Parametric Modeling - Charles W. Davidson College of...
Transcript of Parametric Modeling - Charles W. Davidson College of...
Ken Youssefi Introduction to Engineering, E10. 2
Why draw 3D Models?
• Less expensive than building a physical model.
• Can be used for presentations and marketing.
• 3D models can be altered easily, create
more concepts
• 3D models are easier to interpret.
• 3D models can be used to perform engineering
analysis, finite element analysis (stress,
deflection, thermal…..) and motion analysis
• 3D models can be used directly in manufacturing,
Computer Numerical Control (CNC).
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Ken Youssefi Mechanical Engineering Dept 3
Basics of Finite Element Analysis (FEA)
What is FEA ?
A complex problem is divided into a smaller and
simpler problems that can be solved by using the
existing knowledge of mechanics of materials
and mathematical tools
Why FEA ?
Modern mechanical design involves complicated
shapes, sometimes made of different materials
that as a whole cannot be solved by existing
mathematical tools. Engineers need the FEA to
evaluate their designs
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Ken Youssefi Mechanical Engineering Dept 4
Basics of Finite Element Analysis
The process of dividing the model into small pieces is called meshing. The
behavior of each element is well-known under all possible support and load
scenarios. The finite element method uses elements with different shapes.
Elements share common points called nodes.
mesh analysis results
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Computer Numerical Control (CNC)
A CNC machine is an NC machine with the added feature of
an on-board computer.
2 The program path is generated
by computer
A solid model of the part is
created.
1
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CNC Machines Machining Centers, equipped with automatic tool changers,
are capable of changing 90 or more tools. Can perform
milling, drilling, tapping, boring… on many faces.
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Creating Solid Models
Parametric Modeling Concept
• Parametric is a term used to describe a dimension’s ability to change the shape of model geometry if the dimension value is modified.
• Parametric models are featured-based,
parametric, solid modeling design program:
SolidWorks, Pro-Engineer, Unigraphics (CSG
and parametric), Autodesk Inventor, …..
• Feature-based is a term used to describe the various components of a model. A part can consist of various types of features such as holes, grooves, fillets, and chamfers.
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Design Intent
• In parametric modeling, dimensions control the model.
• Design intent is how your model will react when dimension values are changed.
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Design Intent
2.50
4.00
1.25
2.50
The drawing shows the intent of the
designer that the inclined plane
(chamfer) should have a flat area
measuring 2.5 inches and that it should
start at a point 1.25 inches from the
base of the drawing. These parameters
are what the designer deemed
significant for this model.
Remember that the placement of dimensions is very
important because they are being used to drive the shape
of the geometry. If the 2.5 in. vertical dimension
increases, the 2.5 in. flat across the chamfer will be
maintained, but its angle will change.
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Design Intent
In this drawing, what is important
to the designer is the vertical
location and horizontal dimension
of the chamfer, rather than the flat
of the chamfer.
2.50
4.00
1.25
2.125
2.50
4.00
1.75
30.0O In the last drawing, the designer calls
for a specific angle for the chamfer. In
this case the angle of the chamfer
should be dimensioned.
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Parametric Modeling
The true power of parametric modeling shines through when
design changes need to be made. The design modification is
made by simply changing a dimension.
Since the counterbore is associated with the top surface of the
ring, any changes in the thickness of the ring would automatically
be reflected on the counterbore depth.
60
10
15
30 Pattern: 8 Holes
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Sketching and Features
• Take the word sketch literally. A sketch should be just that, a sketch.
• When sketching it is not necessary to create geometry with accuracy. Lines, arcs, and additional geometry need not be created with exact dimensions in mind.
When discussing the mind-set needed for working with
parametric modelers, two topics need to be expanded:
Sketching and Features
Sketching
In short, the sketch need only be the approximate size and shape
of the part being designed. When dimensions are added, they
will drive the size and the shape of the geometry.
• When the dimensions are added, the sketch will
change size and shape. This is the essence of
Parametric Modeling.
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Sketching and Features
• Sketched Feature
Features
Create a feature from the sketch by extruding,
revolving, sweeping, lofting and blending.
2.75
2.5 1.0
.25
.75
Create a 2D sketch.
Revolved feature Extruded feature
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Creating Solids - Sweep
Sweep feature
Profile (section)
Path (guide)
A Sweep feature requires a profile and a path. The profile will
follow the path to create the solid.
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Creating Solids – Loft (different profiles)
• Sections (profiles) do
not have to be sketched
on parallel planes
• All sections must be
either closed or open
Round profile
Round
profile
Square
profile
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Creating Features from Sketches
Loft in
SolidWorks
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Applied Feature
Applied feature does not require a sketch.
It is applied directly to the model.
Fillets and chamfers are very common
applied features.
Chamfer
Fillet
Applied Features - Patterns
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Linear (rectangular) pattern
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Applied Features - Patterns Linear (rectangular) pattern
1. Select direction 1 and 2
2. Select spacing in dir. 1 and 2
3. Select # of features in dir. 1 and 2
4. Select feature to pattern