The use of an engineeringdatabase for systemintegrationby M. J. BryanWestland Helicopters Limited

Integrated CAE implies the intimate interlinking of many diverseengineering systems. This could be achieved on a piecemeal basiswith data distributed over the various systems and managed in localdatabases. However, a much more elegant solution for systemintegration, and certainly the only viable long-term one, is throughthe medium of a central engineering database. This database muststore all design and manufacturing data and support multidisciplinemultilevel access. More importantly it must store geometric data in acanonical form, thus insulating the company and the data from thevagaries of CAD systems.

Introduction

A great many companies both largeand small have a computer-aideddesign and manufacturing (CADCAM)system of one sort or another. Manycompanies will have more than onesystem, but all those companies thathave an investment in CADCAM will,with very few exceptions, have a draft-ing system. For the majority of com-panies the purchase of a draftingsystem represents the first hesitant stepalong the CADCAM road. Such systemswill generally be treated as electronicdrawing boards, the sole purpose beingto increase the productivity of thedraftsman. The point here is that theend product is a hard-copy engineeringdrawing which is still the master manu-facturing document. One or two of themore adventurous companies may have

explored the CAM interface that someof the drafting systems offer. This willhave been with varying measures ofsuccess, depending on the degree ofcompatibility of the drafting system'sCAM output with the company's owninternal part programming systems.

Some companies will quickly dis-cover the limitations of the draftingsystem and start to investigate the useof three-dimensional systems for surfaceor solids modelling. Again, some com-panies may need to look for specialistCAM systems or finite-element (FE)modellers to supplement whateverfacilities might have been available intheir drafting systems. There will obvi-ously be a requirement to transfer geo-metric data between these varioussystems. Often this can be accom-plished on a piecemeal basis withouttoo much trouble. Sometimes, however,

Computer-Aided Engineering Journal April 1984

because the separate systems will beused by different disciplines within thecompany, they might be used in totallyisolated mode and may require the re-creation of geometry which is alreadyheld on one of the other systems. Oftena great many different kinds of analyseshave to be performed, and the worstthing that can happen is that thegeometry captured by the CAD systemis not used and geometric data for theanalyses are culled from hard-copyoutput.

Companies wishing to invest inCADCAM face a serious philosophicalproblem. Should they purchase a single,general all-purpose system which offersa capability in drafting, FE model prep-aration, kinematics, surface modelling,numerical control (NO tape prep-aration, perhaps even solids modelling,and which comes with some prettyaverage applications software thrown inas well, or should they purchase anumber of individual systems, each onespecialising in a certain discipline? Theformer choice solves the problem ofintersystem data transfer but meansthat the advanced features of thespecialist systems are lost. The latterchoice will create the considerable pro-blem of how to exchange data effi-ciently between the various systems,but it will also more easily allow individ-ual systems to be replaced when asuperior product appears on themarket. This latter choice becomes in-

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creasingly attractive when considered inthe light of a corporate engineering da-tabase. It is through the medium of thedatabase that the individual systemscan intercommunicate (see Fig. 1), and,because the database insulates the datafrom the system which originally gener-ated them, the company is no longertied to that system. This must surely bethe ultimate goal for every company.

Integrated CAE systems and theengineering database

The CADCAM systems shown in Fig. 1would, of course, only have a certainsubset of common geometric entities,but it can be seen how straightfor-wardly a new or replacement systemcan be installed. It is only necessary toproduce a translator capable of post-processing the system output into thedatabase standard form and pre-processing database-resident informa-

tion into the internal format of thereceiving system.

Without such an organisation as thatshown in Fig. 1 the addition of a new orreplacement system or applicationwould require the creation of separateinterfaces to each of the componentsystems. The number of interfaces re-quired grows exponentially with thenumber of components. Because of theimmense problems associated with cre-ating an engineering database, mostcompanies will adopt the solution oftrying to interface each system or appli-cation to every other system or applica-tion. Fig. 2 shows the complexity of asix-component computer-aided engi-neering (CAE) system with all the inter-faces complete. The number oftwo-way interfaces for a CAE systemwith N components is N{N — 1)/2. Theengineering database solution would re-quire only six two-way interfacesagainst the 15 required in Fig. 2. If any

intercompany transfer

maufacturingprocess planningcost estimating

etc.

technicalillustrations

NCtapepreparation

engineeringanalyses

corporateengineeringdatabase

electricaland pipingdiagrams

surfacemodeller

translators

database managementsystem

Fig. 1 Integrated CAE system

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one of the six systems had to be re-placed in Fig. 2, a maximum of fiveinterfaces would have to be rewritten. Atotally integrated CAE system couldhave a dozen or more different com-ponents, and its realistic creation couldonly come about through the existenceof the database. It is of course appre-ciated that some interfaces, such astechnical illustration to NC tape prep-aration, are redundant.

