Industrial Design

Materials and Manufacturing Guide

Industrial Design

Materials and Manufacturing GuideSecond Edition

Jim Lesko

Th is book is printed on acid-free paper.

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Library of Congress Cataloging-in-Publication Data:

Lesko, Jim.

Industrial design : materials and manufacturing guide / Jim Lesko. -- 2nd ed.

p. cm.

ISBN 978-0-470-05538-0 (cloth)

1. Design, Industrial. 2. Manufacturing processes. 3. Materials. I. Title.

TS171.4.L47 2007

745.2--dc22

2007017878

Printed in the United States of America

10 9 8 7 6 5 4 3

Th e idea for Industrial Design: Materials and Manufacturing began

about 1975 when Professor Born asked me to teach the subject at the

University of Cincinnati. I had the good fortune of having an excep-

tional group of students, including John Bucholtz, Mike Gallagher,

and Sam Lucente, whose enthusiastic response to my organizational

structure of the subject convinced me that a simple visual text was

necessary to get the interest of students trained in art. Many of the

existing texts and journals on the subject do a great job for those

students whose interest is in the amount of detail presented, with an

emphasis on quantifi able arguments and explanations. I learned from

these texts and journals, and they remain a necessary part of the learning

process for design students. But impatient industrial design students

who want to understand concepts, need an overview: read a summary,

see examples, and go on to the next topic in some logical manner.

Design students seem to sense that they will not have the prime

responsibility in selecting materials or in specifying the manufacturing

process in the design of products, but intuitively they understand that

they must be conversant on the subject and that materials and manufac-

turing methods will be a determinant in the design process.

Th ere is a growing excitement and exploration in materials and manu-

facturing in the design community because of the recent explosion of

ideas engendered by the advances in aerospace research. Mutant Mate-

rials in Contemporary Design, organized by Paola Antonelli, Associate

Curator at the Museum of Modern Art, and the Material Connex-

tion conceived by George Beylerian, are outstanding examples of this

renewed energy focused on this essential aspect of design. Within the

Industrial Designers Society of America (ISDA), Dave Kusuma was

instrumental in organizing the Materials and Processes Group and

in bringing the Society of Plastics Engineers and IDSA together for

meetings and conferences.

For years I hoped that someone else would produce such a text. After

teaching the subject for more than 15 years, I realized that no designers

were presumptuous enough to try to develop a text for industrial design

students, so I began to collect my notes. While at Pratt Institute, I

received a Mellon grant to produce a structure for the information.

During this fi rst phase, several students assisted me, including Deborah

Zweiker and Eileen Lee. Without the advantage of a computer, we

labored most of the summer laying out the organizational charts and

making the many lists of information by hand. While I was at Carnegie

Mellon University, Professor Alex Bally, head of the Industrial Design

Department, and Professors Greenberg and Paxton of the Materials

Science Department, reviewed my preliminary concepts and provided

many suggestions and encouragement.

While I am responsible for the use I made of the information that I

received, it was impossible to complete this undertaking on my own. In

fact, this book is the work of many people: the many students who sat

through the lectures and provided feedback, and the manufacturers and

suppliers who graciously spent valuable time and had endless patience

with me trying to ensure that I received the information I needed.

Th ere are many who stand out, who went way beyond that call of duty.

Acknowledgments

Th is book would not have been completed without Ed Eslami, who on a

number of occasions, rescued me from panic, and whose calm assurance,

clever drawings, and graphic layout brought the book out of the morass

that it was in at times. I am grateful for his help and his exceptional

talent. Many students helped with research and drawings, including

Kyang Haub Kang, Tong Jin Kim, and Minghsiu Yang.

Don Blair of Talbot Associates was with me almost from the beginning,

and later Jeff Talbot joined him to provide hours of discussion, stacks

of brochures, and many sources of information on casting. Christine

Lagosz and her associates at Trumpf, Inc., Bill Guftner of US Amada

Ltd., Steven Friedman of Peterson, Walter Ackerman of Risdon, John

Matthews of ESAB Welding & Cutting Products, and Bob Cook

of Bridgeport Machines were just some of the great individuals who

provided all the information I requested on metal forming and cutting.

Dave Kusuma and Michael A. D’Onofrio, Jr. and their associates of at

the Bayer Corporation; Jack Avery, George Whitney, and their associ-

ates at GE Plastics; Steve Ham; Dave Beck of Pappago; Victor Gerdes

and his associates at the Stevens Institute; Bill Fallon of Sikorsky; and

George Cekis of Solvay provided important parts in building the plas-

tics section. I am thankful that the publishers of Injecting Molding

Handbook by Rosato & Rosato and Plastics Engineering Handbook

by the Society of the Plastics Industry allowed me to reproduce many

drawings.

For this second edition, I am extremely fortunate that Edward Eslami

again was my guiding light and helped make new ideas happen. Mike

Gallagher, a former student and now a colleague, provided inspiration

and enthusiasm once again by inviting me to Crown Equipment Corp.

for a tour of its design and manufacturing facilities. Jim Kraimer, Jeff ery

Mauch, and Doug Rinderle and their many associates led this tour and

ably answered my many questions. Manuel Saez and Lachezar

Tsvslotinv, also former students, described their work at HumanScale

and provided images of their current projects. Peter Bressler and his

associates and Dave Kaiser and his associates kindly responded to my

call for images. David Stricker of Production Resources and Robert

Hagemeister of Parametric Design Associates provided important

current information.

