The First Materials (Stone Age and Copper–Stone Age)

Materials have accompanied mankind virtually from the very beginning of its

existence. Among the first materials utilized by man were certainly stone and wood, but

bone, fibres, feathers, shells, animal skin, and clay also served specific purposes.

Materials were predominantly used for tools, weapons, utensils, shelter, and for self-

expression, that is, for creating decorations or jewelry.

Materials have been considered of such importance that historians and other scholars

have named certain ancient periods after the material which was predominantly utilized at

that respective time. Examples are the Stone Age, the Copper–Stone Age, the Bronze Age,

and the Iron Age. The Stone Age, which is defined to have begun about 2.5 million years

ago, is divided into the Paleolithic (Old Stone Age), the Mesolithic (Middle Stone Age),

and the Neolithic (New Stone Age) phases.

Until very recently, the mastery of materials has been achieved mainly by empirical

means or, at its best, by a form of alchemy. Only in the nineteenth and twentieth centuries did

systematic research lead to an interdisciplinary field of study that was eventually named

materials science.

Materials often have to be cut, shaped, or smoothed before they reach their final form

and designation. For this, a tool that is harder than the work piece has to be set in action. As

an example, flint stone having a sharp edge was used by early man for cutting and shaping

other materials such as wood.

The transition, from stone age to metals age did not occur at the same time in all

places of the world. The introduction of metals stretched over nearly 5,000 years, if it

occurred at all, and seems to have begun independently at various locations. Copper, in

particular, played an outstanding role because of its appearance and its relative abundance

(especially after man learned how to smelt it). In short, the stone and copper ages coexisted

for a long time. This led to the Chalcolithic, or Copper–Stone Age.

The exact time when Neolithic man begun to use copper will probably never be

exactly known, but it is believed that this was about 8000 B.C. Copper weapons and utensils

were found in Egyptian graves dating about 5000 B.C. Eventually, native copper and other

metals must have been nearly exhausted. Thus, Neolithic man turned his attention to

new sources for metals, namely, those that were locked up in minerals. A widely used

copper ore is malachite. They smelted copper from malachite.

The Bronze Age

Chalcolithic man was clearly aware of the many useful features of copper that made it

preferable to stone or organic materials for some specialized applications. Among these

properties were its elasticity and particularly plasticity, which allowed sheets or chunks of

copper to be given useful shapes. Chalcolithic man also exploited the fact that copper hardens

during hammering, that is, as a result of plastic deformation. Last but not least, molten copper

can be cast into molds to obtain more intricate shapes. On the negative side, surface oxidation

and gases trapped during melting and casting which may form porosity were probably of

some concern to Chalcolithic man. More importantly, however, cast copper is quite soft and

thus could hardly be used for strong weapons or tools. Eventually, the time had come for a

change through innovation. A new material had to be found. This material was bronze. Cast

bronze has a higher hardness than pure copper without necessitating subsequent hammering.

Naturally, some impurities that were already present in the copper ore

transferred into the solidified copper. Among them were arsenic, antimony, silver, lead,

iron, bismuth and occasionally even tin. These impurities, however, were not present in

sufficient quantities that one could refer to the resulting product as an alloy. Small quantities

of these impurities rarely change the properties of copper noticeably except in the case of

bismuth, which even in small amounts makes copper brittle. The first major and deliberate

addition to copper seemed to have been arsenic (at least in the Middle East). Copper–

arsenic alloys, however, were used only for a limited time. Eventually, it must have been

realized that the fumes which were emitted by the arsenic during smelting killed some metal

smiths. Eventually, tin was found to be the ideal addition to copper which was alloyed in an

optimal proportion of 10 mass–%. This copper-tin alloy is generally referred to as bronze.

The melting temperature of Cu–10% Sn is about 950°C (compared to 1084°C for pure

Cu). The melt flows freely into molds and no problems with gas bubbles, that is,

porosity, are encountered. Most importantly, however, the alloy is hard immediately after

casting and subsequent cooling but can be hardened further by hammering. Finally, copper–

tin is harder and less brittle than copper–arsenic.

Recent archaeological evidence indicates that besides the Mediterranean area

(considered by many westerners to be the ―cradle of civilization‖), independent bronze-

producing centers existed in northern Thailand (Ban Chiang) during the third or fourth

millennium B.C., and additionally in the isolation of China during the Shang dynasty starting

at about 1400 B.C. Excavations at Mehrgarh (today‘s Pakistan) have demonstrated that the

Harappans must have been skilled bronze workers as early as 2300 B.C., applying the lost

wax casting technique, annealing, and riveting. They produced human figurines, vessels,

arrowheads, spearheads, knives, and axes.

The Iron Age

Historians claim that the Iron Age began between 1500 and 1000 B.C. The role of

carbon on the hardness of iron and steel was, however, not recognized for a long time. There

were two more discoveries which were probably made during the first millennium B.C. that

improved the quality of carbonized iron even further. One of them (interestingly enough,

described in Homer‘s Odyssey) involves quenching, that is, a rapid cooling of a red-hot piece

of carbonized iron into cold water (hardening). This procedure hardens the work piece

considerably more, sometimes even to the extent of brittleness. As a result, quenched swords,

tools, and other utensils may have cracked or even shattered. The other discovery which was

made during the end of the first millennium B.C. entailed a short-time reheating of a

previously quenched piece of steel to about 600°C. This procedure, which is known today as

tempering, restores some ductility and relieves the brittleness at the expense of some loss in

hardness.

The time at which iron was first smelted in India is not exactly known. However, iron

production is mentioned in the Rigveda, which is the oldest known Hindu religious book.

Conservative estimates place its origin around 1200 B.C. Other sources claim that iron

smelting in India did not commence before 600 B.C.

The Age of Electronic Materials

Stone Age—Bronze Age—Iron Age—what‘s next? Some individuals have called the

present era the space age or the atomic age.However, space exploration and nuclear

reactors, to mention only two major examples, have only little impact on our everyday lives.

Instead, electrical and electronic devices (such as radio, television, telephone, refrigerator,

computers, electric light, CD players, electromotors, etc.) permeate our daily life to a large

extent. Life without electronics would be nearly unthinkable in many parts of the world.

The present era could, therefore, be called the age of electricity. However, electricity

needs a medium in which to manifest itself and to be placed in service. For this reason, and

because previous eras have been named after the material that had the largest impact on

the lives of mankind, the present time may best be characterized by the name Electronic

Materials Age.

Materials Science and Engineering

Sometimes it is useful to subdivide the discipline of materials science and engi-

neering into materials science and materials engineering subdisciplines. Strictly speaking,

―materials science‖ involves investigating the relationships that exist between the

structures and properties of materials. In contrast, ―materials engineering‖ is, on the basis

of these structure–property correlations, designing or engineering the structure of a material

to produce a predetermined set of properties. From a functional perspective, the role of a

materials scientist is to develop or synthesize new materials, whereas a materials engineer is

called upon to create new products or systems using existing materials, and/or to develop

techniques for processing materials. Most graduates in materials programs are trained to

be both materials scientists and materials engineers.

The structure of a material usually relates to the arrangement of its internal components.

Subatomic structure involves electrons within the individual atoms and interactions with

their nuclei. On an atomic level, structure encompasses the organization of atoms or

molecules relative to one another. The next larger structural realm, which contains large

groups of atoms that are normally agglomerated together, is termed ―microscopic,‖

meaning that which is subject to direct observation using some type of microscope. Finally,

structural elements that may be viewed with the naked eye are termed ―macroscopic.‖

The notion of ―property‖ deserves elaboration. While in service use, all materials are exposed

to external stimuli that evoke some type of response. For example, a specimen subjected to

forces will experience deformation, or a polished metal surface will reflect light. A property

is a material trait in terms of the kind and magnitude of response to a specific imposed

stimulus. Generally, definitions of properties are made independent of material shape and

size.

