A versatile, automated, laser-based system, capable of producing complex threedimensional
shapes of ceramic and ceramic composite materials, through either controlled layer
ablation or solid freeform fabrication, is currently under development. The system comprises
a 1.2 kW C021aser, positioning system, beam scanner, non-contacting positioning sensor, beam
conditioner and CAD/CAM system. This paper reports progress in relating machine parameters
(scan rate, feed, beam power and polarization) to process measurables (material removal rate
and surface roughness), and demonstrates the potential for rapid prototyping and direct
manufacturing of: (a) rotationally symmetric components based on ablative ceramics such as
Si3N4 and (b) graphite fuel cell plenumsMechanical Engineerin

Copley, S.M.

Fariborzi, F.

Todd, J.A.

West, K.

Yankova, M.I.

English

Texas ScholarWorks

3-D LASER SHAPING OF CERAMIC AND CERAMIC COMPOSITE MATERIALSJ. A. Todd, S. M. Copley, M. 1. Yankova, F. Fariborzi and K. WestDepartment of Mechanical, Materials and Aerospace EngineeringIllinois Institute of Technology, Chicago, IL 60616ABSTRACTA versatile, automated, laser-based system, capable of producing complex three-dimensional shapes of ceramic and ceramic composite materials, through either controlled layerablation or solid freeform fabrication, is currently under development. The system comprisesa 1.2 kW C021aser, positioning system, beam scanner, non-contacting positioning sensor, beamconditioner and CAD/CAM system. This paper reports progress in relating machine parameters(scan rate, feed, beam power and polarization) to process measurables (material removal rateand surface roughness), and demonstrates the potential for rapid prototyping and directmanufacturing of: (a) rotationally symmetric components based on ablative ceramics such asSi3N4 and (b) graphite fuel cell plenums.INTRODUCTIONAdvanced ceramic and ceramic composite materials based on, for example, Si3N4, SiC,SiAION, AIN, are candidate materials for automotive engine components, bearings, cuttingtools, pump components, valves and valve-train components for conventional piston engines,turbochargers, recuperators, heat exchangers and hot gas filters. I-5 Currently, the high costs anddifficulties of shaping such brittle ceramics by diamond grinding, waterjet cutting, ultrasonicmachining, sintering, and near-net shape processes, such as hot isostatic pressing, are majorfactors limiting their widespread deployment. In this research, the laser based system underdevelopment offers the potential not only for rapid prototyping but also for economical, directmanufacturing of full strength, structural ceramic components.BACKGROUNDThe laser shaping system under development in this program is based on patentsdeveloped by Copley, Bass and Hsu6 and by Bass and Copley7. More than a decade of researchhas shown that for optimized, reproducible, laser machining of complex, three-dimensionalceramic shapes, closed-loop control of beam mode, polarization, beam power, beam speed, beamfeed, and laser firing in synchronization with translational, rotational and tilt stages will berequired. 8-24 Discoveries by Copley, Bass and Hsu6 have identified conditions for removinglayers of ablative ceramics with controlled wall angles (perpendicular or sloping) at all positionsalong the bounding wall of a closed contour.6 Parameters for laser machining Si3N4 surfaceswith arithmetic average surface roughnesses of 3 p.m,19 and post laser machining treatments,which restore the mechanical properties of the laser machined surfaces to those of the as-groundmaterial; have been identified. 22305lasercomputer,------1 conditioner/...-- --1posilion scannersensor- '--r----'---..,r-----' translati onal stageL-_---,.__..