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OCR for page 18
- -
A worker sets up a computer
controlled profiling machine
that cuts complex parts out of
aluminum, steel, and
titanium. The program of
instructions for making a part
is usually generated on ~
separate CAM system, then
transferred to the machine's
computer, which can store
programs for dozens of parts.
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Hidden behind factory
walls throughout the world,
. another industrial revolution
.............................................................................................
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-- i ~s un 0 cling arounc t Ale
computer. It is changing
industry as profoundly as
power machinery did in the
eighteenth century and mass
production, typified by the
assembly line, did early this
century.
Computer-aided design and computer-
aided manufacturing-CAD and CAM-
have already increased speed and efficiency
for many manufacturers. They are improving
the quality of products while decreasing the
time to take them from idea to market. And
they are giving manufacturers the flexibility
to respond to an ever-changing market.
Essentially, CAD covers the use of
computers on the design side of a product
while CAM refers to their use on the manu-
facturing side. On the design side, engineers
use computer graphics to design the new
part or product. Other engineers use analyti-
cal programs to determine whether the part,
as it is designed, will hold up under the
stress of actual use. Drafters use computer-
ized devices to add detail to the design and
produce the final drawings. On the manufac-
turing side, computers help engineers write
instructions for the automatic tools that will
create the part. Small computers on the
machines themselves allow the machines to
be quickly changed from producing one part
to making another. Small computers have
also spread to other areas of the factory,
controlling manufacturing processes,
operating robots that move pieces from one
machine to another, and guiding automatic
carts that move materials, parts, and finished
products around the plant.
Modern CAD and CAM systems began
appearing on the market around 1970,
I following the marriage of CAD and CAM
computer programs to minicomputers in the
$100,000 range. Previously they were limited
to a few large manufacturers of aircraft,
autos, and textiles who wrote their own CAD
and CAM programs and ran them on
mainframe computers that often cost a
million dollars or more.
The roots of CAD and CAM reach back
to two Air Force programs in 1949. CAD
hardware the machines began with
efforts to build an air defense system by
linking radar to computers, whose data were
displayed on video screens. At the same
time, the forerunner of CAM software
programs to run the hardware began with
the creation of punched tapes to operate
numerically controlled (NC) machines. These
machines cut, drill, and perform other tasks
according to instructions fed into their
control units on a punched paper tape. Tapes
for the first generation of commercial NC
machines were laboriously punched by
hand. After the creation of a computer
E N G I N E E ~ I N G A N ~ F H E A D VA ~ C E M E N T O F H U M ~ N W E ~ FA R E
OCR for page 19
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programming language called APT, for
Automatically Programmed Tools, tapes
were generated on mainframe computers.
Modern CAM really began in 1969 with
the appearance on the market of a less
complex language, called Compact II, for
programming NC machines. Before then,
companies produced their NC tapes by
hand, made them with APT on a mainframe
computer, or sent the work to be done on a
time-sharing basis on an out-of-house
mainframe. Compact II was initially a time-
sharing service. But later the program was
sold to run on a minicomputer, further
reducing the cost of the service. With such a
CAM system, an engineer could quickly
write a program to produce a part, press a
button, and the computer would punch out
the correct instructions on an NC tape. The
tape was taken to the NC machine to make
the part.
Today, even easier languages have been
introduced for programming NC machines.
In some systems, the tapes have been
eliminated by hooking the programming
~ computer directly to the machine tool. And
I many NC machines have small computers
that store several programs for producing
different parts.
Computer-aided design has sparked its
own revolution within the broader move-
ment toward factory computerization. Like
the telescope and the microscope, CAD
systems have opened up new worlds of
understanding to the engineers who design,
analyze, and test today's sophisticated
products. CAD is applied to nearly every
large or complex engineering project under-
taken today, from designing modern jumbo
jets to planning energy-efficient buildings. It
was, for example, extensively used in
designing Stars ~ Stripes, the racing yacht
that won the America's Cup competition
held in Australia in 1987. And CAD is
absolutely essential for designing the tiny
I circuits in microprocessors and other inte-
grated-circuit chips that mn most electronic
devices.
