The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares
the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform
PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same
system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters,
tensile, flexure and impact properties are all found to decline after the upgrade is installed.Mechanical Engineerin

Hall, A.

Koo, J. H.

Silverman, T. J.

South, B.

Yong, W.

English

Texas ScholarWorks

Comparison of Material Properties and Microstructureof Specimens Built Using the 3D Systems Vanguard HSand Vanguard HiQ+HS SLS SystemsT. J. Silverman, A. Hall, B. South, W. Yong and J. H. Koo*Laboratory for Freeform FabricationDepartment of Mechanical EngineeringThe University of Texas at AustinAustin, TX 78712*Corresponding author: jkoo@mail.utexas.eduAbstractThe HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine in-corporates a revised thermal calibration system and new control software. The paper comparesthe tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resis-tance and microstructure of two batteries of standard specimens built from recycled DuraformPA (Nylon 12). The first set is built on a Vanguard HS system and the second on the samesystem with the HiQ upgrade installed. The upgrade reduces user intervention, decreases to-tal build time and improves surface finish. However, using the default processing parameters,tensile, flexure and impact properties are all found to decline after the upgrade is installed.1 IntroductionThe Vanguard HS selective laser sintering (SLS) machine can be upgraded to HiQ+HS by themanufacturer, 3D Systems, Incorporated. The upgrade comprises new infrared sensors for the feedbins, a calibrating blackbody mounted on the roller carriage and updated software that performsreal-time temperature calibration and control. In previous work [1], we built a battery of mechani-cal test specimens from recycled DuraForm PA (Nylon 12) powder using a Vanguard HS machine,installed the HiQ upgrade, then repeated the build. The specimens were then tested with referenceto the applicable ASTM standards. The microstructure of typical specimens was evaluated usingscanning electron microscopy (SEM). A summary of the previous work [1] is presented here, fol-lowed by interpretation and recommendations for industrial and research practices and for futurework.392Figure 1: The specimen battery used to quantify the upgrade performance.2 Experimental procedureThe specimen battery contains a total of 240 ASTM standard tensile, flexure and impact test speci-mens [2-4], ten in each possible orientation (Figure 1). The specimens are arranged as close to thecenter of the build area as possible. They are uniquely numbered so that the effects of position andorientation on material properties can be analyzed.The battery was built using DuraForm PA (Nylon 12) material recycled from part cake froma local service bureau. The powder was blended and its consistency checked using a prescribedprocedure based on melt flow index (MFI) [2].The specimen batteries were built using the 3D Systems recommended parameter values,shown in Table 1. The part bed temperature for the HS build was selected manually using the“find temps” procedure. Because of its self-calibration capability, the HiQ+HS machine does notrequire the “find temps” procedure to be performed for materials with a built-in configuration file,including DuraForm PA. For materials without predefined parameter configurations, the proceduremust only be performed once.Table 1: Manufacturer-recommended processing parameters were used for both specimen builds.HS HiQ+HSPart Heater Set Point 152.0 C 173.0 CLeft and Right Feed Heater Set Point 130.0 C 140.0 CFill Laser Power 42 W 42 WPowder Layer Thickness 0.004 in 0.004 inThe HS build lasted 26 hours, while the HiQ+HS build lasted 20 hours. The HS build hada notably stiffer part cake that was harder to remove than the flour-like part cake in the HiQ+HSbuild. The surface finish of the pre-upgrade specimens was noticeably rougher than that of the post-393pre-upgrade887 1045 1203 1361 1519 16772468101214x=1499, Σ=85887 1045 1203 1361 1519 16772468101214x=1595, Σ=50887 1045 1203 1361 1519 16772468101214x=1558, Σ=66post-upgrade887 1045 1203 1361 