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spring 1997 logo1997 MRS Spring Meeting & Exhibit

March 31 - April 4, 1997 | San Francisco
Meeting Chairs: Linda G. Griffith-Cima, David J. Eaglesham, Alexander H. King

Symposium U—Rapid Prototyping and Solid Freeform Manufacturing


Michael Cima 
Dept of MS&E 
Rm 12-011 
Cambridge, MA 02139 

Stephen Danforth
Cntr for Ceramic Research
Rutgers Univ
Brett & Bowser Rds

Harris Marcus 
Inst of Matls Sci 
Univ of Connecticut 
Storrs, CT 06269-3136 

In sessions below "*" indicates an invited paper.

Chair: Harris L. Marcus
Monday Morning, March 31, 1997
Salon 10

8:30 AM U1.1 
NOVEL METHODS OF SOLID FREEFORM FABRICATION FOR CERAMICS, Mohan J. Edirisinghe, Brunel Univ, Dept of Materials Engr, Uxbridge Middlesex, UNITED KINGDOM.

Recent developments in solid freeform fabrication of ceramics in this laboratory involve the use of the jet printer. The success of direct jet printing is dependent crucially on the preparation of a suitable ceramic ink and work in this area is described. The inks have been used in a pressurized continuous jet printer and a conventional drop-on-demand inkjet printer with an unpressurized reservoir to deposit ceramic materials. Small droplets of ceramic ink (3 m) have also been created by electrostatic atomization which will lead eventually to particle-by-particle deposition of ceramics.

9:00 AM U1.2 
STRUCTURAL CERAMICS FABRICATED BY 3-DIMENSIONAL PRINTING, Jason Grau, Jooho Moon, Michael J. Cima, MIT, Dept of MS&E, Cambridge, MA.

Alumina components have been fabricated successfully using a modified method of the 3-Dimensional Printing (3DP) process. Numerous challenges have been addressed to fabricate structural ceramic components via 3DP. Powder bed generation and part retrieval have been significant obstacles for fabricating structural ceramic components. Alumina powder beds have been generated using various wet processing techniques: I) Spraying down slurry, 2) Multiple-layer tape casting, and 3) Printing slurry through a nozzle. High and uniform packing density () is possible by these methods. The powder bed microstructure can be controlled by the slurry chemistry and deposition process. Resolution of components is improved substantially over the standard 3DP process as layer thicknesses can be reduced to 10 m. Pan retrieval from cohesive powder beds has been accomplished by redispersing the powder bed in water. The extent to which the powder bed redisperses has been characterized with respect to chemistry, pore structure, strength, and colloidal stability. This process can be easily adapted to other materials systems and provides the capability to produce 3-dimensional control over composition.

9:30 AM U1.3 
"ROBOCASTING": DIRECT FABRICATION OF CERAMICS FROM COLLOIDAL SUSPENSIONS, Joseph Cesarano, Sandia National Laboratories, Dept of Direct Fabrication Technologies, Albuquerque, NM; Paul Calvert, Univ of Arizona, Dept of MS&E, Tucson, AZ.

A technique has been developed for the freeform fabrication of dense ceramics. The "Robocast" process uses computer aided deposition of highly concentrated colloidal slurries to directly form complicated shapes without the use of molds or containers. Any conceivable two-dimensional pattern may be "written" layer by layer into a three-dimensional shape. Colloidal slurries containing upwards of 50 vol% solids are dispensed through the orifice of a piston driven syringe. Upon drying, green density is routinely greater than 60%. Crackfree alumina components have sintered densities greater than 95%. Using the Robocast process: components may be fabricated into bulk solids with large thicknesses unobtainable using slip casting; or, thin walled pieces made with aspect ratios greater than 20 and wall thicknesses less than 1 mm. A description of the process will be presented and the relations between slurry rheology and deposition behavior will be discussed.

10:00 AM U1.4 
DEVELOPMENT AND PROCESS OPTIMIZATION OF FUSED DEPOSITION OF CERAMICS FOR STRUCTURAL SILICON NITRIDE COMPONENTS, A. Bandyopadhyay, C. Dai, G. Qi, Rutgers Univ, Cntr for Ceramic Research, Piscataway, NJ; M. Agarwala, Univ of Dayton, Research Inst, Dayton, OH; S. Rangarajan, A. Safari, Rutgers Univ, Cntr for Ceramic Research, Piscataway, NJ; N. Langrana, Rutgers Univ, Dept of Mech & Aerospace Engr, Piscataway, NJ; Stephen C. Danforth, Rutgers Univ, Cntr for Ceramic Research, Piscataway, NJ; V. Jamalabad, R. van Weeren, P. J. Whalen, AlliedSignal, Morristown, NJ.

