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How Products Are Made: An Illustrated Guide to Product Manufacturing (How Products Are Made) Volume 1

Año:
1993
Editorial:
Gale
Idioma:
english
Páginas:
518
ISBN 13:
9780810389076
ISBN:
081038907X
File:
PDF, 33.92 MB
Descarga (pdf, 33.92 MB)
 
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NEIL

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SCHLA GER,

Editor

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Illus trate d

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P ro du c t

G u i de

M a n u fa c tu rin g

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NEIL

SCHLAGER,

GaleResearchinc.

to

Editor

* DETROIT

-

WASHINGTON, D.C. * LONDON

STAFF

Neil Schlager, Editor

Elisabeth Morrison, Associate Editor
Christine Jeryan, Kyung-Sun Lim, Kimberley A. McGrath, Bridget Travers, Robyn V. Young,
Contributing Editors

Meggin M. Condino, Jeffrey Muhr, Janet Witalec, Contributing Associate Editors

Victoria B. Cariappa, Research Manager
Maureen Richards, Research Supervisor
Donna Melnychenko, Research Associate
Jaema Paradowski, Research Assistant
Mary Beth Trimper, Production Director
Shanna Heilveil, Production Assistant

Cynthia Baldwin, Art Director
Bernadette M. Gomie, Page Designer
Mark C. Howell, Cover Designer
Electronic illustrations provided by Hans & Cassady, Inc. of Westerville, Ohio.
While every effort has been made to ensure the reliability of the information presented in this publication, Gale Research Inc. neither
guarantees the accuracy of the data contained herein nor assumes any responsibility for errors, omissions or discrepancies. Gale accepts
no payment for listing; and inclusion in the publication of any organization, agency, institution, publication, service, or individual does
not imply endorsement of the editors or publisher. Errors brought to the attention of the publisher and verified to the satisfaction of the
publisher will be corrected in future editions.
The paper used in this publication meets the minimum requirements of American National Standard for Information
(_
Sciences-Permanence Paper for Printed Library Materials, ANSI Z39.48-1984.
This publication is a creative work fully protected by all applicable copyright laws, as well as by misappropriation, trade secret, unfair
competition, and other applicable laws. The authors and editors of this work have added value to the underlying factual material herein
through one or more of the following: unique and original selection, coordinatio; n, expression, arrangement, and classification of the
information.

All rights to this publication will be vigorously defended.

Copyright i 1994
Gale Research Inc.
835 Penobscot Building
Detroit, MI 48226-4094
All rights reserved including the right of reproduction in whole or in part in any form.

ISBN 0-8103-8907-X
ISSN 1072-5091
Printed in the United States of America
Published simultaneously in the United Kingdom
by Gale Research Intemational Limited
(An affiliated company of Gale Research Inc.)
10 9 8 7 6 5 4 3 2 1

i(jp
The trademark ITP is used under license.

Contents
Introduction ................. vii
Contributors ................. xi
Acknowledgments .......... xiii
1
Aluminum Foil ............... 8
Artificial Limb .............. 14
Aspirin ................... 19
Automobile ................. 24
Automobile Windshield ...... 31
Baking Soda ............... 35
Ball Bearing ................ 39
Bar Code Scanner .......... 44
Baseball ................... 50
Baseball Glove ............. 55
Battery ................... 60
Bicycle Shorts ............... 65
Blood Pressure Monitor ...... 69
Blue Jeans .................. 74
80
Book ...................
86
Brick ...................
Bulletproof Vest ............. 91
Candle ................... 96
Carbon Paper...... ....... 100
.105
Cellophane Tape ...
.109
Ceramic Tile .......
.114
Chalk .............
.119
Cheese ............
.124
Chewing Gum......

Air Bag

...................

.......

.......

.......

.......

.......

Chocolate .................
Coffee ....................
Combination Lock .........
Combine ..................

Compact Disc

.............

129
134
139

143
148

Compact Disc Player ....... 153
Concrete .................. 158
Cooking Oil ............... 164
Corrugated Cardboard ..... 169
Cutlery ................... 174
Expanded Polystyrene Foam
(EPF) .................... 180
Eyeglass Lens ............. 185
File Cabinet ............... 190
Fire Extinguisher ........... 194
Floppy Disk ............... 199
Gold ..................... 204
Golf Cart ................. 209

Grinding Wheel

...........

214

219
Helicopter ................. 223
Jet Engine ................. 230
Laboratory Incubator ....... 236
Laser Guided Missile ....... 242
Laundry Detergent ......... 247
Lawn Mower .............. 252
Light Bulb ................. 256
Light-Emitting Diode (LED) . . 261

Guitar

....................

v

Lipstick ............... .... 267 Satellite Dish .............. 390
Screwdriver ............... 395
Liquid Crystal Display
(LCD) ................ . 272 Seismograph .............. 400
Lubricating Oil ........ ....277 Shaving Cream .............406
Mattress .............. ....281 Soda Bottle ............... 410
Microwave Oven ...... ... . 286 Solar Cell ............... 414
Mirror ................ .... 291 Spark Plug ............... 420
Nail Polish............ .... 297 Stainless Steel ............. 424
Necktie ............... .... 301 Stapler ................430
Optical Fiber.......... .... 305 Stethoscope ............... 434
439
Paint ................. ....310 Sugar ................
Pantyhose............. . 315 Super Glue ............... 444
Peanut Butter.......... .... 320 Thermometer .............. 448
453
326 Tire ...............
Pencil ................
Pesticide .............. ....330 Tortilla Chip ............... 458
Porcelain ............. .... 335 Trumpet ............... 464
Postage Stamp ........ .... 340 Umbrella ............... 469
Pressure Gauge ....... .... 345 Washing Machine ......... 473
478
.350 Watch ...............
Rayon ................
Refrigerator ........... .... 355 Wind Turbine ............. 482
488
Revolver .............. .361 Wine ...............
494
.367 Wool ...............
Rubber Band ..........
500
Running Shoe ......... .... 371 Zipper ...............
376 Zirconium ............... 505
Saddle ...............
509
Salsa ................. .... 381 .Index ...............
385
Sandpaper............

...

..

....

v

i

Introduction
About the Series
Welcome to How Products Are Made: An Illustrated Guide to Product Manufacturing. This series provides detailed yet accessible information on the manufacture of a
variety of items, from everyday household products to heavy machinery to sophisticated electronic equipment. With step-by-step descriptions of processes, simple
explanations of technical terms and concepts, and clear, easy-to-follow illustrations,
the series will be useful to a wide audience.
In each volume of How Products Are Made, you will find products from a broad range
of manufacturing areas: food, clothing, electronics, transportation, machinery, instruments, sporting goods, and more. Some are intermediate goods sold to manufacturers
of other products, while others are retail goods sold directly to consumers. You will
find products made from a variety of materials, and you will even find products such
as precious metals and minerals that are not "made" so much as they are extracted and
refined.

Organization
Every volume in the series is comprised of many individual entries, each covering a
single product; Volume 1 includes more than 100 entries, arranged alphabetically.
Although each entry focuses on the product's manufacturing process, it also provides
a wealth of other information: who invented the product or how it has developed, how
it works, what materials it is made of, how it is designed, quality control procedures
used, byproducts generated during its manufacture, future applications, and books and
periodical articles containing more information.
To make it easier for users to find what they are looking for, the entries are broken up
into standard sections. Among the sections you will find are:

* Background
* History
* Raw Materials
* Design
vi i

* The Manufacturing Process
* Quality Control
* Byproducts
* The Future
* Where To Learn More

The illustrations accompanying each entry provide you with a better sense of how the
manufacturing process actually works. Uncomplicated and easy to understand, these
illustrations generally follow the step-by-step description of the manufacturing
process found in the text.

Bold-faced items in the text refer the reader to other entries in this volume.

Volume 1 also contains an added bonus: approximately ten percent of the entries include
special boxed sections. Written by William S. Pretzer, a manufacturing historian and
curator at the Henry Ford Museum, these sections describe interesting historical developments related to a product.
Finally, Volume 1 contains a general subject index with important terms, processes,
materials, and people. Here as in the text, bold-faced items refer the reader to main
entries on the subject.

Contributors/Advisors
The entries in Volume 1 were written by a skilled team of technical writers and engineers, often in cooperation with manufacturers and industry associations.
In addition, a group of advisors assisted in the formulation of the series and of Volume
1 in particular. They are:

Marshall Galpern
Staff Engineer
General Motors Corporation
Dr. Michael J. Kelly
Director
Manufacturing Research Center
Georgia Institute of Technology

Jeanette Mueller-Alexander
Reference Librarian/Business Subject Specialist
Hayden Library
Arizona State University
Dr. William S. Pretzer
Curator
Henry Ford Museum & Greenfield Village
v III

Diane A. Richmond
Head
Science and Technology Information Center
Chicago Public Library

Suggestions
Your questions, comments, and suggestions are welcome. Please send all such correspondence to:

The Editor
How Products Are Made
Gale Research Inc.
835 Penobscot Building
Detroit, MI 48226

ix

Contributors
Jim Acton

Steve Mathias

William L. Ansel

Leslie G. Melcer

Lawrence H. Berlow

L. S. Millberg

Douglas E. Betts

Robert C. Miller

Rick Bockmii/er

Dan Pepper

Robert A. Cortese

Rashid Riaz

Blaine Danley

Rose Secrest

Matthew Fogel

Eva Sideman

Suzy Fucini

Frank Sokolo

Theodore L. Giese

Edward J. Stone

Alicia Haley

Peter Toeg

David Harris

Phillip S. Waldrop

Catherine Kolecki

Jim Wawrzyniak

Greg Ling

Glenn G. Whiteside

Peter S. Lucking

Craig F. Whitlow

Barry M. Marton

x

i

Acknowledgments
The editor would like to thank the following individuals, companies, and associations
for providing assistance with Volume 1 of How Products Are Made:

