Solid Modeling990

7/28/2019 Solid Modeling990

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Introduction

A solid model is a digital representation of thegeometry of an existing or envisioned physicalobject.

Solid models are used in many industries, fromentertainment to health care.

They play a major role in the discrete-partmanufacturing industries where precise models of

parts and assemblies are created using solidmodeling software or more general computer-aideddesign (CAD) systems.


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Introduction

Designers may specify points, curves, and surfaces,and stitch them together to define electronicrepresentations of the boundary of the object.

Alternatively, they may select models of simpleshapes, such as blocks or cylinders, specify theirdimensions, position, and orientation, and combinethem.

The resulting representation is a complete and

detailed digital approximation of the geometry ofan object or of an assembly of objects (such as a carengine or an entire airplane).


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Introduction

Interactive three-dimensional (3D) graphic supportsthe design activities by providing designers with:

1. Easy to understand images of their design

2. Efficient facilities for graphically selecting orediting features of the part being designed

3. Immediate feedback


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Introduction

The use of solid modeling techniques allows for theautomation of several difficult engineering calculationsthat are carried out as a part of the design process.

Simulation, planning, and verification of processes such

as machining and assembly were one of the maincatalysts for the development of solid modeling.

More recently, the range of supported manufacturingapplications has been greatly expanded to include sheetmetal manufacturing, injection molding, welding, piperouting etc.

Beyond traditional manufacturing, solid modelingtechniques serve as the foundation for rapid prototyping.


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Solid Modeling Systems

A solid modeling system, often called a solidmodeler, is a computer program that provides

facilities for storing and manipulating data

structures that represent the geometry of individualobjects or assemblies.

These representations can be created either by ahuman through a graphic user interface (GUI), or

specified by software applications via an applicationprogramming interface (API).


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A modelers GUI generates 3D graphic feedback to auser by immediately displaying selected portions ofthe objects being designed.

In addition, it provides facilities for selecting and forgraphically editing the displayed entities.

Users of modern modelers can describe objects interms offeatures, which are higher-level entities

meaningful for their applications. They can also use dimensions and other constraints

to help in sizing and positioning geometric entities.


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The choice of representations used by the modelerdetermines its domain (i.e., which objects can bemodeled), and has a strong impact on the complexityand performance of the algorithms that create orprocess the representations.

A modeler may support several distinctrepresentation schemes.


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Wire frame model Hidden lines shown

Representation Schemes


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Solid Modeling vs Surface Modeling

Solid modeling is a technique for representing solid objectssuitable for computer processing. It is primarily used for CAD,engineering analysis, computer graphics and animation, rapidprototyping, medical testing, product visualization and

visualization of scientific research.

Surface modeling, on the other hand, involves describing the3-dimensional image. Both have their own significance as far as CAD firms are

concerned. While surface modeling develops shapes by stretching a

surface between 3D curves that you individually create, solidmodeling involves representing an object by describing itssurface boundary and by orienting it, so that we can tell, ateach surface point, on which side the solid interior lies.


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Surface Modeling


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Solid Modeling


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Methods of Creating Solid Models

Boundary Representation (B-rep), mostlyused in finite element programs.

Constructive Solid Geometry (CSG), CAD

packages; Unigraphics, AutoCAD 3Dmodeler.

Parametric Modeling, CAD packages;

Unigraphics, SolidWorks, Inventor byAutoDesk, Pro/Engineer etc


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Boundary Representation (B-rep)

In solid modeling and computer-aided design, boundaryrepresentation often abbreviated as B-rep or BREPis amethod for representing shapes using the limits.

A solid is represented as a collection of connected surface

elements, the boundary between solid and non-solid. A solid model is formed by defining the surfaces that form

its boundary (edges and surfaces)

The face of a B-rep represents an oriented surface, thereare two sides to the surface; solid side (inside) and void

side (outside). Many Finite Element Method (FEM) programs use this

method. Allows the interior meshing of the volume to bemore easily controlled.


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Boundary Representation (B-rep)

In general a solid will consist of faces.

A face will be defined by loops(closed curve).

Each loop will be defined by one or more edges.

Each edge is defined by vertices. Each vertex is defined by a point.

Orientation of a face: The orientation of a face can be

represented in one of the two ways, associating anormal with it or associating an order in the list ofedges that define the face.


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Constructive Solid Geometry, CSG

CSG defines a model in terms of combining basic andgenerated (using extrusion and sweeping operation) solidshapes.

CSG uses Boolean operations to construct a model (GeorgeBoole, 1815-1864, invented Boolean algebra).

There are three basic Boolean operations:Union (Unite, join) - the operation combines two

volumes included in the different solids into a singlesolid.

