modelling techniques in cad
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Modelling techniques
inCAD
Presented by enter your nameCad/Cam - 05
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Geometric Modelling
Geometric modelling is a collection of methods used to define the shape and othergeometric characteristics of an object.
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Geometric modelling is the BASE of manyapplications such as:
Mass property calculations.
Mechanism analysis.
Finite-element modelling.
NC programming.
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Geometric Modelling Types
1. Wire-frame modelling.
2. Solid modelling.
3. Surface modelling.
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Wire-frame Modelling
Wire-frame model Original object
The shape of the object is defined by acollection of points (vertices) and a set of edges.
There are no surfaces in a wireframe model.
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Example
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Solid Modelling
Solid models give designers a complete descriptionsof construction, shape, surface, volume, and densityof a 3D model.
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3D objects can be created by basic 3D shapes:boxes, cones, cylinders, spheres, wedges, andtorus (donuts).
Complex solids can be made by combination of these shapes.
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Example
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Types of Solid Modelling Schemes: Boundary Representation (B-REP).
Constructive Solid Geometry (CSG).
Sweeping.
Primitive creation functions.
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Boundary representation (B-Rep)
Solid model is defined by their enclosingsurfaces or boundaries.
The boundary of asolid separates
points inside frompoints outsidesolid.
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CSG Boolean Operations
Subtract / Cut Intersection Union / Protrusion
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Union / Protrusion Creates a single solid
from two solids thatintersect
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Subtract / Cut subtracts one solid from another One solid is subtracted from the other.
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Sweeping Operations
Operations types: extrude revolve sweep blend
Sweeping is a modelling in which a plane istranslated or revolved to form a solid.
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Extrude
2D closed sketch canbe extruded to form
solid objects.
height of extrusion.
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Revolve
2D closed sketch canbe revolved to form
solid objects.
axis of rotation.angle of revolution.
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Sweep 2D closed sketch
can be sweep alongthe path to form
solid objects.
trajectory defined.
cross section.
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Blend
Smooth transition can bemade between two closed2D sketch with similargeometry.
distance betweensections.angle of twist betweensections.
equal number of vertices.
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Primitives are simple solidshapes with simplemathematical surfaces.
Can be controlled by asmall number of parameters and positionedusing a transformationmatrix.
Primitive Creation
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Advantages of solid modelling Complete representation. Unambiguous description. Real time environment view.
Disadvantages of solid modelling
Requires more storage & CPU processing.
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Surface modellingIn surface modeling not only the edges of a 3Dobject are defined, but also its surfaces.
Extruded surface Revolved surface
Axis of rotation
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Plane surface
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Ruled (lofted) surface
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Surface of revolution
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Bezier surface
B-spline surface
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Disadvantages of surface modelling Does not represent internal features of the
model, no sense of volume.
Limitation for volumetric and mass propertyanalysis.
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Thank you!