-J----IIPj rotary stageFigure 1: Prototype laser shaping system.LASER SHAPING SYSTEMThe laser shaping system shown in Figure 1 comprises: (a) a 1.2 kW CO2 laser capableof both continuous wave and pulsed mode operation; (b) a beam conditioner to control the beampolarization ratio, r = x/(l - x), where x = ~/Io; In = intensity of the laser beam's electricvector oriented normal to the plane of incidence, and 10 = incident beam intensity; (c) a custom-designed polygonal scanner to give linear beam speeds exceeding 100 cm S·l (Figure 2); (d) x,yand z axis translational stages; (e) a motion controller, capable of up to 16 axes of control andequipped with a laser firing card; (t) a non-contacting position sensor for accurately sensing theposition of the machined surface; and (g) a CAD/CAM system which generates scan patterns(Figure 3) and beam paths for layer removal to create a three dimensional shape. Note that,material surfaoeFigure 2: Beam scanner.Figure 3: Plan view for layer removal in a singlequadrant to produce a piecewise linear approxima-tion of a convex spherical contour. The beam isscanned in a single direction.306unlike solid free form fabrication, additional controls are incorporated in this system to selectthe terminal angle at which the laser beam contacts the component surface for wall slope control.The system is capable of generating shapes by ablating material from oversized ceramicpreforms or by solid free form fabrication for prototyping or direct manufacturing ofcomponents.MATERIALSThe materials used in the present study were Ceralloy 147-31E sintered reaction bondedSi3N4 supplied as blocks and 10 mm diameter bar, Allied Signal GS-44 Si3N4 (blocks), NoralideNCX-5102 HIPed Si3N4 (10 mm diameter bar), and nuclear grade graphite received from OakRidge National Laboratory.PARAMETRIC STUDIESMaterial removal rates for single grooves and layers machined in both Si3N4 and graphitewere studied as a function of beam velocity, beam polarization, position of the focal plane andbeam feed to groove width ratio (f/a). Figure 4 compares MRR data for Allied Signal GS-44,........,24......I00C'J 228 P == 940 W t::.<.> 20C'J AI 00 18--t~:xl..........,16 0Q).......cd 14 ©~........0<.d 12 0P-o8 10Q) 0 GS-44,tBl 00~........ 8 ---1:::.--- GS-44, tBl 900cd • NC-132, <3==00• 1""'4~ 6 NC 132, <3==900Q) ---j.---....... t::.cd:::g 40 25 50 75 100 125 150 175 200 225 250Scanning Veloci ty [em s-l]Figure 4: Comparison between material removal rates determined for Allied Signal Si3N4 #8,GS-44 MOR bars (present study) and Norton NC-132 MOR bars (Copley et al.) for beamvelocities from 5 to 240 cm S·l, and electric vector parallel (0°) or perpendicular (90°) to the scandirection.307machined at 940 W with prior data Norton NC-132 collected by Wallace10 and Wallace etal,17 and shows that removal rates were approximately doubled for the GS-44 material.material removal rate of 15 x 10-3 cm is equivalent to removing 1 cm3 of materialseconds. Figures 5a, 5b show single layers machined in GS-44 with fla ratios of 0.9 andTwelve passes of the laser beam can be clearly seen (f/a :::: 0.9). Reductionfla ratio to 0.4 (Fig. 5b) resulted in a significantly smoother surface. Note that althoughentrance surfaces were covered with a layer of silicon in the above example, silicon build up wasminimized during multi-layer removal through optimization of beam power, speed and feed.Figure 5a: Single layermachined in GS-44 with flaratio of 0.9.Figure 5b: Single layermachined in GS-44 with flaratio of 0.3.Material removal of graphite was investigated at 940 W in the velocity range 10 tocm S-1 and· found to increase (a) with increasing velocity, and (b) as the position of the focalplane was changed from to 1.0 or 1 mm below the specimen surface (Fig. 6).Interestingly, the material removal rates were similar in magnitude to those for Si3N4 •groove and .layer morphologies were observed, material removal rates and surface roughnesseswere optimized using a velocity em plane position of -1 mm and fla of 0.35.308B I I IIfI.lQj •8 P == 940W ...