1519 16772468101214x=1174, Σ=105887 1045 1203 1361 1519 16772468101214x=1473, Σ=40887 1045 1203 1361 1519 16772468101214x=1123, Σ=151x orientation y orientation z orientationFigure 2: Histograms for tensile modulus (MPa) by orientation for both builds.upgrade specimens. Surface powder was removed from the specimens using glass bead abrasive.The specimens were then tested with reference to the appropriate ASTM test procedures [2-4].3 Results and discussionThe previously published values [1] for tensile modulus and elongation at break are incorrect dueto an equipment limitation which led to a deviation from the ASTM tensile test procedure [3]. Thevalues given here have been corrected and can be compared to each other. Illustrative comparisonscan be made to other data collected using the same standard, but detailed quantitative comparisonmay not be valid. The material data sheet to which the previous work [1] refers has been shown tocontain errors [4]. The comparisons here are to the old data sheet [5], the corrected data sheet [6],which may contain a spurious impact resistance figure, and the ASTM specification for injected orextruded general purpose Nylon 12 [7].3.1 Tensile propertiesTensile properties show strong variation with respect to orientation in the build volume. His-tograms for tensile modulus (Figure 2), ultimate tensile strength (Figure 3) and elongation at break(Figure 4) are separated by orientation.The tensile properties are best in specimens with the y orientation, that is, with their longestdimension along the build volume’s y axis. The overall mean pre-upgrade tensile modulus and394pre-upgrade21 27 33 40 46 522468101214161819x=47, Σ=121 27 33 40 46 522468101214161819x=49, Σ=221 27 33 40 46 522468101214161819x=48, Σ=2post-upgrade21 27 33 40 46 522468101214161819x=36, Σ=321 27 33 40 46 522468101214161819x=44, Σ=121 27 33 40 46 522468101214161819x=30, Σ=6x orientation y orientation z orientationFigure 3: Histograms for ultimate tensile strength (MPa) by orientation for both builds.ultimate strength approach the manufacturer specified properties, shown in Table 2. Elongation atbreak is shown to be below the specified value both before and after the upgrade.All three tensile properties that were measured substantially declined between the two buildsstudied here. This indicates that, with the default, manufacturer-recommended processing param-eters, the upgrade may not result in improved tensile properties.3.2 Flexural modulusFlexural modulus does not vary substantially with the orientation of the test specimen in the buildvolume. Histograms for flexural modulus are shown in Figure 5.Table 2: Comparison of overall mean of measured material properties with manufacturer and ASTM speci-fications.Old 3D New 3D ASTMHS HiQ+HS spec. [5] spec. [6] spec. [7]Tensile modulus (MPa) 1550 1256 1600 1586 –Ultimate tensile strength (MPa) 48 37 44 43 35Elongation at break (%) 7 5 9 14 –Flexural modulus (MPa) 1860 1383 1285 1387 1000Impact resistance (J/m) 242 211 214 32 –395pre-upgrade2.5 4.1 5.7 7.4 9. 10.62468101213x=7.5, Σ=0.62.5 4.1 5.7 7.4 9. 10.62468101213x=9.5, Σ=0.82.5 4.1 5.7 7.4 9. 10.62468101213x=5.4, Σ=0.6post-upgrade2.5 4.1 5.7 7.4 9. 10.62468101213x=6.1, Σ=0.72.5 4.1 5.7 7.4 9. 10.62468101213x=6.6, Σ=0.82.5 4.1 5.7 7.4 9. 10.62468101213x=3.3, Σ=0.6x orientation y orientation z orientationFigure 4: Histograms for elongation at break (%) by orientation for both builds.pre-upgrade844 1115 1386 1657 1929 2200246810x=1812, Σ=111844 1115 1386 1657 1929 2200246810x=1894, Σ=168844 1115 1386 1657 1929 2200246810x=1876, Σ=178post-upgrade844 1115 1386 1657 1929 2200246810x=1436, Σ=115844 1115 1386 1657 1929 2200246810x=1459, Σ=214844 1115 1386 1657 1929 2200246810x=1249, Σ=244xy plane yz plane zx planeFigure 5: Flexural modulus (MPa) by orientation plane for both builds.396pre-upgrade145 177 209 242 274 306510152025x=248, Σ=23145 177 209 242 274 306510152025x=243, Σ=16145 177 209 242 274 306510152025x=236, Σ=11post-upgrade145 177 209 242 274 306510152025x=205, Σ=35145 177 209 242 274 306510152025x=241, Σ=39145 177 209 242 274 306510152025x=188, Σ=20x orientation y orientation z orientationFigure 6: Impact resistance (J/m) by orientation for both builds.As shown in the histograms and in