Virtually all important properties of solid materials may be grouped into six different

categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative. For each

there is a characteristic type of stimulus capable of provoking different responses.

Mechanical properties relate deformation to an applied load or force; examples include

elastic modulus and strength. For electrical properties, such as electrical conductivity and

dielectric constant, the stimulus is an electric field. The thermal behavior of solids can be

represented in terms of heat capacity and thermal conductivity. Magnetic properties

demonstrate the response of a material to the application of a magnetic field. For optical

properties, the stimulus is electromagnetic or light radiation; index of refraction and

reflectivity are representative optical properties. Finally, deteriorative characteristics relate

to the chemical reactivity of materials.

In addition to structure and properties, two other important components are involved in the

science and engineering of materials—namely, ―processing‖ and ―performance‖. With on

how it is processed. Furthermore, a material‘s performance will be a function of its

properties. Thus, the interrelationship between processing, structure, properties, and

performance is as depicted in the schematic illustration shown in Figure

Microstructure

It is the structure of the metal revealed by an optical or electron microscope. Metals and

alloys consists of number of irregularly shaped crystals ( grains which are usually seen by

naked eye. The grains are elongated or rounded, they may be small or large and arranged in

irregular order or randomly.

The term crystal structure is used to describe the average position of atoms within the unit

cell and is completely specified by the lattice type and fractional coordinates of atoms. In

other words crystal structure describes the appearance of material on an atomic (A0-Angstrom

) scale. The term microstructure is used to describe the appearance of material on an nm

(nanometer) scale.

We can safely say microstructure is the arrangement of phases and defects in a material.

A phase is taken to be any part of the material with distinct crystal structure and/or chemical

composition. Different phase in a material are separated from one another by distinct

boundaries.

A defect is taken to mean any disruption to the perfect periodicity of crystal structure.

Crystal structure

Solids are characterized by in compressibility , rigidity and mechanical strength. This

indicates that the atoms , molecules or ions make up solids is closely packed. Thus in solids

we have a well defined molecular, atomic or ionic arrangement.

Crysatlline materials have regular and periodic arrangement.(Long range order)

Amorphous materials have random arrangements

If the atoms or molecules are uniquely arranged in crystalline solid or liquid we call it as a

crystalline structure. A crystal structure possess long range order or symmetry. The main

property of crystal structure is its periodicity. This periodicity is due to arrangement of atoms

/ molecules in the lattice points. The crystal structure as a whole can be considered as the

repetition of unit cell. For a given crystal structure the shape of the unit cell is same but varies

from crystal to crystal.

Material properties

Classes of property

Economic Price and availability, Recyclability

General Physical Density

Mechanical Modulus, Yield and tensile strength, Hardness ,

Fracture toughness, Fatigue strength , Creep strength

Damping

Thermal Thermal conductivity, Specific heat, Thermal expansion

coefficient

Electrical and Resistivity, Dielectric constant, Magnetic permeability

magnetic

Environmental Oxidation, Corrosion, Wear

interaction

Production Ease of manufacture, Joining, Finishing

Aesthetic Colour, Texture , Feel

Classification of engineering materials

Common engineering materials may be classified into one of the following seven groups:

l. Metals (ferrous and non-ferrous) and alloys

2.Ceramics

3.Organic polymers

4.Composites

5.Semiconductors

6.Biomaterials

7.Advanced materials

Metallic materials are broadly of two kinds—ferrous and non-ferrous materials. Ferrous

materials are those in which iron (Fe) is the principal constituent. All other materials are

categorized as non- ferrous materials.

Ferrous Metals

In ferrous materials the main alloying element is carbon (C). Depending on the amount of

carbon present, alloys will have different properties, especially when the carbon content is

either less/higher than l.5%. This amount of carbon is specific as below this amount of

carbon, material undergoes eutectoid transformation, while above that limit ferrous materials

undergo eutectic transformation. Thus, the ferrous alloys with less than l.5% C are termed as

steels and the ferrous alloys with higher than l.5% (2—4%) C are termed as cast irons.

On the basis of the percentage of carbon and their alloying elements present, these can be

classified into the following groups.

Mild Steels: The percentage of carbon in iron ranges from 0.l5% to 0.25%. These are

moderately strong and have good weldability. The production cost of these materials is also

low.

Medium Carbon Steels: These contain carbon between 0.3% and 0.6%. The strength of

these mate- rials is high but their weldability is comparatively less.

High Carbon Steels: These contain carbon varying from 0.65% to 1.5%. These materials get

hard and tough by heat treatment and their weldability is poor. The steel formed in which

carbon content is up to l.5% silica up to 0.5% and manganese up to l.5% along with traces

of other elements is called plain carbon steel.

Cast Irons: The carbon content in these substances varies between 2% and 4%. The cost of

produc-tion of these substances is quite low and these are used as ferrous casting alloys.

Grey Cast Iron: These alloys consist of carbon in the form of graphite flakes, which are

surrounded by either ferrite or pearlite. Because of the presence of graphite, fractured surface

of these alloys looks greyish, and so is the name for them. Alloying addition of Si (1—3% ) is

responsible for decomposition of cementite and also high fluidity. Thus, castings of intricate

shapes can be easily made. Due to graphite flakes, grey east irons are weak and brittle.

However, they possess good damping properties, and thus typical applications include base

structures, bed for heavy machines etc.; they also show high resistance to wear.

White Cast Iron: When Si content is low (< 1%) in combination with faster cooling rates,

there is no time left for cementite to get decomposed, thus most of the brittle cementite

retains. Because of presence of cementite, fractured surface appears white, hence the name.

They are very brittle mid extremely difficult to machine. Hence their use is limited to wear

resistant applications such as rollers in rolling mills. Usually white cast iron is heat treated

to produce malleable iron.

Nodular (or Ductile) Cast Iron: Alloying additions are of prime importance in producing

these materials. Small additions of Mg/Cr to the grey cast iron melt before casting can result

in graphite to form nodules or sphere-like particles. Matrix surrounding these particles can be

either ferrite or pearlite depending on the heat treatment .These are stronger and ductile than

grey cast irons. Typical applications include pump bodies, crank shafts, automotive

components, etc.

Malleable Cast Iron: These are formed after heat treating white cast iron. Heat treatments

involve heating the material up to 800—900°C and keep it for long hours, before cooling it to

room temperature. High temperature incubation causes cementite to decompose and form

ferrite and graphite.Thus, these materials are stronger with appreciable amount of ductility.

Typical applications include railroad, connecting rods, marine and other heavy-duty services.

Non-ferrous Metals

These substances are composed of metals other than iron. However, these may contain iron in

small proportion. Six non-ferrous materials are available in sufficient quantity reasonably at

low cost and used as common engineering metals. These are aluminium, tin, copper, nickel,

zinc, and magnesium. Some other non-ferrous metals, about 14 in number, are produced in

relatively small quantities but these are of vital importance in modern industry. These include

chromium, mercury, cobalt, tungsten. vanadium, molybdenum antimony,cadmium,

zirconium, beryllium, niobium, titanium, tantalum and manganese.

