2005 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/79955

Proceedings for the 2005 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Sixteenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 1-3, 2005, was attended by 106 national and international researchers from twelve countries. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. 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 process development, design tools, modeling and control, process parameter optimization, applications and materials. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both those presently involved in this fruitful technical area as well as new researchers and users entering the field.

This year’s best oral presentation was given by Nathan Crane of MIT. Selection is based on the overall quality of the paper, the presentation and discussion at the meeting, the significance of the work and the manuscript submitted to the proceedings. The paper title was, “Improving Accuracy of Powder Sintering-based SFF Processes by Metal Deposition from Nanoparticle Dispersion”. Selected from over 50 oral presentations, his presentation appears on Page 261 of this Proceedings. The best poster presentation selected from 11 posters was given by Kunnayut Eiamsa-ard from the University of Missouri-Rolla. The paper title was, “Part Repair using a Hybrid Manufacturing System” and appears on Page 425.

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 are grateful to Bryan Blackmur and Cindy Pflughoft who helped with Proceedings production. 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 (N00014-05-1-0789) and the National Science Foundation (DMI 0522509) 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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    2005 International Solid Freeform Fabrication Symposium Table of Contents
    (2005) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Nanotailoring Stereolithography Resins for Unique Applications using Carbon Nanotubes
    (2005-08-03) Sandoval, J. H.; Ochoa, L.; Hernandez, A.; Lozoya, O.; Soto, K. F.; Murr, L. E.; Wicker, R. B.
    Nanostructured materials and exploiting their properties in stereolithography (SL) may open new markets for unique rapidly manufactured functional devices. Controlled amounts of multiwalled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and complex three-dimensional (3D) parts were successfully fabricated by means of a multi-material SL setup. The effect of the nanosized filler was evaluated using mechanical testing. Small dispersions of MWCNTs resulted in significant effects on the physical properties of the polymerized resin. A MWCNT concentration of .05 wt% (w/v) in DSM Somos® WaterShed™ 11120 resin increased the ultimate tensile stress and fracture stress an average of 17% and 37%, respectively. Electron microscopy was used to examine the morphology of the nanocomposite and results showed affinity between the MWCNTs and SL resin and identified buckled nanotubes that illustrated strong interfacial bonding. These improved physical properties may provide opportunities for using nanocomposite SL resins in end-use applications. Varying types and concentrations of nanomaterials can be used to tailor existing SL resins for particular applications.
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    The Potential of Freeform Construction Processes
    (2005-09-07) Buswell, R. A.; Soar, R.; Gibb, A.; Thorpe, A.
    The level of automation technology and processes control found in modern day construction lags significantly behind other industries such as automotive and aerospace. The construction industry has health and safety issues and still uses traditional methods of procurement. These problems are compounded by diminishing skills in the labour force. Methods of production must change if these issues are to be resolved and Freeform Construction is a collection of processes that could have potential impact. This paper outlines some of the major issues facing construction and sets a context with examples of digital fabrication in construction. Freeform Construction is defined and potential applications are presented and related to application scale. The viability of two potential applications are investigated in terms of cost.
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    Freeform Fabrication of Ionomeric Polymer-Metal Composite Actuators
    (2005-08-03) Malone, Evan; Lipson, Hod
    Ionomeric polymer-metal composite (IPMC) actuators are a type of soft electromechanically active material which offers large displacement, rapid motion with only ~1V stimulus. IPMC’s are entering commercial applications in toys (Ashley 2003) and biomedical devices (Soltanpour 2001; Shahinpoor 2002; Shahinpoor, Shahinpoor et al. 2003; Soltanpour and Shahinpoor 2003; Soltanpour and Shahinpoor 2004), but unfortunately they can only actuate by bending, limiting their utility. Freeform fabrication offers a possible means of producing IPMC with novel geometry and/or tightly integrated with mechanisms which can yield linear or more complex motion. We have developed materials and processes which allow us to freeform fabricate complete IPMC actuators and their fabrication substrate which will allow integration within other freeform fabricated devices. We have produced simple IPMC’s using our multiple material freeform fabrication system, and have demonstrated operation in air for more than 40 minutes and 256 bidirectional actuation cycles. The output stress scaled to input power is two orders of magnitude inferior to that of the best reported performance for devices produced in the traditional manner, but only slightly inferior to devices produced in a more similar manner. Possible explanations and paths to improvement are presented. Freeform fabrication of complete electroactive polymer actuators in unusual geometries, with tailored actuation behavior, and integrated with other freeform fabricated active components, will enable advances in biomedical device engineering, biologically inspired robotics, and other fields. This work constitutes the first demonstration of complete, functional, IPMC actuators produced entirely by freeform fabrication.