Table 2, flexural modulus declines substantially betweenthese two builds. Again, with the recommended processing parameters, the upgrade alone is notadequate to produce an improvement in flexural modulus.3.3 Impact resistancePre-upgrade impact resistance is not sensitive to orientation, but specimens built in the z orientationafter the upgrade have relatively low impact resistance. Histograms for impact resistance are shownin Figure 6.The overall mean impact resistance figures in Table 2 confirm that impact resistance alsodeclined between the two builds. The upgrade does not improve impact resistance when themanufacturer-recommended parameters are used.3.4 DensityThe specimens’ approximate densities were measured by hand using water displacement and abalance. These densities are plotted according to x-y position in the build volume in Figure 7.There is no clear trend in density with position. Density declines slightly between the twobuilds, but this effect may not be significant compared to the measurement error.397××××××××x-coordinate (in)y-coordinate (in)-3 -2 -1 0 1 2 3-3-2-10123××××××××x-coordinate (in)y-coordinate (in)-3 -2 -1 0 1 2 3-3-2-10123density (g/cc)0.8 0.85 0.9 0.95 1 1.05 1.1 1.151Figure 7: Density map (top view) for the pre-upgrade (left) and the post-upgrade (right) builds. The densityfor all specimens (n = 240) was 0.997± 0.048 g/cc (pre-upgrade) and 0.970± 0.056 g/cc (post-upgrade)(x¯±σ ).Figure 8: Scanning electron micrographs of new DuraForm PA powder (left) and the recycled part cake usedfor this work (right).3.5 MicrostructureA sample of the recycled part cake from which the test builds were fabricated was imaged usingscanning electron microscopy (SEM) and compared to a micrograph of fresh material. The recy-cled and new powder have visibly similar texture, particle size and size distribution, as shown inFigure 8.SEM micrographs of tensile-test fracture surfaces of pre- and post-upgrade tensile specimenswere used to characterize their microstructure (Figure 9). The surfaces show visibly similar occur-rence of voids and cracking. Micrographs of cryogenic fracture surfaces, created by breaking thespecimens after chilling them with liquid nitrogen, are also visibly similar (Figure 10).Substantial differences in microstructure between new and recycled SLS powder and betweenpre-upgrade and post-upgrade fracture surfaces are not apparent.398Figure 9: Micrograph of the fracture surfaces for tensile specimens built before (left) and after (right) theupgrade.Figure 10: Micrograph of cryogenic fracture surfaces of tensile specimens built before (left) and after (right)the upgrade at 500× (top) and 1000× (bottom) magnification.3994 Summary and conclusionWhen manufacturer-recommended processing parameters were used, all of the mechanical prop-erties measured in this study declined upon the installation of the upgrade. However, these recom-mended parameters are intended to be a starting point and not a formula for optimal mechanicalproperties. They are chosen by the manufacturer to match the ASTM specifications for injection-molded Nylon 12, as a compromise between better material properties and easier breakout [4].Indeed, both the pre-upgrade and post-upgrade builds exceed the ASTM specifications for generalpurpose Nylon 12 in those properties that are specified [7]. No substantial changes in microstruc-ture were observed before and after the upgrade, indicating that no qualitative microstructural dif-ference accounts for the decline in mechanical properties. This suggests that mechanical propertiescould be improved by adjusting machine settings away from the manufacturer’s initial recommen-dations.Each SLS machine, even of a particular model, performs differently [4]. Specifying the pro-cessing parameters that result in the optimal mechanical properties is currently an iterative process.Like the operation of any complex machine, this optimization process involves a great deal of oper-ator knowledge and experience. The HiQ upgrade does not eliminate this process [4]. Parametersthat are optimal for a HS system are not optimal for a HiQ+HS system.Dozens of SLS processing parameters are available for adjustment (Table 3) and many aresubject to measurement error. The upgrade