Module VI – Lecture 1 of the Computer Aided Design (MEP604) course:

🔷 Module: VI
🔷 Lecture: 1
🔷 Topic: Introduction – Assembly of Parts, Assembly Modelling
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand assembly modeling and simulate mechanical
assemblies.
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction to Assembly Modelling

Assembly modeling is the process of arranging individual components in a CAD system to

represent a complete product. This process includes geometric positioning, mechanical
relations, and interference checking.

✅ 2. Purpose of Assembly Modelling

 To simulate how parts fit and work together.

 To check for interference or clashes.
 To verify kinematics and mechanical constraints.
 To produce exploded views and BOMs (Bill of Materials).

✅ 3. Types of Assembly Approaches

Approach Description
Bottom-Up Parts are created individually and later assembled.
Top-Down Assembly is planned first, and then individual parts are created in context.
Hybrid Combination of both top-down and bottom-up approaches.

✅ 4. Key Elements in Assembly Modelling

 Components: Individual part files (solid models).

 Constraints: Rules for aligning and fixing parts.
 Degrees of Freedom (DOF): Movement allowed before full constraint.
 Subassemblies: Assemblies that act as a single component in larger assemblies.

✅ 5. Common Assembly Constraints

Constraint Type Functionality
Mate Aligns faces/planes together
Flush Keeps two faces in the same plane direction
Insert Aligns cylindrical parts
Angle Maintains a specific angular relationship
Tangent Keeps curved and flat surfaces in contact

✅ 6. Features of Modern CAD Assembly Tools

 Hierarchical structure of assemblies.

 Real-time interference detection.
 Motion simulation.
 Assembly constraints and DOF analysis.
 Exploded view and BOM generation.

✅ 7. Applications of Assembly Modeling

 Mechanical product design (gearbox, engine, etc.).

 Robotics (joint articulation).
 Structural design (trusses, frames).
 Aerospace systems (wing-flap mechanisms).

✅ 8. Advantages of Assembly Modeling

 Better visualization of product structure.

 Easy modification and parametric updates.
 Interference checking before physical prototype.
 Improved collaboration among design teams.
🔷 Module: VI
🔷 Lecture: 2
🔷 Topic: Interference Checking, Position and Orientation
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand assembly modeling and simulate mechanical
assemblies.
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction

When designing assemblies in CAD software, it is essential to:

 Ensure that components do not collide or overlap improperly.

 Maintain accurate position and orientation of each part within the assembly.

✅ 2. Interference Checking

🔹 Definition:

Interference checking is the process of verifying whether two or more components in an

assembly physically intersect or overlap in space.

🔹 Types of Interference:

Type Description
Hard Two solid parts occupy the same space – leads to manufacturing
Interference error.
Clearance The gap between parts – should be adequate to ensure free
movement.
Contact Surfaces touch but do not penetrate – acceptable in mechanical joints.

🔹 Steps for Interference Detection:

1. Load all parts in assembly workspace.

2. Apply constraints and assemble.
3. Use CAD tool’s Interference Detection feature.
4. Analyze results – intersection volumes or conflict areas are highlighted.

🔹 Benefits:

 Prevents manufacturing issues.

 Identifies design flaws early.
 Helps in tolerance optimization.
✅ 3. Position of Parts in Assembly

🔹 Absolute Positioning:

Each part is placed using a global coordinate system reference (X, Y, Z axes).

🔹 Relative Positioning:

The part is placed with respect to another part, using geometric or constraint-based
relationships.

🔹 Tools Used:

 Reference planes (XY, YZ, ZX)

 Assembly constraints (Mate, Insert, Offset, etc.)
 Reference geometry (edges, faces, axes)

🔹 Importance:

Accurate positioning ensures that:

 Assemblies are functionally correct.

 Movements and constraints work as expected.
 The final product is dimensionally accurate.

✅ 4. Orientation of Parts

🔹 Definition:

Orientation defines how a component is rotated relative to another or to the coordinate

system.

🔹 Tools and Techniques:

 Rotational constraints (e.g., angle constraints).

 Axis alignment between two parts.
 Using coordinate systems to define part orientation.

🔹 Use Cases:

 Gears aligned for correct meshing.