Air Bag: Morton International Incorporated-Automotive Products Division; TRW
Vehicle Safety Systems Incorporated. Artificial Limb: Bob Burleson, Southeastern
Orthotics & Prosthetics; Jim Colvin, Ohio Willow Wood Company; Douglas Turner,
Becker Orthopedic; Al Pike, Otto Bock. Baking Soda: Church & Dwight Company
Incorporated; FMC Corporation. Ball Bearing: Thomson Precision Ball Company.
Baseball: Scott Smith, Rawlings Sporting Goods Company. Baseball Glove: Bob
Clevenhagen, Rawlings Sporting Goods Company; Robby Storey, Nocona Athletic
Goods Company. Battery: John Daggett, Rayovac Corporation; Steve Wicelinski,
Duracell Incorporated. Bicycle Shorts: Cannondale Manufacturers. Blue Jeans: Bill
Dunnahoo, Thomaston Mills Incorporated; Allen Slagle, Bristol Jeans Incorporated.
Bulletproof Vest: Al Baker, American Body Armor; Bob Coppage, Progressive Technologies of America; Lester Gray, Keramont Corporation. Carbon Paper: Jim Sellers,
NER Data Products Incorporated. Cellophane Tape: Jerry Miron, Skeist Incorporated.
Chalk: Roger Taylor, Dixon Ticonderoga Company. Chocolate: Bob Zedik, Chocolate Manufacturers Association. Combination Lock: Master Lock Company. Combine: Dick Corken, John Deere Harvester Division. Compact Disc Player: Sanyo
Fisher Company. Corrugated Cardboard: Rod Johnson, Packaging Corporation of
America-Containerboard Products Division. Cutlery: Sandra E. Finley, Oneida,
Limited. Expanded Polystyrene Foam (EPF): E. S. Clark, University of TennesseeMaterials Engineering Department; Ralph Taylor, Constar International Incorporated.
File Cabinet: Phil Bradley, Kwik File Incorporated; Debbie Kniegge, Accuride; K. C.
Thomsen, Electro Painters Incorporated. Golf Cart: Textron Incorporated-E-Z Go
Division. Laundry Detergent: Larry Byrne, Sr., Byrne Laboratories. Lawn Mower:
Dan Ariens, Ariens Company. Optical Fiber: James Bratton, Corning IncorporatedTelecommunications Products Division. Pantyhose: National Association of Hosiery
Manufacturers. Peanut Butter: Russell E. Barker, Peanut Butter and Nut Processors
Association. Pesticide: Reed Bacon, Bacon Products Corporation. Postage Stamp:
Kelly Keough, American Banknote Company. Rubber Band: Michael Halperson,
Plymouth Office Supply Company. Running Shoe: Craig Cartley, Athletic Footwear
Association. Saddle: John DePietra, Equitation Synergist. Salsa: Caroline Fee, Del
Monte Corporation; Lou Rasplicka, Pace Foods Incorporated. Satellite Dish: Jonathan
x

iii

Peschko, Sky Link. Screwdriver: Glenn Allen, Stanley Works. Seismograph: Gene
Tafra, Spreng-Nethers; Teledyne Incorporated-Geotech Division. Shaving Cream:
Leonard Giglio, Contract Packaging Company. Soda Bottle: E. S. Clark, University of
Tennessee-Materials Engineering Department; Ralph Taylor, Constar International
Incorporated. Solar Cell: Mark Stimson, Siemens Solar Industries Incorporated.
Stethoscope: Marc Blitstein, American Diagnostic Corporation; Tom Edmundson,
Tycos; Cynthia Runyon, Minnesota Mining and Manufacturing Company (3M).
Sugar: Suzanne Arnold, Sugar Association Incorporated. Super Glue: Lou Baccei,
Loctite Corporation. Tire: Bill Brown II, Pirelli Armstrong Tire Corporation. Tortilla
Chip: Tortilla Industry Association. Trumpet: Cliff Blackburn, Blackburn.
Umbrella: Ann Cain, Totes Incorporated; Bob Storey and Manny Dubinsky, Zip Jack
Industries, Limited. Washing Machine: Speed Queen Company. Watch: Scott Chou,
SEIKO Corporation of America. Wind Turbine: Kerri E. Miller and Robert Sims,
U.S. Windpower Incorporated.
The historical photographs on pages 25, 51, 81, 175, 225, 257, 321, 454, and 495 are
from the collections of Henry Ford Museum & Greenfield Village, Dearborn,
Michigan. The cover photograph of a tire is courtesy of AP/Wide World Photos.

Finally, the editor would like to thank Hans & Cassady Incorporated of Westerville,
Ohio, for providing the electronic illustrations for Volume 1.

xiv

Air Bag
Background
An air bag is

an

inflatable cushion designed

turn, fits into the steering wheel for driver'sside applications and above the glove compartment for front passenger applications.

to protect automobile occupants from serious

injury in the case of a collision. The air bag is
part of an inflatable restraint system, also
known as an air cushion restraint system

(ACRS) or an air bag supplemental restraint
system (SRS), because the air bag is designed
to supplement the protection offered by seat
belts. Seat belts are still needed to hold the
occupant securely in place, especially in side
impacts, rear impacts, and rollovers. Upon
detecting a collision, air bags inflate instantly
to cushion the exposed occupant with a big
gas-filled pillow.
A typical air bag system consists of an air
bag module (containing an inflator or gas
generator and an air bag), crash sensors, a
diagnostic monitoring unit, a steering wheel
connecting coil, and an indicator lamp. These
components are all interconnected by a
wiring harness and powered by the vehicle's
battery. Air bag systems hold a reserve
charge after the ignition has been turned off
or after the battery has been disconnected.
Depending on the model, the backup power
supply lasts between one second and ten
minutes. Since components vital to the system's operation might sit dormant for years,
the air bag circuitry performs an internal
"self-test" during each startup, usually indicated by a light on the instrument panel that
glows briefly at each startup.

The crash sensors are designed to prevent the
air bag from inflating when the car goes over
a bump or a pothole, or in the case of a minor
collision. The inflator fits into a module consisting of a woven nylon bag and a breakaway plastic horn pad cover. The module, in

In a frontal collision equivalent to hitting a
solid barrier at nine miles per hour (14.48
kilometers per hour), the crash sensors
located in the front of the car detect the sudden deceleration and send an electrical signal
activating an initiator (sometimes called an
igniter or squib). Like a light bulb, an initiator contains a thin wire that heats up and penetrates the propellant chamber. This causes
the solid chemical propellant, principally
sodium azide, sealed inside the inflator to
undergo a rapid chemical reaction (commonly referred to as a pyrotechnic chain).
This controlled reaction produces harmless
nitrogen gas that fills the air bag. During
deployment the expanding nitrogen gas
undergoes a process that reduces the temperature and removes most of the combustion
residue or ash.

The expanding gas inflates
the bag in less than onetwentieth of a second,
splitting open its plastic
cover and inflating in front
of the occupant. The bag
is fully inflated for only
one-tenth of a second and
is nearly deflated by threetenths of a second after
impact.

The expanding nitrogen gas inflates the nylon
bag in less than one-twentieth (1/20) of a second, splitting open its plastic module cover
and inflating in front of the occupant. As the
occupant contacts the bag, the nitrogen gas is
vented through openings in the back of the
bag. The bag is fully inflated for only onetenth (1/10) of a second and is nearly deflated
by three-tenths (3/10) of a second after
impact. Talcum powder or corn starch is
used to line the inside of the air bag and is
released from the air bag as it is opened.

History
The air bag traces its origin to air-filled bladders outlined as early as 1941 and first
patented in the 1950s. Early air bag systems

1

How Products Are Made, Volume 1

A typical driver's-side air bag fits
neatly on the steering wheel column. In case of a collision, the crash
sensor sends an electric spark to the
inflator canister, setting off a chemical readion that produces nitrogen
gas. The gas expands, inflating the
air bag and protecting the driver.

Air bag

were large and bulky, primarily using tanks of
compressed or heated air, compressed nitrogen gas (N2), freon, or carbon dioxide (CO2).
Some of the early systems created hazardous
byproducts. One particular system used gunpowder to heat up freon gas, producing phosgene gas (COC12)-an extremely poisonous
gas.
One of the first patents for automobile air
bags was awarded to industrial engineer John
Hetrick on August 18, 1953. Conceived by
Hetrick after a near accident in 1952, the
design called for a tank of compressed air
under the hood and inflatable bags on the
steering wheel, in the middle of the dashboard, and in the glove compartment to protect front seat occupants, and on the back of
the front seat to protect rear seat passengers.
The force of a collision would propel a sliding weight forward to send air into the bags.
Many other inventors and researchers followed suit, all exploring slightly different
designs, so that the exact technical trail from

2

the early designs to the present system is
impossible to note with certainty.
In 1968, John Pietz, a chemist for Talley
Defense Systems, pioneered a solid propellant using sodium azide (NaN3) and a metallic oxide. This was the first nitrogengenerating solid propellant, and it soon
replaced the older, bulkier systems. Sodium
azide in its solid state is toxic if ingested in
large doses, but in automotive applications is
carefully sealed inside a steel or aluminum
container within the air bag system.

Since the 1960s, air bag-equipped cars in
controlled tests and everyday use have
demonstrated the effectiveness and reliability. The Insurance Institute For Highway
Safety conducted a study of the federal govemnment's Fatal Accident Reporting System
using data from 1985 to 1991, and concluded
that driver fatalities in frontal collisions were
lowered by 28 percent in automobiles
equipped with air bags. According to

Air Bag

another study conducted in 1989 by General
Motors, the combination of lap/shoulder
safety belts and air bags in frontal collisions
reduced driver fatalities by 46 percent and
front passenger fatalities by 43 percent.
In response to consumers' increased safety
concerns and insurance industry pressure, the
federal government has forced automobile
manufacturers to upgrade their safety features. First, Department of Transportation
(DOT) regulations require all cars, beginning
with model year 1990, sold in the United
States to be equipped with a passive restraint
system. (Passive restraint systems-requiring no activation by the occupant-involve
the use of automatic seat belts and/or the use
of air bags.) If car manufacturers choose an
air bag, then regulations require only a driver's-side system until model year 1994,
when air bag-equipped cars must include
passive protection on the passenger's side as
well. A 1991 law requires driver and passenger air bags in all cars by the 1998 model
year and in light trucks and vans by 1999.

Ravv MActerials
As stated above, an air bag system consists of
an air bag module, crash sensors, a diagnostic monitoring unit, a steering wheel connect-

ing coil, and an indicator lamp. Both this section and the next ("The Manufacturing
Process") will focus on the air bag module
itself.
An air bag module has three main parts: the
air bag, the inflator, and the propellant. The
air bag is sewn from a woven nylon fabric
and can come in different shapes and sizes
depending on specific vehicle requirements.
The driver's-side air bag material is manufactured with a heat shield coating to protect
the fabric from scorching, especially near the
inflator assembly, during deployment.
Talcum powder or corn starch is also used to
coat the air bag; either substance prevents the
fabric from sticking together and makes it
easier to assemble. Newer silicone and urethane coated air bag materials require little or
no heat shield coating, although talcum powder or corn starch will probably still be used
as a processing aid.

Preparation of the propellant, the first
step in air bag manufacture, involves
combining sodium azide and an oxidizer. The propellant is then combined with the metal initiator canister
and various filters to form the inflator
assembly.

The inflator canister or body is made from
either stamped stainless steel or cast aluminum. Inside the inflator canister is a filter
assembly consisting of a stainless steel wire
mesh with ceramic material sandwiched in
between. When the inflator is assembled, the
filter assembly is surrounded by metal foil to
maintain a seal that prevents propellant contamination.

3

How Products Are Made, Volume 1

The propellant, in the form of black pellets,
is primarily sodium azide combined with an
oxidizer and is typically located inside the
inflator canister between the filter assembly
and the initiator.

The Manufacturing
Process
Air bag production involves three different
separate assemblies that combine to form the
finished end product, the air bag module.
The propellant must be manufactured, the
inflator components must be assembled, and
the air bag must be cut and sewn. Some
manufacturers buy already-made components, such as air bags or initiators, and then
just assemble the complete air bag module.
The following description of the manufacturing process is for driver-side air bag module
assembly. Passenger-side air bag module
assemblies are produced slightly differently.

