that often arise with production machinery and, sim-ilarly, documenting setup andmonitoring procedures for individual machine tools(Wright and Bourne 1988) In the best situations the personnel are even flatteredthat theirskills are valued and worth capturing for subsequent generations The rulesand qualitative knowledge of the experts are written down as a series of rules of theform "If then "The qualitative parameters in these fields might be nonquanti-tative datasuch as colors or approximate percentages

In other situations where manufacturing data is morequantitative, conventionalrelational databases or object-oriented databases are more useful (see Kamath, Pratt,and Mize, 1995) At a high level, such databases might describe the corporate history,meaning a history of the typical products, batch sizes, and general capabilities of thefinn At a more medium level of abstraction, particular capabilities of the factory-floormachinery might be described, with achievable tolerances, operational costs, and avail-ability At the lowest level, the databases might contain carefully documented proce-dures for lithography and etching times, In any industry, the immediate availability ofaccurate manufacturing parameters for machinery setup and diagnosis is very valu-able, Such databases also facilitate incorporation of DFA and DFM data structures.PDES/STEP has emerged as a worldwide scheme for developing a conunoninformational framework for suchdatabases andCAD/CAM systems Its goal is toensure that information on products and processes among different companies iscompatible Now that so many large firms rely on subcontractors and outside sup-pliers to create their supply chain, the need for a common interchange format is more

8.8.3Economics of Large·Scale Manufacturing

Economically, the aims are to ensure a high-quality product and to reduce marketbyeliminating ambiguities and "rework" during CAM (Richmond, 1995).For example-as reportedbyHalpern (1998)-Grundig states that the dies for thefront and back of its television casings cost approximately $300,000 each Theaverage cost to make a single change to one of these is typically 10% of the originaldie cost, or $30,000 Evidently, integrated CAD/CAM systems of the type described

time-to-at the end of Chapter 6 are very important software tools for minimizing such reworkduring mold design, fabrication, and tryout

Most large-scale manufacturing operations (in either metal or plastic) are by

definition mature technologies that are well along the market adoption curve inChapter 2 But customers deliberately choose these mature technologies becausethey are tried and true, giving reliable, predictable results These basic processes inthermoforming-may not have the glamour of stereollthography or selective lasersintering, but they remain central to many major industries and to the economy as

a whole

Nevertheless, to compete in global markets, all companies in these fieldsmust apply creative methods and innovations These clearly include newCAD/CAM techniques that reduce time-to-market, the use of sensor-basedautomation at the shop-floor level to reduce labor costs, and quality assuranceufacturing flows will need to be broken down into modular segments Garmentproducers have considered such a change in order to address the custom tailoring

market The Economist (2000) argues that traditional manufacturers may wellhave to follow this example

In these polymers, additional elements link one chain to another The best example

is the use of sulfur to cross-link elastomers to create automobile tires

With mechanical processing, such as extrusion or rolling, polymer chains can befolded into explicit structures to give the material more stiffness

8.9.5Design for Assembly

Design for assembly involves reducing the number of components, keeping thequality of the components high so that they can be easily assembled, simplifying fac-tory layout so that individual subcomponents come together easily, and ensuring that

as many operations as possible can be done in a vertical direction Vertical directionsare shown in Figure 8.17

8.9.6Design Guides

A variety of heuristics that have been developed over time to aid the mapping from

a part design to a mold design Frequently a design guide relates to the elimination

of sink and distortions

8.9.7 Gate

The entrance to the mold cavity

8.9.8Glass Transftion Temperature

The glass transition temperature is approximately halfway between the glass plateauand the leathery plateau shown in Figure 8.1 Also, by extrapolating the two curvesshown in Figure 8.2, the glass transition temperature is the intersection of glassybehavior and viscous behavior

8.9.11 Index of Strain-Hardening Sensitivity

Shown in Section 8.6, the strain-hardening sensitivity relates to the amount ofstrength increase with a given strain

8.9.12 Index of lime Sensitivity

Shown in Section 8.6, the time sensitivity is the relaxation-related property of thematerial at a given temperature

8.9.13 Injection Molding

Injection of plastic into a cavity of desired shape The plastic is then cooled andejected in its final form Most consumer products such as telephones, computer cas-ings, and CD players are injection molded

8.9.14 Packing

The phase of injection molding where the ram holds the liquid mold at pressure.During this phase, approximately 10% more polymer is pumped into the mold cavity.8.9.15 Parlson

The dangling tube of plastic that is extruded into a heated mold for blow molding It

is subsequently pinched off at one end and inflated at the other during blow molding.8.9.16 Parting Plane

The separation plane of the two mold halves

8.9.17 Reciprocating-Screw Machine

The most used injection molding machine in industry: it combines the screwingaction for the plasticization process and a ramming action for the injection process.8.9.18 Runners

In a multipart mold, the runners extend from the sprue to the individual gates of each part.8.9.19 Shrinkage

The amount of volume contraction of a polymer Usually this is 1 % t02% given thereciprocating-screw process

8.9.23 Thermoplastic Polymers

Polymers that undergo reversible changes between the glassy, leathery, viscous,

Altos, CA: William Kaufmann.

