21st Century Manufacturing Episode 1 Part 7 pdf

start-up company needing a modest CAD environment would also be wise to investin these products, which include but are not limited to: • AutoCAD commercially available from • SolidWorks

start-up company needing a modest CAD environment would also be wise to invest

in these products, which include but are not limited to:

• AutoCAD commercially available from <www.autodesk.com>

• SolidWorks commercially available from <www.solidworks.com>

• IronCAD commercially available from <www.ironcad.com>

3.12.3 Systems with "'High Overhead"

The next group of products have been built to do high-end solid modeling with real-means that objects are initially created generically without specific dimensions scales up or down to suit The user is able to define constraints between different parts of an object and then scale them

For long-term company growth over several product variants this has enor-mous appeal However, there is a major drawback There is a huge learning time for such systems Also, since they are updated every 18 months or so, further retraining

on new "revs" is likely

These are powerful design tools for a large automobile company or a national laboratory In these environments, many similar components in a family are being designed Their use in a bearing-manufacturing company like TImken Inc is perhaps the easiest to visualize Bore sizes, races, cover plates, and the like, can be created once and then "scaled up or down." For future revisions of a component, any existing parametric designs that might reside in a software library can quickly be reinstanti-ated to create a new object in the same family

These larger systems also have direct links to supplementary packages that will doDFM/A and finite-element analysis Most of them also include a CORBA-based open architecture that allows linking to other software applications (e.g., SDRC, 1996)

• ProEngineer commercially available from <www.ptc.com>

• IDEAS commercially available from <www.sdrc.com>

• Unigraphics commercially available from <www.ugsolutions.com>

• CATIA commercially available from <www.catia.com>

Translations between these different commercial CAD systems were once done with initial graphics exchange system (IGES) and can now be done with product defini-tion exchange system (PDES/STEP) PDESISTEP is evolving into a useful world-wide standard (see ISU, lY/:iY,lYY3)

Other products such as Spatial Technology's ACIS (ACIS, 1993) play an inter-mediate role compared with the aforementioned applications They have specialized

in the "market niche" of creating an open de facto standard for solid representations This is finding adoptions in other systems, including AutoCAD The openness of ACIS is popular with the research community From a management of technology

3.12.4Current Trends in CAD

The CAD field is developing very quickly indeed At the time of this writing, "stu-for only $100 Thus, even these more sophisticated systems are becoming more readily available to the average user and are able to run on modest computer sys-tems in the $1,500to $3,000price range for a well-configured environment This still does not mean an end user should "jump right in" and use them The big issues-dis-cussed above-are the "learning curve" and the "library creation for parametric sys-tems." These trade-offs are captured in Figure 3.32 On the other hand, used in a nonparametric way, these higher end packages can create excellent feature-based models The governing factor seems to "boil down" to how much long-term interest

a person or group has in using CAD tools Here are three scenarios:

• For a start-up company, where a CAD system might be used only once to gen-erate an idea and then an FDM prototype, the cheaper nonparametric approach is recommended

• Also in small, newer companies, today's evidence is that the turnover among young engineers is high It might not be worth investing the training time done with the cheaper systems like AutoCAD, SolidWorks, and so on, which have a short learning curve

• But for large, stable companies, if several product revisions will be designed spanning several months or years, then the time invested in learning the parametric approach in ProEngineer, SDRC, and the like, will

be worthwhile

3.12.5Future Trends in CAD: Multidisciplinary Concurrent

Design/Engineering and Global Manufacturing

For a variety of cultural reasons, today's industrial growth is more and more

dependent on situations where large businesses are distributed Often these large

perhaps to take advantage of excellent design teams in one country and low-cost, efficient manufacturing teams in another These trends place even more emphasis on concurrent engineering (or simultaneous design) and design for manufacturability and assembly(DFMlA). The goals are to coordinate all members of a design and manufacturing team at each stage of product development, manufacturing, sales,and service (see Urban et aI., 1999)

