imp notes on rapid prototyping

7/23/2019 Imp Notes on rapid prototyping

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UNIT 1

Need for the compression in the product development

To increase effective communication.

To decrease development time.

To decrease costly mistakes.

To minimize sustaining engineering changes.

To extend product life time by adding necessary features & eliminating redundant features

early in the design.

History of RP system

It started in 198!s

"irst techni#ue is $tereo lithography %$'(

It )as developed by *+ systems of ,alencia in -alifornia /$' in 1980.

"used deposition modeling %"+( developed by stratasys company in 1988.

aminated ob2ect manufacturing %3( developed by 4elisis %/$'(.

$olid ground -uring developed by -ubitol corporation of Israel.

$elective laser sintering developed by +T of 'ustin Texas %/$'( in 1989.

$anders odel maker developed by 5ilton incorporation /$' in 199.

ulti 6et odeling by *+ systems.

*7+ rinting by $olygen incorporation IT /$'.

Applications

ost of the parts are finished or touched up before they are used for their intended

applications. 'pplications can be grouped into

1



%1(+esign %:( ;ngineering 'nalysis and lanning and %*( Tooling and anufacturing . '

)ide range of industries can benefit from and these include but are not limited to

aerospace automotive biomedical consumer electrical and electronics products.

Classification of RP systems

$tereo lithography %$'(

aminated 3b2ect anufacturing %3(

$elective aser $intering %$$(

"used +eposition odeling %"+(

$olid <round -uring %$<-(

STERE!ITH"RAPH#

Introduction$

It is the first system developed by *+ $=$T;$ of ,alencia in -alifornia /$' in 1990.

"irst odel developed )as :>?> follo)ed by :>?* *> > and @.

Principle$

$' is a laser based apid rototyping process )hich builds parts directly from -'+ by

curing or hardening a photosensitive resin )ith a relatively lo) po)er laser.

Parameters$

aser TypeA 4elium -admium aser %4e7-d(

aser o)erA :Bm5

aser ifeA : hours

e7coat materialA Caphir

2



inimum $lice ThicknessA .1mm

Deam +iameterA .:mm

$can $peedA .@>m?sec

aximum art ,olumeA .:>x.:>x.:> m

aximum art 5eightA 9 kgs

Soft%are$

i. S!A CNTR! AN& SET UP S'T(AREA It operates on $' :> and $' >

machines. It has got three packages.

a( S!A )IE(A /EIF based system for vie)ing and positioning.

b( *RI&"E (R+SA /EIF based soft)are for generating support structures.

c( $' $I-;A $licing and system operation soft)are.

ii. ,AESTRA /EIF based soft)are

iii. ,S (IN&(S NT S'T(ARE -.& !I"HT #EAR/$ It is used for vie)ing

positioning support generation and slicing build station for operating $' machine.

*uild ,aterials Used$

;poxy esin 'crylate esin

;poxy esin has better material properties and less hazardous but re#uire large exposure time

for curing.

S!A HAR&(ARE$

The build chamber of $' contains

1( ' removable ,'T that holds the build resin.:( ' detachable perforated build platen on a C axis elevator frame

*( 'n automated resin level checking apparatus

B( ,'T has a small amount of C movement capability )hich allo)s computer to maintain a

exact height per layer.

>( ' recoated blade rides along the track at the top of the rack and serves to smooth the

li#uid across the part surface to prevent any rounding off edges due to cohesion effects.

0( $ome systems have Caphyr recoater blade )hich actually softens up resin and delivers it

evenly across the part surface.

@( Dehind the build chamber resides the laser and optics re#uired to cure resin.

8( aser unit is long rectangular about B feet long and remains stationary.

3



Stereolitho0raphy Apparatus peration$

1( The process begins )ith the solid model in various -'+ formats

:( The solid model must consist of enclosed volumes before it is translated form -'+

format into .$T "I;*( The solid model is oriented into the positive octant of -artesian co7ordinate system and

then translate out C axis by at least .:> inches to allo) for building of supports

B( The solid model is also oriented for optimum build )hich involves placing complex

curvatures in F= plane )here possible and rotating for least C height as )ell as to

)here least amount of supports are re#uired

>( The .$T "I; is verified

0( The final .$T "I; one )hich supports in addition to original file are then sliced into

horizontal cross sections and saved as slice file.

@( The slice files are then masked to create four separate files that control $' machine

ending )ith > extensions , and .

8( Important one is , file. I.e. ,ector file. The , file contains actual line data that the laser

)ill follo) to cure the shape of the part.

9( file is the range file )hich contains data for solid or open fields as )ell as re7coater

blade parameters.

