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RAPID PRODUCT DEVELOPMENT AND MANUFACTURING B D D 4 0 3 0 3

custom made and distinctive if possible 'ndividual trimmings and

technical details of cars demonstrate this impressively

Environmental requirements

.nvironmental compatibility and the ability to recycle products and theirpackaging determine the buying behavior of customers as subsequent

costs are dependent on them

Decreasing li etime o products

# drastic decline in the lifetime of all types of products is being

witnessed #ccording to leading market research agencies the period of

time over which a product can be placed pro%tably in the market has

nearly halved over the last /0 years Studies from various sources agreethat this trend will continue at a rate of about 1 per year 2)igure

!he speed of change will largely depend on the line of business 5hilst

the electrotechnical industry or suppliers to car manufacturers have,

owing to their intensive use of new methods, already e$hausted the

potential to a great e$tent, more conservative lines of business such as

the machine6tool manufacturing industry still have considerable

potential

Decreasing prices

!he price of a product is gaining increasing in+uence in the buying

decision 7lobal markets and fast communication between continents

enable a worldwide price comparison 7eographical niches can no longer

be occupied, at least not for long

1.1 Critical Factors for Succ ss a!" Co#$ titi% Strat &i s

8ritical factors for success are de%ned by Siegwart and Sieger

9S'.75#:!; < as measures by which single in+uences may be condensed,

thereby enabling the measurement of the degree of success of a company

!he in+uences discussed in the preceding section and the resulting

consequences for product development point to the following factors for

success&

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Shortening of the product development time

:eduction of costs

'ncrease in +e$ibility 2product and production

'mprovement of quality

!his list is not universally applicable but it does represent today=s

generally accepted consensus !he single critical factors of success are

not independent of each other in the mathematical sense* they represent

values that, when weighted and interrelated in a strategy, enable

conclusions to be drawn !he strategy of a company e$presses how it

considers its own interaction with its competitors #ll critical factors for

success of a product, especially time and cost, can be condensed into onekey element& the >time to market ? >!ime to market? means the time that

elapses between the decision to develop and produce a certain product

and its introduction into the market

!his dominance of time over money, typical for today=s products, has

not only an absolute but also a relative dimension 't is not solely a

question of making the right decisions within a short period of product

development* of equal importance is making those decisions as early

as possible 'n addition it should be reali"ed that although the

accumulated e$penditures for product development early in the

process are still low, a large percentage of future costs is already

determined over the course of the development

!he graph shows clearly that the relationships are even more dramatic at

the commencement of product development& 401 of the total costs are

already de%nitely %$ed after the idea and draft phase, although at thispoint in time only negligible costs of /1 to 31 of the total costs have been

incurred .ngineers are often surprised to discover that it is important not

only to make the right decision as early as possible, but also to make that

decision %nal !he later changes are made, the more e$pensive they will

be )igure shows that the costs for a certain late change to a product

grow e$ponentially with the progress of product development 'n a

logarithmic scale this appears as a straight line @ere the same change is

shown but at diAerent stages of product development

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)igure !he costs for identical changes of a product at various phases

of product development

't follows from this not only that changes to the design become more

e$pensive and time6consuming the further the product development has

progressed, but also that product de%ciencies recogni"ed too late can

result in costs that threaten the viability of the entire pro ect 5hoever

doubts these %ndings should bear in mind that the cost for an alteration to

a large machine tool can speedily reach several hundreds of thousands of

dollars and a recall of automobiles can easily top billions even though the

defective part may be valued at mere cents

!o summari"e, it follows that the minimi"ing of product development time

is the key management ob ective, thereby enabling optimal total pro%t to

be achieved and e$penditure to be considered a time6dependent variable'n times when people focus on cost reduction, this is an important point

1.' Mo" ls i! Ra$i" Pro"uct D % lo$# !t Proc ss

Cew product strategies take into account that the requirements on

products and thereby product development have changed !he following

subsections discuss the in+uence of models and prototypes on the optimalimplementation of these new strategies !he observations show that for

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new product development strategies it is important not only to use models

but also to consider how fast they are available, at what step of the

development process, and the interactions that occur !he accepted terms

and de%nitions of classical product development are used !he demands

on models diAer according to the degree of progress the product

development has reached 't is sensible to agree on a model de%nition and

to assign this to certain steps in the product development irrespective of

the question of how these models are produced 'n the relevant literature

a large number of various terms and suggestions for model de%nitions can

be found n the one hand they are often characteri"ed by the planned

use and by specialties typical for certain branches, and on the other hand

they are often too speci%cally orientated to rapid prototyping processesProportional model

Shows the outer shape and the most important proportions )acilitates

communication and motivation, supports fast e$change of

communication about the intended product properties, and enables a

fast consensus on the product idea !he production process must be fast,

simple and cheap Disposal and recycling are very important

-roportional models are often called >concept models? or >show6and6tell

models ?

Degree of abstraction& high* degree of detailed speci%cation& low*

functionalities& none

Ergonomic model

Supports the fast decision about feasibility 2is it possible to develop this

product and should it be done Shows important details for operation

and use, and also, if applicable, important partial functions

Degree of abstraction& medium* degree of detailed speci%cation&

medium* functionalities& some

Styling model

Shows the outer appearance as close as possible to the 2series sample

Surface %nish needs to have >showroom? quality Supports the fast

decision on construction and manufacturing methods .nables third

parties 2customers, sales, press, suppliers to pass their udgments at anearly stage, enables public relations work

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Degree of abstraction& low* degree of detailed speci%cation& partially

high* functionalities& some

Functional model

.nables the proving of the numerical simulation calculations and theearly testing of certain functions 2how it could be assembled, easy

maintenance, and kinematics Shows some or all important functions, if

necessary without showing the outer shape )orms the basis for inquiries

by customers and suppliers 7ives relevant information for tool and mold

manufacturing, for the construction and installation of the means of

production

Degree of abstraction& low* degree of detailed speci%cation& high*

functionalities& several

Prototype

:esembles the 2series sample closely or, if necessary, e$actly 's

produced according to production documents !he only diAerence from

the series product lies in the production process .nables the testing of a

single or several product properties 2how it can be assembled,

electability, start of special approval processes .nables the production

of tools 2rapid tooling .nables the preparation for market introduction

by press campaigns

Degree of abstraction& none* degree of detailed speci%cation& high*

functionalities& all

Sample

#lready produced in series, possibly a pilot batch, production batch,

preproduction, or principal batch .nables the entire testing of all product

properties Supports the training of production and maintenance

personnel, supports the start of mass production, enables the

ad ustment of production and assembly sequence Supports the detailed

planning of customers and suppliers

Degree of abstraction& none* degree of detailed speci%cation& high*

functionalities& all

Solid images

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8overing& -roportional models, ergonomic models and styling models or

>show6and6tell? models Eisuali"ing proportions and general appearance

Geometrical prototypes

!esting of handling, operation and use Eisuali"ing the e$act shapeincluding the desired surface qualities