Aluminium alloys: Aluminium alloys have high thermal and electrical conductivities, and

good corrosion resistant characteristics. As Al has FCC crystal structure, these alloys are

ductile even at low temperatures and can be formed easily. However, the great limitation of

these alloys is their low melting point (660°C), which restricts their use at elevated

temperatures. Strength of these alloys can be increased by both cold and heat treatment—

based on these alloys are designated into two groups: cast and wrought. Chief alloying

elements include Cu, Si, Mn, Mg, Zn. Recently alloys of Al and other low-density metals

like Li, Mg, Ti gained much attention as there is much concern about vehicle weight

reduction. Al-Li alloys draw much more attention of metallurgy especially as they are very

useful in aircraft and aerospace industries. Common applications off Al alloys include

beverage cans, automotive pans, bus bodies, aircraft structures etc. Some of the alloys are

capable of strengthening by precipitation, while others have to be strengthened by cold work

or solid solution methods.

Copper alloys: As history goes by bronze has been used for thousands of years. lt is actually

an alloy of Cu and Sn . Usually Cu is Soft ductile , thus hard to machine and has virtually

unlimited capacity for cold work. One special feature of most of these alloys is their

corrosion resistant in diverse atmospheres. Most of these alloys are strengthened by either

cold work or solid solution methods . Common Cu alloys are brass alloys of Cu and Zn

where Zn is substitutional addition (Eg : yellow brass ,cartridge brass, muntz metal, gliding

metal) ; bronze , alloys of Cu and other alloying additions like Sn, Al,Si and Ni. Bronzes are

stronger and more corrosion resistant than brasses .Mention has to be made about Beryllium

Copper alloys which possesses combination of relatively high strength,excellent electrica l

and corrosion properties ,wear resistance ,can be cast ,hot worked and cold worked

.Application of Cu alloys include costume jewlery,coins ,musical

instruments,electronics,springs,bushes,surgical and dental instruments ,radiators etc.

Magnesium Alloys: The most sticking property of Mg is its low density among all structural

metals. Mg has HCP structure thus Mg alloys are difiieult to form at room temperatures.

Hence Mg alloys are usually fabricated by casting or hot working. As in case of Al, alloys are

cast or wrought type, and some of them are heat treatable. Major alloying additions are Al,

Zn, Mn, and rare earths.Common applications of Mg alloys include hand-held devices like

saws, tools, automotive pans like steering wheels, seat frames, electronics like casing for

laptops, earneoders, cell phones, etc.

Titanium Alloys: Ti and its alloys are of relatively low density, high strength, and have very

high melting point. At the same time they are easy to machine and forge. However, the major

limitation is Ti‘s chemical reactivity at high temperatures, which necessitated special

techniques to extract. Thus, these alloys are expensive. They also possess excellent corrosion

resistance in diverse atmospheres,and wear properties. Common applications include space

vehicles, airplane structures, surgical implants, and petroleum and chemical industries.

Refractory Metals: These are metals of very high melting points. For example, Nb, Mo, W,

and Ta. They also possess high strength and high elastic modulus. Common applications

include space vehicles, X-ray tubes, welding electrodes, and where there is a need for

corrosion resistance.

Plastics

Common organic materials are plastics and synthetic rubbers which are termed as organic

polymers. Other examples of organic materials are wood, many types of waxes and

petroleum derivatives. Organic polymers are prepared by polymerization reactions, in which

simple molecules are chemically combined into long chain molecules or three-dimensional

structures. Organic polymers are solids composed of long molecular chains. These materials

have low specific gravity and good strength.

The two important classes of organic polymers are as follows:

l. Thermoplastics.'On heating, these materials become soft and hardened again upon

cooling,e.g., nylon, polythene, etc.

2. Thermosetting plastics: These materials cannot be resoftened after polymerization, e.g.,

urea-formaldehyde, phenol-formaldehyde, etc. Due to cross-linking, these materials are

hard,tough, non-swelling, and brittle. These materials are ideal for moulding and casting into

components. They have good corrosion resistance. The excellent resistance to corrosion. Ease

of fabrication into desired shape and size, fine lustre, light weight, strength, and rigidity have

established the polymeric materials and these materials are fast replacing many metallic

components. PVC (polyvinyl chloride) and polycarbonate polymers are widely used for

glazing. roofing. and cladding of buildings. Plastics are also used for reducing weight of

mobile objects. e.g.. cars. aircraft. and rockets. Polypropylene and polyethylene are used in

pipes and manufacturing of tanks.

Thermo-plastic films are widely used as lining to avoid seepage of water in canals and

lagoons. To protect metal structure from corrosion, plastics are used as surface coatings.

Plastics are also used as main ingredients of adhesives. The lower hardness ofplastic

materials compared with other materials makes them subjective to attack by insects and

rodents. Because of the presence ofcarbon, plastics are combustible. The maximum service

temperature is of the order of 100°C. These materials are used as thermal insulators because

of lower thermal conductivity. Plastic materials have low modulus of rigidity. which can be

improved by addition of filters, e.g., glass fibres. Natural rubber, which is an organic material

of biological origin, is a thermoplastic material. It is prepared from a fluid provided by the

rubber trees. Rubber materials are widely used for tyres of automobiles, Insulation of metal

componenets, toys, and other rubber products.

Timber: Timber is general name of wood. It is composite of cellulose and lignin. Cellulose

fibres are strong in tension and are flexible. Lignin works as a binding material to bind the

fibres and give them stiffness. It has applications in many engineering works and has been

used as common construction. It has advantages over other engineering materials as easily

available, strongest among cellular materials,easy processing, light weight, good surface

finish, and inexpensive.

Abrasive Materials

Abrasives are hard, non-metallic, sharp edged, and irregular shaped materials used to remove

small amount-of. materials by cutting action. It may be used in bonded fomi or as free

particles. lt is employed in grinding, polishing, super finishing, buffing, and honing

operations. Commonly used abrasives are alumina (Al,O3), silicon carbide (SiC), cubic boron

nitride (CBN), and diamond.

Ceramics

Ceramics are compound of metallic and non-metallic materials. lt has properties of high

compressive strength, low thermal expansion, high elasticity, high hardness, high wear

resistance, and lowelectrical and thermal conductivity. Ceramics are used for tiles, pottery,

and sanitary wares (porcelain). The raw materials used for ceramics are clay having fine sheet

like structure. kaolin (silicate of aluminium) used as clay. flint, and feldspar.

Silica

lt is available in abundance in nature in the form of quartz. Most of the glasses contain more

than 50% of silica. It is also used in electric materials to increase the magnetic permeability

of the materials. lt may be used in the form of silicates of various materials such as clay,

asbestos, mica, glasses, etc.

Glasses

lt is a super cooled amorphous material. lt consists of more than 50% silica and other

additives such- as oxides of aluminium,sodium, calcium, magnesium, titanium, lithium, lead,

and potassium. It has applications in windows ,containers, lighting instruments, cookware,

etc. The availability of various types of is soda-lime glass,lead-alkali glass, borosilicate

glass, etc.

Pure metals and alloys

Pure metals have the following physical properties:

High density

High melting and boiling points

Good conductivity of heat and electricity

Malleability

Ductility

Lustrous

Pure metals are made up of one type of atoms in an orderly arranged and closely packed

manner. The forces of attraction between the very closely packed atoms are very strong. But

they are not rigid – when a force is applied the layers of atoms can slide over one another

.Usually they are ductile and malleable.

Alloy is a mixture of two or more elements with a certain composition in which the major

component is a metal. They are stronger, harder, resistant to corrosion, have better finish and

lustrous. Alloys are made to increase the strength hardness of pure metal , increase corrosion

resistance and improve appearance. They are used in the manufacture of statues, war head

parts , rails ,cutting tools , automobile, ship and aeroplanes , ornamental work and handicraft ,

and daily use articles.

