rproto

RAPID PROTOTYPING - Principles and Applications - Third Edition (with Companion CD-ROM) World Scientific Publishing Co. Pte. Ltd.http://www.worldscibooks.com/engineering/6665.html

Chapter 3LIQUID-BASED RAPID PROTOTYPING

SYSTEMS

Most liquid-based rapid prototyping (RP) systems build parts in a vatof photo-curable liquid resin, an organic resin that cures or solidifiesunder the effect of exposure to light, usually in the UV range. The lightcures the resin near the surface, forming a thin hardened layer. Once thecomplete layer of the part is formed, it is lowered by an elevation con-trol system to allow the next layer of resin to be coated and similarlyformed over it. This continues until the entire part is complete. The vatcan then be drained and the part removed for further processing, if nec-essary. There are variations to this technique by the various vendorsand they are dependent on the type of light or laser, method of scanningor exposure, type of liquid resin and type of elevation and opticalsystem used.

3.1. 3D SYSTEMS STEREOLITHOGRAPHYAPPARATUS (SLA)

3.1.1. Company3D Systems was founded in 1986 by inventor Charles W. Hull andentrepreneur Raymond S. Freed. Amongst all the commercial RP systems,the Stereolithography Apparatus, or SLA as it is commonly called, is thepioneer with its first commercial system marketed in 1988. The companyhas grown significantly through increased sales and acquisitions, mostnotably of EOS GmbHs Stereolithography business in 1997 and DTMCorp., the maker of the Selective Laser Sintering (SLS) system in 2001.By 2007, 3D Systems is a global company that delivers advanced rapidprototyping solutions to every major market around the world. It has aglobal portfolio of nearly 400 US and foreign patents, with additional

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patents filed or pending in the US and several other major industrializedcountries. 3D Systems Inc. is headquartered in 333 Three D SystemsCircle Rock Hill, SC 29730, USA.

3.1.2. Products3D Systems produces a wide range of RP machines to cater to various partsizes and throughput. There are several models available, including thosein the series of Viper SLA, Viper HA SLA, SLA 5000, SLA 7000 andDual-Vat ViperTM Pro SLA system. The Viper SLA is an economical andversatile starter system that uses Nd:YVO4 laser. The Viper system hastwo different built-in modes, which are standard mode and HR (Highresolution) mode, in a single system. Standard mode utilizes a beamdiameter of 0.254 0.0254 mm (0.010 0.001 in.) and HR mode has abeam diameter of 0.0705 0.0127 mm (0.003 0.0005 in.). Dependingon the size of the design part, the function enables the user to choose theappropriate mode to obtain high quality surfaces. HR mode is speciallyused for ultra small parts where parts are built with smooth surface finish,excellent optical clarity, high accuracy and thin straight vertical walls. Itis ideal for a myriad of solid imaging applications, from rapid modelingand prototyping, to injection melding and investment casting. Viper HASLA system shares the same functionality as Viper SLA system and it hasadditional hearing aid specific enhancements. Single-Vat Viper HA SLAsystem can be upgraded to dual-vat to produce two different color hearingaid shells in a single build.

For larger build envelopes, the SLA 5000, SLA 7000 and Dual-VatViper PRO SLA (see Fig. 3.1) are available. These three machines use thesame laser as the Viper SLA system (solid-state Nd:YVO4). The SLA7000 can build parts up to four times faster than the SLA 5000 with thecapacity of building thinner layers (minimum layer thickness 0.025 mm)for finer surface finish. Its fast speed is determined by its dual spot lasersability. For the dual spot laser technology, a smaller beam spot is used forthe border for accuracy, whereas the bigger beam spot is used for internalcross-hatching for the increased speed.

The largest and the top of the series is the ViperTM Pro SLA system.It has a new configuration called dual Resin Delivery Module (RDM)

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36 Rapid Prototyping



Liquid-Based Rapid Prototyping Systems 37

which allows the customer to build parts from two different materialssimultaneously while utilizing a single proprietary imaging and scanningmodule. RDM contains a resin management system which will automati-cally detect and cross-check for the proper resin type in the system.Additionally a new feature is integrated in the system to filter and recir-culate the material to extend the use of materials. With the two inbuiltchambers, the size of parts can be manufactured up to a volume of 737 635 533 mm (29 25 21 in.) while having a similar capability as theViperTM SLA system in producing high resolution products. Specificationsof these machines are summarized in Tables 3.1(a) and 3.1(b).

The ZephyrTM system was introduced in 1996 as a product enhance-ment in all the SLA systems.1 The ZephyrTM system eliminates the needfor the traditional deep dip in which a part is dunked into the resin vatafter each layer and then raised to within one layers depth of the top ofthe vat. With the deep dip, a wiper blade sweeps across the surface ofthe vat to remove excess resin before scanning the next layer. TheZephyrTM system has a vacuum blade that picks up resin from the sideof the vat and applies a thin layer of resin as it sweeps across the part.This speeds up the build process by reducing the time required betweenlayers and greatly reduces the problems involved when building partswith trapped volumes.

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Fig. 3.1. 3D Systems ViperTM Pro SLA system (courtesy 3D Systems).



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Table 3.1. Summary specifications of (a) the Viper and Viper HA SLA machines and(b) the rest of SLA machines (source from 3D Systems).

a

Model

Viper SLA Viper HA SLA

System characteristicsDescription A dual-resolution, A dual-resolution

constant power, system with hearinglonger-life laser. aid specific

enhancements.Vat capacity

Maximum build envelope, 250 250 250mm (in.) (10 10 10)

VolumeVolume, l (US gal) 32.2 (8.5l)

LaserType Solid-state (Nd:YVO4)Wavelength, nm 354.7Power at vat @ h @ 7,500/h 100 mWWarranty, h 7,500

Optical and scanningDual spot YesBeam diameter: standard 0.25 +/0.025 (0.010 0.001)

mode, mm (in.)Beam diameter: HR mode, 0.075 +/0.015 (0.0030 0.0006)

mm (in.)Recoating system

ZephyrFeatures

Interchangeable vat YesSmartSweep NoAuto resin refill No

SoftwareControl software BuildstationTM BuildstationTMOperating systems Windows NT (4.0 with Windows XP

Service Pack 3.0 or higher) Professional

(Continued )




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Table 3.1. (Continued )

b

Model

SLA 5000 SLA 7000 ViperTM Pro SLAsystem

Warranty1 yr from installation date

System characteristicsDescription A large-frame system A supercharged An outstanding system

with three times the large-frame with excellent build build volume of system two speed and SLA 3500. times faster than adjustable beam

SLA 5000 with size. Integratedthe capability of configuration to building thinner build a part with layers for finer two different typessurface finish. of materials.

Vat capacityMaximum build 508 508 584 508 508 600 737 635 533

envelope, (20 20 23) (20 20 23.6) (29 25 21)mm (in.)

VolumeVolume, l (US gal) 253.6 (67) 935 (247)

Laser

Type Solid-state (Nd:YVO4)Wavelength, nm 354.7Power at vat @ @ 5,000/h 216 mW @ 5,000/h 800 mW @ 5,000/h 1000 mWWarranty, h 5,000

Optical and scanningDual spot No YesBeam diameter; 0.25 0.025 0.25 0.025 Nominal 0.13 mm

border @ l/e2, (0.010 0.001) (0.010 0.001) (0.005)mm (in.)

Beam diameter; Nil Nil Nominal 0.3 mmspecialty spot (0.012 in.)@ l/e 2, mm (in.)

(Continued )



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Table 3.1. (Continued )

b

Model

SLA 5000 SLA 7000 ViperTM Pro SLAsystem

Beam diameter; 0.25 0.025 mm 0.7615 0.0765 mm Nominal 0.76 mmhatch @ l/e 2, (0.010 0.001 in.) (0.03 0.003 in.) (0.030 in.)mm (in.)