Propellant
The propellant consists of sodium azide
mixed together with an oxidizer, a substance that helps the sodium azide to burn
when ignited. The sodium azide is received
from outside vendors and inspected to make
sure it conforms to requirements. After
inspection it is placed in a safe storage place
until needed. At the same time, the oxidizer
is received from outside vendors, inspected,
and stored. Different manufacturers use different oxidizers.

2 From storage, the sodium azide and the
2oxidizer are then carefully blended under
sophisticated computerized process control.
Because of the possibility of explosions, the
powder processing takes place in isolated
bunkers. In the event safety sensors detect a
spark, high speed deluge systems will douse
whole rooms with water. Production occurs
in several redundant smaller facilities so that
if an accident does occur, production will not
be shut down, only decreased.
3 After blending, the propellant mixture is
3sent to storage. Presses are then used to
compress the propellant mixture into disk or
pellet form.

Inflator assembly
4 The inflator components, such as the
Imetal canister, the filter assembly-

4

stainless steel wire mesh with ceramic material inside-and initiator (or igniter) are
received from outside vendors and inspected.
The components are then assembled on a
highly automated production line.

5 The inflator sub-assembly is combined

5with the propellant and an initiator to
form the inflator assembly. Laser welding
(using C02 gas) is used to join stainless steel
inflator sub-assemblies, while friction inertial welding is used to join aluminum inflator
sub-assemblies. Laser welding entails using
laser beams to weld the assemblies together,
while friction inertial welding involves rubbing two metals together until the surfaces
become hot enough to join together.

6 The inflator assembly is then tested and
Csent to storage until needed.

Air bag
7 The woven nylon air bag fabric is re7ceived from outside vendors and inspected for any material defects. The air bag
fabric is then die cut to the proper shapes and
sewn, internally and externally, to properly
join the two sides. After the air bag is sewn,
it is inflated and checked for any seam
imperfections.

Final assembly of air bag module
8 The air bag assembly is then mounted to
Uthe tested inflator assembly. Next, the air
bag is folded, and the breakaway plastic horn
pad cover is installed. Finally, the completed
module assembly is inspected and tested.
9 The module assemblies are packaged in
boxes for shipment and then sent to customers.

Other components
The remaining components of the air
l bag system-the crash sensors, the
diagnostic monitoring unit, the steering
wheel connecting coil, and the indicator
lamp-are combined with the air bag module
during vehicle assembly. All the components
are connected and communicate through a
wiring harness.

Air Bag

Quality Control
The quality control aspect of air bag production is, obviously, very important because
many lives depend on the safety feature.
Two major areas where quality control is
critical are the pyrotechnic or propellant tests
and the air bag and inflator static and
dynamic tests.

Propellants, before being inserted into inflators, are first subjected to ballistic tests to pre-

dict their behavior. A representative sample
of inflators are pulled from the production
line and tested for proper operation by a fullscale inflator test, which measures pressurecreated by the generated gas inside a large
tank 15.84 or 79.20 gallons (60 or 300
liters)-versus time in milliseconds. This
gives an indication of the inflator system's

ability to produce an amount of gas at a given
rate, ensuring proper air bag inflation. The air
bags themselves are inspected for fabric and
seam imperfections and then tested for leaks.

The air bag parts are die-cut out of
woven nylon, sewn together, and
riveted. The bag is then carefully
folded so that it will fit inside the
plastic module cover.

Automated inspections are made at every
stage of the production process line to identify mistakes. One air bag manufacturer uses
radiography (x-rays) to compare the completed inflator against a master configuration
stored in the computer. Any inflator without
the proper configuration is rejected.

The Future
The future for air bags looks extremely
promising because there are many different
applications possible, ranging from aircraft
seating to motorcycle helmets. The air bags
of the future will be more economical to pro-

5

How Products Are Made, Volume 1

Crash sensors can be located in several spots on the front of the aubmobile. These sensors are connected to
the air bag module with a wiring harness. Two other key components of
an air bag system are the diagnostic
module and the indicator lamp. The
diagnosfic module performs a system
test each time the car is started, briefly
lighting up the indicator lamp
mounted on the dashboard.

Wiring

harness
duce and lighter in weight; will involve
smaller, more integrated systems; and will
use improved sensors.

Side-impact air bags are another possibility
that would work similar to driver- and passenger-side air bags. Side-impact air bags
will most likely be mounted in the car door
panels and deployed towards the window
during impact to protect the head. Foam
padding around the door structure would also
be used to cushion the upper body in a side
impact. Head and/or knee bolsters (energy
absorbing pads) to complement the air bag
system are also being investigated. Rear-seat
air bags are also being tested but consumer
demand is not expected to be high.
Aftermarket air bag systems-generic systems that can be installed on any vehicle
already built-are not currently available.
Since the effectiveness of an air bag depends
on its sensors recognizing if a crash is severe
enough to trigger deployment, a system must
be precisely tuned to the way a specific car
model behaves in a crash. Still, companies
are exploring the future possibility of producing a modified air bag system for retrofit.
A hybrid inflator is currently being tested
that uses a combination of pressurized inert
gas (argon) and heat from a propellant to significantly expand the gas's volume. These
systems would have a cost advantage, since
less propellant could be used. Air bag manufacturers are also developing systems that
would eliminate the sodium azide propellant,
which is toxic in its undeployed form. Work

6

Indicator
lamp

Crash sensors

Diagnostic

module
is also underway to improve the coatings that
preserve the air bag and facilitate its opening.
Eventually the bags may not need coatings at
all.
In the future, more sophisticated sensors
called "smart" sensors will be used to tailor
the deployment of the air bag to certain conditions. These sensors could be used to sense
the size and weight of the occupant, whether
the occupant is present (especially in the case
of passenger-side air bags where deployment
may be unnecessary if there are no passengers), and the proximity of the driver to the
steering wheel (a driver slumped over the
steering wheel could be seriously injured by
an air bag deployment).

Where To Learn More
Periodicals
Chaikin, Don. "How It Works-Airbags,"
Popular Mechanics. June, 1991, p. 81.

Frantom, Richard L. "Buckling Down on
Passenger Safety," Design News. October 2,
1989, pp. 116-118.
Gottschalk, Mark A. "Micromachined
Airbag Sensor Tests Itself," Design News.
October 5, 1992, p. 26.
Grable, Ron. "Airbags: In Your Face, By
Design," Motor Trend. January, 1992, pp.
90-91.

Air Bag
Haayen, Richard J. "The Airtight Case for Air
Bags," Saturday Evening Post. November,
1986.
Reed, Donald. "Father of the Air Bag,"
Automotive Engineering. February, 1991, p.
67.

Sherman, Don. "It's in the Bag," Popular
Science. October, 1992, pp. 58-63.

Spencer, Peter L. "The Trouble with Air
Bags," Consumers' Research. January, 1991,
pp. 10-13.
-Glenn G. Whiteside

7

Aluminum Foil
The preference for
aluminum in flexible
packaging has become a
global phenomenon. In
Japan, aluminum foil is
used as the barrier
component in flexible
cans. In Europe,
aluminum flexible
packaging dominates the
market for pharmaceutical
blister packages and
candy wrappers.

Background
Aluminum foil is made from an aluminum
alloy which contains between 92 and 99 percent aluminum. Usually between 0.00017
and 0.0059 inches thick, foil is produced in
many widths and strengths for literally hundreds of applications. It is used to manufacture thermal insulation for the construction
industry, fin stock for air conditioners, electrical coils for transformers, capacitors for
radios and televisions, insulation for storage
tanks, decorative products, and containers
and packaging. The popularity of aluminum
foil for so many applications is due to several
major advantages, one of the foremost being
that the raw materials necessary for its manufacture are plentiful. Aluminum foil is inexpensive, durable, non-toxic, and greaseproof. In addition, it resists chemical attack
and provides excellent electrical and nonmagnetic shielding.

Shipments (in 1991) of aluminum foil totaled
913 million pounds, with packaging representing seventy-five percent of the aluminum
foil market. Aluminum foil's popularity as a
packaging material is due to its excellent
imperTneability to water vapor and gases. It
also extends shelf life, uses less storage
space, and generates less waste than many
other packaging materials. The preference
for aluminum in flexible packaging has consequently become a global phenomenon. In
Japan, aluminum foil is used as the barrier
component in flexible cans. In Europe, aluminum flexible packaging dominates the
market for pharmaceutical blister packages
and candy wrappers. The aseptic drink box,
which uses a thin layer of aluminum foil as a
barrier against oxygen, light, and odor, is
also quite popular around the world.

8

Aluminum is the most recently discovered of
the metals that modem industry utilizes in
large amounts. Known as "alumina," aluminum compounds were used to prepare medicines in ancient Egypt and to set cloth dyes
during the Middle Ages. By the early eighteenth century, scientists suspected that these
compounds contained a metal, and, in 1807,
the English chemist Sir Humphry Davy
attempted to isolate it. Although his efforts
failed, Davy confirmed that alumina had a
metallic base, which he initially called "alumium." Davy later changed this to "aluminum," and, while scientists in many
countries spell the term "aluminium," most
Americans use Davy's revised spelling. In
1825, a Danish chemist named Hans Christian
0rsted successfully isolated aluminum, and,
twenty years later, a German physicist named
Friedrich Wohler was able to create larger
particles of the metal; however, Wohler's particles were still only the size of pinheads. In
1854 Henri Sainte-Claire Deville, a French
scientist, refined Wo1hler's method enough to
create aluminum lumps as large as marbles.
Deville's process provided a foundation for
the modem aluminum industry, and the first
aluminum bars made were displayed in 1855
at the Paris Exposition.
At this point the high cost of isolating the
newly discovered metal limited its industrial
uses. However, in 1866 two scientists working separately in the United States and France
concurrently developed what became known
as the Hall-Heroult method of separating alumina from oxygen by applying an electrical
current. While both Charles Hall and PaulLouis-Toussaint Heroult patented their discoveries, in America and France respectively,
Hall was the first to recognize the financial
potential of his purification process. In 1888

Aluminum Foil

he and several partners founded the Pittsburgh Reduction Company, which produced
the first aluminum ingots that year. Using
hydroelectricity to power a large new conversion plant near Niagara Falls and supplying
the burgeoning industrial demand for aluminum, Hall's company-renamed the
Aluminum Company of America (Alcoa) in
1907-thrived. H6roult later established the
Aluminium-Industrie-Aktien-Gesellschaft in
Switzerland. Encouraged by the increasing
demand for aluminum during World Wars I
and II, most other industrialized nations
began to produce their own aluminum. In
1903, France became the first country to produce foil from purified aluminum. The
United States followed suit a decade later, its
first use of the new product being leg bands to
identify racing pigeons. Aluminum foil was
soon used for containers and packaging, and
World War II accelerated this trend, establishing aluminum foil as a major packaging
material. Until World War II, Alcoa
remained the sole American manufacturer of
purified aluminum, but today there are seven
major producers of aluminum foil located in
the United States.