 Hinges or levers rotating along correct axes.
 Mechanical linkages moving in desired motion path.
✅ 5. Combined Role in Assembly Simulation

Task Position Orientation

Placing components ✔️ ✔️
Motion simulation ✔️ ✔️
Interference avoidance ✔️ ✔️
Tolerance analysis ✔️ ✔️
🔷 Module: VI
🔷 Lecture: 3
🔷 Topic: Tolerance Analysis and Mass Property Calculations
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand and evaluate assemblies using tolerance and
physical property analysis.
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction

In assembly modeling, precision is vital. Two critical aspects include:

 Tolerance analysis – ensuring parts fit and function together within specified limits.
 Mass property calculations – determining physical properties like mass, volume,
and center of gravity, which are crucial for performance and manufacturing.

✅ 2. Tolerance Analysis

🔹 What is Tolerance?

Tolerance is the permissible limit of variation in a physical dimension.

🔹 Types of Tolerances:

Type Description
Dimensional Linear variations in length, diameter, etc.
Geometric Shape, orientation, or position constraints (e.g., flatness).
Assembly Tolerance Combined effect of individual part tolerances on final assembly.

🔹 Tolerance Stack-Up:

 The cumulative effect of part tolerances in an assembly.

 Crucial in tight-fit or precision assemblies.

🔹 Methods of Analysis:

 Worst-case analysis: Assumes all tolerances at max limit – very conservative.

 Root Sum Square (RSS): Statistical method assuming independent tolerances.
 Monte Carlo simulation: Probabilistic method using random variations.

🔹 Tools in CAD Software:

 Built-in tolerance analysis modules.

  Tolerance charts and graphical stack-up paths.

✅ 3. Mass Property Calculations

🔹 Purpose:

To analyze mechanical balance, strength, and motion behavior of components.

🔹 Common Mass Properties:

Property Description
Mass Total weight of the solid/assembly.
Volume 3D space enclosed by the object.
Center of Gravity (CG) Point at which the entire weight acts.
Moment of Inertia Resistance to angular motion about an axis.
(MOI)
Density Mass per unit volume – must be defined for accurate
calculations.

🔹 Steps for Calculation:

1. Assign material and density to each component.

2. Use CAD tools to compute properties (e.g., Measure > Mass Properties in
SolidWorks or AutoCAD).
3. Extract CG, MOI, and verify balance and stability.

🔹 Use in Design Decisions:

 Weight reduction (light weighting).

 Improving dynamic performance.
 Achieving balance in rotating assemblies (e.g., turbine rotors, crankshafts).

✅ 4. Integration of Tolerance and Mass Analysis

 Tolerance affects fit and alignment, which impacts mass distribution.

 Misalignment due to poor tolerances can shift CG, causing instability.
 Simultaneous evaluation ensures functionality, safety, and manufacturability.

✅ 5. CAD Software Capabilities

Feature Software Example Purpose

Tolerance Analysis Tools SolidWorks, CATIA Check stack-up and part fit
Mass Properties AutoCAD, Fusion Compute mass, CG, volume
Calculator 360
Simulation Integration ANSYS, Inventor Predict dynamic behavior with
tolerance
🔷 Module: VI
🔷 Lecture: 4
🔷 Topic: Mechanism Simulation and Interference Checking
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand and evaluate assemblies using mechanism
simulation and interference analysis
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction

In advanced CAD-based assembly modeling, mechanism simulation allows engineers to

visualize and analyze how parts move, while interference checking ensures that parts do not
collide during motion or in their assembled state.

✅ 2. Mechanism Simulation

🔹 Definition:

Mechanism simulation is the process of animating and analyzing the motion of parts within
an assembly to verify real-world performance.

🔹 Objectives:

 Understand kinematics of assemblies.

 Check for collisions during movement.
 Evaluate degrees of freedom (DOF).

🔹 Components of a Mechanism:

Element Description
Links Rigid parts that form the mechanism.
Joints Connections that define relative motion.
Constraints Limitations imposed on motion.
Input Motion Defined motion applied to drive simulation.

🔹 Common Joints Used in CAD:

 Revolute (hinge)
 Prismatic (slider)
 Cylindrical
 Spherical
 Planar
🔹 Steps in Mechanism Simulation:

1. Assemble parts with proper mates/joints.

2. Define input motion (rotation, displacement).
3. Run simulation over time.
4. Analyze:
o Position and orientation over time
o Velocity and acceleration
o Collision and contact detection

🔹 CAD Tools for Simulation:

 SolidWorks Motion
 PTC Creo Mechanism
 Autodesk Inventor Simulation
 Fusion 360 Simulation Environment

✅ 3. Interference Checking

🔹 Definition:

Interference checking is a process to detect overlapping volumes between parts in an

assembly, either in static position or during motion.

