A Multimedia Approach to TeachingRapid Prototyping Systems*

C. K. CHUA, K. F. LEONG, H. K. CHENG and L. M. CHOWSchool of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue,Singapore 639798. E-mail: mckchua@ntu.edu.sg

Rapid prototyping (RP) is an emerging technology which is having a significant impact on productdevelopment cycle time and management. This technology enables the making of objects directlyfrom computer models within the time and cost parameters needed by engineers to develop newproducts and prepare them for manufacture in quantities. RP is a multidisciplinary as well as fastevolving technology. The problem with presenting this technology for learning is the difficulty incovering the wide area of knowledge in a coherent manner. This paper presents a multimediaapproach, which, with its visuals, animation and sound, is able to present the RP material in a morecohesive and interactive manner.

INTRODUCTION

RAPID prototyping (RP) systems, otherwiseknown as solid freeform manufacturing (SFM),represent the future in manufacturing [1]. Themajor advantage of this technology is the abilityto build complex and difficult-to-machine modelsin a relatively short time. This means that the timeto market for a new product can be drasticallyreduced. This is especially important in today'sproduct development cycle, which is usually veryshort due to short life span of the product andpressure of first-to-market requirements.

RP systems can create free-form three-dimensional objects of virtually any shape directlyfrom three-dimensional computer representationsusing raw materials and a modulated energysource. RP is best suited for non-repetitive fabri-cation of objects with great complexity in a shorttime without the cost and delay of expensive tools.This is because the objects are built as a stackedsequence of two-dimensional layers. Sequentiallayer building enables high geometric complexityincluding enclosed parts and completed assembliessuch as meshed gears. The early application ofRP was primarily in product design where partswere used for approval and in manufacturingwhere parts were used for small volume tooling.As technology continues to improve, RP can beused to produce finished production parts of multi-ple materials, colours and even designed compositematerials.

Unfortunately, the technology of building physi-cal models is not well understood by many. Thetechnologies involved in RP are multidisciplinaryand therefore difficult to present. Several books[1±3] have been written on the subject but suchworks in the printed form are often inadequate in

explaining or describing such a highly technicaland visual subject; the processing procedures ofthe RP systems are often difficult to visualize andcomprehend. Through reading books on rapidprototyping, one may take a long time to fullyunderstand how the laser beam is focused to thematerial and how the objects can be built in layers.A better solution is to see a RP system in actionbut this is often not possible because these systemsare expensive to acquire and operate. One way toalleviate this problem is to present the material viamultimedia form utilizing a compact disc (CD).This is developed to teach various levels of peoplewho require information on the different aspects ofthis new technology in the shortest possible time.

Multimedia is more than just an effective com-bination of two or more media [4]. Multimediais about using a personal computer (PC) as aneffective tool for integrating a rich blend of mediatypes and making it possible to bring these ele-ments together in an interactive and cohesivemanner. The development of multimedia com-munication has been made possible by the increas-ing power of computer systems and the continuingpervasiveness and diversity of the communica-tions networks that are now part of everyday lifefor many people throughout the world. Thesetwo developments open up a much wider field ofpossibilities for business, commerce, industry andalso education, healthcare and leisure.

The world of education has taken multimediacommunication quite naturally and rapidly. Itappears to be one of the major areas for thegrowth of multimedia products and services formany years to come. Multimedia packages forteaching engineering topics such as thermo-dynamics, robotics, fluid mechanics as well asRP, amongst many others, would make thelearning process more lively and effective.

The multimedia compact disc read only memory* Accepted 8 July 1997.

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Int. J. Engng Ed. Vol. 13, No. 2, p. 108±116, 1997 0949-149X/91 $3.00+0.00Printed in Great Britain. # 1997 TEMPUS Publications.

(CD-ROM) on RP is developed to enhance theusers' understanding and appreciation of this tech-nology. It utilizes animation and video clips todemonstrate the actual building processes of thevarious RP systems. It is easy to use on a PC withsimple multimedia peripherals. The CD-ROM isdeveloped as an integral part of the book by Chuaand Leong [1] and is not meant to replace it. It is toencourage independent learning and allow greaterdiversity of learning for individuals. The CD-ROM includes the animations of the five mostpopular RP systems namely: stereolithography(SLA), laminated object manufacturing (LOM),solid ground curing (SGC), selective laser sintering(SLS) and fused deposition modelling (FDM).Through the CD-ROM, the users can see howthe objects are built from each system and under-stand the capabilities and the limitations of eachsystem.