Many of the casting descriptions were taken from the 2006 Casting

Source Directory, published by Engineered Casting Solutions, with the

kind permission of Publisher and Editor Alfred T. Spada. John Chion of

Talbot Associates reviewed my draft of the casting section and provided

guidance and suggestions. Obviously, many others plowed through my

drafts and patiently corrected my errors and contributed their expertise;

their thoughts are somewhere inside these pages.

I am grateful that an endless number of students are always ready to

help. Zackary Smith helped with the graphic layout, and Soo Hwan

Cho and Wooyeon Cho provided many illustrations. When I arrived

at Dongseo University in Korea Sang-Hwan An, Sang-Wook Eom,

Ji Young Kang, Hyo-Jin Kim, and Joon-Goo Lee helped with illustra-

tions and drawings. I would also like to thank the many companies

at the INTERMOLD KOREA 2007 Exhibition for the stacks of

brochures and endless pictures. Th e enthusiasm and willingness to help

on the part of nearly everyone whom I contacted kept me going. I am

grateful to all.

I would also like to thank the many engineers and designers who helped

and encouraged me. Th is book is dedicated to them; to the memory of

Donald R. Dohner, the father of American industrial design education;

and to Peter Megert, who has provided inspiration and endless wisdom

for so many young designers.

Contents

Acknowledgments v

1.0 Introduction 3

2.0 Overview 5

3.0 Metals 9

3.1 Properties of Metals 10

3.2 Ferrous Metals 12

3.3 Powdered Metallurgy 17

3.4 Nonferrous Metals 18

4.0 Metal Forming 25

4.1 Liquid State Forming 26

4.1.1 Expendable Molds/Waste Molds 31

4.1.2 Nonexpendable Molds 37

4.2 Plastic State Forming 44

4.2.1 Rolling 46

4.2.2 Forging and Swaging 47

4.2.3 Drawn Wire 50

4.2.4 Extrusions 48

4.3 Solid State Forming 50

4.3.1 Simple Bending 51

4.3.2 Compound Bending 55

4.3.3 Form and Cut 58

5.0 Metal Cutting 61

5.1 Sheet Punching and Shearing 62

5.2 Chip Forming Cutting 66

5.3 Nonchip Forming Cutting 71

5.4 Flame/Th ermal Cutting 74

6.0 Metal Joining 79

6.1 Soldering 81

6.2 Brazing/Welding 82

6.2.1 Gas Welding 84

6.2.2 Arc Welding 85

6.2.3 Resistance Welding 90

6.2.4 Solid State Welding 92

6.2.5 High Technology Welding 93

6.3 Adhesives 94

6.4 Mechanical Fasteners 97

7.0 Appearance Finishing and Coatings 102

7.1 Formed Textures/Molded In 103

7.2 Cut Patterns and Abrasive Finishing 106

7.3 Coatings 113

8.0 Plastics 118

8.1 Properties of Molded Plastics 126

8.2 Th ermosets 134

8.3 Th ermoplastics 139

9.0 Plastic Forming Processes 161

9.1 Liquid State Forming 165

9.2 Plastic State Forming 181

9.3 Solid State Forming 187

10.0 Machining Plastics 188

11.0 Joining Plastics 190

11.1 Chemical Bonds 191

11.2 Welding Plastics 192

11.3 Mechanical Fastening 195

12.0 Finishing Plastics 198

12.1 Formed 199

12.2 Paintings/Coatings 200

13.0 Rubbers and Elastomers 204

13.1 Th ermoset Rubbers 205

13.2 Th ermoplastic Elastomers 211

14.0 Natural Engineering Materials 214

14.1 Engineering Ceramics 216

14.2 Glass 219

14.3 Manufactured Carbon 226

14.4 Refractory Hard Metals 227

15.0 Composites 228

15.1 Metal-Matrix Composites 229

15.2 Plastic-Matrix Composites 230

15.3 Advanced Composite Materials 231

16.0 Rapid Prototyping 232

Index 235

02_055380 ftoc.indd 102_055380 ftoc.indd 1 10/31/07 12:19:33 PM10/31/07 12:19:33 PM

Overview Chart

Metals

Forming Cutting Joining Finishing

Plastics

Rubber &Elastomers

EngineeringMaterials

NaturalMaterials*

Ferrous

Nonferrous

Thermoset

Thermoplastics

Thermoset

Thermoplastics

ManufacturedCarbon

Glass

EngineeredCeramics

RefractoryHard Metals

Fibers

WoodProducts

LiquidState

PlasticState

SolidState

SheetCutting

ChipForming

NonchipForming

Flame/Laser

Solder/Braze

Weld Adhesive Mechan-ical

Formed Abrasive/Cut

Coatings

All Processes Most Processes Some Processes No Processes

ManufacturingMethods

*not within the scope of engineering materials, therefore not covered in this book

fi gure 1-1. materials and manufacturing

3

Need for Materials and ManufacturingTh e industrial designer, whether on a design team or

acting alone, is responsible for the appearance and form

of a product. If the form of a product is to some degree

the result of how it was manufactured, it follows that the

designer must have a good understanding of all manufac-

turing processes available, in order to have confi dence that

the proposed manufacturing process is the most economical

and appropriate. If a designer is unaware of certain avail-

able processes creative potential is limited. It would be like

a composer writing a symphony totally unaware of the color

and full range and capability of some instruments.

