2000 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/73461

Proceedings for the 2000 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Eleventh Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 8-10, 2000, was attended by over 100 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. 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 chairs, 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 (N00014-00-1-0674) and the National Science Foundation (DMI-0003777) 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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2000 International Solid Freeform Fabrication Symposium Table of Contents
(2000) Laboratory for Freeform Fabrication and University of Texas at Austin
2000 Preface
(2000) International Solid Freeform Fabrication Symposium
Accuracy Effects of Shelling a Part in the SLS Process 306
(2000) Volpato, Neri; Childs, Thomas H.C.; Pennington, Alan de
In order to reduce SLS process time in the manufacture of a mould insert, the idea of shelling the geometry of the insert has been tested. Some shelling strategies have been successful with the RapidToolTM process, proving the feasibility of the idea. It has been observed in the tests, for both polymer and RapidSteel2.0TM materials, that size accuracy, particularly of small features in the scanning (X) direction, depends on vector length (VL). When a sudden change in VL occurs, this leads to steps on the sintered surface. This paper presents both experimental observations of this and simulation results from a finite element model.
Adaptive Slicing With the Sanders Prototype Inkjet Modeling System 259
(2000) Unnanon, Kittnan; Cormier, Denis; Sanii, Ezat
This paper presents one of the first known in depth studies of the Sanders Prototype inkjet modeling process. A process capability study was performed in order to determine the relationship between process parameter levels and the resulting surface roughness. The data was used to create a predictive model of surface roughness using a backpropagation neural network. Test results indicate that the network is quite effective at generalizing to new process configurations. The predictive surface roughness model is used in a newly developed inkjet modeling adaptive slicing algorithm. On a region-by-region basis, the algorithm determines the fastest machine configuration that can be used to build a part while satisfying the surface roughness requirements. The adaptive slicing system has been tested, and results documenting substantial time and cost savings are presented.
Advanced Sheet Metal Manufacturing using Rapid Tooling 522
(2000) Hui, Du Zhao; Kai, Chua Chee; Sen, Chua Yew; Gek, Loh-Lee Keow; Tiak, Lim Ser
A closed loop process is proposed for making sheet metal prototyping parts by using advanced computer aided techniques and computer controlled machines. The key aspect of this process is the method used to fabricate and modify the sheet metal forming tools, which are not necessarily for mass production but should be suitable for short run production or design evaluation of sheet metal products where the prototyping cost and lead-time are greatly reduced. Various approaches are investigated in the preparation of the tooling for onward embossing on a sheet metal. The three indirect approaches use Selective Laser Sintering (SLS), Stereolithography(SLA), and high speed Computer Numerical Controlled (CNC) milling to build the masters from computer data models. And the masters are then served in the vacuum casting process to generate the non-ferrous tooling. The direct approach uses DTM’s RapidSteel to produce the metal tooling without going through any secondary process. Comparisons on quality, leading time and cost are presented.
Anatomical Modeling and Rapid Prototyping Assisted Surgical Reconstruction 555
(2000) Jiang, T.; Lin, F.; Kaltman, Steven I.; Sun, W.
A CAD-based approach to generate three-dimensional anatomical modeling and its application in analysis and rapid prototyping for surgical reconstruction is presented. The process of modeling technique, starting from processing computed tomography segmentation profiles, reverse engineering to reconstruct 3D anatomical model, and rapid prototyping to fabricate physical models are described. Methods of applying the least-square fitting criteria to simplify CT or MRI anatomical data, to generate NURBS based curves, surfaces, and solids, and to develop a CAD-based anatomical modeling for femur are introduced. Feasibility of using finite element method for femur structural analysis and using rapid prototyping to reproduce tactical medical model for surgical reconstruction is also discussed.
Applications of Powder Densification Maps to Direct Metal SLS/HIP Processing
(2000) Wohlert, Martin; Bourell, David L.; Das, Suman; Beaman, Joseph J.