In this article, the application of multimedia ona CD-ROM for teaching of RP systems is pre-sented. It first gives an overview of the advantagesof using a multimedia approach for teaching RPsystems. The development of the multimedia pack-age is then described. The paper concludes with theevaluation of the design of the RP multimediapackage and presents some recommendations forfuture improvement.

RAPID PROTOTYPING TECHNOLOGIES

The primary motivation for using RP is in theterm `rapid'. In today's market where the com-petition is stiff and requirements stringent, it isabsolutely essential to cut down the time tomarket. Any tools or technologies that canaccelerate this will be imperative. RP helps tosignificantly reduce the prototyping process,resulting in substantial savings in both time andcosts.

The fundamental idea underlying RP is that itsbuilds the physical model layer by layer usually ina horizontal manner as opposed to the conven-tional machining processes which remove excessmaterials from a block of workpiece [1±3]. Thismeans that more complex and difficult-to-machinemodels can now be built as they can be modelledeasily on many of the surface and solid modellersavailable today.

Common to much conventional manufacturing,RP starts from a computer-aided design (CAD)model. But unlike conventional manufacturing themodel must represent the physical part to be builtas closed surfaces that unambiguously define anenclosed volume. This enclosed volume ensuresthat all horizontal cross-sections are closedcurves when the model is sliced. The CAD modelis next converted to the STL file format. The STLformat approximates the surfaces of the modelsby polygons. The STL file can be very large if themodel has many curved surfaces. In some cases,IGES (initial graphic exchange specifications) data

may also be acceptable. A computer program isused to analyze the STL for errors and missingdata and then slice the model into cross-sections ifthere are no errors. Otherwise repairing of invalidmodels is required [5, 6]. These cross-sections arethen systematically recreated through the solidifi-cation of liquids or amalgamation of powders andare then combined to form the 3D model. Oneother possibility is to create the cross-sections asthin and solid laminations that are glued togetherto form the 3D model.

Although there are more than twenty differentRP Systems, they can be classified into three maincategories [1], namely:

(1) liquid-based RP systems,(2) solid-based RP systems(3) powder-based RP systems.

Included in this CD-ROM, five systems arecovered, namely stereolithography (SLA), lami-nated object manufacturing (LOM), solid groundcuring (SGC), selective laser sintering (SLS) andfused deposition modelling (FDM). These repre-sent a major portion of the principal systemsavailable today.

SLA and SGC come under a liquid-based RPsystem because parts are produced from a liquidphotopolymer resin. In the SLA, the resin under-goes a photopolyermerization process whenexposed to a laser beam, which scan across thesurface of the resin. The liquid polymer changesinto a solid state at the point when the laser beamcomes into contact with the surface. The buildingof the part is done layer by layer. Support struc-tures are needed to support some of the criticalareas of the parts. An elevation mechanism willlower the part by a depth equal to the layerthickness after a new layer is formed. Thisprocess continues until the part is completed.Post-processing is necessary to harden the modeland remove the supports, if any.

The process involved in SGC is slightly morecomplicated than in SLA. SGC involves creating atemporary photomask of each layer, applying athin coating of photopolymers and exposing thelayer to a burst of ultraviolet light to cure it.The unsolidified residual photopolymer will beremoved and replaced by liquid wax. The wax isthen cooled to produce a solid layer. Thus the partis supported by solid wax which obviates the needfor special supports needed by SLA. The part isthen milled to give a constant increase in height.The process is repeated with the next layer until theentire model is built. At the end of the process,there is a solid block of wax encasing the finishedmodel. The model is then retrieved by meltingaway the wax.

LOM and FDM are classified under solid-basedrapid-prototyping systems as the parts are madefrom solid material. LOM makes use of sheetmaterials with adhesive backing. Plastics, metaland even ceramics sheets can be used but Kraftpaper with polyethylene-based heat seal adhesive

A Multimedia Approach to Teach Rapid Prototyping Systems 109

backing is most widely used. This is because it isboth cost-effective and environmentally benign.Like most RP system, the building of the part isdone layer by layer. This is done without the needto create additional support structures. A laserbeam traces the outline of the part on one newlayer of material. A new layer of the part is createdwhen a new layer of material is spread over it androlled over by a hot roller, which laminates themtogether. This process is repeated until the part iscomplete. Post-processing is necessary to removethe excess material from the part.