Design EducationIndustrial design students should have an understanding

of materials and manufacturing—ideally in the sophomore

year. Th is is important because as projects are assigned,

students need to visualize and develop forms that ultimately

will be manufactured (even if theoretically). Without a

comprehensive knowledge base of materials and manufac-

turing possibilities, students can only fantasize and fl ounder

along, limited by ignorance of the subject and oblivious to

the variety of possibilities available. Conversely, with a good

knowledge base students can propose an array of possible

design solutions and have some confi dence that they can be

manufactured.

Th is guide is specifi cally designed as a two-semester class-

room guide for industrial design students. It should also

be useful for other professionals who require an introduc-

tory understanding of this information. It is not, and is

not intended to be, an alternative to the standard engi-

neering texts on the subject. It would be wise for designers

to acquire such a text at some point. Industrial Design:

Materials and Manufacturing Guide is intended to give an

overview in simple words and visual images and to serve

as a guide and introduction to this rather complex fi eld, a

necessary part of industrial design education.

An excellent example of the need for a full understanding

of materials and manufacturing is the Crown TSP 6000,

especially the cab shown on the cover. While consumer

products are challenging from many perspectives, including

marketing, industrial products like the TSP require excep-

tional demands for excellence in design and engineering,

such as extreme attention to ergonomics and to cost benefi t

analysis, as well as the traditional design concerns. Th e

TSP is a perfect example of where the designers clearly

demonstrate an understanding of the full range of materials

and processes available. Th is is particularly exemplifi ed in

the cab for the TSP. Th e designers explained that for every

single part they considered all the possible materials and

related processes available. Th e best option for each part

was selected through a rigorous analysis of the cost–benefi t

analysis charts that were developed as a normal operating

procedure of the Crown design program. Th e result is a

spectacular and aesthetically successful use of materials

fulfi lling every demand, economically manufactured to

meet the production requirements, but more important

to anticipate and fulfi ll the rather extreme operational

demands of users.

fi gure 1-2. Crown TSP 6000 Turret

Stockpicker (courtesy Crown Equipment

Corporation)

Introduction1

CAIDmaterial selectionprocess selection

CAD/CAMmaterial selectiontoolingcomponent selectionvendorsassemblyshipping/packagingrepair/maintenance

researchsketchesmock-upsfinish color/texture

ergonomicsbreadboard studiesmanufacturabilitysafety strength of materials

© Jim Lesko and Edward Eslami

Personal andIndividualConsiderations

ObjectiveConsiderations

styleegomarketing/advertising

ergonomicsengineeringmarketinginvestment/profitnational/international salesshippin /distributionCPSA/UL/FDA

ProductDefined

ProductIdentification/Design TeamFormed

ConceptDevelopment

ConceptPresentation

ProductDevelopment

ProductPresentation

Product Design Sequence

Aesthetics Analysis Synthesis

fi gure 2-1. product design sequence

5

Industrial Design Materials and Manufacturing

is an overview of the key processes and salient

related supporting information intended for

(student) industrial designers. It is limited to

engineering materials (excluding natural mate-

rials). Th e goal is to distill the key information

on the subject, organize it, and present it as

simply as possible. One visual representation of

full design process is shown on the facing page.

Th is guide is limited to a discussion of some of

the objective considerations printed in green

text.

Form Is the Resolution of FunctionDesign is in essence a search for form. “Form follows func-

tion” has been on the banner of designers since the Bauhaus.

However, this statement suggests that function leads and

form follows, relegating form to a subordinate position.

Restated, it might read “Form is the resolution of function,”

where function has two major components: (1) performance

specifi cation demands, including all user-friendly aspects,

and (2) cost and manufacturability. Th e former refers to

ergonomics—aspects concerned with the abilities and

limitations of the product’s users. Th e latter refers to the

physical aspects of the product, including material selection

and manufacturability. “Form is the resolution of function”

suggests that form is dynamic and interactive, whereas

“Form follows function” implies that form is passive,

following behind function as the primary determining

factor in a design. If the revised “Form is the resolution of

function,” is used, then manufacturability is understood

in its rightful place as an equal determinant in the design

process.

Form is realized or made visible in a material or a combina-

tion of materials, which are shaped by tools. In creating a

form, the designer is by default selecting a manufacturing

process. Normally the designer creates models to demon-

strate a concept in substitute materials—not the actual

material—and by so doing is removed from a real under-

standing of the way the manufacturing process will impact

the material and form. If product concepts are created on

paper using pencil or on a computer, there is a danger that

the designer is not only removed from an understanding of

actual manufacturing ramifi cations, but is also another step

removed from dimensional reality and material behavior

altogether. It takes a real-world understanding of materials

and manufacturing methods to create successful products.

Th is cannot be accomplished alone in a studio: It requires

teamwork with materials and manufacturing engineering

development and support. Th e Clinto, by Manuel Saez

and his Humanscale team, is an excellent example of a

successful product whose form is not only a celebration of

materials and manufacturing, but is the essence of func-

tion for human need. Each element of this design was

chosen to meet all factors involved. Th e forms seem simple

but perform complex functions under the severe demands

of cost restraints. Th e materials and production process

selected and the form that evolved were developed inter-

dependently, in an optimization process in which the best

possible solution was determined after deliberation and

exhaustive search and testing.

