A previously developed and verified thermal model for Laminated Object Manufacturing
(LOM) was used to investigate the effects of various processing parameters on the temperature
profile in a LOM part during the build cycle. The mathematical model, based on 3-dimensional
transient heat conduction in a rectangular geometry LOM part, allows calculation ofthe transient
temperature distribution within the part during the application of a new layer as well as during
other periods ofthe LOM build cycle. The parameters roller temperature, roller speed, chamber
air temperature, base plate temperature, and laser cutting time were independently varied, and the
LOM process response simulated. The results were analyzed in order to gain insight into
potential strategies for intelligent process control.Mechanical Engineerin

Chartoff, Richard P

Flach, Lawrance

Jacobs, Michelle A.

Klosterman, Donald A.

English

Texas ScholarWorks

SIMULATION OF LAMINATED OBJECT MANUFACTURING (LOM) WITHVARIATION OF PROCESS PARAMETERSLawrance Flach, Michelle A. JacobsDepartment of Chemical and Materials EngineeringDonald A. Klosterman, Richard ChartoffRapid Prototype Development LaboratoryandOhio Rapid Prototype Process Development ConsortiumUniversity of Dayton300 College ParkDayton, OR 45469U.S.A.ABSTRACTA previously developed and verified thermal model for Laminated Object Manufacturing(LOM) was used to investigate the effects of various processing parameters on the temperatureprofile in a LOM part during the build cycle. The mathematical model, based on 3-dimensionaltransient heat conduction in a rectangular geometry LOM part, allows calculation of the transienttemperature distribution within the part during the application of a new layer as well as duringother periods of the LOM build cycle. The parameters roller temperature, roller speed, chamberair temperature, base plate temperature, and laser cutting time were independently varied, and theLOM process response simulated. The results were analyzed in order to gain insight intopotential strategies for intelligent process control.INTRODUCTIONLOM users are fast becoming aware that an understanding of the thermal behavior of aLOM part during the build process is crucial for the fabrication ofparts with good laminationcharacteristics. Low temperatures in the upper layers may result in poor adhesion of theindividual layers causing delamination of the completed part. On the other hand, excessivebuild-up of heat in the body of the part may result in a general loss of structural rigidity duringthe build leading to excessive compression or shearing during application ofpressure by theroller. While this is important for prototype parts made from standard LOM paper and plasticmaterials, it has become extremely significant now that the fabrication of high performance,functional ceramic and composite parts is being considered [1-8].In order to obtain a better understanding of the transient thermal behavior of the partbody during the LOM build cycle, a mathematical model was developed and its performance407verified[9]. As part of a continuation of this work, it was decided to use this process model toinvestigate the effects of varying certain parameters during a number of simulated LOM builds.Use of this model allows a number of experiments to be conducted in a relatively short time, andalso does not require use ofthe actualLOl\1 apPaJatus with associated relatively high cost. Inaddition, this approach allows for variation of process parameters that are not currentlyimplemented on theLOM machine,. such as base plate and chamber air temperatures.A series•ofsil11ulationexperiments was thus planned to see which of the process variableshad significanteffects on the transient thermal behavior and which variables could potentiallY beused for process control purposes. The results of these experiments are presented here togetherwith a brief discussion of their significance.BACKGR.OUNDFull details of the mathematical model have been previously documented [9] so only abrief4escription of the model and its capabilities