introduction to mechanical engineering sciences --- ktu

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Manufacturing Engineering &

Materials

BE 101-2

Introduction to Mechanical Engineering Sciences

Module VI

Prepared by:

Mr. Rejeesh C R, Asst. Professor,

Dept. of Mechanical Engineering

Federal Institute of Science and Technology

Introduction What is Manufacturing?

The word manufacture first appeared in English in 1567 and

is derived from the Latin manu factus, meaning “made by

hand.”

The word manufacturing first appeared in 1683, and the word

production, which is often used interchangeably with the

word manufacturing, first appeared sometime during the 15th

century.

A manufactured item typically starts with raw materials,

which are then subjected to a sequence of processes to make

individual products, it has a certain value.

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History of Manufacturing

• Manufacturing dates back to the period 5000-4000 B.C.,

and thus, it is older than recorded history, the earliest

forms of which were invented by the Sumerians around

3500 B.C.

• Primitive cave drawings, as well as markings on clay

tablets and stone, needed

(1) some form of a brush and some sort of “paint,” as in the prehistoric

cave paintings in Lascaux, France, estimated to be 16,000 years old;

(2) some means of scratching the clay tablets and baking them, as in

cuneiform scripts and pictograms of 3000 B.C.; and

(3) simple tools for making incisions and carvings on the surfaces of

stone, as in the hieroglyphs in ancient Egypt.

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History of Manufacturing • The manufacture of items for specific uses began with the production

of various household artifacts, which were typically made of either

wood, stone, or metal.

• The materials first used in making utensils and ornamental objects

included gold, copper, and iron, followed by silver, lead, tin, bronze

(an alloy of copper and tin), and brass (an alloy of copper and zinc).

• The processing methods first employed involved mostly casting and

hammering, because they were relatively easy to perform. Over the

centuries, these simple processes gradually began to be developed into

more complex operations, at increasing rates of production and higher

levels of product quality.

Note, for example, the lathes for cutting screw threads already were available

during the period from 1600 to 1700, but it was not until some three centuries

later that automatic screw machines were developed. 4

History of Manufacturing Although iron making began in the Middle East in about 1100

B.C., a major milestone was the production of steel in Asia

during the period 600-800 A.D.

A wide variety of materials continually began to be developed.

Today, countless metallic and non-metallic materials with

unique properties are available, including engineered materials

and various advanced materials.

Among the available materials are industrial or high-tech

ceramics, reinforced plastics, composite materials, and nano-

materials that are now used in an extensive variety of products,

ranging from prosthetic devices and computers to supersonic

aircraft.

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History of Manufacturing • Until the Industrial Revolution, which began in England in the

1750s and is also called the First Industrial Revolution, goods

had been produced in batches and required much reliance on

manual labour in all phases of their production.

• The Second Industrial Revolution is regarded by some as having

begun in the mid-1900s with the development of solid-state

electronic devices and computers.

• Mechanization began in England and other countries of

Europe, basically with the development of textile machinery and

machine tools for cutting metal. This technology soon moved to

the United States, where it continued to be further developed.

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History of Manufacturing • A major advance in manufacturing occurred in the early 1800s

with the design, production, and use of interchangeable parts,

conceived by the American manufacturer and inventor Eli

Whitney (1765-1825).

• Prior to the introduction of interchangeable parts, much hand

fitting was necessary because no two parts could be made

exactly alike.

• By contrast, it is now taken for granted that a broken bolt can

easily be replaced with an identical one produced decades after

the original. Further developments soon followed, resulting in

countless consumer and industrial products that we now cannot

imagine being without.

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History of Manufacturing • Beginning in the early 1940s, several milestones were reached in

all aspects of manufacturing. Note particularly the progress that

has been made during the 20th century, compared with that

achieved during the 40-century period from 4000 B.C. to 1 B.C.

• For eg, in the Roman Empire (~500 B.C. to 476 A.D.), factories

were available for the mass production of glassware; however, the

methods used were generally very slow, and much manpower was

involved in handling the parts and operating the machinery.

Today, production methods have advanced to such an extent that

(a) aluminium beverage cans are made at rates of more than 500 per minute,

with each can costing about four cents to make,

(b) holes in sheet metal are punched at rates of 800 holes per minute, and

(c) incandescent light bulbs are made at rates of more than 2000 bulbs per

minute, each costing less than one dollar. 8

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Engineering Materials metals, alloys, composites

• Based on chemical make up and atomic structure, solid

materials have been conveniently grouped into three basic

categories: metals, ceramics and polymers.

• Most materials fall into one distinct grouping or another,

although there are also some intermediates. In addition to these,

there are also three other groups of important engineering

materials: composites, semiconductors and biomaterials.

• There are also advanced materials utilized in high-technology

applications. Recently, a group of new and state of the art

materials called as smart (or intelligent) materials being

developed. Very recently, scientists have developed nano-

engineering materials.

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Engineering Materials

A brief description of the material types and representative

characteristics are: 13

Engineering Materials

Nanomaterials, shape-memory alloys, superconductors, …

Ferrous metals: carbon steels, alloy steels, stainless steels,

tool steels and die steels

Non-ferrous metals: aluminum, magnesium, copper, nickel,

titanium, superalloys, refractory metals,

beryllium, zirconium, low-melting alloys,

gold, silver, platinum, …

Plastics: thermoplastics (acrylic, nylon, polyethylene, ABS,…)

thermosets (epoxies, Polymides, Phenolics, …)

elastomers (rubbers, silicones, polyurethanes, …)

Ceramics: Glasses, Graphite, Diamond, Cubic Boron Nitride

Composites: reinforced plastics, metal-, ceramic matrix composites

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Metals and Alloys • True metals are pure elements, while alloys are blends of two or

more metals that have been melted together.

• Metallic materials have large number of non localized electrons,

i.e. electrons are not bound to particular atoms. Many properties

of metals are directly attributable to these electrons. (Conductivity)

• All metals are characterized by metallic properties, e.g. lustre,

opacity, malleability, ductility and electrical conductivity.

• Although metals compose about 3/4th of the known elements but

few find service in their pure form. The desired properties for

engineering purposes are often found in alloys.

• Typical examples of metallic materials are iron, aluminium,

copper, zinc, etc. and their alloys. They can be used either in bulk

or powder form. 15

Metals and Alloys • Metals are extremely good conductors of electricity and heat are

not transparent to visible light; a polished metal surface has a

lustrous appearance. Moreover, metals are quite strong, yet

deformable, which accounts for their extensive use in structural

applications.

• Metallic materials are always crystalline in nature. Scientists

have developed amorphous (non-crystalline) alloys by very rapid

cooling of a melt or by very high-energy mechanical milling.

• Recently, scientists have developed materials through rapid

solidification called as quasi-crystals. These are neither

crystalline nor amorphous, but form an ordered structure

somewhere between two known structures. These materials are

expected to exhibit far reaching electrical properties.

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Metals

• Ferrous Metals

– Cast irons

– Steels

• Super alloys

– Iron-based

– Nickel-based

– Cobalt-based

• Non-ferrous metals – Aluminum and its alloys

– Copper and its alloys

– Magnesium and its alloys

– Nickel and its alloys

– Titanium and its alloys

– Zinc and its alloys

– Lead & Tin

– Refractory metals

– Precious metals

Metals used in manufacturing are usually alloys, which are

composed of two or more elements, with at least one being a

metallic element. Metals and alloys can be divided into two basic

groups: (1) ferrous and (2) nonferrous.

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Metals • Ferrous metals are based on iron; the group includes steel and

cast iron. Pure iron has limited commercial use, but when

alloyed with carbon, it has greater commercial value than any

other metal.

• Alloys of iron and carbon form steel and cast iron. Steel can be

defined as an iron–carbon alloy containing 0.02% to 2.11%

carbon. It is the most important category within the ferrous metal

group.

• Its composition often includes other alloying elements as well,

such as manganese, chromium, nickel, and molybdenum, to

enhance the properties of the metal.

• Applications of steel include construction (bridges, I-beams, and

nails), transportation (trucks, rails, and rolling stock for railroads),

and consumer products (automobiles and appliances).

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Metals • Cast iron is an alloy of iron and carbon (2% to 4%) used in

casting (primarily sand casting). Silicon is also present in the

alloy (in amounts from 0.5% to 3%), and other elements are often

added also, to obtain desirable properties in the cast part.