For an engineering database to beused as a medium for system integra-tion it must be capable of storinggeometries, and those geometriesshould have a solids representation.This poses an enormous problem asvery little work has been done on thecreation of structured geometry data-bases. The easy solution is to utilise thelocal database of the particular com-pany's mainline CADCAM system, butthat can only be a short-term palliativeand not a long-term solution. There isno way that a CAE system, in its fullestsense, can ever be realised using aCADCAM local database, especially ifthe CADCAM system is a draftingsystem and only stores two- or two-and-a-half dimensional geometries. En-gineering data must be attributed orlinked to the geometry that has givenrise to them. While many CADCAMsystems allow for such attributes, it ismerely as an add-on rather than a seri-ous attempt to create structured data.

Furthermore, the point must be madethat CADCAM systems will evolve andchange, perhaps quite dramatically, andnot necessarily always in an upwards-compatible manner. This could meanthat a company is faced with a decisionto either remain with an obsoletesystem or possibly 'throw away' years ofaccumulated drawings. By 'throw away'it is of course meant that it might notbe possible to translate the digital rep-resentations into the internal form ofthe new CADCAM system, in whichcase they must be converted to hardcopy. It is essential that a company'sdata are insulated from the systemswhich originally generated them.

IGES

There is in existence the Initial GraphicsExchange Specification (IGES) [1], thedevelopment of which is supported byfunds from the US Air Force, Army andNavy and also NASA. It is officially aproject of the US Air Force IntegratedComputer Aided Manufacturing (ICAM)programme. It was commenced in late1979 and was based on work previouslydone by Boeing. Its purpose is to pro-vide a standardised format for two- andthree-dimensional wire-frame geometricdata and so facilitate data exchange

Computer-Aided Engineering Journal April 1984

between differing systems.Standard geometric entities such as

points, lines and arcs are no problem,but general entities like curves and sur-face patches have many different pos-sible representations. The standardsurface patch is taken to be the rationalB-spline representation and, while thiscan be converted exactly into thesimple cubic-polynomial boundarybased patches, severe problems couldbe experienced when attempting to ex-change data with systems using higher-order boundary representations. Wiringor similar schematic systems are notsupported and neither are solids. Fur-thermore, the author has no first-handknowledge of how successfully engi-neering drawings can be transferredbetween systems. It is highly probablethat a certain amount of touching upwould be necessary. Problems couldalso be caused by ICES processors notsupporting the complete specification(now at release 2.0). It must be remem-bered, of course, that not all CADCAMsystems offer ICES support anyway.

Stored geometry and therepresentation of solids

It was stated earlier that the geometrystored in the engineering databaseshould have a solids representation;however, there are a number of suchrepresentations and it is not possible atpresent to convert between all of them.Probably the most widely used form,but not the most concise, is boundaryrepresentations. This is a convenientform in that a wire-frame model caneasily be extracted for quick, initialvisual inspection. An English-language-like description of the actions requiredto create the model from the basicprimitives would be more concise butwould require substantial computa-tional resources every time a graphicalrepresentation was needed. A great dealof literature exists on the represent-ations of solids, and for further readingthe reader is referred to Requicha [2],Braid et al. [3], Kalay [4] and Yama-guchi et al. [5].

IGES has not yet been extended tocover solids, although it is believed thatthere is a future intention to do so.Whatever recommendations might bemade in ICES could form a useful modelfor a potential database canonical form.There is, however, an enormousamount of existing two- and three-dimensional wire-frame models storedin a variety of local CADCAM systemdatabases and therefore, initially, provi-sion must be made to store somecanonical form of these geometries inthe engineering database. It must notbe forgotten, however, that such

geometries are only partially definedand are therefore ambiguous and re-quire human interpretation. Totallyautomatic processes based on thesegeometries are not possible, and soretrospective solids modelling is likely tobe an absolute necessity.