as is pertinent to this discussion will bepresented here.The thermal behavior of a part during a LOM build is determined by heat transfer to thepart frol11theroller,heat conduction withinthe part itself, heat loss from the part to the metalbasepl(lte, and heatloss to the surroundings. The appropriate differential.equation and boundaryconditions were setup for a rectangular geometry part (because allLOM parts are builtasrectangular blocks) and then. together with appropriate initial.conditions, material properties andheat transfer coefficients numericallysolvedto revealthe temperature distribution within thepart. The mod¥l is. capable of handling the. addition ofnew layers ofbuild material as well as allother phases of the build cycle and generates the fu1l3.-dimensional transient temperatureprofileswithin.the part.•• Themo<1eldoes.not include amechanicalsubmodel, and therefore,. thecoupling of thermaland mechanical behavior cannot be fully simulated. However, by tuning oneofthe model parameters (roller to part heat transfer coefficient), excellent agreement wasobtained. between predicted temperatures within a partandthe actual temperature as measured byembedded thermocouples [9], see Figure 1. Thus, the model is fully capable of measuring thethermal behavior of the LOM process.MODELING EXPER.IMENTSA series of simulation experiments was designed around abase simulation taken fromtheprevious work [9]. This workinvolvedlayupof250llm-thick SiC ceramic tapes on aLOM2030machine~A/twenty-layer,12.19cmx 5.33 em block of "green" ceramic material was produced.Material property data and simulation parameters for this base case are summarized in Tabl~ 1.All parameters were experimentally measured, except the roller to part heat transfer coeffiCIentwhich was used as a tuning param.eter.408Table 1: Material properties and machine parameters for base simulation [9].MaterialThermal ConductivityDensityHeat CapacityPart dimensionsLayer thicknessNumber of layersHeattransfer coefficient (part to air)Heat transfer co~ffiCi~nt (patftobase)Air temperatureBase plate temperatureInitial temperatureOfmaterialRoller velocityRoller contact stripwidthRoller temperatureHeat transfer coefficient (roller to part)Build cycle timeSilicon carbide ceramic tapes1.98 g cm-:>1.05Jg- K-1121.9rrun x 53.3 mm0.25rnrn2025.4 mm sec"l9mm3300 Wm-L.K- l120 secondsParameters selected for il1vestigationincluded thefolloW1l1g: roller temperature, baseplate temperature, chamber air temperature (surrounding airtel11perature), roller speed, lasercutting time. The roller temperature and speed influence the amount of heat transfer from rollertopart. Base plate and chamber air temperatures in~?encetherate ofheat loss of the part block.The entire part block as a whole gains negligible heat from the laser cutting (although this maynot be true for the top layer ortwo), so thelaser cutting time affects the amount of coolingbetween application of successive layers. All ofthese/parameters/directlyinfluence t~e.tra~sie~tas well as long term thermal behavior of the part. Table2 sUIIl111arizes the parameter values usedand the changes made totheseparameters.. Insome cases (Trials 15-18) the parameter value waschanged halfway through the simulation in order to observe the dynamic response ofthe processto that variable change. This information is important for process controFpurposes. The fullexperiment and results are documented elsewhere [10].RESULTS AND DISCUSSIONDuring model verification [9] it was observed that the temperature below the 1st layer(bottom most) of build materiaFwasrepresentativeofthe part body temperature, Le. apartfromsurface transient behavior near the part block surface during roller activity, thetel11peraturethrough the depth ofthepart was fairly uniform. Thus, in orderto~omparethe behavior ofthepartwhen subjected to the differentsets of parmneters,.it'r\'asdecidedto?bsen'e the firs; layertemperature only; Thus, the results shown in the various~guresherein represent howthetemperature below theb?ttom most layer v.