Browsing by Subject "Solid freeform fabrication"
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Item Effect of in-plane voiding on the fracture behavior of laser sintered polyamide(2011-12) Leigh, David Keith; Bourell, David Lee; Beaman, Joseph J.Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture.Item Evaluation of Negative Stiffness Elements for Enhanced Material Damping Capacity(2010-05) Kashdan, Lia Beatrix; Seepersad, Carolyn; Haberman, Michael R.Constrained negative stiffness elements in volume concentrations (1% to 2%) embedded within viscoelastic materials have been shown to provide greater energy absorption than conventional materials [Lakes et al., Nature (London) 410, 565–567 (2001)]. This class of composite materials, called meta-materials, could be utilized in a variety of applications including noise reduction, anechoic coatings and transducer backings. The mechanism underlying the meta-material's behavior relies on the ability of the negative stiffness element to locally deform the viscoelastic material, dissipating energy in the process. The work presented here focuses specifically on the design of the negative stiffness elements, which take the form of buckled beams. By constraining the beam in an unstable, S-shaped configuration, the strain energy density of the beam will be at a maximum and the beam will accordingly display negative stiffness. To date, physical realization of these structures has been limited due to geometries that are difficult to construct and refine with conventional manufacturing materials and methods. By utilizing the geometric freedoms allowed by the Selective Laser Sintering (SLS) machines, these structures can be built and tuned for specific dynamic properties. The objective of this research was to investigate the dynamic behavior of SLS-constructed meso-scale negative stiffness elements with the future intention of miniaturizing the elements to create highly absorptive meta-materials. This objective was accomplished first through the development and analysis of a mathematical model of the buckled beam system. A characterization of the Nylon 11 material was performed to obtain the material properties for the parts that were created using SLS. Applying the mathematical model and material properties, a tuned meso-scale negative stiffness structure was fabricated. Transmissibility tests of the meso-scale structure revealed that the constrained negative stiffness system was able to achieve overall higher damping and vibration isolation than an unconstrained system. Quasistatic behavior of the system indicated that these elements would be ideal for implementation within meta-materials. Based on the results of the meso-scale system, a method to test a representative volume element for a negative stiffness meta-material was developed for future completion.Item Extracting Product Performance by Embedding Sensors in SFF Prototypes(2004) Rai, Rahul; Campbell, Matthew; Wood, KristinSFF has been instrumental in improving the design process by providing designers with prototypes that assist them in the communication of design information and design visualization prior to creating fully functional prototypes. Embedding sensors at key locations within an SFF part to extract further data and monitor parameters at critical locations not accessible to ordinary sensors can help immensely in building functional SFF parts. However, this approach requires data acquisition of information such as temperature and strain values from interiors of products. In this work, the authors propose new techniques for embedding thermal sensors and strain gauges into fully dense DuraForm™ during Selective Laser Sintering (SLS) process. The embedded sensors have been used to measure temperatures and strains. They provide higher sensitivity, good accuracy, and high temperature capacity.Item Fab@Home: The Personal Desktop Fabricator Kit(2006) Malone, Evan; Lipson, HodSolid freeform fabrication has the potential to revolutionize manufacturing, perhaps even to allow consumers to customize and manufacture goods cost-effectively in their own home. At present, the florescence of the technology is limited by a “chicken and egg” paradox. There is insufficient consumer demand and too narrow a range of applications for SFF systems to allow mass production to reduce their cost and complexity. At the same time, consumer applications for, demand for, and indeed awareness of SFF technology is limited by its high cost and complexity. We posit that just as the personal computer revolution was spurred by development of computer kits, getting SFF technology into the hands of hobbyists and hackers will simultaneously generate applications for, and improvements to it. To this end, we have developed the Fab@Home personal SFF kit, and are developing a user-group website to promote exchange of ideas and improvements. The designs and software for Fab@Home will be freely distributed, and constructing a first generation kit should cost roughly $2000. The kit design and a working unit will be presented, along with our experience deploying a unit for public use.Item Heterogeneous Solids: Possible Representation Schemes(1999) Morvan, Stephane M.; Fadel, Georges M.Solid freeform fabrication processes allow parts to be built with accuracy and mechanical integrity, permittingthem to be used in tooling or fOrlnandfit applications. There is already a need form~lti ..color Parts.for surgical applications, which will eventually lead to. multi-material RP .machines.WhetherJor on the spot color deposition or for functionally tailored multiple materials parts,.RPmachines with such capabilities are becoming available. They will eventually lead to the trtiepromise of Solid Freeform Fabrication: a system that can build a functional mechanism without assembly, and from multiple materials. This paper is aimed at understanding the new challenges raised from representing solids whose material distribution is changing gradually from one material to another (HC), and those made of a collection .of discrete materials (HD). Several representation schemes are reviewed and critiqued. Techniques borrowed from medical imaging and geoscience modeling are used to better understand the modeling of heterogeneous and gradient solids, from a geometric standpoint.Item Improving Accuracy of Powder Sintering-based SFF Processes by Metal Deposition from Nanoparticle Dispersion(2005-08-26) Crane, N. B.; Wilkes, J.; Sachs, E.; Allen, S. M.Solid Freeform Fabrication processes such as three-dimensional printing (3DP) and selective laser sintering (SLS) produce porous parts that must be densified. New steel infiltration methods can produce parts of standard alloy compositions with properties comparable to wrought materials. However, the infiltration process introduces dimensional errors due to both shrinkage and creep—particularly at the high temperatures required for steel infiltration. A post-processing method has been developed to reduce creep and shrinkage of porous metal skeletons. Tests have achieved over 90% reduction in creep and 50% reduction in shrinkage. In this method, metal is deposited into the porous part from a suspension of metallic nanoparticles. These particles densify at low temperatures to reinforce the bonds and reduce stress concentrations that amplify creep deformation in untreated parts. After treatment, the reinforced parts can be densified by infiltration.Item Laser-based solid freeform fabrication techniques for the direct production of ceramic and metal/ceramic shapes(1995-08) Birmingham, Britton Ray; Not availableItem SFF-Oriented Modeling and Process Planning of Functionally Graded Materials Using a Novel Equal Distance Offset Approach(2004) Xu, Anping; Shaw, Leon L.This paper deals with the modeling and process planning of solid freeform fabrication (SFF) of 3D functionally graded materials (FGMs). A novel approach of representation and process planning of FGMs, termed as equal distance offset (EDO), is developed. In EDO, a neutral arbitrary 3D CAD model is adaptively sliced into a series of 2D layers. Within each layer, 2D material gradients are designed and represented via dividing the 2D shape into several sub-regions enclosed by iso-composition contours. If needed, the material composition gradient within each of sub-regions can be further determined by applying the equal distance offset algorithm to each sub-region. Using this approach, an arbitrary-shaped 3D FGM object with linear or non-linear composition gradients can be represented and fabricated via suitable SFF machines.Item Thermal imaging of a selective laser sintering part bed surface(2010-12) LaRocco, Janna Hayes; Bourell, David Lee; Beaman, JosephIn an effort to gain a more comprehensive and complete understanding of the thermal behaviors occurring during the selective laser sintering process, external temperature measurements were taken during the build process. To accomplish this, an infrared camera was aimed directly through a viewport on the front of the sinterstation. The temperature was monitored during the heating process which showed slightly non-uniform heating of the part bed surface. Temperatures were also recorded while the laser was sintering each layer and the subsequent cooling of the entire machine following the build. By directly capturing infrared images of the part bed’s surface, it is clearer how the temperature gradients behave and the impact such variables have on part build efficiency.