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    Stereolithography: A Basis for Integrated Meso Manufacturing
    (2005-08-03) Palmer, J. A.; Davis, D. W.; Gallegos, P. L.; Yang, P.; Chavez, B. D.; Medina, F. R.; Wicker, R. B.
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    Rapid Fabrication of Smart Tooling with Embedded Sensors by Casting in Molds Made by Three Dimensional Printing
    (2005-08-26) Kobliska, John; Ostojic, Petar; Cheng, Xudong; Zhang, Xugang; Choi, Honseok; Yang, Yong; Li, Xiaochun
    This paper is to investigate the feasibility of constructing “smart tooling” by embedding thin film sensors, specifically, thin film thermocouples (TFTC) in castings made by molds formed by 3 Dimensional Printing (3DP). This study investigates whether thin film sensors can effectively be cast into larger metal structures and if the sensors survive the casting process. The investigation includes making 3DP molds to produce cast lap joint test bars of aluminum A356 and electroplated nickel to characterize by mechanical testing to find the best process conditions to maximize bond strength between the embedded thin film sensors and the cast material. Lastly molds were made and embedded sensors were placed inside the mold for casting. Some of the embedded sensors survived the casting process. In-situ monitoring of casting process with the embedded sensors was accomplished.
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    Improvement of Electrical Conductivity of SLS PEM Fuel Cell Bipolar Plates
    (2005-08-03) Chen, Ssuwei; Bourell, David L.; Wood, Kristin L.
    Previous work in this research demonstrated the feasibility of fabrication of proton exchange membrane (PEM) fuel cell bipolar plates by an indirect selective laser sintering (SLS) route. Properties of the SLS bipolar plate, such as flexural strength, corrosion resistance and gas impermeability, etc. are quite promising and satisfactory. However, initial results showed that there was still room for the improvement in electrical conductivity. This paper summaries the strategies investigated in an effort to increase the electrical conductivity, among which are: (1) infiltration of brown parts with conductive polymer (2) addition of a liquid phenolic infiltration/re-curing step prior to final sealing and (3) reduction of glassy carbon resistivity by curing process parameter control. Results show that the electrical conductivity value may be improved from 80 S/cm to around 108 S/cm, which is equivalent to a 35% jump, when the phenolic infiltration/re-curing step is applied before final epoxy sealing.
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    Rapid Prototyping of PEM Fuel Cell Bi-Polar Plates using 3D Printing and Thermal Spray Deposition
    (2005) Lyons, Brett; Batalov, Marat; Mohanty, Pranavasu; Das, Suman
    This article presents the results of exploratory research on novel methods for the fabrication of functional, metallic, gas flow, bi polar plates (BPP) for use in proton exchange membrane fuel cells (PEMFC). Low cost, high speed, additive manufacturing methods that combine 3D printing (3DP) and thermal spray (TS) technologies are described. Functional flow plates were manufactured by creating 3DP patterns and then depositing, and releasing, dense metals with TS methods. The new method yields dense metal plates, with interesting options for material choices and complex designs.
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    Hydrogels in Stereolithography
    (2005-08-23) Arcaute, Karina; Ochoa, Luis; Mann, Brenda; Wicker, Ryan
    The use of stereolithography (SL) for fabricating complex three-dimensional (3D) tissue engineered scaffolds of aqueous poly(ethylene glycol) (PEG) hydrogel solutions is described. The primary polymer used in the study was PEG-dimethacrylate (PEG-dma) with an average molecular weight (MW) of 1000 in distilled water with the photoinitiator Irgacure 2959 (I-2959). Successful layered manufacturing (LM) with embedded channel architecture required investigation of the photopolymerization characteristics of the PEG solution (measured as hydrogel thickness or cure depth) as a function of photoinitiator concentration and laser energy dosage for a specific photoinitiator type and polymer concentration in solution. Hydrogel thickness was a strong function of PI concentration and energy dosage. Curves of hydrogel thickness were utilized to successfully plan, perform, and demonstrate layered manufacturing of highly complex hydrogel scaffold structures, including structures with internal channels of various orientations. Successful fabrication of 3D, multi-layered bioactive PEG scaffolds containing cells was accomplished using a slightly modified commercial SL system (with 325 nm wavelength laser) and procedure. Human dermal fibroblast (HDF) cells were encapsulated in PEG hydrogels using small concentrations (~ 5 mg/ml) of acryloyl-PEG-RGDS (MW 3400) added to the photopolymerizable PEG solution to promote cell attachment. HDF cells were combined with the PEG solution, photocrosslinked using SL, and successfully shown to survive the fabrication process. The combined use of SL and photocrosslinkable biomaterials such as PEG makes it possible to fabricate complex 3D scaffolds that provide site-specific and tailored mechanical properties (i.e., multiple polymer materials) with a polymer matrix that allows transport of nutrients and waste at the macroscale and facilitates cellular processes at the microscale through precisely placed bioactive agents.
