Post on 31-Dec-2015
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SPECIFICATIONS, CONCEPT GENERATION AND SELECTION SUMMARY
Need
Concept 1
Concept 2
Concept 3
…
Concept n
QFD
Functional Decomposition
Morphological Analysis
Ideation
Brainstorming
Patents
Reference (Books, Trade Journals)
Experts’ help
Feasibility judgment
Technology readiness
Go/no go screening
Decision matrix method
Final conceptRequired
functionality
Des
ign
rev
iew
1
Des
ign
rev
iew
2
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1. Specification Development / Planning PhaseDetermine need, customer and engineering requirements
Develop a project plan
2. Conceptual Design PhaseGenerate and evaluate concepts
Select best solution
3. Detail Design PhaseDocumentation and part specification
Prototype evaluation
4. Production PhaseComponent manufacture and assembly
Plant facilities / capabilities
5. Service PhaseInstallation, use , maintenance and safety
6. Product Retirement PhaseLength of use, disposal, and recycle
IT IS TIME TO START THE NEXT DESIGN PHASE:
THE DETAILED DESIGN
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Quality function deployment
Gantt’s charts
Critical path method
Ideation
Brainstorming
Patents
Reference materials
Functional decomposition and morphological analysis
Sketches
Feasibility judgment
technology readiness assessment
Go/no-go screening
Decision matrix method (with pair-wise comparison)
CAD
Specification Development / Planning Phase
Conceptual Design PhaseConcept generation
Conceptual Design PhaseConcept selection
WE NOW NEED A NEW TOOL: CAD
Detailed Design Phase
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Wire frame geometry
Solid geometry
Manual draftingElectronic drafting board
1970’s
1980’s
1990’s
Surface geometry
EVOLUTION OF CAD TOOLS
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MODERN CAE TOOLS
CAD
SOLID, PARAMETRIC, FEATURE BASED
FINITE ELEMENT ANALYSIS
MOTION ANALYSIS
COMPUTATIONAL FLUID DYNAMICS
…..
…..
Computer Aided Design (CAD) is at the hub of other Computer Aided Engineering (CAE ) tools
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IN MME2259a WE USE SolidWorks CAD SOFTWARE
You can burn your installation DVD on any lab computer
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PARAMETER
BASE FEATURE(“POSITIVE” SOLID)
CHILD OF BASE FEATURE(“NEGATIVE” SOLID)
WHAT IS A SOLID, PARAMETRIC, FEATURE BASED CAD?
SOLID GEOMETRY
panel 01.SLDPRT
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TO TAKE FULL ADVANTAGE OF A SOLID, PARAMETRIC,
FEATURE BASED CAD WE NEED TO UNDERSTAND HOW
TO USE IT.
WE’LL SPLIT OUR REVIEW INTO:
MODELING PHILOSOPHY
SKETCHES
FEATURES
PARTS
ASSEMBLIES
DRAWINGS
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There is one factor of model building philosophy which stands above
others – what matters the most is what we want to do with the final
geometry.
Model geometry is not created to stay – it is meant to be changed.
We need to understand which features we would like to drive and
control some other ones, what portions are to be modified, what are
the boundaries of modifications; and anticipate how the model is going
to be developed further. All of this has to be incorporated in the model
history and developed to a state where the model “behaves” the
intended way. We call this The Design Intent.
MODELING PHILOSOPHY
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The objective is not only to arrive to the destination – build the final
geometry – but to walk the journey towards it. Road to the
destination will teach us the reasons why and after arriving to the
destination we will start to understand. There are no shortcuts or
quick leaps there.
How does this all reflect on the model building techniques?
The model has to be able to easily handle changes down the road
(and, for sure, there will be changes). Changing basic dimensions,
changing number of features, changing shape – the model should
handle all such requests.
MODELING PHILOSOPHY
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3D solid modeling software usually creates 3D geometry by taking
a 2D sketch and extruding, revolving, sweeping and blending it in a
“third“ direction which results in a 3D feature.
MODELING PHILOSOPHY
Both the sketch and the feature are parametric – dimension driven.
Changing the values of dimensions (if they are meaningful) forces
the geometry to assume new shape.
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Proper feature geometry starts with proper parametric sketch.
Sketch is the entry point to incorporate design intent in the model.
Each 2D sketched entity will become a portion of a 3D feature, e.g.
lines will be converted to surfaces, endpoints become edges,
circles will become cylinders, etc.
90% of all errors are errors in sketches!
MODELING PHILOSOPHY
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The way that geometry is built does not necessarily reflect
manufacturing process of a real, physical part. It rather resembles a
step-by-step approach by adding and subtracting material.
For example, while in real life a machined part is created always by
removing material only, 3D modeling combines solid protrusions
(adding) and cuts (removing) to build geometry.