Recoating systemZephyr

Features

Interchangeable vat YesSmartSweep YesAuto resin refill Yes

SoftwareControl software BuildstationTM BuildstationTM 3DViewTM, 3DManageTM,

3DPrintTMOperating system Windows NT Windows NT 4.0 Windows XP

Professional (SP 2)Warranty

1 yr from installation date

All these machines rely on photo-curable liquid resins as the material forbuilding. There are several grades of resins available and usage is depend-ent on the laser on the machine and the mechanical requirements of the part.Specific details on the correct type of resins to be used are available fromthe manufacturer. The other main consumable used by these machines is thecleaning solvent which is required to clean the part of any residual resinafter the building of the part is completed on the machine.

3.1.3. Process3D Systems stereolithography process creates 3D plastic objects directlyfrom computer-aided design (CAD) data. The process begins with the vat




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Laser

Elevating platform

Vat

Sweeping wiper blade

Scanning system

Part

Platform

SupportsPhotocurable liquid resin

Fig. 3.2. Schematic of SLA Process.

filled with the photo-curable liquid resin and the elevator table set justbelow the surface of the liquid resin (see Fig. 3.2). The operator loads a 3DCAD solid model file into the system. Supports are designed to stabilize thepart during building. The translator converts the CAD data into an STL file.The control unit slices the model and supports into a series of cross sectionsfrom 0.025 to 0.5 mm (0.0010.020 in.) thick. The computer-controlledoptical scanning system then directs and focuses the laser beam so that itsolidifies a 2D cross section corresponding to the slice on the surface of thephoto-curable liquid resin to a depth greater than one layer thickness. Theelevator table then drops enough to cover the solid polymer with anotherlayer of the liquid resin. A leveling wiper or vacuum blade (for ZephyrTMrecoating system) moves across the surfaces to recoat the next layer of resinon the surface. The laser then draws the next layer. This process continuesbuilding the part from bottom up, until the system completes the part. Thepart is then raised out of the vat and cleaned of excess polymer.

The main components of the SLA system are a control computer, acontrol panel, a laser, an optical system and a process chamber. The work-station software used by the SLA system, known as 3D Lightyear exploitsthe full power of the Windows NT operating system and delivers far richerfunctionality than the UNIX-based Maestro software. Maestro includesthe following software modules2:

(1) 3dverifyTM module. This module can be accessed to confirm theintegrity and/or provide limited repair to stereolithography (STL) files



before part building without having to return to the original CADsoftware. Gaps between triangles, overlapping or redundant trianglesand incorrect normal directions are some examples of the flaws thatcan be identified and corrected (see Chap. 6).

(2) ViewTM module. This module can display the STL files and slice file(SLI) in graphical form. The viewing function is used for visual inspec-tion and the orientation of these files so as to achieve optimal building.

(3) MERGE module. By using MERGE, several SLI files can be mergedinto a group which can be used together in the future process.

(4) VistaTM module. This module is a powerful software tool that automati-cally generates support structures for the part files. The support structureis an integral part to successful part building, as it helps to anchor partsto the platform when the part is free floating or there is an overhang.

(5) Part ManagerTM module. This software module is the first stage ofpreparing a part for building. It utilizes a spreadsheet format intowhich the STL file is loaded and set-up with the appropriate build andrecoat style parameters.

(6) SliceTM module. This is the second stage of preparing a part for build-ing. It converts the spreadsheet information from the Part ManagerTMmodule to a model of 3D cross sections or layers.

(7) ConvergeTM module. This is the third and last stage of preparing a partfor building. This module creates the final build files used by the SLA.

3.1.4. PrincipleThe SLA process is based fundamentally on the following principles3:

(1) Parts are built from a photo-curable liquid resin that cures whenexposed to a laser beam (basically, undergoing the photo-polymerizationprocess) which scans across the surface of the resin.

(2) The building is done layer by layer, each layer being scanned by theoptical scanning system and controlled by an elevation mechanismwhich lowers at the completion of each layer.

These two principles will be discussed briefly in this section to lay thefoundation for the understanding of RP processes. They are mostly

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applicable to the liquid-based RP systems described in this chapter. Thisfirst principle deals mostly with photo-curable liquid resins, which areessentially photo-polymers and the photo-polymerization process. Thesecond principle deals mainly with CAD data, the laser and the control ofthe optical scanning system as well as the elevation mechanism.

3.1.4.1. Photo-PolymersThere are many types of liquid photopolymers that can be solidified byexposure to electro-magnetic radiation, including wavelengths in thegamma rays, X-rays, UV and visible range, or electron-beam (EB).4,5 Thevast majority of photo-polymers used in commercial RP systems, includ-ing 3D Systems SLA machines are curable in the UV range. UV-curablephoto-polymers are resins which are formulated from photo-initiators andreactive liquid monomers. There are a large variety of them and some maycontain fillers and other chemical modifiers to meet specified chemicaland mechanical requirements.6 The process through which photo-poly-mers are cured is referred to as the photo-polymerization process.

3.1.4.2. Photo-PolymerizationLoosely defined, polymerization is the process of linking smallmolecules (known as monomers) into chain-like larger molecules (knownas polymers). When the chain-like polymers are linked further to oneanother, a cross-linked polymer is said to be formed. Photo-polymerizationis polymerization initiated by a photo-chemical process whereby thestarting point is usually the induction of energy from an appropriateradiation source.7

Polymerization of photo-polymers is normally an energetically favor-able or exothermic reaction. However, in most cases, the formulation ofphoto-polymer can be stabilized to remain unreacted at ambient tempera-ture. A catalyst is required for polymerization to take place at a reasonablerate. This catalyst is usually a free radical which may be generated eitherthermally or photo-chemically. The source of a photo-chemically gener-ated radical is a photo-initiator, which reacts with an actinic photon toproduce the radicals that catalyze the polymerization process.

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The free-radical photo-polymerization process is schematically pre-sented in Fig. 3.3.8 Photo-initiator molecules, Pi, which are mixed with themonomers, M, are exposed to a UV source of actinic photons, with energyof h, where h is the Planck constant and is the frequency of the radia-tion. The photo-initiators absorb some of the photons and are in an excited

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Photoinitiator, Pi Monomer, M

h

Reactive initiator with free radical, P

Photoinitiator, Pi and monomer, MPhotoinitiator excitation and free radical (Pi ) generation

Chain initiation

Chain propagation

Chain propagation

Polymerization initiating molecule PM

Fig. 3.3. Schematic for a simplified free-radical photo-polymerization.




state. Some of these are converted into reactive initiator molecules, P,after undergoing several complex chemical energy transformation steps.These molecules then react with a monomer molecule to form a polymer-ization initiating molecule, PM. This is the chain initiation step. Onceactivated, additional monomer molecules go on to react in the chain prop-agation step, forming longer molecules, PMMM until a chain inhibitionprocess terminates the polymerization reaction. The longer the reaction issustained, the higher will be the molecular weight of the resulting poly-mer. Also, if the monomer molecules have three or more reactive chemicalgroups, the resulting polymer will be cross-linked and this will generatean insoluble continuous network of molecules.

During polymerization, it is important that the polymers aresufficiently cross-linked so that the polymerized molecules do not re-dissolve back into the liquid monomers. The photo-polymerized mole-cules must also possess sufficient strength to remain structurally soundwhile the cured resin is subjected to various forces during recoating.

While free-radical photo-polymerization is well-established andyields polymers that are acrylate-based, there is another newer chem-istry known as cationic photo-polymerization.9 It relies on cationicinitiators, usually iodinium or sulfonium salts, to start polymerization.Commercially available cationic monomers include epoxies, the mostversatile of cationally polymerizable monomers and vinylethers.Cationic resins are attractive as prototype materials as they have betterphysical and mechanical properties. However, the process may requirehigher exposure time or a higher power laser.

3.1.4.3. Layering Technology, Laser and Laser ScanningAlmost all RP systems use layering technology in the creation ofprototype parts. The basic principle is the availability of computer soft-ware to slice a CAD model into layers and reproduce it in an outputdevice like a laser scanning system. The layer thickness is controlled bya precision elevation mechanism. It will correspond directly to the slicethickness of the computer model and the cured thickness of the resin.The limiting aspect of the RP system tends to be the curing thicknessrather than the resolution of the elevation mechanism.



