16. Product Design and CAD/CAM
16.1
16.2
16.3
16.4
16.5
16.6
16.7
16.8
Unit Introduction
Unit Objectives
Product Design and CAD
CAD System Hardware
CAM, CAD/CAM, and CIM
Unit Review
Self Assessment Questions
Self Assessment Answers
16.1 Introduction
Product design serves an important function in the production system. It helps
determine the eventual commercial success of a product; it determines how the
production system should be created, and exactly what equipment should be
bought; and it determines how easily, and how cheaply, the product can be
manufactured. The manufacturing support system contains procedures and
systems used to manage production and solve the technical and logistical
problems associated with designing the products, planning the processes,
ordering the materials, controlling work-in-process as it moves through the plant,
and delivering products to customers. Product design and its associated use of
computer-aided design/computer-aided manufacturing (CAD/CAM) systems,
represents one of the most important aspects of the manufacturing support
system. In CAD/CAM , both design and manufacturing are tightly integrated into
a continuum of activities. Continuing the integration, we have Computer
Integrated Manufacturing (CIM), which includes CAD/CAM, but also extends to
embrace the business functions of a manufacturing firm.
In this unit a discussion and definition of product design and CAD are given,
where an analysis of the design process and the actual application of computeraided design principles are highlighted. CAD system hardware is reviewed (see
Figure 16.1), before a general introduction to CAM, together with its relationship
with CAD, and how it fits into the infrastructure of CIM.
Figure 16.1: Components of CAD
16.2 Learning Objectives
After completing this unit you will be able to:
BULLET LIST
List the six processes of the conventional design process
Define Computer-aided design (CAD)
Specify the benefits of CAD
State the relationship between the Product Data Management system, and the
CAD system
Explain the concept of geometric modelling
Classify types of geometric modelling
Explain Computer-aided engineering (CAE) software, and list typical applications
State how CAD is used to create product prototypes
List the hardware used in a CAD system
State the types of CAD system configurations that may be used
Define Computer-aided manufacturing (CAM)
State and explain the two application areas of CAM
Explain the concept of CAD/CAM
State why CAD/CAM is used in concurrent engineering environments
Define Computer-integrated manufacturing, and its scope
ENDLIST
16.3 Product Design and CAD
Product design is of critical importance to the production system. It contributes
more than any other attribute to the overall design and operation of the
production system, and its success determines whether the production system
will be fit for use in making products over the long term.
LEARNING ACTIVIY 16.1
Learn more about these concepts at the following web-sites:
Computer-Aided Design (CAD)
http://en.wikipedia.org/wiki/Computer-aided_design
Computer-Aided Manufacturing (CAM)
http://en.wikipedia.org/wiki/Computer_aided_manufacturing
Computer Integrated Manufacturing (CIM)
http://en.wikipedia.org/wiki/Computer_Integrated_Manufacturing
END LEARNING ACTIVITY 16.1
16.3.1 The Design Process
The general process of design may be seen as an iterative process with six key
phases (see Figure 16.2):
NUMLIST
Recognition of need—this involves the realisation that a problem or need exists
that may be solved by design. This may mean identifying some deficiency in a
current machine design by an engineer, or perceiving some new product
opportunity by a salesperson.
Problem definition—this involves a thorough specification of the item to be
designed. Specifications include physical characteristics, function, cost, quality,
and operating performance.
Synthesis—closely related with the following step, analysis, synthesis refers to
the bundling of information that occurs after problem definition, and concurrently
during analysis, and after re-analysis.
Analysis and optimization—closely related to the previous step, analysis is
concerned with the investigation of design specification information, and the
optimization of this information, as well as a synthesis of new information, as
required.
Evaluation—involves measuring the design against the specifications established
in the problem definition phase. This evaluation may require the building and
testing of prototype models to assess operative performance metrics for the
proposed design. This may lead to the re-design of certain or all elements.
Presentation—this is the final phase, where the design is documented by means
of drawings, material specifications, assembly lists, and so on. Documentation
means that the design database is created.
