21st Century Manufacturing Part 5 ppt

Reiterating a point made in the introduction, note that this chapter hassolid modeling, to solid modeling with rendering, and now to parametric design.. Art related and high-level: "Desi

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 means that objects are initially created generically without specific dimensions.scales up or down to suit The user is able to define constraints between differentparts of an object and then scale them

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

enor-on new "revs" is likely

These are powerful design tools for a large automobile company or a nationallaboratory In these environments, many similar components in a family are beingdesigned Their use in a bearing-manufacturing company like TImken Inc is perhapsthe easiest to visualize Bore sizes, races, cover plates, and the like, can be createdonce and then "scaled up or down." For future revisions of a component, any existingparametric 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 thatwill 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 withinitial 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 mediate role compared with the aforementioned applications They have specialized

inter-in the "market niche" of creatinter-ing an open de facto standard for solid representations.This is finding adoptions in other systems, including AutoCAD The openness ofACIS 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, for only $100 Thus, even these more sophisticated systems are becoming morereadily 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 stilldoes 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 anonparametric way, these higher end packages can create excellent feature-basedmodels The governing factor seems to "boil down" to how much long-term interest

"stu-a person or group h"stu-as in using CAD tools Here "stu-are three scen"stu-arios:

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

gen-• Also in small, newer companies, today's evidence is that the turnover amongyoung engineers is high It might not be worth investing the training timedone with the cheaper systems like AutoCAD, SolidWorks, and so on, whichhave a short learning curve

• But for large, stable companies, if several product revisions will bedesigned spanning several months or years, then the time invested inlearning 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 onconcurrent engineering (or simultaneous design) and design for manufacturabilityand assembly(DFMlA). The goals are to coordinate all members of a design andmanufacturing team at each stage of product development, manufacturing, sales,andservice (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 integratedcircuits, power supplies, controllers, and mechanical actuators, concurrent engi-

FE = Feature based

PF= Partfamilies

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

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

• 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 importinformation on specific "downstream" processes-in this case, how to fabri-cate negative mold halves Information could also include data on shrinkagefactors, 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, cepts, and general form are studied

con-3.13.3Constructive Solid Geometry (CSG)

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

3.13.4Destructive Solid Geometry (DSG)

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

"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 tion" into dies or molds

"injec-3.13.15 Personal Digital Assistant (PDA)

Current, fashionable term for several handheld computing devices possibly withe-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, tices, and faces A CAD operation on a solid model will be consistent with a physicalaction or deformation that could be performed in the physical world Wire frameCAD modeling does not guarantee this condition

ver-3.13.19 Tessellation

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

3.13.20 Wire Frame Modeling

CAD representations that correspond to abstract lines and points An object can bedrawn 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 nology,Inc

Tech-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

knowl-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 prototypingprocesses manifestto designers Paper presented at the ASME Symposium on Virtual Designand 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

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:Analgorithmic approach Research in Engineering Design 7: 173-192.

Requicha, A A G 1977 Mathematical models of rigid solids Technicalmemo 28 ProductionAutomation 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 (Alsosee Shah, 1 J M Mantyla, and D S Nau 1994 Advances in feature based manufacturing. NewYork: 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 ning in feature based, open architecture manufacturing In Proceedings (on Compact Disc) of the 1996 Design for Manufacturing Conference, University of California, Irvine

plan-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 ofmachining programs In Proceedings Of the IEEE Conference on Robotics and Automation.

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

Pro-Urabe, K., and P K Wright 1997 Parting planes and parting directions in a CAD/CAM systemfor 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 ronment: Data sharing across diverse engineering applications International Journal of Com- puter Integrated Manufacturing 12, no 6: 525-540

envi-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: AddisonWesley

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

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

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 tion 3.2 Specific ideas for a novel snow shovel are shown indented below the maindesign level SORC is the design tool being used in the example Parametric design ishighlighted Reiterating a point made in the introduction, note that this chapter hassolid 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 belowand used to guide the reader into the detailed steps using SDRC's IDEAS system

Sec-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 theBauhaus 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 isplaced 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 lightweightand 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 conditionsbut 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 acheap, lightweight shovel scoop made out of polycarbonate with a hard, toughmolded-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 softwareand iterating the design to improve it