Rcaw Materials
Aluminum numbers among the most abundant elements: after oxygen and silicon, it is

the most plentiful element found in the
earth's surface, making up over eight percent
of the crust to a depth of ten miles and
appearing in almost every common rock.
However, aluminum does not occur in its
pure, metallic form but rather as hydrated
aluminum oxide (a mixture of water and alumina) combined with silica, iron oxide, and
titania. The most significant aluminum ore is
bauxite, named after the French town of Les
Baux where it was discovered in 1821.
Bauxite contains iron and hydrated aluminum oxide, with the latter representing its
largest constituent material. At present,
bauxite is plentiful enough so that only
deposits with an aluminum oxide content of
forty-five percent or more are mined to make
aluminum. Concentrated deposits are found
in both the northern and southern hemispheres, with most of the ore used in the
United States coming from the West Indies,
North America, and Australia. Since bauxite
occurs so close to the earth's surface, mining
procedures are relatively simple. Explosives
are used to open up large pits in bauxite beds,
after which the top layers of dirt and rock are
cleared away. The exposed ore is then
removed with front end loaders, piled in
trucks or railroad cars, and transported to
processing plants. Bauxite is heavy (generally, one ton of aluminum can be produced
from four to six tons of the ore), so, to reduce

The Bayer process of refining bauxite consists of four steps: digestion,
clarification, precipitation, and calcination. The result is a fine white
powder of aluminum oxide.

9

How Products Are Made, Volume 1

Continuous casting is an altemafive
to melting and casting aluminum.
An advantage of continuous casfing
is that it does not require an annealing (heat treatment) step prior to foil
rolling, as does the melting and
casting process.

the cost of transporting it, these plants are
often situated as close as possible to the
bauxite mines.

The Mcanufacturing
Process
Extracting pure aluminum from bauxite
entails two processes. First, the ore is refined
to eliminate impurities such as iron oxide,
silica, titania, and water. Then, the resultant
aluminum oxide is smelted to produce pure
aluminum. After that, the aluminum is rolled
to produce foil.

Refining-Bayer process
The Bayer process used to refine bauxite
comprises four steps: digestion, clarification, precipitation, and calcination. During
10

the digestion stage, the bauxite is ground and
mixed with sodium hydroxide before being
pumped into large, pressurized tanks. In
these tanks, called digesters, the combination
of sodium hydroxide, heat, and pressure
breaks the ore down into a saturated solution
of sodium aluminate and insoluble contaminants, which settle to the bottom.

2 The next phase of the process, clarifica-

2tion, entails sending the solution and the
contaminants through a set of tanks and
presses. During this stage, cloth filters trap
the contaminants, which are then disposed of.
After being filtered once again, the remaining
solution is transported to a cooling tower.
3 In the next stage, precipitation, the aluminum oxide solution moves into a large
silo, where, in an adaptation of the Deville

Aluminum Foil
method, the fluid is seeded with crystals of
hydrated aluminum to promote the formation
of aluminum particles. As the seed crystals
attract other crystals in the solution, large
clumps of aluminum hydrate begin to form.
These are first filtered out and then rinsed.

ROLLING

Coolant/
Lubricant

Foil is produced from aluminum
stock by rolling it between heavy
rollers. Rolling produces two natural
finishes on the foil, bright and
matte. As the foil emerges from the
rollers, circular knives cut it into rectangular pieces.

A Calcination, the final step in the Bayer
refinement process, entails exposing the
aluminum hydrate to high temperatures.
This extreme heat dehydrates the material,
leaving a residue of fine white powder: aluminum oxide.

Smelting
5 Smelting, which separates the aluminum-

5oxygen compound (alumina) produced by
the Bayer process, is the next step in extracting pure, metallic aluminum from bauxite.
Although the procedure currently used derives
from the electrolytic method invented contemporaneously by Charles Hall and PaulLouis-Toussaint Heroult in the late nineteenth
century, it has been modernized. First, the alumina is dissolved in a smelting cell, a deep
steel mold lined with carbon and filled with a
heated liquid conductor that consists mainly
of the aluminum compound cryolite.
6 Next, an electric current is run through
6the cryolite, causing a crust to form over
the top of the alumina melt. When additional
alumina is periodically stirred into the mixture, this crust is broken and stirred in as
well. As the alumina dissolves, it electrolytically decomposes to produce a layer of pure,
molten aluminum on the bottom of the smelting cell. The oxygen merges with the carbon
used to line the cell and escapes in the form
of carbon dioxide.
7 Still in molten form, the purified alu7minum is drawn from the smelting cells,
transferred into crucibles, and emptied into
furnaces. At this stage, other elements can
be added to produce aluminum alloys with
characteristics appropriate to the end product, though foil is generally made from 99.8
or 99.9 percent pure aluminum. The liquid is
then poured into direct chill casting devices,
where it cools into large slabs called "ingots"
or "reroll stock." After being annealedheat treated to improve workability-the
ingots are suitable for rolling into foil.
An alternative method to melting and casting
the aluminum is called "continuous casting."

Aluminum web

This process involves a production line consisting of a melting furnace, a holding hearth
to contain the molten metal, a transfer system, a casting unit, a combination unit consisting of pinch rolls, shear and bridle, and a
rewind and coil car. Both methods produce
stock of thicknesses ranging from 0.125 to
0.250 inch (0.317 to 0.635 centimeter) and of
various widths. The advantage of the continuous casting method is that it does not
require an annealing step prior to foil rolling,
as does the melting and casting process,
because annealing is automatically achieved
during the casting process.

Rolling foil
8 After the foil stock is made, it must be
Oreduced in thickness to make the foil.
This is accomplished in a rolling mill, where
the material is passed several times through
metal rolls called work rolls. As the sheets (or
webs) of aluminum pass through the rolls,
they are squeezed thinner and extruded
through the gap between the rolls. The work
rolls are paired with heavier rolls called
backup rolls, which apply pressure to help
maintain the stability of the work rolls. This
helps to hold the product dimensions within
tolerances. The work and backup rolls rotate
in opposite directions. Lubricants are added
to facilitate the rolling process. During this

I 1

How Products Are Made, Volume 1

rolling process, the aluminum occasionally
must be annealed (heat-treated) to maintain
its workability.
The reduction of the foil is controlled by
adjusting the rpm of the rolls and the viscosity (the resistance to flow), quantity, and
temperature of the rolling lubricants. The
roll gap determines both the thickness and
length of the foil leaving the mill. This gap
can be adjusted by raising or lowering the
upper work roll. Rolling produces two natural finishes on the foil, bright and matte.
The bright finish is produced when the foil
comes in contact with the work roll surfaces.
To produce the matte finish, two sheets must
be packed together and rolled simultaneously; when this is done, the sides that are
touching each other end up with a matte finish. Other mechanical finishing methods,
usually produced during converting operations, can be used to produce certain patterns.

9 As the foil sheets come through the

9 rollers, they are trimmed and slitted with

circular or razor-like knives installed on the
roll mill. Trimming refers to the edges of the
foil, while slitting involves cutting the foil
into several sheets. These steps are used to
produce narrow coiled widths, to trim the
edges of coated or laminated stock, and to
produce rectangular pieces. For certain fabricating and converting operations, webs that
have been broken during rolling must be
joined back together, or spliced. Common
types of splices for joining webs of plain foil
and/or backed foil include ultrasonic, heatsealing tape, pressure-sealing tape, and electric welded. The ultrasonic splice uses a
solid-state weld-made with an ultrasonic
transducer-in the overlapped metal.

Finishing processes
For many applications, foil is used in
combination with other materials. It
can be coated with a wide range of materials,
such as polymers and resins, for decorative,
protective, or heat-sealing purposes. It can be
laminated to papers, paperboards, and plastic
films. It can also be cut, formed into any
shape, printed, embossed, slit into strips,
sheeted, etched, and anodized. Once the foil
is in its final state, it is packaged accordingly
and shipped to the customer.

12

Quality Control
In addition to in-process control of such
parameters as temperature and time, the finished foil product must meet certain requirements. For instance, different converting
processes and end uses have been found to
require varying degrees of dryness on the foil
surface for satisfactory performance. A wettability test is used to determine the dryness.
In this test, different solutions of ethyl alcohol in distilled water, in increments of ten
percent by volume, are poured in a uniform
stream onto the foil surface. If no drops
form, the wettability is zero. The process is
continued until it is determined what minimum percent of alcohol solution will completely wet the foil surface.

Other important properties are thickness and
tensile strength. Standard test methods have
been developed by the American Society For
Testing and Materials (ASTM). Thickness is
determiined by weighing a sample and measuring its area, and then dividing the weight
by the product of the area times the alloy
density. Tension testing of foil must be carefully controlled because test results can be
affected by rough edges and the presence of
small defects, as well as other variables. The
sample is placed in a grip and a tensile or
pulling force is applied until fracture of the
sample occurs. The force or strength
required to break the sample is measured.

The Future
The popularity of aluminum foil, especially
for flexible packaging, will continue to grow.
Four-sided, fin-sealed pouches have gained
wide popularity for military, medical, and
retail food applications and, in larger sizes,
for institutional food service packs. Pouches
have also been introduced for packaging 1.06
to 4.75 gallons (4-18 liters) of wine for both
retail and restaurant markets, and for other
food service markets. In addition, other products continue to be developed for other applications. The increase in popularity of
microwave ovens has resulted in the development of several forms of aluminum-based
semi-rigid containers designed specifically
for these ovens. More recently, special cooking foils for barbecuing have been developed.
However, even aluminum foil is being scrutinized in regard to its environmental "friendli-

Aluminum Foil
ness." Hence, manufacturers are increasing
their efforts in the recycling area; in fact, all
U.S. foil producers have begun recycling
programs even though aluminum foil's total
tonnage and capture rate is much lower than
that of the easy-to-recycle aluminum cans.
Aluminum foil already has the advantage of
being light and small, which helps reduce its
contribution to the solid waste stream. In
fact, laminated aluminum foil packaging
represents just 17/lOOths of one percent of
the U.S. solid waste.
For packaging waste, the most promising
solution may be source reduction. For
instance, packaging 65 pounds (29.51 kilograms) of coffee in steel cans requires 20
pounds (9.08 kilograms) of steel but only
three pounds (4.08 kilograms) of laminated

packaging including aluminum foil. Such
packaging also takes up less space in the
landfill. The Aluminum Association's Foil
Division is even developing an educational
program on aluminum foil for universities
and professional packaging designers in order
to help inform such designers of the benefits
of switching to flexible packaging.

Aluminum foil also uses less energy during
both manufacturing and distribution, with inplant scrap being recycled. In fact, recycled
aluminum, including cans and foil, accounts
for over 30 percent of the industry's yearly

supply of metal. This number has been
increasing for several years and is expected
to continue. In addition, processes used during foil manufacturing are being improved to
reduce air pollution and hazardous waste.

Where To Learn More
Books
Aluminum Foil. The Aluminum Association.
1981.

Periodicals
"Barrier Qualities Stimulate Aluminum Foil
Packaging Growth," FoilPak News. The
Aluminum Association. Fall, 1992.
"The Best Ways to Keep Food Fresh: A
Roundup of the Most Effective and Most
Economical Wraps, Bags, and Containers,"
Consumer Reports. February, 1989, p. 120+.

Gracey, Kathryn K. "Aluminum in Microwaves," Consumers' Research Magazine.
January, 1989, p. 2.
"Promote Even Cookery with Foil,"
Southern Living. December, 1987, pp. 130131.
-L. S. Millberg

13

Artificial Limb
The most exciting
development of the
twentieth century hos been
the development of
myoelectric prosthetic
limbs. Myoelectricity
involves using electrical
signals from the potient's
orm muscles to move the
limb.

