Integrating Rapid

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Background

Prototyping is an integral part of the complete

design process. Its purpose is to expose and

facilitate the elimination of design errors early

in the product life cycle, and preferably before

the majority of the resources required forprodu ction are committed. The benefits of

rapid prot otyping are obvious and well docu-

mented. Still, protot yping is often n ot per-

formed pr ior to a design being put into pro-

duction. An importan t reason for this omis-

sion is the up-front cost and time required to

prototype a design. Unfortun ately, the conse-

quence of infrequent prototyping is frequent

and expensive design changes late in the

prod uct life cycle, with th e extreme, bu t all

too comm on case, being a product recall.Today’s engineering curr icula do not

address adequately the impor tance of proto-

typing for verification and improvement of a

design. In som e cases it might be emphasized

in lectures, bu t it is seldom , if ever, practiced

in hom eworks, projects, or laboratories. T he

reasons for this omission in academia are

similar to those experienced in indu stry.

Successful prototyping requires awareness of

suitable technologies, access to these tech-

nologies, available time, and sufficient p er-sonnel. T he shortage of any of these elements

will effectively limit the opportun ity to realize

student designs physically within the cur ricu-

lum. T his is unfortu nate because students

today seldom gain true hand s-on experiences.

Most often they must settle for virtual or

paper solutions that fail to expose the many

intr icate details of their designs; details that , if

not addressed, will cause their designs to fail if

ever realized.

Recent advances in fabrication technologies

are increasingly enabling fast, inexpensive, and

easy-to-use part fabrication directly from

electronic CAD mod els. It is revolutionizing

the engineering design process as practiced in

industry, and it promises to have a similar

impact within academia by reintroducing

32

Rapid Prototyping Journal

Volume 3 · Number 1 · 1997 · pp. 32–37

© MCB University Press · ISSN 1355-2546

Integrating rapidprototyping into theengineering curriculum

– a case study Jan Helge Bøhn

The authorJan Helge Bøhn is an Assistant Professor in the Depart-

ment of Mechanical Engineering, Virginia Polytechnic

Instit ute and State University, Blacksburg, VA, USA.

Abstract

The emerging rapid prototyping technologies are having a

dramatic impact on the engineering design process. When

properly integrated, these technologies enable aggressive

prototyping throughout the design process and reduce the

likelihood of expensive design changes late in the product

lif e cycle. Unfortunately, few engineering students get to

experience first-hand the power of rapid prot otyping.

Reports on an ongoing experimental int roduction of

physical rapid prototyping t echnologies into the engineer-

ing curriculum at Virginia Tech. The experiments include a

senior technical elective approved for graduate credit

dedicated to rapid prototyping, a pilot programme within

Engineering Fundamentals, and the use of rapid prototyp-

ing equipment in Mechanical Engineering Senior Design.

T hese experiment s were made possible, in part , by

the N aval Surface Warfare Center, D ahlgren

Division un der contract N60921 -89-D-A239,

Order 0045. Any opinions, findings, conclusions,or recommen dations expressed in this paper are

those of the auth or and do not necessarily reflect

the views of the N aval Surface Warfare Center,

Dahlgren Division.



student design realization to the engineering

curricula.

T his paper reports on an ongoing experi-

mental introd uction of physical rapid proto-

typing technologies into the engineering

curriculum at Virginia Tech. T he experiments

include a senior techn ical elective approved

for graduate credit dedicated to rapid proto-

typing, a pilot program me within Engineering

Fu ndam entals, and the use of rapid prototyp-

ing equipment in M echanical Engineering

Senior D esign. To pu t this in perspective,

Virginia Tech is approximately the ten th

largest engineering university in the USA and

offers Bachelor of Science (BS), Master of

Science (MS), and Doctor of Philosophy

(PhD ) degrees in several fields of engineering,

including M echanical Engineering. The BSdegrees in engineering are four-year pro-

grammes in which the first year is comm on to

all fields of engineering. This first year

includes courses on Engineering Fun damen-

tals. T he fourth (senior) year is dominated by

a design experience sequence (senior design)

and a set of technical elective courses. T hese

techn ical electives are often also available to

graduate student s on the MS and P hD levels.

