Rapid Prototyping. ME 682 Dr. Han P. Bao Mechanical Engineering, ODU. ME 682 H.P. Bao Rapid Prototyping 1

Transcription

1 Rapid Prototyping ME 682 Dr. Han P. Bao Mechanical Engineering, ODU ME 682 H.P. Bao Rapid Prototyping 1

2 Introduction The development, ie design phase of a mechanical product 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 ME 682 H.P. Bao Rapid Prototyping 2

3 Introduction (Ctd) Definition: Rapid Prototyping is the technology that allows physical objects to be directly generated from graphical computer 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, hence reduction of errors. Verification: Because RP part can be generated in matters of hours, the CAD model can be modified at minimum cost, thus not allowing any problems to be passed down the path to production. ME 682 H.P. Bao Rapid Prototyping 3

4 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 data from 3D CAD models RP bridges communication gap between customers, designers and manufacturers Definite tool for concurrent product and process development ME 682 H.P. Bao Rapid Prototyping 4

5 The STL System STL stands for StereoLithography, otherwise known as 3-D printing, first introduced in the late 80 s by 3D Systems in Valencia, CA. Currently captures about 80% of market. Schematic of SLA (another name for STL): laser (optics) xy scanner support platform liquid polymer ME 682 H.P. Bao Rapid Prototyping 5

6 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 ME 682 H.P. Bao Rapid Prototyping 6

7 SLA Process ME 682 H.P. Bao Rapid Prototyping 7

8 The STL System (Ctd) Technical issues: Resin Chemistry: Green strength Curl distortion Shrinkage Laser: Types: HeCd, Argon, CO 2 Beam propagation and focusing ME 682 H.P. Bao Rapid Prototyping 8

9 The STL System (Ctd) 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 ME 682 H.P. Bao Rapid Prototyping 9

10 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 D Systems, Inc., Avenue Hall, Valencia, CA Selective photocuring Brief description: A scanned laser delivers light to selected regions on a surface of the photopolymer liquid to turn it into a solid and single cross-section of the desired object. The process is repeated and successive layers are built. ME 682 H.P. Bao Rapid Prototyping 10

11 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 ME 682 H.P. Bao Rapid Prototyping 11

12 SLS Process ME 682 H.P. Bao Rapid Prototyping 12

13 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 to cut 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., Garnier St., Torrance, CA ME 682 H.P. Bao Rapid Prototyping 13

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15 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 between polymer strings on each side. This makes part porous with slight gaps between 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 ME 682 H.P. Bao Rapid Prototyping 15

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17 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 wax used to fill cavities to replace removed resin, 4- Wax allowed to solidify, 5- Milling of layer to exact thickness for next layer, 6- Process repeated for 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 ME 682 H.P. Bao Rapid Prototyping 17

18 SGC Process ME 682 H.P. Bao Rapid Prototyping 18

19 Rapid Prototyping processes -Non laser based (Ctd) 3-D Plotting: Application of inkjet technology: one inkjet head depositing droplets of melted plastic (for part), and the other depositing drops of melted wax (for support) After each layer, a milling device is used to mill off top surface of each layer. Advantages: Excellent surface finish (Milling can be done t ) Finished part can be produced after first pass. Disadvantages: Limited to small parts Very slow ME 682 H.P. Bao Rapid Prototyping 19

20 3D Plotting ME 682 H.P. Bao Rapid Prototyping 20

21 Rapid Prototyping processes -Non laser based (Ctd) 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., Martin Drive, Minneapolis, Mn Solid Ground Curing: Cubital America, Inc., 1307F Allen Drive, Troy, MI D Plotting: Sanders Sprototype, Inc., Pine Valley Mill, Wilton, NH JP System 5: Schroff Development Corp., P.O. Box 1334, Mission, Kansas ME 682 H.P. Bao Rapid Prototyping 21