• Cast iron is available in several different forms, of which grey

cast iron is the most common; its applications include blocks and

heads for internal combustion engines.

• Nonferrous metals include the other metallic elements and their

alloys. In almost all cases, the alloys are more important

commercially than the pure metals.

• The nonferrous metals include the pure metals and alloys of

aluminium, copper, gold, magnesium, nickel, silver, tin, titanium,

zinc, and other metals.

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General Properties and

Applications of Ferrous Alloys

• Ferrous alloys are useful metals in terms of

mechanical, physical and chemical properties.

• Alloys contain iron as their base metal.

• Carbon steels are least expensive of all metals while

stainless steels are costly.

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Carbon and alloy steels Carbon steels

• Classified as low, medium and high:

1. Low-carbon steel or mild steel, < 0.3%C, bolts, nuts and

sheet plates.

2. Medium-carbon steel, 0.3% ~ 0.6%C, machinery,

automotive and agricultural equipment.

3. High-carbon steel, > 0.60% C, springs, cutlery, cable.

Alloy steels • Steels containing significant amounts of alloying elements.

• Structural-grade alloy steels used for construction industries

due to high strength.

• Other alloy steels are used for its strength, hardness, resistance

to creep and fatigue, and toughness.

• It may heat treated to obtain the desired properties.

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High-strength low-alloy steels (HSLA) • It is a type of alloy steel that provides better mechanical

properties like improved strength-to-weight ratio or greater

resistance to corrosion than carbon steel.

• HSLA steels vary from other steels in that they are not made

to meet a specific chemical composition but rather to

specific mechanical properties.

• Used in automobile bodies to reduce weight and in

agricultural equipment.

• Some examples are:

1. Dual-phase steels

2. Micro alloyed steels

3. Nano-alloyed steels

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Stainless Steels • Characterized by their corrosion resistance, high strength

and ductility, and high chromium content.

• Stainless as a film of chromium oxide protects the metal

from corrosion.

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Stainless steels

• Five types of stainless steels:

1. Austenitic steels

2. Ferritic steels

3. Martensitic steels

4. Precipitation-hardening (PH) steels

5. Duplex-structure steels

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Tool and die steels • Tool steel is a type of carbon alloy steel that is well-

matched for tool manufacturing, such as hand tools or

machine dies.

• Hardness and ability to retain shape at increased

temperatures are the key properties of this material.

Designed for high strength, impact toughness, and wear

resistance at a range of temperatures.

• The presence of carbides in their matrix plays the dominant

role in the qualities of tool steel. The four major alloying

elements in tool steel that form carbides are: tungsten,

chromium, vanadium and molybdenum.

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Tool and die steels

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Aluminium and aluminium alloys • Factors for selecting are:

1. High strength to weight ratio.

2. Resistance to corrosion.

3. High thermal and electrical conductivity.

4. Ease of machinability.

5. Non-magnetic.

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Magnesium and Magnesium alloys • Magnesium (Mg) is the lightest metal.

• Alloys are used in structural and non-structural applications.

• Typical uses of magnesium alloys are aircraft and missile

components.

• Also has good vibration-damping characteristics.

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Copper and Copper alloys

Copper alloys are metal alloys that have copper as their

principal component. They have high resistance against

corrosion.

The best known traditional types are bronze, where tin is

a significant addition, and brass, using zinc instead.

Copper alloys have electrical and mechanical

properties, corrosion resistance, thermal conductivity

and wear resistance.

Applications are electronic components, springs and

heat exchangers.

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Nickel and Nickel alloys • Nickel alloys are used extensively because of their corrosion

resistance, high temperature strength and their special magnetic

and thermal expansion properties.

• Used in stainless steels and nickel-base alloys.

• Alloys are used for high temperature applications, such as jet-

engine components and rockets.

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Superalloys • A super-alloy, or high-performance alloy, is an alloy that

exhibits several key characteristics like excellent mechanical

strength, resistance to thermal deformation, good surface stability

and resistance to corrosion or oxidation.

• The crystal structure is typically face centered cubic austenitic.

Superalloys are high-temperature alloys use in jet engines, gas

turbines and reciprocating engines.

• Inconel is a family of austenite nickel-chromium based super

alloys.

• The main alloying ingredient is nickel in hastelloy. Other alloying

ingredients added are varying percentages of elements of

molybdenum, chromium, iron, manganese, cobalt,

copper, titanium, zirconium, aluminium, carbon, and tungsten. 31

Superalloys

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Titanium and Titanium alloys • Titanium (Ti) is expensive, has high strength-to-weight ratio and

corrosion resistance.

• Used as components for aircrafts, jet-engines, racing-cars and

marine crafts.

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Other nonferrous metals 1. Beryllium

2. Zirconium

3. Low-melting-point metals:

- Lead

- Zinc

- Tin

4. Precious metals:

- Gold

- Silver

- Platinum

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Refractory metals • Refractory metals have a high melting point and retain

their strength at elevated temperatures.

• Applications are electronics, nuclear power and chemical

industries.

• Molybdenum, columbium, tungsten and tantalum are

referred to as refractory metal.

1. Shape-memory alloys (i.e. eyeglass frame, helical spring)

2. Amorphous alloys (Metallic Glass)

3. Nanomaterials

4. Metal foams

Special Metals and Alloys

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Classification of Ceramics • Traditional ceramics

– clays: kaolinite

– silica: quartz, sandstone

– alumina

– silicon carbide

• New ceramics

– oxide ceramics : alumina

– carbides : silicon carbide, titanium carbide, etc.

– nitrides : silicon nitride, boron nitride, etc.

• Glass products

– window glass, containers

– light bulb glass, laboratory glass

– glass fibers

– optical glass

• Glass ceramics - polycrystalline structure

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Classification of Polymers • Thermoplastics - reversible in phase by heating and cooling.

Solid phase at room temperature and liquid phase at elevated

temperature.

• Thermosets - irreversible in phase by heating and cooling.

Change to liquid phase when heated, then follow with an

irreversible exothermic chemical reaction. Remain in solid

phase subsequently.

• Elastomers – Rubbers

Characteristics of Plastics are:

immune to corrosion

Good insulator

unsuitable for higher temperatures

to improve their properties additives are added. 37

Thermosets • A thermosetting plastic, also known as a thermoset, is

polymer material that irreversibly cures. The cure may be

done through heat (generally above 2000C), through a

chemical reaction (epoxy, for example).

Amino resins, Epoxies

Phenolics, Polyesters, Polyurethanes

Silicones

Thermosets are usually liquid or malleable prior to curing

and designed to be molded in to their final form, or used as

adhesives. Others are solids like that of the molding

compound used in semiconductors & integrated circuits.

Once hardened, a thermoset resin cannot be reheated and

melted back to a liquid form.

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Thermoplastics • Thermoplastics, also known as a thermosoftening plastic

is a polymer that turns to a liquid when heated and freezes

to a very glassy state when cooled sufficiently.

• Thermoplastic polymers differ from thermosetting

polymers in that they can be remelted and remoulded.

– Acetals, Acrylics - PMMA

– Acrylonitrile-Butadiene-Styrene - ABS

– Cellulosics, Fluoropolymers - PTFE , Teflon

– Polyamides (PA) - Nylons, Kevlar

– Polysters – PET, Polyethylene (PE) - HDPE, LDPE

– Polypropylene (PP), Polystyrene (PS)

– Polyvinyl chloride (PVC)

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Elastomers Characteristics of Rubber are

rough, elastic material

unaffected by water

attacked by oil and steam

Usage: gaskets, flexible couplings, vibration mount

Natural rubber

Different Synthetic rubbers

– butadiene rubber, butyl rubber, styrene-butadiene rubber

– chloroprene rubber, ethylene-propylene rubber

– isoprene rubber, nitrile rubber

– Polyurethanes, silicones, thermoplastic elastomers 40

What is a composite Material?

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Wood is a good example of a natural composite, combination

of cellulose fiber and lignin. The cellulose fiber provides

strength and the lignin is the "glue" that bonds and stabilizes

the fiber.