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    Part Repair using a Hybrid Manufacturing System
    (2005-08-03) Eiamsa-ard, Kunnayut; Nair, Hari Janardanan; Ren, Lan; Ruan, Jianzhong; Sparks, Todd; Liou, Frank W.
    Nowadays, part repair technology is gaining more interest from military and industries due to the benefit of cost reducing as well as time and energy saving. Traditionally, part repair is done in the repair department using welding process. The limitations of the traditional welding process are becoming more and more noticeable when the accuracy and reliability are required. Part repair process has been developed utilizing a hybrid manufacturing system, in which the laser aided deposition and CNC cutting processes are integrated. Part repair software is developed in order to facilitate the users. The system and the software elevate the repair process to the next level, in which the accuracy, reliability, and efficiency can be achieved. The concept of repair process is presented in this paper. Verification and experimental results are also discussed.
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    Workpiece Alignment for Hybrid Laser Aided Part Repair Process
    (2005) Padathu, Ajay Panackal; Sparks, Todd; Liou, Frank
    Work piece alignment is a key issue for hybrid laser aided part repair, a process utilizing both machining and laser deposition. Proper alignment can greatly improve the accuracy of the repair process. This paper introduces a method for aligning a physical work piece and a CAD model using a Renishaw touch probe and software tools. Also discussed is a model for computing 5-axis CNC positions based on a desired work piece orientation.
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    Simplified Production of Large Prototypes using Visible Slicing
    (2005) Karunakaran, K. P.; Solanki, P. D.; Sahasrabudhe, Onkar S.; Pushpa, Vishal; Dwivedi, Rajeev; Kovacevic, Radovan
    Rapid Prototyping (RP) is a totally automatic generative manufacturing technique based on a “divide-and-conquer” strategy called ‘slicing’. Simple slicing used on 2.5-axis kinematics of the existing RP machines is responsible for the staircase error. Although thinner slices will have less error, the slice thickness has practical limits. Visible Slicing overcomes these limitations. A few visible slices exactly represent the object. Each visible slice can be realized using a 3- axis kinematics machine from two opposite directions. Visible slicing is implemented on Segmented Object Manufacturing (SOM) machine under development. SOM can produce soft large prototypes faster and cheaper with accuracy comparable to that of CNC machining.
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    A Model for Error Propagation in the Surface Profile for Solid Freeform Fabrication
    (2005-08-26) Dwivedi, Rajeev; Zekovic, Srdja; Kovacevic, Radovan
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    Techno-Economic Analysis of Hybrid Layered Manufacturing
    (2005) Karunakaran, K. P.; Pushpa, Vishal; Akula, Sreenath Babu; Dwivedi, Rajeev; Kovacevic, R.
    Subtractive manufacturing (CNC machining) has high quality of geometric and material properties but is slow, costly and infeasible in some cases; additive manufacturing (RP) is just the opposite. Total automation and hence speed is achieved in RP by compromising on quality. Hybrid Layered Manufacturing (HLM) developed at IIT Bombay combines the best features of both these approaches. It uses arc welding for building near-net shapes which are finish machined to final dimensions. High speed of HLM surpasses all other processes for tool making by eliminating NC programming and rough machining. The techno-economic viability of HLM process has been proved through a real life case study. Time and cost of tool making using HLM promises to be substantially lower than that of CNC machining and other RP methods. Interestingly, the material cost in HLM was also found to be lower. HLM is a cheaper retrofitment to any 3 or 5 axis CNC milling machine or machining center.
