Lecture 4 - CAD: Introduction and Modeling Operations PDF

Engineering Design and Material Selection Lecture 4 — CAD: Introduction and Modeling Operations Prof. Dr. Kristina Shea Dr. Tino Stankovic Prof. Kristina Shea 1  Course Schedule Week/ Topic...

Engineering Design and Material Selection Lecture 4 — CAD: Introduction and Modeling Operations Prof. Dr. Kristina Shea Dr. Tino Stankovic 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 ▪ Introduction to Kyburz PLUS II case study ▪ Introduction to CAD ▪ Understand the types of geometric models ▪ Learn fundamentals of CAD modeling ▪ Learn the basics of sketching in a CAD system ▪ Introduction to the balloon powered car project Prof. Kristina Shea Engineering Design + Computing Laboratory 6  Electric Mobility By Ferdinand Porsche, 1998 By Jürg Streun By Philwjan From STROMER From Porsche Prof. Kristina Shea Engineering Design + Computing Laboratory 8  Mechanical Systems are Highly Interdisciplinary Engineering Materials Design Mechanics Electronics Computing Image credit: Porsche Prof. Kristina Shea Bachelor Focus Design, Mechanics and Materials 11.10.2024 10 10  Introduction to Kyburz PLUS II PLUS II: single person transport electric vehicle ▪ Target user: elderly people, people without a driver license ▪ Max. speed 10, 20 or 30 km/h ▪ Range: 65 to 120 km ▪ Empty weight: 300 kg ▪ Max. payload: 160 kg Source: https://kyburz-switzerland.ch/en/passenger_vehicles/plus Prof. Kristina Shea Engineering Design + Computing Laboratory 11  CAD Model of the PLUS II: Exploded View Chassis Bodywork Windshield Electronics Door Steering system and front wheels Drivetrain and back wheels Prof. Kristina Shea Engineering Design + Computing Laboratory 13  Drivetrain Prof. Kristina Shea Engineering Design + Computing Laboratory 14  Drivetrain Electric Motor Rear Axle Wheel Differential Suspension Universal Joints Prof. Kristina Shea Engineering Design + Computing Laboratory 15  Use of CAD Models in Product Development CAD Model Documentation Tolerance Model Virtual Reality Visualization Simulation Models e.g. Finite Element Analysis Virtual Prototypes CAD/CAM Physical Prototypes Digital Mock-Up Computer Aided Additive Manufacture Manufacturing Prof. Kristina Shea Engineering Design + Computing Laboratory 17  Types of Geometric Models Geometric models 3D models 2D models 3D 3D surface 3D solid 2D wireframe models models drawings Bézier curves Boundary and surfaces representations (B-reps) B-spline curves Solid Primitives and surfaces NURBS curves and surfaces Prof. Kristina Shea Engineering Design + Computing Laboratory 18  Which Body is Represented by this Wireframe Model? a) b) c) Prof. Kristina Shea Engineering Design + Computing Laboratory 20  3D Solid Models I: Solid Primitives These primitives are defined in most solid modeling systems: Prof. Kristina Shea Engineering Design + Computing Laboratory 23  3D Solid Models I: Boolean Set Operations Take two solid primitives B A and B A B union () difference (–) intersection () AB A–B A B Two solids are The intersecting volume of Only the intersecting unified to make one one solid (B) is removed volume of two solids solid from another solid (A) remains Prof. Kristina Shea Engineering Design + Computing Laboratory 24  3D Solid Models I: Different Modeling Steps A single part, even simple, can be represented by a different modeling sequence. I  Prof. Kristina Shea Engineering Design + Computing Laboratory 26  3D Solid Models II: Boundary Representation Model (B-rep) A B-rep model represents a 3D object through “topology”, i.e.: ▪ faces (F) V1 E1 V2 ▪ edges (E) ▪ vertices (V) F1 v1 and corresponding geometry: ▪ surfaces ▪ lines and curves ▪ points Prof. Kristina Shea Engineering Design + Computing Laboratory 27  Parametric Modeling ▪ Why? - Create models that can be easily changed and updated ▪ Parametric models are created by linking geometric entities through definition of parametric relations ▪ Parametric models can be created and manipulated through: ▪ user interaction with the CAD interface ▪ linked spreadsheets or tables, e.g. Excel ▪ Due to the explicit and bidirectional definition of the links between the parameters, model consistency is maintained after modifications Prof. Kristina Shea Engineering Design + Computing Laboratory 32  Sketch and Parametric Modeling – Overview 1 Define Rough Geometry and Parameters a 1 2 2 Define Geometric R Constraints b 5 3 Evaluate Model Geometric Constraints: (constraint solver) 3 1: line 5 // line 3  2: line 5 ⊥ line 1 4 Create Variants change values 4 add constraints remove constraints Source: Shah and Mäntylä 1995 Prof. Kristina Shea Engineering Design + Computing Laboratory 33  Sketching in CAD systems ▪ Creation of 2D shapes that are then manipulated by various operations (e.g. extruding, revolving, etc.) to produce 3D models ▪ Sketches are composed of sets of basic Dimensioned and constrained rectangular shape is geometric elements, e.g. points, lines and extruded into a block in the z-direction curves, etc. ▪ Sketches are dimensioned using geometric parameters z ▪ Sketches are constrained Prof. Kristina Shea Engineering Design + Computing Laboratory 34  NX Sketching Example Prof. Kristina Shea Engineering Design + Computing Laboratory 35 NX Sketching Example: Movie  Suggested CAD Sketching Process 1. Plan what you want to sketch in CAD 2. Define sketch reference (placement and orientation) 