Bamboo is a very efficient wood composite structure. The

components are cellulose and lignin, as in all other wood,

however bamboo is hollow. This results in a very light yet stiff

structure. Composite fishing poles and golf club shafts copy this

natural design.

The ancient Egyptians manufactured composites!!! Adobe

bricks are a good example. The combination of mud and straw

forms a composite that is stronger than either the mud or the

straw by itself.

Composite Material Defined Two or more chemically distinct materials which when

combined have improved properties over the individual

materials. Composites could be natural or synthetic.

―A composite material is composed of two or more physically

distinct phases/materials whose combination produces

aggregate properties that are different from those of its

constituents‖

Examples:

– Cemented carbides (WC with Co binder)

– Plastic molding compounds containing fillers

– Rubber mixed with carbon black

– Wood (a natural composite) 42

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Why Composites are Important

Composites can be very strong and stiff, yet very light in

weight, so strength-to-weight ratio and stiffness-to-weight

ratio are several times greater than steel or aluminum.

Fatigue properties are generally better than for common

engineering metals.

Toughness is often greater too

Composites can be designed that do not corrode like steel

Possible to achieve combinations of properties not

attainable with metals, ceramics, or polymers alone.

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Components of composite materials

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Composites are combinations of two materials in which one of

the material is called the reinforcing phase, is in the form of

fibers, sheets, or particles, and is embedded in the other material

called the matrix phase.

Typically, reinforcing materials are strong with low densities

while the matrix is a ductile/tough material. When a composite

designed and fabricated correctly, it combines the strength of

reinforcement with the toughness of matrix to achieve a

combination of desirable properties not available in a single

conventional material.

Reinforcement: fibers Carbon, Boron, Organic,

Glass, Ceramic, Metallic

Matrix materials Polymers, Metals,

Ceramics

Interface

Bonding surface

The Reinforcing Phase

Function is to reinforce the matrix phase

Imbedded phase is most commonly one of the following shapes:

Fibers

Particles

Flakes

In addition, the secondary phase can take the form of an

infiltrated phase in a skeletal or porous matrix

Example: a powder metallurgy part infiltrated with polymer

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Fig: Possible physical shapes of imbedded phases in

composite materials: (a) fiber, (b) particle, (c) flake

Composite Structures

Laminar composite structure – conventional

Sandwich structure

Honeycomb sandwich structure

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Consists of a relatively thick core of low density foam

bonded on both faces to thin sheets of a different material.

Fig: Laminar composite

structures: (b) sandwich structure

using foam core

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Sandwich Structure – Foam Core

An alternative to foam core

Either foam or honeycomb achieves high strength -to - weight and stiffness - to - weight ratios

Fig: Laminar composite structures:

(c) sandwich structure using

honeycomb core

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Sandwich Structure –

Honeycomb Core

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Classification Scheme for Composites

1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides and other cermets

2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with fibers to improve properties, especially in high temperature applications

– The least common composite matrix

3. Polymer Matrix Composites (PMCs) - thermosetting resins are widely used in PMCs

– Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders

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Advantages of Composites

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Higher Specific Strength (strength-to-weight ratio)

Composites have a higher specific strength than many other

materials. A distinct advantage of composites over other

materials is the ability to use many combinations of resins

and reinforcements, and therefore custom tailor the

mechanical and physical properties of a structure.

Corrosion Resistance

Composites products provide long-term resistance to severe

chemical and temperature environments. Composites are the

material of choice for outdoor exposure, chemical handling

applications, and severe environment service.


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Design flexibility

Composites have an advantage over other materials because

they can be molded into complex shapes at relatively low

cost. This gives designers the freedom to create any shape or

configuration. Boats are a good example of the success of

composites.

Low Relative Investment

One reason the composites industry has been successful is

because of the low relative investment in setting-up a

composites manufacturing facility. This has resulted in many

creative and innovative companies in the field.


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Durability

Composite products and structures have an exceedingly long

life span. Coupled with low maintenance requirements, the

longevity of composites is a benefit in critical applications. In

a half-century of composites development, well-designed

composite structures have yet to wear out.

In 1947 the U.S. Coast Guard built a series of forty-foot patrol

boats, using polyester resin and glass fiber. These boats were used

until the early 1970’s when they were decommissioned because the

design was outdated. Extensive testing was done on the laminates

after decommissioning, and it was found that only 2-3% of the

original strength was lost after twenty-five years of hard service.

Disadvantages of Composites

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Composites are heterogeneous

Properties in composites vary from point to point in the

material. Most engineering structural materials are

homogeneous.

Many of the polymer based composites are subject to

attack by chemicals or solvents, just as the polymers

themselves are susceptible to attack.

Composite materials are generally expensive.

Manufacturing methods for shaping composite materials

are often slow and costly.


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Composites are highly anisotropic

The strength in composites vary as the direction along

which we measure changes (most engineering structural

materials are isotropic).

As a result, all other properties such as, stiffness, thermal

expansion, thermal and electrical conductivity and creep

resistance are also anisotropic.

The relationship between stress and strain (force and

deformation) is much more complicated than in isotropic

materials.

The experience and intuition gained over the years about the

behavior of metallic materials does not apply to composite materials.

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Composites materials are difficult to inspect with conventional

ultrasonic, eddy current and visual NDI methods such as

radiography.

American Airlines Flight 587, broke apart over New York on Nov.

12, 2001 (265 people died). Airbus A300’s 27-foot-high tail fin

tore off. Much of the tail fin, including the so-called tongues that

fit in grooves on the fuselage and

connect the tail to the jet, were

made of a graphite composite.

The plane crashed because of

damage at the base of the tail that

had gone undetected despite

routine nondestructive testing and

visual inspections.

The Crystal Structure of Metals

When metals solidify from a molten state, the atoms

arrange themselves into various orderly

configurations, called crystals; this atomic

arrangement is called crystal structure or crystalline

structure.

The smallest group of atoms showing the

characteristic lattice structure of a particular metal is

known as a unit cell. It is the building block of a

crystal, and a single crystal can have many unit cells.

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The Crystal Structure of Metals The following are the four basic atomic arrangements in metals:

l. Simple cubic (SC); examples: alpha - polonium

2. Body-centered cubic (bcc); examples: alpha iron, chromium,

molybdenum, tantalum, tungsten, and vanadium.

3. Face-centered cubic (fcc); examples: gamma iron, aluminium,

copper, nickel, lead, silver, gold, and platinum.

4. Hexagonal close-packed (hcp); examples: beryllium, cadmium,

cobalt, magnesium, alpha titanium, zinc, and zirconium.

• These structures when represented in illustrations; each sphere

represents an atom. The distance between the atoms in these

crystal structures is on the order of 0.1 nm.

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Simple Cubic

Fig The Simple cubic (sc) crystal structure: (a) hard-ball model; (b) unit cell;

• Each layer is stacked on the previous layer perfectly.

• There are 8 eighths (one in each corner) for a total of ONE atom in the unit cell. 58

Coordination Number

• CN, the coordination number, which is the number of

closest neighbours to which an atom is bonded.

59 5

Atomic Packing Factor

(No. of atoms/unit cell) X volume of each atom

Volume of unit cell APF =

In crystallography, atomic packing factor (APF), packing

efficiency is the fraction of volume in a crystal structure that

is occupied by constituent particles. It is dimensionless and

always less than unity.

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4

• Rare due to poor packing (only Po has this structure)

• Close-packed directions are cube edges.

• Coordination # = 6

(# nearest neighbors)

Simple Cubic Structure (SC)

APF for a simple cubic

structure = 0.52

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Body-Centered Cubic Crystal Structure

Fig The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell;

• Each layer is offset from the layer before. Arrangements duplicate themselves every other layer.

• There are 8 eights (one in each corner) and one full atom in the centre for a total of Two atoms in the unit cell.

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aR

9

• APF for a body-centered cubic structure = 0.68

Unit cell contains: 1 + 8 x 1/8 = 2 atoms/unit cell

Atomic Packing Factor: BCC


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Face-Centered Cubic Crystal Structure

Fig: The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell;

• Each layer is offset from the layer before. Arrangements duplicate themselves every third layer.

• There are 8 eighths (one in each corner), and 6 halves (one on each face of the cube) for a total of Four atoms in the unit cell.