Th e violin is the absolute epitome and essence of a product

in terms of materials and manufacturing. No other human

invention is so perfect in its resolution. If made by Stradi-

varius, nothing can match it in its ability to reach the

sublime. Of course, it takes a master to play it properly.

Th ere is no use playing a Stradivarius unless the music is

written by a master such as Bach or Beethoven.

fi gure 2-2. Clinto (courtesy Humanscale

Design Studio)

Overview2

6

2.0 Manufacturing Methods Manufacturing Methods

Materials and Manufacturing MethodsTh is guide is an overview of the key materials, processes,

and salient related supporting information intended for

(student) industrial designers. It is limited to engineering

materials (excluding natural materials like wood, stone, etc.).

Th e goal is to distill the key information on the subject,

organize it, and present it as simply as possible. Existing

engineering-oriented texts on this subject attempt to be

inclusive, with extensive technical information geared to

engineering.

Manufacturing Methods

FinishingJoining

Weld

Solder/Braze

Adhesive

Mechanical

Forming

LiquidState

PlasticState

SolidState

Formed

Abrasive/Cut

Coatings

Cutting

SheetCutting

ChipForming

NonchipForming

Flame/Laser

Th is guide summarizes the materials and processes impor-

tant to industrial design. Th is information is presented

simply and graphically. It does not attempt to present

all available materials and manufacturing processes; it is

intended to be a designer’s guide to materials and manu-

facturing. Th e methodology used may help readers organize

additional information on these subjects.

fi gure 2-3. manufacturing methods chart

7

Materials 2.0 Manufacturing Methods

Materials

Rubber/Elastomers

NaturalEngineering

Materials

EngineeringCeramics

Glass

ManufacturedCarbon

RefractoryHard Metals

Ferrous

Nonferrous

Thermoset

Thermoplastic

Thermoset

Thermoplastic

Metals Plastics

fi gure 2-4. materials chart

8

9

Metals

Ferrous NonferrousPowderedMetallurgy

totally new alloys that were not previously avail-

able. Powdered metals are now being alloyed with

nonmetals, including ceramics, rubber, and plastics,

thereby creating new categories of product design.

Pure metals are composed of atoms of the same

type. Metal alloys are composed of two or more

chemical elements, of which at least one is a metal.

Th is blending of elements gives alloys their greater

mechanical properties. Th e majority of metals used

in engineering applications are alloys. Metals are

generally divided into ferrous and nonferrous. Each

metal alloy has specifi c mechanical and physical

properties that will make it a good fi t for a specifi c

application. Fairly recently, metals have become

available in a powdered form. Th is has expanded

the opportunities, making it possible to provide

opposite page: fi gure 3-1. Unisphere, Flushing Meadows Park, New York

fi gure 3-2. metals chart

Metals3

10

3.1 Properties of Metals Mechanical Properties

3.1 Properties of Metals

Brief Defi nitions of Mechanical PropertiesMetals exhibit elastic as well as plastic behavior, both of

which are necessary for the forming process. Th ese unique

behaviors allow most metals to bend and draw during the

shaping process.

Elasticity describes the recovery of a material back to its

original shape and size after being deformed, when a stress

is removed. Th is is called elastic behavior because the defor-

mation the material experienced is not permanent. Th e

stress versus strain curve graphically records how a material

stretches and then fractures. A good example of pure elastic

behavior is demonstrated by a rubber band. When stretched

it deforms and is elongated, the cross-section is reduced.

When the force is removed, the rubber band returns to its

original shape. If the force exceeds its elastic limit then the

rubber band snaps or ruptures. But there is no change in the

cross-section of the rubber band, there is no plastic defor-

mation.

Plastic behavior is quite diff erent from elastic behavior. A

good example of pure plastic deformation can be demon-

strated by gum. When gum is stretched, it deforms and the

cross-section changes; it thins out. Th is is called necking.

When the force is relaxed, the gum does not return to its

original shape. Th is is called plastic deformation.

Tensile strength is the maximum tensile (pulling apart) load

that a material can withstand prior to fracture.

Yield strength is the workable engineering strength of a

metal to stay within its elastic limit. Exceeding a metal's

yield strength puts the metal into permanent deformation.

Percent elongation is the increase in length over the original

length.

Strain is the change a material undergoes during elonga-

tion or contraction. It is given as a measure of deformation

under load.

Compression is a measure of the extent to which a mate-

rial deforms under a compressive load prior to rupture.

Warm bubble gum is a good example. No matter how

hard you squeeze it or step on it, it fl attens but does not

rupture, which is why building foundations are not made

of bubble gum. A foundation requires a strong material

with outstanding compressive strength, such as concrete.

Concrete has good compressive strength, but under a very

heavy load, it will crack. It is brittle.

strain

stre

ss

yield strength

ultimate tensilestrength

ElasticBehavior

PlasticBehavior

uniformelongation

necking

fracture

fi gure 3-5. stress versus strain curve

fi gure 3-3. elastic behavior

fi gure 3-4. plastic behavior

Creep is a slow deformation of stresses below the normal

yield strength. Zinc exhibits poor resistance to creep at

elevated temperatures (above 200˚F).

