ME401T

Computer Aided Design

Fundamentals

Computer Aided Design

Role of computers in Mechanical design

What are the possible areas where computers can assist mechanical design?

Engineering drawings and drafting.

Creating complicated geometries with a good accuracy

Computer Aided Design

In solving structural design, thermal, fluid and problems in mechanical engineering design (known as Computer Aided Simulation and Analysis).

FEA of Machine components, FEM to solve heat problems, CFD to solve fluid problems, to solve coupled structural-heat field problems using numerical methods.

Computer Aided Design

In optimizing the existing design for minimum mass and maximum strength of machine parts, maximum efficiency and minimum power consumption of mechanical equipment.

Why to study CAD?

CAE tool users become inefficient in using them unless, fundamental concepts on which theses systems are built, are understood properly.

Still all the critical shapes can not be modeled in these tools; so getting the fundamental knowledge may help them modeling those shapes.

How can CAD fit in conventional design cycle?

Problem identification and recognition of need

Problem definition and conceptualisation

Geometric modelling and spatial analysis

Engineering analysis and optimisation

Prototype development

Manufacturing process development

Manufacturing

Implementation

For example Design of an office chair

How can CAD fit in conventional design cycle?

How can CAD fit in conventional design cycle?

How can CAD fit in conventional design cycle?

How can CAD fit in conventional design cycle?

How can CAD fit in conventional design cycle?

How can CAD fit in conventional design cycle?

CAM cycle

Marketing Customer feedback

Reasons for implementing a CAD system

Computers can store and handle large amount of eng. Data; that can be utilized for design and analysis.

Complex geometrical shapes can be visually inspected and checked.

CAD tools make design, simulation, analysis and optimization an easy task.

CAD systems can easily be integrated with CAM systems.

CAD applications

Applications are numerous in fields like Mechanical, Electrical and Architectural.

Geometric engine:

Heart of modeling

Provides functions to perform modeling and construction, editing and manipulation, drafting and documentation.

Creating this represents a means and not a goal for engineers.

CAD applications

Checking interference between mating parts in an assembly.

Deformation, stress and strain analysis of machine components.

CAD benefits

Improved productivity

Shorter lead times

Customers modifications are easier to make

Improved accuracy of design

In analysis, easier recognition of component interactions

Fewer errors in NC part programming

Saves materials and machining time by utilizing optimization algorithms.

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

CAD benefits: Analysis example

Without actual manufacturing of the component, stress analysis is done.

How to verify the results???

Make a prototype and by placing strain gauges calculate deformations at various section under loads; and then finding stresses analytically and compare the same with the software results.

Saves a good amount of time

This design can further be optimized

Scope of CAD CAD is a subset of the design process (As shown earlier

in design cycle)

Activities of CAD systems: mass properties, FEA, dimensioning, tolerancing, assembly modeling, generating shaded images, documentation and drafting.

Geometric modeling

Computer graphics

Design

CAD

CAD programming CAD systems are powerful software applications, they

employ complex geometric modeling concepts, computer graphics algorithms, software techniques, design and analysis theories, manufacturing techniques and database and management concepts.

CAD systems evolved over the years; and code itself is very long and complex.

Modifying and programming CAD systems is difficult but possible.

CAD programming CAD software is written in a variety of languages.

Unigraphics and I-DEAS started as Fortran code.

Pro/E ad SolidWorks are written in C and C++.

Most of these systems use JAVA especially for Web-based functionality.

How often do we need to program?

There is a need for customizing these systems.

There are different levels of customizing and programming like writing a simple macro to automate repetitive tasks, the system API (application programming interface) to extend the system functionality.

CAD programming Programming interested users must be familiar with

system functionality, structure, hierarchy, terminology and philosophy.

For example if someone needs to modify spline curve by programming then the one should have used the spline command already.

CAD programming What does it take to program a CAD system?

Knowledge of programming language, geometry and graphic concepts, and database techniques.

For a programming language C, C++ or JAVA is good.

The effective use of these requires a good knowledge of OOP (Object-Oriented Programming).

OOP is programming paradigm that represents concepts as objects that have data fields (attributes that describe objects) and associated procedures known as methods (Examples: C++, JAVA, VB.NET, Python, Pascal, Visual Basic, Fortran, COBOL etc..)

CAD Programming elements Relational database:

CAD system utilizes relational databases to store geometric, graphical and other data that defines a CAD model.

It is conceptually a set of collection of tables and table is a relation. (database with 4 table means there are 4 relations).

Each table stores data about a given entity.

The data in a table is stored as attributes in rows.

Each row is known as a record.

For example customer name and account numbers.

It is usually collection of many such tables

CAD Programming elements Relational database:

CAD Programming elements Relational database:

Another example to store the boundary representation (B-rep) of the model (i.e. faces, edges and vertices).

CAD Programming elements Relational database:

CAD Programming elements Object database:

Here the unit of data storage is an object, instead of a table.

Object database management system is similar to conventional DBMS.

CAD Programming elements The other elements are:

Object definition

Object concepts

Programming levels

List of few selected CAD software Autocad by Autodesk

CATIA by Dassault Systems (DS)

IDEA by 4M

Pro/E by Parametric Technology Corporation (PTC)

Revit Architecture by Autodesk

Solid edge by Siemens PLM software

Solid Works by Solid Works Corp.