T he following sections d escribe available

facilities at Virginia Tech, present an overview

of the experiments, and speculate on the

future of rapid prototyping in engineering

curricula.

Facilities

Hardware

T he main rapid protot yping resource at

Virginia Tech is a fused d eposition modelling

(FD M) rapid p rototyping system[1]. T he

system, an F DM 1600, is equipped for ABS

plastic, nylon, and investment casting waxfabrication. T he students also have access to a

conventional TREE 325 Journ eyman 3-axis

mill with a Dynapath Delta 20M C NC

controller.

T he main rapid prototyping computer

facility is the Virginia Tech C omp uter Aided

Design Laborator y with its 16 IBM RS/6000

model 350 workstations. Each workstation is

equipped with 64 M B RAM, 2 G B local disk,

and a Gt4x graphics accelerator. The labora-

tor y is also serviced by an IBM RS/6000model 980 server with 128 M B RAM and 25

GB disk.

In ad dition, the C ollege of Engineering at

Virginia Tech requires each undergraduate

student to furnish their own IBM PC . T hese

computers are hence an import ant and conve-

nient resource, especially for less demand ing

computer aided design tasks.

Software

Almost any CAD system today is capable of

generating part m odels described in the .ST L

file format. T his is the de facto rapid proto-

typing indu stry standard file form at, and it is

used by the software controlling the F DM

1600 rap id prototyping system. Both I-D EAS

Master Series[2] in the VT CAD Laboratory

and AutoCAD[3] on the students’ PCs can

generate part models described in th is file

format. In add ition, I-D EAS Master Series

can also generate the g-code for the T REE

325 Journeyman mill. The latter required acustom m odification to an existing post-

processor that was made available by

SDRC[2].

T he part models described in the .ST L file

format are converted to g-code for the FD M

1600 rapid prototyping system using Qu ick-

Slice[1]. T his software is curren tly not avail-

able on the IBM RS/6000 platform. H owever,

the IBM RS/6000 workstations in the VT

CAD Laboratory can access this software

through X window sessions to an H P 9000

model 735 (99 MH z) with 96 MB RAM and

400 MB swap space ru nning Q uickSlice.

Senior technical elective

Every spring since 1995 Virginia Tech has

offered a course dedicated to rapid p rototyp-

ing. This course, “Int roduction to rapid

prototyping”, has un til now been offered on

an experimental basis, first as a graduate

course in 1995, and then, in 1996, as a

mechanical engineering senior technicalelective approved for graduate credit. T he

course has since been made perm anent in its

latter form .

First iteration

When t he course was first offered, there were

no layered m anufactur ing facilities available

at Virginia Tech. T his did not affect the lec-

tures, but it challenged the implementation of

the hands-on laboratory component. T he

solution was to expand the no tion of rapidprototyping beyond the emerging layered

manu facturing technologies and acknowledge

that it also includes conventional CN C

machining. U tilizing existing CN C machining

33

Integrating rapid protot yping into the engineering curriculum

Jan Helge Bøhn


Volume 3 · Number 1 · 1997 · 32–37



facilities within the M echanical Engineer ing

Departm ent, the stage was set for an inexpen-

sive course on layered manufacturing and

rapid prototyping[4].

T he main compon ents of the original

course were the lectures, an applied term

project, and a literature review term p aper.

T he applied term project demonstrated the

fundam ental concepts of layered man ufactur-

ing and illustrated t he utility of CN C

machining in rapid pro totyping. T he assign-

ment was to fabr icate a physical scale model

of the hu man nasal airways. Specifically, the

studen ts had to process raw medical comput-

er tomography (CT ) scan data to build a set

of three-dimensional CAD solid models,

each correspond ing to the volum e between

two consecutive C T scan slices. T hese solids

were then scaled up to match the 8" × 8" ×

0.25" (203mm × 203mm × 6.35mm ) sheet of

Lexan, and machined separately with a 3 /8"

(9.5mm ) ball end mill on a 3-axis CNC mill.