Beitz,w.,and K Grote, 1997 Dubbe! tascnenoucn fUr den mascninenbau {Pocket book for mechanical engineering). Berlin: Springer-Verlag

Boothroyd, G., and P Dewhurst 1983 Design and assembly handbook. Amherst: University

Bralla,1 G., ed 1998 Design for manufacturabillty handbook, 2d ed New York: McGraw-HilI.Dewhurst, P., and G Boothroyd 1987 Design for assembly in action Assembly Engineering

Economist: 2000 All yours (April1): 57-58

GE Plastics 2000 GE engineering thermoplastics design guide Pittsfield, MA: General tric Company Also see bttp:l/www.~pla8tics.com

Elec-Glanvill,A B., and E N Denton 1965 Injection mold design fundamentals. New York: trial Press

Indus-Halpern, M 1998 Pushingthe design envelope with CAE Mechanical Engineering Magazine,

759-768.Also seebttp:llwww.okstate.edulcodm,

Magrab, E B 1997 Integrated product and process design and development. Boca Raton and

McCrum, N G., C P Buckley, and C B BucknalJ 1997 Principles of polymer engineering.

Oxford and New York: Oxford Science Publications

Mcloughlin, 1 R., and A V Tobolsky 1952 The viscoelastic behavior of methacrylate Journal of Colloidal Science 7: 555-568.

polymethyl-Niebel, B W.,A B Draper, and R.A Wysk.1989 Modern manufacturing process engineering.

New York: McGraw-Hill

Prentice, 8.1977 Re-engineering the logistics of grain handling:The container revolution In

Managing enterprises: Stakeholders, engineering, logistics, and achievement, 297-305 London:Mechanical Engineering Publications Limited

Pye, R G W 1983 Injection mold design London: Godwin

Richmond, 0.1995 Concurrent design of products and their manufacturing processes basedupon models of evolving physicoeconomic state In Simulation of mate rials processing: Theory, methods, and applications, editedby Shen and Dawson, 153-155 Rotterdam: Balkema

Vrabe, K., and P K.Wright. 1997 Partingdirections and partingplanes for the CAD/CAM ofplastic injection molds Paperpresented at the ASMEDesign Technical Conference, Sacra-rnento,CA

Wright,P K.,and D A Boume.1988 Manufacturing intelligence Reading,MA:Addison Wesley

8." BIBLIOGRAPHY

Modern Plastics Encyclopedia. New York.: McGraw-Hill Published annually

8.'2 URLS OF INTEREST

For mold design: www.cmold.com

General design withpolymers: www.IDESINC.com

Bayer polymers division: http://www.bayerus.comfpolymersl

Magics: http://www.materialise.comf

GE plastics: http://www.ge.comlplasticsl

Society of Plastics Engineers: http://www.4spe.orgi

Trading networks: www.iprocure.com, www.memx.com, andwww.commerceone.com

8.'3 CASE STUDY ON ASSEMBLY

This case study invites the reader to think about how much investment in tion is needed to assemble a product Batch size is a main consideration Productrevision is another: if designs change quickly, it may be difficult to justify automation

automa-if low-cost labor is available

Referring to Figure 2.6, one helpful guide is to consider whether a company'scurrent and future products and typical batch sizes are suited to (a) manual assembly,(b) human-assisted computerized assembly, (c) flexible robotic assembly, or (d) hardautomation withless need for reprogrammability,

Manual assembly:This type of craftsmanship will dominate for one-of-a-kindmachining/assembly of the kind seen in a university or the (R&D) model shop of a com-

pany.At the same time, manual assembly is likely to be the best choice for high-volumeclothing and shoe manufacture Since styles change quickly, the economics favor the use

of intensely human assembly in countries that offer low wage rates For example, shoemanufacturing in such countries is likely to be done more or less entirely by hand, bypeople sitting at simple gluing and sewing machines,or standing at simple transfer lines.3

Human-assisted computerized assembly: This is typically seen in U.S., Japanese, and

other internal finishes on the car In this work, human dexterity is needed to fully manipulate subcomponents into their proper places This situation describesmore of a middle ground of automation The ClM system is installed to orchestrate

care-the line flow and care-the delivery of subcomponents, but human workers are very much

