lecture3 introduction to solid modeling

8/17/2019 Lecture3 Introduction to Solid Modeling

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Mechanical Engineering Dept.1

Geometric modeling is a computer compatiblemathematical description of the geometry of anobject.


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Modeling or Design (CAD)

• Encompass dierent options of generating the modelwith advanced and modifying tools and techniques• Better graphics to visualize the design graphically

Analysis & Optimization (CAE)• ass property calculation !

• "olumemetric#area calculation• $tress analysis#%&' analysis (• )ssembly mating and interference chec*ing• otion analysis of mechanisms + robots• ,olerance chec* analysis• %rash analysis for virtual crash testing

The diferent elds or whih a geometrimodel is !sed are listed "elow withollowing harateristis#$


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Ken YoussefiMechanical Engineering Dept.3

Comp!ter Aided Design Drating & Do!mentation (CADD)•Generating production drawings•"isualizing information and drawings.

-sing hidden line#surface removal.

atched or shaded image.Generating the dimensions( production symbol and )nnotation etc.Generating e/ploded views( cut sections for technical illustrations.)ttaining comments annotations .

Comp!ter Aided Man!at!ring•0rocess planning and scheduling.•%art programming(#Robot programming.•)ctual production control.

ill o Material (OM) 'eneration

•aterial requirement.•anufacturing resource planning

nspetion & !ality Control•1nspection machines#robot 1nspection

•%omparison of design and part $peci2cation


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4

,ypes of Geometric odels


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3' models are easier to interpret. $imulation under real4life conditions. 5ess e/pensive than building a physical

model. 3' models can be used to perform 2nite

element analysis 6stress( de7ection(thermal8..9.

3' models can be used directly inmanufacturing( %omputer :umerical %ontrol

6%:%9. %an be used for presentations and

mar*eting.



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;ireframe modeling $urface modeling $olid modeling


There are three basic types of three!i"ensionalco"puter geo"etric "o!eling "etho!s#


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%ontains information about the locations of allthe points 6vertices9 and edges in space

coordinates. Each verte/ is de2ned by /( y( z coordinate. Edges are de2ned by a pair of vertices. &aces are de2ned as three or more edges.

;ireframe is a collection of edges( there is nos*in de2ning the area between the edges.

Mechanical Engineering Dept.$


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%an quic*ly and e


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'o not represent an actual solids 6nosurface and volume9.

%annot model comple/ curved surfaces. %annot be used to calculate dynamic

properties. )mbiguous views

Mechanical Engineering Dept.&

Disadvantages:


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$urface models de2ne the surface

features( as well as the edges( ofobjects.

) mathematical function describes thepath of a curve 6parametric techniques9.

$urfaces are edited as single entities.


A surface model represents the skin of an object,these skins have no thickness or material type.


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Eliminates ambiguity and uniqueness present inwireframe models by hiding lines not seen.

=enders the model for better visualization andpresentation( objects appear more realistic.

0rovides the surface geometry for %:% machining. 0rovides the geometry needed for mold and diedesign.

%an be used to design and analyze comple/ free4formed surfaces 6ship hulls( airplane fuselages( carbodies( 89.

$urface properties such as roughness( color andre7ectivity can be assigned and demonstrated.


Advantages:


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$urface models provide no informationabout the inside of an object.

%omplicated computation( depending onthe number of surfaces


Disadvantages:


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as all the advantages of surface models6uniqueness( non4ambiguous( realistic(surface pro2le9 plus volumetric information.

)llows the designer to create multipleoptions for a design.

>' standard drawings( assembly drawingand e/ploded views are generated form the3' model.


In the solid modeling, the solid definitions include vertices

(nodes), edges, surfaces, weight, and volume. The model is a

complete and unambiguous representation of a preciselyenclosed and filled volume.

Advantages:


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%an easily be e/ported to dierent &initeElement ethods programs for analysis.

%an be used in newly manufacturingtechniques? computer integrated

manufacturing 6%19( computer aidedmanufacturing 6%)9 and design formanufacturability ans assembly 6'&('&)9

ass and volumetric properties of an

object can be easily obtained? total mass(mass center( area and mass moment ofinertia( volume( radius of gyration( 8


Advantages:


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• Volumetric and Mass properties of an object can be easily obtained.

orresponding mass properties are obtained if density is included.