reduces error in the measurement of temperatures byproviding real-time sensor calibration. This eliminates the find temps procedure for experimentallyfinding the fusion temperature of the part bed and the temperature ramping procedure used tocompensate for sensor drift during the build. This makes builds faster to set up and run and isexpected to support consistency between builds.5 Recommendations and future workFinding the best parameters for a particular SLS machine is still an open-ended, iterative process,even after the upgrade is installed. We recommend that the institutions researching, developing,manufacturing and using SLSmachines cooperate to develop and publish a procedure for searchingthe range of processing parameters and optimizing mechanical properties. Ideally, the procedurewould be performed upon the initial installation of a machine and repeated during major mainte-nance operations, including the installation of the HiQ upgrade.Table 3: Thirty-eight processing parameters are available for user adjustment.Build parameters Part parameterssmart feed enable part cylinder heater output limit pre add powder layer delay outline outside contour onlysmart feed gain part cylinder heater set point post add powder layer delay up/down fill compensationfast add powder layer part heater PID output limit powder layer thickness fill laser powerleft feed distance part heater set point right feed distance fill scan countleft feed heater output limit part heater wait for temp right feed heater output limit outline laser powerleft feed heater set point part heater inner/outer ratio right feed heater set point outline scan countleft feed heater wait for temp piston heater enable right feed heater wait for temp slicer fill spacingminimum layer time piston heater output limit roller speed sorted fill enabledpart cylinder heater enable piston heater set point rotate scan order sorted fill max jumpvector bloom elimination cross fill scan400We also recommend that an improved version of the study, involving the proposed optimizationprocedure, be performed. The procedure, or a prototype thereof, should be used on a pre-upgrademachine and a batch of test specimens should be manufactured from fresh, unrecycled materialusing the resulting optimized parameters. The same optimization and specimen build should thenbe performed on an upgraded machine. This will fairly quantify any benefits of the upgrade anddemonstrate the feasibility and efficacy of the optimization procedure.Further testing and the development of at least part of the optimization procedure is planned atthis laboratory.AcknowledgementsThe authors would like to thank Kevin McAlea, Simon van de Crommert, Kevin Marshall, ArtDelgado, Scott Danniel and Jennifer Torkelson of 3D Systems Corporation for providing a HiQupgrade and subsequent support for the Vanguard HS SLS machine to the Laboratory for FreeformFabrication. Their continuous support of our SLS research activities at the University of Texas atAustin is greatly appreciated. We would also like to thank Kent Firestone of Solid Concepts foradvising us on the SLS build configuration as well as his helpful guidance in our SLS processing.References[1] T.J. Silverman, A. Hall, B. South, W. Yong, and J.H. Koo. Material properties and microstruc-tural characterization of specimens manufactured by selective laser sintering. SME TechnicalPaper TP07PUB58, Society of Manufacturing Engineers, Dearborn, Mich., 2007.[2] T.J. Gornet, K.R. Davis, T.L. Starr, and K.M. Mulloy. Characterization of selective lasersintering materials to determine process stability. In Solid Freeform Fabrication Proceedings,pages 546–553, 2002.[3] ASTM International. ASTM D 638-03: Standard Test Methods for Tensile Properties of Plas-tics.[4] Scott F. Danniel and Jennifer Torkelson of 3D Systems Corp., Rock Hill, S.C. Personal Com-munication, May 2007.[5] 3D Systems Corporation, Rock Hill, South Carolina (formerly in Valencia, California). Du-raform PA and GF Plastic, March 2005.[6] 3D Systems Corporation, Rock Hill, South Carolina (formerly in Valencia, California). Du-raform PA Plastic, November 2006.[7] ASTM International. ASTM D 4066a: Standard Classification System for Nylon Injection andExtrusion Materials (PA).401

Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems

The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters, tensile, flexure and impact properties are all found to decline after the upgrade is installed

Silverman, T.J.

Kinney, Allison

Koo, J.H.

University of Dayton

University of DaytoneCommonsMechanical and Aerospace Engineering FacultyPublicationsDepartment of Mechanical and AerospaceEngineering8-2007Comparison of Material Properties andMicrostructure of Specimens Built Using the 3DSystems Vanguard HS and Vanguard HiQ+HS SLSSystemsT.J. SilvermanUniversity of Texas at AustinAllison KinneyUniversity of Dayton, akinney2@udayton.eduW. YongUniversity of Texas at AustinJ.H. KooUniversity of Texas at AustinFollow this and additional works at: http://ecommons.udayton.edu/mee_fac_pubPart of the Aerodynamics and Fluid Mechanics Commons, Automotive Engineering Commons,Biomechanics and Biotransport Commons, Electro-Mechanical Systems Commons, and the EnergySystems CommonsThis Conference Paper is brought to you for free and open access by the Department of Mechanical and Aerospace Engineering at eCommons. It hasbeen accepted for inclusion in Mechanical and Aerospace Engineering Faculty Publications by an authorized administrator of eCommons. For moreinformation, please contact frice1@udayton.edu, mschlangen1@udayton.edu.eCommons CitationSilverman, T.J.; Kinney, Allison; Yong, W.; and Koo, J.H., "Comparison of Material Properties and Microstructure of Specimens BuiltUsing the 3D Systems Vanguard HS and Vanguard HiQ+HS SLS Systems" (2007). Mechanical and Aerospace Engineering FacultyPublications. Paper 30.http://ecommons.udayton.edu/mee_fac_pub/30Comparison of Material Properties and Microstructureof Specimens Built Using the 3D Systems Vanguard HSand Vanguard HiQ+HS SLS SystemsT. J. Silverman, A. Hall, B. South, W. Yong and J. H. Koo*Laboratory for Freeform FabricationDepartment of Mechanical EngineeringThe University of Texas at AustinAustin, TX 78712*Corresponding author: jkoo@mail.utexas.eduAbstractThe HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine in-corporates a revised thermal calibration system and new control software. The paper comparesthe tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resis-tance and microstructure of two batteries of standard specimens built from recycled DuraformPA (Nylon 12). The first set is built on a Vanguard HS system and the second on the samesystem with the HiQ upgrade installed. The upgrade reduces user intervention, decreases to-tal build time and improves surface finish. However, using the default processing parameters,tensile, flexure and impact properties are all found to decline after the upgrade is installed.1 IntroductionThe Vanguard HS selective laser sintering (SLS) machine can be upgraded to HiQ+HS by themanufacturer, 3D Systems, Incorporated. The upgrade comprises new infrared sensors for the feedbins, a calibrating blackbody mounted on the roller carriage and updated software that performsreal-time temperature calibration and control. In previous work [1], we built a battery of mechani-cal test specimens from recycled DuraForm PA (Nylon 12) powder using a Vanguard HS machine,installed the HiQ upgrade, then repeated the build. The specimens were then tested with referenceto the applicable ASTM standards. The microstructure of typical specimens was evaluated usingscanning electron microscopy (SEM). A summary of the previous work [1] is presented here, fol-lowed by interpretation and recommendations for industrial and research practices and for futurework.392Figure 1: The specimen battery used to quantify the upgrade performance.2 Experimental procedureThe specimen battery contains a total of 240 ASTM standard tensile, flexure and impact test speci-mens [2-4], ten in each possible orientation (Figure 1). The specimens are arranged as close to thecenter of the build area as possible. They are uniquely numbered so that the effects of position andorientation on material properties can be analyzed.The battery was built using DuraForm PA (Nylon 12) material recycled from part cake froma local service bureau. The powder was blended and its consistency checked using a prescribedprocedure based on melt flow index (MFI) [2].The specimen batteries were built using the 3D Systems recommended parameter values,shown in Table 1. The part bed temperature for the HS build was selected manually using the“find temps” procedure. Because of its self-calibration capability, the HiQ+HS machine does notrequire the “find temps” procedure to be performed for materials with a built-in configuration file,including DuraForm