1999 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/73460

Proceedings for the 1999 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Tenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 9-11, 1999, was attended by over 170 national and international researchers. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. New sessions on ceramic materials and multiple materials SFF were added to this year's program. The diverse domestic and foreign attendees included industrial users, SFF machine manufacturers, university researchers and representatives from the government. We are pleased once again with the strong showing of university students. The excitement generated at the Symposium reflects the participants' total involvement in SFF and the future technical health of this growing technology. The Symposium organizers look forward to its being a continuing forum for technical exchange among the expanding body of researchers involved in SFF.

The Symposium was again organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing computer issues, machine topics, and the variety of materials aspects of SFF. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both the people presently involved in this fruitful technical area as well as new researchers and users entering the field.

The editors would like to extend a warm "Thank You" to Rosalie Foster for her detailed handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as registrar and problem solver during the meeting. We would like to thank the Organizing Committee, the session chairmen, the attendees for their enthusiastic contributions, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We look forward to the continued close cooperation of the SFF community in organizing the Symposium. We also want to thank the Office of Naval Research and the National Science Foundation for supporting this meeting financially. The meeting was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering Department, Laboratory for Freeform Fabrication and the Texas Materials Institute at The University of Texas at Austin.

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1999 International Solid Freeform Fabrication Symposium Table of Contents
(1999) Laboratory for Freeform Fabrication and University of Texas at Austin
Direct Fabrication of Polymer Composite Structures with Curved LOM
(1999) Klosterman, Donald; Chartoff, Richard; Agarwala, Mukesh; Fiscus, Ira; Murphy, John; Cullen, Sean; Yeazell, Mark
This report describes the application of Curved LOM to the direct fabrication of polymer matrix composites (PMCs). The overall methodology of directly fabricating PMC parts involved the use of the Curved LOM machine to lay-up and shape "green" composite laminates from prepreg feedstocks, followed by vacuum bag / oven cure and consolidation. The conventional Curved LOM laminator was replaced with a vacuum thermoforming apparatus to better accommodate the bonding of commercially available prepregs. The study also demonstrated that it is possible to interface a general composite design sofiware package with the Curved LOM machine via the curved slice file (.CSF) format. Taken together, these two improvements allow for improved flexibility in manufacturing PMC components, from both a material handling and a design point-of-view. A simple C-shaped panel was fabricated and tested to demonstrate the overall feasibility of the process for PMCs. A glass fiber 1 epoxy prepreg obtained from a commercial supplier was used as a model material system. It was found that the cumulative accuracy of the overall process was good, and the mechanical properties of the laminates were acceptable for nonstructural applications for which the material is normally used.
Coated Feedstock for Fabrication of Ceramic Parts by CAM-LEM
(1999) Liu, Zhien; Suppakarn, N.; Cawley, James D.
In laminated object manufacturing of ceramic components, lamination is one of the most important materials issues. Good lamination ensures monolithic component after firing. Otherwise, lamination defects that inevitably will occur in the parts will affect the properties of ceramic components. Adhesive (both liquid and non-liquid) lamination processes were developed for the cut-then-stack (CAM-LEM) procedure. The non-liquid adhesive lamination is discussed in detail.
Process Maps for Laser Deposition of Thin-Walled Structures
(1999) Vasinonta, Aditad; Beuth, Jack; Griffith, Michelle
In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent deposition conditions and in limiting residual stress-induced warping of parts. In this research, nondimensionalized plots (termed process maps) are developedJrom numerical models of laser-based material deposition of thin-walled structures that.map out the effects of changes in laser power, deposition speed and part preheating on process parameters. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the approach taken is applicable to any solid freeform fabrication process involving. a moving heat source. Similarly, although thinwalled structures treated in the current work, the same approach could be applied to other commonly fabricated geometries. A process map for predicting and controlling melt pool size is presented .and numerically determined results are compared against experimentally measured melt poollengthsfor stainless steel deposition in the LENS process.
Microstructure and Property Optimization of LENS Deposited H13 Tool Steel
(1999) Brooks, J.; Robino, C.; Headley, T.; Goods, S.; Griffith, M.