Functional prototypes or models

8overing& )unctional models, prototypes and samples

Below shows the simpli%ed de%nition of model classes in relation to the

main product development steps as de%ned in )ig /

Figure !" Steps o product development in relation to various model

defnitions

#lthough engineers readily agree on the meaning and the terminology of

functional models, prototypes, and samples, the classi%cation into

proportional models, ergonomically models, and styling models is poorly

understood and the value of these models is generally doubted 't is,

however, a key process in product development to agree on the product

and its general reali"ation

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!he conventional model making process, however, does rely on the oint

database in the form of two6dimensional 2/D drawings and sketches, but

it usually changes the geometry in the course of necessary

>interpretations? of the /D drawings during the model making !his step isoften taken deliberately to create the %nal geometrical form which is then

measured and returned to the design process !his means that during the

time when the model is being made there e$ists no de%ned database to

which other members of the team could refer Simultaneous engineering is

therefore not feasible for the duration of the model making

1.( Ra$i" Protot)$i!& *istor)

!he development of :apid -rototyping is closely tied in with the

development of applications of computers in the industry !he declining

cost of computers, especially of personal and mini computers, has

changed the way a factory works !he increase in the use of computers

has spurred the advancement in many computer6related areas including

8omputer6#ided Design 28#D , 8omputer6#ided Fanufacturing 28#F and8omputer Cumerical 8ontrol 28C8 machine tools 'n particular, the

emergence of :- systems could not have been possible without the

e$istence of 8#D @owever, from careful e$aminations of the numerous :-

systems in e$istence today, it can be easily deduced that other than 8#D,

many other technologies and advancements in other %elds such as

manufacturing systems and materials have also been crucial in the

development of :- systems !able traces the historical development of

relevant technologies related to :- from the estimated date of inception

#a$le ! % &istorical development o 'apid Prototyping and related

technologies

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!he beginning of rapid prototyping techniques are available in the latereighties and were used for the production of prototype and models

@istory of :apid prototyping can be found in the si$ties #n engineeringprofessor, @erbert Eoelcker, thought himself of the possibilities of doinginteresting things with computer controlled and the automatic machinetools @e tried to %nd a way in which the automated machine tools can beprogrammed by using the output of a design program of the computer @edeveloped the fundamental tools of mathematics that clearly e$plains thethree dimensional aspects and resulted in the earliest theories of algorithmic and mathematical theories of solid modeling !hey formed thebasis of modern computer programs and are used for designing almost all

things mechanical, ranging from the small toy car to the tallest skyscraper8arl Deckard, from the Gniversity of !e$as, came up with a goodinnovative idea @e pioneered the layer based manufacturing, where hethought of building the model layer by layer @e printed 3D models byusing laser light for fusing metal powder in solid prototypes, single layer ata time Eoelcker and Deckard %ndings, innovations and researches hadgiven e$treme momentum to the signi%cant new industry known as :apid-rototyping 9Hfaster than what? or at least >how fast > !here is also a

certain danger in using the term >rapid?& it could mean that these

processes are intrinsically faster than others !his is not necessarily so

!here is no general rule to be found here !he speed of rapid prototyping

processes depends to a great e$tent on the geometry 5hoever needs

only a board of / O / O inch is better served by the semi %nished

product and a saw Co computer6aided model making process will be

faster

!he word >prototyping? is also inapt because many applications of

computer6aided production processes do not deal with the production of

prototypes in the strict sense #part from design models and

demonstration models, molds and tools are made and even 2small series

are produced

!he term rapid prototyping has, however, an unbeatable practical

advantage 't is engraved in everyone=s memory 't is viewed as a

synonym for computer6controlled and therefore automatic generative

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processes :apid prototyping together with its most prominent member,

stereolithography, are well known in this combination !hey are self6

e$planatory and thereby ful%ll the most important requirements of a

standard term

'n contrast, most of the other terms used and e$plained in the te$t or in

the appendi$ require additional e$planation by the user& >!hat is

something like rapid prototyping ? )or this the reason we call this process

>rapid prototyping? right from the start

!he terms rapid tooling and rapid manufacturing are subordinate to that of

rapid prototyping and relate to special uses and areas of application

:apid prototyping encompasses the science of generative production

processes and is therefore a technology wing to their newness, some

applications acquire their own terminology for techniques or strategies

2often called >applications? as well which are often used synonymously

with those of the technology 5hereas in milling machine technology there

is no diAerentiation in method between producing positives and negatives,

this is de%nitely the case in rapid prototyping technology where

compulsory standards are only partially available 't is, however, very

important to reali"e that the application of rapid prototyping technology is,

methodically, really a technique !herefore, concept models and geometric

prototypes 2solid imaging as well as functional prototypes and technical

prototypes 2functional prototyping on the one hand, and generative tool

making 2rapid tooling and generative series production 2rapid

manufacturing on the other hand, adopt the status of a strategy

irrespective of their practical signi%cance

Depending on the architecture of the machine and the material used, the

application of rapid prototyping technology leads to solid images or

concept modelsNgeometry prototypes or to functional prototypesNtechnical

prototypes as shown in )igure 3 #pplications especially for metal

materials have brought about the development of generative tool making

2rapid tooling and generative series production 2rapid manufacturing

-rototypers used for the production of solid images or concept

modelsNgeometry prototypes 2concept modeler and those used for the

production of functional prototypesN technical prototypes are

technologically similar 5hereas concept modelers are suitable for the

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production of relatively rough but cheap models, functional prototypers

produce more comple$, more detailed, and more precise P but also more

e$pensive P models

Because rapid prototyping processes are practically unlimited in theirability to form comple$ shapes, they can produce both positives and

negatives Cegatives are produced as dies or molds 2die or mold inserts,

respectively for preproduction or small6batch production with

corresponding positives 'n this case, it is called generative tool making or

rapid tooling :apid tooling is, therefore, of special importance because

the >step into the tool? is very time consuming, prone to faults, and

e$pensive for all product generating processes !he terms generative

series production or rapid manufacturing 2also& rapid production assumethat rapid prototyping methods can be used directly for the production of

all kinds of 2mass products !his is already being done with special

applications such as, for e$ample, medical implants 28-67mb@, 7ermany

or plastic aligners for straightening adult teeth 2#lign !echnology, 8#,

GS#

Figure !* 'apid prototyping technology and its applications

'f we follow the actual terminology the following de%nitions result&

'apid prototyping

:apid prototyping describes the technology of generative production

processes

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Solid imaging and functional prototyping describe the applications of rapid