The four build files are do)nloaded to $' )hich begins building supports )ith platen ad2ust

above the surface level. The first fe) support layers are actually cured into perforations into platen thus providing a solid anchor for the rest of the part.

Dy building $' uses laser to scan the cross section and fill across the surface of resin )hich

is cured or hardened into the cross sectional shape. The platen is lo)ered as the slices are

completed so that more resin is available in the upper surface of the part to be cured. "inal

step is ost rocessing.

Post Processin0$

1( /ltraviolet 3ven %ost -uring 'pparatus(

:( 'n 'lcohol Dath.

-lean the part in the alcohol bath and then go for final curing.

Advanta0es$

1( arts have best surface #uality

4



:( 4igh 'ccuracy

*( 4igh speed

B( "inely detailed features like thin vertical )alls sharp corners & tall columns can be

fabricated )ith ease.

&isadvanta0es$

1( It re#uires ost rocessing. i.e. ost -uring.

:( -areful handling of ra) materials re#uired.

*( 4igh cost of hoto -urable esin.

Applications$

1( Investment -asting.

:( 5ind Tunnel odeling.*( Tooling.

B( In2ection ould Tools.

&ia0ram$

'i0$ Stereolitho0raphy Apparatus

5



SE!ECTI)E !ASER SINTERIN"

Introduction$

$elective aser $intering is a rapid prototyping process that builds models from a

)ide variety of materials using an additive fabrication method. $elective aser

$intering )as developed by university of Texas 'ustin in 198@. The build media for

$elective aser $intering comes in po)der form )hich is fused together by a

po)erful carbon dioxide laser to form the final product.

+T sinter station :> is the machine used for the process.

$elective aser $intering begins like most other rapid prototyping processes )ith a standard

.$T -'+ file format. +T vie) soft)are uses the .$T files. This soft)are do the re#uired

orientation and scaling of parts.

This machine has auto nesting capabilities )hich )ill place multiple part optimally in the

build chamber for best processing speed and results. 3nce the .$T file is placed and

parameters are set the model is directly built from the file.

6



The sinter station has built piston at the center and feed piston on the either side. The model is

built layer by layer like other rapid prototyping process so that the build piston )ill begin at

the top of its range and )ill lo)er in increments of the set layer size as parts are built. 5ith

the build piston at the top a thin layer of po)der is spread across the build area by the roller

from one of the feed piston. The laser then cures in a raster s)eeps motion across the area of

the parts being built. The part piston lo)ers and more po)der is deposited and the process is

continued until all of the part is built.The build media is removed from the machine. It is a

cake of po)der. This cake is taken to the breakout station )here excess po)der is removed

from the part manually )ith brushes the excess po)der that has been removed can be kept for

recycling and can be reused. $ome material needs additional finishing. $ome of the finishing

techni#ues include grid blasting sanding polishing drilling taping and coatin

Purpose of Selective !aser Sinterin0$

To provide a prototyping tool

To decrease the time and cost of design to product cycle.

It can use )ide variety of materials to accommodate multiple application throughout the

manufacturing process

7



Applications$

1. 's conceptual models.

:. "unctional prototypes.

3. As Pattern masters.

Advanta0es$

1. 5ide range of build materials.

:. 4igh throughput capabilities.

*. $elf7supporting build envelop.

B. arts are completed faster.

>. +amage is less.

0. ess )astage of material

&isadvanta0es$

1. Initial cost of system is high.

8



:. 4igh operational and maintenance cost.

*. eripheral and facility re#uirement.

'USE& &EPSITIN ,U!&IN"

Introduction$

"used +eposition odelling is an extrusion based rapid prototyping process although it

)orks on the same layer by layer principle as other systems. "used +eposition odelling

relies on standard $T data file for input and is capable of using multiple build materials in a

build or support relationship.

Soft%are Used$

"+ machine uses Guick $lice soft)are to manipulate and prepare the incoming $T date

for use in "+ machines. $oft)are can be operated on various types of )orkstations from

/EIF to - based.

*uild ,aterials$

1( Investment -asting 5ax.

:( 'crilonitrile Dutadine $tyrene plastic.

*( ;lastomer.

Etrusion Head$

1( It is a key to "+ technology.

:( -ompact and removable unit.

*( It consists of +ry Dlocks 4eating -hamber and Tips.

&ry *loc2s$

a/ These are ra) material feeding mechanisms and are mounted on back of head.

3/ These are computer controlled.

c/ -apable of precision loading and unloading of filament.

d/ It consists of t)o parallel )heels attached to a small electric motor by gears.

e/ The )heels have a plastic and rubber thread and are spaced approximately .@inches

apart and turn opposite to one another.

f/ 5hen the )heels are turned in and end of the filament is placed bet)een them theycontinue to push or pull the material depending on direction of rotation.