Difference between an alloy and composite

Alloys mixes at atomic level or molecular level. Not even an electron microscope would

show you the structure. Composite mixes at physical level. We can see the different materials

with naked eye or a simple magnifying glass.

For making alloy , the procedure is – melt , mix and allow to cool. Composites are more

difficult to make – prepare a mould , apply a resin with a brush soak the materials and allow

to cure. Composites are usually made up of thermosetting or thermoplastic resins ,

reinforcement fillers and additives. A bulk of resin material , known as matrix acts as the glue

, which holds the composite together and will play an important role in defining the property

and characteristics of final composite. A reinforcing material which is usually a fibre form

adds strength and thickness to the bulk material known as reinforcement. The reinforcing

fibre give composites stiffness and excellent strength to weight ratio. Some composites use

particles or sheet materials for their matrix, these composites usually contain ceramics and /

or metals.[GRP , Carbon fibre ,Tungsten carbide ]

Mechanical properties

A steel ruler is easy to bend elastically—‗elastic‘ means that it springs back when released.

Its elastic stiffness (here, resistance to bending) is set partly by its shape—thin strips are easy

to bend—and partly by a property of the steel itself: its elastic modulus, E. Materials with

high E, like steel, are intrinsically stiff; those with low E, like polyethylene, are not. Figure

(b) illustrates the consequences of inadequate stiffness.

The steel ruler bends elastically, but if it is a good one, it is hard to give it a

permanent bend. Permanent deformation has to do with strength, not stiffness. The ease with

which a ruler can be permanently bent depends, again, on its shape and on a different

property of the steel—its yield strength, σy. Materials with large σy, like titanium alloys, are

hard to deform permanently even though their stiffness, coming from E, may not be high;

those with low σy, like lead, can be deformed with ease. When metals deform, they generally

get stronger (this is called ‗work hardening’), but there is an ultimate limit, called the tensile

strength, σts, beyond which the material fails (the amount it stretches before it breaks is called

the ductility). Figure (c) gives an idea of the consequences of inadequate strength.

If the ruler were made not of steel but of glass or of PMMA (Plexiglas, Perspex), as

transparent rulers are, it is not possible to bend it permanently at all. The ruler will fracture

suddenly, without warning, before it acquires a permanent bend. We think of materials that

break in this way as brittle, and materials that do not as tough. There is no permanent

deformation here, so σy is not the right property. The resistance of materials to cracking and

fracture is measured instead by the fracture toughness, KIC. Steels are tough—well, most are

(steels can be made brittle)—they have a high K1c. Glass epitomizes brittleness; it has a very

low KIC. Figure (d) suggests consequences of inadequate fracture toughness.

The property density is , mass per unit volume, symbol ρ. Density, in a ruler, is

irrelevant. But for almost anything that moves, weight carries a fuel penalty, modest for

automobiles, greater for trucks and trains, greater still for aircraft, and enormous in space

vehicles. Minimizing weight has much to do with clever design, but equally to choice of

material. Aluminum has a low density, lead a high one. If our little aircraft were made of

lead, it would never get off the ground at all (Figure (e)). These are not the only mechanical

properties, but they are the most important ones.

Thermal properties

The properties of a material change with temperature. Its strength falls, it starts to

‗creep‘ (to sag slowly over time), it may oxidize, degrade or decompose (Figure 1.3(a)). This

means that there is a limiting temperature called the maximum service temperature, Tmax,

above which its use is impractical. Stainless steel has a high Tmax—it can be used up to

800°C; most polymers have a low Tmax and are seldom used above 150°C.

Most materials expand when they are heated, but by differing amounts depending on

their thermal expansion coefficient, α. The expansion is small, but its consequences can be

large. If, for instance, a rod is constrained, as in Figure 1.3(b), and then heated, expansion

forces the rod against the constraints, causing it to buckle. Railroad track buckles in this way

if provision is not made to cope with it.

Some materials—metals, for instance—feel cold; others—like woods—feel warm. This feel

has to do with two thermal properties of the material: thermal conductivity and heat

capacity. The first, thermal conductivity, λ, measures the rate at which heat flows through the

material when one side is hot and the other cold. Materials with high λ are what you want if

you wish to conduct heat from one place to another, as in cooking pans, radiators and heat

exchangers; Figure (c) suggests consequences of high and low λ for the cooking vessel. But

low λ is useful too—low λ materials insulate homes, reduce the energy consumption of

refrigerators and freezers, and enable space vehicles to re-enter the earth‘s atmosphere.

These applications have to do with long-time, steady, heat flow. When time is limited,

that other property—heat capacity, Cp—matters. It measures the amount of heat that it takes

to make the temperature of material rise by a given amount. High heat capacity materials—

copper, for instance—require a lot of heat to change their temperature; low heat capacity

materials, like polymer foams, take much less. Steady heat flow has, as we have said, to do

with thermal conductivity. There is a subtler property that describes what happens when heat

is first applied. Think of lighting the gas under a cold slab of material with a bole of ice-

cream on top (here, lime ice-cream) as in Figure 1.3(d). An instant after ignition, the bottom

surface is hot but the rest is cold. After a while, the middle gets hot, then later still, the top

begins to warm up and the ice-cream first starts to melt. How long does this take? For a given

thickness of slab, the time is inversely proportional to the thermal diffusivity, a, of the

material of the slab. It differs from the conductivity because materials differ in their heat

capacity—in fact, it is proportional to λ/Cp.

Electrical, magnetic and optical properties

We start with electrical conduction and insulation (Figure (a)). Without electrical conduction

we would lack the easy access to light, heat, power, control and communication that—

today—we take for granted. Metals conduct well—copper and aluminum are the best of those

that are affordable. But conduction is not always a good thing. Fuse boxes, switch casings,

the suspensions for transmission lines all require insulators, and in addition those that can

carry some load, tolerate some heat and survive a spark if there were one. Here the property

we want is resistivity, ρc, the inverse of electrical conductivity kc. Most plastics and glass

have high resistivity (Figure(a))—they are used as insulators—though, by special treatment,

they can be made to conduct a little.

Figure (b) suggests further electrical properties: the ability to allow the passage of microwave

radiation, as in the radome, or to reflect them, as in the passive reflector of the boat. Both

have to do with dielectric properties, particularly the dielectric constant εD. Materials with

high εD respond to an electric field by shifting their electrons about, even reorienting their

molecules; those with low εD are immune to the field and do not respond.

Electricity and magnetism are closely linked. Electric currents induce magnetic fields; a

moving magnet induces, in any nearby conductor, an electric current. The response of most

materials to magnetic fields is too small to be of practical value. But a few—called

ferromagnets and ferrimagnets—have the capacity to trap a magnetic field permanently.

These are called ‗hard‘ magnetic materials because, once magnetized, they are hard to

demagnetize. They are used as permanent magnets in headphones, motors and dynamos. Here

the key property is the remanence, a measure of the intensity of the retained magnetism. A

few others—‗soft‘ magnet materials—are easy to magnetize and demagnetize. They are the

materials of transformer cores and the deflection coils of a TV tube. They have the capacity

to conduct a magnetic field, but not retain it permanently (Figure (c)). For these a key

property is the saturation magnetization, which measures how large a field the material can

conduct.

Materials respond to light as well as to electricity and magnetism—hardly surprising, since

light itself is an electromagnetic wave. Materials that are opaque reflect light; those that are

transparent refract it, and some have the ability to absorb some wavelengths (colors) while

allowing others to pass freely (Figure 1.4(d)).

Density and elastic modulus

Stress causes strain. If you are human, the ability to cope with stress without undue strain is

called resilience. If you are a material, it is called elastic modulus. Stress is something that is

applied to a material by loading it. Strain—a change of shape—is its response; it depends on

the magnitude of the stress and the way it is applied—the mode of loading.