Data management

There is no intention here to delve toodeeply into the structure the databaseshould take. It may well be a hybridsupporting the relational, hierarchicaland network models. The Boeing Com-pany's Integrated Program for Aero-space Vehicle Development (IPAD)project [6] is an example of an attemptto develop an engineering databasewhose main design goal is to achievehorizontal integration of all the variouscomputer-assisted engineering activities.The Boeing concensus is that geometryis the single common thread linking the

various engineering processes andtherefore must be stored in the corpo-rate engineering database in a highlystructured form to facilitate flexibleaccess. Most current database systemswere designed primarily for the man-agement of commercial and businessdata, which may only have a singlelevel of interpretation. They are gener-ally not at all suitable for the multiplelevels of interpretation which are re-quired for geometric data.

Individual companies can generate atremendous amount of raw data; this iscertainly true of the aerospace industry.Ignoring the geometry, which is gener-ally pretty well managed either in theform of hard copy, microfilm or in digi-tal form, there is a plethora of analyticaldata which may not be very well man-aged at all. Even if only design data areconsidered they can take the form ofweights, stresses, vibration, tem-perature, noise, aerodynamics, kine-

Fig. 2 Linked CAE system

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technicalillustrations

FEbulk data

manufacturingdata

analyticaldata

geometry anddata knowledge

AI knowledge base:manufacturing andengineering science

attributed data:manufacturing andanalytical

A I layer

Fig. 3 Effect of artificial intelligence on an integrated CAE system

matics etc. Such data could bescattered around the company andwould probably be held in some in-stances by individuals in a somewhathaphazard fashion. The sudden depar-ture of one of these individuals couldseriously embarrass the company andcause a damaging increase in projectlead times while results of tests andvarious analyses are unearthed and sub-stantiated. Multiple analyses .will beconducted in the search for an accept-able design (or an optimum one). Thebulk of raw data which results, unless itis very well managed, could prove verydifficult to evaluate and might becomea morass which bogs the whole designprocess down.

Although it was previously statedthat geometric data are usually well or-ganised in companies, serious problemscan still very easily occur. Most readerswill be aware of the traditional rivalrieswhich exist between design and pro-duction departments, but potentiallymore serious are the interdisciplinary ri-

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valries that can exist within the overalldesign function. Such rivalries arecaused by an elitist outlook and cancause problems in the flow of dataacross the various discipline boundaries.Most companies will have gone throughthe trauma of basing costly and time-consuming analyses on out-of-date geo-metric data. The introduction of CADtechniques will have gone a long waytowards alleviating this problem. How-ever, the point must be made againthat the geometric data in a CADsystem local database are organised tofacilitate the operation of the CADsystem itself. It is not structured topermit multidiscipline access, and. itsmanagement system will not necessarilybe good enough to ensure the provisionof uncorrupted up-to-date geometries.

One of the great afflictions ofmodern manufacturing industry is thepoor availability of up-to-date informa-tion. Often an FE stress analysis canonly be done to verify that somethingalready made, or which cannot now be

altered, is strong enough. Ideally, if thegeometric data were 'on tap', then,within the allotted design lead time,several design/stress iterations could bemade to attempt to optimise the designfrom a weight/strength standpoint.Similarly, assemblies and whole prod-ucts are often only costed out when theprototype is made. At this stage it maywell be too late to attempt a cost re-duction exercise. The use of new tech-niques such as parametric costingcould, when used with readily acces-sible geometric and manufacturingdata, allow accurate cost predictions tobe made at the design stage, thusallowing time for ways of cost reductionto be investigated.

Drafting systems

A brief mention has been made ofdrafting systems, and perhaps it isworth assessing their use in an inte-grated CAE environment. It is not toodifficult to show that they are obsol-escent. Historically, man was forced togenerate two-dimensional represent-ations of three-dimensional objects be-cause of the medium used to carry theinformation. The computer has freed usfrom this straitjacket so there is noreason why the engineering drawingshould be perpetuated, but this isexactly what the drafting system does.

There is no cause to dimensiongeometry held in a CADCAM system; itis redundant information. The geometryitself is sufficient when it is suitablyattributed to carry tolerancing data.Neither the part programmer nor thestressman requires dimensioning infor-mation. However, the geometry mustbe accurate otherwise it is useless. Thisis the true discipline of CADCAM. Thetwo-dimensional geometries created bydrafting systems have only a limitedvalue. Section properties can be evalu-ated and some two- or two-and-a-half-axis NC machining is possible, butbecause of the ambiguous nature of thegeometric description some humaninput and control cannot be avoided.The argument is always put forwardthat drafting systems can becomequickly productive, but it would betotally short sighted to try to use such asystem as the basis for integrated CAE.The drafting system is obsolescent be-cause the engineering drawing is obsol-escent.