9



0/ 5hen loading the filament is pushed horizontally into the head through a hole a little

longer than the filament diameter )hich is the entry to the heating chamber.

Heatin0 Cham3er$

a( It is a 9! curved elbo) )rapped in a heating element )hich serves t)o primary

functions

To change the direction of the filament flo) so that the material is extruded vertically

do)n)ards.

To serve as a melting area for the material

b( The heating element is electronically controlled and has feedback thermocouple to allo)

for a stable temperature throughout.c( The heating elements are held at a temperature 2ust above the melting point of the

material so that the filament passes from the exit of the chamber is in molten state. This

allo)s for smooth extrusion as )ell as time control on material placement.

d( 't the end of the heating chamber )hich is about B inch long is the extrusion orifice or

tip.

Tip$

a( The t)o tips are externally threaded and scre)ed up into the heating chamber exit and

are used to reduce the extruded filament diameter to allo) for better detailed modelling

b( .The tips are heated by heating chamber up to above the melting point of the material.c( The tips can be removed and replaced )ith different size openings the t)o most

common being .1: inch and .:> inches.

d( The extruding surface of the tip is flat serving as the hot shearing surface to maintain a

smooth upper finish of extruded material.

e( The tip is the point at )hich the material is deposited onto a foam substrate to build the

model..

*uild Su3strate$

1( The foam substrate is an expendable )ork table once )hich parts are built.

:( The substrate is about 1 inch thick and is passed on into a removable tray by one

#uarter inch pins.

*( The foam used is capable of )ithstanding higher temperature. 's for the first fe)

layers of the part the hot extrusion orifices are touching the substrate.

B( The support material is used to support overhangs internal cavities and thin sections

during extrusion as )ell as to provide a base to anchor %part( to the substrate )hile

building.

10



'&, PERATIN$

i4 CA& file preparation$

• Defore building the part the $T file has to be converted into the machine language

understood by "+. Guick $lice soft)are is used for this purpose.• The $T file is read into Guick $lice and is displayed graphically on screen in

-artesian co7ordinate system %F=C(

• Duilding box represents maximum build envelope of "+.

• Guick slice gives us options on the "+ system being used the slice layer thickness

the build and support materials as )ell as tip sizes.

ii4 Part Si5e$

The part must fit into the building box if not it )ill either have to be scaled do)n to fit or be

sectioned so that the pieces can be built separately and then bonded together later.

iii4 rientation and Positionin0$

3nce the part has been built in appropriate built size the part should be oriented in an

optimum position for building. The shape of the part plays an important role in this in that

some orientations may re#uire less supporting of overhangs than the others.

iv4 Slicin0$

3nce the part has been properly oriented and or scaled it must be sliced. $licing is a soft)are

operation that creates thin horizontal cross sections of $T file that )ill later be used

to create control code for the machine.

In Guick $lice the slice thickness can be changed before slicing the typical slices ranging

from .> inches to .1> inches.

Guick $lice allo)s

• To perform simple editing functions on slice files. 'lso editing function allo)s repair of

minor fla)s in the $T file )ith the options of closing and merging of curves.

*uild Parameters$

A4 Sets$

11



Guick $lice uses sets or packages of build parameters. $ets contain all of the build

instructions for a selected set of curves in a part. $ets allo) a part to be built )ith several

different settings

;.g. 3ne set may be used for supporting structure of the part one for part face another for

thicker sections of the part and still another for exposed surfaces of the part. This allo)s

flexibility of building bulkier sections and internal fills #uickly by getting finer details on

visible areas of a part.

$ets also allo) chosen sections of a part to build hollo) cross hatched or solid if so desired.

T)o of the build parameters commonly )orked )ith are road )idth and fill spacing.

A4 Road (idth$

oad 5idth is the )idth of the ribbon of molten material that is extruded from the tip.

5hen "+ builds a layer it usually begins by outlining the cross section )ith a perimeter

road sometimes follo)ed by one or more concentric contours inside of perimeters.

Eext it begins to fill remaining internal area in a raster or hatched pattern until a complete

solid layer is finished.

Therefore three types of roads are erimeter -ontour and aster.

*4 'ill Spacin0$

"ill spacing is the distance left bet)een raster!s or contours that make up interior solids of

the parts. ' fill spacing set at zero means that part )ill be built solid.

C4 Creatin0 and utputtin0 Roads$

3nce all parameters have been set road are created graphically by Guick $lice. The user is

then allo)ed to previe) each slice if so desired to see if the part is going to build as re#uired.