prototyping technology Solid imaging includes the production of relatively

simple, mechanical6technological nonresilient models that nonetheless

display the outer form and the features of the %nal component relatively

well )unctional prototyping is the application of rapid prototyping

technology to prototypes made of plastic, metal, or other materials that

simulate one or more mechanical6technological functionalities of the %nal

series component 'n many cases solid imaging and functional prototyping

often become the time6determining factor during the %rst phase of product

development

'apid tooling

:apid tooling describes those applications that are aimed at making tools

and molds for the production of prototypes and preseries products by

using the same processes as those used in rapid prototyping !his

concerns both the model 2positive as well as the mold 2negative

#nglophones talk here of >pattern making? and of >mold making ? #gainst

this background, rapid tooling becomes the time6determining factor in the

second phase of product development, that of optimi"ing the actual

product, developing the means of production, and the production itself

'apid manu acturing

By rapid manufacturing or rapid production we understand rapid

prototyping applications that produce products with serial character !hese

can be positives produced directly with rapid prototyping methods 2e g ,

plugs in smallest series or tools produced with rapid prototyping

processes usable directly for the production of the required quantities !he

mechanical6technological properties of today=s rapid materials are in most

cases still far from the target characteristics of the products )or largerproduction quantities production times are still relatively lengthy )or these

reasons rapid prototyping is usually uneconomical and rapid

manufacturing, with a few e$ceptions, does not 2yet belong to the

production processes that are in use

!he possibilities of rapid manufacturing inspired the phantasies of

engineers immediately after details of the %rst rapid prototyping processes

were published Scenarios in which spare6part stocks are completely

eliminated and replaced by appropriate rapid prototyping installations

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> ust in time? have been known for some time now ne suggestion of

making the entire stock6keeping of naval units, for e$ample on an aircraft

carrier, super+uous while simultaneously guaranteeing a +e$ible provision

by using appropriate rapid prototyping 2metal installations was especially

discussed in detail

ther scenarios in which the use of rapid manufacturing methods alone

can enable the transport of tools and spare parts to distant celestial

bodies such as Fars are also being seriously discussed at present !hese

re+ections are of value only, however, if the prototypers are able to work

with the materials available there .ven if these scenarios still seem

unrealistic today, recogni"able development trends make such

applications ever more probable :apid manufacturing as a tool of >customi"ed mass production? processes will gain more importance in

future in view of the following development trends in rapid prototyping

processes and the demands made on the products&

shorter product life time,

increasing product comple$ity,

growing individuality of products,

smaller series)igure 4 shows the relationships of rapid prototyping, rapid tooling and

rapid manufacturing to the basic product development phases

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Figure !+ 'elating o rapid prototyping, rapid tooling and rapid

manu acturing processes to the $asic product development phases

1.0 G ! ric C+aract ristics of Ra$i" Protot)$i!& Tc+!olo&)

'ndustrial rapid prototyping systems on the market today are sub ect to a

high development speed Cew processes still in the laboratory stage or

under development today will break into the market #t the same time,

well tried and tested systems will be upgraded within a relatively short

time

#s the equipment presently on the market will be obsolete or approaching

obsolence over relatively short periods the physical6technological bases of

the various processes not only facilitates the assessment of the current

processes, but it also supplies the basis for the assessment of future

industrial processes 'n reality, however, overlaps and repetitions are

unavoidable :apid prototyping processes belong to the generative 2or

additive production processes 'n contrast to abrasive 2or subtractive

processes such as lathing, milling, drilling, grinding, eroding, and so forth

in which the form is shaped by removing material, in rapid prototyping the

component is formed by oining volume elements

#ll industrially relevant rapid prototyping processes work in layers Kike

the half6breadthplan of a ship, known from classical model making, single

layers are produced and oined to a component 'n the strict sense, rapid

prototyping processes are therefore /QD processes, that is stacked up /Dcontours with constant thickness !he layer is shaped 2contoured in an 2$6

y plane two6dimensionally !he third dimension results from single layers

being stacked up on top of each other, but not as a continuous "6

coordinate !he models are therefore three6dimensional parts, very e$act

on the build plane 2$6y direction and owing to the described procedure the

stepped in the "6direction whereby the smaller the "6stepping is, the more

the model looks like the original

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#lthough all rapid prototyping processes known today work in this way as

/QD processes, some processes 2e g , e$trusion processes are in principle

3D processes, which means they can add incremental volume elements at

any chosen point of the model

!he special characteristic feature of rapid prototyping processes is that the

physical models are produced directly from computer data 'n principle it is

thereby unimportant whence the data are provided as long as they

describe a 3D volume completely Data from 8#D design, from the

processing of measurings and reverse engineering or other measurements

9computer tomography 28! , magnetic resonance tomography 2F:! < may

be used equally well

'n this way model making has become an integral part of the computer6

integrated product development )rom the product development aspect

rapid prototyping models can, therefore, be regarded as three6dimensional

plots or facsimiles of the corresponding 8#D data !he decisive advantage

in contrast to classical manual or semiautomatical model6making

processes lies in the fact that the data remain unaltered by the model

making #s a result no data need to be taken from the model Because themaking of rapid prototyping models does not alter the common database,

rapid prototyping processes have become the most important elements of

modern product development strategies such as simultaneous engi6

neering !he generation of layer information is based on a purely

computer6orientated 8#D model !he 8#D model is cut into layers by

mathematical methods !his layer information is used for the generation

of physical single layers in a rapid prototyping installation, the so6called

prototyper !he total sum of the single layers forms the physical model

!his is the principle of model generation by rapid prototyping as shown on

)igure

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)igure !he principle of model generation by rapid prototyping

Proc ssst $

D scri$tio!

8onvert8#D modelto S!Kformat

8#D model is converted into S!K format that represents thesurface of the part by many triangles

rient part2s

perator uses e$perience to select best orientation fore$ample to minimise build time or to achieve tolerances onkey dimensions

7eneratesupports ifrequired

Software normally automatically generates supports whereneeded, however e$perienced operators can usually editthese for e$ample to minimise need for manual supportremoval during post6processing )igure 4 shows the design of a part with supports in place

8reate slice%les

Software generates the /D pro%le description of each layerof the part plus supports to be made

)abricatepart plussupports

/D pro%les are sent to the machine to drive part creation, fore$ample by controlling mirrors that allow lasers to scanacross a powder bed to sinterNfuse powder where required

-ost6process

5hen parts have been fabricated they need to be cleaned,for e$ample to remove e$cess unfused powder or to removesupport structures )urther work such as sanding,in%ltration, painting or electroplating may also berequired depending on the process used and the

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intended application for the part

1. Classi catio! Of Ra$i" Protot)$i!& S)st #s

5hile there are many ways in which one can classify the numerous :-

systems in the market, one of the better ways is to classify :- systems

broadly by the initial form of its material, i e the material that the

prototype or part is built with 'n this manner, all :- systems can be easily

categori"ed into 2 liquid6based 2/ solid6based and 23 powder6based

)undamentally, the development of :- can be seen in four primary areas

!he :apid -rototyping 5heel in )igure J depicts these four key aspectsof :apid -rototyping !hey are& 'nput, Fethod, Faterial and #pplications