3. Sketch the rough geometry 4. Relate sketch to the environment (min. one point) 5. Add constraints and then dimensions 6. Check if sketch is fully constrained (CAD status) 7. Define correct dimensions 8. Test the sketch behavior – Is it stable? Prof. Kristina Shea Engineering Design + Computing Laboratory 37  Basic Sketch Geometry ▪ Keep sketches simple – complex 3D model features could be added later 1. Define shape Sketching tch base 2. Extrude shape Modeling 3. Round edges operations 4. Mirror around x-z plane Prof. Kristina Shea Engineering Design + Computing Laboratory 38  Reference Sketch Plane Selection ▪ Any datum plane or planar face serves as a sketch basis Global coordinate system datum planes 3D object’s planar face Prof. Kristina Shea Engineering Design + Computing Laboratory 39  Sketch Positioning ▪ Align towards the global coordinate system carefully, think about model symmetry! 1. Create one flange 2. Add holes 3. Mirror flange over y-z 4. Create pipe Prof. Kristina Shea Engineering Design + Computing Laboratory 40  Constraints and Dimensions in Sketches Basic Geometric Constraints: Dimensional Constraints: ▪ Vertical ▪ Distance ▪ Horizontal ▪ Horizontal distance ▪ Perpendicular ▪ Vertical distance ▪ Coincident ▪ Angle ▪ Tangent ▪ Diameter ▪ Parallel ▪ Radius ▪ Co-linear ▪ Offset ▪ … Prof. Kristina Shea Engineering Design + Computing Laboratory 42  Constraining Sketches Always keep shapes roughly proportional and to scale during a dimensioning ▪ Parametric constraints are typically solved sequentially using constraint propagation 1 2 ▪ The order of constraints is either defined or R determined ▪ The results can be: b 5 ▪ Under-constrained: too few constraints, some degrees of freedom left unconstrained 3 ▪ Over-constrained: too many constraints ▪ Fully-constrained: sufficient amount of  Geometric constraints such that no degrees of freedom 4 Constraints: are left unconstrained 1: line 5 // line 3 2: line 5 ⊥ line 1 Source: Shah and Mäntylä 1995 Prof. Kristina Shea Engineering Design + Computing Laboratory 44  Modeling Operations – Based on one profile or “sketch” Planar Sketch extruding revolving sweeping Prof. Kristina Shea Engineering Design + Computing Laboratory 45  Extrusion 6. 1. 5. 2. 3. 4. Prof. Kristina Shea Engineering Design + Computing Laboratory 46  Patterns Revolving Section cut view ▪ Extrude the profile around rotation axis for a given angle. ▪ Non-intersecting sketch. Rotate sketch ▪ The sketch should not around vertical axis and mirror contain more than one closed element. Prof. Kristina Shea Engineering Design + Computing Laboratory 49  Sweeping ▪ Sweep a profile (sketch) along a defined path or curve to create a 3D object. ▪ Watch self-intersection. Example: Variable pitch spring 1. Three helixes 2. profile 3. 3D object (bottom, middle, created with top) sweep Prof. Kristina Shea Engineering Design + Computing Laboratory 50  Example: Wheel hub from the PLUS II Wheel hub Drum brake Brake back plate Bearing Axle shaft Prof. Kristina Shea Engineering Design + Computing Laboratory 53  Example: Wheel hub from the PLUS II Wheel hub: Connector between the wheel and drive shaft and the wheel and the brake. Prof. Kristina Shea Engineering Design + Computing Laboratory 54  6. Hole Wheel hub modeling steps 1. Sketch 7. Circular pattern 5. Extrude/Cut 2. Revolve 3. Edge 4. Sketch features Sketch pattern Prof. Kristina Shea Engineering Design + Computing Laboratory 55  Modeling operations: which statements are true? A. This part can be created with a single revolve operation. B. This part can be created without revolve operations. C. Using a revolve operation could decrease the number of extrudes. D. A sweep operation is necessary. Note: Exclude chamfer and rounding features. Prof. Kristina Shea Engineering Design + Computing Laboratory 56  CAD Introduction and Modeling Operations – Wrap-Up CAD systems and models are an integral part of the entire design and the product development process. Solid geometry can be represented by B-rep, which is the main solid representation used in CAD systems. 2D sketches consist of basic geometric elements and constraints and should be well-constrained. Modeling operations (extrude, revolve and sweep) are used to create complex solid models from 2D sketches. Many different modeling sequences can lead to the same end results. It is up to you to choose the appropriate path. Prof. Kristina Shea Engineering Design + Computing Laboratory 58  Design Task: Design a self-powered toy car and and make it using additive manufacturing (3D printing) ▪ How can you make your car travel the longest distance? ▪ How can you make your car style desirable? ▪ How do you design your car for AM? Prof. Kristina Shea Engineering Design + Computing Laboratory ? 63  Balloon Propelled Car – Assembly Model Top Back Chassis Wheel Axle Prof. Kristina Shea Engineering Design + Computing Laboratory 65  Exercise – CAD Modeling Introduction and Car Chassis Can you model these parts in CAD? Prof. Kristina Shea Engineering Design + Computing Laboratory 66  Balloon Propelled Car – Example CAD Models Prof. Kristina Shea Engineering Design + Computing Laboratory 67  Car Competition – Exercise Week 13 Awards ▪ Car Race – the car that travels the furthest per day. 4 x winners! ▪ Design Award – the top two voted designs per day. 8 x winners! Prof. Kristina Shea Engineering Design + Computing Laboratory 68