(PCB) assembly firms, many of which are subcontractors to the brand-name puter companies These are the new service industries for the computer industry,flow lines, but a noticeable amount of human interaction is needed to load machines,monitor progress, and step in if there is a problem The economics in this industryseems to justify U.S.-based assembly operations, perhaps because the batch sizes aresmaller and communications between design and subcontractors are enhanced byproximity These speciality PCB assembly firms are also able to buy large quantities

com-of electronic devices in bulk and thus achieve economies com-of scale

Flexible robotic assembly: Further along the spectrum, all the leading automobile

com-panies in the United States and Japan have installed medium-cost robots and ClM tems to spot-weld and paint cars The large batch sizes, heavy and/or unpleasant tasks,and a willingness to invest for the long haul have justified the investment in elM Atour of today's standard automobile line reveals that almost no shop personnel areever, that a great deal of personnel are needed to participate in final assembly.)

sys-Hard automation: In Chapter 2 it was emphasized that for extremely large batch sizes,

it might even be economical to revert to noncomputerized machines Speaking veyor lines pump out the same product day in, day out As stated, this is often referred

collo-to as fixed or hard aucollo-tomation In such faccollo-tories, some basic computer controls andsensors are needed for monitoring and control, but reprogramming is not needed.Chapter 6 reviewed the increasing miniaturization of disc-drive componentsand how difficult it is becoming to assemble them by hand with microscopes andtweezers What are the considerations for automation? In the final analysis, willautomating disc-drive assembly payoff? The batch sizes are large, but are they largesufficient reliability Perhaps it is not worth risking a huge investment in automated

3U is a disheartening fact, but in today's civilization, some people are pleased to leave a rural ronment (0 earn only $100 a month in an industrial setting, while others spend more than $100 at a shop-ping center on the purchase of just one pair of running shoes

envi-assembly systems Whether this will always be true though, especially as componentsbecome even more miniaturized, remainsto be seen.

To summarize, there is no question that an appropriate investment inelMtems is important for U.S and European firms For large batches unattended elMsystems are the only way foru.s.and European firms to compete globally Research

sys-in this area to develop more agile systems is vital (see Hollis and Quaid, 1995) ever, in cases where batch sizes are low and product designs change frequently,assembly may still be subcontracted to countries where labor costs are low Finally,there are the intermediate cases where human-assisted low-costelMsystems are theappr.-ariate solution for both high-wage and low-wage operations

How-In summary, while this might seem a frustratingly vague conclusion to animportant topic, it is best left open because each case is special and warrants prudentanalysis By contrast, in the period around 1980, theu.s.research community andU.S industry were not so prudent and were enthralled with the potential of robotics.Over time it has been more useful to think about robotics and automation with a dif-ferent (although overlapping) emphasis:

• Robotics should encompass autonomous systems that emulate human

capa-bilities and allow exploration or operation in environments that are too ardous, tiring, or inappropriate for humans

haz-• Automation of factories should be analyzed strictly in context and provide an

economic solution This may range from intensely manual assembly through aspectrum of part-humanipart-robotic elM systems to hard automation.8.14 INTERACTIVE FURTHER WORK

Visit the Metalcast Website and consider the following;

L Find information on five different prototyping methods used to create the tial molds and describe, with diagrams where possible, the methods

ini-2 Make a table that lists the shrink rates for the following popular plastic rials: Allied Signal Capron, 8267 nylon, Amoco Polypropylene, Chevron(Poly)Styrene, Dow ABS, GE Lexan FL-4W, Hoecht acetal, and Santoprenerubbers

mate-3 After clicking on "Data Exchange," list the six file formats that Metalcast canreceive from customers

4 View "Past Exhibits" and "Lost Core Manifold."

8.15 REVIEW MATERIAL

1 Based on the work of Kienzle, which became the German standard DIN 8580,manufacturing processes can be described in a two-dimensional taxonomy orframework (see Beitz and Grote, 1997) Six major groups arc shown in Figure8.21: (a) primary shaping, (b) forming (based on deformation), (c) dividing/sep-arating, (d) bonding, (e) coating, and (f) changing of material properties As areview activity for Chapters 2, 7, and 8, list five processing operations for each

2 The alternative Figure 8.22 shows an "ongoing three-dimensional taxonomy"that also includes rapid prototyping methods Also, revisit the MAS and notethat there are 20 manufacturing processes listed there.