In the FDM process, the modelling material,usually wax or plastic, is in spool form. Thefilament on the spool is fed into an extrusionhead and heated to a semi-liquid state. The semi-liquid material is then extruded through the extru-sion head and then deposited in ultra-thin layers,one layer at a time at the desired location. Thisprocess continues until the part is complete. TheFDM Software, SupportWorks, can automaticallydetermine if supports are needed and generatethem if required. Supports created can then beeasily broken away when the part is complete.

SLS is one of the systems classified as a powder-based RP system. The SLS process is the onlytechnology with the capability to directly processa variety of materials including engineeringthermoplastics, investment casting wax, metalsand thermoplastic composites. To start the pro-cess, a thin layer of the heat-fusible powder isdeposited onto the part-building cylinder within aprocess chamber. A laser beam scans out the shapeof the part. The interaction of the laser beam withthe powder elevates the temperatures to the pointof melting, fusing the powder particles and form-ing a solid mass. The intensity of the laser beam ismodulated to melt the powder only in the areasdefined by the part's geometry. The rest wouldremain in powder form serving as natural sup-port for the part. When the cross-section iscompletely drawn, an additional layer of powderis deposited via a roller mechanism on top of thepreviously scanned layer. This prepares the nextlayer for scanning. This process continues untilthe part is complete. The final part is solidenough and does not need post-curing. Thefinished part is reasonably fine and requires onlyminimal post-processing such as sanding.

The technologies involved in RP are multi-disciplinary, involving computer science, chemis-try, physics, software engineering, mechanicalengineering, electronics, etc. and is therefore diffi-cult to present in a simple straightforward manner.Words are often inadequate in explaining ordescribing such a highly technical and visualsubject. Even diagrams have their limitations asthey are invariably static. Most RP technologiesand machines have different working principlesand materials, thus some form of visuals or anima-tion are important and essential. The processingprocedures of the RP systems are the most visuallyintensive part. One can understand the working

principles of RP systems better by seeing them inaction than reading directly from printed books.As the information comes from different sources,especially from different vendors, there is a need toconsolidate and present the information in acoherent manner. Multimedia is chosen to teachRP because it offers the most effective and expres-sive tool to enhance communication. Multimediateaching is more effective and efficient as moretopics are covered in a short time without subduingany information. Moreover, multimedia provides ahigh degree of accuracy in presenting information,especially the principles and functions of type ofRP technologies are ensured. Adapting multimediateaching for RP is a useful and rewarding experi-ence for the users. They can peruse the principlesof RP systems and navigate through the programat their own pace without going through pagesand pages of texts. For users who do not havemuch engineering background, multimedia teach-ing offers the easiest way to learn and understandthe principles of RP systems.

DESIGNING A MULTIMEDIA PACKAGE

Multimedia is a combination of texts, graphics,sound and animation. The success of a multimediaproduction requires an effective combination ofthe various media. A well designed multimediapackage should enhance the communication ofideas and balance the functionality of the programwith its usability. The main goal of communicationis to draw the user's attention and priority to moreimportant information on the screen. This involvesgiving attention and priority to critical informa-tion while not emphasizing the less importantinformation.

The phases of a multimedia production couldbe seen as a cross between the traditional soft-ware development cycle and that of a movieproduction [7]. They can be broadly categorizedinto the following:

� analysis and planning� design� storyboarding and scripting� media preparation� testing and revision� packaging and distribution.

The analysis and planning stage involves con-tent analysis, target audience, delivery require-ments, media requirements, staffing requirementsand project planning. It is at this stage that thedesigner decides what should be included in themultimedia software in order to cater to the needsof the target audience, the strengths and weaknessof different media with respect to the content, thetype of skills involved and the time available.

Multimedia production requires many skillscovering several disciplines. Both creative andtechnical people are needed to bring out high

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quality in a production. Figure 1 shows the level ofstaffing for a typical multimedia production.

For this multimedia package development, theconfiguration is scaled down to that shown inFig. 2 because of personnel constraints. With thisconfiguration, the design-cum-media developerwill have to cover the duties of the designer,animation producer, sound track producer andmedia author.

With an understanding of the goals and thescope of the development, the flow of the pro-gram is established with a task list and the time

allocated for each task. This is extremely crucialespecially when there is severe time and personnelconstraints.

The design stage involves the specification of thecontent and the user interface. Content focuses onthe look or appearance of the material on thescreen and the user interface defines the ways auser interacts with the program. There are twokinds of elements in user interface design: struc-tural and cosmetic. The structural element defineshow information is structured and linked and whatfunctions to provide at each point in the applica-tion. The cosmetic element defines the design ofthe appearance of buttons and icons and how theyare placed on the screen.