This is why the dimensioning scheme on model cannot effectively
replicate manufacturing dimensioning scheme.
MODELING PHILOSOPHY
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Sketch can be placed on a reference place or a flat face of already
existing geometry.
If possible, use underlying geometry to position sketch entities
SKETCHES
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SKETCHES
Construct the first sketch on the first reference plane
Extrude in positive direction
Keep sketches simple
Use sketch relations where possible
Test relations by rebuilding sketch with different dimensions
Constrain all sketches
Give sketches some meaningful names
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Sketch should not contain more than 12-15 geometric entities (lines, arcs,
conics, etc.) included construction geometry (centerlines, sketched
points). The more complex the sketch the harder is to control it with
minimum number of dimensions. Less is more.
Sketch implicit rules (assumptions or constraints) should be maximized to
simplify the geometry. Abundance of dimensions is worst than their
scarcity. The more dimensions we have to drive a sketch, the easier it is
to omit one when modifying feature geometry. This is one of the most
frequent mistakes.
SKETCHES
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SKETCHES
Use relations in sketches
plate 001.prt
No symmetry relations With symmetry relations
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SKETCHES
Use relations in sketches
plate 001.prt
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Use construction geometry to create “intelligent” sketches.
Here we want to control the bolt circle diameter of three holes placed in
120º. increments about the center axis of a flange.
SKETCHES
sketch extrusion pattern
flange.prt
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SKETCHES
“Massage” the sketch – change
values of crucial dimensions and
update it to find out if it behaves the
way you like.
flange.prt
Use underlying parent features for
proper alignments of sketches. This
will create parent-child relationship
between features. Use consciously
for controlling children through
parents
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Exaggerate the sketch when creating features. Say we would like to sketch a line
1º. from vertical. It is easier to sketch it about 10º from vertical, dimension it and
modify the dimension to 1 deg, than try to sketch it almost vertical, dimension it
and expect the system to accept the value. The system’s implicit rules will kick-in
assuming the line should be vertical and we will have hard time to overrule it.
SKETCHES
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SKETCHES
cup.prt
NO YES
Add details to features, not to sketches (also see the next slide)
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BASE FEATURE
FILLET FEATURE
SKETCHES
cup.prt
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Create main geometryThis is usually the main volume - the biggest feature, although it does not have to be. This feature becomes parent to majority of following features.
Add half-detailThese will be features like shells, construction ribs, cutouts, etc.
Finally create fine detailThese features are usually pick-and-place features such as rounds, chamfers, drafts, cosmetic grooves, etc.
FEATURES
Main geometry Half detail Detail
plate with boss.prt
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When creating features avoid undesirable parent-child relationships. Features
representing “cosmetic” (fine detail) geometry should not be parent of any
subsequent features, unless driven by design intent
FEATURES
YES NO
plate with boss.prt
Cosmetic feature
Cosmetic feature
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When orienting the sketch use construction planes, rather than solid
features in case the solid feature will be later redefined and its children
fail by losing their references.
FEATURES
YES
Sketch on reference plane
NO
Sketch on face
pipes.prt
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When creating features of one kind (e.g. revolved), use the same
construction plane for sketching and orientation. Sketch the entities
always on the same side of the centerline of rotation (e.g. left-hand)
FEATURES
Axis of rotation
Sketch
pipes.prt
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Avoid unattached geometry (two or more solid bodies within part).
The part geometry is by definition a continuum and should remain
continuum anytime during the history of feature creation.
FEATURES
NO
pipes.prt
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All part features should be unsuppressed when releasing (making the final version) the part.
Part must have material property and color assigned
Part must not be in roll-back mode
Features and sketches must be named
All sketched must be fully defined
Use mm, N, s, K units ( important for analysis)
Zoom to fit and position in isometric view before saving
PARTS
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ASSEMBLIES
Assembly of 3D solid modeling software in general does not
contain “assembly” geometry. The assembly contains
components (i.e. parts and lower level assemblies) assembled
together in the intended manner.
Assembly contains information on where to find parts and how
are parts oriented relative to each other (mated).
The only features that can be defined in assembly are “negative”
features (cut)
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ASSEMBLIES
When retrieving the assembly (opening assembly file), CAD program
needs the following information:
- BOM (Bill of Material) structure: This information is stored within
assembly file and is used to retrieve all listed components. It is obvious,
that the system has to be able to “see” and retrieve all components
regardless where they reside on the network.
- “Mating” information: How feature surfaces of individual components are
assembled - mated to their parent components.
- Feature information: Assembly cuts (in case they have been created) and
parts/features that are being intersected by them.
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ASSEMBLIES
BOM
MATING INFO
ASSEMBLY FEATURE (CUT)
shear pin.sldasm
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ASSEMBLIES
bracket002.sldasm
Mating can use parts geometry or reference geometry