PA. For materials without predefined parameter configurations, the proceduremust only be performed once.Table 1: Manufacturer-recommended processing parameters were used for both specimen builds.HS HiQ+HSPart Heater Set Point 152.0 C 173.0 CLeft and Right Feed Heater Set Point 130.0 C 140.0 CFill Laser Power 42 W 42 WPowder Layer Thickness 0.004 in 0.004 inThe HS build lasted 26 hours, while the HiQ+HS build lasted 20 hours. The HS build hada notably stiffer part cake that was harder to remove than the flour-like part cake in the HiQ+HSbuild. The surface finish of the pre-upgrade specimens was noticeably rougher than that of the post-393pre-upgrade887 1045 1203 1361 1519 16772468101214x=1499, Σ=85887 1045 1203 1361 1519 16772468101214x=1595, Σ=50887 1045 1203 1361 1519 16772468101214x=1558, Σ=66post-upgrade887 1045 1203 1361 1519 16772468101214x=1174, Σ=105887 1045 1203 1361 1519 16772468101214x=1473, Σ=40887 1045 1203 1361 1519 16772468101214x=1123, Σ=151x orientation y orientation z orientationFigure 2: Histograms for tensile modulus (MPa) by orientation for both builds.upgrade specimens. Surface powder was removed from the specimens using glass bead abrasive.The specimens were then tested with reference to the appropriate ASTM test procedures [2-4].3 Results and discussionThe previously published values [1] for tensile modulus and elongation at break are incorrect dueto an equipment limitation which led to a deviation from the ASTM tensile test procedure [3]. Thevalues given here have been corrected and can be compared to each other. Illustrative comparisonscan be made to other data collected using the same standard, but detailed quantitative comparisonmay not be valid. The material data sheet to which the previous work [1] refers has been shown tocontain errors [4]. The comparisons here are to the old data sheet [5], the corrected data sheet [6],which may contain a spurious impact resistance figure, and the ASTM specification for injected orextruded general purpose Nylon 12 [7].3.1 Tensile propertiesTensile properties show strong variation with respect to orientation in the build volume. His-tograms for tensile modulus (Figure 2), ultimate tensile strength (Figure 3) and elongation at break(Figure 4) are separated by orientation.The tensile properties are best in specimens with the y orientation, that is, with their longestdimension along the build volume’s y axis. The overall mean pre-upgrade tensile modulus and394pre-upgrade21 27 33 40 46 522468101214161819x=47, Σ=121 27 33 40 46 522468101214161819x=49, Σ=221 27 33 40 46 522468101214161819x=48, Σ=2post-upgrade21 27 33 40 46 522468101214161819x=36, Σ=321 27 33 40 46 522468101214161819x=44, Σ=121 27 33 40 46 522468101214161819x=30, Σ=6x orientation y orientation z orientationFigure 3: Histograms for ultimate tensile strength (MPa) by orientation for both builds.ultimate strength approach the manufacturer specified properties, shown in Table 2. Elongation atbreak is shown to be below the specified value both before and after the upgrade.All three tensile properties that were measured substantially declined between the two buildsstudied here. This indicates that, with the default, manufacturer-recommended processing param-eters, the upgrade may not result in improved tensile properties.3.2 Flexural modulusFlexural modulus does not vary substantially with the orientation of the test specimen in the buildvolume. Histograms for flexural modulus are shown in Figure 5.Table 2: Comparison of overall mean of measured material properties with manufacturer and ASTM speci-fications.Old 3D New 3D ASTMHS HiQ+HS spec. [5] spec. [6] spec. [7]Tensile modulus (MPa) 1550 1256 1600 1586 –Ultimate tensile strength (MPa) 48 37 44 43 35Elongation at break (%) 7 5 9 14 –Flexural modulus (MPa) 1860 1383 1285 1387 1000Impact resistance (J/m) 242 211 214 32 –395pre-upgrade2.5 4.1 5.7 7.4 9. 10.62468101213x=7.5, Σ=0.62.5 4.1 5.7 7.4 9. 10.62468101213x=9.5, Σ=0.82.5 4.1 5.7 7.4 9. 10.62468101213x=5.4, Σ=0.6post-upgrade2.5 4.1 5.7 7.4 9. 10.62468101213x=6.1, Σ=0.72.5 4.1 5.7 7.4 9. 10.62468101213x=6.6, Σ=0.82.5 4.1 5.7 7.4 9. 