The important component of the building process is the laser and itsoptical scanning system. The key to the strength of the SLA is its abilityto rapidly direct focused radiation of appropriate power and wavelengthonto the surface of the liquid photo-polymer resin, forming patterns ofsolidified photo-polymer according to the cross-sectional data generatedby the computer.10 In the SLA, a laser beam with a specified power andwavelength is sent through a beam expanding telescope to fill the opticalaperture of a pair of cross axis, galvanometer driven and beam scanningmirrors. These form the optical scanning system of the SLA. The beamcomes to a focus on the surface of a liquid photo-polymer, curing a pre-determined depth of the resin after a controlled time of exposure(inversely proportional to the laser scanning speed).

The solidification of the liquid resin depends on the energy per unitarea (or exposure) deposited during the motion of the focused spot onthe surface of the photo-polymer. There is a threshold exposure that mustbe exceeded for the photo-polymer to solidify.

To maintain accuracy and consistency during part building using theSLA, the cure depth and the cured line width must be controlled. As such,accurate exposure and focused spot size become essential.

Parameters which influence performance and functionality of theparts are physical and chemical properties of resin, speed and resolutionof the optical scanning system, the power, wavelength and type of thelaser used, the spot size of the laser, the recoating system and the post-curing process.

3.1.5. Strengths and WeaknessesThe main strengths of the SLA are:

(1) Round the clock operation. The SLA can be used continuously andunattended round the clock.

(2) Build volumes. The different SLA machines have build volumes rang-ing from small (250 250 250 mm) to large (737 635 533 mm)to suit the needs of different users.

(3) Good accuracy. The SLA has good accuracy and can thus be used formany application areas.

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(4) Surface finish. The SLA can obtain one of the best surface finishesamongst RP technologies.

(5) Wide range of materials. There is a wide range of materials,from general-purpose materials to specialty materials for specificapplications.

The main weaknesses of the SLA are:

(1) Requires support structures. Structures that have overhangs andundercuts must have supports that are designed and fabricatedtogether with the main structure.

(2) Requires post-processing. Post-processing includes removal of sup-ports and other unwanted materials, which is tedious, time-consumingand can damage the model.

(3) Requires post-curing. Post-curing may be needed to cure the objectcompletely and ensure the integrity of the structure.

3.1.6. ApplicationsThe SLA technology provides manufacturers cost justifiable methods forreducing time to market, lowering product development costs, gaininggreater control of their design process and improving product design. Therange of applications includes:

(1) Models for conceptualization, packaging and presentation.(2) Prototypes for design, analysis, verification and functional testing.(3) Parts for prototype tooling and low volume production tooling.(4) Patterns for investment casting, sand casting and molding.(5) Tools for fixture and tooling design and production tooling.

Software developed to support these applications includes QuickCastTM, asoftware tool which is used in the investment casting industry.QuickCastTM enables highly accurate resin patterns that are specificallyused as an expendable pattern to form a ceramic mould to be created. Theexpendable pattern is subsequently burnt out. The standard processuses an expendable wax pattern which must be cast in a tool. QuickCastTM



eliminates the need for the tooling use to make the expendable patterns.QuickCastTM produces parts which have a hard thin outer shell and con-tain a honeycomb like structure inside, allowing the pattern to collapsewhen heated instead of expanding, which would crack the shell.

3.1.7. Examples3.1.7.1. INCS Prototyping and Manufacturing Services

Make Japan a Model for the World MarketINCS is one of the largest manufacturing and prototyping process bureausin Japan. It offers innovative 3D prototyping services to reduce the prod-uct life cycle and to produce the prototype within the tight lead time.Some of INCSs customers include leading automotive and electronicsmanufacturers and they require INCS to provide highly complex anddurable prototypes (an example is shown Fig. 3.4).

INCS founder, Yamada saw the great potential of the SLA from 3DSystems for the Japanese market and started INCS in 1990. It began withthe SLA 250 and in 1993 INCS obtained the distributor rights from 3DSystems for Japan. Subsequently in 1997, INCS increased the number ofsystems to 10 and installed more than 30 systems by 2007. With all thedifferent range of systems, INCS is able to handle prototypes of differentsizes, providing high accuracy and tight tolerances. INCS is able todeliver products within an average of four days with the systems workinground the clock.

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Fig. 3.4. Prototype made by INCS (courtesy 3D Systems).




3.1.7.2. 3D Systems Helps Walter Reed Army Medical CentreRebuild Lives

Walter Reed Army Medical Centre is one support unit which cannot beremoved from action. Walter Reed provides continuous health care andservices to soldiers, their families and a large population of militaryretirees. The key operation of the Medical Centre is to support and treatthe military personnel in surgical, accidental or combat trauma.

Walter Reed 3D Medical Applications Centre plays an important rolein providing 3D models in assisting surgeons for pre-surgical and post-surgical planning. In 2001, the SLA 7000 system was installed in theMedical Centre. Besides allowing the physicians to physically examineand identify problems from the actual 3D model, the SLA 7000 systemhas dual-spot technology and high throughput to produce highly complex3D models. With the combination of computed tomography (CT) or mag-netic resonance imaging (MRI) together with third-party software, the2D images are transformed into accurate 3D rendering files. The data gen-erated is then transferred to the SLA 7000 system. Models can also bemulti-colored to specifically indicate different regions to plan an opera-tion and for other activities, such as biomedical education. In months afterthe installation of SLA 7000, the fabricated models have been involved innearly 90 cases. Not only have the 3D models provided great opportunityfor the physicians to plan surgery, the models have also effectivelyshortened the operating time and cutting cost.

Having a prototype also means laying a communication bridgebetween the patient and the surgeon as the patient is able to understandand discuss the available options with the surgeon. A typical example isshown in Fig. 3.5.

3.1.7.3. DePuy Speeds Down the Information HighwayThe demand for RP models for medical application is growing rapidly andfabricating models eases the working procedure for surgeons to identifythe problems which eventually reduces the risk of the operation. DePuy,one of the worlds largest suppliers of orthopedic appliances and surgical



tooling, has long learnt about the advantages of building models bystereolithography. Time is always the crucial parameter when it comes tomedical services, not only the total fabrication time but also the time takenfor the transferring of the models data. Together with stereolithographyand the internet, things can be made possible. Depuy Inc. has a total ofthree SLA systems: one in Leeds and the other two in Warsaw, Indiana.Transferring SLA files from Leeds to Warsaw can be very efficient andcost-saving as the process of transmitting data in intergraphys engineer-ing modeling system, (EMS) or STL is fast and the downloading of a filecan be completed in a short time, depending on its size.

With the reduction in development time, new appliances and toolingcan be created and this benefits the surgeons and patients. Figure 3.6shows an example. Over the years, DePuy has always updated itself withthe latest technologies to provide the best services to its existing andfuture customers.

3.1.7.4. Stereolithography Makes a Strategic Difference atXerox by Helping Designers Muffle Copier Noise

Mufflers are what copiers have in common with auto mobile vehicles. Tofilter the copier noise, the air turbulence must be tightly controlled.Stereolithography was the key drive to generating a new copiers mufflerassembly design at Xeroxs RP laboratories. To conduct a simulation,the centre muffler components were built into two pieces usingStereolithography and then assembled together (see Fig. 3.7). The compo-nents that were built using Stereolithography were then used for silicone

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Fig. 3.5. Medical model prototype (courtesy 3D Systems).




molding. Through this process, Xerox was able to optimize the budget fordesign as well as meet the limitation of the tight schedule.

Stereolithography has helped Xerox to hold firm in their position in anumber of areas:

(1) confirmation in assemblies with the manufactured parts,(2) rapid, easy and low cost method for testing new design ideas,(3) money saving before embarking on tooling investing and(4) usage of silicone molding.

In the fabrication process, the design drawings were first produced by aXerox project group which used Intergraph wireframes to represent the

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Fig. 3.6. Bone joint made using SLA system and QuickCastTM (courtesy 3D Systems).