Brief Defi nitions of Physical PropertiesPhysical properties are inherent aspects of a material that

are generally not easily altered. Physical properties generally

remain intact, whereas mechanical properties are changed

by work hardening and/or through heat treatment.

Opacity/transparency is the ability to transmit light.

Color is the inherent refl ected wavelength.

Density is weight per unit volume (specifi c gravity).

Electrical conductivity is the ease with which a material

conducts a current.

Th ermal conductivity is the ease with which heat fl ows

within and through a material.

Th ermal expansion is expressed in units of 1/°F or 1/°C.

Generally, the coeffi cient of thermal expansion is inversely

proportional to the melting point of a material: higher-melt

temperature materials have less expansion. Steel is a signifi -

cant exception.

Magnetic/nonmagnetic/ferromagnetism is the alignment of

iron, nickel, and cobalt atoms into domains.

Melting point is the energy required to separate a material’s

atoms, changing its state from solid to liquid.

Corrosion resistance is the ability to resist surface deteriora-

tion caused primarily by oxygen, chemicals, or other agents.

(Degradation in plastics can also be caused by ultraviolet

light, moisture, and other environmental factors.)

11

Mechanical/Physical Properties 3.1 Properties of Metals

fi gure 3-6. indentation for hardness test

fi gure 3-7. optical inspection of glass products

using the physical properties of color, transpar-

ency, and density.

Hardness is the ability of a material to withstand penetration

and scratching. Hardness and brittleness are related. Warm

bubble gum is not hard: a hard sphere dropped on it will

penetrate into the gum. But a hard sphere will not penetrate

the surface of glass. If the sphere hits the surface with great

force, it will shatter the glass.

Hardness is important in manufacturing. For example, when

a sword is made (which is forged), it is important to have

hardness in the steel blade in order to get a sharp edge. But

a sword must also bend. If the sword is hard and brittle (in

a hardened state) it will shatter if it is bent—an undesir-

able characteristic. Th e sword must also be fl exible. Th rough

clever heat treatment and manipulation of these properties,

it is possible to have hardness and fl exibility—the precise

but contradictory mechanical properties required for a great

sword.

Brittleness is the opposite of ductility. If bubble gum is

frozen, it becomes brittle and can break your teeth or shatter

if you hit it with a hammer. Glass is a classic example of a

brittle material.

Ductility is the ability of a material to withstand plastic

deformation without rupture. Again, bubble gum is a

good example. As it is chewed it does not break up but is

molded by the teeth into a new shape. Ductility is impor-

tant in discussing bendability and drawability in solid-state

forming.

Bending is characterized by the outside fi bers of a beam in

tension and the inside fi bers in compression.

Torsion is the application of torque to a member to cause

it to twist about its longitudinal axis. A crankshaft must be

made of metal with superior torsional strength or it will fail

under the stress it is subjected to in an engine.

Shear strength is the maximum load a material can with-

stand without rupture when subjected to a shearing action.

Bubble gum has very little shear strength; it will shear very

easily.

12

3.2 Ferrous Metals Overview

Ferrous Metals

Iron PowderedMetallurgy (Fe PM)Iron Steel

CarbonSteel

Wrought

Wrought

Cast Cast

CastIron

AlloySteel

StainlessSteel

ToolSteel

Steels forStrength

High-StrengthLow Alloy

Iron BasedSuper Alloys

Fe PowderMetals

Gray

Ductile

White

Compacted Graphite

Malleable

High Alloy

A0.25% C0.70% Mn

B0.30% C1.00% Mn

C0.25% C1.25% Mn

Chemical Composition

Mechanical Properties

Method of Deoxidation:Killed, Semi- killed, Capped, Rimmed

Thermal Treatment

Through Hardenable

Carburizing Grades

Specialty Nitriding

Austenitic

Ferritic

Martensitic

Precipitation Hardening

Similar corresponding Grades

Magnetic

Type W

Water Hardening

Type S

Shock Resisting

Type O, A, D

Cold Working

Type H

Hot Working

High Speed

T: TungstenM: Molybdenum

Type L

Low Alloy

Type F

Carbon/Tungsten

Type P

Mold Steels

Improved Formability

Structural Forms

45K–50K psi

High-Yield Strength Quenched and Tempered

Ultrahigh Strength

Medium Carbon Alloy

Modified Tool Steel

Maraging Steel

18% Nickel

601–604

MartensiticLow Alloy

610–613

Martensitic Secondary Hardening

614–619

Martensitic Chromium

630–635 Semi-Austenitic, Martensitic, Precip. Hardened Stainless Steel

650–653

Austenitic Hot/Cold Worked

660–665

Austenitic Super Alloys

MIM

(Metal Injection Molding)

High-Density PM

(often withNi, Mo, Fe)

fi gure 3-8. ferrous metals chart

1313

Heat Treatment/Hardening 3.2 Ferrous Metals

Heat Treatment

Annealing: soft structure with good ductility/formability.

Normalizing: uniform structure with good ductility/grain refi ne-

ment.

Sphereoldize annealing: softest structure, with maximum ductility

and improved machinability.

Stress relieving: reduces internal stresses and minimizes subse-

quent distortion, leaving the original structure unchanged.