~ries with time during the build, and this Can beinterpreted as how the part bodytemperature .as a whole varies with time (referred to as the"representative part body temperature"). In all cases, fluctuation of the representative part body409Table 2: schedule of investigated LOM parameters.Roller Base Plate Chamber Air Roller Speed Laser CuttingTrial # Temperature Temperature Temperature (em/sec) Time (sec)(0C) (0C) (0C)1 91 22 22 2.54 772 150 22 22 2.54 773 200 22 22 2.54 774 250 22 22 2.54 773 200 22 22 2.54 775 200 50 22 2.54 776 200 75 22 2.54 777 200 100 22 2.54 773 200 22 22 2.54 778 200 50 50 2.54 779 200 75 75 2.54 773 200 22 22 2.54 7710 200 22 22 3.81 7711 200 22 22 5.08 7712 200 22 22 2.54 573 200 22 22 2.54 7713 200 22 22 2.54 9714 200 22 22 2.54 11715 91 22/50 22 2.54 7716 91 22/100* 22 2.54 7717 91 / 150 22 22 2.54 7718 91 /200* 22 22 2.54 77*Parameter changed halfway through the run from the first value to the second.temperature tends to dampen as more layers are added, and an "average part body temperature"is also referred to throughout the discussion.The first parameter investigated was roller temperature. The roller temperature wasvaried in the range 91°e to 250oe, and all other parameters were kept the same as the base casesimulation (trial #1 is the base case simulation). Figure 2 reveals that peak temperatures aredramatically increased and the long-term part body temperature is only minimally affected. Theaverage part body temperature increased about 100 e for every 500 e increase in rollertemperature. Although not shown in Figure 2, the temperature of the surface layer (in directcontact with the roller) is most dramatically affected.The next test involved variation of the base plate temperature only. At this point in thestudy, it was decided to deviate from the base case parameters by using a roller temperature of2000e for many of the remaining trials. The reason for doing this was to amplify the effects ofchanges in the other parameters such as base plate temperature, chamber air temperature, etc.The results for parametric variations in the base plate temperature are given in Figure 3. As can410be seen, higher base plate temperature resulted in higher temperatures·ofthe part being built.The average part body temperature for this simulation seems to increase approximately 9°C foreach 2SoC rise in base plate temperature. This effect was considered to be more "efficient" or"sensitive" than the roller temperature effect.next test involved parametric variations in the chamber air temperature. It should benoted that in all cases the base plate temperature was assumed to vary with the chamber airtemperature. This would seemto he reasonable cOl1sideringthe geometry andlayouf of the LOMapparatus. Figure 4 shows how the part bodytemperature varies with time for different LOMchamber air and base plate temperatures. The response of the part is similattothat oftheprevious test, with the exception that the magnitude of the parttemperaturechange was more.The average part body temperature for this simulation increases approximately 20°C for each2SoC air andbase plate temperature. Thus, this effectwas viewed as the Inost "efficient"or "sensitive" so far .• With the previous test inmind,thisresultwas qualitativelyexpecte~,the block loses less heat because all surfaces are maintained at elevated temperature, notjustthebase plate as before. From a process control viewpoint, however, it may be a lot easier and morepractical to manipulate the base plate temperature only and not the combination ofhaseplate andchamber air temperature.The roller speed was. also investigated since time of roller contact will also influence theamount.ofheat transferred to the part..•.• Changil1g the roller speed also has the effect ofchangingthe overall build time.of thepart,so.these result are nofsoeasily•compared graphically.