Fig. 3.7. Muffle copier noise using SLA (courtesy 3D Systems).



assembly. The file was then converted to solids using Intergraphs EMS.At times, when a large portion of a component was to be constructedin one SLA system, the other portion was constructed on another SLAsystem to shorten the time taken. With SLA systems, two machines can beintegrated together to provide greater versatility.

3.1.8. Research and DevelopmentTo stand as a leading company in the competitive market and to improvecustomers needs, 3D Systems research has made great improvement notonly in developing new materials and applications, but also in softwareapplications.

3D Systems and Ciba-Geigy Ltd are in a joint research and developmentprogram continually working on new resins which have better mechanicalproperties, are faster and easier to process and are able to withstand highertemperatures.11

One of the other most important areas of research is in rapid tooling,i.e., the realization of prototype moulds and ultimately production tool-ing inserts.12 3D Systems is involved in 15 cooperative rapid toolingpartnerships with various industrial, university and government agencies.Methods studied, tested or being evaluated include those used for softand hard tooling. With the purchase of 3D Keltool in September 1996,3D Systems now has a means for users to go from a CAD model, to anSL master to Keltool cores and cavities capable of producing in excess ofone million injection molded parts in a wide range of engineering ther-moplastics such as polypropylene, nylon, ABS, polyethylene andpolycarbonate.

3.2. OBJET GEOMETRIES LTD.S POLYJET3.2.1. CompanyObjet was founded in 1998 and has established itself as the leading plat-form for high-resolution three-dimensional printing (3DP). Objet also hasproven installations worldwide where 3D modeling can be created inoffice environment.13 Using its patented and market-proven PolyJet

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inkjet-head technology, it is able to print out the most complex 3D modelswith exceptionally high quality. PolyJet-based systems are used in hun-dreds of manufacturing sites across the world and across a wide spectrumof industries: automotive, electronics, toy, consumer goods, medicalfootwear and more. It has been awarded more than 40 patents with addi-tional patents filed or pending internationally. Objet Geometries Ltd iscurrently headquartered at 2 Holzman St. Science Park P.O. Box 2496,Rehovot 76124, Israel.

3.2.2. ProductsObjets current line of PolyJet-based systems, the Eden family, is agroup of four machines that can deliver high-resolution prototypes withinan office environment.14 The Eden family consists of the Eden 500V,Eden 350/350V, Eden 260 and Eden 250, giving options to theusers in terms of build size, productivity and budget requirements. Foreconomical and effective small models, both Eden 250 and Eden 260are able to fit in a small office. Eden 250 features of two printingmodes, high quality (HQ) and high speed (HS), for user to choose from inorder to produce high quality prototype. Eden 260 consists of 8 units ofsingle head replacement (SHR) to jet identical amounts of resin comparedto Eden 250 resulting in better and more even surface finish. Eden350/350V are the medium build professional machines in the Edenseries which features printing modes (HQ and HS) and higher materialcapacity. The Eden 500V (see Fig. 3.8) is the largest build system witha build volume of 490 390 200 mm. It has the best features includingdual printing modes, 8 units of SHR and an automatic function to switchbetween cartridges. Specifications of the Eden family of machines aresummarized in Table 3.2.

The Eden systems utilize Objet FullCure materials and ObjetStudio software to provide a complete 3DP solution for any RP appli-cation. Objet systems provide a range of different materials for user tochoose from, depending on the required properties. All Eden systemsare able to print high accuracy ultra-thin 16 m layers, producing modelswith exceptionally fine details and ultra-smooth surfaces. The Edenfamily works on the same principle where the jetting head lays both the



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Fig. 3.8. Eden 500VTM (courtesy Objet Geometries Ltd).

Fullcure M (model material) and Fullcure S (support material) on thebuild tray. At the same instance, the UV light integrated with the jettinghead cures the already just-laid FullCure materials, virtually laying andcuring the model in a single process.

3.2.3. ProcessThe EdenTM family of all PolyJet systems undergoes the same simple 3DPprocess. Objet PolyJetTM process creates 3D objects with the use of ObjetStudio software. The designer loads the 3D CAD solid model file intothe system which is compatible with Windows XP and Windows 2000.The Objet Studio will convert the CAD data into an STL or SLC file. Thedesigner will also have to set the orientation arrangement of the designedpart on the build tray.

Before the actual building process commences, the designer has toensure that the build tray and the two types of material cartridges areinserted into the machine. The two types of material cartridges consist ofthe part material and the supporting material. When the procedure is done,the jetting heads, based on Objets patent Polyjet inkjet technology, willmove along the x-axis and lay the first layer of material onto the tray(see Fig. 3.9). Depending on the size of the part, the jetting head will




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Tabl

e 3.

2. S

umm

ary

spec

ifica

tions

of E

denT

M s

erie

s (so

urce f

rom O

bjet G

eome

tric Lt

d).M

odel

s

Eden

500

V

Eden

350

/350

V

Eden

260

Ed

en 2

50

Tray

Siz

e (X

Y

Z)

, mm

500

40

0

200

350

35

0

200

260

26

0

200

250

25

0

200

Net

bui

ld si

ze

490

39

0

200

340

34

0

200

258

25

0

205

250

25

0

200

(X

Y

Z), m

mPr

int r

esol

utio

nX

axi

s60

0 dp

i: 42

m

600

dpi:

42

m60

0 dp

i: 42

m

600

dpi:

42

m

Yax

is60

0 dp

i: 42

m

600

dpi:

42

m30

0 dp

i: 84

m

300

dpi:

84

m

Z ax

is1,

600

dpi:

16

m1,

600

dpi:

16

m1,

600

dpi:

16

m1,

600

dpi:

16

m

Acc

urac

y, m

m0.

10.

3 ty

pica

l0.

10.

3 ty

pica

l0.

10.

2 ty

pica

lM

ater

ials

cartr

idge

sSe

aled

4

3.6

kgSe

aled

2

3.6

kg/

Seal

ed 2

2

kgSe

aled

2

2 kg

4

3.6

kgca

rtrid

ges

cart

ridge

sTa

ngo

net

bui

ld (m

m)49

39

20

31

25

10/

Not

ava

ilabl

e34

34

20

Mat

eria

ls su

ppor

ted

FullC

ure

720

FullC

ure

720

FullC

ure

720

FullC

ure

720

Vero

Whi

teVe

roW

hite

Vero

Whi

teVe

roW

hite

Vero

Blu

eVe

roB

lue

Vero

Blu

eVe

roB

lue

Vero

Bla

ckVe

roB

lack

Vero

Bla

ckVe

roB

lack

Tango

Blac

kTa

ngo

Blac

kFu

llCur

e70

5 Su

ppor

tFu

llCur

e70

5 Su

ppor

tTa

ngo

Gra

yTa

ngo

Gra

yFu

llCur

e70

5 Su

ppor

tFu

llCur

e70

5 Su

ppor

t

(Con

tinue

d)



FA


Tabl

e 3.

2. (C

ontin

ued)

Mod

els

Eden

500

V

Eden

350

/350

V

Eden

260

Ed

en 2

50

Inpu

t for

mat

STL

and

SLC

File

STL

and

SLC

File

STL

and

SLC

File

STL

and

SLC

File

Softw

are

Obje

t Stu

dioT

M

Jetti

ng h

eads

SHR

(sing

le he

adSH

R (si

ngle

head

SH

R (si

ngle

head

SHR

(sing

le he

ad

repl

acem

ent),

8 unit

sre

plac

emen

t), 8 u

nits

repl

acem

ent),

8 unit

sre

plac

emen

t), 4 u

nits

Mac

hine

dim

ensio

n1,

320

99

0

1,20

01,

320

99

0

1,20

087

0

740

1,

200

870

74

0

1,20

0(W

D

H

), mm

Wei

ght,

kg41

041

028

028

0O

pera

tiona

l env

ironm

ent

Tem

pera

ture

Tem

pera

ture

Tem

pera

ture

Tem

pera

ture

18

25

C18

25

C18

25

C18

25

C re

lativ

ere

lativ

ere

lativ

ere

lativ

e hu

mid

ity 3

070

%hu

mid

ity 3

070

%hu

mid

ity 3

070

%hu

mid

ity 3

070

%




move on the y-axis and move on to the x-axis to lay the next layer afterthe first layer is completed. During the printing process, the jetting headwill release the actual amounts of part material and support material.The materials will be immediately cured by the UV light from the jet-ting head. Whenever the materials are about to be used up, the materialcartridges can be easily replaced without interrupting the fabricationprocess. Once the jetting head cures the first 2D cross section, the buildtray will drop by one layer thickness of 16 m. The jetting head willrepeat the process continuously until the system completes the part. Thepart will be raised up and can be taken out for post-processing. The sup-port material can then be removed easily by the water jet and the part iscomplete.