Background
Artificial arms and legs, or prostheses, are
intended to restore a degree of normal function to amputees. Mechanical devices that
allow amputees to walk again or continue to
use two hands have probably been in use
since ancient times, the most notable one
being the simple peg leg. Surgical procedure
for amputation, however, was not largely successful until around 600 B.c. Armorers of the
Middle Ages created the first sophisticated
prostheses, using strong, heavy, inflexible
iron to make limbs that the amputee could
scarcely control. Even with the articulated
joints invented by Ambroise Pare in the
1500s, the amputee could not flex at will.
Artificial hands of the time were quite beautiful and intricate imitations of real hands, but
were not exceptionally functional. Upper
limbs, developed by Peter Baliff of Berlin in
1812 for below-elbow amputees and Van
Peetersen in 1844 for above-elbow amputees,
were functional, but still far less than ideal.
The nineteenth century saw a lot of changes,
most initiated by amputees themselves. J. E.
Hanger, an engineering student, lost his leg in
the Civil War. He subsequently designed an
artificial leg for himself and in 1861 founded a
company to manufacture prosthetic legs. The
J. E. Hanger Company is still in existence
today. Another amputee named A. A.
Winkley developed a slip-socket below-knee
device for himself, and with the help of
Lowell Jepson, founded the Winkley
Company in 1888. They marketed the legs
during the National Civil War Veterans
Reunion, thereby establishing their company.
Another amputee named D. W. Dorrance
invented a terminal device to be used in the
place of a hand in 1909. Dorrance, who had

14

lost his right arm in an accident, was
unhappy with the prosthetic arms then available. Until his invention, they had consisted
of a leather socket and a heavy steel frame,
and either had a heavy cosmetic hand in a
glove, a rudimentary mechanical hand, or a
passive hook incapable of prehension.
Dorrance invented a split hook that was
anchored to the opposite shoulder and could
be opened with a strap across the back and
closed by rubber bands. His terminal device
(the hook) is still considered to be a major
advancement for amputees because it
restored their prehension abilities to some
extent. Modified hooks are still used today,
though they might be hidden by realisticlooking skin.

The twentieth century has seen the greatest
advances in prosthetic limbs. Materials such
as modern plastics have yielded prosthetic
devices that are strong and more lightweight
than earlier limbs made of iron and wood.
New plastics, better pigments, and more
sophisticated procedures are responsible for
creating fairly realistic-looking skin.
The most exciting development of the twentieth century has been the development of
myoelectric prosthetic limbs. Myoelectricity
involves using electrical signals from the
patient's arm muscles to move the limb.
Research began in the late 1940s in West
Germany, and by the late sixties myoelectric
devices were available for adults. In the last
decade children have also been fitted with
myoelectric limbs.
In recent years computers have been used to
help fit amputees with prosthetic limbs.
Eighty-five percent of private prosthetic
facilities use a CAD/CAM to design a model

Artificial Limb
Plaster cast

4

Making the socket

Vacuum
of the patient's arm or leg, which can be used
mold from which the new limb
can be shaped. Laser-guided measuring and
fitting is also available.

to prepare a

Raw Materials
The typical prosthetic device consists of a
custom fitted socket, an internal structure
(also called a pylon), knee cuffs and belts
that attach it to the body, prosthetic socks
that cushion the area of contact, and, in some
cases, realistic-looking skin. Prosthetic limb
manufacture is currently undergoing changes
on many levels, some of which concern the
choice of materials.
A prosthetic device should most of all be
lightweight; hence, much of it is made from

plastic. The socket is usually made from
polypropylene. Lightweight metals such as
titanium and aluminum have replaced much
of the steel in the pylon. Alloys of these
materials are most frequently used. The
newest development in prosthesis manufacture has been the use of carbon fiber to form
a lightweight pylon.
Certain parts of the limb (for example, the
feet) have traditionally been made of wood
(such as maple, hickory basswood, willow,
poplar, and linden) and rubber. Even today
the feet are made from urethane foam with a
wooden inner keel construction. Other materials commonly used are plastics such as
polyethylene, polypropylene, acrylics, and
polyurethane. Prosthetic socks are made
from a number of soft yet strong fabrics.
Earlier socks were made of wool, as are some

After a plaster cost of the amputee's
stump is made, a thermoplastic
sheet is vacuum-formed around this
cast to form a test socket. In vacuum-forming, the plastic sheet is
heated and then placed in a vacuum chamber with the cost (or
mold). As the air is sucked out of the
chamber, the plastic adheres to the
cast and assumes its shape. After
testing, the permanent socket is
formed in the some way.

15

How Products Are Made, Volume 1

modem ones, which can also be made of cotton or various synthetic materials.
Physical appearance of the prosthetic limb is
important to the amputee. The majority of
endoskeletal prostheses (pylons) are covered
with a soft polyurethane foam cover that has
been designed to match the shape of the
patient's sound limb. This foam cover is then
covered with a sock or artificial skin that is
painted to match the patient's skin color.

The Manufacturing
Process
Prosthetic limbs are not mass-produced to be
sold in stores. Similar to the way dentures or
eyeglasses are procured, prosthetic limbs are
first prescribed by a medical doctor, usually
after consultation with the amputee, a prosthetist, and a physical therapist. The patient
then visits the prosthetist to be fitted with a
limb. Although some parts-the socket, for
instance-are custom-made, many parts
(feet, pylons) are manufactured in a factory,
sent to the prosthetist, and assembled at the
prosthetist's facility in accordance with the
patient's needs. At a few facilities, the limbs
are custom made from start to finish.

Measuring and casting
Accuracy and attention to detail are
I important in the manufacture of prosthetic
limbs, because the goal is to have a limb that
comes as close as possible to being as comfortable and useful as a natural one. Before
work on the fabrication of the limb is begun,
the prosthetist evaluates the amputee and
takes an impression or digital reading of the
residual limb.
2 The prosthetist then measures the lengths
of relevant body segments and determines the location of bones and tendons in
the remaining part of the limb. Using the
impression and the measurements, the prosthetist then makes a plaster cast of the stump.
This is most commonly made of plaster of
paris, because it dries fast and yields a
detailed impression. From the plaster cast, a
positive model-an exact duplicate-of the
stump is created.

Making the socket
3 Next, a sheet of clear thermoplastic is
3heated in a large oven and then vacuum-

16

formed around the positive mold. In this
process, the heated sheet is simply laid over
the top of the mold in a vacuum chamber. If
necessary, the sheet is heated again. Then,
the air between the sheet and the mold is
sucked out of the chamber, collapsing the
sheet around the mold and forcing it into the
exact shape of the mold. This thermoplastic
sheet is now the test socket; it is transparent
so that the prosthetist can check the fit.
4 Before the permanent socket is made, the
prosthetist works with the patient to
ensure that the test socket fits properly. In
the case of a missing leg, the patient walks
while wearing the test socket, and the prosthetist studies the gait. The patient is also
asked to explain how the fit feels; comfort
comes first. The test socket is then adjusted
according to patient input and retried.
Because the material from which the test
socket is made is thermoplastic, it can be
reheated to make minor adjustments in
shape. The patient can also be fitted with
thicker socks for a more comfortable fit.
1

5 The permanent socket is then formed.

5Since it is usually made of polypropylene, it can be vacuum-formed over a mold in
the same way as the test socket. It is common
for the stump to shrink after surgery, stabilizing approximately a year later. Thus, the
socket is usually replaced at that time, and
thereafter when anatomical changes necessitate a change.

Fabrication of the prosthesis
6 There are many ways to manufacture the
of a prosthetic limb. Plastic
pieces-including soft-foam pieces used as
liners or padding-are made in the usual plastic forming methods. These include vacuumforming (see no. 3 above), injecting molding
-forcing molten plastic into a mold and letting it cool-and extruding, in which the
plastic is pulled through a shaped die. Pylons
that are made of titanium or aluminum can be
die-cast; in this process, liquid metal is forced
into a steel die of the proper shape. The
wooden pieces can be planed, sawed, and
drilled. The various components are put
together in a variety of ways, using bolts,
adhesives, and laminating, to name a few.

6parts

7 The entire limb is assembled by the pros7thetist's technician using such tools as a
torque wrench and screwdriver to bolt the

Artificial Limb
A typical artiFicial limb, in this case
an above-the-knee prosthesis. The
foam cover is covered with artificial
skin that is pointed to match the
patient's natural skin color.

prosthetic device together. After this, the
prosthetist again fits the permanent socket to
the patient, this time with the completed custom-made limb attached. Final adjustments
are then made.

Physical Therapy
Once the prosthetic limb has been fitted, it is
necessary for the patient to become comfortable with the device and learn to use it in
order to meet the challenges of everyday life.
At the same time, they must learn special
exercises that strengthen the muscles used to
move the prosthetic device. When the patient
has been fitted with a myoelectric device, it
is sometimes true that the muscles are too
weak to effectively signal the device, so
again the muscles are exercised to strengthen
them. Some new amputees are trained to
wash the devices-including the socksdaily, and to practice getting them on and off.
A patient fitted with an artificial arm must
learn to use the arm and its locking device as

well as the hand. If the amputee lost an arm
due to an accident and is subsequently fitted
with a myoelectric device, this is relatively
easy. If the loss of the limb is congenital, this
is difficult. An instruction system has been
developed to teach amputees how to accomplish many small tasks using only one hand.
Some patients fitted with an artificial leg also
undergo physical therapy. It typically takes a
new amputee 18-20 weeks to learn how to
walk again. Patients also learn how to get in
and out of bed and how to get in and out of a
car. They learn how to walk up and down
hill, and how to fall down and get up safely.

Quality Control
No standards exist for prosthetic limbs in the
United States. Some manufacturers advocate
instituting those of the International Standards Organization of Europe, particularly
because U.S. exporters of prosthetic limbs to
Europe must conform to them anyway.

1 7

How Products Are Made, Volume 1

Others believe these regulations to be confusing and unrealistic; they would rather see
the United States produce their own, more
reasonable standards.
Lack of standards does not mean that prosthetic limb manufacturers have not come up
with ways to test their products. Some tests
evaluate the strength and lifetime of the
device. For instance, static loads test
strength. A load is applied over a period of
30 seconds, held for 20 seconds, then
removed over a period of 30 seconds. The
limb should suffer no deformation from the
test. To test for failure, a load is applied to the
limb until it breaks, thus determining strength
limits. Cyclic loads determine the lifetime of
the device. A load is applied two million
times at one load per second, thus simulating
five years of use. Experimental prosthetic
limbs are usually considered feasible if they
survive 250,000 cycles.

The Future
Many experts are optimistic about the future
of prosthetic limbs; at least, most agree that
there is vast room for improvement. A prosthetic limb is a sophisticated device, yet it is
preferably simple in design. The ideal prosthetic device should be easy for the patient to
learn how to use, require little repair or
replacement, be comfortable and easy to put
on and take off, be strong yet lightweight, be
easily adjustable, look natural, and be easy to
clean. Research aims for this admittedly
utopian prosthetic device, and strides have
been made in recent years.