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)igure J& !he :apid -rototyping 5heel depicting the four ma or

aspects of :-

-rof R - ruth suggests the later term T'ncrescent= means Ubecoming

gradually greaterU 25ebster Dictionary and is more general than UdepositUor UadditionU Some techniques use direct 3D solidi%cation 2e g holographic

polymeri"ation and do not really deposit material in successive layers

UFaterial 'ncress FanufacturingU clearly identi%es those techniques as the

antipode of UFaterial :emoval FanufacturingU !he classi%cations of

material incress manufacturing techniques are given bellow which relates

to the way material is created or solidi%ed

Ra$i" Protot)$i!&

Li2ui"/3as "

Kiquid6based :- systems have the initial form of its material in liquid state

!hrough a process commonly known as curing, the liquid is converted into

the solid state !he following :- systems fall into this category&

2 3D Systems= stereolithography apparatus 2SK#

2/ b et 7eometries Ktd =s -oly et

23 D6F.8=s solid creation system 2S8S

24 .nvision!ec=s -erfactory

2 #utostrade=s .6Darts

2J 8F.!=s solid ob ect ultravioletPlaser printer 2S G-

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2H .nvision!ec=s Bioplotter

Soli"/3as "

.$cept for powder, solid6based :- systems are meant to encompass all

forms of material in the solid state 'n this conte$t, the solid form can

include the shape in the form of a wire, a roll, laminates and pellets !he

following :- systems fall into this de%nition&

2 Stratasys= fused deposition modeling 2)DF

2/ Solidscape=s benchtop system

23 8ubic !echnologies= laminated ob ect manufacturing 2K F

24 3D Systems= multi6 et modeling system 2FRF

2 Solidimension=s plastic sheet lamination 2-SK N3D System=s

invision

Po4" r/3as "

'n a strict sense, powder is by6and6large in the solid state @owever, it is

intentionally created as a category outside the solid6based :- systems to

mean powder in grain6like form !he following :- systems fall into this

de%nition&

2 3D Systems=s Selective Kaser Sintering 2SKS

/ 2/ L 8orporation=s !hree6Dimensional -rinting 23D-

3 23 . S=s . S'C! systems4 24 ptomec=s laser engineered net shaping 2K.CS

2 #rcam=s electron beam melting 2.BF

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RAPID PRODUCT PROCESS

!he ob ective of rapid prototyping is to quickly fabricate any comple$6shaped, three6dimensional part from 8#D data :apid prototyping is an

e$ample of an additive fabrication process 'n this method, a solid 8#D

model is electronically sectioned into layers of predetermined thickness

!hese sections de%ne the shape of the part collectively

!he focus of this chapter is on those system elements that aAect the

shape of the part& the 8#D %le, the S!K 2stereolithography %le, problems

and repairs of S!K %les, and other %le formats 'n short, the modeling

principles of rapid prototyping will be discussed in this chapter

'.1 3ASIC AUTOMATION PROCESS

:apid prototyping is essentially a part of automated a$rication, a

technology that lets us make three6dimensional parts from digital designs

9 < !here are several advantages of automated a$rication over manual

fabrication and molding processes Some of these advantages are

computer6aided design, quick design changes, and precise dimensioning

)abrication processes, manual or automated, can be classi%ed as

subtractive, additive, or formative !hese processes are shown in )igure

/

Su$tractive Process 'n this process, one starts with a solid block of

material larger than the %nal si"e of the %nished ob ect, and then

material is removed slowly until the desired shape is reached

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CHAP

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Subtractive processes include most forms of machining processesM

computer numerical control 28C8 or otherwise Fost widely used e$6

amples include milling, turning, drilling, planning, sawing, grinding,

electrical discharge machining 2.DF , laser cutting, water6 et cutting, and

many other methods

-dditive Process Gnlike the subtractive process, this process involves ma6nipulation of material so that successive pieces of it combine in the right

form to produce the desired ob ect !he rapid prototyping process 2layered

manufacturing falls into the additive fabrication category )igure / /

shows the additive layer6by6layer process of rapid prototyping .$amples

of :- processes include SK#, )DF, K F, SKS, solid ground curing 2S78 ,

direct shell production casting 2DS-8 , and 3D printing 23D-

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Fi&ur '.' #dditive layer6by6layer process

Formative Process 'n this process, mechanical forces are applied to ma6

terial so as to form the desired shape .$amples of the formative

fabrication process include bending, forging, electromagnetic forming,

and plastic in ection molding

!wo or three of these processes can be combined to form a hy$rid process

@ybrid processes are e$pected to contribute signi%cantly to the production

of goods in the future -rogressive press working is an e$ample of hybrid

machines that combine two or more fabrication processes 'n progressive

press working a hybrid of subtractive 2as in blanking or punching and

formative 2as in bending and forming is used

'.' PROCESS C*AIN

#ll prototypes made with both the current and evolving :- processes have

several features in common 9/, 3< # solid or surface 8#D model is elec6

tronically sectioned into layers of predetermined thickness !hese sections

de%ne the shape of the part collectively 'nformation about each section is

then electronically transmitted to the :- machine layer by layer !he :-

machine processes materials only at TTsolid== areas of the section

Subsequent layers are sequentially processed until the part is complete 't

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is this sequential, layered, or lithographic approach to parts manufacturing

that de%nes :- !he :- process basically uses the following steps to make

prototypes&

8reate a 8#D model of the design

/ 8onvert the 8#D model to S!K %le format

3 Slice the S!K %le into /D cross6sectional layers

4 7row the prototype

-ostprocessing

!he %ve6step process is shown in )igure / 3

Fi&ur '.( )ive6step process of rapid prototyping

'.( (/DIMENSIONAL MODELING

!he %rst step in creating a prototype is the creation of a 8#D solid model:- requires that we make a fully closed, water6tight model such that even

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if we were to pour water into the volume of the model, it would not leak #

solid is a volume completely bounded by surfaces, which means the edges

of all surfaces must be coincident with one, and only one, other surface

edge Gnlike wire6frame and surface modeling, solid modeling stores

volume information # 8#D solid model not only captures the complete

geometry of an ob ect, it can also diAerentiate the inside and the outside

of the space of that ob ect Fany other volume6related data can be

obtained from the model

!he creation of a 3D body is the indispensable prerequisite for the

production of a rapid prototyping model !herefore, the application of

prototyping is linked especially closely with 8#D processes )or this reason

3D 8#D processes will be looked into only as far as is absolutely necessary

for the understanding of the fundamental relationships in the production of

rapid prototyping models .very 8#D system uses certain data elements

and data structures to describe a component in detail !he data record

includes not only the component geometry but also the materials, the

quality of the surface, the production process, and much more !he

component geometry therefore comprises only one part of the

information !he complete information registered in the database of a 8#D

system for a component is called a 8#D model 2the product to be made 'f

the geometric description of a component is 3D then it is called a 3D 8#D

model

By choosing a certain 8#D system the user commits himself to its

database !he structure and the data elements decide to a high degree

the quality of a 8#D system and its compatibility with other systems via

interface 8#D models are de%ned by model types regardless of the kindof 8#D system 2)igure / 3 !he corner model de%ned by points is of less

practical importance 't is used, for e$ample as an intermediate model for

the semiautomatic transformation of grid data or of /D 8#D models into

3D 8#D models

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)igure / 3 8#D .lements and Fodel !ypes