Fused Deposition of Ceramics (FDC) is an SFF technique based on commercial FDM technology to produce functional quality ceramic components. Thermoplastic polymer filaments loaded with 50 to 60 volume ceramic particles are used as a feed material for this process. Green ceramic objects that are produced by FDC need post processing such as binder burn out and sintering. The FDC process is being developed for functional quality silicon nitride parts. GS 44 silicon nitride powders (Allied Signal, Torrance, CA) were compounded with various thermoplastic binders and extruded through a single screw extruder to produce 0.070 0.001 diameter green ceramic filaments as the feed stock for FDC. Various FD parameters were studied and optimized to produce nearly defect free green ceramic parts. These parts were subjected to a multistage binder burn out cycle to remove the binder and then sintered. Microstructural characterization of FDC processed silicon nitride parts reveals microstructures similar to conventionally processed GS 44 silicon nitride ceramics. Room temperature four point bend flexural strengths and fracture toughness of FDC processed silicon nitride bars were also evaluated. In this presentation, process development and optimization of structural and functional silicon nitride components with simple and complex shapes will be discussed.

11:00 AM U1.5 
DIRECT WRITE FABRICATION OF HIGHLY INTEGRATED MULTILAYER CERAMIC COMPONENTS, Duane Dimos, Mark V. Raymond, Pin Yang, Sandia National Laboratories, Albuquerque, NM.

The need for advanced (electronic) ceramic components with smaller size, greater functionality, and enhanced reliability requires the ability to integrate various materials in complex 3-D architectures. While tape casting and screen printing techniques have been used to fabricate such multifunctional, multimaterial components, this approach is poorly suited to rapid prototyping and small-lot manufacturing of custom components. To address this need, we are developing a micropen direct write approach for fabricating highly integrated, multilayer components. The micropen technique can be used to build components layer by layer, which can simplify fabrication, and is compatible with a wide variety of thick-film materials. It can also be used to produce relatively novel structures, such as those combining several materials in a single layer, by depositing ceramic slurries in precise patterns. We are currently using this technique to fabricate devices such as miniature solid-state RCL networks and dc-dc converters. Micropen writing is also being combined with tape processing to develop a flexible hybrid integration scheme for LTCC packages and for customizing commercial surface mount components. The parts are consolidated either by cofiring or by sequential firing after each layer of material(s) is deposited. However, differential shrinkage and chemical reactions between materials during firing, especially cofiring, remain critical issues which will also be discussed along with geometries and performance of devices. This work was performed at Sandia National Laboratories and supported by the US Dept. of Energy under contract No. DE-ACO4-94AL8500.

11:30 AM U1.6 
3-DIMENSIONAL PRINTING APPLICATIONS AND NEW MATERIALS DEVELOPMENTS, Michael J. Cima, Jason Grau, Jooho Moon, MIT, Dept of MS&E, Cambridge, MA; Ben Wu, Jaedok Yoo, Robert Palazzolo, MIT, Cambridge, MA.

Three-dimensional printing (3DP) has seen rapid development in several areas. 3DP is now being used to produce ceramic filters for hot gas filtration, investment casting shells and cores, rapid metal tooling, facsimile prototypes, and drug delivery devices. 3DP is being scaled-up to capitalize on rapid, flexible manufacturing capabilities. Novel components can be manufactured that cannot be produced by traditional methods. Progress in functionally-graded materials (FGMs) has been realized in many of these applications. New printing techniques make it possible to control composition and microstructure on a 3-dimensional scale. Zirconia-toughened alumina FGMs were fabricated with controlled residual stress distributions. Microstructure, strength, and toughness were controlled by selectively doping the components. Another application is the fabrication of drug delivery devices with spatially arranged micro reservoirs, each loaded with varying composition and concentration of drugs. Highly reproducible release profiles have been achieved with 3D- printed pharmaceutical oral dosage forms.

Chair: Michael J. Cima
Monday Afternoon, March 31, 1997
Salon 10

1:30 PM *U2.1 
LASER RAPID PROTOTYPING DIRECTLY FROM THE GAS PHASE, Michael Stuke, Olaf Lehmann, Michael Wanke, Max-Planck-Inst, Dept of Biophysic Chemistry, Gottingen, GERMANY.