Each solid requ ired two set-ups and a custom

wood fixture to support the Lexan sheet.

Doub le-sided tape was used to hold down th e

Lexan sheet and prevent it from buckling

away from the wood fixtu re du ring milling. A

mod el of the hum an n asal airways was then

realized by stacking th e mach ined Lexan

sheets[5].

T he students completed their assignments

in teams of three using I-DEAS Master Series

with its Generat ive Machining; XV, Xpaint ,

and PBM image processing utilities; and C ,

C++ , FORTRAN77, and FORTRAN90

compilers. It was assumed that the stud ents

were familiar with I-DEAS. In case they were

not , the students were given three weeks to

refresh their basic I-D EAS modelling skills

using a series of non-graded self-paced work-

shops. With these basic skills in p lace, the

students completed two graded self-paced

workshops on I-D EAS Generative Machin-

ing, one of which included m ultiple setups.

Figures 1-3 illustrate the assignm ent:

Figure 1 shows the raw CT slice that includes

the hu man nasal airways. From this the stu-

dent s extracted the cont ours of the airways

(F igure 2), and comb ined adjacent slices to

form a finite thickness layer (F igure 3). T he

approp riate g-code was then generated with

the help of I-D EAS Generative Machining

for subsequent dou ble set-up, 3-axis CNC

machining.

Second iteration

T he second time the cour se was offered, the

students also had access to an FD M 1600

rapid prototyping system. T he literature

review assignm ent was therefore dropped to

make room for a second applied hands-on

assignment d esigned t o simulate a realistic

industry situation. The student s were asked to

present an idea for a new consumer product

and advocate its development. T he use of the

rapid prototyping system was encouraged t o

help make the po int of why their produ ct idea

should be developed.


Jan Helge Bøhn

Figure 1 Raw comput er tomography (CT) scan data


Volume 3 · Number 1 · 1997 · 32–37

34

Figure 2 Extracted nasal airway contour



T he six three-student teams were each

assigned a 22-hour time slot on the FDM

1600 rapid prototyping system. T heir designs

were devised using I-DEAS Master Series and

saved to the .ST L file format. T hese files were

then prepared for fabrication u sing Qu ick-

Slice. To prepare them for this task, the stu-

den ts were asked to com plete two sets of

graded self-paced workshops on QuickSlice.

T he produ ct ideas conceived by the stu-

dents included a snowboard b inding, a bicy-

cle binding, a cellular telephone, a miniature

pager, a multi-device remote cont rol unit, and

a combined wall clock and smoke detector.

Future improvements

Students tend to want to fabricate as late in

the semester as possible, in par t because they

want more t ime to refine and minimize flaws

in their designs. Still, every single studentteam to d ate has requested perm ission to

redesign and refabricate after seeing the result

of their first iteration. While this experience

has clearly indicated to these students the

need for mu ltiple rapid prototyping-redesign

iterations, th e future challenge for the course

will be to implement an actua l design-fabr ica-

tion-redesign-refabrication sequence within

the already tight t ime-frame of a single semes-

ter, especially when com bined with a signifi-

cant CN C assignment.One solution to this challenge is to cond uct

the CN C and F DM assignments in parallel

throughout the semester by having half of the

teams complete their CN C assignments

dur ing the first half of the semester and their

FD M assignments during the second half,

and the rest of the teams complete their

assignments in the opposite order. Then,

within their respective half of a semester, each

student team is assigned two separate fabrica-

tion days three weeks apart. T his permits a

single rapid prototyping system to ser vice 15

student teams with a d esign-fabrication-

redesign-refabr ication sequence within a six-

week period, or rather, 30 t eams within a

semester, all while leaving weekends open for

make-ups and other activities. H ence, with

four students to a team, on e rapid prototyping

system can service 120 students per semester.