Recent investigations have shown that Direct Selective Laser Sintering in conjunction with Hot Isostatic Pressing (HIP) is capable of producing fully dense, near net shape, high performance metal components. A key aspect of this combined processing method is the selection of appropriate HIP process parameters to obtain full density parts. Powder Densification Maps provide a powerful tool for predicting the effect of time, temperature, pressure, and material properties on part density. This paper summarizes developments in Powder Densification Map production for Ti-6Al-4V and Inconel 625 materials. A comparison of theoretically predicted and experimentally determined densities for a variety of processing conditions is presented.
Characterization of Mechanically Alloyed Polymer Blends for Selective Laser Sintering 92
(2000) Martin, Julie P.; Kander, Ronald G.
Cryogenic mechanical alloying (CMA) is presented in this work as an effective technique for creating materials for selective laser sintering (SLS) applications. CMA offers a solid state method for creating micro-composites consisting of finely dispersed phases, which can then be selectively laser sintered into parts containing co-continuous phases. Particle size and shape, microstructure, and melting characteristics of mechanically alloyed particles are discussed in terms of applications to the SLS process. The characteristics of several model polymer blend systems are investigated using scanning electron microscopy, light scattering particle size analysis, and differential scanning calorimetry. Although only polymer/polymer blend particles are studied here, the CMA process is also a viable technique for creating SLS powders using ceramics or metals.
Characterization of Polyolefin – Alumina compounded mix for FDC processing
(2000) Bhat, V.V.; Geetha, K.; Das, R.N.; Gurumoorthy, B.; Umarji, A.M.
Fused deposition of ceramics (FDC) uses thermoplastic binder and ceramic blend as feed material. The geometry of the fused deposition machine restricts the workability of the FDC feed material, which is in the form of a filament. The feasibility of the usage of these filaments is mainly based on the viscosity at the working temperature and the compressive modulus of the feed material at near room temperature. The polymers based on Polyethylene (PE), having two molecular weights 3,000 (LDWAX) and 341,000 (LDPE) were mixed in various weight proportions by solvent method using toluene as solvent, to develop a binder system for Fused Deposition Modeling of alumina. Variation of viscosity as a function of composition, temperature and solid loading was measured using spindle viscometer and capillary rheometer. Dilatometric thermal expansion of 50 Vol% alumina compounded binders is measured up to 120°C. The pronounced softening of the compounded mixture is observed beyond 70°C, when the volume % of LDWAX is in excess of 50% total binder content. The compression strength decreases from 720 N to 310 N for pellet having 1.2cm diameter and 1.5 aspect ratio, when the percentage of LDWAX varies from 40 to 70% in the binder composition. The suitability of the compounded mix of LDWAX and LDPE binder with 40 Vol. % alumina for FDC is being evaluated in a StratasysTM1600 machine.
Colour Rapid Prototyping Based on SLS Process 227
(2000) Ming, Ling Wai; Gibson, Ian
Currently, the colour of parts made by the Selective Laser Sintering (SLS) process depends on the colour of the material used. SLS cannot make multiple coloured prototypes because only homogeneous powder (or powder composites) can be used during the process. In this paper, an ink-jet based mechanism is designed to print multiple colours onto the prototypes. The surface tension of conventional ink used in bubble jet printers is so high that it cannot penetrate into the SLS powders. To reduce the surface tension, ethanol is added to it. The ratio of ink to ethanol for necessary penetration is determined by experiments. This paper will go on to describe how the ink affects the structure of SLS materials. The effect of temperature on the penetration of ink into powders will also be discussed.