The goals of a good design are to enhance thecommunication of ideas and to balance the func-tionality of the program with its usability. Toachieve these goals, there is a need to organizethe content to meet the following requirements:

� good information balance� good visual balance� simplicity and functionality in design.

By having good information balance, it meansdrawing the user's attention to the more impor-tant information while de-emphasizing the lessimportant information. As the user is getting

Fig. 1. Ideal staffing for a small multimedia production.

Fig. 2. Actual staffing level.

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information directly from the screen, a good visualbalance between static and dynamic screen ele-ments are very important. The designer has tomanage the use of the screen space in order tomake sure that the screen is visually appealing andthe colours chosen promote clarity in the deliveryof the information. In an interactive display, theuser is frequently prompted to act on the informa-tion. Thus, the screen design must not only beclear, it must also be consistent. This aids usernavigation through the program. If this rule isnot observed, then it might leave the user frus-trated and disinterested to use the software, thusdefeating the original purpose of the software.

Colour is a useful tool for capturing attention.Effective use of it will enable the user to focus onthe important things on a particular screen. On theother hand, indiscriminate usage of colours willleave the user disorientated, confused and frus-trated. The colours chosen for the text shouldpromote clarity of the information and the back-ground colour should be light in order to give asmoothing and comfortable feeling.

The storyboarding processes for the productionof the multimedia software serves to present alogical sequence of events to the user whereas thescript describes the mood of the various events.This part is important as it serves to control theuser attention and thus improve on the informa-tion retention rates of the users. This can be doneby suitably selecting the fonts used, introducingvoice-over or background music, creating specialeffects like blinking buttons and synchronizing textwith animation sequences [8].

Pure animation cannot stand alone by itself.When animation is effectively combined withsound, the program becomes more exciting. Theselection of an appropriate sound-track can makea significant impact on the program. When soundis well synchronized with the animation, the pre-sentation becomes more lively and well organized.

Correct combinations of colours and light areadded to various objects to make them morephoto realistic.

DESIGN OF THE RP MULTIMEDIAPACKAGE

The primary objective of this multimedia packageis to aid the understanding and visualization of fiveRPsystemsdescribedearlier inthisarticle.Thetargetaudiences for this multimedia package are generallyuniversity students or lecturers who are using thisas a teaching aid or for technologists and engineerswho are keen to learn about RP technology.

The hardware configuration to run the programincludes an IBM compatible PC (with at least4 MB random access memory), a 1� 2 quartz(minimum) CD-ROM drive, a display monitorwith a minimum of 256 colours and a resolutionof 640� 480 or higher and two speakers. Thisprogram is executable in the Microsoft Windowsenvironment (version 3.11, Windows 95 andWindows NT compatible). A media control inter-face (MCI) compatibles sound card is required toplay the wave or musical instrument digitalinterface (MIDI) audio.

The program is designed to be both user-friendlyand interactive. Users can navigate through theprogram simply by using the mouse. The programstarts with a main menu (see Fig. 3) which promptsthe user to select the system to be explored. Thenames of the RP systems are spelt out in full toensure clarity. A soft `Quit' button at the bottomend of the menu allows users to quit the programeasily. Upon clicking on a selected system, theprogram will bring the user to a system menu.From there, the user can choose to view the detailsof the description product, its process, its applica-tions, its key benefits and company manufacturingthe selected system.

Fig. 3. Main menu showing the contents.

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In each of these topics, the users can access thefollowing information.

(a) In the products module, the specifications andother technical information of the system aredisplayed (see Fig. 4). Users can check out themachine size, work volumes, machine accuracyand the price range of the system. The differenttypes of material that can be used by thesystem are also listed here.

(b) In the process module, the program has theability to animate the building sequence of aprototype layer by layer. The procedure ateach stage of the animation is highlighted inblue. After the completion of the animation ofthat stage, the blue wordings will change togrey. When the entire animation sequence ofthe building process has completed, a `Replay'

button appears automatically at the bottomleft of the text (see Fig. 5). Users can eitherchoose to replay the animation of the buildingprocess, to recapitulate or go for other optionsavailable on the menu.

(c) In the applications module (see Fig. 6), theuser can browse through still visuals of theproducts manufactured by the selected systemusing the `forward' and `backward' keys dis-played on screen. They can also check out thecomments made by some users of the system tohave an understanding of its capability.

(d) In the key benefits module (see Fig. 7), theadvantages of using the selected system arelisted.