The second wave of the CAD revolution
rose In 1981 with the introduction of single-
user CAD workstations. Workstation
computers are powered by microprocessors
and generally have more computing power
C O M P U T E R - A I D E D D E S I G N A N D M A N U FA C T U R I N G
The screen of a CAD/CAM
system illustrates the complex
tool path that a milling
machine must follow to create
the curving surface of an
impeller blade for a jet
engine.
19
OCR for page 20
and graphics capability than personal
computers, which are also based on micro-
processors. However, a workstation costs
about one-tenth as much as a minicomputer.
Today, the price of some workstations is
under $10,000, and their power equals that of
most minis.
Modern CAD did not spring full grown
into existence. It began as a drawing aid for
e~
A microprocessor is designed
with the aid of an electronic
CAD system. Using this
program, an engineer can
quickly design an electronic
circuit by placing and
connecting symbols of
components on the screen.
The computer automatically
adds the details to the
final design.
l ~
. . ..~
An engineer uses a
workstation and a mechanical
CAD program to design
a new wheel hub assembly.
20
as_
drafters and developed along two parallel
paths. One led through electronic design,
and the other through mechanical design.
In the electronics industry, the great
problem facing engineers in the late 1960s
was the design of increasingly smaller and
more complex integrated circuits on tiny
silicon chips. NC machines had been devel-
oped for cutting the stencil-like masks used
in etching circuit patterns onto chips. But
instructions for the machines were still
calculated and punched into the tapes by
hand. In 1970 one of the first commercial
electronic CAD systems, called Design
Assistant, appeared on the market. It consist-
ed of a minicomputer, screen, sketch pad,
and keyboard plus software. The engineer
drew the circuit on the pad, watching the
design appear on the screen. After correcting
mistakes, the engineer pressed a button, and
instructions for cutting the design were
punched into an NC tape. This early CAD
system sold for about $150,000. But just two
years later, improved versions were selling
for half that price.
In the mid-1970s, new electronic CAD
programs for "design rule check" came to the
market. They not only copied the circuit
pattern but also told the engineer whether
the patterns were too close together or
violated any other design rules. In the early
1980s, even more intelligent programs were
developed. Called "performance models,"
they could tell a design engineer what would
happen when electric signals flowed through
the circuit and point out flaws in the design.
Today, no self-respecting engineer would
design a circuit without performance
modeling.
One of the first modern CAD systems
for mechanical design arrived in 1971 on the
heels of electronic CAD. It was really a
drafting aid that consisted of a drawing table,
computer, screen, and plotting arm that
digitized its movements: that is, translated
them into digital electronic signals. By
moving the plotter to different points on the
table and telling the computer what to draw
between them, a draftsman could copy a
design into the computer while watching it
materialize on the screen. After correcting the
design, the draftsman pressed a button, and
the plotting arm automatically redrew the
design on a clean piece of paper. Called
Interact I, this mechanical CAD system ran
on a minicomputer with four terminals and
cost around $375,000.
The early mechanical CAD systems
could draw points, lines, circles, arcs, and
symbols in two dimensions but with no
mathematical idea of what they were doing.
By 1973 more intelligent programs were
developed that could not only create three-
dimensional figures on the computer screen
but understood the geometry and mathemat-
ics associated with them. These were wire-
frame models like the 3-D figures engineers
traditionally drew.