🔹 Types of Interference:

Type Description
Static Parts interfere at a fixed position.
Dynamic Interference occurs during motion.
Clearance Checks minimum separation between moving parts.

🔹 Process:

1. Use CAD software tools to detect interferences.

2. Run motion simulation to check for dynamic collisions.
3. Identify and correct design issues.

🔹 Output:

 Graphical highlights of interference regions.

 Reports listing part names and interference volumes.
 Timepoints in motion when interferences occur.

✅ 4. Integration of Simulation and Checking

Mechanism simulation and interference detection go hand-in-hand:

 Simulation allows motion visualization.

 Interference checking ensures mechanical integrity.
 Both tools aid in design validation before physical prototyping.
🔷 Module: VI
🔷 Lecture: 5
🔷 Topic: CAD Standards: GKS, Standards for Exchange of Images, OpenGL
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand and apply standards in CAD for graphical data
exchange and rendering
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction

CAD systems rely on standardized frameworks and protocols to ensure compatibility and
efficiency in data visualization, exchange, and rendering. These standards improve
interoperability among different software platforms and support collaborative design.

✅ 2. GKS – Graphical Kernel System

🔹 Definition:

GKS is the first ISO standard for computer graphics, providing a common interface for 2D
graphics across different platforms.

🔹 Purpose:

 Ensure device-independent graphics programming.

 Provide a standard API for graphical output in CAD/CAM.

🔹 Key Features:

 Supports 2D vector graphics (lines, curves).

 Enables interaction through input devices (keyboard, mouse).
 Supports multiple output devices (printers, screens).

🔹 GKS-3D (Extension):

 Supports 3D graphics, including transformations and viewing.

🔹 Applications:

 Early CAD software

 Engineering analysis tools
 Technical drawing environments
✅ 3. Standards for Exchange of Images and Models

🔹 Need for Exchange Standards:

 CAD models need to be shared across different software.

 Ensures data integrity, geometry preservation, and interoperability.

🔹 Common Standards:

Format Full Form Use Case

IGES Initial Graphics Exchange Transfer of 2D/3D CAD models across
Spec platforms
STEP Standard for Product Model Preferred for 3D CAD interoperability
Data
DXF Drawing Exchange Format AutoCAD drawings (2D/3D)
STL Stereolithography 3D printing & rapid prototyping
VRML/X3D Virtual Reality Modelling Interactive 3D web models
Lang
Parasolid/X_T Proprietary solid modeling Used in SolidWorks, NX, etc.
kernel

✅ 4. OpenGL (Open Graphics Library)

🔹 Definition:

OpenGL is a cross-platform, industry-standard API for rendering 2D and 3D graphics.

🔹 Applications in CAD:

 Real-time rendering of wireframe and shaded models

 Creating interactive interfaces
 Used in almost all modern CAD software

🔹 Key Features:

 High-performance graphics rendering

 Support for shading, lighting, and textures
 Compatible with GPU acceleration

🔹 Advantages:

 Open-source and extensible

 Platform-independent
 Widely adopted across CAD, gaming, and simulations
✅ 5. Summary:

Standard Type Role in CAD

GKS Graphics API 2D graphics standardization
IGES/STEP Exchange Format Cross-platform model sharing
OpenGL Rendering API High-performance 2D/3D rendering in CAD
🔷 Module: VI
🔷 Lecture: 6
🔷 Topic: Data Exchange Standards – IGES, STEP, CALS
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand and apply standards in CAD for graphical data
exchange and rendering
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction to Data Exchange in CAD

 Data exchange in CAD refers to the ability to transfer geometry, attributes, and
product data from one system to another.
 It enables interoperability, collaboration, and long-term archiving.
 Standard file formats and protocols ensure accuracy, consistency, and efficiency.

✅ 2. IGES (Initial Graphics Exchange Specification)

🔹 Overview:

 Developed in 1980 by the U.S. Air Force, ANSI, and industry collaborators.
 Focused on neutral file format for CAD model exchange.

🔹 Features:

 Supports 2D and 3D wireframe, surface, and solid models.

 Used for geometry, annotations, and structural data.
 ASCII text format, human-readable.

🔹 Advantages:

 Broadly supported by older and modern CAD systems.

 Simple structure.

🔹 Limitations:

 Limited support for product manufacturing information (PMI).

 May result in data loss or inaccuracies during translation.

✅ 3. STEP (Standard for the Exchange of Product Model Data)

🔹 Overview:
  ISO 10303 standard, developed to overcome IGES limitations.
 Supports full product lifecycle data exchange.