Using Laser Chemical Vapor Deposition with two suitably overlapping beams, complex three-dimensional microstructures can be written directly with presently sub 10 m precision and writing speeds exceeding 80 m/sec. Examples will be presented for electrically/thermally isolating and conducting microstructures for applications such as: (a) microoptics for charged particles [1], 
(b) laser driven micromotor [2], 
(c) photonic bandgap structures. 
An outlook to future possibilities and challenges will be given.

2:00 PM U2.2 
SALD AND SALDVI GAS PHASE SFF, Kevin Jakubenas, Harris L. Marcus, Shay Harrison, James Crocker, Christopher Costa, Univ of Connecticut, Inst of Matls Sci, Storrs, CT; J. Sanchez, Univ of Texas-Austin, Ctr for MS&E, Austin, TX.

Gas phase precursors for use in solid freeform fabrication have been studied over the last few years. This paper will describe the latest results obtained using SALD and SALDVI approaches to making shapes out of a variety of materials including SiN, SiC, TiO, SiO and Co. The discussion will include various experimental and modeling approaches that were used to further the development of the gas phase approaches.

2:30 PM U2.3 
REAL-TIME GROWTH RATE CONTROL FOR 3-D LCVD OF WALL STRUCTURES, Joseph Pegna, David V. Messia, Woo Ho Lee, David D. DeAngelis, Rensselaer Polytechnic Inst, Center for Integrated Electronics & Electronics Mfg, Troy, NY; James L. Maxwell, Louisiana Tech Univ, Dept of Mech & Industrial Engr, Ruston, LA.

A method for controlling the reaction rate during laser induced chemical vapor deposition was employed to grow a series of three-dimensional rods and wall structures. The specific emission spectra generated during the heterogeneous reaction was used to extract a measure of the volumetric growth rate. This rate measure was fed back to a control software so as to modulate the laser power and scanning velocity in real time. High aspect ratio axi-symmetric forms and panels were grown from vapor phase precursors using this technique. Materials deployed include pyrolytic graphite, nickel, iron, and nickel-iron alloys. Respective precursors were ethylene, nickel tetracarbonyls, iron pentacarbonyls and a mixture of the latter two.

3:00 PM U2.4 
FLOW, CURING AND PROCESSING KINETICS IN THE EXTRUSION FREEFORM FABRICATION OF POLYMERS, Paul Calvert, Univ of Arizona, Dept of MS&E, Tucson, AZ; Robert Crockett, Univ of Arizona, Arizona Matls Labs, Tucson, AZ.

Extrusion freeform fabrication is a 3-D layerwise writing technique for forming objects directly under the control of a CAD program. A fine needle extrudes a stream of material which forms a linear bead on the substrate. Good resolution depends on limited flow of the beads as they merge to form layers, and the layers are stacked to form a solid. Good mechanical strength depends on good bonding between beads and between layers, An analysis is presented for shape control in a viscous or thixotropic slurry, considering the balance between viscous flow and surface tension. The control of cure is discussed for liquid monomers under conditions where polymerization proceeds rapidly during deposition. For addition polymers, thermal runaway is an important limiting factor on the accessible rate of polymerization. Oxygen inhibition of free radical polymerizations depends on the presence or absence of a surface skin.

4:00 PM U2.5 
MODELING OF MICROSTRUCTURAL EVOLUTION DURING LASER ENGINEERED NETSHAPING, Veena Tikare, Sandia National Laboratories, Dept of Theoretical & Computational Matls Sci, Albuquerque, NM; Michelle L. Griffith, Sandia National Laboratories, Dept of Adv Manufacturing, Albuquerque, NM; David M. Keicher, Sandia National Laboratories, Dept of Direct Fabrication Tech, Albuquerque, NM.

Laser Engineered NetShaping, LENS, is an advanced manufac- turing Technology which can be used to fabricate complex shapes from a variety of metals. The resulting microstructures of LENS components are unique due to the novel fabrication method and depend on the solidification of the small regions and the microstructural evolution of the solidified regions during cooling to ambient temperature. In this paper, we will present a technique to simulate the microstructural evolution of LENS components during processing. The Potts model, a statistical-mechanical model that has been used extensively to simulate a variety of microstructural evolution processes, will be modified to accommodate the LENS processing parameters. Specifically, the solidification of small amounts of materials in a complex, non-linear temperature field bounded by grains of particular crystallo- graphic orientation under and adjacent to the solidifying region. Simulated microstructures will be compared to those in real LENS components.