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ore intensive computation thanwireframe and surface modeling.

=equires more powerful computers 6faster

with more memory and good graphics9( nota problem any more.

Mechanical Engineering Dept.1$

Disadvantages:


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Boundary =epresentation 6B4rep9(mostly used in 2nite element programs.

%onstructive $olid Geometry 6%$G9(

%)' pac*ages? -nigraphics( )uto%)' @3' modeler. 0arametric odeling( %)' pac*ages?

-nigraphics( $olid;or*s( 1nventor by

)uto'es*( 0ro#Engineer( 8.

Mechanical Engineering Dept.1%


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) solid model is formed by de2ning the surfacesthat form its boundary 6edges and surfaces9

,he face of a B4rep represents an oriented

surface( there are two sides to the surface? solidside 6inside9 and void side 6outside9( unli*efaces in a wireframe.

B4rep model is created using Euler operation

any &inite Element ethod 6&E9 programsuse this method. )llows the interior meshing ofthe volume to be more easily controlled.

Mechanical Engineering Dept.1&


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Mechanical Engineering Dept.2'


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(eo"etric entities store! in )*ep !ata structuresare the shell, face, loop, edge, an! vertex.

+perators are nee!e! to "anipulate these entities

,e.g.- an operator to "ae an e!ge- an operator to!elete an e!ge-/0


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pplies to the geo"etric entities


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Mechanical Engineering Dept.


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%$G de2nes a model in terms of combining basic

and generated 6using e/trusion and sweepingoperation9 solid shapes.

%$G uses Boolean operations to construct amodel 6George Boole( AAC4AD( inventedBoolean algebra9.

,here are three basic Boolean operationsFUnion (*nite+ ,oin) $ the operation

om"ines two -ol!mes inl!ded in thediferent solids into a single solid.

Subtract (!t) $ the operation s!"tratsthe -ol!me o one solid rom the othersolid o",et.

Intersection $ the operation /eeps onlythe -ol!me ommon to "oth solids



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The basic primitive solid!


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The location of

the insertion baseor base point an!

!efault aes

orientation.


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"nion

#ubtract

Intersection


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onsider solids A and B.


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The intersection curves of all the faces of solid A and B are calculated. These intersections are inscribed on the

associated faces of the two solids.


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The faces of solid A are classified according to their relative location

with respect to solid B. $ach face is tested to determine whether it islocated inside, outside, or on the boundary surface of solid %.

The faces in group A& are outside solid B, and those of group B

& are

inside solid A.


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'roups of faces are collected according to the specific

%oolean operation and the unnecessary face groups are

eliminated. or eample, for union operation, group A& and

B* are collected and A

* and B

& are eliminated.


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The two solids are glued at their common boundary.


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nion

lan your "o!eling strategy before you start creating the

soli! "o!el

Solid Modeling Example Using CSG

ut

ut


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Parametric is a term used to describe adimensions ability to change the shape ofmodel geometry if the dimension value ismodi2ed.

Feature-based is a term used to describethe various components of a model. &ore/ample( a part can consists of varioustypes of features such as holes( grooves(2llets( and chamfers.

0arametric modeler are featured4based(parametric( solid modeling designprogramF 0olid 1or/s+ %ro$Engineer+*nigraphis (C0' and parametri)+ 8..



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1n parametric modeling( dimensionscontrol the model.

'esign intent is how your model willreact when dimension values arechanged.



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+emember that the placement of dimensions is very importantbecause they are being used to drive the shape of the geometry. If

the *. in. vertical dimension increases, the *. in. flat across the

chamfer will be maintained, but its angle will change.

The drawing shows the intent of the

designer that the inclined plane(chamfer) should have a flat area

measuring *. inches and that it

should start at a point &.* inches

from the base of the drawing. These

parameters are what the designer

deemed significant for this model.

2.5'

4.''

&.*

*.-

$ample!


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n this !ra7ing- 7hat is i"portantto the !esigner is the 8ertical

location an! hori9ontal !i"ension

of the cha"fer- rather than the flat

of the cha"fer.

2.5'

4.''

