Engineering Design and Material Selection Lecture 5 — CAD Features and Parametric Modeling PDF

Engineering Design and Material Selection Lecture 5 — CAD: Features and Parametric Modeling Dr. Tino Stankovic Prof. Dr. Kristina Shea Prof. Kristina Shea 1  Course Schedule Week/ Topic...

Engineering Design and Material Selection Lecture 5 — CAD: Features and Parametric Modeling Dr. Tino Stankovic Prof. Dr. Kristina Shea Prof. Kristina Shea 1  Course Schedule Week/ Topic Case study Quiz Lecturer Dates 1 Introduction and Sketching 2 Introducing Engineering Design Health Prof. Dr. Kristina Shea 3 Technical Drawing: Projections and Cuts 4 CAD: Introduction and Modeling Operations 5 CAD: Features and Parametric Modeling Future Mobility 6 CAD: Freeform Modeling Dr. Tino Stankovic 7 CAD: Assemblies and Standard Mechanical Parts X (45 min) 8 Technical Drawing: Dimensioning Health 9 Sustainability in Engineering Design 10 Materials and their Properties 11 Manufacturing Processes with Focus on Additive Manufacturing Sustainable Materials Prof. Dr. Kristina Shea 12 Material Selection 13 Review and Q+A X (75 min) Prof. Kristina Shea Engineering Design + Computing Laboratory 2  Learning Objectives ▪ Learn to think parametrically about design in CAD systems. ▪ Understand the concept of a feature, basic feature types and their properties. ▪ Understand what part families are and how they are used. ▪ Introduce Additive Manufacturing (3D Printing). Prof. Kristina Shea Engineering Design + Computing Laboratory 3  CAD Model of the PLUS II Chassis Bodywork Windshield Electronics Door Steering system and front wheels Drivetrain and back wheels Prof. Kristina Shea Engineering Design + Computing Laboratory 4  Drivetrain Prof. Kristina Shea Engineering Design + Computing Laboratory 5  Drivetrain Section Electric Motor Wheel Suspension Prof. Kristina Shea Engineering Design + Computing Laboratory 6  Example part from Kyburz: Motor Shaft Motor Shaft Major parts in model: ▪ Orange: bearings ▪ Green: sealings ▪ Blue: drive shaft including universal joints Motor Shaft ▪ Pink: coupling motor - shaft ▪ Red: differential drive ▪ Grey: gears, transmission from motor to differential drive / drive shaft Prof. Kristina Shea Engineering Design + Computing Laboratory 7  Question: Modeling operations (Lecture 4) Which modeling sequence is best suited to represent the basic shape of this part? 1. Extrudes only 2. Revolve only Prof. Kristina Shea 8  How can we encode the engineering meaning of geometry? Gear Key seat Chamfer Center hole Locking pattern Groove 1. Define the basic shape → “Design-by-Features” 2. Add features Prof. Kristina Shea Engineering Design + Computing Laboratory 9  What is a feature? ▪ Definition: A feature represents the engineering meaning, or semantics, of the geometry of a part or assembly. Cross-section cut of a Stepped blind hole block showing a stepped blind hole feature Prof. Kristina Shea Engineering Design + Computing Laboratory 10  Feature-Based Design (FBD) and Parametric Modeling ▪ Fast propagation of design changes and building-in design/engineering information in the model Geometric elements ℎ Treat as unit with necessary Key seat feature parameters Prof. Kristina Shea Engineering Design + Computing Laboratory 11  Form Features Stepped thru-hole ▪ Portions of a part’s geometry Wedge ▪ Recurring and common shapes Slot (back- Boss face) ▪ Independent and dependent feature parameters Pocket Pocket Form features example Slot (ANC101 object) Prof. Kristina Shea Engineering Design + Computing Laboratory 12  Feature-Based Model 1. Define the basic shape 2. Add features 3. The model (feature) history tree contains operations performed to create a part. Prof. Kristina Shea Engineering Design + Computing Laboratory 13  Feature-Based Model Independent and dependent properties Prof. Kristina Shea Engineering Design + Computing Laboratory 14  Independent (intra-feature) properties Thru-slot example ▪ User-defined parameters and dimensions (ℎ) ▪ Geometric shape (block, sketch based) ℎ 𝑤 ▪ Parameter labels or names (“thru-all”) ▪ Derived parameters and dimensions (e.g. 