!he edge model too is more of historical interest today in regard to rapid

prototyping wing to its small amount of data it enables a fast graphic

representation of 3D elements even with low computer performance 'ts

importance is therefore growing again in connection with virtual reality

2E: applications and digital mockup 2DFG !he most important

disadvantage of the edge model is the missing information about the

e$act position of the surfaces and the volumes )or this reason it cannot

be recommended as a basis for the production of rapid prototyping

models

#ll 8#D6systems that process components as surface models in their

geometrical databases are in principle suitable for the issuing of data via a

rapid prototyping interface 5hen a component is de%ned by its e$ternal

surface, the user is usually able to calculate the e$act component volume

as well !his is usually achieved by appointing and storing an additional

normal vector for each surface pointing away from the inside of the

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component )or the complete description of a component therefore it is

absolutely necessary that the orientation of the component volume is

known Solids are optimal for the modeling of 8#D models that 2among

other things are also used for rapid prototyping !he orientation of the

volume is preset e$actly and need not be e$plicitly appointed by the user

Solid models can be created using a 8#D software package such as

#uto8#D, -roN.ngineer, 8#!'#, Solid 5orks, or many other commercially

available solid modeling programs

'.- Data Tra!sf r a!" D li% r)

nce a solid model is created and saved, it is then converted to a special

%le format known as S!K 2stereolithography 94< !his %le format originated

from 3D Systems, which pioneered the stereolithography process

#ctually, the #lbert 8onsulting 7roup under contract to 3D Systems

developed the S!K %le format to support the new revolutionary

manufacturing technology, called stereolithography !hough not ideal, it is

suf%cient to meet the needs of today=s rapid prototyping technology,

which generally build monomaterial parts !he success of this %le formathas been impressive !oday, a decade later, the S!K %le format remains

the de facto standard for the rapid prototyping industry

!he success of the S!K %le format is due to its suf%ciency, its simplicity,

and its monopoly 9 < 'ts mathematical suf%ciency stems from the fact that

it describes a solid ob ect using a boundary representation 2B6rep

technique #n S!K %le format represents the virtual 8#D model of the

ob ect to be prototyped as a collection of triangular facets !hese

triangular facets, when taken together, describe a polyhedral

appro$imation of the ob ects= surface, that is, a polyhedral appro$imation

of the boundary between material and nonmaterial 'n short, an S!K %le is

nothing more than a list of . , y , and z coordinate triplets that describe a

connected set of triangular facets 't also includes the direction of the

normal vector for each triangle, which points to the outer surface of the

model

Fost 8#DN8#F software vendors supply the S!K %le interface Since ;;0,

many 8#DN8#F vendors have developed and integrated this interface into

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their systems !essellation is the process of appro$imating a surface by

triangular facets !he 8#D S!K %le interface performs surface tessellation

and then outputs the facet information to either a binary or #S8'' S!K %le

format

!he output of S!K %le formats can be e$pressed in binary or #S8'' format

!he characteristics of binary and #S8'' S!K outputs are shown in !able /

)igures / 4 and / show a binary S!K %le format and an #S8'' S!K %le

format, respectively

!here are three steps to S!K %le creation 9J

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Default output type:eferred to as human6readable

format:eferred to as machine6readable

format

.asily read and understood by

humans

Fore compact and ef%cient, easier tomove

through networkN transmit

Cot very ef%cient, slower toprocess,

larger %le si"esCot easily read or understood by

humans

without some translation

Cot recommended if moving %les

through a network

Address Length Type Description/ 0/ char &eader in ormation

0/ + long Num$er o acets insolidFirst acet 12/ $ytes3%0+ + 4oat Normal 1. component300 + 4oat Normal 1y component35" + 4oat Normal 1z component356 + 4oat )erte. 1. component3// + 4oat )erte. 1y component3/+ + 4oat )erte. 1z component3/0 + 4oat )erte. " 1. component3" + 4oat )erte. " 1y component36 + 4oat )erte. " 1z component3"/ + 4oat )erte. * 1. component3"+ + 4oat )erte. * 1y component3"0 + 4oat )erte. * 1z component3*" " short -ttri$ute in o! 1notused3Second acet 12/ $ytes3%*+!!!

Fi&ur '.- Binary S!K format

#riangulation tolerance" -d7acency tolerance* -uto8normal generation 1on9o:3+ Normal display 1on9o:32 #riangle display 1on9o:36 &eader in ormation 1te.t3

S;ain old zF-?E# N;'>-< /!//////e@// !//////e@// "!6*+ +5e@/5;A#E'

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+!//////e@//

)E'#EB +!//////e@// !+/////e@// +!//////e@//

)E'#EB +!//////e@// !+/////e@// *!//////e@//

END

Some of the features of triangulation tolerance are as follows&

Determines how smooth the appro$imation of the surface or solid will

be 'n other words, how close the triangles appro$imate the surface @ow close the sides of the triangles that lie along the edges are to

the actual edges of the surface

Gsually set to one half the desired accuracy of the :- process being

utili"ed

Default is set at 0 00/ in , or 0 0 mm

!he dramatic eAects of decreasing the values of triangle tolerances are

shown in )igure / J Some of the features of ad acency tolerance are as

follows&

't does not aAect processing of solids

/ !he default value is 0 00 in , or 0 / mm

3 !he system uses this value to determine if two surfaces will be

attached to one another

4 .dges whose length is smaller than the ad acency tolerance can

cause ad acency problems

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Fi&ur '. .Aects of decreasing values of triangle tolerances

!he eAects of ad acency tolerance are shown in )igure / H Some of the

features of auto6normal generation are as follows&

't does not aAect processing of solids

/ 8hoose a base surface, check the normal, and calculate all others

from this surface

3 Default should be on

E5a#$l '.1

)or the ob ect shown in )igure / I&

2a Draw the part using -roN.ngineer or a similar 8#DN8#F system

2b 8reate S!K #S8'' %le with chord height of 0 and 0

2c Discuss the changes that take place when chord height is varied 2%le

si"e, number of triangles, etc

Solution

2a !o generate the solid ob ect, a simple rectangular protrusion was

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%rst created Gsing the cut command in the %le menu, the

rectangular sections were $lind cut to the speci%ed depths !he

circles were then cut completely through the part !he solid ob ect is

shown in )igure / ;

2b !he part was saved in an #S8'' S!K %le format with the speci%ed

chord heights and is shown in )igure / 0

2c Earying the chord height changes the number of triangles created

5hen the chord height is decreased, there are more triangles, thus a

larger %le si"e !he smaller the chord height, the resolution is better

and accurate for the ob ect @owever, the more accurate model will

take longer to produce )igure / shows the ob ect sliced at

diAerent chord heights

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)igure / ; !he solid ob ect

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Fi&ur '.16 S!K #S8''

'.0 R %isio! a!" Pr $aratio!