3.2.4. PrincipleObjets PolyJetTM technology creates high quality models directly from thecomputerized 3D files. Complex parts are produced with the combinationof Objets Studio software and the jetting head.

The process is based on the following principles:

(1) Jetting heads release the required amount of material which shares thesame method as the normal inkjet printing method. At the same timewhen the material is printed on the tray, the material is cured by

FA

Fig. 3.9. Schematic of the Objet Polyjet process (courtesy Objet Geometries Ltd).



the UV light which is integrated with the jetting head. Parts are builtlayer by layer, from a liquid photo-polymer where a similar polymer-ization process as described in Sec. 3.1.4 takes place.

(2) Jetting heads are moved only along the xy-axes and each slice of thebuilding process is the cross section of the parts arranged in the soft-ware.

(3) With the completion of a cross-sectional layer, the build tray will belowered for the next layer to be laid. The z-height of the elevator isleveled accurately so that the corresponding cross-sectional data canbe calculated for that layer.

(4) Both the part material and support material will be fully cured whenthey are exposed to the UV light and most importantly the nontoxicsupport material can be removed easily by the water jet.

3.2.5. Strengths and WeaknessesThe EdenTM system has the following strengths15:

(1) High quality. The PolyJet can build layers as thin as 16 m in thick-ness with accurate details depending on the geometry, part orientationand print size.

(2) High accuracy. Precise jetting and build material properties enablefine details and thin walls (600 m or less depending on the geometryand materials).

(3) Fast process speed. Certain RP systems require draining, resin strip-ping, polishing and others whereas Eden systems only require aneasy wash of the support material which is a key strength.

(4) Smooth surface finish. The models built have smooth surface and finedetails without any post-processing.

(5) Wide range of materials. Objet has a range of materials suited fordifferent specifications, ranging from tough acrylic-based polymer, topolypropylene-like plastics (Duruswhite) to the rubber-like Tangomaterials.

(6) Easy usage. The Eden family utilizes a cartridge system for easyreplacement of build and support materials. Material cartridges provide

FA





an easy method for insertion without having any risk of contact withthe materials.

(7) SHR technology. The Eden machines nozzles consist of heads andnozzles. With Single Head Replacement (SHR) these individual nozzlescan be replaced instead of replacing the whole unit whenever the needarises.

(8) Safe and clean process. Users are not exposed to the liquid resinthroughout the modeling process and the photo-polymer support isnontoxic. EdenTM systems can be installed in the office environmentwithout increasing the noise level.

The EdenTM system has the following weaknesses:

(1) Post-processing. A water jet is required to wash away the supportmaterial used in PolyJet, meaning that water supply must benearby. This is somewhat a let-down to the claim that the machine issuitable for an office environment. In cases where the parts built aresmall, thin or delicate, the water jet can damage these parts, so care inpost-processing must be exercised.

(2) Wastage. The support material which is washed away with watercannot be reused, meaning additional costs are added to the supportmaterial.

3.2.6. ApplicationsThe applications of Objets systems can be divided into different areas:

(1) General applications. Models created by Objets systems can be used forconceptual design presentation, design proofing, engineering testing,integration and fitting, functional analysis, exhibitions and pre-productionsales, market research and inter-professional communication.

(2) Tooling and casting applications. Parts can also be created for invest-ment casting, direct tooling and rapid, tool-free manufacturing of plasticparts. Also they can be used to create silicon molding, aluminum epoxymoulds, VLT Molding (alternative rubber mould) and vacuum forming.



(3) Medical imaging. Diagnostic, surgical,16 operation and reconstructionplanning and custom prosthesis design. Parts built by PolyJetTM haveoutstanding detail and fine features which can make the medical prob-lems more visible for analysis and surgery simulation. Due to its fastbuilding time, prototype models are always built for trauma ortumors. Most importantly, it reduces the surgical risks and provides acommunication bridge for the patients.

(4) Jewelry industry. Presentation of concept design, actual display,design proof and fitting. Pre-market survey and market research canbe conducted using these models.

(5) Packing. Vacuum forming is an easy method to produce inexpensiveparts and it requires a very short time for the part to be formed.

3.2.7. Examples3.2.7.1. AdidasSalomon AG Uses Objets PolyJet

to Produce PrototypesAdidasSalomon AG is always among the top athletic footwear manufac-turers worldwide. To keep up with the highly competitive market, productenhancements and timely product presentations to the market are verycrucial. The search for systems to produce high quality models ended withthe presence of PolyJetTM inkjet technology. Physical models are directlyproduced from STL files in a short period of time. Objet GeometricRP systems assistance has brought AdidasSalomon AG closer to theircompanys vision of streamlined digital process for sharing among allbusiness units. Physical models have proven to AdidasSalomon AG thatthey would greatly benefit using the Objet machines where parts can beused for design verification, development review and production toolingin a short development time.

Objet Geometries PolyJet has given AdidasSalomon AG theflexibility to collaborate with each factory in Asia on specific productenhancements while reducing the time necessary. With Objet GeometricLtd sales and training services, AdidasSalomon AG is now working withObjet to search for ways to apply this technology into other aspects oftheir products (Fig. 3.10).

FA





3.2.7.2. Realizing Efficiency and Reducing Cost in the Designand Development Process Through the Installationof an Eden Machine at MegaHouse

Tokyo-based MegaHouse develops and manufactures high-precision figuresand toy foods targeted at both adults and children. Because the companyserves a wide range of customers and its products often comprise manyfinely detailed parts and usually have short life cycles, MegaHouse workshard to streamline development.

MegaHouse considered its RP options and decided that installingan RP system onsite was the best way to reduce prototyping costs,increase access to prototypes, improve design quality and reduce devel-opment time. It selected Objets Eden 260TM because the 3D printingsystem enabled molding with high precision, supporting their need toverify mechanisms and because it was easy to use. This enabledMegaHouse to create molds with nonexpert staff. The strength ofObjets FullCure materials was another advantage of the Eden 260TMas it allowed MegaHouse designers to test the models without fear ofdamaging them.

The Eden 260TM brings benefits that went far beyond what MegaHousehad expected. It makes it possible to easily obtain a high-precision proto-type in the early stages of conceptual design. This means that design workcan now proceed without the delays MegaHouse used to incur whilewaiting for the service bureau, thus considerably reducing design time.

FA

(a) (b)

Fig. 3.10. High quality finishing part that (a) appear close to a real part and (b) fitted ontoa real soccer boot (courtesy Objet Geometric Ltd).



Also, the Eden 260TM enables design defects to be discovered before tool-ing, avoiding expensive tool delays due to changes that needed to bemade. The ability to handle virtually all prototyping in-house has createdsignificant cost savings for MegaHouse. With the Eden260TM producedmodels, product strength and parts fit can be verified during developmentbefore tooling is committed.

As it is so easy and cost effective to make models that can be testedusing the Eden 260TM, it become possible to allow everyone in the designand development team to have a hand with them, improving understand-ing and enabling more effective product development (Fig. 3.11).

Even the sales department has benefited from the installation of theEden260TM, as presentation models are now used in sales activities rightfrom the early stages an important competitive advantage for MegaHouseCorporation.