To further complicate such trends, engineering products are more complex Concurrent engineering is difficult enough when the product is nearly all mechan-mobiles, aircraft, robots, and computers become a highly complex mix of integrated circuits, power supplies, controllers, and mechanical actuators, concurrent

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multidisciplinary design teams These trends will create the need for environments that allow, for example:

• The integration of electrical-CAD tools with mechanical·CAD tools Chapter 6 describes a domain unified computer aided design environment (DUCADE) that facilitates multidisciplinary concurrent design for consumer electronic products

• The creation of intelligentagentsfor Internet-based design An example might

be an agent for plastic injection-mold design (Urabe and Wright, 1997) Internet-based design environments allow the original part designer to import information on specific "downstream" processes-in this case, how to fabri-cate negative mold halves Information could also include data on shrinkage factors, recommended draft angles for the mold, and snap fit geometries (Brock, 2000)

3.13 GLOSSARY

3.13.1Boundary Edge Representation

Boundary representations, or b-reps, describe an object in terms of its surface

bound-aries: vertices, edges, and faces

3.13.2 Creative Design

The formative, early phases of the design process, where market identification, con-cepts, and general form are studied

3.13.3Constructive Solid Geometry (CSG)

The addition, subtraction, or intersection of simpler blocklike primitives to create more complex shapes

3.13.4Destructive Solid Geometry (DSG)

A special case of CSG where the designer begins with "graphical stock" and changes its shape with only the subtraction01intersection commands, in order to suit later operations on a "downstream" machine tool

3.13.5Detail Design

The later phases of design in which specific shapes, dimensions, and tolerances are specified on a CAD system

3.13.6Design for Assembly, Menufaeturability, end the

Environment

The collection of terms used to encourage designers to adjust their design activities

3.13.7 Feature-Based Design

The use of specific primitive shapes in design that suit a particular "downstream" manufacturing process

3,13.8 Ink-Jet Printing in 3-D

Rapid prototyping by rolling down a layer of powder and hardening it in selected regions with a binder phase that is printed onto the powder layer

3.13.9 Injection Molding

Viscous polymer is extruded into a hollow mold (or die) to create a product 3.13.10 Investment Casting

The wordinvestment is used when time and money are invested in a ceramic shell that is subsequently broken apart and destroyed The original positive master that is wax and ceramic mold are the two most common

3.13.11 Machining

General manufacturing by cutting on a lathe or mill; chip formation from a solid block rather than forging, forming, or joining

3.13.12 Parametric Design

CAD techniques that represent general relationships (e.g.,height-to-width), not nec-essarily specific dimensions

3.13.13 Prototyping (Prototypel

"The original thing in relation to any copy, imitation, representation, later specimen

or improved form" (taken from Webster's Dictionary)

3.13.14 Plastic Injection Molding

As "injection molding," described above Note:Zinc die casting also involves "injec-tion" into dies or molds

3.13.15 Personal Digital Assistant (PDA)

Current, fashionable term for several handheld computing devices possibly with e-mail link, cell phone, and modest display

3.13.16 Rapid Prototyping IRPI

A new genre of prototyping, usually associated with the SFF family of fabrication

3.13.17 Solid Freeform Fabrication (SFF'

A family of processes in which a CAD file of an object is tessellated, sliced, and sent

to a machine that can quickly build up a prototype layer by layer

3.13.18 Solid Modeling ("Solids'"

CAD representations that correspond to real-world physical objects with edges, ver-tices, and faces A CAD operation on a solid model will be consistent with a physical action or deformation that could be performed in the physical world Wire frame CAD modeling does not guarantee this condition

3.13.19 Tessellation

Representing the outside surfaces of an object by many small triangles, like a mesh thrown overand drawn around the object This leads to an ".STL" file of the vertices and the surface normals of the triangles

3.13.20 Wire Frame Modeling

CAD representations that correspond to abstract lines and points An object can be drawn and evenrendered, but the computer does not store an object that is "under-stood" in a physical sense

3.14 REFERENCES

ACIS Geometric Modeler 1993 Version 1.5 Technical Overview Boulder, Co Spatial Tech-nology,Inc

Baumgart, B G 1972 Winged edge polyhedron representation. Technical Report

STAN-CS-320, Computer Science Department, Stanford University,

Baumgart, B G 1975 A polyhedron representation for computer vision NCC 75: 589-596.