Carbon fiber is a strong, lightweight material
that is now being used as the basis of
endoskeletal parts (the pylons). In the past it
was used primarily for reinforcement of
exoskeletal protheses, but some experts
claim that carbon fiber is a superior material
that will eventually replace metals in pylons.
One researcher has developed software that
superimposes a grid on a CAT scan of the
stump to indicate the amount of pressure the
soft tissue can handle with a minimum
amount of pain. By viewing the computer
model, the prosthetist can design a socket

1 8

that minimizes the amount of soft tissue that
is displaced.
An experimental pressure-sensitive foot is
also in the works. Pressure transducers
located in the feet send signals to electrodes
set in the stump. The nerves can then receive
and interpret the signals accordingly.
Amputees can walk more normally on the
new device because they can feel the ground
and adjust their gait appropriately.
Another revolutionary development in the
area of prosthetic legs is the introduction of
an above-knee prosthesis that has a built-in
computer that can be programmed to match
the patient's gait, thereby making walking
more automatic and natural.

Where To Learn More
Books
Forester, C. S. Flying Colours. Little,
Brown, 1938.

Sabolich, John. You're Not Alone. Sabolich
Prosthetic and Research Center, 1991.
Shurr, Donald G. and Thomas M. Cook.
Prosthetics and Orthotics. Appleton and
Lange, 1990.

Periodicals
Abrahams, Andrew. "An Amazing 'Foot'
Puts Legless Vet Bill Demby Back in the
Ballgame," People Weekly. April 4, 1988, p.
119.
Hart, Lianne. "Lives that Are Whole," Life.
December, 1988, pp. 112-116.

Heilman, Joan Rattner. "Medical Miracles,"
Redbook. May, 1991, p. 124+.
"A Helping Hand for Christa," National
Geographic World. November, 1986, p. 10.

"Off to a Running Start," National
Geographic World. August, 1991, pp. 29-3 1.
-Rose Secrest

Aspirin
Background
Aspirin is one of the safest and least expensive pain relievers on the marketplace. While
other pain relievers were discovered and
manufactured before aspirin, they only
gained acceptance as over-the-counter drugs
in Europe and the United States after
aspirin's success at the tum of the twentieth

that cause pain and inflammation. Since then,
scientists have made further progress in
understanding how aspirin works. They now
know, for instance, that aspirin and its relatives actually prevent the growth of cells that
cause inflammation.

History

century.

Today, Americans alone consume 16,000
tons of aspirin tablets a year, equaling 80
million pills, and we spend about $2 billion a
year for non-prescription pain relievers,
many of which contain aspirin or similar
drugs.
Currently, the drug is available in several
dosage forms in various concentrations from
.0021 to .00227 ounces (60 to 650 milligrams), but the drug is most widely used in
tablet form. Other dosage forms include capsules, caplets, suppositories and liquid elixir.
Aspirin can be used to fight a host of health
problems: cerebral thromboses (with less
than one tablet a day); general pain or fever
(two to six tablets a day; and diseases such as
rheumatic fever, gout, and rheumatoid arthritis. The drug is also beneficial in helping to
ward off heart attacks. In addition, biologists
use aspirin to interfere with white blood cell
action, and molecular biologists use the drug
to activate genes.
The wide range of effects that aspirin can
produce made it difficult to pinpoint how it
actually works, and it wasn't until the 1970s
that biologists hypothesized that aspirin and
related drugs (such as ibuprofen) work by
inhibiting the synthesis of certain hormones

The compound from which the active ingredient in aspirin was first derived, salicylic
acid, was found in the bark of a willow tree
in 1763 by Reverend Edmund Stone of
Chipping-Norton, England. (The bark from
the willow tree-Salix Alba-contains high
levels of salicin, the glycoside of salicylic
acid.) Earlier accounts indicate that
Hippocrates of ancient Greece used willow
leaves for the same purpose-to reduce fever
and relieve the aches of a variety of illnesses.

Today, Americans alone
consume 16,000 tons of
aspirin tablets a year,
equaling 80 million pills,
and we spend about $2
billion a year for nonprescription pain relievers,
many of which contain
aspirin or similar drugs.

During the 1800s, various scientists
extracted salicylic acid from willow bark and
produced the compound synthetically. Then,
in 1853, French chemist Charles F. Gerhardt
synthesized a primitive form of aspirin, a
derivative of salicylic acid. In 1897 Felix
Hoffmann, a German chemist working at the
Bayer division of I.G. Farber, discovered a
better method for synthesizing the drug.
Though sometimes Hoffmann is improperly
given credit for the discovery of aspirin, he
did understand that aspirin was an effective
pain reliever that did not have the side effects
of salicylic acid (it bumed throats and upset
stomachs).
Bayer marketed aspirin beginning in 1899
and dominated the production of pain relievers until after World War I, when Sterling
Drug bought German-owned Bayer's New

1 9

How Products Are Made, Volume 1

WEIGHING

Active ingredient

Lubricant
Corn starch

I,
DRY
SCREENING

The first three steps in aspirin manufacture: weighing, mixing, and dry
screening. Mixing can be done in a
Glen Mixer, which both blends the
ingredients and expels the air from
them. In dry screening, small
batches are forced through a wire

mesh screen by hand, while larger
batches can be screened in a
Fitzpatrick mill.

York operations. Today, "Aspirin" is a registered trademark of Bayer in many countries
around the world, but in the United States
and the United Kingdom aspirin is simply the
common name for acetylsalicylic acid.

The manufacture of aspirin has paralleled
advancements in pharmaceutical manufacturing as a whole, with significant mechanization occurring during the early twentieth
century. Now, the manufacture of aspirin is
highly automated and, in certain pharmaceutical companies, completely computerized.
While the aspirin production process varies
between pharmaceutical companies, dosage
forms and amounts, the process is not as
complex as the process for many other drugs.
In particular, the production of hard aspirin
tablets requires only four ingredients: the

20

active ingredient (acetylsalicylic acid),
starch, water, and a lubricant.

corn

Raw Materials
To produce hard aspirin tablets, corn starch
and water are added to the active ingredient
(acetylsalicylic acid) to serve as both a binding agent and filler, along with a lubricant.
Binding agents assist in holding the tablets
together; fillers (diluents) give the tablets
increased bulk to produce tablets of adequate
size. A portion of the lubricant is added during mixing and the rest is added after the
tablets are compressed. Lubricant keeps the
mixture from sticking to the machinery.
Possible lubricants include: hydrogenated
vegetable oil, stearic acid, talc, or aluminum
stearate. Scientists have performed considerable investigation and research to isolate the

Aspirin
most effective lubricant for hard aspirin
tablets.
Chewable aspirin tablets contain different
diluents, such as mannitol, lactose, sorbitol,
sucrose, and inositol, which allow the tablet
to dissolve at a faster rate and give the drug a
pleasant taste. In addition, flavor agents,
such as saccharin, and coloring agents are
added to chewable tablets. The colorants currently approved in the United States include:
FD&C Yellow No. 5, FD&C Yellow No. 6,
FD&C Red No.3, FD&C Red No. 40, FD&C
Blue No. 1, FD&C Blue No. 2, FD&C Green
No. 3, a limited number of D&C colorants,
and iron oxides.

ents meet pre-determined specifications for
the batch size and dosage amount.

Mixing
2 The corn starch is dispensed into cold
2purified water, then heated and stirred
until a translucent paste forms. The corn
starch, the active ingredient, and part of the
lubricant are next poured into one sterile canister, and the canister is wheeled to a mixing
machine called a Glen Mixer. Mixing blends
the ingredients as well as expels air from the
mixture.

3 The mixture is then mechanically sepa-

3rated into units, which are generally from
The Manufacturing
Process
Aspirin tablets are manufactured in different
shapes. Their weight, size, thickness, and
hardness may vary depending on the amount
of the dosage. The upper and lower surfaces
of the tablets may be flat, round, concave, or
convex to various degrees. The tablets may
also have a line scored down the middle of
the outer surface, so the tablets can be broken
in half, if desired. The tablets may be
engraved with a symbol or letters to identify
the manufacturer.
Aspirin tablets of the same dosage amount are
manufactured in batches. After careful weighing, the necessary ingredients are mixed and
compressed into units of granular mixture
called slugs. The slugs are then filtered to
remove air and lumps, and are compressed
again (or punched) into numerous individual
tablets. (The number of tablets will depend on
the size of the batch, the dosage amount, and
the type of tablet machine used.) Documentation on each batch is kept throughout
the manufacturing process, and finished
tablets undergo several tests before they are
bottled and packaged for distribution.
The procedure for manufacturing hard
aspirin tablets, known as dry-granulation or
slugging, is as follows:

Weighing
The corn starch, the active ingredient, and
the lubricant are weighed separately in
sterile canisters to determine if the ingredi-

7/8 to 1 inches (2.22 to 2.54 centimeters) in
size. These units are called slugs.
Dry screening
4 Next, small batches of slugs are forced
x through a mesh screen by a hand-held
stainless steel spatula. Large batches in sizable manufacturing outlets are filtered
through a machine called a Fitzpatrick mill.
The remaining lubricant is added to the mixture, which is blended gently in a rotary granulator and sifter. The lubricant keeps the
mixture from sticking to the tablet machine
during the compression process.

Compression
5 The mixture is compressed into tablets
_either by a single-punch machine (for
small batches) or a rotary tablet machine (for
large scale production). The majority of single-punch machines are power-driven, but
hand-operated models are still available. On
single-punch machines, the mixture is fed
into one tablet mold (called a dye cavity) by
a feed shoe, as follows:
* The feed shoe passes over the dye cavity
and releases the mixture. The feed shoe
then retracts and scrapes all excess mixture
away from the dye cavity.

* A punch-a short steel rod-the size of the
dye cavity descends into the dye, compressing the mixture into a tablet. The
punch then retracts, while a punch below

2 1

How Products Are Made, Volume 1

This drawing illustrates the principle
of compression in a single-punch
machine. First, the aspirin mixture is
fed into a dye cavity. Then, a steel
punch descends into the cavity and
compresses the mixture into a
tablet. As the punch retracts,
another punch below the cavity
rises to eject the tablet.

COMPRESSION

Compress

-

I3

n

H
Eject

the dye cavity rises into the cavity and
ejects the tablet.

* As the feed shoe returns to fill the dye cavity again, it pushes the compressed tablet
from the dye platform.

On rotary tablet machines, the mixture runs
through a feed line into a number of dye cavities which are situated on a large steel plate.
The plate revolves as the mixture is dispensed
through the feed line, rapidly filling each dye
cavity. Punches, both above and below the
dye cavities, rotate in sequence with the rotation of the dye cavities. Rollers on top of the
upper punches press the punches down onto
the dye cavities, compressing the mixture into
tablets, while roller-activated punches
beneath the dye cavities lift up and eject the
tablets from the dye platform.
Testing
6 The compressed tablets are subjected to a
6tablet hardness and friability test, as well

22

as a tablet disintegration test (see Quality
Control section below).

