87 research outputs found
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Machine Issues Associated with Solid Freeform Fabrication
Before we begin a discussion of machine issues it is important that we categorize
exactly what we mean. There are differences between the design of a research piece of
equipment as compared to a commercial piece of equipment. A research piece of
equipment has to have the flexibility to demonstrate a success pattern. A commercial
piece of equipment, on the other hand, assumes that you have a stable platform and you
are now trying to assess how broad a success path you have (Figure 1). In fact, you are
trying to make that path as broad as possible so that the machine will not fail and will
always work the same way. This particular talk, and my expertise, is much more along
the lines of design of a research piece of equipment. What I will be talking about today
are machine issues associated with developing a success path in Solid Freeform
Fabrication. The machines we will be talking about have to have the flexibility to operate
in a wide variety of ways with a wide variety of experiments.Mechanical Engineerin
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Application of Factorial Design in Selective Laser Sintering
Selective Laser Sintering (SLS) is a complex process involving many process parameters.
These parameters are not all independent. A factorial design technique is utilized to study the
effects of three main process parameters, laser power, laser beam scanning speed, and powder
packing density as well as their interactions on the sintering depth and fractional density. The
results of this investigation provide useful information for the further experimental analysis of
the process parameters and for selecting suitable parameters for SLS process.Mechanical Engineerin
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Laser Polishing of Silica Rods
Lasers have been widely used in surface modification. In this research a CO2 continuous
wave laser has been used to polish the slot surface of the silica rods. The strong absorption of the
lO.6 um C02 radiation by the silica surface promotes the softening of a very thin layer of material
that flows under the action of surface tension. As a result, a mirror smooth glassy surface has been
formed which decreases the surface roughness without any substantial change in the surface
geometries. The effect of laser to surface inclination angle on the requisite power requirement was
assessed experimentally and theoretically. With laser beam scanning controlled by a computer aided design (CAD) database without specific tooling or human intervention, reliability and
reproducibility of this process have been greatly improved compared to conventional fire polishing.
The potential use of laser polishing as a post-processing step for freeform-fabricated parts is very
promising.Mechanical Engineerin
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Solid Freeform Fabrication: An Historical Perspective
Mechanical Engineerin
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A Model for Partial Viscous Sintering
A mathematical model describing the sintering rate of a viscous material powder
bed is presented. This model assumes that the powder bed is composed of cubic
packed, equal-size spherical particles. The sintering rate equation is derived in
terms of a unit cell dimension or the relative density of a powder bed. A
mathematical factor, fraction of sintering, is introduced to explain the
phenomena of partial sintering. Key words: model, viscous sintering.Mechanical Engineerin
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Parametric Analysis of the Selective Laser Sintering Process
Qualitative and quantitative analyses are required to develop Selective Laser
Sintering into a viable Manufacturing process. A simplified mathematical model for
sintering incorporating the heat tJ;ansfer equation. and the sintering rate equation, but using
temperature independent thermal properties, is presented in this paper. A practical result is
the calculation of sintering depthdeftned as the depth of powder where the void fraction is
less than 0.1 as a function of control parameters, such as the laser power intensity, the laser
scanning velocity, and the initial bedtemperature. We derive the general behavior of laser
sintering. A comparison of model predictions with laser sinterlng tests is provided.Mechanical Engineerin
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An Evaluation of the Mechanical Behavior of Bronze-NI Composites Produced by Selective Laser Sintering
Mechanical properties of Bronze-Nickel composites produced by Selective Laser Sintering (SLS)
were evaluated by constant displacement tension tests. These were studied as a function of SLS
process parameters - laser power density, scan speed, scan spacing, scan direction and layer
thickness. The strength data was then correlated to the microstructure and the part bulk density. To
further enhance the part densities and the mechanical properties, post-SLS sintering was studied.
The relationships between SLS process parameters, post-SLS sintering parameters and the
resulting microstructures, part bulk density and the mechanical properties will be described.Mechanical Engineerin
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Selective Laser Sintering of Zirconia with Micro-Scale Features
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.Mechanical Engineerin
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Geometry Processing for SLS/HIP
SLS/HIP is a new net shape manufacturing method that combines
the strengths of direct selective laser sintering and hot isostatic pressing.
Direct selective laser sintering is a rapid manufacturing technique that can
produce high density metal parts of complex geornetry with an integral,
gas iinpenneable skin. These parts can then be directly post-processed by
containerless HIP. Sophisticated processing of the part geometry is
required to facilitate the desired results from SLS/HIP. This paper presents
geometry processing algorithms being developed for in-situ canning of
SLS/HIP components. This research is funded by DARPA IONR contract
NO00 14-95-C-0 139 titled "Low Cost Metal Processing Using SLS/HIP".Mechanical Engineerin
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Discrete Multi-Material Selective Laser Sintering (M2 SLS): Development for an Application in Complex Sand Casting Core Arrays
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.Mechanical Engineerin
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