Berners-Lee, T.1989 Information management: A proposal CERN internal proposal Boothroyd, G., and P Dewhurst 1999 DFMA software. On CD from the company, or contact

<www.dfmlll.com>

Braid, l C 1979 Notes on a geometric modeler CAD GroupDocument, 101, Computer lab-oratory, University uf Cambridge

Brock, 1.M 2000 Snap-fit geometries for injection molding Master's thesis, University of Cal-iforrria.Berkeley,

Compton, W D 1997 Engineering management, "Creating and managing world class opera-tions." UpperSaddle River, N.J.: Prentice-Hall

Cutkosky, M R., and J M Tenenbaum 1990 A methodology and computational framework for concurrent product and process design Mechanism and Machine Theory 25, no 3: 365 381,

Pinin, T., D McKay, R Fritzson, and R McEntire 1994 KOML: An information and knowl-edge exchange protocol In Knowledge building and knowledge sharing Editedby Kazuhiro

Foley, 1 D.,A van Dam, S K Feiner, and 1 F Hughes 1992 Computer graphics: Principles and practice, 2nd ed., Reading, Mass: Addison Wesley

Frost, R., and M Cutkosky 1996 An agent-based approach to making rapid prototyping processes manifestto designers Paper presented at the ASME Symposium on Virtual Design and Manufacturing

Grayer,A R.1976.A computer link between design and manufacture, Ph.D diss., University

of Cambridge

Greenfeld,l,EB Hansen, and P K Wright 1989 Self-sustaining.open-system machine tools

In Proceedings of the 17th North American Manufacturing Research Institution 17: 281-292 Hauser, 1 R., and D Clausing 1988 The house of quality Harvard Business Review

(May-June); 63-73

Hazelrigg, G 1996 Systems engineering: An approach to information-based design. Upper Saddle River, N.1.: Prentice-Hall

Hoffmann, C M 1989 Geometric and solid modeling. San Mateo, CA: Morgan Kaufmann ISO 1989 External representation of pro duet definition data (STEP) ISO DP 10303-0 ISO 1993 Product data representation and exchange-Part I: Overview and fundamental principles ISODIS 10303-1, TC184JSC4IWG4 N193 Also see thefollowing papers on PDES/STEP:

Wilson, P 1989 PDES STEP forward IEEE Computer Graphics and Application 79-80.

Eastman, C 1994 Out of STEP? Computer-Aided Design 26, no 5.

Kamath, R R., and 1.K Liker.1994.A second look at Japanese product development Harvard Business Review, reprintnumber 94605

KimL H., F C Wang, C Sequin, and p.K Wright 1999 Design for machining over Internet

Design Engineering Technical Conference (DETC) on Computer Integrated Engineering,

Paper Number DETC'99/CIE-9082, Las Vegas

Mead, C, and L Conway 1980 The CalTech intermediate form for LSI layout description In

Introduction to VLSI Systems, 115-127 Addison Wesley

MOSIS 2000 University of Southern California's Information Sciences Institute-The MOSIS VLSI Fabrication Service,http://www.lsLedulmosW.

Pratt, M J., and P R Wtlson.1987 Conceptual design of a feature-oriented solid modeler Draft

Document 3B, General Electric Corporate R&D

Puttre, M 1992 Sculpting parts from storedpatterns Mechanical Engineering, 66-70.

Regli, W C, S K Gupta, and D S Nau 1995 Extracting alternative machining features:An algorithmic approach Research in Engineering Design 7: 173-192.