Bottling and packaging
7 The tablets are transferred to an auto/mated bottling assembly line where they
are dispensed into clear or color-coated polyethylene or polypropylene plastic bottles or
glass bottles. The bottles are topped with cotton packing, sealed with a sheer aluminum
top, and then sealed with a plastic and rubber
child-proof lid. A sheer, round plastic band is
then affixed to the circular edge of the lid. It
serves as an additional seal to discourage and
detect product tampering.
8 The bottles are then labeled with product

8information and an expiration date is

affixed. Depending on the manufacturer, the
bottles are then packaged in individual cardboard boxes. The packages or bottles are
then boxed in larger cardboard boxes in
preparation for distribution to distributors.

Aspirin
Finished aspirin tablets often have a
line "scored" down the center so
that the tablet can be broken into
two parts with ease.

Quality Control
Maintaining a high degree of quality control
is extremely important in the pharmaceutical
manufacturing industry, as well as required
by the Food and Drug Administration
(FDA). All machinery is sterilized before
beginning the production process to ensure
that the product is not contaminated or
diluted in any way. In addition, operators
assist in maintaining an accurate and even
dosage amount throughout the production
process by performing periodic checks,
keeping meticulous batch records, and
administering necessary tests. Tablet thickness and weight are also controlled.
Once the tablets have been produced, they
undergo several quality tests, such as tablet
hardness and friability tests. To ensure that
the tablets won't chip or break under normal
conditions, they are tested for hardness in a
machine such as the Schleuniger (or
Heberlein) Tablet Hardness Tester. They are
also tested for friability, which is the ability
of the tablet to withstand the rigors of packaging and shipping. A machine called a
Roche Friabilator is used to perform this test.
During the test, tablets are tumbled and
exposed to repeated shocks.

Another test is the tablet disintegration test.
To ensure that the tablets will dissolve at the
desirable rate, a sample from the batch is
placed in a tablet disintegration tester such as
the Vanderkamp Tester. This apparatus consists of six plastic tubes open at the top and
bottom. The bottoms of the tubes are covered
with a mesh screen. The tubes are filled with

tablets and immersed in water at 37 degrees
Fahrenheit (2.77 degrees Celsius) and
retracted for a specified length of time and
speed to determine if the tablets dissolve as
designed.

Where To Learn More
Books
HIJSA'S Pharmaceutical Dispensing, 6th
edition, Mack Publishing Company, 1966.

History of Pharmacy, 4th edition, The
American Institute of History of Pharmacy,
1986.
An Introduction to Pharmaceutical Formulation, Pergamon Press, 1965.

Mann, Charles C. The Aspirin Wars: Money,
Medicine & One Hundred Years of Rampant
Competition. Alfred A. Knopf, Inc. 1991.
Remington's Pharmaceutical Sciences, 17th
edition, Mack Publishing, 1985.

Periodicals
Draper, Roger. "A Pharmaceutical Cinderella (History of Aspirin)," The New Leader.
January 13, 1992, p. 16.

Weissmann, Gerald. "Aspirin," Scientific
American. January, 1991, pp. 84-90.
Wickens, Barbara. "Aspirin: What's in
Name?," Maclean's. July 16, 1990, p. 40.

a

Greg Ling

23

Automobile
The development of the
electric automobile will
owe more to innovative
solar and aeronautical
engineering and
advanced satellite and
radar technology than to
traditional automotive
design and construction.
The electric car will have
no engine, exhaust system,
transmission, muffler,
radiator, or spark plugs. It
will require neither tuneups nor gasoline.

Background

ups in the production process as faster workers overtook slower ones. In Detroit in 1913,

In 1908 Henry Ford began production of the
Model T automobile. Based on his original
Model A design first manufactured in 1903,
the Model T took five years to develop. Its
creation inaugurated what we know today as
the mass production assembly line. This revolutionary idea was based on the concept of
simply assembling interchangeable component parts. Prior to this time, coaches and
buggies had been hand-built in small numbers by specialized craftspeople who rarely
duplicated any particular unit. Ford's innovative design reduced the number of parts
needed as well as the number of skilled fitters who had always formed the bulk of the
assembly operation, giving Ford a tremendous advantage over his competition.

he solved this problem by introducing the
first moving assembly line, a conveyor that
moved the vehicle past a stationary assembler. By eliminating the need for workers to
move between stations, Ford cut the assembly task for each worker from 2.5 minutes to
just under 2 minutes; the moving assembly
conveyor could now pace the stationary
worker. The first conveyor line consisted of
metal strips to which the vehicle's wheels
were attached. The metal strips were
attached to a belt that rolled the length of the
factory and then, beneath the floor, returned
to the beginning area. This reduction in the
amount of human effort required to assemble
an automobile caught the attention of automobile assemblers throughout the world.
Ford's mass production drove the automobile industry for nearly five decades and was
eventually adopted by almost every other
industrial manufacturer. Although technological advancements have enabled many
improvements to modern day automobile
assembly operations, the basic concept of
stationary workers installing parts on a vehicle as it passes their work stations has not
changed drastically over the years.

Ford's first venture into automobile assembly
with the Model A involved setting up assembly stands on which the whole vehicle was
built, usually by a single assembler who fit an
entire section of the car together in one place.
This person performed the same activity over
and over at his stationary assembly stand. To
provide for more efficiency, Ford had parts
delivered as needed to each work station. In
this way each assembly fitter took about 8.5
hours to complete his assembly task. By the
time the Model T was being developed Ford
had decided to use multiple assembly stands
with assemblers moving from stand to stand,
each performing a specific function. This
process reduced the assembly time for each
fitter from 8.5 hours to a mere 2.5 minutes by
rendering each worker completely familiar
with a specific task.
Ford soon recognized that walking from
stand to stand wasted time and created jam-

24

Rsw Materials
Although the bulk of an automobile is virgin
steel, petroleum-based products (plastics and
vinyls) have come to represent an increasingly large percentage of automotive components. The light-weight materials derived
from petroleum have helped to lighten some
models by as much as thirty percent. As the
price of fossil fuels continues to rise, the
preference for lighter, more fuel efficient
vehicles will become more pronounced.

Automobile
Design
Introducing a new model of automobile generally takes three to five years from inception
to assembly. Ideas for new models are developed to respond to unmet pubic needs and
preferences. Trying to predict what the public will want to drive in five years is no small
feat, yet automobile companies have successfully designed automobiles that fit public
tastes. With the help of computer-aided
design equipment, designers develop basic
concept drawings that help them visualize
the proposed vehicle's appearance. Based on
this simulation, they then construct clay
models that can be studied by styling experts
familiar with what the public is likely to
accept. Aerodynamic engineers also review
the models, studying air-flow parameters and
doing feasibility studies on crash tests. Only
after all models have been reviewed and
accepted are tool designers permitted to
begin building the tools that will manufacture the component parts of the new model.

The M a n u f a c t u r i n g
Process
Components

The automobile assembly plant represents
only the final phase in the process of manufacturing an automobile, for it is here that
the components supplied by more than 4,000
outside suppliers, including company-owned
parts suppliers, are brought together for
assembly, usually by truck or railroad. Those
parts that will be used in the chassis are
delivered to one area, while those that will
comprise the body are unloaded at another.

1

Chassis

2

The typical car or truck is constructed
from the ground up (and out). The frame
forms the base on which the body rests and
from which all subsequent assembly components follow. The frame is placed on the
assembly line and clamped to the conveyer to
prevent shifting as it moves down the line.
From here the automobile frame moves to
component assembly areas where complete
front and rear suspensions, gas tanks, rear
axles and drive shafts, gear boxes, steering
box components, wheel drums, and braking
systems are sequentially installed.

3

An off-line operation at this stage of production mates the vehicle's engine with
its transmission. Workers use robotic arms
to install these heavy components inside the
engine compartment of the frame. After the
engine and transmission are installed, a

25

How Products Are Made, Volume 1

On automobile assembly lines,
much of the work is now done by
robots rather than humans. In the
first stages of automobile manufacture, robots weld the floor pan
pieces together and assist workers
in placing components such as the
suspension onto the chassis.

worker attaches the radiator, and another
bolts it into place. Because of the nature of
these heavy component parts, articulating
robots perform all of the lift and carry operations while assemblers using pneumatic
wrenches bolt component pieces in place.
Careful ergonomic studies of every assembly
task have provided assembly workers with
the safest and most efficient tools available.

Body
4 Generally, the floor pan is the largest
s body component to which a multitude of
panels and braces will subsequently be either
welded or bolted. As it moves down the
assembly line, held in place by clamping fixtures, the shell of the vehicle is built. First,
the left and right quarter panels are robotically disengaged from pre-staged shipping

26

containers and placed onto the floor pan,
where they are stabilized with positioning
fixtures and welded.
5 The front and rear door pillars, roof, and
Jbody side panels are assembled in the
same fashion. The shell of the automobile
assembled in this section of the process lends
itself to the use of robots because articulating
arms can easily introduce various component
braces and panels to the floor pan and perform a high number of weld operations in a
time frame and with a degree of accuracy no
human workers could ever approach. Robots
can pick and load 200-pound (90.8 kilograms) roof panels and place them precisely
in the proper weld position with tolerance
variations held to within .001 of an inch.
Moreover, robots can also tolerate the

Automobile

PAINT

BODY

smoke, weld flashes, and gases created during this phase of production.
As the body moves from the isolated
Vweld area of the assembly line, subsequent body components including fully
assembled doors, deck lids, hood panel,
fenders, trunk lid, and bumper reinforcements are installed. Although robots help
workers place these components onto the
body shell, the workers provide the proper fit
for most of the bolt-on functional parts using
pneumatically assisted tools.
Paint
7

Prior to painting, the body must

pass

7through a rigorous inspection process,

the body in white operation. The shell of the
vehicle passes through a brightly lit white
room where it is fully wiped down by visual
inspectors using cloths soaked in hi-light oil.
Under the lights, this oil allows inspectors to
see any defects in the sheet metal body panels. Dings, dents, and any other defects are
repaired right on the line by skilled body
repairmen. After the shell has been fully
inspected and repaired, the assembly conveyor carries it through a cleaning station
where it is immersed and cleaned of all residual oil, dirt, and contaminants.

As the shell exits the cleaning station it
8goes through a drying booth and then
through an undercoat dip-an electrostatically charged bath of undercoat paint (called
the E-coat) that covers every nook and
cranny of the body shell, both inside and out,
with primer. This coat acts as a substrate surface to which the top coat of colored paint
adheres.
After the E-coat bath, the shell is again
dried in a booth as it proceeds on to the
final paint operation. In most automobile
assembly plants today, vehicle bodies are
spray-painted by robots that have been programmed to apply the exact amounts of paint
to just the right areas for just the right length
of time. Considerable research and programming has gone into the dynamics of robotic
painting in order to ensure the fine "wet" finishes we have come to expect. Our robotic
painters have come a long way since Ford's
first Model Ts, which were painted by hand
with a brush.
9

The body is built up on a separate
assembly line from the chassis.
Robots once again perform most of
the welding on the various panels,
but human workers are necessary to
bolt the parts together. During welding, component pieces are held
securely in a jig while welding operations are performed. Once the
body shell is complete, it is attached
to an overhead conveyor for the
painting process. The multi-step
painfing process entails inspection,
cleaning, undercoat (electrostatically applied) dipping, drying, topcoat spraying, and baking.

