rp handout1

7/29/2019 RP Handout1

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Rapid Prototyping (RP)

Introduction of RP

Generate a prototyping by Laying ManufacturingTechnology - composite material layer by layer

Build in one step - directly from model to

manufacturing


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Development of RP

First Phase : Manual (or Hard) Prototyping

Age-old practice for many centuries

Prototyping as a skilled craft is traditional and manual

and based on material of prototype Natural prototyping technique


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Development of RP

Second Phase : Soft (or Virtual) Prototyping

Mid 1970s

Increasing complexity

Can be stressed, simulated and tested with exactmechanical and other properties


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Development of RP

Third Phase : Rapid Prototyping

Mid 1980s

Hard prototype made in a very short turnaround time

(relies on CAD modelling) Prototype can be used for limited testing

prototype can consist in the manufacturing of theproducts

3 times complex as soft prototyping


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Fundamentals of RP

Building computer model

Model is building by CAD/CAM system

Model must be defined as enclosed volume or solid

Converting model into STL file format

STereoLithography (STL) file is a standard format todescribe CAD geometry used in RP system

STL file file approximates the surfaces of the model

by polygons


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Fundamentals of RP

Fabricating the model

Building model layer by layer

Forming a 3D model by solidification of liquid/powder


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Applications of RP

For design evaluation

Touch and holding a physical prototype

For function verification

e.g. assembly, kinematics performance, andaerodynamic performance

Models for further manufacturing processes

e.g. Vacuum casting, spray metal moulding,

investment casting, etc.

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Advantages and Disadvantages

No planning of process sequences

No specific equipment for handling materials

No transportation between machining

Features-based design and feature recognition areunnecessary

Defining a blank geometry is unnecessary

Defining different setups or complex sequences ofhandling material is unnecessary

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Advantages and Disadvantages

No need to consider jigs and fixtures

Designing and manufacturing moulds and dies

Specific materials are restricted

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Role of RP in Product Development Cycle

Product design

Increase part complexity and diversity with littleeffect on lead time and cost

Minimise time-consuming discussion and evaluationsof manufacturing possibilities

Tool design and manufacturing

Minimise design, manufacturing and verification of

tooling Reduce parts count and eliminate tool wear

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Role of RP in Product Development Cycle

Assembly and test

Reduce labour content of manufacturing (e.g.machining, casting, inspection and assembly, etc.)

Reduce material costs (e.g. handling, waste,transportation, spare and inventory, etc.)

Function testing

Avoid design misinterpretations, i.e. what you design

is what get)

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Due to the newness of the technology, thereare already so many words for RP used today:

RP( most commonly used) - Rapid Prototyping

RPTM(inc. new development trends) - Rapid

Prototyping, Tooling and Manufacture Direct CAD Manufacturing/Desktop

Manufacturing/Instant Manufacturing/CAD OrientedManufacturing = RP

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Layer Manufacturing/Material Addition

Manufacturing/Material Deposit Manufacturing/Material Increase Manufacturing/Solid FreedomManufacturing - Emphasis the unique characteristicof RP

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Classification of RP Systems

By the initial form of its material, RP systemscan be categorised into:

Liquid-based

Liquid-based material Curing Process Solid

(e.g. SLA, SGC, SOUP, etc.)

RP


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Classification of RP Systems

Solid-based

Encompass all forms of material in the solid form,such as in the form of wire, a roll, laminates and

pellets.(e.g. LOM and FDM, etc.)

Powder-based

Grain-like material

Joining/Binding

Solid(e.g. SLS and 3DP, etc.)

RP


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Features of RP Systems

The features of some commercially available RPsystems can be summarised into:

Process type - Stereo lithography, Laminating,Fused deposition modelling, Sintering of powder,Solid ground curing, etc.

Work space(mm) - depends on the models

Material - photopolymer resin, coated paper, ABS,wax, metal alloy, etc.

RP


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Features of RP Systems

Layer thickness(mm) - 0.05 - 0.3(SLA); 0.1 -1(LOM.); ~0.05(FDM); ~0.08(SLS); 0.01 -0.15(SGC)

Accuracy(mm) - 0.01- 0.2(SLA); 0.1 - 0.2(LOM);0.127 - 0.254(FDM); 0.03 - 0.38(SLS); 0.05 -0.5(SGC)

Manufacturer - 3D System, Stratasys, Helisys, DTM,

EOS, etc.