Direct laser metal deposition is a means of near net shape processing that offers a number of advantages including rapid prototyping and small lot production. With the LENS (Laser Engineered Net Shape) process [Ref 1], parts are fabricated by creating a laser melted pool into which particles are injected. Fabrication proceeds by moving the work piece, thereby building the structure line by line and layer by layer. In this manner a wide variety of geometries and structures can be fabricated. During fabrication, a complex thermal history is experienced in different regions of the build. These thermal histories include remelting and numerous lower temperature thermal cycles. Furthermore, the use of a finely focused laser to form the rapidly traversing pooL can result in relatively high solidification velocities and cooling rates. Previous work has developed LENS as an advanced manufacturing tool rather than exploiting its potentially unique attributes: real time control of microstructure, tailored material properties at different part locations, the production of graded structures, etc. Very often, however, material properties are not significantly different than those of wrought materials. The. goal of this program is to exploit the unusual thermal environment experienced during fabrication, and the ability to design and vary alloy composition. In this paper we describe this approach using H13 tool steel in which only the thennal fields are varied through changing process parameters to achieve desired properties.
Process Variable Effects on Laser Deposited Ti-6Al-4V
(1999) Brice, C.A.; Schwendner, K.l.; Mahaffey, D.W.; Moore, E.H.; Fraser, H.L.
An initial study ofthe processing parameters affecting deposition quality ofTi-6AI-4V was conducted using the LENSTM direct laser deposition system. The significant number ofprocess variables presents a problem in determining relative effects. A few ofthe easily identifiable variables were isolated and the deposits were characterized qualitatively by comparison oflayer adhesion, porosity, and dimensional accuracy. These characteristics were compared for each deposit while processing variables such as laser power, travel speed, and hatch spacing were varied. The results led to the development of a set of optimum processing conditions that produce a quality deposit.
Novel Ceramics and Metal-Ceramic Composites via Fused Deposition Process
(1999) Bandyopadhyay, Amit; Atisivan, Raj; Bose, Susmita
Indirect fused·· deposition process is utilized.·.. to ·fabricate controlled porosity ceramic structures using alumina, mullite, zirconia, LSCF-perovskite, tricalcium phosphate and hydroxyapatite, where pore size, pore shape and pore connectivity are varied from one end to the other end of the parts. Some of these porous ceramics are then infiltrated with metals via pressureless reactive metal infiltration to form novel metal-ceramic composites. Thispaper will describe processing, structures of various porous and metal-infiltrated composites and their physical and mechanical properties.
Mechanical and Rheological Properties of Feedstock Material for Fused Deposition of Ceramics and Metals (FDC and FDMet) and their Relationship to Process Performance
(1999) Venkataraman, N.; Rangarajan, S.; Matthewson, M.J.; Safari, A.; Danforth, S.C.; Yardimci, A.; Guceri, S.I.
Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of a highly loaded thermoplastic binder system. The present FDC process uses filament feedstock of 1.780 mm ± 0.025 mm diameter. The.filament acts as both the piston driving the extrusion process as well as the molten feedstockbeing deposited. The filaments need to be able to provide and sustain the pressure needed to drive the extrusion process. Failure to do this results in failure via "buckling". The filament compressive modulus determines the ability ofthe filament to provide·and sustain the required pressure to drive the extrusion. The viscosity ofthe feedstock material, nozzle geometry and volumetric flow rates employed determine the pressure needed to drive the extrusion process. In this worktheiextrusion pressure for a particular material termed PZT ECG9 (52.6 Vol.% PZT powder in ECG9i~inder) was measured experimentally as a function of volumetric flow rate and nozzle geometry.rhe compressive modulus ofthe material was determined using a miniature materials tester (Rheoinetrics, Inc., Piscataway, NJ). A process map has been developed. The map is based .on the quantity MIE, and predicts the performance of the material in a FDC process as a.functioIl.ofnozzleg~ometry and volumetric flow rate. In general, it is observed that when MIE exceeds a critical value, called APcr/E, there is an increased tendency for the filament to buckle. A. preliminary fluid flow model for extrusion of PZT ECG9 through a FDC nozzle has also been developed using Polyflow™ software. The model predicts the observed trend in pressure drop with flow rate and nozzle geometry with reasonable accuracy.