Requicha, A A G 1977 Mathematical models of rigid solids Technicalmemo 28 Production Automation Project New York: University of Rochester

Requicha, A A G 1980 Representations for rigid solids-Theory, methods,and systems ACM Computing Surveys, 437-464.

Requicha.A A G., and H B Voelckcr 1977 Constructive solid geometry Technicalmemo 25 Production Automation Project New York: University of Rochester

Richards, B., and R Brodersen 1995 InfoPad: The design of a portable multimedia terminal

In Proceedings of the Mobile Multimedia Conference-2, Bristol, England

Riesenfeld, R 1993 Modeling with NURBS curves and surfaces.In Fundamental

Develop-Roberts, L G.1963 Machine perception three-dimensional solids Technical report no 315

Lin-coln Laboratory, MIT

SORe 1996 The Open-IDEAS Programming Course ManualiMS 5282-5 Milford,OH: Structural Dynamics Research Corporation

Sequin, c.S 1997 Virtual prototyping of Scherk-Collins saddle rings Leonardo 30, no 2: 89-96

Shah I 1., and M Mantyla 1995 Parametric and feature based CAD/CAM. Wiley NY (Also see Shah, 1 J M Mantyla, and D S Nau 1994 Advances in feature based manufacturing. New York: Elsevier.)

Sidall, 1 N 1970 Analytical decision-making in engineering design Upper Saddle River, N.J.: Prentice-Hall

Smith, C; and P K Wright. 1996 CyberCut: A World Wide Web based design to fabrication

tool Journal of Manufacturing Systems 15, no 6: 432 - 442

Stcri, 1 A, and P K Wrighl.199" A knowledge based system for machining operation plan-ning in feature based, open architecture manufacturing In Proceedings (on Compact Disc) of the 1996 Design for Manufacturing Conference, University of California, Irvine

Sub, N P.1990 The principles of design New York and Oxford: Oxford University Press.

Sungertekin, LlA, and H B Voelcker.1986 Graphic simulation and automatic verification of machining programs In Proceedings Of the IEEE Conference on Robotics and Automation.

Sutherland, I E 1963 Sketchpad: A man-machine graphical communication system In Pro-ceedings of Spring Joint Computer Conference, 23.

Urabe, K., and P K Wright 1997 Parting planes and parting directions in a CAD/CAM system for plastic injection molding Paperpresented at the ASMEDesign for Manufacturing Sym-posium, the Design Engineering Technical Conferences Sacramento, CA

Urban S D., K.Ayyaswamy, L Fu, 1.1 Shah, and 1 Liang 1999 Integrated product data envi-ronment: Data sharing across diverse engineering applications International Journal of Com-puter Integrated Manufacturing 12, no 6: 525-540

Woo, T 1992 Rapid prototyping in CAD Computer Aided Design 24: 403-404.

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

Wright, P K., and D A Dornfeld 1996 Agentbased manufacturing systems In Transactions

of the 24th North American Manufacturing and Research Institution, 241-246.

3,'5 BIBLIOGRAPHY

Bartels, R H., 1 C Beatty, and B Barsky 1987 An introduction to splines for use in computer graphics and geometric modeling San Mateo, CA: M Kaufmann Publishers

Hyman, B 1998 Fundamentals of engineering design UpperSaddle River, N.J.: Prentice-Hall Proceedings of the Institute of Mechanical Engineers 1993 Effective technologies for engi-neering success-Making CAD/CAM pay No 1993-12.

Regli, W C, and D M Gaines.1997 A repository for design, processplanning and assembly

Computer Aided Design 29, no 12: 895-905.