4:30 PM U2.6 
ADVANCED MATERIALS FOR FABRICATING COMPLEX SHAPES USING THE LASER ENGINEERED NET SHAPING (LENS) PROCESS, Michelle L. Griffith, Sandia National Laboratories, Dept of Adv Manufacturing, Albuquerque, NM; L. D. Harwell, Sandia National Laboratories, Alberquerque, NM; David M. Keicher, Sandia National Laboratories, Dept of Direct Fabrication Tech, Albuquerque, NM; J. A. Romero, J. E. Smugeresky, Sandia National Laboratories, Albuquerque, NM.

Solid Freeform Fabrication (SFF) is one of the fastest growing automated manufacturing technologies which has significantly impacted the length of time between initial concept and actual part fabrication. This paper will describe recent developments in the LENS (Laser Engineered Net Shaping) process, to fabricate metal components directly from CAD solid models and thus further reduce the lead times for metal part fabrication. As with other SFF techniques, the LENS process builds metal path line by line and layer by layer. Metal particles are injected into a laser beam where they are melted and deposited onto a substrate as a miniature weld pool. The trace of the laser beam on the substrate is driven by the definition of CAD models until the desired net-shaped densified metal component is produced. The LENS process results in excellent materials' properties for homogeneous processed materials. However, there are many applications for graded material components for which the LENS process is well suited. Results with graded materials will be discussed in terms of controlling their microstructure, where spatial control of the deposition is important. Processing conditions, including powder flow methods and rates, for a candidate material system will be determined to obtain high quality parts with good material properties.

Chair: Stephen C. Danforth
Tuesday Morning, April 1, 1997
Salon 10

8:30 AM U3.1 
PROCESSING OF ADVANCED COMPOSITE MATERIALS BY LAMINATED OBJECT MANUFACTURING (LOM), Donald A. Klosterman, Richard Chartoff, Brian Priore, Nora Osborne, George Graves, Univ of Dayton, RPD Lab, Dayton, OH; Jerry Weaver, Jerico Co, Templeton, MA.

Laminated Object Manufacturing (LOM) is an established Solid Freeform Fabrication method that is used to create solid prototypes by sequentially laminating and cutting layers of paper bonded by an adhesive. This report provides a description of how LOM is being extended for the production of functional advanced composite laminates. Several material systems have been examined, including thermoset and thermoplastic polymer matrix composites (PMCs) and ceramic matrix composites (CMCs). The feasibility of processing with these materials has been established. However, one of the primary challenges, which will be addressed in this report, involves the post-LOM processing of these parts, e.g., ceramic densification, polymer post cure. The key goal is to obtain a final part that exhibits maximum layer compaction/bonding, minimum shape distortion, the desired microstructure, and maximum mechanical properties. The traditional processing techniques for obtaining PMCs and CMCs are not applicable for most LOM parts due to their inherent geometrical complexity. Therefore, in order to achieve success in the overall process, it is necessary to innovate and coordinate several new techniques that are employed during various steps in the processing cycle. This multidisciplinary effort will be described in detail during the presentation.

9:00 AM U3.2 
BINDER-POWDER BED INTERACTIONS IN THE SLURRY-BASED 3-DIMENSIONAL PRINTING PROCESS, Jooho Moon, Jason Grau, MIT, Dept of MS&E, Cambridge, MA; Peter J. Baker, Michael Caradonna, MIT, Dept of Mech Engr, Cambridge, MA; Michael J. Cima, MIT, Dept of MS&E, Cambridge, MA.

The binder system for slurry-based 3-Dimensional Printing (3DP) process has been developed. Unbound loose powders are easily removed by brushing in the conventional dry powder-based 3DP process. The slurry-based process, in contrast, produces a rigid unbound powder matrix which must be removed from the part by redispersion in water. Several binder system types are compared in terms of binding mechanism, strength, and burnout behavior. In addition, interaction between binder and powder bed in both continuous-stream (CS) and drop-on-demand (DOD) inkjet printings is investigated. Properties of binder system and powder bed characteristics, such as binder viscosity, contact angle, and powder bed particle size have a significant influence on binder primitive formation and subsequently on resolution of 3DP parts.