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Unit cell contains: 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell

a

7

• APF for a body-centered cubic structure = 0.74

Atomic Packing Factor: FCC

Coordination # = 12

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Hexagonal Close Packed Crystal Structure

Fig: The hexagonal close-packed (hcp) crystal structure: (a) unit

cell; and (b) single crystal with many unit cells.

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Number of atoms per unit cell :

12 (corner atoms) x 1/6 + 3 (interior atoms) + 2

(face atoms) x 1/2= 6 atoms / unit cell

• APF = 0.74

Hexagonal Close-packed Structure

(HCP)

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Definition of Heat Treatment

Heat treatment is an operation or combination of

operations involving heating at a specific rate,

soaking at a temperature for a period of time and

cooling at some specified rate.

The aim is to obtain a desired microstructure to

achieve certain predetermined properties (physical,

mechanical, magnetic or electrical).

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Objectives of Heat Treatment Processes

The major objectives are

• to increase strength, hardness and wear resistance

(hardening)

• to increase ductility, toughness and softness (tempering,

annealing)

• to obtain fine grain size (annealing, normalising)

• to remove internal stresses induced by differential

deformation by cold working, non-uniform cooling from

high temperature during casting and welding (stress

relief annealing)

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• to improve machinability (annealing and normalizing)

• to improve cutting properties of tool steels (hardening

and tempering)

• to improve surface properties (surface hardening,

corrosion resistance-stabilizing treatment and surface

treatment)

• to improve electrical properties (recrystallization,

tempering, age hardening)

• to improve magnetic properties (hardening, phase

transformation)

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Objectives of Heat Treatment Processes

Annealing • It alters the physical and chemical properties of a material to

increase its ductility and reduce its hardness, making it more

workable.

• It involves heating of material above recrystallization

temperature, maintaining it for some time and then cooling.

• In the cases of copper, steel, silver and brass, this process is

performed by heating the material (until glowing) for a while and

then slowly cooling to room temperature in still air.

• Copper, silver and brass can be cooled slowly in air, or quickly

by quenching in water, unlike ferrous metals, such as steel, which

must be cooled slowly to anneal.

• In this fashion, the metal is softened and prepared for further

work -- such as shaping, stamping, or forming. 71

Hardening • Hardening is used to increase the hardness of a metal. A

harder metal will have a higher resistance to plastic

deformation than a less hard metal.

• Hardening is a form of heat treatment in which a metal

part is heated and then quenched. The quenched metal

undergoes a martensitic transformation, increasing the

hardness and brittleness of the part.

• Martensitic transformation, is a hardening mechanism specific for steel. The steel must be

heated to a temperature where the iron phase changes from ferrite into austenite, i.e. changes

crystal structure from BCC to FCC.

• In austenitic form, steel can dissolve more carbon. Once the carbon has been dissolved, the

material is then quenched with a high cooling rate so that the carbon does not have time to form

precipitates of carbides. When the temperature is low enough, the steel tries to return to the low

temperature crystal structure BCC. This change is very quick and is called a martensitic

transformation. This phase is called martensite, and is extremely hard.

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Quenching • Quenching is the rapid cooling of a work piece to obtain

favourable material properties… For instance, it can

reduce crystallinity and thereby increase the hardness of

both alloys and plastics.

• It is commonly used to harden steel by

introducing martensite, in which case the steel must be

rapidly cooled, the temperature at which austenite becomes

unstable.

• Extremely rapid cooling can prevent the formation of crystal

structure, resulting in amorphous metal or "metallic glass".

• If the percentage of carbon is less than 0.4 %, quenching is

not possible.

73

Tempering • Tempering is used to increase the toughness of iron-

based alloys.

• Tempering is usually performed after hardening, to reduce

some of the excess hardness, and is done by heating the

metal to some temperature below the critical point for a

certain period of time, then allowing it to cool in still air.

• The exact temperature determines the amount of hardness

removed, and depends on both the composition of the alloy

and on the desired properties in the finished product.

• For instance, very hard tools are often tempered at low

temperatures, while springs are tempered to much higher

temperatures.

74

Normalizing • Normalizing is for making the material softer but does not

produce the uniform material properties of annealing.

• A material can be normalized by heating it to a specific

temperature and then letting the material cool to room

temperature outside of the oven.

• Normalising refines the grain size, improves the uniformity

of microstructure and properties of hot rolled steel.

• Normalizing is used in some plate mills, in the production

of large forgings such as railroad wheels and axles, some

bar products. This process is less expensive than

annealing.

75

Carburizing • In carburization iron or steel absorbs carbon, when the

metal is heated in the presence of carbon bearing materials

like charcoal or carbon monoxide, with the intent of

making the metal harder.

• Depending on the amount of time and temperature, the

affected area can vary in carbon content. Longer

carburizing times and higher temperatures typically increase

the depth of carbon diffusion.

• When the iron or steel is cooled rapidly by quenching, the

higher carbon content on the outer surface becomes hard via

the transformation from austenite to martensite, while the

core remains soft and tough as a ferritic and/or pearlite

microstructure. 76

Carburizing • This manufacturing process can be characterized by the

following key points:

It is applied to low-carbon work pieces;

work pieces are in contact with a high-carbon gas, liquid or

solid;

it produces a hard work piece surface;

work piece cores largely retain their toughness and ductility;

it produces case hardness depths of up to 0.25 inches (6.4 mm).

• In some cases it serves as a remedy for undesired

decarburization that happened earlier in a manufacturing

process.

77

Properties of materials

Mechanical properties of materials

Strength, Toughness, Hardness, Ductility,

Elasticity, Fatigue and Creep

Chemical properties

Oxidation, Corrosion, Flammability, Toxicity, …

Physical properties

Density, Specific heat, Melting and boiling point,

Thermal expansion and conductivity,

Electrical and magnetic properties

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Mechanical Properties

• Subgroup of physical properties.

• response to force or stress

– force – a push or pull

– stress – force causing a deformation or distortion (force per unit area)

Stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it.

79 80

Types of Stresses

Tension Compression

Torsion Shear

Mechanical Properties Examples

• Workability

– malleability – can be flattened

– ductility – can be drawn into wire (stretched), bent,

or extruded

• Brittleness - breaks instead of deforming when stress is

applied

81

• elasticity

– ability to return to original shape after being deformed by

stress

– rubber ball or piece of elastic

• plasticity

– retains new shape after being deformed by stress

– wet clay ball or piece of saran wrap


82

• hardness

– resistance to denting or scratching

– Brinell Hardness, Vickers hardness and Rockwell

test are used to measure hardness.


83

Mechanical Properties Examples • Strength is the ability of a material to resist deformation.

The strength of a component is usually considered based on

the maximum load that can be borne before failure.

• Toughness is the ability of a material to absorb energy and

plastically deform without fracturing.

Impact strength is the ability to withstand sudden impact without

fracture.

• Impact strength/Toughness –- Charpy test, IZOD test.

• Universal testing machine is used to find compressive

strength, tensile strength and bending strength.

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Mechanical Properties Examples • Fatigue is the phenomenon of sudden fracture of a component

after a period of cyclic loading in the elastic regime. Failure is

the end result of a process involving initiation and growth of a

crack, usually at the site of stress concentration on the surface.

Eventually after reaching a critical size, the crack will

propagate suddenly, and the structure will fracture.

• Creep (cold flow) is the tendency of a material to deform

permanently under the influence of mechanical stresses. It can

occur as a result of long-term exposure to high levels of stress

that are still below the yield strength of the material.

A yield strength of a material is defined as the stress at which

a material begins to deform plastically. Prior to the yield point the

material will deform elastically and will return to its original shape

when the applied stress is removed.

85

Methods of Manufacturing

1. Shaping processes

Casting, forging, rolling etc..

2. Machining processes

Turning, Milling, drilling, grinding etc..

3. Joining processes

Welding, soldering, riveting etc..

86

Moulding Mould

A mould is a cavity or void made in a compact sand mass,

which when filled molten metal, will produce a casting of the

desired shape.

The mould made in the sand is known as sand mould.

The process of producing a mould or cavity in the sand is

called moulding.

A casting can be defined as a molten material that has

been poured into a prepared cavity and allowed to

solidify.

Casting

Sand Casting

Making of castings in moulds of sand or similar

material.

The principal metals used are cast irons and

steel, brass and other copper alloys, aluminium

and magnesium alloys.