Thermo-mechanical Analysis of Parts Fabricated via Fused Deposition Modeling (FDM)
(1999) Bharvirkar, Manish; Nguyen, Phong; Pistor, Christoph
The quality of Fused Deposition Modeling parts that are built using the standard parallel road approach depends significantly on the orientation of the slices. In this study the expansion coefficient, tensile strength and elastic. modulus of FDM parts made from ABS were determined experimentally. The parts were built using the standard toolpath (parallel roads) with a uni directional stacking sequence. The results were used to determine the thermo-mechanical properties for an.individual slice. Classical lamination theory was applied to predict properties and stiffness of matrix parts with arbitrarily oriented stacking sequences. The results of these predictions are compared with experimental results for a quasi-isotropic stacking sequence.
Maximizing the Strength of Fused-Deposition ABS Plastic Parts
(1999) Rodriguez, J. F.; Thomas, J.P.; Renaud, J. E.
Fused-Deposition (FD) creates parts using robotic extrusion of set.D.i-liquid .polymer fiber, which molecularly bonds with neighboring fibers via thermal-dlffuslo.n bonding. T~e strength ofthe. part depends on the bulk polymer strength, themesostructure ~flber layout, vOid geom~try, extent of fiber bonding), and thefiber-t~-fiber ~ond strength. The ~nfluence of these factors on the mechanical strength of FD-ABS.plasttc parts IS reported.along with the.FD process variable settingsfor maximum strength. Substantial increases in transverse strength are achieved at the optirnal settings and additional increases can be achieved by post..fabrication annealing. Keywords: Stratasys, fused-deposition, ABSplastic, functional parts, strength, mesostructure, polymer diffusion.
Extrusion Freeform Fabrication of Functional Ceramic PrototypeS
(1999) Vaidyanathan, R.; Lombardi, J.L; Walish, J.
Extrusion Freeforming (EFF) and Fused Deposition Modeling (FDM) processes are established freeforming techniques capable of fabricating complex shaped ceramic prototypes by the sequential deposition and solidification of green ceramic feedstock, layer by layer until the final part results. The freeforming of ceramic parts was accomplished using a commercially available Stratasys 3D Modeler retrofitted with a high-pressure extrusion head designed by Advanced Ceramics Research, Inc. (ACR). The manufactured objects had good dimensional tolerances, as well as real engineering compositions and microstructures. Ceramic feedstock based on two different silicon nitride powders were developed and successfully used to make prototype parts. Mechanical properties and microstructural characterization of prototype parts were performed.
Processing, Characterization and Modeling of Non-Random Porous Ceramic Structures
(1999) Hattiangadi, Ashwin; Bandyopadhyay, Amit
Processing of non-random porous ceramic structures via fused deposition process is discussed. structures are characterized experimentally and statistically based on their compressive strength. Finite element modeling is used to understand the effect of stress concentration leading to the strength degradation ofthese brittle elastic solids.
Cryogenic Mechanical Alloying of Poly (ether ether ketone) - Polycarbonate Composite Powders for Selective Laser Sintering
(1999) Schultz, J.; Kander, R.; Suchicital, C.
Mechanical alloying is a solid state processing technique traditionally used in the metallurgical industry to extend solubility limits in alloy systems. Mechanical alloying can also be used to blend polymer systems at ambient or cryogenic temperatures. In this work, cryogenic mechanical alloying was employed to create composite powders of Poly (ether ether ketone) (PEEK) - Polycarbonate (PC) for use in selective laser sintering applications. The microstructural development of the PEEK-PC system that occurs during laser sintering and the effects of this microstructure on mechanical properties of the laser sintered parts was investigated.
Measurement of the Sintering Dynamics of polymeric powders at Near SLS Conditions
(1999) Steinberger, J.; Manetsberger, K.; Shen, J.; MulIers, J.
The sintering dynamics of materials used in the Selective Laser Sintering process impact greatly the thermal conditions of the powder bed. An experimental setup was developed to obtain sintering rate information at conditions very near to those of the SLS process. The system consists of a powder sample heated by a CO2 laser while maintained at constant thermal boundary conditions. The powder height is measured by means of an optical sensor, which avoids stress on the powder and allows fast data. acquisition. This paper discusses experiments conducted with this apparatus and further compares the obtained results with theoretical models and the previous work of others.