Stiffness is the resistance to change of shape that is elastic, meaning that the material returns

to its original shape when the stress is removed. Strength is its resistance to permanent

distortion or total failure. Stress and strain are not material properties; they describe a

stimulus and a response. Stiffness (measured by the elastic modulus E, defined in a moment)

and strength (measured by the elastic limit σy or tensile strength σts) are material properties.

Stiffness and strength are central to mechanical design, often in combination with the density,

ρ.

Density and elastic moduli reflect the mass of the atoms, the way they are packed in a

material and the stiffness of the bonds that hold them together. There is not much you can do

to change any of these, so the density and moduli of pure materials cannot be manipulated at

all. If you want to control these properties you can either mix materials together, making

composites, or disperse space within them, making foams.

Density

Many applications (e.g. sports equipment, transport systems) require low weight and this

depends in part on the density of the materials of which they are made. Density is mass per

unit volume. It is measured in kg/m3.

Density is measured by ‗double weighing‘ method: the sample is first weighed in air and then

when fully immersed in a liquid of known density. When immersed, the sample feels an

upwards force equal to the weight of liquid it displaces (Archimedes‘ principle1). The density

is then calculated as shown in Figure.

Measurement of Young’s modulus

A way of measuring E is to measure the natural frequency of vibration of a round rod of the

material, simply supported at its ends and heavily loaded by a mass M at the middle (so that

we may neglect the mass of the rod itself). The frequency of oscillation of the rod, f cycles

per second (or hertz), is given by

(

)

where l is the distance between the supports and d is the diameter of the rod. From this,

The Tensile Test: Use of the Stress-Strain Diagram

The tensile test is popular since the properties obtained could be applied to design different

components. The tensile test measures the resistance of a material to a static or slowly applied

force. The strain rates in a tensile test are very small ( ̇ = 10-4

to 10-2

s-1

).A test setup is

shown in Fig. ; a typical specimen has a diameter of 1.263 cm and a gage length of 5 cm. The

specimen is placed in the testing machine and a force F, called the load, is applied. A strain

gage or extensometer is used to measure the amount that the specimen stretches between the

gage marks when the force is applied. Thus, what is measured is the change in length of the

specimen (Δl ) over a particular original length (l0). Information concerning the strength,

Young‘s modulus, and ductility of a material can be obtained from such a tensile test.

The stress and strain relation is commonly shown by means of a stress-strain diagram. These

diagrams are obtained by drawing a graph or curve from the data obtained in a tensile test, in

which an increasing tensile stress is applied to the specimen. There are resulting changes in

length which can be observed and recorded by strain measuring devices.

Properties Obtained from the Tensile Test

Yield Strength : As we apply a low level of stress to a material, the material initially

exhibits elastic deformation. In this region the strain that develops is completely and quickly

recovered when the applied stress is removed. However, as we continue to increase the

applied stress the material begins to exhibit both elastic and plastic deformation. The material

eventually ‗‗yields‘‘ to the applied stress. The critical stress value needed to initiate plastic

deformation is defined as the elastic limit of the material. The proportional limit is defined as

the level of stress above which the relationship between stress and strain is not linear

In most materials the elastic limit and proportional limit are quite close. However, neither the

elastic limit nor the proportional limit values can be determined precisely. Measured values

depend on the sensitivity of the equipment used. We, therefore, define them at an offset strain

value (typically, but not always, 0.002 or 0.2%). We then draw a line starting with this offset

value of strain and draw a line parallel to the linear portion of the engineering stress-strain

curve. The stress value corresponding to the intersection of this line and the engineering

stress-strain curve is defined as the offset yield strength, also often stated as the yield

strength. The 0.2% offset yield strength for gray cast iron is 276 MPa as shown in Figure (a).

Engineers normally prefer to use the offset yield strength for design purposes.

For some materials the transition from elastic deformation to plastic flow is rather abrupt.

This transition is known as the yield point phenomenon. In these materials, as the plastic

deformation begins the stress value drops first from the upper yield point (σ2) [Figure(b)].

The stress value then decreases and oscillates around an average value defined as the lower

yield point (σ1). For these materials, the yield strength is usually defined from the 0.2% strain

offset as shown in Figure (a). The stress-strain curve for certain low-carbon steels displays a

double yield point [Figure(b)].

When we design parts for load-bearing applications we prefer little or no plastic deformation.

As a result we must select a material such that the design stress is considerably lower than the

yield strength at the temperature at which the material will be used. We can also make the

component cross-section larger so that the applied force produces a stress that is well below

the yield strength. On the other hand, when we want to shape materials into components (e.g.,

take a sheet of steel and form a car chassis), we need to apply stresses that are well above the

yield strength.

Tensile Strength : The stress obtained at the highest applied force is the tensile strength

(σTS), which is the maximum stress on the engineering stress-strain curve. In many ductile

materials, deformation does not remain uniform. At some point, one region deforms more

than others and a large, local decrease in the cross-sectional area occurs (Figure 6-8). This

locally deformed region is called a ‗‗neck.‘‘ This phenomenon is known as necking.

Because the cross-sectional area becomes smaller at this point, a lower force is required to

continue its deformation, and the engineering stress, calculated from the original area A0,

decreases. The tensile strength is the stress at which necking begins in ductile materials. With

the reduced area, now less force is necessary for additional deformation. However, since

engineering stress is based on A0, the overall stress decreases after necking. Many ductile

metals and polymers show the phenomenon of necking. In compression testing, the materials

will bulge, thus necking is seen only in a tensile test.

The yield strength of pure metals is smaller. For example, ultra-pure metals have a yield

strength of ≈ (1–10 MPa). On the other hand, the yield strength of alloys is higher. The yield

strength of plastics and elastomers is generally lower than metals and alloys, ranging up to

about (10–100 MPa). Tensile strength of most ceramics is much lower (@100–200 MPa).

The tensile strength of glasses is about ≈ 70 MPa and depends strongly on surface flaws.

Elastic Properties : The modulus of elasticity, or Young’s modulus (E ), is the slope of the

stress-strain curve in the elastic region. This relationship is Hooke’s Law:

Young‘s modulus is a measure of the stiffness of a component. A stiff component, with a

high modulus of elasticity, will show much smaller changes in dimensions if the applied

stress is relatively small and, therefore, causes only elastic deformation. In general, most

engineers view stiffness as a function of both the Young‘s modulus and the geometry of a

component.

Poisson’s ratio, µ , relates the longitudinal elastic deformation produced by a simple tensile

or compressive stress to the lateral deformation that occurs simultaneously:

For many metals in the elastic region the Poisson‘s ratio is typically about 0.3.

The modulus of resilience (Er), the area contained under the elastic portion of a stress-strain

curve, is the elastic energy that a material absorbs during loading and subsequently releases

when the load is removed. For linear elastic behaviour :

=

The ability of a spring or a golf ball to perform satisfactorily depends on a high modulus of

resilience.

Tensile Toughness: The energy absorbed by a material prior to fracturing is known as tensile

toughness and is sometimes measured as the area under the true stress-strain curve (also

known as work of fracture).

Ductility: Ductility measures the amount of deformation that a material can withstand

without breaking. We can measure the distance between the gage marks on our specimen

before and after the test. The percent elongation describes the permanent plastic deformation

before failure (i.e., the elastic deformation recovered after fracture is not included). Note that

the strain after failure is smaller than the strain at the breaking point.

x 100

where is the distance between gage marks after the specimen breaks.