The softer alloys of lead, tin etc. are usually cast

in steel moulds or dies.

The principal raw material used in moulding.

The sand in moulding is silica, the oxide of silica.

The factors to be controlled in the preparation of

sand for making moulds are clay content,

moisture content, grain size permeability, and

strength of the sand.

Moulding Sand

89

Green sand It is moist sand containing about 5% moisture. Moulds and

cores may be made from green sand.

Both moulds and cores may be baked to drive out the

moisture.

However, the most commonly used moulds are of that is not

dried. They are called green sand moulds.

The moisture content and permeability may be closely

controlled to prevent the trapping of gases which could cause

voids in the casting.

Green sand moulds are those sand moulds, in which

moisture is present in the sand at the time of pouring the

molten metal. 90

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Main Constituents of Mould Sand

• Silica sand Binder

• Additives Water

Binder impart sufficient strength and cohesiveness to the

moulding sand so as to retain its shape after the mould has

been rammed and the pattern withdrawn.

Additives are added to the moulding sand to improve upon

some of its existing properties or to impart new properties to

it.

Water content is mainly responsible for enabling the clay to

impart the desired strength to the sand.

91

Green-Sand Moulding

The sand is mixed with water and suitable

proportions of bonding agents, as this mixture, in wet

(or “green”) state, is used for making the moulds.

The mould is prepared in the usual manner. Molten

metal is poured into the mould through the runner.

There is no need of baking the mould before pouring.

Most of the small and medium sized castings,

particularly non-ferrous ones, are made by green-sand

moulding.

92

Advantages of Casting Complicated shapes can be obtained in quantities at low cost.

Within certain limits the units are identical in size and properties.

Replacement can be quickly obtained, provided the pattern is kept safe.

Certain castings, being solid integral units, are more rigid than built up units.

Cast metals and alloys, in general, resist creep under high temperature conditions better than the wrought product.

Steps in making a Casting

• The making of a pattern, which may be in exactly the

same form as the finished product

• The actual making of the mould in sand.

• The pouring into the mould of molten metal, which is

allowed to solidify.

• The removal of casting from the sand, and its cleaning

by removing all superfluous adherent metal a process

called dressing or fettling.

94

Properties of Moulding Sands

Permeability

Cohesiveness

Adhesiveness

Plasticity

Refractoriness

95

Making a Sand Mould

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Core and Core Prints

• Castings are often required to have holes, recesses, etc. of

various sizes and shapes. These impressions can be obtained by

using cores.

• So where core is required, provision should be made to support

the core inside the mold cavity. Core prints are used to serve this

purpose.

• The core print is an added projection on the pattern and it forms

a seat in the mold on which the sand core rests during pouring of

the mold.

• The core print must be of adequate size and shape so that it can

support the weight of the core during the casting operation.

• Depending upon the requirement a core can be placed

horizontal, vertical and can be hanged inside the mold cavity.

97

Pattern having core prints. 98

Pattern Making:

A Pattern is a model or the replica of the object to

be cast.

Except for the various allowances a pattern exactly

resembles the casting to be made.

A pattern is required even if one object has to be

cast.

99

Pattern Allowances:

A pattern is larger in size as compared to the final

casting, because it carries certain allowances due to

metallurgical and mechanical reasons for example,

shrinkage allowance is the result of metallurgical

phenomenon where as machining, draft, distortion,

shake and other allowances are provided on the

patterns because of mechanical reasons.

100

Types of Pattern Allowances:

The various pattern allowances are:

1. shrinkage or contraction allowance.

2. Machining or finish allowance.

3. Draft or tapper allowances.

4. Distortion or camber allowance.

5. Shake or rapping allowance.

101

1. Shrinkage Allowance:

All most all cast metals shrink or contract volumetrically on cooling.

The metal shrinkage is of two types:

1. Liquid Shrinkage:

It refers to the reduction in volume when the metal changes from liquid

state to solid state at the solidus temperature. To account for this

shrinkage; riser, which feed the liquid metal to the casting, are

provided in the mold.

2. Solid Shrinkage:

It refers to the reduction in volume caused when metal loses

temperature in solid state. To account for this, shrinkage allowance is

provided on the patterns.

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Almost all cast metals shrink or contract volumetrically

after solidification and therefore the pattern to obtain a

particular sized casting is made oversize by an amount

equal to that of shrinkage or contraction.

Different metals shrink at different rates because shrinkage

is the property of the cast metal/alloy.

The metal shrinkage depends upon:

1. The cast metal or alloy.

2. Pouring temp. of the metal/alloy.

3. Casted dimensions(size).

4. Casting design aspects.

5. Molding conditions(i.e., mould materials and molding

methods employed)

103

Rate of Contraction of Various Metals :

Material Dimension Shrinkage allowance (inch/ft)

Grey Cast Iron

Up to 2 feet 2 feet to 4 feet

over 4 feet

0.125 0.105 0.083

Cast Steel


over 6 feet

0.251 0.191 0.155

Aluminum


over 6 feet

0.155 0.143 0.125

Magnesium

Up to 4 feet Over 4 feet

0.173 0.155

104

2. Machining Allowance: A Casting is given an allowance for machining, because: i. Castings get oxidized in the mold and during heat treatment; scales etc.,

thus formed need to be removed.

ii. It is the intended to remove surface roughness and other imperfections

from the castings.

iii. It is required to achieve exact casting dimensions.

iv. Surface finish is required on the casting.

How much extra metal or how much machining allowance

should be provided, depends on the factors listed below:

i. Nature of metals.

ii. Size and shape of casting.

iii. The type of machining operations to be employed for cleaning the

casting.

iv. Casting conditions.

v. Molding process employed 105

Machining Allowances of Various Metals:

Metal Dimension (inch) Allowance (inch)

Cast iron Up to 12 12 to 20 20 to 40

0.12 0.20 0.25

Cast steel Up to 6 6 to 20 20 to 40

0.12 0.25 0.30

Non ferrous Up to 8 8 to 12 12 to 40

0.09 0.12 0.16

106

3. Draft or Taper Allowance: It is given to all surfaces perpendicular to parting line.

Draft allowance is given so that the pattern can be easily

removed from the molding material tightly packed around

it with out damaging the mould cavity.

The amount of taper depends upon:

i. Shape and size of pattern in the depth direction in contact with the mould cavity.

ii. Moulding methods.

iii. Mould materials.

iv. Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces.

107 108

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Fig: Taper in design

109

Table 2 : Draft Allowances of Various Materials:

Pattern material

Height of the given surface

(inch)

Draft angle (External surface)

Draft angle (Internal surface)

Wood

1 1 to 2 2 to 4 4 to 8

8 to 32

3.00 1.50 1.00 0.75 0.50

3.00 2.50 1.50 1.00 1.00

Metal and plastic

1 1 to 2 2 to 4 4 to 8

8 to 32

1.50 1.00 0.75 0.50 0.50

3.00 2.00 1.00 1.00 0.75

110

4. Distortion or Camber allowance:

A casting will distort or wrap if:

i. It is of irregular shape,

ii. All it parts do not shrink uniformly i.e., some parts shrinks

while others are restricted from during so,

iii. It is u or v-shape,

iv. The arms possess unequal thickness,

v. It has long, rangy arms as those of propeller strut for the

ship,

vi. It is a long flat casting,

vii. One portion of the casting cools at a faster rate as

compared to the other.

111 112

5. Shake Allowance: A pattern is shaken or rapped by striking the same with a

wooden piece from side to side. This is done so that the

pattern a little is loosened in the mold cavity and can be

easily removed.

In turn, therefore, rapping enlarges the mould cavity which

results in a bigger sized casting.

Hence, a –ve allowance is provided on the pattern i.e., the

pattern dimensions are kept smaller in order to compensate

the enlargement of mould cavity due to rapping.

The magnitude of shake allowance can be reduced by

increasing the taper.

113

Die Casting

114

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Die Casting

115 116

Casting Defects Blowholes:

Blowholes/Pinholes: These defects can appear in any region of a

casting. They are caused when gas is trapped in the metal during

solidification.

Caused due to excess moisture content in moulding sand or low

permeability/venting.

Scab

It is caused when sand erodes from mould due to uneven

ramming and the recess is filled with metal.