Engineering fundamentals

Rapid prototyping was introd uced du ring the

spring 1996 semester to a pilot group of

students in EF 1006 “Introdu ction to engi-

neer ing” at Virginia Tech. This is a first-year

und ergraduate, second-semester course in

engineering fundamentals. Stud ents in this

course are introd uced to elementary three-

dimensional design using AutoCAD, and by

mid-semester th ey are well on their way with

their term design projects.

An informal experiment was devised to

introduce interested Engineering Fundamen-

tals students and their faculty to rapid proto-

typing. In the experiment, six teams of three

students each were offered an extracurricular

one-hour evening lecture on rap id prototyp-

ing, followed b y an evening laboratory session

in which they would process their CAD mod-

els and fabricate their par ts. T hese sessions

were schedu led in the latter half of the semes-

ter and it was assumed that th e students

would have their designs ready for fabrication

at the time of the laboratory session.

Observations

It was assumed that the student edition of

AutoC AD (release 13) was capable of gener-

ating CAD m odels described in the .ST L file

format. It had been assured by the distributor,

it was documented in the instruction m anu-

als, and it was verified with a set of experi-

ments using the machines in th e Engineering

Fu ndam entals PC laboratory. Still, it was

discovered on the n ight of the first laboratorysession that the software version installed on

the machines of most students and all the

Engineering Fundam entals faculty was

unab le to generate .ST L files. T his problem

35


Jan Helge Bøhn


Volume 3 · Number 1 · 1997 · 32–37

Figure 3 3D CAD model of slice ready for NC tool path

generation using I-DEAS Master Series Generative

Machining



was resolved in time for the subsequ ent

sessions by having the par ticipating students

create .STL files using machines that were

known to operate correctly.

Another class of problems encoun tered was

designs that were unsuitable for F DM fabri-

cation. Th is included non-solids that did n ot

enclose a volum e, massive volumes of mater ial

that would have taken too long to bu ild, an d

structurally weak configurations with mem-

bers too thin to be bu ilt once scaled down to

fit within the build volume. T he solutions to

these problems varied. Some students submit-

ted sub-par ts that could be fabricated, while

others redesigned their parts, for instance by

converting a surface or wireframe model into

a solid.

Future improvements

T he above problems were all minor in nature

and are all easily solved. F or instance, the

problems encountered when generating .ST L

files using AutoCAD were on ly a logistical

inconvenience and will be eliminated in time

for the next entering engineering class.

Solving the problems that are du e to

designs that are unsuitable for FD M fabrica-

tion, on the oth er hand, will require a more

concerted effort. T hese problems are largelydue to stud ents’ unfamiliarity with C AD

modelling in general and the FD M 1600’s

fabrication abilities in part icular. T here

appear to be at least two solutions to these

problems: first, studen t assignments shou ld

be formulated such th at they are inherently

suited for FD M fabrication. Second, a short

list of written design guidelines out lining the

most significant FDM fabrication limitations

should be made available to students. Togeth-

er, these solutions should streamline th e rapidprototyping process and afford a relatively

large number of students the oppor tun ity to

explore rapid p rototyping as an integral part

of the design process.

Senior design

T he rapid prototyping facilities were also used

in two senior d esign p rojects at Virginia Tech

dur ing the spring 1996 semester. In the first

project the student s were required to fabricate

a dimensionally precise air intake restrictor for

the formula car project. T he competition

rules required that all air to th e engine had to

pass through a circular cross-section not to

exceed 20mm in diameter. The students

therefore designed an “ideal” interior of the

air intake restrictor, shaped to m inimize the

turbu lence of the air flowing throu gh the

restrictor an d thereby maximizing the air flow.

T he shape was first described using C adkey;

then it was exported to I-D EAS and made

into a solid. T he solid was fabricated on the

FD M 1600 rapid prototyping system using

investmen t casting wax. T he surface of the

wax par t was cleaned and polished with an

effective and, in this case, readily available

solvent, n amely, 100 octane gasoline. F iber-

glass was then laid over the wax, and th e wax

was melted ou t with a heat gun . F inally, the

wax remains were washed away to reveal a

smooth and dimensionally precise air intake

restrictor.

