Transcript Team-based design and CAD modelling using Lego in first
ES050 – Introductory Engineering Design and Innovation Studio
Features
Prof. Paul Kurowski Oct. 30, 2009 1
Feature-Based Solid Modeling
Parts modeled by adding
features
to a base part Features “represent” manufacturing “operations” holes, ribs, fillets, chamfers, slots, pockets, etc.
Material can be added or subtracted Features can be created by extrusion, sweeping, revolving, etc.
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Feature-based Modeling Process
Create base part Add features until final shape is achieved Extruded Base Extruded Cut ES1050 part 01.SLDPRT
Extruded Cut 3
Examples
Extruded Base Rib ES050 part 03.SLDPRT
Extruded Cut 4
Extruded Base Extruded Cut Extruded Cut Fillet Extruded Boss 5
Tools for Creating Features
Geometry is defined by sketching a 2D profile on a plane, and “extending” it into 3D These profiles can be extended to 3D by: Extruding Revolving Sweeping Lofting These operations can add material or cut it away 6
Tools for Creating Features
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Extrusion
Sample of features
Revolution Sweep Hole Loft Extruded cut
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Extruded Part
Profile Extrude 9
Revolved Part
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Swept Part
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Lofted Part
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Other Features
Fillets, chamfers and rounds Shelling Holes Ribs 13
Example
Rib Shell Hole Fillet Round 14
Alternative Modeling Approaches
There are usually many ways to model an object A good approach requires few steps, and is easy to modify if necessary The modeling steps do not necessarily correspond to manufacturing steps
Think the steps through before you start!
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Modeling a Bracket
ES050 part 04.SLDPRT
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One Method
Step 1 Step 2 ES050 part 04.SLDPRT
Step 3 17
Alternative method
Step 1 Step 2 Step 3 18
Exercise Alternative sequence of modeling operations Extruded Base Rib Extruded Cut 19
Exercise Alternative sequence of modeling operations 20
Exercise Alternative sequence of modeling operations 21
ES050 – Introductory Engineering Design and Innovation Studio
Parameters and Sketching
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Outline
Design intent and parametric modelling Constraint types “Smart sketching” Examples 23
Parametric modeling Also know as Constraint-based User constrains geometry based on Design Intent Design variations can be generated by changing a few key dimensions Geometry is automatically regenerated based on constraints 24
Example
•The part should be twice as long as it is wide •The hole should be centered in both directions •The hole diameter should be 50mm D5=50 D1 D2=D1/2 D4=D3/2 D3=2*D1 25
Sketch parameters (dimensions) constrained by equations Feature created with that sketch + Cut extrude added ES050 part 02.SLDPRT
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Smart Sketching
Most CAD systems use “smart” sketching tools Design intent is inferred, and constraints added automatically as you draw For example, two lines that are nearly perpendicular “snap” perpendicular, with a constraint SolidWorks calls this “Automatic Relations” 27
SolidWorks Automatic Relations (Geometric Constraints) 28
Before adding constraints 29
After adding geometric constraints
Perpendicular Concentric Tangent
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After adding dimensional constraints 31
Unconstrained sketch Constrained sketch 32
Constraint Types
Geometric constraints Dimensional constraints 33
Boolean operations
Geometric constraints Dimensional constraints boolean.SLDPRT
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Summary
Parametric modeling captures
design intent
Easy to modify part geometry by changing parameters 35
Select the correct answer: A. First feature must be a positive feature B. Each new feature always adds more material to model C. Parameters are changed into dimensions once model has been saved D. 2D sketch is used to create 2D geometry, 3D sketch is used too create 3D geometry E. Wireframe models are used primarily to model electric circuits 36
Select the correct answer: A. Sketch can only be created on a face of a solid B. Sketch can be created on a reference plane or on a flat face of solid geometry C. 3D solid geometry is created by closing-up space with surfaces D.
2D sketch can’t be used to construct 3D geometry E. Once solid has been created the sketch use for its definition can be safely deleted 37