1.25

2.125

n the last !ra7ing- the !esigner

calls for a specific angle for the

cha"fer. n this case the angle of

the cha"fer shoul! be

!i"ensione!.

2.5'

4.''

&.

/-.-0


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Heep in mind that dimensioning schemecan be changed at any time. Iou are notloc*ed into a speci2c design. Iou can alsodesign without dimensioning( rough out a

s*etch( and then later go bac* and fullyde2ne it. 'o not be concerned with dimensioning to

datum or stac*ed tolerances in the part. ,hose issues can be addressed in thedrawing layout. Be more concerned withyour design intent.



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The ability to go bac on so"e earlier stage in the

!esign process an! "ae changes by e!iting a setch

or changing so"e !i"ensions is etre"ely i"portant

to a !esigner. This is the "ain a!8antage of a parametric ,:oli!;ors- nigraphics- n8entor- ro

Engineer0 o8er a non-parametric "o!eler ,utoD

3D "o!eler < )oolean operation0


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$ample!

=et>s assu"e that it is !esire! to !esign a part

consisting of a ring 7ith a certain thicness an! a

series of counter bore holes along the peri"eter.


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Mechanical Engineering Dept. 5'

%oolean operation

Mae the base part by

creating t7o cylin!ers an!

subtract the s"all one fro"

the large one

reate the soli! geo"etry that 7ill

beco"e the counter bore holes an!generate the pattern.


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osition the pattern about the peri"eter of the

base part. =ocating the holes is critical tocreating an accurate soli! "o!el.

1hat would happen if you had to come bac2 to this part to change

the thic2ness of the ring or si3e of the counterbore holes4

:ince )oolean operation 7as use! to create the part- changing the

thicness 7oul! not increase the height of the holes. There is no

association bet7een the thicness an! the hole pattern location.

:ubtract the pattern fro" the base part to

create the actual holes.


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Mechanical Engineering Dept. 52

5arametric modeling ,:oli!;ors- roE- (- /0

reate the initial base- the ring- by

etru!ing the profile ,circles0 in a

particular !irection ,ro?E or

:oli!;ors0 or use pri"iti8e soli!san! )oolean operation ,(0.

reate the counter bore as a

feature. :elect the top surface of

the ring an! either setch the t7oholes an! etru!e at !ifferent !epth

or use the hole feature option.


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The net step 7oul! be to pattern the

hole.

The pattern 7oul! actually be

consi!ere! a feature in itself- an!

7oul! ha8e its set of para"etric8ariables- such as the nu"ber of

copies an! the angle bet7een copies.

The "o!el create! 7oul! be i!entical to the one create!

using )oolean operation- but with intelligence built into

the model.


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The true po7er of para"etric "o!eling shines through 7hendesign changes nee! to be "a!e. The !esign "o!ification is

"a!e by si"ply changing a !i"ension.

:ince the counterbore is associate! 7ith the top surface of the

ring- any changes in the thicness of the ring 7oul! auto"atically

be reflecte! on the counterbore !epth.


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;hen !iscussing the "in!set nee!e! for 7oring 7ith

para"etric "o!elers- there are t7o topics that nee! to be

epan!e!# Sketching and Featres

n short- the setch nee! only be the approi"ate si9e an! shape

of the part being !esigne!. ;hen !i"ensions an! constraints are

a!!e!- they 7ill !ri8e the si9e an! the shape of the geo"etry.

Sketching ;hen the !i"ensions are a!!e!- the setch 7ill change si9e

an! shape. This is the essence of parametric modeling :etches are able to capture the !esigner>s intent for the part

lie no other techni@ue.


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Ken YoussefiMechanical Engineering Dept. 56


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Sketched Feature

Mechanical Engineering Dept. 5$

Featres

reate a feature fro" the setch by etru!ing-

re8ol8ing- s7eeping- lofting an! blen!ing.

2.$5

2.51.'

.25

.$5

reate a 2D setch.

*e8ol8e! feature Etru!e! feature


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Mechanical Engineering Dept. 5%


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Mechanical Engineering Dept. 5&

A Applied Feature

pplie! feature !oes not re@uire a setch.

They are applie! !irectly to the "o!el.

Billets an! cha"fers are 8ery co""on

applie! features.hamfer

illet


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lecture3 introduction to solid modeling

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