Ductility is important to both designers of load-bearing components and manufacturers of

components (bars, rods, wires, plates, I-beams, fibers, etc.) utilizing materials processing.

Effect of Temperature : Mechanical properties of materials depend on temperature . Yield

strength, tensile strength, and modulus of elasticity decrease at higher temperatures, whereas

ductility commonly increases. A materials fabricator may wish to deform a material at a high

temperature (known as hot working) to take advantage of the higher ductility and lower

required stress. When temperatures are reduced, many, but not all, metals and alloys and

polymers become brittle. Increased temperatures also play an important role in forming

polymeric materials and inorganic glasses. In many polymer-processing operations, such as

extrusion, the increased ductility of polymers at higher temperatures is advantageous. Also,

many polymeric materials will become harder and more brittle as they are exposed to

temperatures that are below their glass temperatures. The loss of ductility played a role in

failures of the Titanic in 1912 and the Challenger in 1986.

Hardness

Another mechanical property that may be important to consider is hardness, which is a

measure of a material‘s resistance to localized plastic deformation (e.g., a small dent or a

scratch)

Brinell Hardness Tests : In Brinell tests, a hard, spherical indenter is forced into the surface

of the metal to be tested. The diameter of the hardened steel (or carbide) indenter is 10.00

mm (0.394 in.). Standard loads range between 500 and 3000 kg in 500-kg increments; during

a test, the load is maintained constant for a specified time (between 10 and 30 s). Harder

materials require greater applied loads. The Brinell hardness number, HB, is a function of

both the magnitude of the load and the diameter of the resulting indentation. This diameter is

measured with a special low-power microscope, utilizing a scale that is etched on the

eyepiece. The measured diameter is then converted to the appropriate HB number using a

chart; only one scale is employed with this technique.

Brinell Hardness Number HB =

[ √ ]

where P is the applied load in kilograms, D is the diameter of the indentor in millimeters, and

d is the diameter of the impression in millimeters. The Brinell hardness has the units of stress

(e.g., kg/mm2)

Impact test

When a material is subjected to a sudden, intense blow, in which the strain rate is extremely

rapid, it may behave in much more brittle a manner than is observed in the tensile test. This,

for example, can be seen with many plastics and materials such a Silly Putty .If you stretch a

plastic such as polyethylene or Silly Putty very slowly, the polymer molecules have time to

disentangle or the chains to slide past each other and cause large plastic deformations. If,

however, we apply an impact loading, there is insufficient time for these mechanisms to play

a role and the materials break in a brittle manner. An impact test is often used to evaluate the

brittleness of a material under these conditions. In contrast to the tensile test, in this test the

strain rates are much higher.

Many test procedures have been devised, including the Charpy test and the Izod test .The

Izod test is often used for plastic materials. The test specimen may be either notched or

unnotched; V-notched specimens better measure the resistance of the material to crack

propagation. In this test, a heavy pendulum, starting at an elevation h0 , swings through its

arc, strikes and breaks the specimen, and reaches a lower final elevation hf . If we know the

initial and final elevations of the pendulum, we can calculate the difference in potential

energy. This difference is the impact energy absorbed by the specimen during failure. For the

Charpy test, the energy is usually expressed in joules (J). The results of the Izod test are

expressed in units of J/m. The ability of a material to withstand an impact blow is often

referred to as the impact toughness of the material. In both tensile tests and impact test, we

are measuring the energy needed to fracture a material. The difference is that, in tensile tests,

the strain rates are much smaller compared to those used in an impact test. Another difference

is that in an impact test we usually deal with materials that have a notch. Fracture toughness

of a material is defined as the ability of a material containing flaws to withstand an applied

load.

STRUCTURE

A close examination of atomic arrangement allows us to distinguish between materials that

are amorphous or crystalline (those that exhibit periodic arrangements of atoms or ions).

Amorphous materials have only short-range atomic arrangements while crystalline

materials have short- and long-range arrangements. In short-range atomic arrangements, the

atoms or ions show a particular order only over relatively short distances. For crystalline

materials, the long-range atomic order is in the form of atoms or ions arranged in a three-

dimensional pattern that repeats over much larger distances (from ≈ > 100 nm to up to few

cm).

Solid materials may be classified according to the regularity with which atoms or ions are

arranged with respect to one another. A crystalline material is one in which the atoms are

situated in a repeating or periodic array over large atomic distances; that is, long-range order

exists, such that upon solidification, the atoms will position themselves in a repetitive three-

dimensional pattern, in which each atom is bonded to its nearest-neighbor atoms. All metals,

many ceramic materials, and certain polymers form crystalline structures under normal

solidification conditions. For those that do not crystallize, this long-range atomic order is

absent; these are noncrystalline or amorphous materials.

Lattice, Unit Cells, Basis, and Crystal Structures

A lattice or space lattice is a collection of points called lattice points that are arranged in a

periodic pattern so that the surroundings of each point in the lattice are identical. A lattice

may be one, two, or three dimensional. In materials science and engineering, we use the

concept of ‗‗lattice‘‘ to describe arrangements of atoms or ions. A group of one or more

atoms, located in a particular way with respect to each other and associated with each lattice

point, is known as the motif or basis. We obtain a crystal structure by adding the lattice and

basis (i.e., crystal structure = lattice + basis).

The unit cell is the subdivision of a lattice that still retains the overall characteristics of the

entire lattice. Unit cells are shown in Figure. By stacking identical unit cells, the entire lattice

can be constructed. There are seven unique arrangements, known as crystal systems, which

can be used to fill up a three-dimensional space. These are cubic, tetragonal, orthorhombic,

rhombohedral (also known as trigonal), hexagonal, monoclinic, and triclinic. Although there

are seven crystal systems, we have a total of 14 distinct arrangements of lattice points. These

unique arrangements of lattice points are known as the Bravais lattices. Lattice points are

located at the corners of the unit cells and, in some cases, at either faces or the center of the

unit cell. Note that for the cubic crystal system we have simple cubic (SC), face-centered

cubic (FCC), and body-centered cubic (BCC) Bravais lattices. Similarly, for the tetragonal

crystal system, we have simple tetragonal and body centered tetragonal Bravais lattices. Any

other arrangement of atoms can be expressed using these 14 Bravais lattices.

Lattice Parameter The lattice parameters, which describe the size and shape of the unit cell,

include the dimensions of the sides of the unit cell and the angles between the sides. In a

cubic crystal system, only the length of one of the sides of the cube is necessary to

completely describe the cell (angles of 900 are assumed unless otherwise specified). This

length is the lattice parameter a (sometimes designated as a0 ). The length is often given in

nanometers (nm) or Angstrom (A0) units, where:

1 nanometer ( nm ) = 10-9

m = 10-7

cm = 10 A0

1 angstrom (A0) = 0.1 nm = 10

-10 m = 10

-8 cm

Cubic Structures

There are three important characteristics of every unit cell. They are the atomic radius, the

co-ordination number and density of packing or atomic packing factor

Average number of atoms per unit cell : In a cubic structure the comer atoms are shared by

8 cells (4 atoms from below and 4 atoms from above). Face atoms are shared by adjacent two

cells and the atoms in the inside are shared by only one cell. In general the average number of

atoms per unit cell can be written as;

=

Where - Total corner atoms in unit cell

Total face atoms in unit cell

Inside or centre atom

Coordination number : It is the number of the nearest equidistant neighbours that an atom

has in an unit cell. The value of which depends on the type of crystal structure.

Density of packing or Atomic packing factor : It is the ratio of the volume occupied by

atoms in a unit cell to the total volume of the unit cell.

Atomic packing factor , APF =

where v is the volume occupied by the atoms in the unit cell and V is the total volume of the

unit cell..

