Rapid Prototyping - Old Dominion University

ME 682 H.P. Bao Rapid Prototyping 1

Rapid Prototyping

ME 682

Dr. Han P. Bao

Mechanical Engineering, ODU


Introduction

• The development, ie design phase of a mechanicalproduct can be summarized as follows:– 1- Design product on CAD– 2- Build prototype with RP technology– 3- Inspect the RP product for errors– 4- Correct errors in CAD– 5- Verify corrected product– 6- Iterate RP process to improve design– 7- Build functional test model– 8- Functional testing– 9- When satisfactory, proceed to manufacture


Introduction (Ctd)

• Definition:Rapid Prototyping is the technology that allowsphysical objects to be directly generated from graphicalcomputer data.

• Benefits of RP:– Visualization: “A picture is worth a thousand words” now

becomes “A real prototype is worth a thousand picture”.Visualization leads to reduction of ambiguities, hencereduction of errors.

– Verification: Because RP part can be generated in matters ofhours, the CAD model can be modified at minimum cost, thusnot allowing any problems to be passed down the path toproduction.


Introduction (Ctd)

• Benefits (Ctd):– Verification of fits: for assembly work, as example a lid onto

a box

– Design iteration leading to optimization.

– As reported by users:• Development time and cost reduced by 20 to 40%

• Prototype parts can be made within 24 hrs of receipt of CAD datafrom 3D CAD models

• RP bridges communication gap between customers, designers andmanufacturers

• Definite tool for concurrent product and process development


The STL System

• STL stands for StereoLithography, otherwise known as3-D printing, first introduced in the late 80’s by 3DSystems in Valencia, CA.

• Currently captures about 80% of market.• Schematic of SLA (another name for STL):

laser (optics) xy scanner

liquidpolymer

support platform


The STL System (Ctd)

• One layer at a time, starting from bottom• Laser “Draws” layer structure on surface of resin and

cure layer• Platform indexed down into bath, allowing new layer of

resin to adhere to previous one.• Post curing required at end of process• Typical data:

– Laser is HeCd with wavelength of 325 nm. 20 to 40 mW.– Photo-curable resin is vinyl-type monomer, e.g. Citatool XB

5081 from Ciba-Geigy


SLA Process



• Technical issues:

– Resin Chemistry:• Green strength

• Curl distortion

• Shrinkage

– Laser:• Types: HeCd, Argon, CO2• Beam propagation and focusing



• Technical Issues (Ctd):– CAD processes:

• Standard solid modelers: CATIA, I-DEAS, Unigraphics,Pro/Engineer, others

• Specialized solid modelers: 3-D Systems, Silverscreen, others• Part orientation• Supports• Management

– Part Building:• Selection of resin and system• Verify STL files• Select support files


Rapid Prototyping Processes

• Two major categories:– Laser-based (SLA,SLS,LOM)– Non-laser based (FDM,SGC, 3-D Plotting, JP5)

• Stereolithography Apparatus (SLA):– First RP system on the market, circa 1980– 3-D Systems, Inc., 26081 Avenue Hall, Valencia, CA 91355– Selective photocuring– Brief description: A scanned laser delivers light to selected

regions on a surface of the photopolymer liquid to turn it intoa solid and single cross-section of the desired object. Theprocess is repeated and successive layers are built.


Rapid Prototyping Processes-Laser Based(Ctd)

• Selective Laser Sintering (SLS):– Laser used to sinter a powdered material into the prototype

shape.– Advantages:

• Many types of polymer can be used• Potential for using powedered metal or ceramic.• Unsintered powder acts as support for the part under construction.

– Disadvantages:• Warping is more serious with this process than with SLA

To prevent warping, elevated temperature must be maintained in chamber. But this makes the powder combustible.

– Manufacturer: DTM Corp., 1611 Headway Circle Bld 2,Austin, TX 786753


SLS Process


Rapid Prototyping processes -Laser Based(Ctd)

• Laminated Object Manufacturing (LOM):– Laser is used not to cure resin but to cut cross-sections from

thin sheets of construction material. Laser is also required tocut outline as well as grid surrounding part

– Each layer is bonded to previous layer by a heated roller– Advantages:

• Faster than competing processes• Low cost material, essentially paper sheets and plastic adhesive sheets

– Disadvantages:• Lower accuracy than SLA• Difficult to remove surrounding wall• Lots of scrap

– Manufacturer: Helysis Inc., 24015 Garnier St., Torrance, CA90505



Rapid Prototyping processes -Non laser based

• Fused Deposition Modeling (FDM):– Thin trail of plastic (as small as .002” thick by .01” wide)

extruded onto part. Plastic must solidify instantaneously.– No cross-over of plastic trails allowed in same cross-section,

but path of extruder is varied from layer to layer.– Advantages:

• good bondage between layers but not so good bondage betweenpolymer strings on each side. This makes part porous with slight gapsbetween strings of polymer.

• Lower cost than SLA• Thermoplastic polymer is not a major hazardous material• No post-processing required

– Disadvantages:• Requires support system like SLA system• Porous structure as mentioned above



Rapid Prototyping processes -Non laser based(Ctd)

• Solid Ground Curing (SGC):– Steps: 1- Photomask generated for each cross-section and used to expose

resin; 2- Unexposed resin removed with vacuum cleaner, 3- Liquid waxused to fill cavities to replace removed resin, 4- Wax allowed to solidify,5- Milling of layer to exact thickness for next layer, 6- Process repeatedfor next layer, 7- wax is melted away after all layers have been created

– Advantages:• Slab of solid wax holds and protects part very well• Nested parts in same wax block• No need for support• Intricate parts can be made

– Disadvantages:• Time consuming• Messy and delicate, specially when there are nested parts


SGC Process



• 3-D Plotting:– Application of inkjet technology: one inkjet head depositing

droplets of melted plastic (for part), and the other depositingdrops of melted wax (for support)

– After each layer, a milling device is used to mill off topsurface of each layer.

• Advantages:– Excellent surface finish (Milling can be done t0 0.0001”)– Finished part can be produced after first pass.

• Disadvantages:– Limited to small parts– Very slow


3D Plotting



• JP System 5:– Same principle as many previous processes except for bonding of

sequential layers– Very low cost RP technique– Excellent and affordable teaching tool

• Manufacturers of Non-Laser Based systems:– Fused Deposition Modeling: Stratasys Inc., 14950 Martin Drive,

Minneapolis, Mn 55344– Solid Ground Curing: Cubital America, Inc., 1307F Allen Drive, Troy, MI

48083– 3-D Plotting: Sanders Sprototype, Inc., Pine Valley Mill, Wilton, NH

03086– JP System 5: Schroff Development Corp., P.O. Box 1334, Mission,

Kansas 66222

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Rapid Prototyping - Old Dominion University