23,056 research outputs found
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Further Developments in Process Mapping and Modelling in Direct Metal Selective Laser Melting
This paper advances previous reported work on the mapping and modelling of single
tracks and layers produced in powder beds of tool steel and stainless steel powders by a CO2
laser. For single tracks it reports on predicted and simulated track masses. It validates the
simulations, including the use of absorption close to 1.0 when cylindrical tracks are formed. It
also reports on melt pool temperature calculations and estimated melt pool dimensions which are
used, in conjunction with bed physical properties, to explain why the single tracks form as either
continuous with a crescent shape cross-section, continuous with an elliptical section,
discontinuously irregularly broken, discontinuously balled or only partially melted as scan
speeds and laser powers change. It then extends its scope, experimentally, to consider effects of
scan spacing on single layer formation.Mechanical Engineerin
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Spiral Growth Manufacturing (SGM) – A Continuous Additive Manufacturing Technology for Processing Metal Powder by Selective Laser Melting
Spiral growth manufacturing is a new innovative powder based rapid manufacturing
technique. The innovation exists in the methodology in which powder layers are deposited.
Unlike other pre-placed powder systems, the deposited layers move relative to the location at
which they are processed. This is made possible by a rotating build drum into which powder is
deposited, in spiralled layers, from a stationary hopper. With this configuration powder can be
continuously deposited and levelled and simultaneously processed, eliminating delays in the
build cycle. Stainless steel and cobalt-chrome powder is selectively melted using a 100W flash
lamp pumped Nd:YAG laser. This paper reports on factors affecting build rate and on build
strategies for creating a number of axis-symmetric thin and thick walled cylinders. Experimental
results suggest that build rate for thin walled structures bonded to a substrate will ultimately be
governed by tangential movements of the powder particles when frictional forces are not
sufficient to accelerate the particles along a curved path, provided that enough laser power is
available for melting. Even melt pool balling, which is evident when melting one layer at high
speeds, diminishes in multiple layer builds due to re-melting and infilling.Mechanical Engineerin
Expandable coating cocoon leak detection system
Development of system and materials for detecting leaks in cocoon protective coatings are discussed. Method of applying materials for leak determination is presented. Pressurization of system following application of materials will cause formation of bubble if leak exists
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Selective Laser Sintering of Stainless Steel 314S HC Processed Using Room Temperature Powder Beds
Metal powder bed pre-heating is a proposed route for the homogenisation of
temperature gradients that can otherwise cause individual layer warping and cracking in direct
metal Selective Laser Sintering (SLS). However, the high temperatures involved complicate a
relatively simple process. This paper reports on the conditions for successful small scale SLS
of binderless stainless steel 314S powders within the surrounds of a room temperature powder
bed. Results show that a scan length around 15.0mm and a scan spacing around 0.275mm
produce sintered layers showing no signs of warping. Experimentation also indicates that
single layer shape. effects warping but length oflayer propagation does not.Mechanical Engineerin
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Atmospheric Control during Direct Selective Laser Sintering of Stainless Steel 314S Powder
Stainless steel grade 314S powders have been Selective Laser Sintered (SLS) in three
different argon/air (oxygen) atmospheric mixtures. The amount of oxygen present during the
heating, melting and fusing of the metal powder strongly limits the range of laser powers and
scanning speeds for successful processing. As oxygen levels diminish, powder oxidation
reduces. This reduces absorption of laser energy as well as balling and other detrimental
surface phenomena. This paper reports the conditions for creating sintered layers and
observations of part quality variation within these conditions. Sintered microstructure
observations are also helpful in determining thermal history changes.Mechanical Engineerin
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Image Transformations and Printing of Plaster Layers in Spiral Growth Manufacturing
Spiral growth manufacturing (SGM) is a high speed rapid manufacturing technique in
which objects are built up, layer by layer, by simultaneously depositing, levelling and selectively
consolidating thin powder layers onto a rotating build platform. The size and position of the
jetted droplets are mapped by the position and greyscale level of pixels within an 8 bit greyscale
bitmap image. This paper reports on the development of software in which mathematical
algorithms apply geometric transformations to images in preparation for printing onto a rotating
substrate. In support of this work, dimensional accuracy measurements of printed images and
methods to correct radial print density variations are reported. The accuracy of printed images
were found to be within ±0.2mm of their predicted size. The experimental work is briefly
extended to the direct printing of plaster layers, formed by mixing two reactive ink solutions.Mechanical Engineerin
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. I. and limits on the near-IR background
This paper is devoted to studying the CIB through its correlation properties.
We studied the limits on CIB anisotropy in the near IR (1.25, 2.2, and 3.5 \um,
or ) bands at a scale of 0.7\deg\ using the COBE\footnote{ The
National Aeronautics and Space Administration/Goddard Space Flight Center
(NASA/GSFC) is responsible for the design, development, and operation of the
{\it COBE}. Scientific guidance is provided by the {\it COBE} Science Working
Group. GSFC is also responsible for the development of the analysis software
and for the production of the mission data sets.} Diffuse Infrared Background
Experiment (DIRBE) data. In single bands we obtain the upper limits on the
zero-lag correlation signal \w2m4sr2 for the
bands respectively. The DIRBE data exhibit a clear color between the
various bands with a small dispersion. On the other hand most of the CIB is
expected to come from redshifted galaxies and thus should have different color
properties. We use this observation to develop a `color subtraction' method of
linear combinations of maps at two different bands. This method is expected to
suppress the dominant fluctuations from foreground stars and nearby galaxies,
while not reducing (or perhaps even amplifying) the extragalactic contribution
to . Applying this technique gives significantly lower and more isotropic
limits.Comment: 44 pages postcript; includes 5 tables, 14 figures. Astrophysical
Journal, in pres
Encoding algebraic power series
Algebraic power series are formal power series which satisfy a univariate
polynomial equation over the polynomial ring in n variables. This relation
determines the series only up to conjugacy. Via the Artin-Mazur theorem and the
implicit function theorem it is possible to describe algebraic series
completely by a vector of polynomials in n+p variables. This vector will be the
code of the series. In the paper, it is then shown how to manipulate algebraic
series through their code. In particular, the Weierstrass division and the
Grauert-Hironaka-Galligo division will be performed on the level of codes, thus
providing a finite algorithm to compute the quotients and the remainder of the
division.Comment: 35 page
Gurses' Type (b) Transformations are Neighborhood-Isometries
Following an idea close to one given by C. G. Torre (private communication),
we prove that Riemannian spaces (M,g) and (M,h) that are related by a Gurses
type (b) transformation [M. Gurses, Phys. Rev. Lett. 70, 367 (1993)] or,
equivalently, by a Torre-Anderson generalized diffeomorphism [C. G. Torre and
I. M. Anderson, Phys. Rev. Lett. xx, xxx (1993)] are neighborhood-isometric,
i.e., every point x in M has a corresponding diffeomorphism phi of a
neighborhood V of x onto a generally different neighborhood W of x such that
phi*(h|W) = g|V.Comment: 10 pages, LATEX, FJE-93-00
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