!he %le is taken from its 3D model surfaces and converted to many

triangles, a step referred to as slicing! !he more comple$ the ob ect, the

more triangles are required, and thus the bigger the %le that makes up the

8#D model as well as a support structure for the part to be grown on !he

sliced ob ect is saved as an S!K %le and is now in a format the :-

computer recogni"es

'. Co!structio!

!he part is submitted to the :- computer and the machine runs until the

part is complete :- machines build one layer at a time from polymers,

paper, or

Fi&ur '.11 2a 8hord @eight 0 and 2 $ chord height 0

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powdered metals Fost machines are fairly autonomous needing little

human intervention Build times vary depending on si"e and number of

parts required

'. Post$roc ssi!&

!he %nal step in rapid prototyping is postprocessing 't essentially consists

of part removal and cleaning and of postcuring and %nishing !his step

generally involves manual operations where an operator does the

postprocessing with e$treme care therwise, the part may be damaged

and may need to be prototyped again 9Hreverse engineering > !he conversion of measured data

in the form of point clouds directly into solid body descriptions in a neutral

data format, possible in principle, should be done only in e$ceptionalcases 't is not usually possible to relate point clouds clearly even to

simple geometrical bodies, and they contain an enormous amount of data

'n any case, the geometrical information of the entire body or of single

layers must be converted for transfer via interface into a neutral format

9stereolithography language 2S!K , SK8 which is a entire 3D6Systems or

Stratasys slice contour format, @ewlett -ackard graphic language 2@-7K ,

etc < as only then is the access to diAerent rapid prototyping processessecured !he generation of au$iliary geometries such as supports and

similar ones, which are not necessary with every rapid prototyping

process, is done P depending on the process P either together with the

generation of geometrical data or separately with the aid of rapid

prototyping software )inally, all data, the geometry and the supports, are

together sliced into layers by mathematical means and provide the layer

information that, together with machine speci%c parameters, is necessary

for the production of each layer Depending on the process, the layer

information is either completely calculated and stored before the process

is started, or it is calculated for each layer simultaneously with the build

#n S!K is a type of standardi"ed computer e$change %le which contains a

3D model !he representation of the surface2s of the ob ect2s in the %le is

in the form of one or more polygon meshes !he polygon meshes in an S!K

%le are entirely composed of triangular faces, edges and vertices )urther,

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the faces have assigned normals which indicate their orientation

2insideNoutside

!he name >S!K? is taken from its e$tension, stl, originally because

the %les were intended for the rapid prototyping process called

Stereolithography !he %le format has become a world standard for

e$changing 3D polygon mesh type ob ects between programs, and stl=s

are now used as input for virtually all rapid prototyping processes, as well

as some 3D machining

'.( STL Fil Pro8l #s

5hile the S!K %le format is meeting the needs of the industries that are

using :- and while it is the de facto standard in :- industry, it has some

inadequacies 9/, H< Some of these inadequacies are due to the very

nature of the S!K %le format as it does not contain topological data #lso,

many 8#D vendors use tessellation algorithms that are not robust

8onsequently, they tend to create polygonal appro$imation models, which

e$hibit the following types of problems&

Gaps 2?rac s, &oles, Punctures Indicating >issing Faces 5hen a

solid model is converted into an S!K %le format, the solid model forms are

replaced with a simpli%ed mathematical form 2triangles @owever, if the

simpli%ed operation is not done properly, it introduces undesirable

geometric anomalies, such as holes or gaps in the boundary surface !his

problem is more prone to surfaces with large curvature Such gaps are

shown in )igure / /

/ Inconsistent Normals 'n general, surface normals should be pointed

outward @owever, the normals of some surfaces could be +ipped over, as

shown in )igure / 3, thus, becoming inconsistent with the outward

orientation of the original surface

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3 Incorrect Normals Sometimes, surface normals stored in the S!K %le

are not the same as those computed from the vertices of the correspond6

ing surfaces

4 Incorrect Intersections )acets may sometimes intersect at locations

other than their edges resulting in overlapping facets 2)ig / 4

Internal all Structure 7eometric algorithms are used for closing

gaps in S!K %les @owever, faulty geometric algorithms could generate

internal walls and structures that can cause discontinuities in the solid6

i%cation of the material 2)ig /

J Facet Degeneracy Degeneration of facets occurs when they may

not represent a %nite area and consequently have no normals 7enerally,

there are two kinds of facet degeneracies& geometric degeneracy and

topological degeneracy # geometric degeneracy takes place when all the

vertices of the facet are distinct and all the edges of the facet are

collinear # topological degeneracy takes place when two or more verticesof a facet coincide Since it does not aAect the geometry or the

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connectivity of the remaining facets, the faults can be discarded 2)ig / J

H Inconsistencies Sometimes two S!K %les are combined to create a

prototype 'f these S!K %les were created using diAerent tolerance val6

ues, it will lead to inconsistencies such as gaps

'.- R alit) a!" Not R alit) Co!structio! R sult

!he problems and inef%ciencies of the S!K %le format have prompted the

search for alternate translators .$amples of some of these translators are'7.S, @-7K, and computed tomography 28! data

IGES File 'nitial graphics e$change speci%cation is a common format

to e$change graphics information between various 8#D systems 't was

initially developed and promoted by the then #merican Cational Standards

'n6stitute 2#CS' in ;I

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!he '7.S %le can precisely represent both geometry and topological

information for a 8#D model #n '7.S %le contains information about

surface modeling, constructive solid geometry 28S7 and boundary

representation 2B6rep !he Boolean operations for solid modeling such as

union, intersection, and di:erence are also de%ned in the '7.S %le 't can

precisely represent a 8#D model by providing entities of points, lines, arcs,

splines, CG:BS surface, and solid elements !he primary advantage of

'7.S format is its widespread adoption and comprehensive coverage

@owever, there are some disadvantages of the '7.S format as it relates

to its use as an :- format !hese are&

!he inclusion of redundant information for :- systems

/ !he algorithms for slicing '7.S %le are more comple$ than those for

slicing S!K %le

3 !he support structures that are needed for some :- systems cannot

be created using '7.S format

'7.S is a very good interface standard for e$changing informationbetween various 8#D systems 't does, however, fall short of meeting the

standards for :- system

&e(lett Pac ard Graphics

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format )irst, since @-7K is a /D data format, the %les are not appended,

leaving hundreds of small %les needing logical names and transformation

Second, all the required support structures must be generated in the 8#D

system and sliced in the same way

/ ?# Data 8! scan data is a new format used for medical imaging !he

format has not been standardi"ed yet )ormats are proprietary and vary

from machine to machine !he 8! scan generates data as a grid of three6

dimensional points, where each point has a varying shade of gray

indicating the density of body tissue present at that point Data from 8!