Scar and blister

Due to improper permeability or venting. A scar is a shallow

blow. It generally occurs on flat surf; whereas a blow occurs on

a convex casting surface. A blister is a shallow blow like a scar

with thin layer of metal covering it. 117

Casting Defects Wash

They appear as rough spots or areas of excess metal, and are caused

by erosion of moulding sand by the flowing metal.

This is due to loose ramming of moulding sand, and not having enough

strength and if the molten metal flowing at high velocity.

The former can be taken care of by proper choice of moulding sand

and the latter can be overcome by the proper design of the gating

system.

Misrun

A mis-run is caused when the metal is unable to fill the mould cavity

completely and thus leaves unfilled cavities.

A mis-run results when the metal is too cold to flow to the extremities

of the mould cavity before freezing.

Long, thin sections are subject to this defect and should be avoided in

casting design. 118

Casting Defects Cold shut

• A cold shut is caused when two streams while meeting in the mould

cavity, do not fuse together properly thus forming a discontinuity in

the casting.

• When the molten metal is poured into the mould cavity through more-

than-one gate, multiple liquid fronts will have to flow together and

become one solid.

• If the flowing metal fronts are too cool, they may not flow together, but

will leave a seam in the part and is called a cold shut, and can be

prevented by superheat in the poured metal and sufficiently thick walls

in the casting design.

• The mis-run and cold shut defects are caused either by a lower fluidity

of the mould or when the section thickness of the casting is very small.

Fluidity can be improved by changing the composition of the metal

and by increasing the pouring temperature of the metal. 119

Casting Defects Hot Tear

Hot tears are cracks which appear when the solidifying melt does not

have sufficient strength to resist tensile forces produced during

solidification.

They may be due to

excessively high temperature of casting metal,

increased metal contraction,

incorrect design of the gating system or casting,

poor deformability of the cores, and

non-uniform cooling which gives rise to internal stresses.

This defect can be avoided by improving the design of the casting and

by having a mould of low hot strength and large hot deformation.

120

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Extrusion is defined as the process of shaping material, by

forcing it to flow through a shaped opening in a die.

Extruded material emerges as an elongated piece with the

same profile as the die opening.

Drawing is defined as the process of shaping material, by

pulling the material through a shaped opening in a die

(draw die).

This process of drawing is not to be confused with the

drawing process related to the forming of sheet metals

Extrusion and Drawing

121

Extruded items

Railings for sliding doors

Window frames

Tubing having various

cross-sections

Aluminum ladders

Numerous structural and

architectural shapes

Rods and wires Including:

Rods for shafts

Machine and structural

components

Electrical wiring

Tension-loaded structural

members

Welding Electrodes

Springs, Cables & Paper clips

Spokes for bicycle wheels

Stringed musical instruments

Drawing Products

122

Extrusion • Metal is compressed and forced to flow through a shaped

die to form a product with a constant cross section

• A ram advances from one end of the die and causes the metal to flow plastically through the die

Figure Direct extrusion schematic showing the various equipment components.

(Courtesy of Danieli Wean United, Cranberry Township, PA.) 123

Extrusion

• Definition:

– Process of forcing a billet through a die above its

elastic limit, taking shape of the opening.

• Purpose:

– To reduce its cross-section or to produce a solid or

hollow cross section.

• Analogy: “Like squeezing toothpaste out of a tube”.

124

Extrusion Extruded products always have a constant cross-section.

It can be a semi-continuous or a batch process.

Extrusions can be cut into lengths to become discrete

parts like gears, brackets, etc.

A billet can also extruded individually in a chamber, and

produces discrete parts.

Typical products: railings, tubing, structural shapes, etc.

125

Typical Extruded Products

(Left) Aluminum products. (Right) Steel products.

Figure Typical shapes produced by extrusion.

(Courtesy of Aluminum Company of America, Pittsburgh, PA.). (Courtesy of Allegheny

Ludlum Steel Corporation, Pittsburgh, PA.)

126

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Extrusion • Can be performed at elevated temperatures or room

temperatures, depending on material ductility.

• Commonly extruded materials include aluminum,

magnesium (low yield strength materials), copper, and

lead.

• Steels and nickel based alloys are far more difficult to

extrude (high yield strength materials).

• Lubricants are essential to extrude high strength alloys

to avoid tendency of material to weld to die walls.

127

Advantages of Extrusion

• Many shapes can be produced that are not possible

with rolling

• No draft is required

• Amount of reduction in a single step is only limited

by the equipment, not the material or the design

• Dies are relatively inexpensive

• Small quantities of a desired shape can be produced

economically

128

Extrusion Methods Methods of extrusion:

Hot extrusion is usually done by either the direct or indirect methods.

– Direct extrusion

Solid ram drives the entire billet to and through a stationary die.

Must provide additional power to overcome friction between billet

surface and die walls.

– Indirect extrusion

A hollow ram pushes the die back through a stationary, billet.

No relative motion and no friction between billet and die walls.

Lower forces required, can extrude longer billets.

More complex process, more expensive equipment required.

129

Extrusion Methods

Fig. Direct and Indirect extrusion.

In direct extrusion, the ram and billet both move and friction

between the billet and the chamber opposes forward motion.

For indirect extrusion, the billet is stationary. There is no billet-

chamber friction, since there is no relative motion. 130

Extrusion of Hollow Shapes • Mandrels may be used to produce hollow shapes or shapes

with multiple longitudinal cavities.

Fig. Two methods of extruding hollow shapes using internal mandrels.

(a) the mandrel & ram have independent motions; (b) they move as a single unit. 131

Cold Extrusion

Fig. (Right)

Steps in the

forming of a

bolt by cold

extrusion, cold

heading and

thread rolling.

Fig.

(a) Reverse

(b) forward

(c) combined

forms of cold

extrusion.

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Drawing

• Cross section of a round rod / wire is reduced by

pulling it through a die.

• Work has to be done to overcome friction. Force increases

with increasing friction.

• Cannot increase force too much, or material will reach

yield stress.

• Maximum reduction in cross-sectional area per pass =

63%.

• To produce a desired size or shape, multiple draws may be

required through a series of progressively smaller dies.

• Intermediate annealing may also be required to restore

ductility and enable further deformation.

133

Deep Drawing

Blanking

Deep Drawing

Redrawing

Ironing

Doming

Necking

Seaming

134

135

Examples of Deep

Drawing

136

Tube and Wire Drawing

• Tube sinking does not use a

mandrel

– Internal diameter precision is

sacrificed for cost and a floating

plug is used

Fig. Tube drawing with a floating

plug.

Fig. Schematic of wire drawing with a

rotating draw block. The rotating motor on

the draw block provides a continuous pull

on the incoming wire. 137

Examples of Sheet metal parts

138

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Bending

• Beyond yield strength but below the ultimate

tensile strength

• Placed on die and bent using a simple punch.

139

Bending Mechanism

140

What is Spinning?

• Spinning is the process of forming sheet metals or

tubing into contoured and hollow circular shapes.

141

Conventional Spinning- Mandrel

142

Forging Forging is defined as the controlled plastic

deformation of metal at elevated temperatures into a

predetermined size or shape by operations like

hammering, bending and pressing etc.

These operations can be carried out by hand

hammers, power hammers, drop hammers or by forging

machines.

Forging is generally employed for those components

which require high strength and resistance to shock or

vibration and uniform properties.

Forging Tools

• Smith’s forge or hearth

• Swage block

• Tongs

• Punches and drafts

• Swages

• Flatter

• Anvil

• Sledge hammers

• Chisels

• Fullers

• Set hammer

• Beck iron

144

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Forging Operations

• Upsetting

• Drawing

• Setting down

• Cutting

• Bending

• Welding

• Punching

• Rotary swaging

• Cold heading

• Riveting and stacking

• Hobbing

• Coining

• Embossing

145

Forging Operations

Upset forging

Upsetting

FINISHED PART

Bending (on Anvil) Setting down Punching 146

Forging Operations

Cold heading

Riveting

Coining Hobbing Embossing

Stamping

147

Rolling

•Rolling is a process of compressing and squeezing a metal piece between two rolls rotating in opposite directions.

•It is the method of forming metal into desired shapes by plastic deformation as the metal passes between the rolls.