10.62468101213x=3.3, Σ=0.6x orientation y orientation z orientationFigure 4: Histograms for elongation at break (%) by orientation for both builds.pre-upgrade844 1115 1386 1657 1929 2200246810x=1812, Σ=111844 1115 1386 1657 1929 2200246810x=1894, Σ=168844 1115 1386 1657 1929 2200246810x=1876, Σ=178post-upgrade844 1115 1386 1657 1929 2200246810x=1436, Σ=115844 1115 1386 1657 1929 2200246810x=1459, Σ=214844 1115 1386 1657 1929 2200246810x=1249, Σ=244xy plane yz plane zx planeFigure 5: Flexural modulus (MPa) by orientation plane for both builds.396pre-upgrade145 177 209 242 274 306510152025x=248, Σ=23145 177 209 242 274 306510152025x=243, Σ=16145 177 209 242 274 306510152025x=236, Σ=11post-upgrade145 177 209 242 274 306510152025x=205, Σ=35145 177 209 242 274 306510152025x=241, Σ=39145 177 209 242 274 306510152025x=188, Σ=20x orientation y orientation z orientationFigure 6: Impact resistance (J/m) by orientation for both builds.As shown in the histograms and in Table 2, flexural modulus declines substantially betweenthese two builds. Again, with the recommended processing parameters, the upgrade alone is notadequate to produce an improvement in flexural modulus.3.3 Impact resistancePre-upgrade impact resistance is not sensitive to orientation, but specimens built in the z orientationafter the upgrade have relatively low impact resistance. Histograms for impact resistance are shownin Figure 6.The overall mean impact resistance figures in Table 2 confirm that impact resistance alsodeclined between the two builds. The upgrade does not improve impact resistance when themanufacturer-recommended parameters are used.3.4 DensityThe specimens’ approximate densities were measured by hand using water displacement and abalance. These densities are plotted according to x-y position in the build volume in Figure 7.There is no clear trend in density with position. Density declines slightly between the twobuilds, but this effect may not be significant compared to the measurement error.397××××××××x-coordinate (in)y-coordinate (in)-3 -2 -1 0 1 2 3-3-2-10123××××××××x-coordinate (in)y-coordinate (in)-3 -2 -1 0 1 2 3-3-2-10123density (g/cc)0.8 0.85 0.9 0.95 1 1.05 1.1 1.151Figure 7: Density map (top view) for the pre-upgrade (left) and the post-upgrade (right) builds. The densityfor all specimens (n = 240) was 0.997± 0.048 g/cc (pre-upgrade) and 0.970± 0.056 g/cc (post-upgrade)(x¯±σ ).Figure 8: Scanning electron micrographs of new DuraForm PA powder (left) and the recycled part cake usedfor this work (right).3.5 MicrostructureA sample of the recycled part cake from which the test builds were fabricated was imaged usingscanning electron microscopy (SEM) and compared to a micrograph of fresh material. The recy-cled and new powder have visibly similar texture, particle size and size distribution, as shown inFigure 8.SEM micrographs of tensile-test fracture surfaces of pre- and post-upgrade tensile specimenswere used to characterize their microstructure (Figure 9). The surfaces show visibly similar occur-rence of voids and cracking. Micrographs of cryogenic fracture surfaces, created by breaking thespecimens after chilling them with liquid nitrogen, are also visibly similar (Figure 10).Substantial differences in microstructure between new and recycled SLS powder and betweenpre-upgrade and post-upgrade fracture surfaces are not apparent.398Figure 9: Micrograph of the fracture surfaces for tensile specimens built before (left) and after (right) theupgrade.Figure 10: Micrograph of cryogenic fracture surfaces of tensile specimens built before (left) and after (right)the upgrade at 500× (top) and 1000× (bottom) magnification.3994 Summary and conclusionWhen manufacturer-recommended processing parameters were used, all of the mechanical prop-erties measured in this study declined upon the installation of the upgrade. However, these recom-mended parameters are intended to be a starting point and not a formula for optimal mechanicalproperties. They are chosen by the manufacturer to match the ASTM specifications for injection-molded Nylon 12, as a compromise between better material properties and easier breakout [4].Indeed, both the pre-upgrade and post-upgrade builds exceed the ASTM specifications for generalpurpose Nylon 12 in those properties that are specified [7]. No substantial changes in microstruc-ture were observed before and after the upgrade, indicating that no qualitative microstructural dif-ference accounts for the decline in mechanical properties. This suggests that mechanical propertiescould be improved by adjusting machine settings away from the manufacturer’s initial recommen-dations.Each SLS machine, even of a particular model, performs differently [4]. Specifying the pro-cessing parameters that result in the optimal mechanical properties is currently an iterative process.Like the operation of any complex machine, this optimization process involves a great deal of oper-ator knowledge and experience. The HiQ upgrade does not eliminate this process [4]. Parametersthat are optimal for a HS system are not optimal for a HiQ+HS system.Dozens of SLS processing parameters are available for