More important than creating 3-D design
models, though, was the intelligence of such
a CAD program. Using a mathematical
model of the design in its data base, it could
answer questions from the engineer: How
long is that line? What is the area of this
plane? Where is the center of gravity? And if,
for example, the engineer tried to put a 2-
inch piece in a space 1.75 inches wide, the
CAD program would reply that the piece
was 0.25 inch too long. It was smart enough
to calculate and draw a new line through a
model if the engineer so requested. It could
also calculate a section, in effect slicing the
model in two so the engineer could see how
~ E N G ~ N E E R ~ N G A N D T H E A D VA N C E M E N T O F H U M A N W E ~ FA R E
OCR for page 21
parts fit together inside the design. And it
could turn the model to be viewed from
different angles. This was not just a drafting
device but a true CAD system that helped an
engineer design a part.
The newer mechanical CAD programs
were also intelligent enough to perform
simple analyses on the design, to see how it
would hold up under the stress of actual use.
They could also prepare a design for more
complex analysis by dividing the model into
the hundreds or thousands of geometrical
shapes that formed it. The data were then
sent to analytical engineers who tested the
design on powerful mainframe computers.
This preparation, which the CAD program
did in seconds, would have taken engineers
hundreds of hours to do by hand.
In the late 1970s, computer models of
solid objects came onto the market. These
were even better for analysis than 3-D wire-
frame models. Nevertheless, since there are
so many variables in designing a mechanical
part, mechanical CAD systems today are
only beginning to reach the level of perfor-
mance modeling that electronic CAD
systems achieved nearly a decade ago.
However, programs are being developed
that allow engineers to analyze mechanical
systems for a large number of variables. For
example, engineers soon could be able to
model the performance of a mechanical
system as complex as a commercial power
plant.
CAD programs of the late 1970s also
began linking to CAM systems on the
manufacturing side of factories, eliminating
the need for many paper design drawings
and reducing the time manufacturing
engineers need to write instruction programs
for the NC machines that make the parts.
Previously, engineers had to study the paper
drawings in order to calculate tool move-
ments. These CAD systems, however, could
simulate the movement of a cutting tool
around the design model in order to deter-
mine the necessary tool movements. These
were not only determined more quickly
using CAD models, they were also more
accurate.
In the future, engineers will seek ways to
use CAD and CAM more effectively. Today
CAD programs are linked to CAM systems
in only a small number of factories. On the
design side of factories, separate CAD
systems often exist independently in design,
drafting, and engineering departments.
Drawings are still often carried from one
office to another, where it may take 50 to 100
hours to enter the data into another comput-
er system. On the manufacturing side,
computers are only slowly being applied to
tasks that they could perform faster and
more effectively. In addition, many factories
could greatly increase their productivity by
joining isolated computerized systems into
integrated networks. Such computer-
integrated manufacturing, or CIM, has
begun in a few factories, and some of the
results have been spectacular. For example,
the highly integrated use of computerized
systems at one company that manufactures
motor-starter components helps it produce
and ship the parts in less than 24 hours, a job
that used to take about 15 days.
Another challenge in computerizing the
manufacturing process lies in integrating
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computers throughout the company, not just
at an individual factory. Such a CIM network
might include finance, market forecasting,
material ordering, customer service, and
stocking, as well as CAD and CAM. Current
debate swirls around how to integrate the
computers whether to design one big
network or to integrate computers only
where and when it becomes necessary. Too
much integration could flood and slow the
network with needless data.
Computers have found an indispensable
role to play in manufacturing through CAD,
CAM, and other automated systems. No one
really disagrees. How big a role they will
play, and when, are the real questions for the
future.
C O M P U T E R - A ~ D E D D E 51 G N A N D M A N U FA C T U R I N G I
An engineer uses a
mechanical CAD program to
analyze stress on the lifting
arm in the design of an
automobile jack assembly.
The program creates a solid
model of the device, top. It
uses a mesh to divide the
lifting arm into small "finite
elements" that are analyzed
for stress individually, center
The program then uses color
coding to indicate varying
levels of stress throughout the
component, telling the
I engineer where to strengthen
the design, bottom.
21
Representative terms from entire chapter:
electronic cad