scan are being regularly used to prototype skull, femur, knee, and other

biomedical components on )DF, SK#, and other :- systems !he 8! data

essentially consist of raster images of the physical ob ects being imaged't is used to produce models of human temporal bones

Fodels using 8! scan images can be made using 8#D systems, S!K

interfacing, and direct interfacing 8! data is used to make human parts

such as leg prostheses, which are used by doctors for implants @owever,

the main problem with 8! image data is the comple$ity of the data and

the need for a special interpreter to process this data

(.- STL Fil corr ctio! # t+o"

Since an S!K mesh is composed entirely of triangles, it is the simplest form

of mesh model format .ach facet is necessarily planar 'n principle, for

rapid prototyping processes, a completely closed ob ect is required, that is

to say, the mesh completely encloses a volume, with no holes, gaps, or

overlaps 5e sometimes speak of this as a >watertight solid? 'n addition,

the software controlling some processes requires that there is only one

ob ect 2volume in the %le

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Each o the illustrations a$ove sho( one slice o an !S#< model! In

order produce the layer, the 'P machine so t(are needs a closed loop

that defnes an interior, (hich is then flled (ith the model material!

Some procedures use the !S#< normals to defne the interior (ith

respect to the e.terior o the curves, (hereas others use nestingin ormation!

'n actual practice, there may be some tolerance allowed Small errors or

gaps may be tolerated by the prototyping software, or can be quickly

repaired Some software may allow multiple and overlapping ob ects .ach

process and software will work diAerently, some are more error6tolerant

than others !herefore, in general it is best to aim to achieve a perfect

001 closed model, otherwise, depending on who is doing the prototyping

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and what process is being used, it may be time consuming 2read&

e$pensive to %$

-rofessional service bureaus and frequent users of :- parts will have

speci%c software designed to manipulate and %$ stl models and prepare

them for prototyping ne e$ample of this might be Fagics by Fateriali"e

2B !his type of software is e$pensive, but has speci%c tools for analy"ing

the integrity of stl models and rapidly correcting defects 2often

automatically !hey may also have other functions that permit the model

to be cut into smaller parts, shelled, nested, etc

nce the stl is 001 correct and veri%ed, it can then be imported into the

machine6speci%c :- software which will generate the commands to run

the machine !his data is then sent to the machine 2like a printer and themodel construction is started

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LI9UID/3ASEDRAPID

PROTOTYPINGSYSTEMS

Fost liquid6based rapid prototyping 2:- systems build parts in a vat of

photo6curable liquid resin, an organic resin that cures or solidi%es under

the eAect of e$posure to light, usually in the GE range !he light cures the

resin near the surface, forming a thin hardened layer nce the complete

layer of the part is formed, it is lowered by an elevation control system to

allow the ne$t layer of resin to be coated and similarly formed over it !his

continues until the entire part is complete !he vat can then be drained

and the part removed for further processing, if necessary !here are

variations to this technique by the various vendors and they are

dependent on the type of light or laser, method of scanning or e$posure,

type of liquid resin and type of elevation and optical system used

-.1. (D SYSTEMS: STEREOLIT*OGRAP*Y APPARATUS ;SLAoutput? device like a laser

scanning system !he layer thickness is controlled by a precision elevation

mechanism 't will correspond directly to the slice thickness of the

computer model and the cured thickness of the resin !he limiting aspect

of the :- system tends to be the curing thickness rather than the

resolution of the elevation mechanism

!he important component of the building process is the laser and its

optical scanning system !he key to the strength of the SK# is its ability to

rapidly direct focused radiation of appropriate power and wavelength onto

the surface of the liquid photo6polymer resin, forming patterns of solidi%ed

photo6polymer according to the cross6sectional data generated by the

computer 0 'n the SK#, a laser beam with a speci%ed power and

wavelength is sent through a beam e$panding telescope to %ll the optical

aperture of a pair of cross a$is, galvanometer driven and beam scanningmirrors !hese form the optical scanning system of the SK# !he beam

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comes to a focus on the surface of a liquid photo6polymer, curing a pre6

determined depth of the resin after a controlled time of e$posure

2inversely proportional to the laser scanning speed

!he solidi%cation of the liquid resin depends on the energy per unit area

2or >e$posure? deposited during the motion of the focused spot on the

surface of the photo6polymer !here is a threshold e$posure that must be

e$ceeded for the photo6polymer to solidify

!o maintain accuracy and consistency during part building using the

SK#, the cure depth and the cured line width must be controlled #s such,

accurate e$posure and focused spot si"e become essential

-arameters which in+uence performance and functionality of the parts

are physical and chemical properties of resin, speed and resolution of theoptical scanning system, the power, wavelength and type of the laser

used, the spot si"e of the laser, the recoating system and the post6curing

process

-.1.0. Str !&t+s a!" = a7! ss s

!he main strengths of the SK# are&

2 'ound the cloc operation! !he SK# can be used continuously

and unattended round the clock

/ 2/ Huild volumes! !he diAerent SK# machines have build

volumes ranging from small 2/ 0 \ / 0 \ / 0 mm to large 2H3H

\ J3 \ 33 mm to suit the needs of diAerent users

3 23 Good accuracy! !he SK# has good accuracy and can thus be

used for many application areas

4 24 Sur ace fnish! !he SK# can obtain one of the best surface

%nishes amongst :- technologies

0 2 ide range o materials! !here is a wide range of materials,

from general6purpose materials to specialty materials for speci%c

applications

/!he main weaknesses of the SK# are&

2 'equires support structures Structures that have overhangs

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and undercuts must have supports that are designed and

fabricated together with the main structure

J 2/ 'equires post8processing! -ost6processing includes removal

of supports and other unwanted materials, which is tedious, time6

consuming and can damage the model

H 23 'equires post8curing! -ost6curing may be needed to cure the

ob ect completely and ensure the integrity of the structure

-.1. . A$$licatio!s

!he SK# technology provides manufacturers cost usti%able methods for

reducing time to market, lowering product development costs, gaininggreater control of their design process and improving product design !he

range of applications includes&

2 Fodels for conceptuali"ation, packaging and presentation

/ 2/ -rototypes for design, analysis, veri%cation and functional

testing

3 23 -arts for prototype tooling and low volume production tooling

4 24 -atterns for investment casting, sand casting and molding2 !ools for %$ture and tooling design and production tooling