In the second project, students were

designing a nozzle for the active mixing of fuel

and oxidizer un der the control of micro-

electromechanical system (MEM S) actuators.

T he final design incorporated a com plex set

of inter nal air channels, complete with space

for installing the actuators. An experimental

version of the nozzle was described using

AutoCAD and fabricated on the FD M 1600

rapid prototyping system using ABS plastic.

Conclusions

Physical rapid proto typing has b een intro-

duced on an experimental basis into the

engineering cur riculum at Virginia Tech. T his

includes a senior- level techn ical elective

dedicated to rapid prot otyping, a pilot pro-

gramme within Engineering Fun damentals,

and the use of rapid prototyping equipment in

senior design.

T he senior-level technical elective has

matured and will continue as a permanent

course with few modifications. Its laboratory

componen t can easily be stru ctured effectively

to accommodate 30 groups, or 120 students,

per semester per rapid prototyping system

without conflicting significant ly with ongoing

research activities.

T he pilot programme in Engineering

Fu ndam entals has demonstrated that rapid

prototyping with first-year undergraduate

students is feasible. H owever, the logistics of

how best to fit these activities within the

existing programme, and the resources that

will be required, need to be explored further.

36


Jan Helge Bøhn


Volume 3 · Number 1 · 1997 · 32–37



T he experiments with rapid p rototyping in

senior design have demonstrated their utility,

both for developing physical conceptual

designs, and for enabling advanced and inno-

vative manufactu ring processes.

T he experiments have also shown that

initiating educational activities in rap id proto-

typing need not be expensive[4], especially in

an environment with existing computer-aided

design activities. While minor hardware addi-

tions may be needed, existing fabrication

equipm ent will often suffice. In the case where

new equipment is needed, a table top CNC

milling machine can be acqu ired for less than

US$1 ,300[7] and a low-end layered manufac-

turing system for less than U S$5,000 [8].

Ind eed, the experiments at Virginia Tech have

shown th at it is not imperative that stud ents

use industry-grade systems. Rather, it is more

impor tant that they get to realize their designs

through an iterative design-fabrication-

redesign-refabrication sequence. Specifically,

for a course like the senior technical elective, it

suffices to provide a class of 15 to 30 teams

with one CN C machining and one layered

manu facturing system. T his represents an

expense of US$6,300 , assuming that the

necessary CAD workstations, CAD software,

and (old) PC s to dr ive the fabrication systems

are alread y available.

References

1 Stratasys, Inc., 14950 Martin Drive, Eden Prairie,

Minnesota 55344-2020, USA, http://www.stratasys.com

2 Structural Dynamics Research Corporation, 2000

Eastman Drive, Milford, Ohio 45150, USA,

http://www.sdrc.com

3 Autodesk, Inc., 2320 Marinship Way, Sausalito,

California 94965, USA, ht tp://www.autodesk.com

4 Bøhn, J.H., “An inexpensive course on layered manu-

facturing and rapid prototyping” , Proceedings of 16th

ASME Computers in Engineering Conference , Irvine,

CA, 18-22 August 1996, paper 96-DETC/CIE-1430.

5 Guilmette, R.A. and Gagliano, T.J., “ Construction of a

model of human nasal airways using in vivo morpho-

metric data” , Proceedings of 7th International

Symposium on Inhaled Particles , Edinburgh, Scotland,

16-21 September 1991.

6 Burns, M.,Automated Fabrication: Improving Produc-

tivity in Manufacturing , Prentice-Hall, Englewood

Cli ffs, NJ, 1993.

7 MAXNC, Inc., 6509 W. Frye Rd., Suite No. 3, Chandler,

Arizona 85224, USA, ht tp://www.maxnc.com

8 Schroff Development Corporation, PO Box 1334,

Mission, Kansas 66222, USA, http://www.schroff.com

37


Jan Helge Bøhn


Volume 3 · Number 1 · 1997 · 32–37

Integrating Rapid

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