RP


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Pre-Processing Tasks

Prepare geometric model in STL file format

Solid or surface CAD model to be built is nextconverted into format dubbed the .STL file format

because it is a standard input data to any RPprocess. STL originates from 3D Systems, whichpioneers the Stereolithography system in 1987. Theformat approximates the surfaces of the modelusing tiny triangles. Since 1990, almost all majorCAD/CAM vendor supply the CAD-STL interface.

RP


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Building up direction

The direction affects many key aspects of RPprocess, quality of the surface finish, build time,

amount of support structures needed, and amountof trapped volume. For experience, minimising theheight of the geometry will reduce the no. of layersrequired, thereby decreasing build time, but alsosacrifice part resolution or accuracy.

RP


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Trapped volume

It is the amount of liquid resin in the RP process(e.g. SLA) that was entrapped by the processed or

solidified region. Thus trapped volumes can exist inconcave regions that as containers. It may beeliminated by either building a part with a drain holeand fill the hole after solidification or modifying theorientation of the part.

RP


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Part placement

In RP, the time spent building a prototype does notdepend on the no. of parts but on the total no. of

slices required. By closely packing multiple partsinto feasible volume, several parts can be built atthe same time.

RP


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Support structure

The support structure in RP process has thefollowing functions:

ensure the recoater blade will not strike the platformwhen the first layer is swept

improve uniformity of layer thickness

provide a simple means of removing the part from

the platform upon its completion

/RP


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Support structure

However, overdesign of support structures results inadded design and manufacturing time, as well as

finishing operations

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Post-Processing Tasks

Part removal and cleaning

After a part is built, drain excess liquid resin at theplatform and the part back into the vat. Next, the

part and the platform are placed in a cleaningapparatus with solvent (e.g. TPM). It will producelittle swelling distortion on a part. Once the part hasbeen thoroughly cleaned of excess resin, bothplatform and part are rinsed with water to remove

TPM film. The last step is to remove the part fromthe platform by flat-bladed knife.

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Post curing

During some RP processes, such as SLA, the laserscans each layer along the boundary and hatching

lines only. This means that inside portions of thelayers may not be completely solidified. Thus thepart is post-cured to complete the polymerisationprocess by exploring with UV radiation in a speciallydesigned apparatus.

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Part finishing

This process is to remove the supports by using adull edged blade or putty knife. Care must be taken

to avoid damaging a part that contains fragilesections. Once the supports have been removed,minor sanding is applied to eliminate residual tracesof the supports.

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R id P t t i (RP)


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Principle of Stereolithography Apparatus (SLA)

SLA was developed in 1986 by 3D Systems. Theprocess is based on the following principles:

Parts are built from a photo-curable liquid resin that

solidifies when sufficiently exposed to a laser beamwhich scans across the surface of the resin

The building is done layer by layer, each layer beingscanned by the optical scanning system and

controlled by an elevation mechanism which lowersat the completion of each layer

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Process of SLA

Step 1 - A liquid state photosensitive polymer thatsolidifies when exposed to a lighting source

Step 2 - A platform that can be elevated is located

just one layer of thickness below the surface

Step 3 - According to the cross section of the part(starting with bottom layer). The laser scansthe polymer layer above the platform to

solidify the polymer

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Process of SLA

Step 4 - The Platform is lowered into the polymerbath to the layer thickness

Step 5 - Repeat 3 and 4 until the top layer of the part

is generated

Step 6 - Post-curing and part finishing will then beperformed

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Applications of SLA

Models for conceptualisation,packaging and presentation

Prototypes for design, analysis, verification andfunctional testing

Masters for prototype tooling and low volume productiontooling

Patterns for investment casting, sand casting andmoulding

Tools for fixture and tooling design and productiontooling

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Principle of Selective Laser Sintering (SLS)

SLS was developed by DTM Corporation in 1992. The

process is based on the following principles:

Parts are built by sintering when a CO2 laser beam hit a

thin layer a powdered material. The interaction of thelaser beam with the powder raises the temperature,resulting in particle melting and bonding together

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Principle of Selective Laser Sintering (SLS)

The building of the part is done layer by layer. Eachlayer of the building process contains the cross sectionsof one or many parts. The next layer built directly on thetop of the sintered layer after an additional layer of

powder is deposited via a roller mechanism on the top ofthe previously formed layer