10:00 AM U3.4 
CHARACTERIZATION OF THE LASER-ENGINEERED NET SHAPING (LENS) PROCESS FOR OPTIMIZATION OF SURFACE FINISH AND MICROSTRUCTURAL PROPERTIES, David M. Keicher, Sandia National Laboratories, Dept of Direct Fabrication Tech, Albuquerque, NM; J. E. Smugeresky, J. A. Romero, Sandia National Laboratories, Livermore, CA; Michelle L. Griffith, Sandia National Laboratories, Dept of Adv Manufacturing, Albuquerque, NM; L. D. Harwell, Sandia National Laboratories, Alberquerque, NM.

Rapid prototyping techniques have revolutionized the approach to fabricating geometrically complex hardware from a CAD solid model . These techniques allow component designers to directly fabricate conceptual models in plastics and polymer coated metals; however, each of these techniques requires additional post processing to allow the fabrication of functional metallic hardware. This limitation has provided the impetus for further development of freeform fabrication techniques which enable fabrication of functional metallic hardware directly from the CAD solid model. The Laser Engineered Net Shaping (LENS) process holds promise in satisfying this need. This newly emerging technology possesses the capability to fabricate fully dense components with good dimensional accuracy and with unique material properties. Relatively complex geometrical shapes have been fabricated using this technology. In continuing to develop the LENS process, further advancements are required. The functional dependence of the component surface finish and microstructural characteristics on process parameters including powder size and size distribution are being characterized. A set of statistically designed experiments is being used to sort through the various process parameters and identify significant process variables for improving surface finish and achieving optimum material microstructural properties. As part of this study, infrared imaging has been used to measure thermal gradients in the deposited materials during processing and high speed photography has been used to observe the deposition process. Thermal characteristics were measured to quantify quench rates during processing and then correlated to the material microstructure.

11:00 AM U3.5 
EXTRUSION FREEFORM FABRICATION OF FIBER-REINFORCED EPOXY RESINS, Paul Calvert, Univ of Arizona, Dept of MS&E, Tucson, AZ; Graeme George, Llew Rintoul, Queensland Univ of Technology, Dept of Chemistry, Brisbane, AUSTRALIA.

Extrusion freeform fabrication is a 3-D layerwise writing technique for forming objects directly under the control of a CAD program. A fine needle extrudes a stream of MY720/DDS resin at 90C with up to 30 wt of chopped carbon fiber. The substrate is held at 150C in order to initiate curing during the writing process. Test bars have been formed and measured in 3-point bend. A series of bilayer bars have also been formed with an upper reinforced surface and a lower unreinforced surface. The potential for the use of reinforcement distribution for the optimization of properties will be discussed. Epoxy blocks have also been freeformed with embedded optical silica fiber sensors. Monitoring the fiber in the NIR region allows the extent of cure and water uptake to be monitored.

11:30 AM U3.6 
MICROSTRUCTURAL DESIGN AND ANALYSIS OF ELECTRO-MECHANICAL DEVICES, Xianoping Ruan, Univ of Delaware, Dept of Mechanical Engr, Newark, DE; Stephen C. Danforth, A. Safari, Rutgers Univ, Cntr for Ceramic Research, Piscataway, NJ; Tsu-Wei Chou, Univ of Delaware, Dept of Mechanical Engr, Newark, DE.

In recent years, a concerted research effort has been devoted to the development of electromechanical devices. Actuators such as ''moonie'' and ''rainbow'' are the notable examples. The processing of such electromechanical composites is a highly challenging task. At Rutgers University, a solid freeform fabrication (SFF) process coupled with CAD/CAM manufacturing system techniques is being developed for fabrication of net shape components with high dimensional accuracy and functional engineering properties This manufacturing system will enable fabrication of affordable, complex electromechanical devices and, therefore, the development of microstructural models is required to predict the component mechanical response. In this paper, the electromechanical behavior of one type of piezoelectric ceramic-polymer-metal composite actuator has been studied. A unit cell of the composite actuator is identified first, and an analytical model is presented to predict the effective elastic constants, piezoelectric coupling constants, and dielectric constants. A commercially available finite element code (ABAQUS) is used to determine the mechanical response. The results of finite element analysis for the unit cell and the device are obtained and compared. The effect of geometrical changes in the metal, the volume fractions of ceramic and polymer, and the poling direction of the piezoelectric ceramic on the composite actuator response have been identified, and performance map for this composite actuator is presented. It is concluded that a ceramic-metal composite with transversely alternating poling direction exhibits the largest displacement response to a given electric field.