Heat Treatment

Heat treatment is an operation or a combination of operations involving heating and cooling

of metal/alloy in solid state in order to obtain certain desired properties.

Objectives of heat treatment

1. Relieve internal stresses.

2. Improve harness and tensile strength.

3. Refine grains.

4. Improve ductility.

5. Change the electrical and magnetic properties.

6. Improve toughness. .

7. To produce special microstructures to increase rnachinability or corrosion resistance.

Heat treatment process variables

A number of factors influence the heat treatment process.

They are;

1. The temperature to which the metal or alloy is heated.

2. The time period for which the metal or alloy is held at that elevated temperature. It is

called holding time or soaking time.

3. The rate of cooling.

4. The atmosphere surrounding the metal/alloy during the heating process.

5. The quenching (cooling) medium used.

6. The heat treatment process variables are selected depending upon the size, shape of

the component the chemical composition of the component and the final properties

desired.

What is manufacturing?

The word manufacture is derived from two Latin words, manus (hand) and factus

(make);the combination means made by hand.

Manufacturing can be defined as the transformation of raw materials into useful

products through the use of the easiest and least expensive methods. It is not enough,

therefore, to process some raw materials and obtain the desired product. It is, in fact, of major

importance to achieve this goal by employing the easiest, fastest, and most efficient methods.

Manufacturing processes can be classified into five categories:

1. Forming or primary forming processes - processes in which an original shape is

created from a molten or gaseous state, or from solid particles of an undefined shape.

During primary forming processes, cohesion is normally created among particles. Eg :-

casting.

2. Deforming processes - processes that convert the original shape of a solid to

another shape without changing its mass or material composition. During this process,

cohesion is maintained among particles. Eg :-forging , rolling , extrusion etc.

3. Removing processes - processes during which material removal occurs; cohesion among

particles is destroyed. Eg :-Turning , drilling , milling etc

4. Joining processes- processes that unite individual workpieces to make subassemblies or

final products. These include additive processes, such as filling and impregnating of

workpieces; cohesion among particles is increased. Eg :-welding, brazing, soldering,

adhesive bonding, mechanical joining etc.

5. Material properties modification processes - processes that purposely change the

material properties of a workpiece in order to achieve desirable characteristics without

changing its shape. Eg :-shot peening, mechanical coating, carburizing, thermal spraying ,

Vapor Deposition Etc.

History of Manufacturing

The history of manufacturing can be separated into two subjects: (l) man's discovery and

invention of materials and processes to make things, and (2) development of the systems of

production.

Some of the processes casting, hammering (forging), and grinding date back 6000

years or more. The early fabrication of implements and weapons was accomplished more as

crafts and trades than manufacturing as we know it today. The ancient Romans had what

might be called factories to produce weapons, scrolls, pottery and glassware and other

products of the time, but the procedures were largely based on handicraft.

It was during Neolithic period (8000 – 3000 B C) that processes such as the

following were developed;'carving and other woodworking, hand forming and firing of clay

pottery, grinding and polishing of stone spinning and weaving of textiles, and dyeing of cloth.

Origin of casting

Casting describes a family of processes during which the molten metal is

introduced into a mold and then becomes solidified.Casting of metals can be traced back

to around 4000 B C. Gold was the first metal to be discovered and used by the early

civilizations; it was malleable and could be readily hammered into shape at room

temperature. There seemed to be no need for other ways to shape gold. It was the subsequent

discovery of copper that gave rise to the need for casting. Although copper could be forged to

shape, the process was more difficult [due to strain hardening] and limited to relatively

simple forms. Historians believe that hundreds of years elapsed before the process of casting

copper was first performed, probably by accident during the reduction of copper ore in

preparation for hammering the metal into some useful form. Thus, through serendipity, the art

of casting was born. It is likely that the discovery occurred in Mesopotamia, and the

"technology" quickly spread throughout the rest of the ancient world.

Origin of deformation process

Metalworking is a deformation process used to fabricate metal products.The

earliest records of metalworking describe the simple hammering of gold and copper in

various regions of the Middle East around 8000 B.C. The forming of these metals was crude

because the art of refining by smelting was unknown and because the ability to work the

material was limited by impurities that remained after the metal had been separated

from the ore. With the advent of copper smelting around 4000 B.C., a useful method

became available for purifying metals through chemical reactions in the liquid state. Later, in

the Copper Age, it was found that the hammering of metal brought about desirable increases

in strength (a phenomenon now known as strain hardening). The quest for strength spurred

a search for alloys that were inherently strong and led to the utilization of alloys of copper

and tin (the Bronze Age) and iron and carbon (the Iron Age). The Iron Age, which can be

dated as beginning around 1200 B.C., followed the beginning of the Bronze Age by some

1300 years. The reason for the delay was the absence of methods for achieving the high

temperatures needed to melt and to refine iron ore.

Most metalworking was done by hand until the 13th century. At this time, the

tilt hammer was developed and used primarily for forging bars and plates. The machine

used water power to raise a lever arm that had a hammering tool at one end; it was called a

tilt hammer because the arm tilted as the hammering tool was rised. After raising the

hammer, the blacksmith let it fall under the force of gravity, thus generating the forging blow.

This relatively simple device remained in service for some centuries.The development of

rolling mills followed that of forging equipment. Leonardo da Vinci's notebook includes a

sketch of a machine designed in 1480 for the rolling of lead for stained glass windows.

Origin of removing processes

Before the middle of the 18th century, wood was the main material used in

engineering structures. To shape wooden parts, craftsmen used machine tools - the lathe

among them – which were typically constructed of wood as well. The boring of cannons and

the production of metal screws and small instrument parts were the exceptions: these

processes required metal tools. It was the steam engine, with its large metal cylinders and

other parts of unprecedented dimensional accuracy, which led to the first major developments

in metal cutting in the 1760s.At the inception of the steam engine, no machine tool industry

existed. The century from 1760 to 1860 saw the establishment of enterprises devoted to the

production of machine tools.

Origin of Joining processes

Next to mechanical attachment and fastening, which began when humans or,

perhaps, humanoids wedged and later lashed stones into sticks to produce clubs and

spears for hunting, welding is unquestionably the oldest method for joining materials.

Examples of bracelets from prehistoric times have been discovered that were made by

hammering nuggets of gold or silver into rods, forming the rods into circles or segments of a

circle, and then forging the ends together to form a continuous ring. This earliest

welding process is called forge welding.

Miossanof France, in 1881, originated the use of the carbon arc for melting metals.

In Russia, Bernandos applied this arc to the welding of metals in 1887, and shortly

thereafter, Slavianoff experimented with consumable metal electrodes for arc welding. The

first patents for metal-arc welding in the United States were granted in 1889 to

Coffin.Paralleling the emergence and evolution of welding with an electric arc was the

evolution of welding with mixtures of air and organic fuels. Although known and practiced

even in prehistoric times primarily using fanned charcoal fires, it wasn‘t until the

invention of the oxyacetylene blowpipe by Le Chatelier in 1895 that modern torch

welding systems emerged.

Casting

Manufacture of a machine part by heating a metal or alloy above its melting point and

pouring the liquid metal/alloy in a cavity approximately of same shape and size as the

machine part is called casting. After the liquid metal cools and solidifies, it acquires the shape

and size of the cavity and resembles the finished product required. The term casting also

applied to the part that is made by this process. It is one of the oldest shaping processes,

dating back 6,000 years .The department of the workshop, where castings are made is called

foundry.