ENDLIST
Figure 16.1: Design Process and Computer aided design
KEYPOINT
The conventional design process consists of six processes: recognition of need;
problem definition; synthesis; analysis and optimization; evaluation; and
presentation.
END KEYPOINT
16.3.2 Applications of Computers in Design
CAD is any design activity involves the effective use of computers to create,
modify, analyze, or document an engineering design. It is most commonly
associated with the use of an interactive computer graphics system, referred to
as a CAD system. CAD provides the following benefits:
BULLETLIST
Increased design productivity—CAD reduces the time required to conceptualize
and physically draw product designs;
Increased available geometric forms in the design—CAD allows the design to
choose from a range of geometrical shapes that would normally be outside the
manual drawing process.
Improved quality of the design—the use of a CAD system with appropriate
hardware and software capabilities permits the designer to do a more complete
engineering analysis and to consider a larger number and variety of design
alternatives. The quality of the resulting design is thereby improved.
Improved design documentation—the output of a CAD system results in better
documentation of the design than what is usually seen as practical in manual
drafting.
Creation of a manufacturing database—by creating product design
documentation, much of the required database to manufacture the product is
also created.
Design standardization—design rules can be included in CAD software to
encourage the designer to utilize company-specified models for certain design
features.
ENDLIST
KEYPOINT
Computer-aided design (CAD) is any design activity that involves the effective
use of a computer to create, modify, analyze, or document an engineering
design.
END KEYPOINT
The use of a CAD system creates huge amounts of additional data that is often
stored and managed in a product data management (PDM) system. A PDM
system consists of computer software that provides links between users and a
central database, where engineering design data and related documentation is
stored. The PDM system manages the database by tracking the identities of
users, facilitating and documenting engineering changes, recording a history of
the engineering changes on each part and product, and providing documentation
management functions.
KEYPOINT
The output of the CAD system is stored in a product data management (PDM)
system. A PDM system consists of computer software that provides links
between users and a central database, where engineering design data and
related documentation is stored.
END KEYPOINT
The CAD system can facilitate four of the design phases depicted in Figure 16.2.
Geometric modelling is a special use of CAD data to create a mathematical
description of the geometry of an object. The geometric model, which contains
the mathematical description, is contained in the computer memory; and the CAD
system—upon accessing the computer memory—can display the resultant model
as an image on its graphics terminal, allowing the operator to manipulate certain
aspects of the geometric model displayed. The operator can create new
geometric models from basic building blocks available in the system, can zoomin on certain features of the image on-screen, can move two or more geometric
models into close relation to each other, and so on. These capabilities allow the
operator to interrogate existing product models, and create new variations on
existing products to cater for a wide variety of needs.
KEYPOINT
Geometric modelling creates a mathematical description of the geometry of an
object, so that the subsequent description can be displayed as an image on CAD
systems, which may be manipulated by the operator.
END KEYPOINT
There are two types of geometric models used in CAD; these are:
NUMLIST
Two-dimensional modelling—dating from the late 1960s and early 1970s, when
the first CAD systems began to appear, this is primarily used for design
problems, such as flat objects and layouts of buildings. To enable some degree
of three-dimensionality, these models were often drawn from various viewpoints,
so as to capture the multitude of dimensions on an individual product.
Three-dimensional modelling—emerging after two-dimensional modelling, these
systems are capable of modelling an object in three dimensions according to
user instructions, which has been found useful for conceptualising the object, as
the three-dimensional model can be displayed in various views and from different
angles.
ENDLIST
KEYPOINT
Geometric modelling can appear in the form of two-dimensional modelling, and
three-dimensional modelling.
END KEYPOINT
Geometric models in CAD can also be classified as wire-frame models, or solid
models (see Figure 16.3). Wire-frame models use inter-connecting lines to depict
the object drawn; these inter-connecting lines can sometimes be confusing when
used on complex part geometries, as multiple overlapping lines may occur. Solid
models are objects that have been modelled in solid three dimensions, providing
the user with a vision of the object that is similar to its appearance in reality.