(e) In the company module (see Fig. 8), theaddress, phone number and e-mail address ofthe manufacturer of the systems are listed. The

Fig. 4. Specifications of a sterolithography system.

Fig. 5. Process module of a selective laser sintering system.

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person to contact for further information onthe system is also listed here to enable the userto follow up on more information, if necessary.It also serves as a direct source of contact forthe vendor concerned.

After exploring some or all of the five modules,the user can then return to the main menu andview another system. When the user has finishednavigating all the five different systems, he or shewill have a good understanding of RP and the typeof system that is most suitable for a particularapplication.

For this CD-ROM, it is estimated the averageuser can attain a reasonable understanding of theRP technology within an hour or so withouthaving to go through the many pages of texts.Realistic animation of the different RP systems

allows the user to observe how prototypes arebeing made on these systems. The user can appreci-ate the advantages of these systems and under-stand the limitations of these systems withouthaving to come in contact with the physical hard-ware. The information included in this CD-ROMis presented in an interactive manner so that theuser can access it easily. The user can browsethrough the program at will, without losing trackof the information.

Like any other software, the present programhas the need for improvement. Future work willinvolve designing a tutorial that can test andenhance user's level of understanding of RP sys-tems. When the user happens to answer a questionwrongly, the program can re-route to the appro-priate section in the program that provides theright answer. In this manner, the user can clear up

Fig. 6. Application of a laminated object manufacturing system.

Fig. 7. Key benefits of using a sterolithography system.

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any misconceptions or doubts more effectively.Another improvement will be synchronizing thesound with the animation. The program can run ina narrative manner. In this way, the user can gainbetter understanding of the RP systems when he orshe can see the animation of the RP system andlisten to the narrator explaining the process at thesame time.

CONCLUSION

Multimedia is widely acknowledged as anenvironment with great potential for learningand education. Rapid prototyping is a highly

visual and technical subject. The technologiesinvolved are multidisciplinary and fast evolving.The ability of multimedia to explain the principlesof RP systems far surpasses that of books. This RPmultimedia package is a useful tool for teachingRP to engineering students or technical personnel.It can serve as a quick reference for engineers whoare keen to know more about rapid prototypingbut can not afford the time to go through thebooks. Future work in developing the software willinvolve refining the program to run in a narrativemanner and to add in tutorial, which may serve asa gauge of the level of the user's understanding ofRP systems.

REFERENCES

1. C. K. Chua and L. F. Leong, Rapid Prototyping: Principles and Applications in Manufacturing, JohnWiley & Sons, Inc (1997).

2. M. Burns, Automated Fabrication: Improving Productivity in Manufacturing, New Jersey: Prentice-Hall (1993).

3. D. Kochan, Solid Freeform Manufacturing, Amsterdam: Elsevier Science Publishers (1993).4. A. Sloane, Multimedia Communication, McGraw-Hill (1996).5. K. F. Leong, C. K. Chua and Y. M. Ng, A study of stereolithography file errors and repair, Part 1:

Generic solution, Int. J. of Advanced Manufacturing, 12 (1996) pp. 407±414.6. K. F. Leong, C. K. Chua and Y. M. Ng, A study of stereolithography file errors and repair, Part 2:

Special cases, Int. J. of Advanced Manufacturing, 12 (1996) pp. 415±422.7. F. Botto, Multimedia, CD-ROM and Compact Disc: A Guide for Users and Developers, Winslow,

England: Sigma Press (1993).8. T. Yager, The Multimedia Production Handbook for PC, Macintosh and Amiga, London: Academic

Press (1993).

Chee-Kai Chua is a senior lecturer in the School of Mechanical Production Engineering. Hehas published over 70 technical papers in the area of CAD/CAM and rapid prototyping andco-authored a book on Rapid Prototyping Principles and Applications in Manufacturing. Hesits on several international conferences international program committees dedicated torapid prototyping.

Kah-Fai Leong is also a senior lecturer the School of Mechanical Production Engineering.He is also the co-author of the book on Rapid Prototyping Principles and Applications inManufacturing. Other than in RP he has also published in areas in product design anddesign education.

Fig. 8. Manufacturer of stereolthography system.

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Huang-Kheng Cheng is a researcher in the Gintic of Manufacturing Technology, NanyangTechnological University. He graduated from the School of Mechanical and ProductionEngineering in 1996.

Lai May Chow is an undergraduate in the School of Mechanical and ProductionEngineering, Nanyang Technological University. She received her Diploma in Mechatro-nics Engineering from Ngee Ann Polytechnic in 1994.

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