🔹 Features:

 Represents solid, surface, wireframe, product structure, tolerances, and materials.

 Uses a modular approach (Application Protocols like AP203, AP214, AP242).
 Uses ASCII or XML representations.

🔹 Advantages:

 More comprehensive and accurate than IGES.

 Facilitates PLM (Product Lifecycle Management) integration.

🔹 Common Application Protocols (APs):

Protocol Application
AP203 Configuration controlled 3D design
AP214 Automotive design processes
AP242 Combined 3D and PMI data

✅ 4. CALS (Continuous Acquisition and Life-cycle Support)

🔹 Overview:

 Developed by the U.S. Department of Defense.

 Designed for technical data interchange throughout a system’s lifecycle.

🔹 Features:

 Includes graphics standards (CALS raster format), electronic data interchange

(EDI), and technical documentation.
 Emphasizes long-term archiving, support documentation, and data reuse.

🔹 Applications:

 Used in aerospace, defence, and complex manufacturing industries.

🔹 Advantages:

 Facilitates interoperability across military and contractor systems.

 Supports logistics, maintenance, and supply chain operations.

✅ 5. Summary Table: IGES vs STEP vs CALS

 Feature IGES STEP CALS
Developed By ANSI/U.S. Air Force ISO U.S. Department of
Defense
Format Type ASCII Text ASCII/XML Raster, EDI, Document
Formats
Geometry 2D, 3D Full 3D product Limited (focus on
Support wireframe/surface models docs/standards)
PMI Support Limited Excellent (via Documentation focus
AP242)
Industry General CAD Aerospace, Aerospace, Defense,
Usage Automotive, PLM Maintenance
🔷 Module: VI
🔷 Lecture: 7
🔷 Topic: Communication Standards
🔷 Duration: 1 Hour
🔷 CO: CO-VI – Understand and apply standards in CAD for graphical data
exchange and rendering
🔷 POs: 1, 2, 3, 5

✅ 1. Introduction to Communication Standards

 In CAD/CAM environments, communication standards ensure the seamless

exchange of design data, commands, and simulation inputs between software,
hardware, and networks.
 These standards define the protocols, data formats, and procedures for effective
interaction among systems.

✅ 2. Importance of Communication Standards

 Enable interoperability between different CAD/CAM platforms.

 Facilitate collaborative engineering and global design workflows.
 Ensure data integrity and consistency during transfer.
 Support real-time simulation, remote rendering, and cloud-based CAD.

✅ 3. Common Communication Standards in CAD

Standard Description Application

GKS (Graphical Kernel Early ISO standard for 2D Basis for later standards
System) graphics communication. Defines like PHIGS.
primitives and device
independence.
PHIGS (Programmer’s Extends GKS to 3D. Supports CAD, visualization,
Hierarchical Interactive hierarchical graphics structures. engineering design.
Graphics System)
OpenGL (Open Graphics Cross-platform API for rendering Real-time rendering in
Library) 2D and 3D graphics. CAD/CAM/CAE.
DXF (Drawing Exchange Developed by AutoDesk for CAD Exchange of 2D
Format) data exchange. drawings and 3D
models.
DGN (Design) Format used by MicroStation for Civil, architectural, and
CAD files. infrastructure projects.
VRML/X3D Web-based 3D model Interactive design and
representation formats. virtual reality.
JT (Jupiter Tessellation) Lightweight 3D data format for PLM, digital twin
visualization and collaboration. environments.

✅ 4. GKS – Graphical Kernel System

 Developed by ISO to provide a standard interface for 2D graphics.

 Key Features:
o Device independence.
o Use of primitive graphics operations (lines, text, fill).
o Early foundation for CAD graphic communication.

✅ 5. OpenGL – Open Graphics Library

 Developed by Silicon Graphics Inc. (SGI); now maintained by Khronos Group.

 Industry standard for rendering 2D and 3D vector graphics.
 Used in:
o CAD visualization
o Simulation software
o Gaming and virtual design

✅ 6. Communication Protocols

 TCP/IP: Used for transmitting CAD data over networks.

 HTTP/HTTPS: For cloud-based collaboration and rendering.
 Web Sockets: Real-time data exchange between CAD systems and servers.
 FTP/SFTP: Secure file transfer of CAD files between design teams.

✅ 7. Key Benefits of Standardized Communication

 Reduced translation errors between software.

 Enhanced product development speed.
 Supports distributed design environments.
 Enables cloud-based CAD and IoT integration in manufacturing.