(a)
(b)
Figure 16.3: Wire-frame model (a), and Solid model (b)
KEYPOINT
Geometric models in CAD can also be classified as wire-frame models, or solid
models.
END KEYPOINT
16.3.2.1 Engineering Analysis
Once a design has been developed, it must then be subjected to engineering
analysis. This engineering analysis may include various tests, depending on the
product, but may include: stress-strain calculations, heat transfer analysis, or
dynamic simulation. These analyses tend to be quite complex, which has led to
the development of computer-aided engineering (CAE) software packages, so
that complicated engineering analysis may be performed by computer.
KEYPOINT
Computer-aided engineering (CAE) software packages are used to perform
complex engineering calculations by computer.
END KEYPOINT
CAE packages in common use with CAD systems include:
BULLETLIST
Mass properties analysis—involving the computation of features on the solid
model, such as volume, surface area, weight, and centre of gravity;
Interference checking—this checks to see if multiple components in a product
design would actually interfere with each other in reality;
Tolerance analysis—this determines how product tolerances would affect product
function and performance, how easy it would be to assemble the product, and
how variations in component dimensions may affect the overall size of the
assembly;
Finite element analysis—this aids in stress-strain, heat transfer, fluid flow, and
other engineering calculations;
Kinematic and dynamic analysis—this studies the operation of mechanical
linkages and analyzes their motions; and
Discrete-event simulation—this models complex operational systems where
events occur at discrete moments in time and affect the status and performance
of the system.
ENDLIST
KEYPOINT
Common CAE packages include: mass properties analysis; interference
checking; tolerance analysis; finite element analysis; kinematic and dynamic
analysis; and discrete-event simulation.
END KEYPOINT
16.3.2.2 Design Evaluation and Review
Following comprehensive engineering analysis, the proposed design must be
evaluated and reviewed for consistency. Some CAD features that are helpful in
evaluating and reviewing a proposed design include:
BULLETLIST
Automatic dimensioning—upon model completion, the CAD software can
automatically generate the dimensions of the drawn model;
Error checking—this checks the accuracy and consistency of dimensions and
tolerances, to assess whether the proper design documentation format has been
followed;
Animation of discrete-event simulation solutions—this displays the result as a
discrete-event simulation, where input parameters, probability distributions, and
other factors can be changed to assess their effect on the performance of the
system being modelled; and
Plant layout design scores—this provides numerical scores for plant layout
designs, based upon such factors as material flow, and closeness ratings.
ENDLIST
KEYPOINT
CAD features helpful in evaluating and reviewing a proposed design include:
automatic dimensioning; error checking; animation of discrete-event simulation
solutions; and plant layout design scores.
END KEYPOINT
In many cases, the geometric model is now used to replace the physical
prototype that would traditionally be built at this stage. Physical prototypes are
usually time-consuming to create, and analyse; and so replacements in the form
of rapid prototyping, and virtual prototyping—both based upon the geometric
model, may be used instead.
KEYPOINT
Evaluating and reviewing a proposed design can use the CAD geometric model
to create a prototype, either by rapid prototyping or virtual prototyping.
END KEYPOINT
Rapid prototyping is a term applied to a family of fabrication technologies that
allow engineering prototypes of solid parts to be made in a minimum lead time,
based upon the CAD geometric model. This is done by dividing the solid object
into layers, and then defining the area of each layer. The rapid prototyping
process then fabricates the object by starting at the base layer, and building
towards the top layer. The fidelity of the approximation that is produced by this
method is dependent on the layer thickness used at the start (with greater
accuracy achieved with thinner layers used).
Virtual prototyping is based upon virtual reality technology, and uses the CAD
geometric model to construct a digital mock-up of the product. This mock-up
allows the designer to obtain the sensation of the real physical product, without
actually building the physical prototype.
KEYPOINT
Rapid prototyping creates a physical prototype by means of segmenting the CAD
geometric model into a series of layers, and building to that specification; while
virtual prototyping uses the CAD geometric model to construct a digital mock-up
of the product.