Subtract(cut) - the operation subtracts the volume of

one solid from the other solid object.Intersection- the operation keeps only the volumecommon to both solids


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Extrusion or sweep

This approach comprises sketching of a cross sectionon a plane and stretching it through a curved orstraight path.

According to the path, you can have solids ofrevolution and straight extruded figures.

The cross section can also have inner loops bulgingto hollow shapes. The distance can also be provided

for having straight extrusion.


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Extrusion or sweep


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Primitive Solids and BooleanOperations

The basic primitive solid:


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Primitive Solids


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Boolean Operations

Union

Subtract

Intersection


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Implementing Boolean Operation

Consider solidsA andB.


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Boolean Operation

The intersection curves of all the faces of solidA andB arecalculated. These intersections are inscribed on the associatedfaces of the two solids.


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Union

Plan your modelingstrategybefore you startcreating the solid model

Solid Modeling Example Using CSG

Cut

Cut


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Parametric Modeling Concept

Parametricis a term used to describe a dimensionsability to change the shape of model geometry if thedimension value is modified.

Feature-basedis a term used to describe the

various components of a model. For example, a part can consists of various types of

features such as holes, grooves, fillets, and chamfers.

Parametric modeler are featured-based, parametric,solid modeling design program: SolidWorks, Pro-Engineer, Unigraphics etc


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Design Intent

In parametric modeling,dimensions control the model.

Design intent is how your modelwill react when dimension valuesare changed.


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Design Notes

Dimensioning scheme can be changed at anytime.

You are not locked into a specific design.

You can also design without dimensioning, rough

out a sketch, and then later go back and fullydefine it.

Do not be concerned with dimensioning totolerances in the part. They can be addressed in

the drawing layout. Be more concerned with your design intent.


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Boolean Versus Parametric Modeling

The ability to go back on some earlier stage in thedesign process and make changes by editing asketch or changing some dimensions is extremely

important to a designer. This is the main advantage of aparametric

(SolidWorks, Unigraphics, Inventor, Pro-Engineer)over a non-parametric modeler (AutoCAD 3D

modeler Boolean operation)


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Parametric Modeling


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Parametric Modeling


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Sketching and Features

When discussing the mind-set needed for workingwith parametric modelers, there are two topics thatneed to be expanded:Sketching and Features


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Sketching

Take the word sketch literally. A sketch should be justthat, a sketch.

When sketching, it is not necessary to create geometrywith accuracy. Lines, arcs, and additional geometryneed not be created with exact dimensions in mind.

When the dimensions are added, the sketch will changesize and shape. This is the essence of ParametricModeling.

In short, the sketch need only be the approximate size

and shape of the part being designed. When dimensionsand constraints are added, they will drive the size andthe shape of the geometry.


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Sketching

When the dimensions are added, the sketchwill change size and shape. This is the essenceofparametric modeling

In short, the sketch need only be theapproximate size and shape of the part beingdesigned. The geometric constraints anddimensions, when added, will drive the size

and the shape of the geometry. Curves are parametrically associated to each

other and the solid that is created by them.


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Creating Features from Sketches


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What are constraints in solid modeling

Most solid modelers support 'geometric constraints'. Ageometric constraint is the relationship of an entity toother entities.

Constraints are only used on the underlying sketch or

wireframe entities that define the solid objectboundaries.

Some common 'constraints' for these entities arecoincident, collinear, intersect, parallel, perpendicular,and tangent.

When one or more entities are 'constrained' to eachother, changing any of the entities will most likely havean effect on the others.


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Any dimensions added to a sketch are constraints.Notice how changing the sketch dimensions changesand updates the entire solid.

Some solid modelers automatically assign theconstraints for you as you design the part.

Others provide the ability to assign constraints asyou are designing.

Some solid modelers will automatically assignconstraints where it thinks you want them and thenallow you to modify or remove them manually later.


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Solid Models Advantages

In the solid modeling, the solid definitions include vertices(nodes), edges, surfaces, weight, and volume. The model isa complete and unambiguous representation of a preciselyenclosed and filled volume.

Has all the advantages of surface models (uniqueness, non-

ambiguous, realistic, surface profile) plus volumetricinformation. Allows the designer to create multiple options for a design. 2D standard drawings, assembly drawing and exploded

views are generated form the 3D model.


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Solid Models Advantages

Can easily be exported to different FiniteElement Methods programs for analysis.

Can be used in newly manufacturingtechniques; computer integrated

manufacturing (CIM), computer aidedmanufacturing (CAM) and design formanufacturability and assembly (DFM, DFA)

Mass and volumetric properties of an object

can be easily obtained; total mass, masscenter, area and mass moment of inertia,volume, etc.


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Solid Models Disadvantages:

More intensive computation than wireframe andsurface modeling.

Requires more powerful computers (faster with

more memory and good graphics), not a problemany more.

Date post:	03-Apr-2018
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Solid Modeling990

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