Th rough Hardening

Quench and tempering: improves toughness, tensile, and compres-

sive strength. It also increases hardness and provides improved

wear resistance.

Austempering: similar to quench-and-temper, with minimum

distortion after heat treating. No temper cycle is usually required.

Martempering: similar to quench-and-temper, providing high

strength with minimum distortion.

Precipitation hardening: low temperature process with no

quench required and provides the least distortion of all hardening

processes.

Case Hardening

Gas carburizing: improves fatigue strength, wear resistance,

torsional strength, and bend strength.

Carbonitriding: identical to carburizing except that the case is

shallower and harder on the surface, with less distortion.

Gas nitriding: provides the best wear resistance and anti-galling

surface of all hardening processes. It improves fatigue and

torsional strength, with less distortion than all other case-hard-

ening processes.

Soft nitriding: identical to nitriding but can be applied to a wider

variety of steels, providing slightly softer surfaces.

Induction hardening: provides the deepest case of all case-hard-

ening processes, with the greatest load-carrying capacity. It also

improves wear resistance, fatigue, and torsional strength.

3.2 Ferrous Metals

When ferrous metals solidify from a molten state, crys-

tals are formed and their atoms are arranged into orderly

confi gurations that are face-centered cubic (FCC), body-

centered cubic (BCC), or body-centered tetragonal (BCT).

Th ese crystal arrangements are determined by the rate at

which the metal cools from a liquid state to the solid state

(called a phase transformation) and establishes whether the

metal will be brittle and stressed or soft and ductile. How

metals behave during manufacturing and how they perform

in service depends on their chemical composition, atomic

structure, and heat treatment history.

Post-heat treatment of steel is one of the most commonly

used methods of enhancing mechanical properties. Th e

processes available are described as through or case hard-

ening. To harden a metal after heating, it is necessary to

quench, or cool, it quickly. Besides enhancing the hardness

of a metal with a quick chill, generally considered a positive

change, quenching aff ects other mechanical properties, such

as increased brittleness—generally considered a negative

change. When a metal freezes quickly it is said to be stressed

(as you would be if you stepped off a plane going from

Florida to New York in the middle of winter). On the other

hand, if the change occurs slowly at room temperature, the

metal is said to be stressed-relieved (also called normalized,

tempered, or annealed).

HardeningHardness is an important mechanical property for certain

applications, such as hardness to resist cutting of a steel

chain. But steel becomes brittle as it is hardened. For

example, if not properly heat-treated, hardened steel chain

may snap while lifting a load. So heat treatment must be

done carefully, with a full understanding of the desired

results. In case hardening, only the surface is hardened while

the interior remains unaff ected. Th is is important if the part

has to resist wear but dampen vibration, or bend easily and

maintain a sharp edge—as in a sword.

fi gure 3-9. austenite or gamma phase at high

temperature FCC—Face-Centered Cubic lattice

in iron

fi gure 3-10. Ferrite—BCC—Body-Centered

Cubic lattice formed by slowly cooled iron at

room temperature. Wide interatomic spacing

makes this structure soft and ductile.

fi gure 3-11. martensite body-centered tetrag-

onal lattice is formed when iron is quenched,

causing it to be stressed and distorted.

14

3.2 Ferrous Metals Iron

IronIrons are available as cast or wrought. All cast irons contains

at least 2 percent carbon and from 1–3 percent silicon. Th e

six kinds of iron are:

Gray iron is used in automotive engine blocks, gears,

fl ywheels, disc brakes and drums, and large machine bases.

A supersaturated solution of carbon in an iron matrix,

gray iron has excellent fatigue resistance and an ability to

dampen vibration. Th is is important for applications such as

machine tools. Although gray iron has poor tensile strength

and a lower impact strength than that of most other cast

ferrous metals, it has a high compressive strength.

Ductile iron, or nodular iron, applications include crank-

shafts and heavy-duty gears because of its machinability,

fatigue strength, and high modulus of elasticity. But it has

less vibration-dampening capacity than gray iron. Ductile

iron contains trace amounts of magnesium, which improves

the stiff ness, strength, and shock resistance gray iron

produces.

White iron is specifi ed where wear and abrasion resis-

tance are required for applications such as clay mixing and

brick-making equipment such as crushers, pulverizers, and

nozzles; railroad brake shoes, and rolling-mill rolls. White

iron gets its name from the whitish appearance of the metal,

caused by chilling selected areas of gray or ductile iron in

the mold.

Compacted graphic iron (CGI) is used in automotive engine

blocks, brake drums, exhaust manifolds, and high pressure

gear pumps. It has a strength and a dampening capacity

similar to those of gray iron, with high thermal conductivity

and machinability superior to those of ductile iron.

Malleable iron is used for heavy-duty bearing surfaces in

automobiles, trucks, and railroad rolling stock. It is also

used for farm and construction machinery. Malleable iron

is white iron that has been transformed by a heat-treatment

process, providing a malleable and easily machined iron.