END KEYPOINT
16.3.2.3 Automated Drafting
CAD may also be used as a presentation application, in that the CAD system can
produce highly accurate engineering drawings quickly and conveniently, and also
provide associated documentation as necessary. It is estimated that a CAD
system increases productivity in the drafting function by about fivefold over
manual preparation of drawings.
KEYPOINT
CAD may also be used for automated drafting—that is, the creation and
presentation of highly accurate engineering drawings.
END KEYPOINT
16.4 CAD System Hardware
Hardware is used in CAD systems is described in Table 16.1. The relationship
between the components discussed is depicted in Figure 16.4.
Table 16.1: Hardware used in CAD systems
Hardware
Design workstations
Digital computer
Output devices
Description
This has the following functions: (1) communication with the computer’s
central processing unit; (2) continuously generate a graphic image; (3)
provide digital descriptions of the image; (4) translate user commands
into operating functions; and (5) facilitate interaction between the user
and the system.
CAD workstation design has an important influence on the convenience,
productivity, and quality of user’s output. The workstation consists of a
display terminal and a set of user input devices, with which the user
interacts with geometric model via: entering alphanumeric data; entering
system commands to perform various graphics operations; and by
controlling cursor position on the display screen.
This uses a high-speed central processing unit to process CAD
operations. There are several CAD system configurations, such as host
and terminal; engineering workstation; and a CAD system based upon a
personal computer. These are discussed in the paragraphs below.
These include plotters and printers, which generate the output from the
CAD system. Plotters include: pen plotters, which are x-y plotters of
various type, used to produce high accuracy line drawings; and
electrostatic plotters, which are based upon the same principal as
photocopying, and produce lower quality drawings. Printers used
include inkjet printers, where drawings are produced by high-speed jets
Secondary Storage
of ink impacting the paper.
This includes various storage devices attached to the CAD system to
store programmes and data files. The storage mediums used can
include: magnetic discs, magnetic tape, floppy discs, external harddrives etc.
Figure 16.4: Configuration of a typical CAD system
KEYPOINT
The hardware used in a CAD system includes: design workstations; digital
computers; output devices, such as plotters and printers; and various secondary
storage devices.
END KEYPOINT
16.5 CAM, CAD/CAM, and CIM
We can now give more precise explanations of the terms CAM and CIM and their
relationships to CAD.
16.5.1 Computer-Aided Manufacturing
Computer-Aided Manufacturing (CAM) is the effective use of computer
technology in manufacturing planning and control. It is closely associated with
certain functions in manufacturing engineering, such as process planning and
numerical control (NC) part programming. It is applied in two broad categories:
manufacturing planning, and manufacturing control.
KEYPOINT
Computer-Aided Manufacturing (CAM) is the application of computer technology
to the areas of manufacturing planning and control.
END KEYPOINT
Manufacturing planning concerns the use of CAM to support the production
function, without a direct connection between the computer and the process.
Effective planning is achieved “off-line”; that is, the computer is used to provide
information for planning and managing production activities, without directly
accessing the process in real-time.
Important applications of CAM in manufacturing planning are outlined in Table
16.2.
Table 16.2: Applications of CAM for manufacturing planning
Application
Computer-aided
process planning
(CAPP)
Computer-aided NC
part programming
Computerized
machinability data
systems
Computerized work
standards
Cost estimating
Production and
inventory planning
Computer-aided line
balancing
Description
This is concerned with creation and dissemination of route sheets that
list the sequence of operations and work centres required to produce
the product and its components.
We discussed numerical control in unit 5. This application supports the
creation of computer-assisted part programmes for numerical control,
which represents a more efficient solution for their creation over
traditional manual methods.
This is concerned with creation and dissemination of part programmes
that can determine optimal cutting conditions for machine tools in the
factory.
These are computer packages that can be deployed to determine time
standards for direct labour jobs in the factory. They supersede tedious
manual time-and-motion studies used to perform the same task.
