7.3 Introduction to computer-aided design (CAD) software

Computer-aided design (CAD) software revolutionized engineering graphics. It's a game-changer, allowing us to create precise 2D and 3D models with ease. CAD tools streamline the design process, from sketching to final drawings.

In this section, we'll dive into CAD basics. We'll explore the interface, modeling techniques, and how to add constraints and dimensions. Plus, we'll learn to create professional drawings from our 3D models. It's all about boosting productivity and accuracy.

Basic CAD Tools

Interface and Navigation

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• CAD software interfaces consist of modeling workspace, toolbars, feature trees, and property panels allowing efficient organization and access to tools
• Selection tools choose specific entities (points, lines, faces) for editing or referencing forming the foundation for all CAD operations
• View manipulation tools enable navigation in 3D space
  • Pan moves the view parallel to the screen
  • Zoom adjusts the magnification level
  • Rotate changes the viewing angle of the model
• Feature tree provides hierarchical representation of model construction history crucial for complex model editing
• Shortcut keys and customizable interfaces enhance productivity
  • Common shortcuts include Ctrl+S for save, Ctrl+Z for undo
  • Customization options allow rearrangement of toolbars and creation of macros

Productivity Enhancements

• Snap tools automatically align geometry to existing points, lines, or grids improving precision (endpoint snap, midpoint snap)
• Layer management organizes model elements into categories for easier manipulation and visualization
• Measurement tools calculate distances, angles, and areas between model elements aiding in analysis and verification
• Rendering capabilities generate photorealistic images of models useful for presentations and marketing materials
• File management features handle large assemblies and facilitate collaboration (PDM systems, cloud-based storage)

2D & 3D Modeling

2D Sketching Fundamentals

• 2D sketching tools create accurate planar geometry forming the basis for 3D modeling
  • Line tool draws straight segments between two points
  • Circle tool creates perfect circles from center point and radius
  • Arc tool generates curved segments defined by three points or center and endpoints
  • Rectangle tool produces four-sided shapes with right angles
  • Spline tool creates smooth curves through multiple control points
• Sketch relations define geometric relationships between entities
  • Horizontal and vertical constraints align lines to coordinate axes
  • Perpendicular constraint ensures 90-degree angles between lines
  • Tangent constraint makes curves smoothly touch other entities
• Sketch patterns replicate geometry in linear or circular arrays saving time for repetitive designs

3D Modeling Techniques

• Feature-based modeling builds 3D geometry from 2D sketches using various operations
  • Extrusion creates 3D objects by extending 2D profiles along a linear path
  • Revolution generates 3D shapes by rotating 2D profiles around an axis
  • Sweep produces 3D forms by moving a 2D profile along a 3D path
  • Loft creates smooth transitions between multiple 2D profiles
• Boolean operations modify 3D solid bodies
  • Union combines multiple bodies into a single entity
  • Subtraction removes material from one body using another
  • Intersection creates a new body from overlapping volumes
• Surface modeling techniques generate complex curved geometry
  • Creating surfaces from curves or by extending existing faces
  • Trimming surfaces to create precise boundaries
  • Stitching multiple surfaces to form watertight bodies
• Fillet and chamfer features modify edge geometry
  • Fillets create rounded transitions between faces (constant radius, variable radius)
  • Chamfers create angled transitions between faces (equal distance, two distances)
• Assembly modeling combines multiple 3D parts
  • Mate constraints define relationships between components (coincident, concentric, distance)
  • Kinematic analysis simulates movement of assembled mechanisms

Constraints & Dimensions

Geometric Constraints

• Geometric constraints in 2D sketches define relationships between entities ensuring design intent
  • Parallel constraint maintains equal distance between two lines
  • Concentric constraint aligns circular entities around a common center
  • Symmetric constraint mirrors entities across a line or plane
  • Fixed constraint prevents entities from moving during sketch modifications
• Constraint solving algorithms automatically adjust sketch geometry to satisfy defined relationships
• Over-constraining occurs when conflicting or redundant constraints are applied
  • Identifying over-constrained conditions through software warnings or sketch behavior
  • Resolving conflicts by removing or modifying constraints to maintain model flexibility

Dimensional Constraints

• Dimensional constraints specify exact sizes and positions of geometry
  • Linear dimensions define lengths and distances between entities
  • Angular dimensions specify angles between lines or faces
  • Radial and diametral dimensions control sizes of circular features
• Driving dimensions actively control sketch geometry
• Driven dimensions passively report sizes without affecting the sketch
• Reference dimensions provide information without constraining the model
• Tolerance annotations indicate acceptable variations in dimensions ($\pm0.1$, $+0.2/-0.1$)

Parametric Design Tools

• Equation-driven constraints create relationships between dimensions
  • Mathematical formulas define dependencies ($Length = 2 * Width$)
  • Trigonometric functions calculate complex relationships ($Angle = \arctan(Height/Base)$)
• Global variables store commonly used values accessible throughout the model
  • Assigning meaningful names to variables improves model readability ($Bolt\_Diameter = 10mm$)
  • Modifying global variables updates all dependent features simultaneously
• Design tables generate families of parts by varying dimension values
  • Spreadsheet-based input allows quick creation of multiple configurations
  • Automated model updates based on table entries streamline design iterations

Drawings from Models

Standard Drawing Views

• Orthographic projections display 3D objects on 2D planes
  • Front view shows object as seen from the front
  • Top view represents object as viewed from above
  • Side view depicts object from the left or right side
• Isometric view provides a 3D representation with equal foreshortening on each axis
• Scale settings adjust the size of views relative to the actual model (1:2, 2:1)
• View arrangements follow standard conventions (third-angle projection, first-angle projection)

Specialized Views and Annotations

• Section views reveal internal features by cutting through the model
  • Full sections show the entire cut through the object
  • Half sections display both interior and exterior features
  • Offset sections use multiple cutting planes for complex geometries
• Detail views magnify small or intricate areas of the model
  • Circular details highlight round features
  • Rectangular details focus on specific regions of interest
• Dimensioning follows standards to ensure clear communication
  • Linear dimensions for straight features
  • Angular dimensions for rotational features
  • Baseline and chain dimensioning for related measurements
• Drawing annotations provide additional information
  • Notes convey non-geometric information (material specifications, finish requirements)
  • Surface finish symbols indicate required surface quality ($\sqrt{}$, Ra)
  • Geometric tolerances specify allowable variations in form and position (flatness, true position)

Drawing Management

• Bill of Materials (BOM) lists components in an assembly
  • Automatically generated from 3D assembly models
  • Customizable formats to include part numbers, quantities, and descriptions
• Part lists provide detailed information for individual components
  • Extracted from model properties (mass, volume, material)
  • Linked to 3D model to ensure consistency with design changes
• Drawing templates standardize layout and formatting
  • Predefined sheet sizes and title blocks
  • Company-specific logos and information fields
• Revision control tracks changes to drawings over time
  • Revision tables document modification history
  • Clouding highlights areas of recent changes for easy identification