3.2.8. Research and DevelopmentObjet is doing research in developing faster processing, higher perform-ance, higher resolution graphics and smoother and more accurate details.One way of improving the accuracy of the Polyjet procedure can be doneby optimizing the scaling factor.17 Objet Geometries Ltd has generated anew solution for fast and cost-effective production of high quality hearing

FA


Fig. 3.11. Prototype of an illuminated cube created on the Eden 260TM (courtesy ObjetGeometric Ltd).




aids (see Fig. 3.12). With the combination of easy operation and highspeed capabilities, Objet Hearing Aid Solution reduces the hearing aidmakers time and cost to market.

In software development, Materialise NV, world leader in softwaredevelopment for RP industry and Objet Geometries Ltd have cooperatedto develop a customized version of Materialises Magics Software to betuned for Objets 3DP. This agreement will definitely benefit both partiesin satisfying customers and increasing their competitive advantage in theRP industry. Fabrication materials are increasing the end users ability toselect mechanical properties for specific applications. With the new rub-ber mold materials, molds can be made by spin casting where parts can becast within hours.

3.3. D-MECS SOLID CREATION SYSTEM (SCS)3.3.1. CompanyThe SCS has been jointly developed by Sony Corporation, JSRCorporation and D-MEC Ltd. The software and hardware have been cre-ated by Sony Corporation, the UV curable resin by JSR Corporation andthe forming and applied technology by D-MEC Ltd, a company that wasestablished in 1990. The address of the D-MEC Ltd is Hamarikyu ParkSide Place, 5-6-10, Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.

FA

Fig. 3.12. Prototype of hearing aid (courtesy Objet Geometric Ltd).



3.3.2. ProductsBased on the principle of laser cured polymer using layer manufacturing,D-MEC Ltd is the first company to offer a 0.5 m cubic tank size, amongstthe largest in the market, with a scanning speed of up to 5 m/s. In cooper-ation with JSR which developed the resin used in the system, the SolidCreator was well received in Japan, especially among auto makers andelectronics industries. D-MEC has five models: SCS-1000HD, SCS-6000,SCS-8100, SCS-8100D and SCS-9000. Each model has its own scanspeed in producing different quality of parts and SCS-9000 has the high-est scan speed of 20 m/s. SCS-1000HD is the smallest size model whichuses HeCd laser producing the smallest size of at least 0.3mm. SCS-8100(see Fig. 3.13) is a high speed modeling system which has advance fea-tures like improved radiation effect, dual-beam function and newlydeveloped self-running tank which has been adopted in the system foreasy replacement of resins.

The specifications of D-MECs available models are summarized inTable 3.3.

3.3.3. ProcessThe SCS creates the 3D model by laser curing polymer layer by layer. Itsprocess comprises five steps: generating the CAD model, slicing the CAD

FA


Fig. 3.13. Solid creation system SCS-8100 (courtesy D-MEC Corporation).




FA

Tabl

e 3.

3. S

olid

cre

atio

n sy

stem

s mod

el sp

ecifi

catio

ns (c

ourte

sy D

-MEC

Corp

oratio

n).M

odel

SCS-

1000

HD

SCS-

6000

SCS-

8100

SCS-

8100

DSC

S-90

00

Des

crip

tion

Hig

h pr

ecisi

on,

Smal

l-siz

e m

odel

ing

Larg

e-siz

e La

rge-

size

Larg

e-siz

e ultr

alin

e m

odel

ing

lase

rm

ode

ling

mode

ling

mode

ling

mac

hine

mac

hine

m

achi

nem

achi

ne

Lase

r typ

e, p

ower

,H

eCd

lase

rSo

lid-s

tate

sem

i-con

duct

or la

ser

and

frequ

ency

200

mW

, 25

kH

z1,

000

mW

, 60

kH

z1,

000

mW

, 1,

000

mW

, 60

kH

z60

kH

z

2(fi

rst in

Japa

n)M

odul

ator

AO

M (a

custo

-optic

elem

ent)

Bui

lt-in

AO

M (a

custo

-optic

elem

ent)

Def

lect

ion

Gal

vano

met

er m

irror

syste

m (i

nclud

es sw

eep-d

efocu

s corr

ectio

n fun

ction

)eq

uipm

ent

Mod

el c

reat

ion

rang

e (m

m)30

0

300

27

030

0

300

25

061

0

610

50

061

0

610

50

01,

000

80

0

500

Spot

size

, mm

(auto

matic

0.05

0.3

0.07

50.

40.

150

.4

0.15

0.4

0.

20.

4ad

justm

ent)

Scan

spee

d, m

/sM

ax. 2

m/s

Max

. 7.5

m/s

Max

. 10

m/s

Max

. 10

m/s

Max

. 20

m/s

Laye

r thi

ckne

ss, m

m0.

020

.15

0.05

0.2

0.1

0.2

0.1

0.2

0.1

0.4

Tank

volu

me

45 L

55 L

280

L28

0 L

840

L(ex

chan

geab

le)Po

wer

sou

rce

100

V, 20

A10

0 V,

30

A10

0 VA

C, 4

0 A

100

VAC,

45

A10

0 V,

35

A

Cool

ant

Not

nee

ded

Mai

n un

it di

men

sions

1,42

5

1,10

0

1,42

5

1,11

5

1,94

0

1,15

0

1,94

0

1,15

0

2,34

0

1,64

0

(W

D

H) (

mm)

1,59

01,

610

1,99

01,

990

2,76

0M

ain

unit

wei

ght

710

kg71

0 kg

1,70

0 kg

1,75

0 kg

2,92

0 kg

(inclu

ding r

esin)



model and transferring data, scanning the resin surface, lowering theelevator, completion of prototype and post-processing.

First, a CAD model, usually a solid model, is created in a commercialCAD system, like CATIA or Pro/Engineer. Three-dimensional CAD dataof the part from the CAD system are converted to the sliced cross-sec-tional data which the SCS will use in creating the solid. This is the slicingprocess. Editing may be necessary if the slicing is not carried out properly.Both the slicing and editing processes can be done either ON- or OFF-line. Consequently, the section data is passed to the laser controller for theUV curing process.

The ultraviolet laser then scans the resin surface in the tank to draw thecross-sectional shape based on the data. The area of the resin surfacewhich is hit by the laser beam is cured, changing from liquid to solid onthe elevator. This process is similar to the one that is illustrated in Fig. 3.2.The elevator than descends to allow the next solid layer to be created bythe same process. This is repeated continuously to laminate the necessarynumber of thin cross-sectional layers to form the 3D part. Finally, whenthe model is complete, the elevator is raised and the model is lifted outbefore post-curing treatment is applied.

The main hardware of the SCS includes:

(1) the Sony NEWS UNIX workstation,(2) the main machine controller (VME based, MTOS multi-tasking

operating system),(3) the galvanometer mirror and its controller,(4) the optical system including the laser, the lens and the acoustic optical

modulator (AOM).(5) the photo-polymer tank and(6) the elevator mechanism.

The main software of the SCS consists of two parts: the slice data gener-ator which uses inputs from various CAD systems and creates thecross-sectional slices and the editing software for slice data whichincludes the automatic support generation software. The software used tocontrol the SCS also uses principles of manmachine interfaces.

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3.3.4. PrincipleD-MECs SCS is based on the principle of polymer curing by exposure toultraviolet light and manufacturing by layering. The basic principles andtechniques used are similar to that described in Sec. 3.1.4.

In the process, parameters which affect performance and functionalityof the machine are scanning pitch, step period, step size, scanner delay,jump size, jump delay, scanning pattern and resins properties.

The required software for SCS models are:

Magics SCS models use the Magics series, produced by MaterialiseCorporation, as data processing software. Magics offers functions suchas STL measurement and correction, support creation and output in slic-ing data format.

Solidware Solidware is a software which enables user to browseslice data and to detect an error layer automatically. Solidware pro-vides options such as adding or combining or deleting lines whenerrors are detected during the processing of slice data.