This is a programme that can estimate the cost of a new product, by
computerizing several of the key steps required to prepare the
estimate (such as the application of labour and overhead rates to the
sequence of planned operations).
Functions here include maintenance of inventory records, automatic
re-ordering of stock items when inventory is depleted, production
scheduling, maintaining current priorities for the different production
orders, material requirements planning, and capacity planning.
This programme helps to find the best allocation of work elements
among stations on an assembly line. Can be used in situations where
the line balancing problem is particularly complex and difficult, owing
to the number of workstations, and complicating factors.
KEYPOINT
Applications of CAM for manufacturing planning include: Computer-aided
process planning (CAPP); Computer-aided NC part programming; Computerized
machinability data systems; Computerized work standards; Cost estimating;
Production and inventory planning; and Computer-aided line balancing.
END KEYPOINT
Manufacturing control uses CAM applications to manage and control the physical
operations of the factory. Here computer systems are developed that can be
used to implement the manufacturing control function. Important applications of
CAM in manufacturing control are outlined in Table 16.3.
Table 16.3: Applications of CAM for manufacturing control
Application
Process monitoring and control
Description
This is concerned with observing and regulating the production
equipment and manufacturing processes in the plant. They
Quality control
Shop floor control
Inventory control
Just-in-time production systems
include the control of transfer lines, assembly lines, numerical
control, robotics, material handling, and flexible manufacturing
systems.
This includes a variety of approaches to maintain the highest
possible quality levels in the manufactured product. They
include the use of quality functional deployment techniques.
This refers to the use of production management techniques
to collect data from factory operations, and the deployment of
this data to aid the control of production and inventory in the
factory.
This is concerned with maintaining the most appropriate levels
of inventory in the face of two opposing objectives: minimizing
the investment and storage costs of holding inventory; and
maximizing service to customers.
Just-in-time (JIT) production systems deliver the right number
of components to downstream workstations, at the right time.
JIT refers to both production operations and supplier delivery
operations.
KEYPOINT
Applications of CAM for manufacturing control include: process monitoring and
control; quality control; shop floor control; inventory control; and just-in-time
production systems.
END KEYPOINT
16.5.2 CAD/CAM
The integration of CAD functions with CAM applications gives us the acronym
CAD/CAM. CAD/CAM is concerned with engineering functions in both design
and manufacturing; it denotes an integration of design and manufacturing
activities by means of computer systems. Since the way a product is
manufactured depends upon the specific design that is supplied, the combining
of CAD with CAM in CAD/CAM, creates a direct link between product design and
product manufacture that can be exploited in the production system.
Conventional practices, practiced for many years in industry, saw design and
manufacturing as essentially separate functions: engineering drawings were
created by the design department, and these were later used by manufacturing
engineers to develop the process plan. This two-step procedure was timeconsuming and duplicated the efforts of design and manufacturing personnel.
The application of CAD/CAM removed this problem. In an ideal CAD/CAM
system, it is possible to take the design specification of the product as it resides
in the CAD database, and convert it automatically into a process plan for making
the product. As such, therefore, CAD/CAM operates as a system that facilitates
concurrent engineering practices.
KEYPOINT
CAD/CAM is concerned with engineering functions in both design and
manufacturing; it denotes an integration of design and manufacturing activities by
means of computer systems.
END KEYPOINT
The term ‘concurrent engineering’ defines a system whereby the whole life cycle
of a product is considered concurrently. The pressure to decrease design and
development time-scales is leading companies to conduct the design,
development, analysis and the production of manufacturing information in
tandem. Within this setting, advances such as CAD/CAM help to avoid certain
problems occurring, such as a lack of quality design or a lack of communication
between design and manufacturing personnel, as everybody understands and
appreciates what everyone else is doing. The organisation of the company in the
case of a concurrent engineering approach is usually dictated by product group
rather than by individual function, with applications such as CAD/CAM being
cross-functional, rather than being department-specific.
