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Simplified Production of Large Prototypes using Visible Slicing
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.Mechanical Engineerin
Using Computer Technology Tools to Improve the Teaching-Learning Process in Technical and Vocational Education: Mechanical Engineering Subject Area
This paper discusses the integration of computer assisted instructions (CAI) with traditional class room teaching. It describes a teaching method to bring real-world of industrial work into the classroom that underscores the need to learn fundamental principles while adding excitement and relevance to the experience. This paper presents results of a case study undertaken to understand the effect of computer assisted teaching methodology on learning effectiveness in classroom environment. The effects of computer assisted instructions on different levels of cognition of individual learners have also been evaluated. The computer aided drawing (CAD), computer aided manufacturing (CAM) and computer numerical control (CNC) courses at the Bahrain institute are an integral part of this attempt. These courses emphasize the development of a 3-D geometric computer model and application of this digital database to all phases of the design process. The students make freehand sketches, build computer models, mate assemblies of parts, perform various analysis, create kinematics simulations, generate final design drawings, import engineering drawing as DXF file, generate NC file to build rapid prototypes as shown in the table 1 below.
Keywords: Computer Technology, C.N.C and AutoCad Softwar
Crack propagation in shells due to impact against sharp objects
The present paper is concerned with the development of an effective finite element tool for the simulation of crack propagation in thin structures, induced by contact or impact against sharp objects. In particular the purpose is the refinement and further development of a recently proposed finite element approach for the simulation of the blade cutting of thin membranes [1]. Standard cohesive interface elements are not suited for the simulation of this type of cutting, dominated by the blade sharpness and by large failure opening of the cohesive interface. The new concept of “directional” cohesive element, to be placed at the interface between adjacent shell elements, where the cohesive forces can have different directions on the two sides of the crack whenever the cohesive region is crossed by the cutting blade, was introduced in [1] for elastic 4-node full-integration shell elements with dissipation localized inside the interface elements, in the framework of an explicit dynamics formulation. In the present paper the computational efficiency of the proposed approach is investigated by considering applications to different test problems, modifying the shell element kinematics. Some considerations about a reduced integration solid-shell element are here reported; the interaction between this kind of element and directional cohesive elements is under study
Mass Flows in Cometary UCHII Regions
High spectral and spatial resolution, mid-infrared fine structure line
observations toward two ultracompact HII (UCHII) regions (G29.96 -0.02 and Mon
R2) allow us to study the structure and kinematics of cometary UCHII regions.
In our earlier study of Mon R2, we showed that highly organized mass motions
accounted for most of the velocity structure in that UCHII region. In this
work, we show that the kinematics in both Mon R2 and G29.96 are consistent with
motion along an approximately paraboloidal shell. We model the velocity
structure seen in our mapping data and test the stellar wind bow shock model
for such paraboloidal like flows. The observations and the simulation indicate
that the ram pressures of the stellar wind and ambient interstellar medium
cause the accumulated mass in the bow shock to flow along the surface of the
shock. A relaxation code reproduces the mass flow's velocity structure as
derived by the analytical solution. It further predicts that the pressure
gradient along the flow can accelerate ionized gas to a speed higher than that
of the moving star. In the original bow shock model, the star speed relative to
the ambient medium was considered to be the exit speed of ionized gas in the
shell.Comment: 34 pages, including 14 figures and 1 table, to be published in ApJ,
September 200
Experiments in fixturing mechanics
This paper describes an experimental fixturing system wherein fixel reaction forces, workpiece loading, and workpiece displacements are measured during simulated fixturing operations. The system's configuration, its measurement principles, and tests to characterize its performance are summarized. This system is used to experimentally determine the relationship between workpiece displacement and variations in fixed preload force or workpiece loading. We compare the results against standard theories, and conclude that commonly used linear spring models do not accurately predict workpiece displacements, while a non-linear compliance model provides better predictive behavior
Kinematics of planet-host stars and their relation with dynamical streams in the solar neighbourhood
We present a detailed study on the kinematics of metal-rich stars with and
without planets, and their relation with the Hyades, Sirius and Hercules
dynamical streams in the solar neighbourhood. Accurate kinematics have been
derived for all the stars belonging to the CORALIE planet search survey. We
used precise radial velocity measurements and CCF parameters from the CORALIE
database, and parallaxes, photometry and proper motions from the HIPPARCOS and
Tycho-2 catalogues. The location of stars with planets in the thin or thick
discs has been analysed using both kinematic and chemical constraints. We
compare the kinematic behaviour of known planet-host stars to the remaining
targets belonging to the volume-limited sample, in particular to its metal-rich
population. The high average metallicity of the Hyades stream is confirmed. The
planet-host targets show a kinematic behaviour similar to that of the
metal-rich comparison subsample, rather than to that of the comparison sample
as a whole, thus supporting a primordial origin for the metal excess observed
in stars with known planetary companions. According to the scenarios proposed
as an explanation for the dynamical streams, systems with giant planets could
have formed more easily in metal-rich inner Galactic regions and then been
brought into the solar neighbourhood by dynamical streams.Comment: 14 pages, 12 figures, accepted for publication in A&A (28 August
2006
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