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    Mechanism for Determination of G-factors for Solid Freeform Fabrication Techniques Based on Large Heat Input
    (2005) Dwivedi, Rajeev; Zekovic, Srdja; Kovacevic, Radovan
    A major class of Solid Freeform Fabrication (SFF) methods for metal deposition are based on large heat input. The geometry and microstructural properties of the deposition depend primarily on the heat input and the subsequent distribution at the substrate. On one hand the insufficient heat may lead to the inadequate melting of the metal, on the other hand overheating and heat accumulation leads to the overmelting, resulting in the deformation of the build up geometry. The heat distribution is governed by the available heat sink . For a better control of the process, the estimation of heat sinks and the subsequent control of the energy input allows a better control of the process. A parameter G-factor that estimates the heat sink based on the local geometry of a part has been introduced. The estimation of G-factor is based on the simulation and the experimental results. Also a mechanism to determine the G-factor for various substrate geometries has been introduced.
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    Thermal Modeling of Metal Powder-Based Selective Laser Sintering
    (2005-08-03) Chen, Tiebing; Zhang, Yuwen
    In order to get a better understanding of Selective Laser Sintering (SLS) process of the metal powders, three-dimensional modeling of laser sintering of a metal powder mixture that contains two kinds of metal powder with significantly different melting points under a moving Gaussian laser beam is investigated numerically. Laser induced melting and resolidification accompanied by shrinkage are modeled using a temperature transforming model. The liquid flow of the melted low melting point metal driven by capillary and gravity forces is also included in the physical model. Both complete and partial shrinkages are considered in the model. Simulations are performed for both single line laser scanning and multiple-line laser scanning. The numerical results are compared with experimental results and a detailed parametric study is performed. The effects of the moving heat source intensity, the scanning velocity, the thickness of the powder layer and the number of existing sintered layers underneath on the sintering depth, the shape of the heat affected zone (HAZ) and the temperature distribution are discussed. The optimized dimensionless moving heat source intensity increases with increasing scanning velocity in order to achieve the desired sintering depth and bond the newly sintered layer to the previously sintered layers.
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    Thermo-structural Finite Element Analysis of Direct Laser Metal Deposited Thin-Walled Structures
    (2005-08-26) Zekovic, Srdja; Dwivedi, Rajeev; Kovacevic, Radovan
    Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which particles are injected. During fabrication, a complex thermal history is experienced in different regions of the build, depending on the process parameters and part geometry. The thermal history induces residual stress accumulation in the buildup, which is the main cause of cracking during the fabrication. The management of residual stress and the resulting distortion is a critical factor for the success of the process. A thermostructural finite element model (FEM) of the process is developed, and the analysis reveals different patterns of residual stress in the thin-walled structures depending on the deposition strategy and the geometry of the structures. The residual stress patterns obtained from finite element analysis (FEA) are in good agreement with the experimental results.
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    Compensation Zone Approach to Avoid Z Errors in Mask Projection Stereolithography Builds
    (2005-08-26) Limaye, Ameya; Rosen, David W.
    Print-through results in unwanted polymerization occurring beneath a part cured using Mask Projection Stereolithography (MPSLA) and thus creates error in its Z dimension. In this paper, the "Compensation zone approach" is proposed to avoid this error. This approach entails modifying the geometry of the part to be cured. A volume (Compensation zone) is subtracted from underneath the CAD model in order to compensate for the increase in the Z dimension that would occur due to Print-through. Three process variables have been identified: Thickness of Compensation zone, Thickness of every layer and Exposure distribution across every image used to cure a layer. Analytical relations have been formulated between these process variables in order to obtain dimensionally accurate parts. The Compensation zone approach is demonstrated on an example problem.
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    Use of Parameter Estimation for Stereolithography Surface Finish Improvement
    (2005-08-03) Sager, Benay; Rosen, David W.
    In order to improve Stereolithography (SLA) surface finish, a systematic approach based on estimation of process parameters is needed. In this paper, the exposure on a desired SLA build surface is formulated as a function of process parameters. The deviation of exposure on this surface from the critical exposure, which is the threshold that determines curing in the SLA process, is formulated using least squares minimization. By applying inverse design techniques, SLA process parameters that satisfy this least squares minimization are determined. Application of parameter estimation formulation to important SLA geometries is presented and the results, including surface finish improvement, are discussed.
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    Determination of Dynamic Powder Modeling Parameters via Optical Methods
    (2005-08-03) Sparks, Todd; Pan, Heng; Liou, Frank