Selective Laser Sintering of Zirconia with Micro-Scale Features
(1999) Harlan, Nicole; Park, Seok-Min; Bourell, David L.; Beaman, Joseph J.
Recent work in Selective Laser Sintering of ceramics at the University of Texas at Austin demonstrates the capability to produce zirconia parts with fine features. Zirconia powder was pre-processed into spherical particles, laser sintered with a sacrificial polymer binder, infiltrated and post-sintered to higher density. Optical micrographs show that hole sizes of 180 /-tm are possible in fully ceramic components.
Si/SiC-Ceramic Prototypes via LS2I-Process (Liquid Silicon Infiltration of Laser Sintered C-SiC Parts)
(1998) Stierlen, Peter; Eyerer, Peter
The liquid silicon infiltration of laser sinteredC-~iC parts (LS2 I) is solidfreeform fabrication technique which allows the production of complexshapedSi/SiC prototypes. A mixture of SiC powder and reactive polymer binder isused in the las~r sinteringprocessto generate a porous green part. In the\postprocessing, the porous green part structure has to be infiltrated with a.precursor·resin, carbonised and finally·.infiltrated•. with molten silicon. The infiltrated silicon reacts with the residualcarbontobuild~~SiC.Results generated by the use of reduced primary particle sizes as well asaltemative infiltration materials and the use of other·RPtechniquesfor the green partfabrication will be discussed in this paper.
Direct Laser Fabrication of High Performance Metal Components Via SLS/HIP
(1999) Wohlert, Martin; Das, Suman; Beaman, Joseph J.; Bourell, David L.
Recent research in the area of direct freeform fabrication of components via selective laser sintering/hot isostatic pressing (SLS/HIP) has focused on the processing of Alloy 625. Alloy 625 is a nickel-based superalloy which provides high temperature strength and corrosion resistance. Alloy 625 test specimens were successfully SLS processed with an integral gas impenneable skin or "can". These samples were subsequently HIPed to high density (>99.5%). Characterization of the test specimens indicated that microstructures similar to conventionally processed P/M materials are achieved in the HIP consolidated "core" region ofthe parts, while structures similar to those found in cast materials are present in the SLS processed "can" regions. Mechanical analysis of Alloy 625 SLS/HIP parts and production of complex structures will commence shortly.
Selective Laser Sintering of Stainless Steel 314S HC Processed Using Room Temperature Powder Beds
(1999) Hauser, C.; Childs, T.H.C.; Dalgamo, K.W.
Metal powder bed pre-heating is a proposed route for the homogenisation of temperature gradients that can otherwise cause individual layer warping and cracking in direct metal Selective Laser Sintering (SLS). However, the high temperatures involved complicate a relatively simple process. This paper reports on the conditions for successful small scale SLS of binderless stainless steel 314S powders within the surrounds of a room temperature powder bed. Results show that a scan length around 15.0mm and a scan spacing around 0.275mm produce sintered layers showing no signs of warping. Experimentation also indicates that single layer shape. effects warping but length oflayer propagation does not.
Atmospheric Control during Direct Selective Laser Sintering of Stainless Steel 314S Powder
(1999) Hauser, C.; Childs, T.H.C.; Dalgarno, K.W.; Eane, R.B.
Stainless steel grade 314S powders have been Selective Laser Sintered (SLS) in three different argon/air (oxygen) atmospheric mixtures. The amount of oxygen present during the heating, melting and fusing of the metal powder strongly limits the range of laser powers and scanning speeds for successful processing. As oxygen levels diminish, powder oxidation reduces. This reduces absorption of laser energy as well as balling and other detrimental surface phenomena. This paper reports the conditions for creating sintered layers and observations of part quality variation within these conditions. Sintered microstructure observations are also helpful in determining thermal history changes.
Optimization of Powder Layer Density in Selective Laser Sintering
(1999) Karapatis, N.P.; Egger, G.; Gygax, P.E.; Glardon, R,
An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shownthatthe control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose ofthis study. is to determine if,and to what extent, the density of thin powder layers can be ineteased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder,/with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant.

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