3.3.5. Strengths and WeaknessesSCS has the following strengths:

(1) Large build volume. The tank size is among the largest in the market andlarge prototypes (especially large full-scale prototypes) can be produced.

(2) Accurate. High accuracy (0.04 mm repeatability) models may beproduced.

(3) Wide variety of resins with special characteristic. D-MEC offers awide variety of generally used resins and they include epoxy resins,heat resistant resins, ABS-like resins and elastomer-like resins.

It has the following weaknesses:

(1) Requires support structures. Structures that have overhangs andundercuts must have supports that are designed and fabricated withthe main structure.





3.3.6. ApplicationsThe general application areas are given as follows:

(1) Mock-up in product design.(2) Design study, medical models analysis and sales sample of new products.(3) Use as parts without need of modification in small lot production.(4) Simplified mold tool and master for investment casting and other

similar processes.

D-MEC Corporation has used SCS mainly to design and prototype its ownproducts like the drum base for video tape recorders. By using SCS, D-MECis able to ascertain the optimum design for its products. Important functionaltests can be carried out on the prototype as well.

When Solid Creator is used for medical purposes, surgical operationtime can be significantly shortened by checking the defective or diseasedareas using models reconstructed on the system from other frequentlyused computer images such as from CT-scans.

3.3.7. OthersSolid Creator machines have been installed throughout the world, thoughmainly in Japan and Taiwan. Besides these, D-MEC provides comprehen-sive bureau services to many industries in Japan.

3.4. ENVISIONTECS PERFACTORY3.4.1. CompanyThe company was founded when it was a young start-up as EnvisionTechnologies GmbH in August 1999 and corporatized as Envisiontec

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GmbH in 2002. Envisiontec provides RP systems and solutions to servecustomers in a wide variety of applications. Envisiontec even deals withsoftware and materials development to increase productivity and costeffectiveness. Currently, it has over 20 patents and patents applicationpending worldwide. The companys address is Brsseler Strae 51, 45968Gladbeck, Germany.

3.4.2. ProductPerfactory18 (see Fig. 3.14) is the RP system built by Envisiontec andit is a versatile system suitable for an office environment. Perfactoryundergoes the basic process by means of converting a CAD file to STLformat and then transferring the STL data to the system to build themodel. Resins are cured by photo-polymerization but Perfactory uses adifferent approach in curing the resins. The photo-polymerization processis created by an image projection technology called digital light process-ing technology (DLPTM) from Texas Instrument and it requires maskprojection to cure the resin layer by layer. The standard system alone canachieve resolutions between 148 and 93 m but with Voxel, resolution can

FA

Fig. 3.14. Perfactory SXGA+ standard (courtesy Envisiontec GmbH).



be adjusted to between 50 and 150 m. Additional components or devicessuch as the mini multi lens system and the enhanced resolution module(ERM) enable designers and manufacturers to build smaller figures whichrequired high surface quality. Perfactory mini is able to create parts ofa higher quality of 32 m in solution and voxel thickness adjusted tobetween 25 and 50 m.

The specifications of Perfactory systems are shown in Tables 3.4(a)and 3.4(b).

3.4.3. ProcessTo build the part in a layer-by-layer manner, Perfactory undergoes a sim-ple process (see Fig. 3.15) where the 3D model of a solid model is firstcreated with a commercial CAD system. For medical applications, dataacquired with MRT or CT systems can be processed directly. The 3D datamodel in the STL format acquired is sliced within the software and eachsliced layer is converted into a bitmap file with which the mask image isgenerated. The bitmap image consists of black and white where white rep-resents the material and black represents the void. When the image isprojected onto the resin with DLPTM, the illuminated white portion willcure the resin while the black areas will not.

With the embedded operating system in Perfactory, it can operateindependently and is monitored by the device driver software installed inthe PC. The software provides two types of mode which are auto andexpert mode. The auto mode allows direct conversion of 3D-CAD data toSTL format and other required set-ups are programmed automatically.The expert mode is specially programmed for advanced users to offerthem with choice of manual set-up according to their experience, needsand preferences.

Unlike almost all other RP systems that build the model frombottom up, Perfactory builds the model top down (see Fig. 3.16). Thebuild or carrier is first immersed into a shallow trough of acrylate-based photo-polymer resin sitting on a transparent contact window.The mask is projected from below the build area onto the resin tocure it. Once the resin is cured, the build platform is raised a singlelayer, the thickness being dependent on the voxel thickness. While the

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FA

Table 3.4. (a) Perfactory SXGA+ W/ERM mini multi lens system specifications and (b)Perfactory SXGA+ standard and standard UV systems specifications (courtesyEnvisiontec GmbH).

a

System Perfactory SXGA+ W/ERM mini multi lens

Lens system, focal 60 (2.3) 75 (3) 85 (3.3)length, mm (in.)

Build envelope 84 63 230 59 44 230 45 34 230XYZ, mm, (in.) (3.3 2.5 9) (2.3 1.7 9) (1.77 1.3 9)

Dynamic voxel 1550 (0.0050.0019)thickness Z, m (in.)

Voxel size XY 30 (0.0011) 21 (0.0008) 16 (0.0006)W/ERM, m (in.)

Resolution SXGA+ 2800 2100W/ERM

b

Perfactory SXGA+

StandardZOOM

withintegrated

System ERM Standard UV system

Lens system, focal 2545 Fixed focal UV lenslength, mm

Build envelope 120 90 230 100 75 230 140 105 230 175 131 230XYZ (mm) to

190 142 230Native voxel 86136 71 100 125

size XY, mERM voxel 4368 35 50 62

size XY, mDynamic voxel 25150 25150

thickness Z, mResolution SXGA+ 1400 1050 1400 1050

ResinGroup AcrylateColor Red-brown (not transparent)Light source High pressure mercury vapor lamp

+ Double Perfactory, Resolution.



platform is raised, it peels the model away from the transparentcontact window, thus allowing fresh resin to flow in through capillaryaction. The next layer is then built in a similar manner. The wholecycle takes about 25 s without the need for planarization or leveling foreach layer.

The two key differences of the Perfactory with other RP systems arethe use of mask projection for photo-polymerization and the part is movedupwards with each completed cured layer instead of moving downwardsin other systems. Once the model is built, the user simply has to peel themodel off from the platform as the model is stuck to the carrier platformduring the entire process.

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Z-Positioning Unit

Carrier platform

Model

Trough Photopolymer

Transparent contact window Housing

DLPTM

light source

Fig. 3.16. Schematic of the Perfactory build process with DLPTM technology (adaptedfrom Envisiontec GmbH).

Fig. 3.15. Perfactory process (courtesy Envisiontec GmbH).




3.4.4. PrinciplePerfactory uses the basic principles of stereolithography by undergoingthe following:

(1) Parts are built from acrylate photo-polymer and the user is able toselect different material properties with different materials colors.Resins are cured when exposed to a mask projection image usingdigital light processing (DLPTM) technology from Texas Instrument.

(2) Every completion of cured layer is moved away from the build troughcontaining the resin vertically upwards by a precision linear drive.This is due to the projection system integrated at the bottom of the RPsystem. Also, the fabricated part does not require any support andremoving the model from the transparent platform is easy.

3.4.4.1. Digital Light Processing Technology (DLPTM)DLPTM is a projection technology invented by Dr. Larry Hornbeck andDr. William E. Ed Nelson of Texas Instruments in 1987. In DLPTMtechnology, the key device is the digital micromirror device (DMD), theproducer of image. DMD is an optical semi-conductor and each DMDchip has hundreds of thousands of mirrors arranged in a rectangular arrayon its surface to steer the photons with great accuracy. This means thateach mirror is represented as one pixel in a projected image and thereforethe resolution of an image depends on the number of mirrors.

The mirrors in the DMD are made of aluminum and are 16 m in size.Each individual mirror is connected to two support posts where it can berotated 1012 of an ON or OFF state. In the ON state, the light sourceis reflected from the mirrors into the lens making pixels on the screen. Forthe OFF state, the reflected light is redirected to the other direction allow-ing the pixels to appear in a dark tone. During each mask projection, thecross section of each layer is projected by mirrors in the ON state andresins are cured by the visible light projected from below the transparentcontact window.