adjustment (Table 3) and many aresubject to measurement error. The upgrade reduces error in the measurement of temperatures byproviding real-time sensor calibration. This eliminates the find temps procedure for experimentallyfinding the fusion temperature of the part bed and the temperature ramping procedure used tocompensate for sensor drift during the build. This makes builds faster to set up and run and isexpected to support consistency between builds.5 Recommendations and future workFinding the best parameters for a particular SLS machine is still an open-ended, iterative process,even after the upgrade is installed. We recommend that the institutions researching, developing,manufacturing and using SLSmachines cooperate to develop and publish a procedure for searchingthe range of processing parameters and optimizing mechanical properties. Ideally, the procedurewould be performed upon the initial installation of a machine and repeated during major mainte-nance operations, including the installation of the HiQ upgrade.Table 3: Thirty-eight processing parameters are available for user adjustment.Build parameters Part parameterssmart feed enable part cylinder heater output limit pre add powder layer delay outline outside contour onlysmart feed gain part cylinder heater set point post add powder layer delay up/down fill compensationfast add powder layer part heater PID output limit powder layer thickness fill laser powerleft feed distance part heater set point right feed distance fill scan countleft feed heater output limit part heater wait for temp right feed heater output limit outline laser powerleft feed heater set point part heater inner/outer ratio right feed heater set point outline scan countleft feed heater wait for temp piston heater enable right feed heater wait for temp slicer fill spacingminimum layer time piston heater output limit roller speed sorted fill enabledpart cylinder heater enable piston heater set point rotate scan order sorted fill max jumpvector bloom elimination cross fill scan400We also recommend that an improved version of the study, involving the proposed optimizationprocedure, be performed. The procedure, or a prototype thereof, should be used on a pre-upgrademachine and a batch of test specimens should be manufactured from fresh, unrecycled materialusing the resulting optimized parameters. The same optimization and specimen build should thenbe performed on an upgraded machine. This will fairly quantify any benefits of the upgrade anddemonstrate the feasibility and efficacy of the optimization procedure.Further testing and the development of at least part of the optimization procedure is planned atthis laboratory.AcknowledgementsThe authors would like to thank Kevin McAlea, Simon van de Crommert, Kevin Marshall, ArtDelgado, Scott Danniel and Jennifer Torkelson of 3D Systems Corporation for providing a HiQupgrade and subsequent support for the Vanguard HS SLS machine to the Laboratory for FreeformFabrication. Their continuous support of our SLS research activities at the University of Texas atAustin is greatly appreciated. We would also like to thank Kent Firestone of Solid Concepts foradvising us on the SLS build configuration as well as his helpful guidance in our SLS processing.References[1] T.J. Silverman, A. Hall, B. South, W. Yong, and J.H. Koo. Material properties and microstruc-tural characterization of specimens manufactured by selective laser sintering. SME TechnicalPaper TP07PUB58, Society of Manufacturing Engineers, Dearborn, Mich., 2007.[2] T.J. Gornet, K.R. Davis, T.L. Starr, and K.M. Mulloy. Characterization of selective lasersintering materials to determine process stability. In Solid Freeform Fabrication Proceedings,pages 546–553, 2002.[3] ASTM International. ASTM D 638-03: Standard Test Methods for Tensile Properties of Plas-tics.[4] Scott F. Danniel and Jennifer Torkelson of 3D Systems Corp., Rock Hill, S.C. Personal Com-munication, May 2007.[5] 3D Systems Corporation, Rock Hill, South Carolina (formerly in Valencia, California). Du-raform PA and GF Plastic, March 2005.[6] 3D Systems Corporation, Rock Hill, South Carolina (formerly in Valencia, California). Du-raform PA Plastic, November 2006.[7] ASTM International. ASTM D 4066a: Standard Classification System for Nylon Injection andExtrusion Materials (PA).401

Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HS SLS Systems

https://ecommons.udayton.edu/cgi/viewcontent.cgi?article=1005&amp;context=mee_fac_pub

Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems

Abstract

Similar works

Full text

Available Versions

Texas ScholarWorks

University of Dayton