The concurrent engineering practice involves work through multi-disciplinary
teams comprising expertise from every area of the organisation, from materials
right through to marketing and sales. There may also be input from outside
specialists. This is opposed to the conventional engineering approach, whereby
the responsibility for the product moves from department to department. For
example, the materials personnel may purchase the raw materials, which they
see as suited to the finished product, but this may not comply with the
expectations of the maintenance people or the production engineers. In the
concurrent engineering approach the materials, production and maintenance
staff would all be working together, enhancing communication on a project team.
Leadership of such teams will vary according to the stage in the product life
cycle.
KEYPOINT
Concurrent engineering defines a system whereby the whole life cycle of a
product is considered concurrently. CAD/CAM is an example of an application
widely used in concurrent engineering.
END KEYPOINT
16.5.3 Computer-Integrated Manufacturing
Computer-integrated manufacturing (CIM) includes all of the engineering
functions of CAD/CAM, but it also includes the firm’s business functions that are
related to manufacturing. The component geometry developed through the use of
CAD systems may be reused in the generation of manufacturing instructions for
numerically controlled production processes, and in the planning of
manufacturing operations through computer aided process planning (CAPP).
This is in line with our discussion above.
Further, they suggest that these activities in turn feed information, together with
bill of materials information, from CAD, into an activity called computer aided
production management (CAPM). All of these manufacturing activities are
integrated through the use of computer aids and a shared database. They are
collectively known in industry as CIM, and they can be summarised in a graphical
format as shown in Figure 16.8. The computer aids the interface between design
and manufacture through the interaction between CAD and CAM, by developing
computer aided process plans. There are problems with this approach: computer
plans are trying to generate and automate process plans for manufacturing, while
the ideal scenario would be to automate the techniques of design for
manufacture and design for assembly in the CAPP system. Examples are
techniques for product/process analysis that gives the manufacturer an influence
or input into the design. CAPP systems constitute both process planning and
product/process analysis with influences from CAD and CAM.
CIM Environment
Market
needs
Geometry
CAD
CAM
Routes
Priority
ls
ia
er
at
Manufacturing
cell capability
profile
m
CAPP
of
Geometry
ll
Bi
Manufacturing
strategy
Manufacturing
CAPM
Cell capacity
profile
Figure 16.8: Data Exchange in a CIM Environment
KEYPOINT
Computer-integrated manufacturing (CIM) includes all of the engineering
functions of CAD/CAM, but it also includes the firm’s business functions that are
related to manufacturing.
END KEYPOINT
Comparing the scope of CIM to the more limited scope of CAD/CAM, is
instructive (see Figure 16.9). The ideal CIM system applies computer and
communications technology to all the operational functions and information
processing functions in manufacturing, from order receipt through design and
production, to product shipment. CAD/CAM, on the other hand, is not so allembracing, and does not cover what may loosely be termed the ‘business
functions’ of the factory. Thus, at higher levels, CIM subsumes CAD/CAM, and
adds functions of its own.
Figure 16.9: The scope of CAD/CAM and CIM
KEYPOINT
CIM has a wider scope than CAD/CAM, so that at higher levels CIM subsumes
CAD/CAM and adds functions of its own.
END KEYPOINT
A specific examination of the computerized elements of a CIM system may also
be analysed (see Figure 16.10). Here we can see the elements of CAD and CAM
being captured within the CIM remit, at different stages of design and
manufacturing. CIM adds a series of computerized business systems that
account for peripheral elements entering and exiting the manufacturing system,
proper. Customer orders are initially logged by an order entry system, with
product specifications being derived from this, and acting as initial input to the
design function, where CAD functions may occur. The output of the design
department, in its turn, serves as input to manufacturing engineering at both
control and planning levels, and both product and process planning is performed
in detail. Full implementation of CIM results in the automation of the information
flow through every aspect of the company’s organization. During the process,
accounting and payroll activities ensure that personnel, product and production
considerations are fully in line with planned expenditure; while at process end,
customer billing completes the operation of the CIM architecture.