Every single mirror is mounted on a yoke by compliant torsion hingeswith its axle fixed on both ends and able to twist in the middle. Due to its



extremely small scale, damages hardly occur and the DMD structure isable to absorb shock and vibration thus providing high stability.

Position control of each mirror is done by two pairs of electrodes aspositioning significantly affects the overall image of the cross-sectionallayer. One pair is connected to the yoke while the other is connected to themirror and every pair has an electrode on each side of the hinge. Most ofthe time, equal bias charges are applied to both sides to hold the mirrorfirmly in its current position. In order to move the mirrors, the requiredstate has to load into a static random access memory (SRAM) cell con-necting to the electrodes and mirror. Once all the SRAM cells have beenloaded, the bias voltage is removed, allowing every individual movementof the mirrors through released charges from the SRAM cell. When thebias is restored, all of the mirrors will be held in their current position towait for the next loading into the cell. Bias voltage enables instantremoval from the DMD chip so that every mirror can be moved togetherproviding more accurate timing while requiring a lower amount of voltagefor the addressing of the pixel.

3.4.5. Strengths and WeaknessesThe main strengths of Perfactory systems are:

(1) High building speed. The use of a mask image directly exposed to theresin enables a part to be built at approximately 10 mm height perhour at 100 m pixel height. This speed is independent of part sizeand geometry and is one of the fastest systems in the RP market.

(2) Office friendly process. Perfactory allows operation in an officeenvironment as its foot print is under 0.3 sq m. The curing of thephoto-polymer does not use UV light and there is no need for specialfacility. It operates with low noise and zero dust emissions.

(3) Small quantity of resin during build. The shallow trough of resinmeans that the amount of material in use at any one time is small(about 200 ml). This means that should a number of different resinsare required, they can be swapped out easily with minimal wastage.

(4) No wiper or leveler. When the carrier platform is raised with themodel, there is no need for planarization or leveling. This eliminates

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the possibility of causing problems to the stability of the parts duringthe build, e.g., a wiper damaging a small detail on the part during thewiping action.

(5) Less shrinkage. Due to immediate curing of a controlled layer (basedon the voxel thickness) there is less shrinkage during the process.

(6) Safe supply cartridges. Liquid photo-polymers are packed in cartridgesand this reduces the risk of users coming into contact with them.

(7) Additional components. Perfactory is able to build even higherquality tough parts with the use of additional components which canbe integrated into the system.

The main weaknesses of Perfactory systems are:

(1) Limited building volumes. Structures are built from the bottom of thebuild chamber and stuck to the carrier platform; this limits the size ofthe build.

(2) Peeling of completed part. The user has to peel the completed modelfrom the build platform as the model is built on a movable carrier plat-form which moves vertically upwards. Care has to be taken so as notto damage the model during the peeling process.

(3) Requires post-processing. After the model is complete, cleaning andpost-processing, sometimes including post-curing are required.

3.4.6. ApplicationsThe application areas of the Perfactory systems include the following:

(1) Concept design models for design verification, visualization, marketingand commercial presentation purposes.

(2) Working models for assembly purpose, simple functional tests and forconducting experiments.

(3) Master models and patterns for simple molding and investment castingpurposes.

(4) Building and limited production of completely finished parts.(5) Medical19 and dental applications. Creating exact physical models of

patients anatomy from CT and MRI scans.



3.4.7. OthersEnvisionTecs main offices are located in Germany, North Americaand United Kingdom. Perfactory systems have been sold worldwide,especially in Europe and the US.

3.5. AUTOSTRADES E-DARTS3.5.1. CompanyAutostrade Co., Ltd, the Japanese manufacturer of the E-DARTS systemthat is based on stereolithography, was founded in 1984. Besides theE-DARTS system, the company is also involved with developing CAE andsimilar software tools for its E-Darts systems. It also developed a parallelvirtual machines (PVM) system, a software package that permits a het-erogeneous collection of UNIX and Windows computers that areconnected together in a network to be used as a single large parallel com-puter. Autostrade Co., Ltd is located at 13-54 Ueno-machi, Oita-City, Oita870-0832, Japan. Its first machine was sold in 1998.

3.5.2. ProductsThe E-DARTS system uses the stereolithography method of hardeningliquid resin by a beam of laser light. The set-up of the laser system isfound under the resin tank. The laser beam is directed into the resin whichis in a container with a clear bottom plate. This system uses an acrylicphoto-polymer resin to produce models. Figure 3.17 shows the E-DARTSsystem while Table 3.5 lists its specifications.

3.5.3. ProcessThe software comprises two components. Firstly, the STL file editingsoftware changes the CAD data into slice data. Secondly, the controllersoftware drives the hardware. Both of these components use WindowsOperating System.

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Like many other RP process, the E-DARTS system builds the modelin a layer-by-layer manner. Similar to the Envisiontec Perfactory method,the modeling platform is linked to the Z-position elevator over the buildchamber. The build or carrier is first immersed into a shallow trough ofacrylate-based photo-polymer resin sitting on a transparent contact win-dow. The semiconductor laser mounted on an xy table cures a singlelayer of resin through a plotting action that is similar to that of the

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Table 3.5. Specifications of E-DARTS machine.

Model E-DARTS

Laser type SemiconductorLaser power, mW 30Spot size, mm 0.1XY sweep speed, m/s 0.03Elevator vertical resolution, mm 0.05Work volume, XYZ, mm 200 200 200Maximum part weight, kg No countMinimum layer thickness, mm 0.05Size of unit, XYZ, mm 430 500 515Data control unit Win 98/MEOverall system weight, kg 21Power supply, V 12

Fig. 3.17. E-DARTS system (courtesy Autostrade Co., Ltd).



3D Systems. The main difference here is that the resin is cured through atransparent window from the bottom of the model. Once the resin is cured,the build platform is raised a single layer upwards and fresh resin to flowin between the model and the transparent table is ready for the next layer.The cycle repeats in a similar manner until the whole model is complete.The whole cycle takes about 25 s without the need for planarization orleveling for each layer (see Fig. 3.18).

3.5.4. PrincipleThe model is formed by liquid resin which is cured by laser lightbeamed from below the resin chamber. While 3D Systems SLA uses aplatform which is dipped into the resin tank when one layer iscompleted, E-DARTS system uses another method. The platform ormodeling base is raised upwards each time a layer is completed.Otherwise, the E-DARTS is based on the laser lithography technologywhich is similar to that described in Sec. 3.1.4. Parameters whichinfluence performance and functionality are the control and precisionof the xy table, laser spot diameter, slicing thickness and resinproperties.

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Modeling platform Z-positioning elevator

Resin

Resin vatLaser beam unit on x-y table

Laser

Model or part

Transparent base

Fig. 3.18. E-DARTS process.




3.5.5. Strengths and WeaknessesThe E-DARTS system has the following strengths:

(1) Low price. The price of the E-Darts system is 2,980,000 yen (US$27,000), which has one of the more affordable prices amongst mostRP systems.

(2) Low operating cost. The introduction of an improved fluid surfaceregulation system has decreased the necessary volume of resin, whichactually eliminates the need to stock the resin. This in turn reduces therunning cost of the system.

(3) Compact size. The overall system size is 430 500 515 mm, requiringonly a relatively small foot-print for the machine.

(4) Portable. The overall weight of the system is less than 25 kg,allowing the system to be easily transported by one person.

(5) Ease of installation. The E-DARTS is designed compact and lightweight and this enables the system to be set up by one person. The set-up time for the system is less than 1 h.

The E-DARTS system has the following weaknesses:

(1) Requires support structures. Structures that have overhangs andundercuts must have supports that are designed and fabricatedtogether with the main structure.



3.5.6. ApplicationsThe application areas of the E-DARTS include the following:

(1) Concept design models for design verification, visualization, marketingand commercial presentation purposes.



(2) Working models for assembly purpose, simple functional tests andconducting experiments.

(3) M

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