Conformal Cooling and Heating Channels using Laser Sintered Tools 490
(2000) Hopkinson, Neil; Dickens, Phill
The EOS Direct Metal Laser Sintering (DMLS) and DTM Rapid Steel 2 processes may be used to create tools incorporating conformal channels behind the tool surface through which fluids may be passed. To date, a significant amount of work has been carried out to investigate the efficiency of using conformal channels to cool tools. This work suggests the use of conformal channels to both cool and heat a single tool. This may appear self-defeating at first but the selective nature by which conformal channels may make this a worthwhile means of generating hitherto unavailable thermal conditions within a tool. Such conditions may then allow the successful production of geometries which had previously been impossible to mould.
Designing and Slicing Heterogeneous Components for Rapid Prototyping 428
(2000) kumar, Ashok V.; Lee, Jongho
Many rapid prototyping techniques have the potential for fabricating components whose composition is non-uniform and varies in a desired fashion. A shape and composition modeling technique was developed to enable the representation and design of such heterogeneous components. Techniques for interactively and automatically designing such components are presented. Automatic design is made possible using optimization techniques where the optimal composition distribution is computed based on specified design objective and constraints. Software was also developed to slice 3D heterogeneous solids to generate cross-sectional images as well as composition distribution for each cross-section. Slicing and generation of cross-sectional data are essential to enable rapid prototyping of these components.
Determination and Improvement of Building Speed in Rapid Freeze Prototyping 514
(2000) Zhang, Wei; Sui, Guanghua; Leu, Ming C.
Rapid freeze prototyping (RFP) is a solid freeform fabrication process that builds an ice part by rapidly freezing water in a layer by layer manner. One advantage of this process is the ability to build ice parts faster than other SFF processes. The factors that affect the speed of contour building and interior filling in RFP are identified. The influence of these factors is analyzed through heat transfer and material flow analyses. A model based on heat transfer analysis is proposed to determine the maximum achievable speed of contour building under stable conditions. Experiments are conducted to validate the performance of the proposed model for determination of building speed.
Development of A Precision Rapid Metal Forming Process 362
(2000) Liou, F.W.; Zhang, J.; Agarwal, S.; Laeng, J.; Stewart, J.
This paper presents the important issues pertaining to the development of a precision rapid metal forming process. A five-axis configuration provides a flexible building capability to produce free-form fabrication capability. The laser cladding process is able to produce functional mechanical parts and machining capability is able to produce industrial grade surface quality. A machine configuration that combines the laser cladding and CNC machining processes is presented. The related parameters and components are discussed.
Development of Freeform Master I – a Desktop RP Machine Based on a New Sheet Lamination Process 283
(2000) Lee, Kwan H.; Park, Joung O.
A novel process was developed for building Rapid Prototyping(RP) parts using a sheet lamination technique. The building process of existing sheet lamination RP machines consist of the following steps : feeding, lamination and cutting. In this process, the laminated part of an object is often scratched by a cutter or damaged by a laser beam due to the cutting operation after the lamination step. In addition, decubing of the unused portion from the laminated block is difficult. In the new process, however, cutting is performed before lamination. The cutting operation takes place while a paper sheet is firmly attached, using electrostatic force on the plate. Then liquid glue is applied only to the calculated region of the given contour for lamination. This new process aims to manufacture a $2k RP machine, what we call the Freeform Master I and can use A4 size or letter size sheets of paper. A prototyping machine that demonstrates the concept design was built and further research issues are discussed
Die Reconfiguration and Restoration Using Laser-Based Deposition 219
(2000) Skszek, Tim; Lowney, M.T.J.
POM Company, Inc., located in Plymouth, Mich., has successfully commercialized the laser-based, free form fabrication process known as DMD,™ or Direct Metal Deposition. Since the company incorporated in 1998, POM has been directed towards the commercialization of the DMD process equipment, and the demonstration of value-added, cost-effective applications specific to the fabrication, repair and reconfiguration of plastic injection molds and die cast tooling. POM currently operates as a service bureau and original equipment manufacturer (OEM), providing engineering analysis, design and fabrication services, as well as the sale of DMD process equipment. An overview of the POM closed-loop, laser-based DMD process, available services and several case study applications are presented.