&4 "ettin0 a *uild Time Estimate$

Guick slice has a very good build time estimator )hich activates )hen an $ file is )ritten.

$ stands for $tratasys achine anguage. Dasically it displays in the command )indo)s

the approximate amount of time and material to be used for given part. Duild time estimate

allo)s for a efficient tracking and scheduling of "+ system )ork loads.

12



E4 *uildin0 a part$

The "+ receives a $ file and )ill begin by moving the head to the extreme F and =

portions to find it and then raises the platen to a point to )here the foam substrate is 2ust

belo) heated tips. 'fter checking the ra) material supply and temperature settings the user

then manually places the head at point )here the part has to be built on the foam and then

presses a button to begin building. 'fter that "+ )ill build part completely )ithout any

user intervention.

'4 'inishin0 a '&, part$

"+ parts are an easiest part to finish.

Applications$

a4 -oncept or +esign ,isualization.

34 +irect /se -omponents.

c4 Investment -asting.

d4 edical 'pplications

e4 "lexible -omponents

Advanta0es$

a4 $trength and temperature capability of build materials.

34 $afe laser free operation.

c4 ;asy ost rocessing.

&isadvanta0es$

a4 rocess is slo)er than laser based systems.

34 Duild $peed is lo).

c4 Thin vertical column prove difficult to build )ith "+.

d4 hysical contact )ith extrusion can sometimes topple or at least shift thin vertical

columns and )alls.

'&, ,aterial Properties$

13



,aterial Tensile Stren0th

-,pa/

Tensile ,odulus

-,pa/

'leural Stren0th

-,pa/

'leural ,od

-,pa/

'D+B *>.: 1>*> 00.9 :0:0

edical <rade

'D$ >

*8 :1B >8.9 181

Investment casting

)ax %I-50(

*.0 :8: B9.0 :8:

;lastomer 0.>> @ 89.09 1B1

&ia0rams$

14



'i0 a$ '&, Etrusion Head

'i0 3$ 'used &eposition ,odel Apparatus

15



UNIT .

Solid 0round curin0

The early versions of the system )eighed several tons and re#uired a sealed room. $ize

)as made more manageable and the system sealed to prevent exposure to photopolymers but

it )as still very large. Instead of using a laser to expose and harden photopolymer element by

element )ithin a layer as is done in stereo lithography $<- uses a mask to expose the entire

ob2ect layer at once )ith a burst of intense /, light. The method of generating the masks is

based on electrophotography %xerography(.

Hi0hli0hts

1. arge parts of >x>x*>mm can be fabricated #uickly.

:. 4igh speed allo)s production of many parts.

*. asks are created.

B. Eo post curing re#uired

>. illing step ensures flatness of subse#uent layers.

0. 5ax supports model hence no extra support is re#uired.

@. -reate a lot of )astes.

8. Eot as prevalent as $' and $$ but gaining ground because of high throughput and large

parts.

Process

16



"irst a

-'+ model of the part is created and it is sliced in to layers using cubitos data front end

soft)are.

14 Spray photosensitive resin$ 't the beginning of a layer creation step the flat )ork surface

is sprayed )ith photosensitive resin.

64 &evelopment of photo mas2 "or each layer a photo mask is produced using cubitals proprietary ionographic printing techni#ue.

17



.4 Epose photo mas2 The photo mask is positioned over the )ork surface a po)erful /,

lamp hardens the exposed photosensitive resin.

74 )acuum uncured resin and solidify the remnants 'fter the layer is cured all the

uncured resin is vacuumed for recycling leaving the hardened area intact the cured layer is

passed beneath a strong linear /, lamp to fully cure in and solidify any remnants particles as

sho)n in figure.

18



84 (a is applied to replace uncured resin area 5ax replaces the cavities left by

vacuuming the li#uid resin. The )ax is hardened by cooling to provide continuous solid

support for the model as it is fabricated extra supports are not needed.

94 The top surface is milled flat In the final step before the next layer the )ax resin surface

is milled flat to an accurate reliable finish for next layer.

3nce all layers are completed the )ax is removed and any finishing operations such as

sanding etc can be performed no post curing is necessary.

19



Advanta0es

The entire layer is solidified at once.

eduction in the part build time for multipart builds.

arger prototypes can be nested to utilize the build volume fully.

No post curing is required.

&isadvanta0es

The system is large noisy and heavy.

It )astes a large amount of )ax )hich cannot be recycled.

$<- systems are prone to breakdo)ns.

The resin models of $<- are not suitable for investment casting because coefficient of

thermal expansion is more than ceramics in resin )hich may lead to cracks in casting.