() 7 c- -t"'JI0 •"I""""l~ A........., 6 - III -Q)~ ...c.O •p::j......-Ic.O 5 - ->-08Q) II~ II....... 4 f- III !:::,.Z == -0.5 mm(.Q....... ... !:::,.z == -1.0 mmHQ) • 6.z == 1.5mm......,>(.QI I I::g5 10 15 20 25Scanning Velocity [cm s-l]Figure 6: Material removal rates determined for graphite for beam scanning velocities from5 to 20 cm s-t, electric vector parallel (0°) to the scan direction, and three different focalplane positions.APPLICATIONSRotationally Symmetric Si3N4 ComponentsThe material removal rate data collected above were applied to demonstratefeasibility of concept for laser machining rotationally symmetric Si3N4 components, such asvalve stems and injector nozzles. Layers were laser machined from the 10 mm diameterCeraloy 147-31E and Noralide NCX-5102 HIPed Si3N4 bars. It should be noted that theNCX-5102 HIPed bars were bowed, out of round and exhibited two seams and a flat on theexternal surface. Figure 7a shows as-laser machined (940 W, 100 cm S-1) surfaces of NCX-5102, with the seam on the original surface labelled A. Regions B, and D were machinedto cylinders, eliminating the surface features and out-of round shape. Note that region Cwas a shallower depth which was insufficient to eliminate the surface seam. Conditionswhich retained the surface profile with depth were also identified. Region E has beenmachined to the same depth as region D, but the surface seam is now clearly visible.Minimal silicon build was observed on the sample, unlike the continuous silicon films shownon individual layers of GS-44 in Figures 5a, 5b. Surfaces B, C and D also exhibited asmooth, brown film, thought to be a silicon oxy-nitride. Residual silicon was removed byan etching treatment but the time was insufficient to completely remove the brown film(Figure 7b). Studies to optimize etching conditions are now in progress.309Figure 7a: As-laser machined surfacesof Noralide NCX-5102 HIPed Si3N4•Fuel Cell PlenumsFigure 7b: Etched surfaces ofNoralide NCX-5102 HIPed Si3N4•Fuel cells convert chemical energy directly into electrical energy by oxidation of thefuel which flows through a complex array of channels in the plenum. Multiple plenums,typically made of graphite, are assembled to make the fuel cell stack. Each plenum containschannels approximately 1 mm in width, depth and spacing. Machining the complex arrayof channels is slow, produces carcinogenic graphite dust, and is expensive, even with CNCmilling machines, since excessive force or speed results in chipping of the graphite. Plenumscontaining developmental 1 x 1 inch arrays of channels were conventionally machined forlIT's fuel cell program at a cost of $500 each.In contrast, laser machining offers an economical and clean method for two- andthree-dimensionally shaping graphite. Using the parameters developed above, a prototypefuel cell was machined as shown in Figure 8. Production costs, based on laser operatingcosts of $100.00 per hour, were estimated at approximately $8.00.SUMMARYThe above studies demonstrate the potential for direct manufacturing of lasermachined components of Si3N4 and graphite. The research on fuel cells is being scaled up310Figure 8: Laser machining atechnology transfer to .11..11..11.,,""'"'''''''.11.production of complex""JlJl ....' ..... A.II.J."" system continuesREFERENCESCombustionFifthRidge,Oxidation and925-35 inMichaelStinton, A.forced Composites by Chemical FossilEnergy Advanced Research TechnologyDevelopment Materials Program,Semiannual Progress 30, Laboratory,TN, pp. 103-7.R. A. Lowden andAnnual onTN, May 15-17, 1991.R. James, R. A. andCorrosion on the PropertiesCeramic Transactions, Vol. 19, Composite Materials,D. Sacks, The American Ceramics Society,1.3115. A. Lowden: "Fiber Coatings and the Mechanical Properties of a Fiber-Reinforced Ceramic Composite," pp. 619-30 in Ceramic Transactions, Vol. 