Future CAE systems

It is probably very worth while attempt-ing a forecast of what the de iactoCADCAM system will be like in, say,five years time. From a hardware pointof view the engineer will have his own

Computer-Aided Engineering Journal April 1984

workstation with high-resolution colourgraphics which will certainly offer theraw processing power of a VAX 11/780or equivalent. Workstations will belinked through a local area network to amainframe computer for databasehandling. The main CADCAM systemrunning on this workstation will be asolids modeller. It is extremely doubtfulif any reader would offer a serious chal-lenge to this forecast. It is quite obvi-ously pointed to by the present-daytechnological hardware and softwaredevelopments. Although solids model-ling is in its relative infancy at the pre-sent time, it must form the nucleus ofall future integrated computer-aided en-gineering systems. Furthermore, the useof solids modelling paves the way forthe fully automated factory. Unam-biguously defined geometries precludethe need for human interpretation, andit is this need for human interpretationthat causes so many problems in thedesign and manufacturing process.

The extra toil and tears associatedwith generating unambiguous geome-tries through the use of solids modellerswill be repaid manifold by the easewith which NC tool paths, FE models,technical illustrations, mass propertiesand models (full-size or otherwise) canbe obtained. Present-day modellers arebeginning to move away from the fac-eted representations of curved surfacesto true mathematical representationssuch as B-spline surfaces. Therefore theywill be able to offer a complete model-ling capability for all engineering com-ponents. The writing is therefore also onthe wall for the surface modellers.While they have the ability to model allthe boundaries met in engineering com-ponents, they do not store their topo-logical relationships. It is thereforeimpossible to automatically calculatemass properties or identify invalidsolids; to do so requires human inter-vention.

Artificial intelligence (Al) is a burgeon-ing science and must make a majorimpact on CADCAM and CAE in thenear future. It should be possible for acompany to capture a substantial bodyof engineering and manufacturing sci-ence in a knowledge base. This knowl-edge base would be continuallyupdated and eventually should containthe sum recordable knowledge per-taining to the particular industry. Itspossible effect on the structure of anintegrated CAE system is shown inFig. 3. The stressman's art, the part pro-grammer's art, the process planner's art,the draftsman's art; all can be capturedin the knowledge base. It is, however,impossible to capture the innovativeflair and creative genius which are thehallmarks of the true designer. Expert

Fig. 4 Solids model representation of a valve assembly. Solids modelling will almostcertainly form the nucleus of future integrated CAOCAM systems

[Photograph courtesy of McAuto]

an engineering database must first besolved. This database must store unam-biguous geometric representations in ahighly structured form, together with allthe attributed data such as weight,material, cost, mechanical properties,analytical data and manufacturing infor-mation. No such database currentlyexists. Several major companies areknown to be attacking this problem;others have swept it under the mat.Guess who the survivors will be?

systems are, even today, much morethan just fanciful imagination. Further-more, the Japanese are heavily com-mitted to the development offifth-generation hardware which is in-tended to offer the proper environmentfor such systems.

Conclusion

To realise the dream of integrated CAEthe problems associated with creating

References

1 Initial Graphics Exchange Specification (ICES) Version 2.0. National Bureau of Standards,US Department of Commerce, Washington, DC, USA, NBSIR 82-263KAF), Feb. 1983

2 REQUICHA, A. A. C.: 'Representations for rigid solids: theory, methods and systems',Computing Surveys, 1980, 12, pp. 437-464

3 BRAID, I. C, HILLYARD, R. C, and STROUD, I. A.: 'Stepwise construction of polyhedra ingeometric modelling', in BRODLIE, K.W. (Ed.): 'Mathematical methods in computergraphics and design' (Academic Press, 1980)

4 KALAY, Y. E.: 'A relational database for non-manipulative representation of solid objects',Computer-Aided Design, 1983, 15, pp. 271-275

5 YAMACUCHI, K., KUNII, T. L, and FUJIMURA, K.: 'Octree related data structures andalgorithms', IEEE Computer Graphics & Applications, 1984, 4, Jan., pp. 53-59

6 DUBE, R. P., and RIVERS SMITH, M.: 'Managing geometric information with a databasemanagement system', IEEE Computer Graphics & Applications, 1983, 3, Oct., pp. 57-62

M. J. Bryan is with the CADCAM Systems Department, Westland Helicopters Limited, West-land Road, Yeovil, Somerset BA20 2YB, England

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