Modelling Techniques in CAD

7/31/2019 Modelling Techniques in CAD

1/33

Modelling techniques

inCAD

Presented by enter your nameCad/Cam - 05


2/33

Geometric Modelling

Geometric modelling is a collection of methods used to define the shape and othergeometric characteristics of an object.


3/33

Geometric modelling is the BASE of manyapplications such as:

Mass property calculations.

Mechanism analysis.

Finite-element modelling.

NC programming.


4/33

Geometric Modelling Types

1. Wire-frame modelling.

2. Solid modelling.

3. Surface modelling.


5/33

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.


6/33

Example


7/33


8/33


9/33

Solid Modelling

Solid models give designers a complete descriptionsof construction, shape, surface, volume, and densityof a 3D model.


10/33

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.


11/33

Example


12/33

Types of Solid Modelling Schemes: Boundary Representation (B-REP).

Constructive Solid Geometry (CSG).

Sweeping.

Primitive creation functions.


13/33

Boundary representation (B-Rep)

Solid model is defined by their enclosingsurfaces or boundaries.

The boundary of asolid separates

points inside frompoints outsidesolid.


14/33


15/33


16/33

CSG Boolean Operations

Subtract / Cut Intersection Union / Protrusion


17/33

Union / Protrusion Creates a single solid

from two solids thatintersect


18/33


19/33

Subtract / Cut subtracts one solid from another One solid is subtracted from the other.


20/33

Sweeping Operations

Operations types: extrude revolve sweep blend

Sweeping is a modelling in which a plane istranslated or revolved to form a solid.


21/33

Extrude

2D closed sketch canbe extruded to form

solid objects.

height of extrusion.


22/33

Revolve

2D closed sketch canbe revolved to form

solid objects.

axis of rotation.angle of revolution.


23/33

Sweep 2D closed sketch

can be sweep alongthe path to form

solid objects.

trajectory defined.

cross section.


24/33

Blend

Smooth transition can bemade between two closed2D sketch with similargeometry.

distance betweensections.angle of twist betweensections.

equal number of vertices.


25/33

Primitives are simple solidshapes with simplemathematical surfaces.

Can be controlled by asmall number of parameters and positionedusing a transformationmatrix.

Primitive Creation


26/33

Advantages of solid modelling Complete representation. Unambiguous description. Real time environment view.

Disadvantages of solid modelling

Requires more storage & CPU processing.


27/33

Surface modellingIn surface modeling not only the edges of a 3Dobject are defined, but also its surfaces.

Extruded surface Revolved surface

Axis of rotation


28/33

Plane surface


29/33

Ruled (lofted) surface


30/33

Surface of revolution


31/33

Bezier surface

B-spline surface


32/33

Disadvantages of surface modelling Does not represent internal features of the

model, no sense of volume.

Limitation for volumetric and mass propertyanalysis.


33/33

Thank you!

Modelling Techniques in CAD

Documents

Transcript of Modelling Techniques in CAD