19,Advanced Composite Materials, ed. Michael D. Sacks, The AmericanCeramics Society, Westerville, Ohio, 1991.6. S. M. Copley, M. Bass and R. Hsu: "Method and Apparatus for ShapingArticles Using a Laser Beam," U. S. Patent 4,914,270, April, 1990.7. M. Bass and S. M. Copley, "Noncontacting Position Sensor," U.S. Patent 4,888,490,December 19, 1989.8. S. M. Copley, M. Bass and R. J. Wallace: "Shaping Silicon CompoundCeramics with a Continuous Wave Carbon Dioxide Laser," Proc. SecondInternat. Symposium on Ceramic Machining and Finishing," NBS, 1978, pp.97-104.9. S. M. Copley, M. Bass and R. J. Wallace: "Shaping Silicon CompoundCeramics with a Continuous Wave Carbon Dioxide Laser," Proc. SecondInternat. Symposium on Ceramic Machining and Finishing," NBS, 1978, pp.97-104.10. R. J. Wallace: "A Study of the Shaping of Hot-Pressed Silicon Nitride with a HighPower CW CO2 Laser," Ph. D. Dissertation, University of Southern California, LosAngeles, 1983.S. M. Copley, R. J. Wallace and M. Bass: "Laser Shaping of Materials," inLasers in Materials Processing, A. Metzbower, ed. ASM Conf. Proc., 1983,pp.82-92.12. S. M. Copley, M. Bass and R. G. Wallace, "Shaping Silicon Compound Ceramicswith a Continuous Wave Carbon Dioxide Laser," in The Science of Ceramic Machin-and Surface Finishing II, eds. B. J. Hockey and R. W. Rice, NBS SpecialPublication 562, U. S. Government Printing Office, Washington, D.C., 1979, pp. 283-92.13. R. K. C. Hsu: "Shaping Articles by Vaporization with a CO2 Laser," Ph. D.Dissertation, Department of Mechanical Engineering, University of SouthernCalifornia, Los Angeles, CA, April, 1984.14. S. M. Copley, "Laser Machining," in Encyclopedia of Materials Science, M. Bever,2511-12, Pergamon Press (1985).R. J. Wallace and S. M. Copley: Extended Abstracts - American Ceramic Society87th Annual Meeting, Forum II - Ceramics for Heat Engines, Paper 8-FII-85,Cincinnati, Ohio, May, 1985.16. R. J. Wallace, M. Bass and S. M. Copley, "Curvature of Laser-Machined Grooves inSi3N4," J. Appl. Phys. 59, 10, 3555-60 (1986).17. R. J. Wallace, M. Bass and S. M. Copley: "Laser Machining of Silicon Nitride:Energetics," Advanced Ceramic Materials, Vol. 1, No.3, 1986, pp. 277-283.18. M. Copley, "Shaping Ceramics with Lasers," in Interdisciplinary Issues in MaterialsProcessing and Manufacturing, S. K. Samanta et aI., eds., Vol. 2, 631-36 ASMEPublication, New York, NY (1987).19. R. J. Wallace and S. M. Copley, "Shaping Silicon Nitride with a Carbon DioxideLaser by Overlapping Multiple Grooves," ASME Journal of Engineeringfor Industry,111, 1989, pp. 315-21.31220. H. Tao, W. Chang, S. M. Copley and J. A. Todd: "Effect of Surface Treat-ment on the Strength of Laser Machined Silicon Nitride," in Laser MaterialsProcessing III, J. Mazumder and K. N. Mukherjee, eds. The Minerals, Metalsand Materials Society, AIME, 1989, pp. 199-215.21. R. K. C. Hsu and S. M. Copley: "Producing Three-Dimensional Shapes byLaser Milling," ASME Journal of Engineering for Industry, Vol. 112, No.4,1990, pp. 375-79.22. S. M. Copley, HongYi Tao and J. A. Todd, "Post Treatment to Improve the Strengthof Laser Shaped Silicon Compound Ceramics", U. S. Patent 5,022,957, June 11, 1991.23. J. A. Todd, S. M. Copley and R. C. Dix: "Laser Machining of AdvancedCeramic Materials," Invited Paper in "Beam Processing of Materials," eds. S.M. Copley and J. Singh, TMS Fall Meeting Symposium Proceedings, Chicago,II, October 1992, TMS, 1993, pp. 111-130.24. S. M. Copley: Laser Processing Systems: An Overview: Invited Paper in"Beam Processing of Materials," eds. S. M. Copley and J. Singh, TMS FallMeeting Symposium Proceedings, Chicago, II, October 1992, TMS, 1993, pp.33-39.313

3-D Laser Shaping of Ceramic and Ceramic Composite Materials

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3-D Laser Shaping of Ceramic and Ceramic Composite Materials

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