🖥️Computer Aided Drafting and Design Unit 9 – Parametric & Feature-Based Design

Key Concepts

• Parametric modeling defines geometric relationships and constraints to create adaptable designs
• Feature-based design constructs models using a series of features (extrude, revolve, sweep, loft)
• Associativity maintains connections between features, allowing updates to propagate throughout the model
• Design intent captures the purpose and function of a model, guiding the creation and modification process
• Model tree organizes and displays the sequence of features and operations used to create a model
  • Allows for easy navigation and editing of the model's construction history
• Sketch-based modeling creates 2D profiles that serve as the basis for 3D features
• Solid modeling represents objects as solid volumes, enabling mass property analysis and interference checking

Software and Tools

• CAD software (SolidWorks, Autodesk Inventor, Creo) provides parametric and feature-based modeling capabilities
• Sketching tools allow for the creation of 2D profiles using lines, arcs, splines, and dimensions
• Feature tools (extrude, revolve, sweep, loft) transform 2D sketches into 3D geometry
• Assembly modeling tools enable the creation of multi-part designs and the definition of part relationships
• Visualization tools (rendering, animation) help communicate design intent and functionality
• Data management tools (PDM, PLM) facilitate collaboration and version control for complex projects
• Simulation tools (FEA, CFD) allow for virtual testing and optimization of designs

Parametric Modeling Basics

• Parametric modeling uses variables and equations to define the size and shape of geometry
• Dimensions and parameters drive the geometry, allowing for easy modification and design exploration
• Sketches form the foundation of parametric models, capturing design intent through geometric relationships
  • Sketch constraints (coincident, parallel, perpendicular, tangent) maintain desired geometry during updates
• Base features (extrude, revolve) create the initial 3D geometry from sketches
• Secondary features (cut, fillet, chamfer) modify and refine the base geometry
• Feature order and dependencies impact the model's behavior and adaptability
• Parametric models enable rapid design iterations and what-if scenarios by adjusting key parameters

Feature-Based Design Techniques

• Extrude features create 3D geometry by projecting a 2D sketch along a straight path
  • Can add or remove material, with options for blind, through-all, or up-to-surface extents
• Revolve features create 3D geometry by rotating a 2D sketch around an axis
  • Ideal for creating cylindrical or axisymmetric shapes (shafts, bottles, bowls)
• Sweep features create 3D geometry by moving a 2D profile along a path
  • Path can be a sketch or reference geometry, allowing for complex shapes (pipes, ducts, moldings)
• Loft features create 3D geometry by interpolating between multiple 2D profiles
  • Useful for creating smooth transitions between different cross-sections (aircraft wings, car hoods)
• Shell features hollow out solid geometry, creating thin-walled parts with uniform wall thickness
• Rib features add reinforcing structures to thin-walled parts, improving strength and stiffness
• Draft features apply angled faces to molded parts, facilitating removal from molds

Constraints and Relationships

• Geometric constraints define the desired shape and behavior of sketches and features
  • Sketch constraints (coincident, parallel, perpendicular, tangent) maintain relationships between sketch entities
  • Assembly constraints (mate, angle, tangent, insert) define the position and orientation of parts in an assembly
• Dimensional constraints control the size and location of geometry using numeric values or equations
  • Driving dimensions directly impact the geometry and can be easily modified
  • Driven dimensions are calculated based on other dimensions and geometric relationships
• Parametric relationships link dimensions and features, allowing changes to propagate throughout the model
  • Equations establish mathematical relationships between dimensions (length = width * 2)
  • Global variables store values that can be referenced across multiple features and parts
• Design tables capture multiple configurations of a model by defining different sets of parameter values
  • Enables the creation of part families and variations within a single model file

Advanced Modeling Strategies

• Multi-body modeling creates multiple solid bodies within a single part file
  • Useful for creating complex shapes that are difficult to achieve with a single feature
  • Bodies can be combined using Boolean operations (union, subtract, intersect) to create the final geometry
• Surface modeling creates freeform shapes using NURBS (Non-Uniform Rational B-Splines) surfaces
  • Ideal for creating organic or sculptural forms (car bodies, consumer products, medical devices)
  • Surfaces can be stitched together and thickened to create solid geometry
• Direct editing allows for push-pull modification of geometry without relying on parametric features
  • Useful for quick changes or working with imported geometry lacking feature history
• Topology optimization iteratively removes material from a design space to create lightweight, efficient structures
  • Requires defining loads, constraints, and optimization goals (minimize mass, maximize stiffness)
• Generative design explores multiple design options based on user-defined goals and constraints
  • Generates optimized geometry that may be difficult to conceive or create manually

Practical Applications

• Product design and development
  • Parametric modeling enables rapid iteration and optimization of designs (consumer products, machinery, vehicles)
  • Feature-based design captures design intent and facilitates changes throughout the development process
• Manufacturing and tooling
  • Parametric models can be easily adapted to accommodate manufacturing constraints and requirements
  • Feature-based design supports the creation of molds, dies, and fixtures (injection molding, casting, stamping)
• Architecture and construction
  • Parametric modeling allows for the exploration of building forms and the generation of complex geometries
  • Feature-based design facilitates the creation of detailed building components (walls, windows, roofs)
• Medical and dental applications
  • Parametric modeling enables the creation of patient-specific implants and prosthetics based on anatomical data
  • Feature-based design supports the development of surgical guides and dental restorations

Tips and Best Practices

• Plan your modeling approach before starting, considering the desired outcome and potential changes
• Create robust sketches that capture design intent and allow for flexibility
  • Use sketch constraints and dimensions to control geometry and maintain relationships
  • Avoid over-constraining sketches, as this can limit adaptability and cause errors
• Use descriptive names for features, sketches, and parameters to improve model clarity and collaboration
• Organize the model tree by grouping related features and using folders
• Leverage symmetry and pattern features to simplify the modeling process and reduce file size
  • Mirror features across planes of symmetry
  • Use linear, circular, or sketch-driven patterns to replicate features
• Create reusable design elements (templates, libraries, custom features) to streamline modeling tasks
• Validate designs using interference checking, mass property analysis, and simulation tools
• Document design decisions, assumptions, and rationale to facilitate future modifications and troubleshooting