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

(Web-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 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 Unlikeconventional drafting packages where the dimensions are added to document aspecific line length, parametric design controls the size of the part with thesedimensions They are therefore calledconstraints rather than dimensions in para-metric design Figure 3.34 shows the side view of the wire frame sketch of theshovel head after the angle constraint has been modified from 32 degrees to 45degrees 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 createdwhen 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 theshovel head, which will become the stiffening ribs when the part is turned into ashell Figure 3.37 shows a view perpendicular to the back edge of the shovel head

gen-Flgure3.33 Wire frame model ofsnow shovel (Thanks are due to DanOdcllforhiscontributions)

flgure3.34

Ftpn3.35 F1gure3.36

with the wire frame for the rib cutouts sketched on it The wire frame cutoutsextend past the actual part that they are intended to cut to ensure that they cutthrough the entire part

Figure 3.38 shows an isometric view of the bottom of the shovel after the wireframe sketch has been extruded at an angle as a cutout to form the inverse of the ribprofile In a similar way, Figure 3.39 shows an isometric view of the top of the shovel

after it has undergone a shell operation and a filleting operation The shell operation

.•• ,.,

thickness An option in the shell command allows specified surfaces to be removedfrom the shell operation, and in this case the top and front surfaces have been

in design for the injection molding process where a uniform wall thickness is able to achieve uniform cooling and shrinkage It can also be useful for processes

desir-is used as the raw material

The ribs were added to increase the moment of inertia of the shovel in thedirection of the expected snow load and thereby to stiffen the shovel head Stiffeningwhich relates to a reduction in cost and weight Notice how the use of the shell com-cult to model without use of this command

The next step in the design of the shovel head is to add the interfacebetween the shovel head and the shaft The wire frame sketch of this interface

is shown in Figure 3.40 To make this sketch and locate it properly, a referenceplane has been added to the shovel This plane is placed to be perpendicular tothe rear face of the shovel so that wire frames that will be sketched and extruded

••••••,.40

Figure3A2

Figure;,t44

on it will be parallel to the rear of the shovel Onto this plane, the outermost

lines of the shovel head have been focused to give a reference for centering the

interface The interface is sketched as a tubelike structure to create a slip-fit withthe shaft

Figure 3.41 shows the shovel head after the interface section is extruded Thisinterface is extruded to a distance so that its full length extends past the shovel head.lengthened, and the remaining wall of the shovel head inside the tube is removed.The result of these operations is shown in Figures 3.42 and 3.43

Next, as shown in Figure 3.44, the resulting hole on the bottom of theshovel is sealed and a hole is added for the fastener that attaches the shovelnext step is to add the molded-in aluminum cutting blade Figure 3.45 shows abottom view of the shovel with a wire frame sketch of the plastic section thatwill encase the cutting blade Once this section is extruded, the wire frame forthe blade itself is generated as in the bottom front isometric view in Figure 3.46.Notice that in this case the blade is drawn as an integral component of the shovelhead Later, a second model of the blade will have to be generated that includesthe section that is encased in the plastic This section will require several slots sothat during injection molding, the plastic will flow through them and mechani-

Figure 3,45

FIgure 3.47 l!'igure3AS

Once the blade is extruded, the remaining fillets are added to the part and thedesign is complete The top and bottom isometric views of the completed shovel areshown in Figures 3.47 and 3.48

It is important to note that the strength of parametric design is the ability torapidly modify steps in the design to improve the final design The steps that are doc-umented for this case study are for the final shovel design, but many intermediatedesigns were modified to obtain the final one If something in this design were found

to be inadequate, any of these steps in the design could be reached and modified byaccessing the "history tree" of the part

For this design, the step of greatest interest was the design of the stiffening ribs

To help optimize these ribs, the solid model of the shovel head was imported into theious conditions Figure 3.49 shows this simulation for stress under a buckling load.This load produced the worst results for the shovel but is not expected to be encoun-tered often, and the addition of the metal blade (which is not modeled in this simu-

.•• ,

3.18 QUESTION FOR REVIEW

1 For Figure 3.50, give the CSG representation in the form of a CSG tree using thetwo basic primitives of a cylinder and a block with their local coordinates asshown The origin of the world coordinates should be taken at the base of theshown in the CSG tree

R Does the pointP(6,0,3) lie in the object? Clearly show all necessary calculationsusing theesctree to make conclusions

b After having marked all the vertices, determine how many edges and faces theobject had

CoeSGrepresentationis not unique Prove this statementby creating anotherCSG lreefor the above object Use different-sizedshapes (Cylindersmay be the same size.)