•••1f~asdiscovered thatfora50% increase in roller speed,the average part·body temperature decreasedbyabout 7°C, and for a 100% increase by about 23°C (10). Again,the surface layer in directcontact with the roller was the most affected.A laser cutting. time of 77 seconds was used in the .basesimulation. Changing the lasercutting time between the application ofsuccessive layersofbuildmaterialshould<affectthe parttemperature due to the fact that increasing.this delaytime allows additional time for the part tocool by heat loss to the surroundings and baseplate. The reasonfor investigating this effect isbecause the cycle··time.usually varies throughouta bl.lild··.dueto •• changesinthelasercuttil1gfrol11layer to layer. It was discovered that this effectwasfairlysmall,.inmostcasesresultinginonlyabout a 3°C drop in part body temperature for every20-secondincrease in delay time. [10]Some dynamic tests were also conducted where the baseplate and rollertemp¢ratureswere changed halfway through the build process.• Thiswas>donetoestimatehowmanYicycl~s(or layers) were required for the parttorespond.tothechangeinthep~ran1etervalue.Theeffectofchanging the baseplate temperature halfwaythroughthebuildisshowniinFigure5.• It<canheseen that the part.body temperature typically reachesitsnew)averagetemperaturewithi113to 4cycles. A.. similar result was observed for the change inrollerte111perature (Figure 6)'iTheseresults are significant when considering· on-line controL.of the process<andgivesone sOnleideaofthe overall speed of response.411CONCLUSIONSUse of the LOMprocess for the fabrication offunctional ceramic and composite parts hasresultedinad.dition(;llrequiJ:ements being placed onthe LOM build.environment to ensure theintegrity and functionality of the produced parts. One of these requirements concerns thethermal environment of the part. ·Control of this environment thus has become an importantconsideration for the development ofLOM using ceramic and composite materials.The simulation and modeling work done has revealed that a number ofparameters haveinfluence over the thermal environment of the part and that some of these show promise as beingsuitable for manipulation of the process during online control. In particular, the chamber airtemperature and base plate temperature combinationwould seem to be the most effective forcontrol of the overall part temperature. From an overall practicality viewpoint, limited controlcould also be achieved. using the base plate temperature only. The roller temperature proved tobe the most effective in affecting the temperature of the surface layers of the part, i.e. those closeto the roller during lamination. Thus, if high temperatures are required in the surface layers andsomewhat lower temperatures throughout the remainder of the part, then control of the rollertemperature would provide a means to accomplish this. However, large fluctuations in thetemperatures near the surface would have to be tolerated.The simulations also revealed some useful information with regard to the dynamicresponse of the temperature of the part. While. this is known tobe a function of the overall partdimensjons and thermal properties of the build material, the response times obtained indicatedthat online control of the process is feasible and that reasonable dynamic responses should beobtained.REFERENCES1. Klosterman, D., R. Chartoff, N. Osborne, G. Graves, A. Lightman, G. Han, A. Bezeredi, S.Rodrigues, S. Pak, G. I(almanovich, L.Dodin, S. Tu, "Curved Layer LOM of Ceramics andComposites," Prototyping Technology International '98, (Annual Review Book), ed.Jonathan Lawson, UK & International Press, Surrey, UK, April, 1998, pp.145-149.2. Klosterman, D., R. Chartoff,et aI., "Automated Fabrication of Monolithic and CeramicMatrix Composites via Laminated Object Manufacturing (LOM)," Proceedings ofthe SolidFreeform FabricationSymposium, Austin, TX, August, 1997, pp. 537-549.3. Klosterman, D.A.,B.E. Priore and R.P. Chartoff, "Laminated Object Manufacturing ofPolymer Matrix Composites", Proc. i h Int. Conf. Rapid Prototyping, University of Daytonand Stanford University, San Francisco, CA, March 1997.4. Steidle, C.C., Automatgd Fabrication ofBioceramic Bone Implants Using Laminated ObjectManufacturing, M.S. Thesis, Chemical Engineering, University of Dayton, May, 1998.5. Chi, C., L. Dodin, and