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Process of SLS

Step 1 - A part cylinder is located at the heightnecessary for a layer of powdered materialto be deposited on the cylinder to thedesired thickness. The powder is appliedfrom the feed cylinder by the levelling roller

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Process of SLS

Step 2 - The layer of powder is selectively raster-scanned and heated with a laser, causingparticles to adhere to each other. The laserscan forms the powder into the requiredcross section shape. Again this step startswith the bottom cross section

Step 3 - The part cylinder is lowered by the layer

thickness to permit a new layer of powder tobe deposited

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Process of SLS

Step 4 - The new layer is scanned, conforming it tothe shape of the next upper cross-sectionand adhering it to the previous layer

Step 5 - Repeat 3 and 4 until the top layer of the partis generated

Step 6 - Post-curing may be required for somematerial

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Applications of SLS

Concept models

Functional models and working prototypes

Wax casting pattern

Polycarbonate patterns. These build faster than waxpatterns and are ideally suited for design with thin wallsand fine features. These pattern are also durable andheat resistant

Metal Tools. Direct rapid prototype of tools of mouldsfor small or short production runs.

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Process of FDM

The process of FDM is relatively simple and fast but itsuse is limited to thermoplastic materials

Step 1 - The thermoplastic material in the form of

filament is heated to just above itssolidification temperature

Step 2 - The extrusion head is heated and movesaccording to the pattern of the cross section

of each layer of the part

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Process of FDM

Step 3 - The material is extruded on the foundationor previously built layer. As it is extruded, itis cooled and thus solidifies to form therequired pattern of part


Step 5 - Part finishing may be required

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Applications of FDM

Models for conceptualisation and presentation

Prototypes for design, analysis and functionaltesting

Patterns and masters for tooling. Models can beused as patterns for investment casting, sand castingand moulding

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Principle of Laminated Object Manufacturing

(LOM)

LOM was developed by Helisys Inc. in 1991. The

process is based on the following principles:

Parts are built, layer by layer, by laminating and laser-trimming materials that are delivered in sheet form. Thesheets are laminated into block by a thermal adhesivecoating

AE/RP



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Process of LOM

The accuracy of the process of LOM is high. The mostpopular laminated material is paper sheet.

Step 1 - Sheet material is supplied from a continuous

roll form. Each sheet attached to the block,using heat and pressure to form a new layer

Step 2 - The platform is lowered by the thickness ofthe sheet whenever a sheet is attached to

the stack

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Process of LOM

Step 3 - After a layer is deposited, a CO2 laser istraced on the layer along the contourscorresponding to the current cross section

Step 4 - Areas of the layer outside the contours arecross-hatched by the laser (i.e. cut into smallpieces for removal afterwards)

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Process of LOM

Step 5 - After the part is built, the result is imbeddedwithin a block of supporting material. Thismaterial is then broken into chunks alongthe cross-hatching lines

Step 6 - The resulting part may then be coated witha sealant to keep out moisture

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Applications of LOM

Applicable for a wide range of product, equipmentfor aerospace or automotive, consumer products,and medical devices

Prototypes for design, analysis and functional

testing

Tools for production

Small volume of finished goods

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Principle of 3D Printing (3DP)

3DP was invented by MIT in 1994

Parts are created by a layered printing processand adhesive bonding, based on sliced crosssection data. A layer is created by adding another

layer of powder. The powder layer is selectivelyjoined, where the part is to be form, by ink-jetprinting of a blinder material

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Process of 3DP

The process of 3DP is more efficient and relativelycheaper than sintering types.

Step 1 - Platform is located at the height necessary

for a layer of ceramic powder to bedeposited

Step 2 - The layer of ceramic powder is selectivelyraster-scanned with a print head that

delivers a liquid binder, causing particles toadhere to each other

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Process of 3DP

Step 3 - The platform is lowered by the layerthickness to permit a new layer of powderto be deposited

Step 4 - The new layer is scanned, conforming it tothe shape of the next upper cross sectionand adhering it to the previous layer

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Process of 3DP


Step 6 - A post-process heat treatment is applied to

solidify the part

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Applications of 3DP

CAD-Casting metal parts.A ceramic shell withintegral cores can be fabricated directly from the CADmodel

Direct metal parts. It is adaptable to a variety of

material systems, allowing the production ofmetallic/ceramic parts with novel composition

Prototypes with colours and elastic feature

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