!A,INATE& *:ECT ,ANU'ACTURIN"

Introduction$

aminated 3b2ect anufacturing is a rapid prototyping techni#ue that produces *+ models

)ith paper plastics or composites. 3 )as developed by 4elices -orporation Torrance

-alifornia. 3 is actually more of a hybrid bet)een subtractive and additive process. In

that models are built up )ith layers of cross section of the part. 4ence as layers are been

added the excess material is not re#uired for that cross section is being cut a)ay. 3 is one

of the fastest processes for parts )ith longer cross sectional areas )hich make it ideal for

producing large parts.

System Hard%are$

1( 3 system is available in t)o sizes.

3 11> produces parts up to 1x1>x1B inches.

20



3 :* produces parts upto:x*x:B inches.

:( -ommon build material is paper.

*( Duild material has pressure and heat sensitive additive on the banking.

B( aterial thickness ranges from .*87.> inches.

Soft%are;s$

!, S!ICE S'T(ARE$

It provides interface bet)een operator and the system. 3 does not re#uire a pre slice of

$T "I; i.e. once the parameters are loaded into 3 $I-; the $T file slices as the

part builds. The process of continuous slicing is called slice on the fly. The 3 has a feed

spindle and a take up spindle for the build material. The feed spindle holds the roll of virgin

material )hereas the take up spindle serves to store the excess material after the layer is cut.

' heated roller travels across the face of the part being built after each layer to activate

adhesive and bond the part layer together.

'n invisible :>5atts -3: laser is housed on the back of the 3 and reflected off three

mirrors before finally passing through a focusing lens on the carriage. The carriage moves in

the F direction and the lens moves in the = direction on the carriage thus allo)ing focal

cutting point of laser to be moved like a plotter pen )hile cutting through build material in

the shape desired.

This F and = movement allo)s for t)o degrees of freedom or essentially a :7+ sketch of part

cross section. The part being built is adhered to a removable metal plate )hich holds the part

stationary until it is completed. The plate is bolted to the platen )ith brackets and moves in

the C direction by means of a large threaded shaft to allo) the parts to be built up. This

provides the third degree of freedom )here in the 3 is able to build *+ models.

$ome smoke and other vapors are created since the 3 functions by essentially burning

through the sheets of material )ith a laser therefore 3 must be ventilated either to the

outside air or through a large filtering device at rates around >cubic feet per minute.

!, PERATIN$

The )ay the 3 constructs the parts is by consecutively adhering layers of build material

)hile cutting the cross section of the parts )ith a laser. The 3 $I-; soft)are that comes

21



)ith 3 machine controls all these. The follo)ing description of operation is described

)ith paper as build material.

S'T(ARE$

1( 's )ith all systems the 3 must begin )ith the standard computer file or $T

file.

:( The $T is loaded into the 3 $I-; )hich graphically represents the model on the

screen.

*( /pon loading the $T file 3 $I-; creates initialization files in the background for

controlling the 3 machine. Eo) there are several parameters the user must consider

and enter before building the part.

Part rientation$

The designed shape of the parts to be built in 3 must be evaluated for determining the

orientation in )hich to build the parts.

'irst Consideration$

Accuracy desired for curved surfaces$ arts )ith curved surfaces tend to have a better

finish if the curvatures of the cross sections are cut in the F= plane. This is true due to thefact that the controlled motion of the laser cutting in the F= plane can hold better curve

tolerances dimensionally than the layered effects of FC and =C planes.

If a part contains curvatures in more than one plane one alternative is to build the part at an

angle to the axis. The benefits here are too full as the part )ill not only have more accurate

curvatures but )ill also tend to have better laminar strength across the length of the part.

Second Consideration$

Time ta2en to fa3ricate a part$ The slo)est aspect of build process for 3 is movement

in C direction or time bet)een the layers. This is mainly because after laser cuts across the

surface of the beam material the 3 must bring more paper across the top face of the part

and then adhere to the previous layer before the laser can begin cutting again.

"or this reason a general rule have come for orienting long narro) parts is to place the

lengthiest sections in the F= plane. This )ay the slo)est part of the process the actual laser

cutting is minimized to a smaller amount of layers.

22



There are some third party soft)are renders that have automatic testing functions that )ill

strategically place parts in optimum orientations for the selected section.

Cross Hatchin0$

-ross 4atching is necessary to get rid of excess paper on the individual layers. -ross hatch

sizes are set in 3 $I-; by the operator and can vary throughout the part. Dasically the

operator puts in a range of layers for )hich )e )ant a certain cross hatch pattern for sections

of the part that do not have integrate features or cavities a larger cross hatch can be set to

make a part build faster but for thin )alled sections and hollo)ed out areas a finer cross

hatch )ill be easier to remove. The cross hatch size is given in values of F and =. Therefore

the hatch pattern can vary from s#uare to long thin rectangles.