3 As a review activity, using pens of different colors if needed, write on Figure 8.22diagram to include all the other processes SLA and SLS are done already Castingand machining are perhaps done, but rethink the various types of machining andcasting to make sure they fit OK It might be interesting to add another layerabove the diagram for the bulk shaping methods of forging and so forth

Coberenc:e

Maintain I Reduce

(2) Bulk I(3) Divi~inglI(4) Bondingforming separating(1) Primary

shaping (6) Changes to material properties by. (5) Coating

Laser drilling Machining

(holes)

FDM

3D printSLA

SLS

VolumesLayer b)

layerPoint bj

Biotechnology is defined for this book as the "utilization of biological processes

to manufacture a desired product." However the biotechnology industry draws on acumulative base of scientific knowledge from a number of disciplines, includingmath,physics, chemistry, and biology Thus,it may not be realistic to be too pedanticabout definitions

The biological techniques used in the biotechnology industry include nant DNA, cell fusion, and advanced processing techniques to grow or modify livingorganisms in order to produce useful products or processes Since a recombinantgene was first used to clone human insulin in the 1970s,biotechnology has grown into

recombi-a multibillion-dollrecombi-ar international industry Along with microelectronics and puters, biotechnology is one of today's most technology-intensive industries.Biotechnology and bioengineering! could be considered the "fifth pillar" of the engi-neering world, joining civil, mechanical, chemical, and electrical engineering

com-'How dobioengineering and biomedical engineering differ from biotechnology? Bioengineering

could be defined as "the utilization of engineering analysis tools for the design and fabrication of devicesneering"-a1so refer to Berger, Goldsmith, and Lewis (1996) Biomedical engineering could have a sim-ilar definition to that of bioengineering However, it can he extended to include medical monitoringequipment and drug delivery systems The considerable overlap between these three fields reemphasizesthe caution concel1lUlj overly pedantic definitions

Biotechnology is now an international business, but its roots can be traced tothe San Francisco Bay Area In the early 1970s,research ongene splicingandcloning,

conducted at the University of California at San Francisco (UCSF) and at StanfordUniversity, provided the basis for the creation of companies such as Genentech andChiron as well as a plethora of smaller companies

Colloquially described by the shortened word biotech, these industries

expanded dramatically during the 19808.Today's picture is that of a well-establishedworldwide industry looking for life sciences graduates, facility engineers, processdevelopment experts, information systems experts, and product support personnel.The industry is hiring people with management, manufacturing, and marketingskills as well as technical skills and experience in the biological sciences Venture cap-knowledge of biotech products and processes

There are also emerging prospects for the synergy of biotech and electronics

As an example, the genetic information for many bacteria has now been stored oninexpensive memory chips, and such information is of great importance Suchmemory chips are useful in recombinant DNA procedures, gene cloning, and manu-facturing (Campbell, 1998)

9.2 MODERN PRACTICE OF AN ANCIENT ART

Despite all the hype, biotechnology is nothing new Over 10,000 years ago, inSumeria, Babylon, and Egypt, yeast (a single-celled organism) was used to carry outone of the most fundamental industrial bioprocesses (fermentation) for the produc-continued to grow Besides alcohol, yeast was found to be useful for making bread.and selective breeding to grow bigger crops and fatter livestock

Also, in the 1850s,Louis Pasteur showed that microorganisms could be killed by theapplication of controlled heat Such use of controlled heat became known as pasteuriza-work his controlled processes were used to kill damaging microorganisms attacking silk-France, and perhaps he can be regarded as one of the founders of modem biotechnologyunderstood how to transfer the results from experimental science into industrial productsand quickly "crossed the chasm" described in Chapter 2 (Figure 2.3)

In recent decades, the understanding of cellular and molecular biology hasadvanced to a remarkable degree This new knowledge is opening a wide range ofcommercial opportunities as well as exciting possibilities for resolving many oftoday's great problems The most widely visible applications are in the medical arena.Research in molecular and cell biology has played a critical role in the ability torosis, and other diseases The tools and techniques of molecular biology have made

it easier to diagnose or even anticipate an individual's risk of contracting specific eases Biotechnology researchers have synthesized products such as insulin and

dis-Inaddition to these medical advances, biotechnology has played a rolein igating environmental problems and increasing global food supplies Thus, beyondhealth care, biotechnology is creating tools and applications in such wide rangingfields as agriculture, genetics, energy, and environmental science.

mit-Bioengineers have invented biodegradable plastics, organic pesticides, andmicroorganismsthat break down oiland chemical spills.Improvements incroppro-ductivity and resistance to disease will eventually help feedand clothe an increasinglypopulated world And while it failed to impress the jury in the O 1 Simpson trial,

and reprinted from An Introduction to Genetic

Engineering by Desmond S T Nicholl, © 1994;reprinted with the permission of CambridgeUniversity Press),Inthetopsketch,fertilizedeggs were ftrsl removed from a female In thesecond skel:ch,DNA carrying MGH-a fusion

of the mouse genetic information to the ratgrowth hormone-e-wes injected into the eggsThe eggs were then implanted In a fosteroffspring expresses the MGH construct thatis.the offspring is MGH+-and grows to anabnonnalsize

Implant into

foster mother

MGH