3.4: Computer-Aided Design (CAD)

CAD

The generation, creation, development and analysis of a design or system using computer software

Advantages:

• Cost effective- eliminate high costs of testing and manufacturing

Where is computer-aided design used?

• For conceptual design

• Layout of product

In…

• Fashion

• Construction

• Automotive

• Architecture

• Planning electric/mechanical layout

Surface modelling

A realistic picture of the final model, offering some machining data.

Advantages:

• Offers some machining data (reflects performance and condition of product in design process)

Disadvantages:

• Offers no data about the interior of a product

Solid modelling

Clear representations of final product

• Provides complete set of data for product to be realised- includes internal dimensions + volume UNLIKE surface modelling

Data (mathematical/statistical) modelling

A data model explicitly determines data structure including statistical modelling

E.g. data bases, information systems

Virtual prototyping

Use of surface and solid modelling to develop photo-realistic interactive models (“digital mockups”)

E.g. Jaguar + Land Rover moving virtual 3D vehicle prototyping

Bottom-up modelling

Designer creates parts of the product independent of the assembly or any other component

• Once all part models are completed they are brought together in the assembly

• E.g. Mars rover Curiosity

Advantage:

• We know what the parts are

Disadvantage:

• Slow progress- all parts need to be completed

• Lack of coherence- final product assembled from individual parts

• Have to update each part separately because theyre independent of each other

Top-down modelling

Product development process obtained through 3D, parametric and associated CAD systems

• Design originates as a concept and gradually evolves into a completed product consisting of components

• Begins with design criteria, then creates components that meet the criteria

• begins with known parameters, then designers engineer a layout (2D design that evolves…)

Advantage:
- Much less rework needed when design changes occur (parts know how to update themselves)

Disadvantage:

• Can be too broad and inaccurate- may overlook details

What is the name of the strategy that incorporates both top-down and bottom-up modelling?

Hybrid Strategy / Mid-Out Strategy

• some parts designed individually (bottom-up)

• others designed using the top-down approach

Most modern CAD allows for a combo of both

Digital humans

Computer simulations of a variety of mechanical and biological aspects of the human body

• Used to interact with a virtual prototype

Advantages:

• enables product to be developed quickly- can be more design iterations in less time

• results in higher product quality that meets human requirements more accurately

• digital prototypes cheaper than physical

• products are safer as a result of a more thorough safety aspects analysis

• enhanced automation of development process improves productivity

Motion capture

Recording of human/animal movement by any means- video, magnetic…

• A person wears a set of reflective markers at each joint

• Sensors track markers’ positions as person moves- develops a digital representation of motion

Advantages:

• reduce animation time and cost (have to develop multiple frames)

• Creates more natural movements

Disadvantages:
- Limited to motions that are anatomically possible

Haptic technology / Force feedback technology

Technology that interfaces the user via a sense of touch

• Uses mechanical actuators to apply forces to user

• By simulating physics of user’s virtual world- can compute forces into real time

• Allows user to become part of computer simulation + interact with it

Advantages:

• Designers can observe user’s performance and design a better outcome

• Can be used in situations where its difficult to train in real world environment

Used in- home entertainment consoles (video game consoles)

Virtual reality (VR)

Ability to simulate a real situation on screen + interact with it in a near-natural way

Animation

Ability to link graphic screens together to simulate a motion or a process

Finite element analysis (FEA)

Calculation and simulation of unknown factors in products using CAD systems

Uses colour indication to show:

• Structural load (stress + strain)

• Aerodynamics

• Thermodynamics

E.g. simulating stresses within a virtual model

Advantages:

• Cost effective

• Improved accuracy

Disadvantages:

• All presumed stresses are approximate- hard to tell difference between obtained results and real results