•Rolling is used to produce structural shapes like channels, I-beams, rail-road rails, bars of circular or hexagonal cross-section and sheets, plates etc.

Types of Rolls

• Grooved Roll

produce structural shapes, like channels, angles etc.

• Plain Roll

produce sheets, plates, strips etc.

149

Methods of Rolling

• Hot Rolling

• Cold Rolling

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Rolling Mills

• Two-high reversing mill

• Three-high mill

151

Rolling

152

Welding

Welding is the process of joining two pieces

of metal by application of heat.

Soldering and brazing are adhesive bonds,

whereas welding is a cohesive bond.

Arc Welding

Arc welding is used in fusion processes for joining metals and alloys.

The heat required is developed by striking an arc between a metal rod and the parts to be joined.

By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created.

Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts.

Energy for the arc is provided by AC transformed from the mains supply to 50-100V, 10-300A. DC may be used at 40-60V.

Arc Welding Prepared joints for Arc Welding

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Welding Operation

Before welding, earthing connections should be

checked, voltage and amperage has to be

adjusted.

welding rod is selected to suit the nature and

thickness of the metal to be joined.

157 158

Gas Welding

In gas welding, combustion is obtained by

mixing oxygen with a fuel to support combustion

at high temperature.

The most common fuel is acetylene. The fuel gas

could also be hydrogen, natural or producers gas.

Oxy-Acetylene Welding

CaC2 + 2H2O = C2H2 + Ca(OH)2

Calcium Carbide Water Acetylene Hydrated lime

Types of Flames

• Carburizing flame - excess of acetylene

• Neutral flame - aprox. equal volume of O2 and C2H2

• Oxidizing flame

161

Machining (a) Purpose of Machining

• Most of the engineering components such as gears, bearings,

clutches, tools, screws and nuts etc. need dimensional and form

accuracy and good surface finish for serving their purposes.

• Preforming like casting, forging etc. generally cannot provide

the desired accuracy and finish.

• Such preformed parts are called blanks, and need semi-finishing

or finishing and is done by machining and grinding. Grinding is

also basically a machining process.

• Machining to high accuracy and finish enables a product to:

• fulfill its functional requirements

• improve its performance

• prolong its service

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(b) Principle of Machining • The basic principle of machining is illustrated in Figure.

• A metal rod of irregular shape, size and surface is

converted into a finished rod of desired dimension and

surface by machining by proper relative motions of the

tool-work pair. 163

Definition of Machining:

• Machining is an essential process of finishing by

which jobs are produced to the desired dimensions

and surface finish by gradually removing the excess

material from the preformed blank in the form of

chips with the help of cutting tool(s) moved past the

work surface(s).

164

Machining Requirements The essential requirements for machining work are schematically illustrated as

The blank and the cutting tool are properly mounted (in fixtures) and moved

in a powerful device called machine tool enabling gradual removal of

material from the work surface resulting in its desired dimensions and

surface finish.

Additionally environment like cutting fluid is generally used to ease

machining by cooling and lubrication. 165

Basic functions of Machine Tools

• Machine Tools basically produce geometrical surfaces like

flat, cylindrical or any contour on the preformed blanks by

machining work with the help of cutting tools.

• The physical functions of a Machine Tool in machining

are:

firmly holding the blank and the tool.

transmit motions to the tool and the blank.

provide power to the tool-work pair for the machining

action.

control of the machining parameters, i.e., speed, feed and

depth of cut.

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Machine Tool - definition

• A machine tool is a non-portable power operated and

reasonably valued device or system of devices in

which energy is expended to produce jobs of desired

size, shape and surface finish by removing excess

material from the preformed blanks in the form of

chips with the help of cutting tools moved past the

work surface(s).

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Lathe

The main function of a lathe is to remove the metal from

the piece of work to give it the required shape & size. 168

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This is accomplished by holding the work securely &

rigidly on the machine & then turning it against a

cutting tool, which will remove metal from the work in

the form of chips.

If the tool is moved parallel to the axis of rotation of

the work then a cylindrical surface is produced as

shown.

If the tool is moved perpendicular to the axis of

rotation of the work, then a flat surface is produced as

shown.

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Working Principle of a lathe

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Diagram of a Lathe

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Schematic Diagram of a Lathe

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Diagram of a Lathe

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Specification of a lathe

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Principal parts of a Lathe

Bed: - the body structure supported at both ends. The head

stock, tail stock, carriage etc. are mounted on it. The bed

provides required strength and rigidity to the machine.

Head stock:-the head stock is mounted on the bed at the left end

permanently. It has got a gear box for getting different speeds

for the spindle and work piece.

Tail stock: - this is mounted on the right hand end of the bed

which can however clamp at any position. Tail stock supports

one end of work piece and used for holding the tool for drilling

and reaming operations.

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Lathe Bed

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Carriage: -the carriage consists of so many parts that serve to

support the cutting tool and control the action of the cutting tool. It

can be moved along the bed ways provided at the top of the bed.

Lathe centers: -these are tapered components fit in to spindles

provided in the tail stock and head stock. The center fitted to the tail

stock is called dead center which supports the work piece and that

connected to the head stock is called live center since it will rotate

along with the spindle.

Tool post: -tool post is mounted on the carriage to hold the cutting

tool and enable the cutting tool to be adjusted to a convenient

position.

Lead screw: -this is a long threaded shaft used for cutting threads

and to give automatic movements to carriage and cross slide to

achieve the tool movements in the longitudinal and lateral

directions with respect to the bed.

Principal parts of a Lathe

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Compound Rest & Tool Post

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Chucks

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Holding & Turning job

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Various operations performed on lathe Facing

facing is the operation of producing flat end surface that is normal to the axis of rotation.

While facing cutting tool is moved right angles to the axis of rotation and the cutting edge must be set at the same height at the centre of the work.

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TURNING

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Drilling: Drilling is a process used extensively by which through or

blind holes are originated or enlarged in a work piece.

This process involves feeding of a cutting tool (drill) into a

rotating work piece fixed on a chuck.

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Boring

It is the operation of enlarging the previously drilled hole

with the aid of single point cutting tool called boring tool.

The feed is given parallel to the axis of revolution.

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REAMING

The process of making a hole smoothly and

accurately, holes may be reamed by a straight

shank or taper shank reamer.

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Thread Cutting (Internal & External)

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Knurling

The process of indentation of various forms on

cylindrical work surfaces, a knurl tool is held in tool

post and pressed against the rotating work piece with a

cross slide and then it is fed for required length with the

carriage.

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Chamfering

It is the beveling or turning at the end of the work

piece.

This operation is done to remove burrs from the end of

work piece.

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Drilling Machine

189 190

Shaper It is reciprocating type of machine tool used for producing flat surfaces. Surfaces may be horizontal, vertical or inclined.

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Working Principle of a Shaper

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Machining

vertical surfaces: Machining

horizontal surfaces:

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Milling Operations

Milling is the removal of metal by feeding the work

past a rotating multi toothed cutter.

In this operation the material removal rate (MRR) is

enhanced as the cutter rotates at a high cutting speed.

The surface quality is also improved due to the multi

cutting edges of the milling cutter.

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195

Milling Cutters

The action of the milling cutter is totally different from that

of a drill or a turning tool.

In turning and drilling, the tools are kept continuously in

contact with the material to be cut.

whereas milling is an intermittent process, as each tooth

produces a chip of variable thickness.

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UP MILLING DOWN MILLING

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1.Face milling

2. Side milling

3.End milling

4.T-slot milling

5.Angular milling

6.Form milling

7.Gear cutting

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Grinding Machine

The process of metal removal by a rotating abrasive

wheel is called grinding.

The wheels are made of abrasive materials called

silica, bauxite, mixed with the bonding material and

casting in the form of wheels of different diameters

and shapes.

The feed is given to the work while the wheel rotates.

199 200

Surface Grinding Machine

work

201 202

Computer Integrated Manufacturing • Computer-integrated manufacturing (CIM), integrates the

software and hardware needed for computer graphics,

computer-aided modelling and computer-aided design and

manufacturing activities, from initial product concept through its

production and distribution in the marketplace.

• This comprehensive and integrated approach began in the 1970s

and has been particularly effective because of its capability of

making possible the following tasks:

Responsiveness to rapid changes in product design modifications

and to varying market demands.