Figure 16.10: Computerized elements of a CIM system
KEYPOINT
CIM adds a series of computerized business systems that account for peripheral
elements entering and exiting the manufacturing system, alongside those that
emerge from CAD/CAM.
END KEYPOINT
16.6 Unit Review
BULLETLIST
Product design, and associated CAD/CAM systems, are important parts of the
manufacturing support system.
The conventional design process consists of six processes: recognition of need;
problem definition; synthesis; analysis and optimization; evaluation; and
presentation.
Computer-aided design (CAD) is any design activity that involves the effective
use of a computer to create, modify, analyze, or document an engineering
design.
Benefits of CAD include: increased design productivity; increased available
geometric forms in the design; improved quality of the design; improved design
documentation; creation of a manufacturing database; and design
standardization.
The output of the CAD system is stored in a product data management (PDM)
system. A PDM system consists of computer software that provides links
between users and a central database, where engineering design data and
related documentation is stored.
Geometric modelling creates a mathematical description of the geometry of an
object, so that the subsequent description can be displayed as an image on CAD
systems, which may be manipulated by the operator.
Geometric modelling can appear in the form of two-dimensional modelling, and
three-dimensional modelling.
Geometric models in CAD can also be classified as wire-frame models, or solid
models.
Computer-aided engineering (CAE) software packages are used to perform
complex engineering calculations by computer.
Common CAE packages include: mass properties analysis; interference
checking; tolerance analysis; finite element analysis; kinematic and dynamic
analysis; and discrete-event simulation.
CAD features helpful in evaluating and reviewing a proposed design include:
automatic dimensioning; error checking; animation of discrete-event simulation
solutions; and plant layout design scores.
Evaluating and reviewing a proposed design can use the CAD geometric model
to create a prototype, either by rapid prototyping or virtual prototyping.
Rapid prototyping creates a physical prototype by means of segmenting the CAD
geometric model into a series of layers, and building to that specification; while
virtual prototyping uses the CAD geometric model to construct a digital mock-up
of the product.
CAD may also be used for automated drafting—that is, the creation and
presentation of highly accurate engineering drawings.
The hardware used in a CAD system includes: design workstations; digital
computers; output devices, such as plotters and printers; and various secondary
storage devices.
Different types of CAD system configurations may be used, including: host and
terminal configurations; engineering workstation configurations; and CAD
systems based on the use of personal computers.
Computer-Aided Manufacturing (CAM) is the application of computer technology
to the areas of manufacturing planning and control.
CAM can be considered to have principal application areas: manufacturing
planning, and manufacturing control.
Manufacturing planning uses CAM in an “off-line” setting; that is, computers are
used to support planning and management activities, without a direct connection
being maintained between the computer and the process.
Applications of CAM for manufacturing planning include: Computer-aided
process planning (CAPP); Computer-aided NC part programming; Computerized
machinability data systems; Computerized work standards; Cost estimating;
Production and inventory planning; and Computer-aided line balancing.
Manufacturing control uses CAM applications to manage and control the physical
operations of the factory.
Applications of CAM for manufacturing control include: process monitoring and
control; quality control; shop floor control; inventory control; and just-in-time
production systems.
CAD/CAM is concerned with engineering functions in both design and
manufacturing; it denotes an integration of design and manufacturing activities by
means of computer systems.
Concurrent engineering defines a system whereby the whole life cycle of a
product is considered concurrently. CAD/CAM is an example of an application
widely used in concurrent engineering.
Computer-integrated manufacturing (CIM) includes all of the engineering
functions of CAD/CAM, but it also includes the firm’s business functions that are
related to manufacturing.
CIM has a wider scope than CAD/CAM, so that at higher levels CIM subsumes
CAD/CAM and adds functions of its own.
CIM adds a series of computerized business systems that account for peripheral
elements entering and exiting the manufacturing system, alongside those that
emerge from CAD/CAM.
ENDLIST
16.7 Self-Assessment Questions
NUMLIST
What are the six processes of the conventional design process?