Discrete Multi-Material Selective Laser Sintering (M2 SLS): Development for an Application in Complex Sand Casting Core Arrays
(2000) Jackson, Brad; Wood, Kris; Beaman, Joseph J.
Conventional sand casting processes often take many weeks or months to produce the tooling required for a casting, in particular the fabrication of sand core arrays for hollow features in a casting. SLS is already being applied to produce complex sand core geometries and reduce production times, but a new development of discretely laying down two different materials and removing one after sintering will allow even more complex geometries and drastically decrease the production times of sand cores. Two of the most significant problems in the current use of SLS for sand cores are the mechanical removal of unsintered powder and damage during part breakout. The second discrete material serves as a support medium through the build and fabrication of the sand core and is removed before casting; the sacrificial second material increases green strength and eliminates time consuming post-processing. The development and plan for implementation of the discrete M2 SLS process is presented.
Effects of Cu and SiO2 on Laser Sintering of Polycarbonate 110
(2000) Fan, K.M.; Cheung, W.L.
Additives of different thermal properties, Cu and SiO2 (amorphous and crystalline), were blended to polycarbonate (PC) powder to modify its heat transfer properties and fusion behavior during laser sintering. The blends were sintered under different energy densities of the laser beam to produce mono-layer films. The surface morphology and the thickness of the films were studied. When sintering under the same condition, the composite films which contained a high content of Cu powder exhibited a more porous surface structure. This was caused by the increased heat loss because the Cu powder has a higher thermal conductivity. Also, the solid Cu particles would hinder the flow of the molten polymer, resulting in a low degree of fusion. For a given Cu powder content, reducing its particle size gave a more porous surface structure and a smaller thickness of the sintered films. This was probably due to a more even distribution of the fine Cu particles, which increased the heat loss and reduced the effective amount of energy for fusion. On the other hand, fine SiO2 and quartz powders caused degradation of the polymer because of the increased energy dissipation near the film surface and poor heat transfer properties of the additives comparing with Cu.
Embedding of Fiber Optic Sensors in Layered Manufacturing 314
(2000) Li, Xiaochun; Prinz, Fritz B.
Layered manufacturing enables integrating sensors during production of tooling or structural components. Sensors may be placed close to the points of interest prior to enclosure. Structures with embedded sensors are capable of monitoring parameters at critical locations not accessible to ordinary sensors. This work presents a methodology for embedding fiber optic sensors in metallic structures via Shape Deposition Manufacturing. Some of the main manufacturing issues are discussed. Embedded fiber optic sensors have been employed to measure temperature and strain. Proof-of-concept experiments on a non-contact fiber optic sensing system have been performed. By implementing the remote sensing system it is possible to measure temperature and strain of rotating components exposed to potentially hostile environments such as blades in gas turbine engines.
Evaluation of Microstructure and Properties for Multi-Materials Laser Densification of Dental Restoration 159
(2000) Li, Xiaoxuan; Crocker, James E.; Geiss, Erik; Shaw, Leon L.; Marcus, Harris L.; Cameron, Thomas B.
Traditional dental restorations are produced by the porcelain-fused-to-metal (PFM) process, in which a dental restoration is cast from a metallic alloy and then covered with dental porcelains by several firing processes, which is both labor intensive and expensive. In this paper, the feasibility of dental restorations is investigated using a multi-materials laser densification (MMLD) process. To evaluate the effectiveness of the MMLD process, nickel powders and commercial dental porcelain powders are laser densified using YAG and CO2 lasers respectively. Effects of processing parameters, e.g. laser scanning rate and target temperature, are evaluated and the microstructure of processed nickel and porcelain materials are characterized for the optimization of laser densification. Results indicate that densities of laser processed nickel and dental porcelain are strongly dependent of processing parameters. Fully dense layers are achievable with proper processing conditions.

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