Sequin, C H., and Y Kalay 1998 A suite of prototype CAD tools to support early phases of

3.16 URLS OF INTEREST: COMMERCIAL CAD/CAM SYSTEMS AND

DESIGN ADVISERS

1 Parametric Technology Corp, Pro/ENGINEER, http://www.ptc.com

2 Autodesk, AutoCAD,bttp://www.autodesk.com

3 SolidWorks,bttp://www.solidworks.com

4 Spatial Technologies, ACIS,http://www.spatial.com

5 3D/EYE Inc, TriSpectives, http://www.eye-com

6 SDRC, I-DEAS,http://www.sdrc.com

7 EDS, Unigraphics,http://www.edsug.com

8 MSC,ARIES, http://www.macsch.com

9 DesignSuite by Inpart, Saratoga, California,http://www.inpart.com

10 Cambridge process selector,bttp:f/www.granta.co.uklproducts.btml

3.17 CASE STUDY

The goal of this case study is to reinforce the four levels of design described in Sec-tion 3.2 Specific ideas for a novel snow shovel are shown indented below the main design level SORC is the design tool being used in the example Parametric design is highlighted Reiterating a point made in the introduction, note that this chapter has solid modeling, to solid modeling with rendering, and now to parametric design Sec-tion 3.2 summarized four main phases of the design process These are repeated below and used to guide the reader into the detailed steps using SDRC's IDEAS system

1 Art related and high-level: "Design in any of its forms should be functional,

based on a wedding of art and engineering" (W A Gropius, founder of the Bauhaus movement)

The snow shovel will be designed in this case study as an attractive, colorful, lightweight, foldable device that mountaineers will buy at their local "outdoors shop."

2 Engineering related and high-level: "Design is the process of creating a product

(hardware, software, or a system) that has not existed heretofore" (Suh, 1990)

A collapsible snow shovel is designed in the next few pages with the purpose

of improving the weight, cost, and usefulness over existing shovels Emphasis is placed on the shovel head as the component with the most potential for improve-ment The shovels that were found in the marketplace were separated into two pri-mary design classifications The first was the plastic shovel, which was lightweight and cheap but was not hard or stiff enough to be useful in ice or dense snow con-ditions The second was the aluminum shovel, which was useful in all conditions but was significantly heavier and more expensive than a plastic shovel

3 Engineering related and at the analytical level: "Design is a decision making

process" (Hazelrigg,1')96)

The new shovel incorporates the best of both shovel designs by combining a cheap, lightweight shovel scoop made out of polycarbonate with a hard, tough molded-in cutting blade made from aluminum 6061 Emphasis is placed on

stiff-shovel wall thickness (and thus a weight and cost reduction) This is accomplished

by simulating load conditions using the ANSYS finite element analysis software and iterating the design to improve it

4 Detailed design: "Design is to make original plans, sketches, patterns, etc." (Web-ster's Dictionary)

The first step in the design of the shovel is the creation of a wire frame drawing to

be extruded into the initial solid of the model.The most complex view of the part is gen-for the wire frame drawing.The final shovel design wire frame is shown in Figure 3.33 Notice the dimensions on the wire frame in Figures 3.33 and 3.34 Unlike conventional drafting packages where the dimensions are added to document a specific line length, parametric design controls the size of the part with these dimensions They are therefore calledconstraints rather than dimensions in para-metric design Figure 3.34 shows the side view of the wire frame sketch of the shovel head after the angle constraint has been modified from 32 degrees to 45 degrees Notice how this simple change dramatically alters the shape of the shovel then redimensioned to make this change.The ability to rapidly change such design parameters is one of the key strengths of parametric design. Also notice that in addi-tion to the standard constraints of length, there are constraints for angular, radial, perpendicular, tangent, and coincident objects in Figures 3.33 and 3.34 Figure 3.35 shows the solid object from an isometric front view that is created when the wire frame shown in Figure 3.33 isextruded a distance of 225 millime-ters (9 inches) and draft angles are added for strength and manutacturabillty Figure 3.36 shows the same view afterfillets have been added to the shovel head The next step in the shovel design is to add cutouts to the bottom of the shovel head, which will become the stiffening ribs when the part is turned into a shell Figure 3.37 shows a view perpendicular to the back edge of the shovel head

Flgure3.33 Wire frame model of snow shovel (Thanks are due to Dan Odcllforhiscontributions)

flgure3.34