High-alloy irons are ductile, gray, or white irons that contain

up to 35 percent alloy content. High-chromium irons are

oxidation and wear resistant. Nickel irons are nonmagnetic,

have good corrosion resistance, and have an extremely low

coeffi cient of thermal expansion.

fi gure 3-13abc. hand iron and Japanese cast iron teapots. Th e expression

“too many irons in the fi re” probably originated while using these irons,

which were heated on a cast iron coal stove.

fi gure 3-12. Electric Arc Furnace (courtesy of

the American Iron and Steel Institute)

15

Steel 3.2 Ferrous Metals

SteelCarbon, alloy, stainless, tool, high-strength low-alloy, steels

for strength, and iron-based super alloys are the general

kinds of steel. Nearly a million tons of steel are produced in

the United States every week. Carbon steel (especially cold-

rolled sheet and mill products), stainless (mostly sheet and

standard shapes), and tools steels (for molds) are of interest

to industrial designers. Other types of steels are used in

construction, in heavy industrial equipment, and in other

specialized applications. Th e following discussion on steel

will be somewhat limited to steels used in products and

applications that involve industrial designers.

Carbon SteelCarbon steel (or common steel) is an iron-based metal

containing carbon and small amounts of other elements.

Steel is available as cast or wrought mill products such as

sheet, angles, and bar and tube, from which fi nished parts

are formed, cut, and/or joined. Th e method of deoxidation

is important in steel making. Molten steel contains oxygen,

and how oxygen is removed or killed—is allowed to escape

as the steel solidifi es—determines the properties of steel.

In addition, the combined eff ects of several elements infl u-

ence steel’s properties—its hardness, machinability, corro-

sion resistance, and tensile strength. Th ere are four types

of carbon steel (based on method of deoxidation). Killed

and semi-killed are specifi ed for forging, hot rolled sheet,

cold rolled sheet, and for casting. Rimmed steel skin is free

of carbon, which makes it ductile and is often specifi ed for

cold-forming applications. Capped steel has characteris-

tics similar to those of rimmed steels but is intermediate

between semi-killed and rimmed steels in behavior and

properties which make it suited for cold-forming applica-

tions.

Alloy Steel and Stainless SteelAlloy steel is specifi ed when high strength is needed in

moderate to large sections. Alloy steel is heat treated to

increase mechanical properties, for example, tensile strength

can be raised from 55,000 psi to 300,000 psi.

Stainless steel has a minimum of 10.5 percent chromium as

the principal alloying element. Th e four major categories of

wrought stainless steel based on their metallurgical structure

are: austenitic, ferritic, martensitic, and precipitation hard-

ening. Cast stainless-steel grades are generally designated as

either heat resistant or corrosion resistant.

Austenitic stainless steel is commonly used for processing

chemicals and food and dairy products, as well as for shafts,

pumps, fasteners, and piping in sea water equipment where

corrosion resistance and toughness are primary require-

ments. Nonmagnetic. Not heat treatable (300 Series).

Ferritic wrought alloy is used for automotive exhaust

systems and heat-transfer equipment for the chemical and

petrochemical industries. Th ese alloys are magnetic, with

moderate toughness and corrosion resistance. Not heat

treatable (400 Series).

Martensitic stainless steel is typically used for bearings,

molds, cutlery, medical instruments, aircraft structural parts,

and turbine components. Th ey are magnetic and can be

hardened by heat treatment. Th ese alloys are normally used

where strength and/or hardness is the primary concern, in

a relatively mild corrosive environment. Heat treatable (400

Series).

Precipitation-hardening stainless steel is used for aircraft

components, high-temper springs, fasteners, and high

pressure pump parts. Th e precipitation-hardening process

produces very high strength in a low temperature heat

treatment that does not signifi cantly distort precision parts.

Th ese alloys are used where high strength, moderate corro-

sion resistance, and ease of fabrication are required (Alloys:

13-8, 15-5, 15-7, 17-4, 17-7).

fi gure 3-14. in the production of steel, refi ned

iron ore and limestone are heated by coke (coal

baked in an oven, to remove sulphur and other

impurities) in a furnace. Slag is removed

and the molten iron is transported to a steel-

making furnace.

Pig Iron

Iron Ore Limestone Coke

Furnace

fi gure 3-15. the Unisphere was designed by

Gilmore D. Clarke for the 1964 World's Fair

in Flushing Meadows Park, New York. It

has 500 pieces of stainless steel and weighs

900,000 pounds. Th e Unisphere was a gift

of the United States Steel Corporation. Th e

base was designed by the Peter Müller-Munk

industrial design offi ce.

16

3.2 Ferrous Metals Steel

Tool SteelsTool steels are metallurgically “clean,” high-alloy steels that

are used for tools and dies and for parts that require resis-

tance to wear, stability during heat treatment, strength at

high temperatures, or toughness. Th ey are often specifi ed for

toughness or wear-resistant applications.

Tool (mold) steels (type P) are created specifi cally for

machine plastic injection molding and die-cast tools.

Shock-resisting tool steels (type S) are used for pneumatic

tooling parts, chisels, punches, shear blades, bolts, and

springs subjected to moderate heat in service. Th ey are

strong and tough, but are not as wear resistant as other tool

steels.

Hot-work steels (type H) are used for high performance

aircraft parts such as primary airframe structures, cargo-

support lugs, catapult hooks, and elevon hinges.

High-speed tool steels (type T/M) make good cutting tools

because they resist softening and maintain a sharp cutting

edge at high service temperatures.