S. Pak, "Developmentand Fabrication of Metallic LOM Objects",Proc. i h Int. Con! Rapid Prototyping, University of Dayton and Stanford University, SanFrancisco, CA, March 1997.6. Griffin, A., et aI., "Bioceramic RP Materials for Medical Models", Proc. i h Int. Con! RapidPrototyping, University of Dayton and Stanford University, San Francisco, CA, March 1997.4127. Griffin, E.A., D.R. Mumm, D.B. Marshall, "RapidPrototyping ofFunctional CeramicComposites," The American Ceramic Society Bulletin, Vol. 75, No.7, July 1996.8. Pope, M., M. Patterson, W. Zimbeck, M. Fehrenbacher, "Laminated Object Manufacturing ofSi3N4 with Enhanced Properties," Proceedings ofthe Solid Freeform FabricationSymposium, Austin, TX, August, 1997, pp. 529-536.9. Flach, L., D. Klosterman, R. Chartoff, "A Thermal Model for Laminated ObjectManufacturing Process," Proceedings ofthe Solid Freeform FabricationSymposium, Austin,TX, August, 1997, pp. 677-688.10. Jacobs, M.A., Thermal Modeling and Control ofthe LOMProcess, Undergraduate HonorsThesis, Chemical Engineering, University of Dayton, April, 1998. (note,trial numbers in thispaper and Jabob's thesis do not correspond).ACKNOWLEDGEMENTSThis work was made possible by a grant from the Ohio Board ofRegents, ResearchChallenge Program at the University of Dayton. The LOM equipmentwas available through agrant from DARPAlONR, NOOOI4-95-1-0059. Student participation was through the Universityof Dayton Honors Program.ILLUSTRATIONSModef----- Expdoto100gO -8070w 60IX=:>f-«IXILl0-:zILl1--20 -1000 250 500 750 1000 1250 1500 1750 2000·. 2250 2500TIME (sec)Figure 1: Base sill11.l1ation andexperil11entally mea.suredtempera.tllreprofilefor a 20Qayer,SiCLOMpart, as measured by a thermocouple just above the Olhlayer (foam tal'e base)during the.build process [9].The cycle time is 120 seconds per layer. The experimental conditions are given in Table 1 andTable 2(trial #1).413200E180Q)5 160el!i 140EQ)I- 120>."0S 1001::if. 80Q).~iii 60E~ 40l 20250·C200·C150·C91·Co '---'---;!:o--'---;::6*:oo::----:1;-;;2:'::-oo=--~---::1-:80:::0::-.---~--;::2~40:-:0:-­time (sec)Figure 2: Parametricv~riationofroller temperature: simulated, dynamic temperature profilesinside a 20-layer SiC LOM part during the building process (120 seconds per layer) using theparameters given in Table 2 (trials 1-4).200baseplatetemperature100·C75·C5o·e22·Co 600 1200time (sec)Figure 3: P~l"al11etricvariationOfbaseplatetell).perature: simulated, dynamic temper~ture profiles insidea 20-layer SiC LOMpart during the building process {120 seconds periayer) using the parameters givenin Table.2 (trial 3, 5, 6, 7).4146 200~l!::3 180-i!!& 160E~ 140>. air"C0 120 temperaturem'I: 75°CIII 100Q.CI>> 80 50°CEc 22°CCI> 60II)l!Co 40&! 20 '-----''---=_~ _ __l._..._~------L__~_ __l._..._~_ _____L__o 600 1200time (sec)1800 2400Figure 4: Parametric variation of chamber air temperature: simulated, dynamic temperature profilesinside a 20-layer SiC L()M part during the building process (120 seconds per layer) using the parametersgiven in Ta.ble 2 (trials 3,8,9).E 90l!1::> 80~&E 70CI>I--g 60a:J~ 50c...~ 40Et:CI>~ 30Q.& 20o 600,base platechanges temperature1200time (sec)1800baseplatefinaltemperature100°C50°C22°C2400Figure 5: Effect of changing base plate temperature halfway through a run: simula.ted, dynamictemperature profiles inside a 20-layer SiC LOM part during the building process (120 secondsper layer) using the parameters given in Table 2 (trials 15, 16).415906 800.........~ 70.a~Q) 60a.EQ)l- SO>."'C0CD 40t::«Ia.30200 600 1200time (sec)1800 2400Figure 6: Effect of changing the roller temperature (from 91°C) halfway through a run:simulated, dynamic temperature profiles inside a 20-layer SiC LOM part during the buildingprocess (120 seconds per layer) using the parameters given in Table 2 (trials 17, 18).416

Simulation of Laminated Object Manufacturing (LOM) with Variation of Process Parameters

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Simulation of Laminated Object Manufacturing (LOM) with Variation of Process Parameters

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