7.13 - CAD

Overview

Computer Aided Design (CAD) tools are aids to the entire design process. From a basic draughting tool, CAD can be expected to carry out complex and repetitive design calculations and to communicate both with other CAD installations and with manufacturing systems and equipment.

The CAD process that creates the generic specification of a product and its components should incorporate aids such as FMEA, Quality Function Deployment (QFD), Design for Manufacture (DFA) rules by careful parallel operation with Computer Aided Process Planning (CAPP) tools and its links to Computer Aided Manufacturing (CAM) systems. This is known as Product Life-cycle Management (PLM).

Levels of Software

Two Dimensional CAD Systems generally following the designer’s traditional approach to his work. Effectively these systems replace the drawing board, pencil and T square etc.

Three Dimensional Wireframe CAD Systems build up a three dimensional model with the benefit of automatic isometric views. The software only knows the edges of the part.

Two Dimensional Surface Modelling Systems hold information on surface characteristics allowing shaded colour drawings to be generated with respect to a light source. It produces the equivalent of a computer generated photograph.

Three Dimensional Surface Modelling Systems build up a product from primitive building blocks which can be either added or subtracted. The computer knows what is solid and consequently has sufficient information for automatic NC or CNC machine programming.

With knowledge of the shape of a component CAD has the potential for Finite Element (FE) engineering analysis with examples in stress, heat flow and vibration analysis.

Levels of Hardware

With continuing hardware and software development the early limitations on speed and part model size have largely gone away. Some of the limitations dependent on machine size and memory capacity are:-

• Response time
• Some software limits model size
• Integration capabilities, including those required for distributed database integration.

The general levels of hardware are:-

• Stand alone PC
• Stand alone workstation
• Networked PC’s and workstations
• Fully distributed centrally managed systems (may use hardware configured from above)
• Mainframe (or powerful server) to handle database management and complex in context design systems

Benefits of CAD

• More likely to get design ‘right first time’
• Faster changes
• Faster response to tendering
• More design time
• Improved job satisfaction
• Potential to communicate product information with suppliers
• Links to CNC machines
• Promotes component rationalisation
• Encourages experimentation
• Reinforces the importance of the links to manufacture
• Can be used to produce a cost estimate from solid models

With effective development of CAD benefits compound as progress is made towards total system integration. Effectiveness is achieved by ensuring:-

• CAD is used as building block in an integrated business development function and must integrate with CAPP, CAM and Product Cost Management (PCM).
• Paperwork is simplified and non-value added activities eliminated before applying automation.
• The level of CAD is appropriately selected to meet the requirements as complexity and costs increase during the progression from 2D CAD to 3D solid modelling.

In specifying a CAD system and its distributed workstation structures care should be taken to:-

• Design it around the multi-disciplinary team requirement
• Match it with the requirements of the matrix style of management to support concurrent engineering.
• Specify the organisational disciplines for engineering database and product life cycle management

Notes:

CAD and associated technologies still continue to move at a rapid rate and in some cases outstrips a company’s abilities to deploy the new levels of capability. However deployed appropriately and aggressively it can be a source of maintaining a competitive advantage and improving new product introduction rates.

Some CAD systems are used to design products in a complete environment where the four product elements of performance, price, profit, and production capability are all considered virtually simultaneously. This is known as Value Driven Design.