What is Computer-aided design (CAD)?
What are the benefits of CAD?
What is the relationship between the Product Data Management system, and the
CAD system?
What is meant by the concept of geometric modelling?
Classify types of geometric modelling.
What is Computer-aided engineering (CAE) software? List typical applications of
CAE software.
How is CAD used to create product prototypes?
What hardware is used in a CAD system?
What are the different types of CAD system configurations that may be used?
What is Computer-aided manufacturing (CAM)?
What are the two application areas of CAM?
What is meant by the concept of CAD/CAM?
Why is CAD/CAM used in concurrent engineering environments?
What is Computer-integrated manufacturing (CIM)? What is its scope?
ENDLIST
16.8 Answers to Self-Assessment Questions
NUMLIST
The conventional design process consists of six processes: recognition of need;
problem definition; synthesis; analysis and optimization; evaluation; and
presentation.
Computer-aided design (CAD) is any design activity that involves the effective
use of a computer to create, modify, analyze, or document an engineering
design.
The benefits of CAD include: increased design productivity; increased available
geometric forms in the design; improved quality of the design; improved design
documentation; creation of a manufacturing database; and design
standardization.
The output of the CAD system is stored in a product data management (PDM)
system. A PDM system consists of computer software that provides links
between users and a central database, where engineering design data and
related documentation is stored.
Geometric modelling creates a mathematical description of the geometry of an
object, so that the subsequent description can be displayed as an image on CAD
systems, which may be manipulated by the operator.
Geometric modelling can appear in the form of two-dimensional modelling, and
three-dimensional modelling. Geometric models in CAD can also be classified as
wire-frame models, or solid models.
Computer-aided engineering (CAE) software packages are used to perform
complex engineering calculations by computer. Common CAE packages include:
mass properties analysis; interference checking; tolerance analysis; finite
element analysis; kinematic and dynamic analysis; and discrete-event simulation.
Evaluating and reviewing a proposed design can use the CAD geometric model
to create a prototype, either by rapid prototyping or virtual prototyping. Rapid
prototyping creates a physical prototype by means of segmenting the CAD
geometric model into a series of layers, and building to that specification; while
virtual prototyping uses the CAD geometric model to construct a digital mock-up
of the product.
The hardware used in a CAD system includes: design workstations; digital
computers; output devices, such as plotters and printers; and various secondary
storage devices.
Different types of CAD system configurations may be used, including: host and
terminal configurations; engineering workstation configurations; and CAD
systems based on the use of personal computers.
Computer-Aided Manufacturing (CAM) is the application of computer technology
to the areas of manufacturing planning and control.
CAM can be considered to have principal application areas: manufacturing
planning, and manufacturing control. Manufacturing planning uses CAM in an
“off-line” setting; that is, computers are used to support planning and
management activities, without a direct connection being maintained between the
computer and the process. Manufacturing control uses CAM applications to
manage and control the physical operations of the factory.
CAD/CAM is concerned with engineering functions in both design and
manufacturing; it denotes an integration of design and manufacturing activities by
means of computer systems.
The term ‘concurrent engineering’ defines a system whereby the whole life cycle
of a product is considered concurrently. The pressure to decrease design and
development time-scales is leading companies to conduct the design,
development, analysis and the production of manufacturing information in
tandem. Within this setting, advances such as CAD/CAM help to avoid certain
problems occurring, such as a lack of quality design or a lack of communication
between design and manufacturing personnel, as everybody understands and
appreciates what everyone else is doing. The organisation of the company in the
case of a concurrent engineering approach is usually dictated by product group
rather than by individual function, with applications such as CAD/CAM being
cross-functional, rather than being department-specific.
Computer-integrated manufacturing (CIM) includes all of the engineering
functions of CAD/CAM, but it also includes the firm’s business functions that are
related to manufacturing. CIM has a wider scope than CAD/CAM, so that at
higher levels CIM subsumes CAD/CAM and adds functions of its own.
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