Once the shell has been fully covered
V with a base coat of color paint and a
clear top coat, the conveyor transfers the
bodies through baking ovens where the paint
is cured at temperatures exceeding 275
degrees Fahrenheit (135 degrees Celsius).

1

27

How Products Are Made, Volume 1

The body and chassis assemblies
are mated near the end of the production process. Robotic arms lift
the body shell onto the chassis
frame, where human workers then
bolt the two together. After final
components are installed, the vehicle is driven off the assembly line to
a quality checkpoint.

After the shell leaves the paint area it is ready
for interior assembly.

Interior assembly
The painted shell proceeds through the
interior assembly area where workers
assemble all of the instrumentation and
wiring systems, dash panels, interior lights,
seats, door and trim panels, headliners,
radios, speakers, all glass except the automobile windshield, steering column and
wheel, body weatherstrips, vinyl tops, brake
and gas pedals, carpeting, and front and rear
bumper fascias.
Next, robots equipped with suction

12cups remove the windshield from a
shipping container, apply a bead of urethane
sealer to the perimeter of the glass, and then
place it into the body windshield frame.
Robots also pick seats and trim panels and
transport them to the vehicle for the ease and
efficiency of the assembly operator. After
passing through this section the shell is given
a water test to ensure the proper fit of door
panels, glass, and weatherstripping. It is now
ready to mate with the chassis.
Mate
The chassis assembly conveyor and
body shell conveyor meet at this

13the
28

stage of production. As the chassis passes
the body conveyor the shell is robotically
lifted from its conveyor fixtures and placed
onto the car frame. Assembly workers, some
at ground level and some in work pits
beneath the conveyor, bolt the car body to the
frame. Once the mating takes place the automobile proceeds down the line to receive
final trim components, battery, tires, antifreeze, and gasoline.

1 4 The vehicle can now be started. From
here it is driven to a checkpoint off the
line, where its engine is audited, its lights and
horn checked, its tires balanced, and its
charging system examined. Any defects discovered at this stage require that the car be
taken to a central repair area, usually located
near the end of the line. A crew of skilled
trouble-shooters at this stage analyze and
repair all problems. When the vehicle passes
final audit it is given a price label and driven
to a staging lot where it will await shipment
to its destination.

Quality Control
All of the components that go into the automobile are produced at other sites. This
means the thousands of component pieces
that comprise the car must be manufactured,

Automobile
tested, packaged, and shipped to the assembly plants, often on the same day they will be
used. This requires no small amount of planning. To accomplish it, most automobile
manufacturers require outside parts vendors
to subject their component parts to rigorous
testing and inspection audits similar to those
used by the assembly plants. In this way the
assembly plants can anticipate that the products arriving at their receiving docks are
Statistical Process Control (SPC) approved
and free from defects.
Once the component parts of the automobile
begin to be assembled at the automotive factory, production control specialists can follow
the progress of each embryonic automobile
by means of its Vehicle Identification Number
(VIN), assigned at the start of the production
line. In many of the more advanced assembly
plants a small radio frequency transponder is
attached to the chassis and floor pan. This
sending unit carries the VIN information and
monitors its progress along the assembly
process. Knowing what operations the vehicle has been through, where it is going, and
when it should arrive at the next assembly
station gives production management personnel the ability to electronically control the
manufacturing sequence. Throughout the
assembly process quality audit stations keep
track of vital information concerning the
integrity of various functional components of
the vehicle.
This idea comes from a change in quality
control ideology over the years. Formerly,
quality control was seen as a final inspection
process that sought to discover defects only
after the vehicle was built. In contrast, today
quality is seen as a process built right into the
design of the vehicle as well as the assembly
process. In this way assembly operators can
stop the conveyor if workers find a defect.
Corrections can then be made, or supplies
checked to determine whether an entire batch
of components is bad. Vehicle recalls are
costly and manufacturers do everything possible to ensure the integrity of their product
before it is shipped to the customer. After
the vehicle is assembled a validation process
is conducted at the end of the assembly line
to verify quality audits from the various
inspection points throughout the assembly
process. This final audit tests for properly
fitting panels; dynamics; squeaks and rattles;

functioning electrical components; and
engine, chassis, and wheel alignment. In
many assembly plants vehicles are periodically pulled from the audit line and given full
functional tests. All efforts today are put
forth to ensure that quality and reliability are
built into the assembled product.

The Future
The development of the electric automobile
will owe more to innovative solar and aeronautical engineering and advanced satellite
and radar technology than to traditional automotive design and construction. The electric
car has no engine, exhaust system, transmission, muffler, radiator, or spark plugs. It will
require neither tune-ups nor-truly revolutionary-gasoline. Instead, its power will
come from alternating current (AC) electric
motors with a brushless design capable of
spinning up to 20,000 revolutions/minute.
Batteries to power these motors will come
from high performance cells capable of generating more than 100 kilowatts of power.
And, unlike the lead-acid batteries of the past
and present, future batteries will be environmentally safe and recyclable. Integral to the
braking system of the vehicle will be a power
inverter that converts direct current electricity back into the battery pack system once the
accelerator is let off, thus acting as a generator to the battery system even as the car is
driven long into the future.
The growth of automobile use and the
increasing resistance to road building have
made our highway systems both congested
and obsolete. But new electronic vehicle
technologies that permit cars to navigate
around the congestion and even drive themselves may soon become possible. Turning
over the operation of our automobiles to
computers would mean they would gather
information from the roadway about congestion and find the fastest route to their
instructed destination, thus making better use
of limited highway space. The advent of the
electric car will come because of a rare convergence of circumstance and ability.
Growing intolerance for pollution combined
with extraordinary technological advancements will change the global transportation
paradigm that will carry us into the twentyfirst century.

29

How Products Are Made, Volume 1

Where To Learn More
Books

Abernathy, William. The Productivity
Dilemma: Roadblock to Innovation in the
Automobile Industry. Johns Hopkins
University Press, 1978.
Gear Design, Manufacturing & Inspection
Manual. Society of Manufacturing Engineers,
Inc., 1990.

Hounshell, David. From the American
System to Mass Production. Johns Hopkins
University Press, 1984.
Lamming, Richard. Beyond Partnership:
Strategies for Innovation & Lean Supply.
Prentice Hall, 1993.
Making the Car. Motor Vehicle Manufacturers Association of the United States, 1987.

Mortimer, J., ed. Advanced Manufacturing in
the Automotive Industry. Springer-Verlag
New York, Inc., 1987.
Mortimer, John. Advanced Manufacturing in
the Automotive Industry. Air Science Co.,
1986.

Nevins, Allen and Frank E. Hill. Ford: The
Times, The Man, The Company. Scribners,
1954.

Seiffert, Ulrich. Automobile Technology of
the Future. Society of Automotive Engineers, Inc., 1991.
Sloan, Alfred P. My Years with General
Motors. Doubleday, 1963.

Periodicals
"The Secrets of the Production Line," The
Economist. October 17, 1992, p. S5.
- Rick Bockmiller

30

Automobile Windshield
Background
Glass is a versatile material with hundreds of
applications, including windshields. Glass
has a long history and was first made more
than 7,000 years ago in Egypt, as early as
3,000 B.C. Glass is found in a natural state as
a by-product of volcanic activity. Today,
glass is manufactured from a variety of
ceramic materials (main components are
oxides). The main product categories are flat
or float glass, container glass, cut glass,
fiberglass, optical glass, and specialty glass.
Automotive windshields fall into the flat
glass category.
There are more than 80 companies worldwide that produce automotive glass, including windshields. Major producers in the
United States include PPG, Guardian
Industries Corp., and Libby-Owens Ford.
According to the Department of Commerce,
25 percent of flat glass production is consumed by the automotive industry (including
windows) at a total value of approximately
$483 million. In Japan, 30 percent of flat
glass goes to the automotive industry, valued
at around $190 billion in 1989. Major
Japanese flat glass manufacturers include
Asahi Glass Co., Central Glass Co., and
Nippon Sheet Glass Co. Little growth is
expected for the flat glass industry overall in
both countries. Germany has a more positive
outlook, with high growth rates expected
from the automotive industry.
Glass windshields first appeared around 1905
with the invention of safety glass-glass tempered (tempering is a heat treatment) to make
it especially hard and resistant to shattering.
This type of windshield was popular well into
the middle of the century, but it was eventu-

ally replaced by windshields made of laminated glass-a multilayer unit consisting of a
plastic layer surrounded by two sheets of
glass. In many countries, including the U.S.,
auto windshields are required by law to be
made of laminated glass. Laminated glass can
bend slightly under impact and is less likely
to shatter than normal safety glass. This quality reduces the risk of injury to the automobile's passengers.

Rawv Materials
Glass is composed of numerous oxides that
fuse and react together upon heating to form
a glass. These include silica (SiO2), sodium
oxide (Na2O), and calcium oxide (CaO).
Raw materials from which these materials
are derived are sand, soda ash (Na2CO3), and
limestone (CaCO3). Soda ash acts as a flux;
in other words, it lowers the melting point of
the batch composition. Lime is added to the
batch in order to improve the hardness and
chemical durability of the glass. Glass used
for windshields also usually contains several
other oxides: potassium oxide (K20 derived
from potash), magnesium oxide (MgO), and
aluminum oxide (AI203 derived from
feldspar).

A bi-layer windshield has
been developed that
consists of one sheet of
glass joined to a single
sheet of polyurethane.
Unique features of this

windshield include
ultraviolet resistance, selfhealing of scratches,
weight savings, more
complex shapes,
increased safety due to
retention of glass splinters,
and anti-fog capability.

The Manufacturing
Process
The raw materials are carefully weighed
I in the appropriate amounts and mixed
together with a small amount of water to prevent segregation of the ingredients. Cullet
(broken waste glass) is also used as a raw
material.

2 Once the batch is made, it is fed to a

2large tank for melting using the float

31

How Products Are Made, Volume 1

The glass for automible windshields
is made using the float glass
process. In this method, the raw
material is heated to a molten state
and fed onto a bath of molten tin.
The glass literally floats on top of the
fin; because the fin is perfectly flat,
the glass also becomes flat. From
the float chamber, the glass passes
on rollers through an oven (the
"annealing lehr"). After exiting the
lehr and cooling to room temperature, the glass is cut to the proper
shape and tempered.

glass process. First, the batch is heated to a
molten state, and then it is fed into a tank
called the float chamber, which holds a bath
of molten tin. The float chamber is very
large-from about 13 feet to 26.25 feet (4 to
8 meters wide and up to almost 197 feet (60
meters) long; at its entrance, the temperature
of the tin is about 1,835 degrees Fahrenheit
(1,000 degrees Celsius), while at the exit the
tin's temperature is slightly cooler-1,115
degrees Fahrenheit (600 degrees Celsius). In
the float chamber, the glass doesn't submerge into the tin but floats on top of it, moving through the tank as though on a conveyor
belt. The perfectly flat surface of the tin
causes the molten glass also to become flat,
while the high temperatures clean the glass
of impurities. The decreased temperature at
the exit of the chamber allows the glass to
harden enough to move into the next chamber, a furnace.

3 After the glass exits from the float cham-

3ber, rollers pick it up and feed it into a
special furnace c