The t)o main considerations for cross hatching are

• ;ase of part removal.

• esulting build time.

' very small hatch sizes )ill make for easy part removal. 4o)ever if the part is rather large

or has large void areas it can really slo) do)n the build time. This is the reason for having

varying cross hatch sizes throughout the part.

The 3 operator can either 2udge )here and ho) the part should be cross hatched visually

or use long slice to run a simulation build on the computer screen to determine layer ranges

for the needed hatch sizes.

'lso since the 3 $I-; creates slices as the part build parameters can be changed during

a build simply by pausing a 3 machine and typing in ne) cross hatch values.

System Parameters$

There are various controlling parameters such as laser po)er heater speed material advance

margin and support )all thickness and heater compression.

23



!aser Po%er$ It is the percentage of total laser output )attage.

"or e.g. 3 11> is operated at a laser po)er of about 9H of maximum :>5 laser or

approximately :.:>5. This value )ill be different for various materials or machines but

essentially it is set to cut through only one sheet of build material.

Heater Speed$ It is the rate at )hich hot roller passes across the top of the part. The rate is

given in inches?second. It is usually 0?sec for Jinitial pass and *?sec for returning pass of

heater. The heater speed effects the lamination of the sheet so it must be set lo) enough to get

a good bond bet)een layers.

,aterial Advance ,ar0in$ It is the distance the paper is advanced in addition to length of

the part.

Support (all Thic2ness$ It controls the outer support box )alls throughout a part. The

support )all thickness is generally set .:> in the F and = direction although this value can

be changed by operator.

Compression$ It is used to set the pressure that the heater roller exerts on the layer. It is

measured in inches )hich are basically the distance the roller is lifted from its initial track by

the top surface of part. ,alues for compression )ill vary for different machines and materials but are typically .1>7.:>.

24



&ia0ram$

'i0$ !aminated 3<ect ,anufacturin0 Process

'i0$ Typical Cross Hatch Pattern

Unit 8

RAPI& T!IN"

25



apid Tooling refers to mould cavities that are either directly or indirectly fabricated using

apid rototyping techni#ues.

Soft Toolin0$

It can be used to intake multiple )ax or plastic parts using conventional in2ection moulding

techni#ues. It produces short term production patterns. In2ected )ax patterns can be

used to produce castings. $oft tools can usually be fabricated for ten times less than a

machine tool.

Hard Toolin0$

atterns are fabricated by machining either tool steel or aluminum into the negative shape of the desired component. $teel tools are very expensive yet typically last indefinitely building

millions of parts in a mass production environment. 'luminum tools are less expensive than

steel and are used for lo)er production #uantities.

Indirect Rapid Toolin0$

's is becoming more mature material properties accuracy cost and lead time are

improving to permitting to be employed for production of tools. Indirect T methods arecalled indirect because they use pattern obtained by appropriate techni#ue as a model

for mould and die making.

Role of Indirect methods in tool production$

technologies offer the capabilities of rapid production of *+ solid ob2ects directly from

-'+. Instead of several )eeks a prototype can be completed in a fe) days or even a fe)

hours. /nfortunately )ith techni#ues there is only a limited range of materials from

)hich prototypes can be made. -onse#uently although visualization and dimensional

verification are possible functional testing of prototypes often is not due to different

mechanical and thermal properties of prototype compared to production part.

'll this leads to the next step )hich is for industry to target tooling as a natural )ay to

capitalize on *+ -'+ modeling and technology. 5ith increase in accuracy of

techni#ues numerous processes have been developed for producing tooling from masters.

The most )idely used indirect T methods are to use masters to make silicon room

26



temperature vulcanizing moulds for plastic parts and as sacrificial models or investment

casting of metal parts. These processes are usually kno)n as $oft Tooling Techni#ues.

Silicon Ru33er Toolin0$

It is a soft tooling techni#ue. It is a indirect rapid tooling method.

'nother root for soft tooling is to use model as a pattern for silicon rubber mould )hich

can then in turn be in2ected several times. oom Temperature ,ulcanization $ilicones are

preferable as they do not re#uire special curing e#uipment. This rubber moulding techni#ue is

a flexible mould that can be peeled a)ay from more implicate patterns as suppose to former

mould materials. There are as many or more techni#ues for silicon moulding as there are

processes but the follo)ing is the general description for making simple t)o piece moulds.