Better use of materials, machinery, and personnel.

Reduction in inventory.

Better control of production and management of the total

manufacturing operation.

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Computer Integrated Manufacturing

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Elements in CIM 1. Computer numerical control (CNC).

First implemented in the early 1950s, this is a method of

controlling the movements of machine components by the direct

insertion of coded instructions in the form of numerical data.

2. Adaptive control (AC).

The processing parameters in an operation are automatically

adjusted to optimize the production rate and product quality and to

minimize manufacturing cost. For example, machining forces,

temperature, surface finish, and the dimensions of the part can be

constantly monitored; if they move outside the specified range, the

system adjusts the appropriate variables until the parameters are

within the specified range. 205

Elements in CIM 3. Industrial robots.

Introduced in the early 1960s, industrial robots have rapidly been

replacing humans, especially in operations that are repetitive,

dangerous, and boring. As a result, variability in product quality is

decreased and productivity improved. Robots are particularly

effective in assembly operations, and some (intelligent robots) have

been developed with sensory perception capabilities and movements

that simulate those of humans.

4. Automated materials handling.

Computers have made possible highly efficient handling of

materials and components in various stages of completion (work in

progress), as in moving a part from one machine to another, and

then to points of inspection, to inventory, and finally, to shipment. 206

Elements in CIM 5. Automated assembly systems.

These systems continue to be developed to replace assembly by

human operators, although humans still have to perform some

operations. Assembly costs can be high, depending on the type of

product; consequently, products are now being designed so that

they can be assembled more easily, and faster by automated

machinery, thus reducing the total manufacturing cost.

6. Computer-aided process planning (CAPP).

By optimizing process planning, this system is capable of

improving productivity, product quality, and consistency and hence

reducing costs. Functions such as cost estimating and monitoring

world standards (time required to perform a certain operation) are

also incorporated into the system.

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Elements in CIM 7. Just-in-time production (JIT).

The principle behind JIT is that

(1)supplies of raw materials and parts are delivered to the

manufacturer just in time to be used,

(2)parts and components are produced just in time to be made

into subassemblies, and

(3)products are assembled and finished just in time to be

delivered to the customer.

As a result, inventory carrying costs are low, defects in components

are detected right away, productivity is increased, and high-quality

products are made at low cost.

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Elements in CIM 8. Group technology (GT).

The concept behind group technology is that parts can be grouped

and produced by classifying them into families according to

similarities in design and the manufacturing processes employed

to produce them. In this way, part designs and process plans can

be standardized and new parts (based on similar parts made

previously) can be produced efficiently and economically.

9. Cellular manufacturing (CM).

This system utilizes workstations that consist of a number of

manufacturing cells, each containing various production machines

controlled by a central robot, with each machine performing a

different operation on the part, including inspection.

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Elements in CIM 10. Flexible manufacturing systems (FMS).

These systems integrate manufacturing cells into a large production

facility, with all of the cells interfaced with a central computer.

Although very costly, flexible manufacturing systems are capable of

producing parts efficiently, but in relatively small quantities, and of

quickly changing manufacturing sequences required for different

parts. Flexibility enables these systems to meet rapid changes in

market demand for all types of products.

11. Expert systems (ES).

Consisting basically of complex computer programs, these systems

have the capability of performing various tasks and solving difficult

real-life problems, much as human experts would, including

expediting the traditional iterative process in design optimization. 210

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Elements in CIM 12. Artificial intelligence (AI).

Computer-controlled systems are now capable of learning from

experience and of making decisions that optimize operations

and minimize costs, ultimately replacing human intelligence.

13. Artificial neural networks (ANN).

These networks are designed to simulate the thought processes

of the human brain, with such capabilities as modelling and

simulating production facilities, monitoring and controlling

manufacturing processes, diagnosing problems in machine

performance, and conducting financial planning and managing

a company’s manufacturing strategy.

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Lean Production

Lean production is a methodology that involves a

thorough assessment of each activity of a company, with

the basic purpose of minimizing waste at all levels and

calling for the elimination of unnecessary operations that

do not provide any added value to the product being

made.

This approach, also called lean manufacturing, identifies

all of a manufacturer’s activities from the viewpoint of the

customer and optimizes the processes used in order to

maximize added value.

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Lean Production • Lean production focuses on

(a) The efficiency and effectiveness of each and every

manufacturing operation,

(b) The efficiency of the machinery and equipment used, and

(c) The activities of the personnel involved in each operation.

This methodology also includes a comprehensive

analysis of the costs incurred in each activity and

those for productive and for non productive

labour.

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Lean Production • The lean production strategy requires a fundamental

change in corporate culture, as well as an

understanding of the importance of cooperation and

teamwork among the company’s workforce and

management.

• Lean production does not necessarily require cutting

back on a company’s physical or human resources;

rather, it aims at continually improving efficiency and

profitability by removing all waste in the company’s

operations and dealing with any problems as soon as

they arise.

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Agile Manufacturing • The principle behind agile manufacturing is ensuring agility

and hence flexibility-in the manufacturing enterprise, so that

it can respond rapidly and effectively to changes in product

demand and the needs of the customer.

• Flexibility can be achieved through people, equipment,

computer hardware and software, and advanced

communications systems.

• As an example of this approach, it has been predicted that

the automotive industry could configure and build a car in 3

days and that, eventually, the traditional assembly line will

be replaced by a system in which a nearly custom made car

will be produced by combining several individual modules.

215

Agile Manufacturing

• The methodologies of both lean and agile production

require that a manufacturer benchmark its operations.

• Benchmarking involves assessing the competitive

position of other manufacturers with respect to one’s

own position (including product quality, production

time, and manufacturing cost) and setting realistic

goals for the future.

• Benchmarking thus becomes a reference point from

which various measurements can be made and to

which they can be compared.

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Environmentally Conscious

Manufacturing • An inherent feature of virtually all manufacturing processes is

waste. The most obvious examples are material removal

processes, in which chips are removed from a starting work piece

to create the desired part geometry. Waste in one form or another

is a by-product of nearly all production operations.

• Another unavoidable aspect of manufacturing is that power is

required to accomplish any given process. Generating that power

requires fossil fuels, the burning of which results in pollution of

the environment.

• At the end of the manufacturing sequence, a product is created

that is sold to a customer. Ultimately, the product wears out and

is disposed of, perhaps in some landfill, with the associated

environmental degradation. 217


Manufacturing

• More and more attention is being paid by society to the

environmental impact of human activities throughout the

world and how modern civilization is using our natural

resources at an unsustainable rate.

• Global warming is presently a major concern. The

manufacturing industries contribute to these problems.

• Environmentally conscious manufacturing refers to

programs that seek to determine the most efficient use of

materials and natural resources in production, and

minimize the negative consequences on the environment.

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Manufacturing • Other associated terms for these programs include green

manufacturing, cleaner production, and sustainable

manufacturing.

• They all boil down to two basic approaches:

(1) design products that minimize their environmental impact,

(2) design processes that are environmentally friendly.

• Product design is the logical starting point in environmentally

conscious manufacturing.

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Design For Environment (DFE) • The term design for environment (DFE) is sometimes used for the

techniques that attempt to consider environmental impact during

product design prior to production.

• Considerations in DFE include the following:

(1) select materials that require minimum energy to produce,

(2) select processes that minimize waste of materials and energy,

(3) design parts that can be recycled or reused,

(4) design products that can be readily disassembled to recover the parts,

(5) design products that minimize the use of hazardous and toxic materials,

(6) give attention on how the product will be disposed at the end of its useful

life.

• To a great degree, decisions made during design dictate the materials

and processes that are used to make the product. These decisions limit

the options available to the manufacturing departments to achieve

sustainability. 220

Design For Environment (DFE) • However, various approaches can be applied to make plant

operations more environmentally friendly. They include the

following:

(1) adopt good housekeeping practices—keep the factory clean,

(2) prevent pollutants from escaping into the environment (rivers and

atmosphere),

(3) minimize waste of materials in unit operations,

(4) recycle rather than discard waste materials,

(5) use net shape processes,

(6) use renewable energy sources when feasible,

(7) provide maintenance to production equipment so that it operates at

maximum efficiency,

(8) invest in equipment that minimizes power requirements. 221

Organization for Manufacture

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THE END

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