𝑤 =.6ℎ) ▪ (Form and size tolerances) ▪ (Orientation tolerances) Prof. Kristina Shea Engineering Design + Computing Laboratory 15  Dependent (inter-feature) properties Thru-slot example ▪ Derived parameters and dimensions (e.g. 𝐿) 𝐿 ▪ Feature location (Sketch on 𝑓1 ) 𝑓1 ▪ Feature orientation (Orthogonal to 𝑓1 ) 𝑑1 ▪ Constraints on feature size, location, or orientation parameters ▪ (Inter-feature tolerances) Prof. Kristina Shea Engineering Design + Computing Laboratory 16  Composite Features ▪ Composite features share two or more “simpler” features ▪ Only one element in history tree ▪ Pattern features – represent recurring relations ▪ Compound features among– consists of several features, e.g. a “pattern” of holes: features which are grouped together, e.g. a stepped hole: Prof. Kristina Shea Engineering Design + Computing Laboratory 19  Pulley - Goal Model Pattern Feature Example 2. Revolve 360° 1. Sketch 3. Hole Feature (center) 4. Hole Feature 5. Pattern Hole Feature Prof. Kristina Shea Engineering Design + Computing Laboratory 20  Pattern Feature Example 6. Reference Plane 7. Sketch 8. Extrude (“until next”) 9. Pattern Rib 10. Chamfer and Round 11. Mirror Geometry Prof. Kristina Shea Engineering Design + Computing Laboratory 21  Assembly and Tolerance Features Co-axial assembly feature Profile tolerance example Actual surface must be within a tolerance zone spaced equally about each line element of the profile Prof. Kristina Shea Engineering Design + Computing Laboratory 22  Feature Verification I Extrusion “to-next” Termination? Step 1 Step 2 Step 3 Fillet Round Overlapping fillet and round Prof. Kristina Shea Engineering Design + Computing Laboratory 23  Feature Verification II Model History: Model History: Sketch 1 Sketch 1 Cylinder (Extrude) Cylinder (Extrude) Hole 𝜙10 Hole 𝜙10 Sketch 1 Sketch 2 Cylinder (Extrude) Model History: Model History: Sketch 1 Sketch 2 Block (Extrude) Block (Extrude) Edge Blend Prof. Kristina Shea Engineering Design + Computing Laboratory 24  History Dependency and Interaction I Prof. Kristina Shea Engineering Design + Computing Laboratory 25  History Dependency and Interaction II 1. block 2. hole 3. pattern 4. shell 5. hole Bottom view of the object after all modeling operations and features have been applied Prof. Kristina Shea Engineering Design + Computing Laboratory 26  Question: Alternative Model 1. block Which alteration of the CAD modeling steps leads to the model shown below? 2. hole 3. pattern a) Switching the order of the “shell” and “hole” steps. 4. shell b) Replacing one modeling step with a different one 5. hole c) Changing the parameters of one modeling step ? Prof. Kristina Shea Engineering Design + Computing Laboratory 27  History Dependency and Interaction III 1. block 2. hole 3. pattern 4. hole 5. shell Bottom view of the object after all modeling operations and features have been applied Prof. Kristina Shea Engineering Design + Computing Laboratory 28  Sketch (L4) and Parametric Modeling Overview 1 Define Rough a Geometry and Parameters 1 2 R 2 Define Geometric Constraints b 5 3 Evaluate Model 3 (constraint solver) 4  A 4 Create Variants Parametric relations and constraints: change values 1: line 5 // line 3 4: lines 1 & 3 tangential to arc 2 add constraints 2: line 5 ⊥ line 1 5: line 5 vertical remove constraints 3: R = b/2 6: point A constrained to (0,0) Source: Shah and Mäntylä 1995 Prof. Kristina Shea Engineering Design + Computing Laboratory 29  Question: Parametric Modeling ▪Imagine replacing p0 = 90mm with the following relation: p0 = p1 + 10mm →What would the CAD system do? a) Solve the constraints and update the model b) Return an error Prof. Kristina Shea Engineering Design + Computing Laboratory 30  How to Create a Parametric Model ▪ Parametric models are created by linking geometric entities through definition of parametric relations Height2 – governs the Name Formula Value cylinder extrusion height Length 100 100 Height1 10 10 Height2 5 5 L if (Length