"irst an process is used to fabricate the pattern. Eext the pattern is fixture into a holding

cell or box and coated )ith a special release agent %a )ax based cerosal or a petroleum 2elly

mixture( to prevent it from sticking to the silicon. The silicon rubber typically in a t)o part

mix is then blended vacuumed to remove air packets and poured into the box around the

pattern until the pattern is completely encapsulated. 'fter the rubber is fully cured )hich

usually takes 1: to :B hours the box is removed and the mould is cut into t)o %not necessarily

in halves( along a pre determined parting line. 't this point the original pattern is pulled from

the silicon mould )hich can be placed back together and repeatedly filled )ith hot )ax or

plastic to fabricate multiple patterns. These tools are generally not in2ected due to the soft

nature of the material. Therefore the final part materials must be poured into the mould each

cycle.

(ire Arc Spray$

These are the thermal metal deposition techni#ues such as )ire arc spray and vacuum plasma

deposition. These are been developed to coat lo) temperature substrates )ith metallic

materials. This results in a range of lo) cost tools that can provide varying degrees of

durability under in2ection pressures.

The concept is to first deploy a high temperature high hardness shell material to an

pattern and then backfill the remainder of the t)o shell )ith inexpensive lo) strength lo)

temperature materials on tooling channels. This provides a hard durable face that )ill endure

27



the forces on temperature of in2ection moulding and a soft banking that can be )orked for

optimal thermal conductivity and heat transfer from the body.

In 5ire 'rc $pray the metal to be deposited comes in filament form. T)o filaments are fed

into the device one is positively charged and the other is negatively charged until they meet

and create an electric arc. This arc melts the metal filaments )hile simultaneously a high

velocity gas flo)s through the arc zone and propels the atomized metal particles on to the

pattern. The spray pattern is either controlled manually or automatically by robotic control.

etal can be applied in successive thin coats to very lo) temperature of patterns )ithout

deformation of geometry. -urrent )ire arc technologies are limited to lo) temperature

materials ho)ever as )ell as to metals available in filament form.

,acuum lasma $pray technologies are more suited in higher melting temperature metals.

The deposition material in this case comes in po)der form )hich is then melted accelerated

and deposited by plasma generated under vacuum.

'i0$ (ire Arc Sprayin0

Epoy Tools$

;poxy tools are used to manufacture prototype parts or limited runs of production parts.

28



;poxy tools are used asA7

• oulds for prototype in2ection plastic

• oulds for casting

•

-ompression moulds• eaction In2ection oulds

The fabrication of moulds begins )ith the construction of a simple frame around the parting

line of model. $cre) gauges and runners can be added or cut later on once the mould is

finished. The exposed surface of the model is coated )ith a release agent and epoxy is poured

over the model. 'luminum po)der is usually added to epoxy resin and copper cooling lines

can also be placed at this stage to increase the thermal conductivity of the mould. 3nce the

epoxy is cured the assembly is inverted and the parting line block is removed leaving the pattern embedded in the side of the tool 2ust cast. 'nother frame is constructed and epoxy is

poured to form the other side of the tool. Then the second side of the tool is cured. The t)o

halves of the tool are separated and the pattern is removed. 'nother approach kno)n as soft

surface rapid tool involves machining an oversized cavity in an 'luminum plate. The offset

allo)s for introduction of casting material )hich may be poured into the cavity after

suspending the model in its desired position and orientation. $ome machining is re#uired for

this method and this can increase the mould building time but the advantage is that the

thermal conductivity is better than for all epoxy models.

'i0$ Soft Surface

/nfortunately epoxy curing is an exothermic reaction and it is not al)ays possible directly to

cast epoxy around a model )ithout damaging it. In this case a $ilicon T, ould is cast

from pattern and silicon T, model is made from the mould and is used as pattern for

aluminum fill deposited. ' loss of accuracy occurs during this succession of reproduction

steps. 'n alternative process is to build an mould as a master so that only a single silicon

29



T, reproduction step is needed because epoxy tooling re#uires no special skill or

e#uipment. It is one of the cheapest techni#ues available. It is also one of the #uickest.

$everal hundred parts can be moulded in almost any common casting plastic material.

;poxy Tools have the follo)ing limitations.

• imited tool life

• oor thermal transfer

• Tolerance dependent on master patterns

• 'luminum filled epoxy has lo) tensile strength

The life of the in2ection plastic aluminum epoxy tools for different thermoplastic materials is

given belo)

aterial Tool ife %$hots(

'D$ :7*

'cetol 171

Eylon :>7*

Eylon %gas filled( >7:

DT 17>

-?'D$ blends 171

oly -arbonate 171

oly ;thylene >7>

oly ropylene >7>oly $tyrene >7>

.& +eltool Process$

This process is based on metal sintering process. This process converts master patterns

into production tool inserts )ith very good definition and surface finish. The production of

inserts including the *+ Keltool process involves the follo)ing steps

1( "abricating the master patterns of core and cavity.