Alloy SteelsHigh-strength low-alloy steels (HSLA) are used for trans-

portation equipment components in which weight reduc-

tion is important. Because of their strength, they can be

used in thinner sections, providing increased strength-to-

weight ratios over those of conventional low-carbon steels.

Steels for strength are heat-treated constructional alloy steels

and ultrahigh-strength steels that are used in situations

in which weight saving is an advantage. Some have added

toughness and weldability.

Iron-based superalloys are iron, nickel, and cobalt-based

alloys that are specifi ed for high temperature applications.

fi gure 3-16. in Ascent of Man, Jacob

Bronowski argues that technology is at the

foundation of human advancement. He

presents the master samurai sword maker

Getsu, using ancient metallurgy and

ritual to forge a steel billet, as an example

of how technology was passed down

through the ages. A sword must be fl ex-

ible yet hard enough to hold a sharp edge.

To achieve these opposing attributes the

billet is folded over many timess to make

multiple layers. In some cases well over

30,000 layers are produced. During the

fi nal stages, the sword is covered with clay

of diff erent thicknesses, so that when it is

heated and plunged into water it will cool

at diff erent rates, which hardens the sword

and fi xes the diff erent properties within. fi gure 3-17. plastic injection tool with the Mold Base (courtesy Peter

Kobal, AUDAX, www.audax.51/c3p–reference.php)

17

Powdered Metallurgy 3.3 Powdered Metallurgy

3.3 Powdered Metallurgy

Powdered metallurgy (P/M) bridges ferrous and nonfer-

rous metals and has provided new processes and new metal

alloys that can signifi cantly reduce weight while providing

enhanced mechanical properties. P/M parts are used in

sports products; electronic and offi ce equipment compo-

nents such as actuators, sprockets, levers, fasteners, bearings,

impellers, cams, and gears; and for automotive engines,

transmissions, and chassis, as well as off -road vehicles. Parts

are formed by a compaction process and then sintered. Th ey

can then be forged in a second step for greater strength.

Additional forming processes include injection molding,

hot isostatic pressing, and cold isostatic pressing. In addi-

tion to conventional iron and steel alloys, the list of available

powders includes new classes of tool steels and cermets,

and alloys of aluminum, copper, nickel, titanium, and other

nonferrous metals.Th e letter designations for the

elements used in P/M:

A aluminum

C copper

CT bronze

CNZ nickel silver

CZ brass

D molybdenum

F iron

FC copper iron or steel

FN nickel iron or steel

FX infiltrated iron or steel

FL pre-alloyed ferrous material

except stainless steel

FM pre-alloyed ferrous material

G free graphite

M manganese

N nickel

P lead

S silicon

SS stainless steel (pre-alloyed)

T tin

R titanium

U sulfur

Y phosphorus

Z zinc

fi gure 3-18. powdered metal parts (courtesy Metal Powder Industries Federation)

Basic Metallurgical Element

Minimum Yield Strength

Percent Combined Carbon(by weight)

Next Major Noncarbon Element

Percent Major Alloy

FN–0205–35Th e P/M coding system, developed by the Metal Powder

Industries Federation (MPIF), includes (1) a prefi x indi-

cating the major alloying constituents, (2) four digits that

indicate chemical content, and (3) a two-digit code that

indicates minimum yield strength for as-sintered material,

sometimes followed by HT, indicating minimum ultimate

tensile strength for heat-treated material. Ferrous alloys

begin with an F (for iron) followed by a letter designating

the next major noncarbon alloying element. Unalloyed

carbon steels and irons have only an F in the prefi x, with

the percentage of the major alloying element is designated

by the fi rst two digits. Th e last two digits designate the

percentage of metallurgically combined carbon. Stainless-

steel alloys are an exception; they begin with SS followed by

the standard stainless-steel designations.

fi gure 3-19. powdered metal designation chart

18

3.4 Nonferrous Metals Overview

Nonferrous Metals

High Melt TemperatureHigh Performance

High Cost

Low Melt TemperatureModerate Cost

Standard Products

Low to High Melt TemperatureLow to High Cost

Copper(Cu)

Aluminum(Al)

Magnesium(Mg)

Zinc(Zn)

Wrought Alloys

Casting Alloys

Aluminum Matrix Composites

Superplastic Aluminum

Casting Alloys

Standard Die Casting Alloys

ZA Casting Alloys

Wrought Alloys

High Copper Alloys

Copper and Zinc

Copper Nickel

Nickel Silver

Copper Be

Lead Brass

Alloys

Copper and Tin

Al Bronze

Si Bronze

Chromium(Cr)

Beryllium(Be)

Nickel(Ni)

Super Alloys

Inconel MA754

Inconel MA956

Inconel 903

Inconel 617

NiCu (Monel)

NiCr/NiCrFe

Other

RefractoryMetals

Titanium(Ti)

Alpha

AlphaBeta

Beta

Columbium and Tantalum

Molybdenum (Mo)

Tungsten (W)

Pure Ni and Extra High Ni Alloys

Binary Nickel Alloys

Ternary Nickel Alloys

Lead(Pb)

PreciousMetals

Gold(Au)

Silver

Platinum

Palladium,Iridium,Rhodium

RutheniumandOsmium

Tin(Sn)

Pewter

Bearing Alloys

Die-Casting Tin-Based Alloys

Tin andTin Alloy

fi gure 3-20. nonferrous metals chart