Software developed to support these applications includes ]uick8ast !F , a

software tool which is used in the investment casting industry ]uick8ast !F

enables highly accurate resin patterns that are speci%cally used as an

e$pendable pattern to form a ceramic mould to be created !he

e$pendable pattern is subsequently burnt out !he standard process uses

an e$pendable wa$ pattern which must be cast in a tool ]uick8ast !F

eliminates the need for the tooling use to make the e$pendable patterns

]uick8ast !F produces parts which have a hard thin outer shell and contain

a honeycomb like structure inside, allowing the pattern to collapse when

heated instead of e$panding, which would crack the shell

-.1.> DLP ? Di&ital Li&+t Proc ssi!&

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DK- M or digital light processing M is a similar process to

stereolithography in that it is a 3D printing process that works with

photopolymers !he ma or diAerence is the light source DK- uses a more

conventional light source, such as an arc lamp, with a liquid crystal display

panel or a deformable mirror device 2DFD , which is applied to the entire

surface of the vat of photopolymer resin in a single pass, generally making

it faster than SK#^

#lso like SK#, DK- produces highly accurate parts with e$cellent resolution,

but its similarities also include the same requirements for support

structures and post6curing @owever, one advantage of DK- over SK# is

that only a shallow vat of resin is required to facilitate the process, which

generally results in less waste and lower running costs

@'>

-.'. O3 ET GEOMETRIES LTD.:S POLY ET

-.'.1. Co#$a!)

b et was founded in ;;I and has established itself as the leading plat6

form for high6resolution three6dimensional printing 23D- b et also has

proven installations worldwide where 3D modeling can be created in o(ce

environment 3 Gsing its patented and market6proven -olyRet_ ink et6head

technology, it is able to print out the most comple$ 3D models with

e$ceptionally high quality -olyRet6based systems are used in hundreds of

manufacturing sites across the world and across a wide spectrum of industries& automotive, electronics, toy, consumer goods, medical

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footwear and more 't has been awarded more than 40 patents with addi6

tional patents %led or pending internationally b et 7eometries Ktd is

currently headquartered at / @ol"man St Science -ark - Bo$ /4;J,

:ehovot HJ /4, 'srael

-.'.'. Pro"ucts

b et=s current line of -olyRet6based systems, the .den_ family, is a group

of four machines that can deliver high6resolution prototypes within an

o(ce environment 4 !he .den_ family consists of the .den 00E_, .den

3 0_N3 0E_, .den /J0_ and .den / 0_, giving options to the users in

terms of build si"e, productivity and budget requirements )or economical

and eAective small models, both .den / 0_ and .den /J0_ are able to

%t in a small o(ce .den / 0_ features of two printing modes, high

quality 2@] and high speed 2@S , for user to choose from in order to

produce high quality prototype .den /J0_ consists of I units of single

head replacement 2S@: to et identical amounts of resin compared to

.den / 0_ resulting in better and more even surface %nish .den

3 0_N3 0E_ are the medium build professional machines in the .den

series which features printing modes 2@] and @S and higher material

capacity !he .den 00E_ 2see )ig 3 I is the largest build system with a

build volume of 4;0 \ 3;0 \ /00 mm 't has the best features including

dual printing modes, I units of S@: and an automatic function to switch

between cartridges Speci%cations of the .den_ family of machines are

summari"ed in !able 4 /

!he .den_ systems utili"e b et )ull8ure V materials and b et Studio_

software to provide a complete 3D- solution for any :- application b et

systems provide a range of diAerent materials for user to choose from,

depending on the required properties #ll .den_ systems are able to print

high accuracy ultra6thin J `m layers, producing models with

e$ceptionally %ne details and ultra6smooth surfaces !he .den_ family

works on the same principle where the etting head lays both the )ullcure

F 2model material and )ullcure S 2support material on the build tray #t

the same instance, the GE light integrated with the etting head cures the

already ust6laid )ull8ureV

materials, virtually laying and curing the modelin a single process

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Fi&. -.B. E" ! 066V TM ;court s) O8 t G o# tri s Lt"

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of the building process is the cross section of the parts arranged

in the software

3 23 5ith the completion of a cross6sectional layer, the build tray

will be lowered for the ne$t layer to be laid !he z 6height of the

elevator is leveled accurately so that the corresponding cross6

sectional data can be calculated for that layer

4 24 Both the part material and support material will be fully cured

when they are e$posed to the GE light and most importantly the

nonto$ic support material can be removed easily by the water et

4 / Strengths and 5eaknesses

!he .den !F system has the following strengths &

2 &igh quality !he -olyRet_ can build layers as thin as

J `m in thickness with accurate details depending on the

geometry, part orientation and print si"e

/ 2/ &igh accuracy! -recise etting and build material

properties enable %ne details and thin walls 2J00 `m or less

depending on the geometry and materials3 23 Fast process speed! 8ertain :- systems require

draining, resin stripping, polishing and others whereas .den_

systems only require an easy wash of the support material

which is a key strength

4 24 Smooth sur ace fnish !he models built have smooth

surface and %ne details without any post6processing

2 ide range o materials b et has a range of materials

suited for diAerent speci%cations, ranging from tough acrylic6

based polymer, to polypropylene6like plastics 2Duruswhite to

the rubber6like !ango materials

2J Easy usage !he .den_ family utili"es a cartridge

system for easy replacement of build and support materials

Faterial cartridges provide an easy method for insertion without

having any risk of contact with the materials

J 2H S&' technology !he .den_ machines= no""les consist

of heads and no""les 5ith Single @ead :eplacement 2S@:

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these individual no""les can be replaced instead of replacing the

whole unit whenever the need arises

2I Sa e and clean process! Gsers are not e$posed to the

liquid resin throughout the modeling process and the photo6

polymer support is nonto$ic .den !F systems can be installed in

the o(ce environment without increasing the noise level

!he .den !F system has the following weaknesses&

H 2 Post8processing # water et is required to wash away

the support material used in -olyRet_, meaning that water

supply must be nearby !his is somewhat a let6down to the claimthat the machine is suitable for an o(ce environment 'n cases

where the parts built are small, thin or delicate, the water et

can damage these parts, so care in post6processing must be

e$ercised

I 2/ astage !he support material which is washed away

with water cannot be reused, meaning additional costs are

added to the support material

-.'. . A$$licatio!s

!he applications of b et=s systems can be divided into diAerent areas&

2 General applications! Fodels created by b et=s

systems can be used for conceptual design presentation, design

proo%ng, engineering testing, integration and %tting, functional

analysis, e$hibitions and pre6production sales, market research

and inter6professional communication

/ 2/ #ooling and casting applications! -arts can also be

created for investment casting, direct tooling and rapid, tool6

free manufacturing of plastic parts #lso they can be used to

create silicon molding, aluminum epo$y moulds, EK! Folding

2alternative rubber mould and vacuum forming

3 23 >edical imaging Diagnostic, surgical, J operation and

reconstruction planning and custom prosthesis design -arts

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built by -olyRet !F have outstanding detail and %ne features which

can make the medical problems more visible for analysis and

surgery simulation Due to its fast building time, prototype

models are always built for trauma or tumors Fost importantly,

it reduces the surgical risks and provides a communication

bridge for the patients

4 24 e(elry industry! -resentation of concept design, actual

display, design proof and %tting -re6market survey and market

research can be conducted using these models

2 Pac ing! Eacuum forming is an easy method to

produce ine$pensive parts and it requires a very short time for

the part to be formed

modul bdd 40303

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