:( roducing T, silicon rubber mould from the pattern.

*( "illing the silicon rubber mould )ith metal mixtures to produce green parts duplicating

the masters. etal mixture is po)dered steel tungsten carbide and polymer binder )ith

30



particle sizes of around > mm. <reen parts are po)dered metal held together by polymer

binder.

B( "iring the green parts in a furnace to remove the plastic binder and sintering the metal

particles together.

>( Infiltrating the sintered parts %@H dense inserts( )ith copper in the second furnace cycle

to fill the *H void space.

0( "inishing the core and cavity.

*+ Keltool inserts can be built in t)o materials. $terlite of '0 composite tool steel. The

material properties allo) the inserts using this process to )ithstand more than 1lakh mould

cycles.

&irect Toolin0$

Indirect methods for tool production necessitate a minimum of one intermediate replication

process. This might result in a loss of accuracy and to increase the time for building the tool.

To overcome some of the dra)backs of indirect method ne) rapid tooling methods have

come into existence that allo) in2ection moulding and die casting inserts to be built directly

from *+ -'+ models.

Classification of &irect Rapid Toolin0 methods$

+irect apid Tooling rocesses can be divided into t)o main groups

1st 0roup$

It includes less expensive methods )ith shorter lead times.

+irect T methods that satisfy these re#uirements are called methods for firm tooling or

bridge tooling.

processes for firm tooling fill the gap bet)een soft and hard tooling.

6nd 0roup$

$olutions for hard tooling are based on fabrication of sintered metal steel iron copper

po)der inserts infiltrated )ith copper or bronze.

It includes T methods that allo) inserts for pre production and production tools to be

built.

These methods come under hard tooling.

Classification of &irect RT methods$

31



1/ 'irm Toolin0 ,ethods

• +irect 'I

• +T -3; ' T33IE<

• +T $'E+"3 T33IE<

• ;;-T3 3TI-' $=$T; +I;-T -43EIE< 3-;$$

• 3 T33IE< IE 3=;

• *+ -;'I- $4;$

6/ Hard Toolin0 ,ethods

• ;3$ +I;-T T33

• +T 'I+ T33 3-;$$

• 3 T33IE< IE -;'I-

• *+ +I;-T ;T' T33IE<

&IRECT AI,$

&IRECT ACES IN:ECTIN ,U!&S$

'-;$ refer to 'ccurate -lear ;poxy $olid.

$tereolithography is used to produce epoxy inserts for in2ection mould tools for thermoplastic

parts because the temperature resistance of curable epoxy resins available at present is up to

:!- and thermoplastics are in2ected at temperature as high as *!-. $pecific rules apply to

the production of this type of in2ection moulds.

The procedure detailed in is outlined belo).

/sing a *+ -'+ package the in2ection mould is dra)n. unners fan gates e2ector pins and

clearance holes are added and mould is shelled to a recommended thickness of 1.:@mm. The

mould is then built using accurate clear epoxy solid style on a $tereolithography machine.

The supports are subse#uently removed and the mould is polished in the direction of dra) to

facilitate part release. The thermal conductivity of $' resin is about * times lo)er than

that of conventional tool steels %.:: 5?mK for cibatool $>1@ epoxy resin(

To remove the maximum amount of heat from the tool and reduce the in2ection moulding

cycle time copper )ater cooling lines are added and the back of the mould is filled )ith a

mixture made up of *H by volume of aluminum granulate and @H of epoxy resin. The

cooling of the mould is completed by blo)ing air on the mould faces as they separate after

the in2ection moulding operation.

&isadvanta0es$

32



• Eumber of parts that can be obtained using this process is very dependent on the shape

and size of the moulded part as )ell as skills of good operator )ho can sense )hen to

stop bet)een cycles to allo) more cooling.

• rocess is slightly more difficult than indirect methods because finishing must be done on

internal shapes of the mould.

• 'lso draft angles of order up to one and the application of the release agent in each

in2ection cycle are re#uired to ensure proper part in2ection.

• ' +irect 'I mould is not durable like aluminum filled epoxy mould. In2ection cycle

time is long.

Advanta0es$

It is suitable for moulding up to 1 parts.

• Doth resistance to erosion and thermal conductivity of +7'I tools can be increased by

deposition of a :>micron layer of copper on mould surfaces.

imp notes on rapid prototyping

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