So the following steps are involved in producing a cast part:

1. Preparing the mould.

2. Preparing the molten metal.

3. Introducing the molten metal into the mould.

4. Solidifying the metal.

5. Removing the piece.

Casting processes are most often selected over other manufacturing methods for the

following reasons (Advantages of casting):

• Casting can produce complex shapes and can incorporate internal cavities or hollow

sections.

• Very large parts can be produced in one piece.

• Casting can utilize materials that are difficult or uneconomical to process by other

means.

• The casting process can be economically competitive with other manufacturing

processes.

Forming

Forming is a basic process in which the workpiece is shaped by compressive forces applied

through various dies and tooling. Forging may be carried out at room temperature (cold

forging) or at elevated temperatures (warm or hot forging) depending on the homologous

temperature;

Homologous temperature =

Where T – Temperature of metal during working

-melting temperature of metal

Metal forming processes, also known as mechanical working processes, are primary

shaping processes in which a mass of metal or alloy is subjected to mechanical forces. Under

the action of such forces, the shape and size of metal piece undergo a change. By mechanical

working processes, the given shape and size of a machine part can be achieved with great

economy in material and time.

Metal forming is possible in case of such metals or alloys which are sufficiently malleable

and ductile. Mechanical working requires that the material may undergo ―plastic

deformation‖ during its processing. Frequently, work piece material is not sufficiently

malleable or ductile at ordinary room temperature, but may become so when heated. Thus we

have both hot and cold metal forming operations.

Many metal forming processes are suitable for processing large quantities (i.e., bulk) of

material, and their suitability depends not only upon the shape and size control of the product

but also upon the surface finish produced. There are many different metal forming processes

and some processes yield a better geometry (i.e., shape and size) and surface-finish than some

others. Cold working metal forming processes result in better shape, size and surface finish as

compared to hot working processes. Hot working results in oxidation and decarburisation of

the surface, formation of scales and lack of size control due to contraction of the work piece

while it cools to room temperature.

Advantages of Mechanical Working Processes

Apart from higher productivity, mechanical working processes have certain other advantages

over other manufacturing processes. These are enumerated below:

1. Mechanical working improves the mechanical properties of material like ultimate tensile

strength, wear resistance, hardness and yield point while it lowers ductility. This phenomenon

is called ―strain hardening‖.

2. It results in grain flow lines being developed in the part being mechanically worked. The

grain flow improves the strength against fracture when the part is in actual use. This is best

explained by taking illustration of a crankshaft. If the crankshaft is manufactured by

machining from a bar of large cross-section, the grain flow lines get cut at bends whereas in a

crankshaft which is shaped by forging (which is a mechanical working process), the grain

flow lines follow the full contour of the crankshaft making it stronger. This is illustrated in

Fig.

Material removal process

The material removal processes are a family of shaping operations in which excess material

is removed from a starting work part so that what remains is the desired final geometry.

There are four types of material removal mechanisms:

• Mechanical - the mechanical stresses induced by a tool surpass the strength of the

material (conventional machining )

• Thermal - thermal energy provided by a heat source melts and/or vaporizes the volume of

the material to be removed

• Electrochemical - electrochemical reactions induced by an electrical field destroy the

atomic bonds of the material to be removed

• Chemical - chemical reactions destroy the atomic bonds of the material to be removed

The most important branch of the family is conventional machining, in which a sharp cutting

tool is used to mechanically cut the material to achieve the desired geometry. The three

principal machining processes are turning, drilling, and milling. The ―other machining

operations‖ include shaping, planing, broaching, and sawing.

Machining is a manufacturing process in which a sharp cutting tool is used to cut away

material to leave the desired part shape. The predominant cutting action in machining

involves shear deformation of the work material to form a chip; as the chip is removed, a new

surface is exposed. Machining is most frequently applied to shape metals.

Machining is important commercially and technologically for several reasons :

Variety of work materials:- Machining can be applied to a wide variety of work materials.

Virtually all solid metals can be machined. Plastics and plastic composites can also be cut by

machining. Ceramics pose difficulties because of their high hardness and - brittleness;

however, most ceramics can be successfully cut by the abrasive machining

Variety of part shapes and geometric features : - Machining can be used to create any

regular geometries, such as flat planes, round holes, and cylinders. By introducing variations

in tool shapes and tool paths, irregular geometries can be created, such as screw threads and

T-slots. By combining several machining operations in sequence, shapes of almost unlimited

complexity and variety can be produced.

Dimensional accuracy: - Machining can produce dimensions to very close tolerances.Some

machining processes can achieve tolerances ( of much more accurate than most

other processes.

Good surface finishes: - Machining is capable of creating very smooth surface finishes.

Roughness values less than 0.4 microns can be achieved in conventional machining

operations. Some abrasive processes can achieve even better finishes.

On the other hand, certain disadvantages are associated with machining and other material

removal processes:

Wasteful of material :- Machining is inherently wasteful of material. The chips generated in

a machining operation are wasted material. Although these chips can usually be recycled, in

terms of the unit operation, the material that is removed is waste.

Time consuming :- A machining operation generally takes more time to shape a given part

than alternative shaping processes such as casting or forging.

Machining is generally performed after other manufacturing processes such as casting or bulk

deformation (e.g., forging).

Joining process

Welding is a materials joining process in which two or more parts are coalesced at their

contacting surfaces by a suitable application of heat and/or pressure. Many welding processes

are accomplished by heat alone, with no pressure applied; others by a combination of heat

and pressure; and still others by pressure alone, with no external heat supplied. In some

welding processes a filler material is added to facilitate coalescence. The assemblage of parts

that are joined by welding is called a weldment. Welding is most commonly associated with

metal parts, but the process is also used for joining plastics. Our discussion of welding will

focus on metals.

Welding is a relatively new process. Its commercial and technological importance

derives from the following:

Welding provides a permanent joint. T'he welded parts become a single entity.

The welded joint can be stronger than the parent materials if a filler metal is used that

has strength properties superior to those of the parents, and if proper welding

techniques are used.

Welding is usually the most economical way to join components in terms of material

usage and fabrication costs. Alternative mechanical methods of assembly require

more complex shape alterations (e.g., drilling of holes) and addition of fasteners (e.g.,

rivets or bolts). The resulting mechanical assembly is usually heavier than a

corresponding weldment.

Welding is not restricted to the factory environment. It can be accomplished ―in the

field.‖

Although welding has the advantages indicated above, it also has certain limitations and

drawbacks (or potential drawbacks):

Most welding operations are performed manually and are expensive in terms of labor

cost. Many welding operations are considered ―skilled trades,‖ and the labor to

perform these operations may be scarce.

Most welding processes are inherently dangerous because they involve the use of high

energy.

Since welding accomplishes a permanent bond between the components, it does not

allow for convenient disassembly. If the product must occasionally be disassembled

(e.g., for repair or maintenance), then welding should not be used as the assembly

method.

The welded joint can suffer from certain quality defects that are difficult to detect.

The defects can reduce the strength of the joint.

Welding processes, in turn, are generally classified into three basic categories:

Fusion welding

Solid-state welding

Brazing and soldering.

Shielded Metal Arc Welding : It is the most commonly used fusion welding process.

Shielded metal arc welding (SMAW) is a process that melts and joins metals by heating

them with an arc established between a sticklike covered electrode and the metals, as shown

in Figure. It is often called stick welding. The electrode holder is connected through a

welding cable to one terminal of the power source and the workpiece is connected through a

second cable to the other terminal of the power source (Figure.a).

The core of the covered electrode, the core wire, conducts the electric current to the arc

and provides filler metal for the joint. For electrical contact, the top 1.5cm of the core wire is

bare and held by the electrode holder. The electrode holder is essentially a metal clamp

with an electrically insulated outside shell for the welder to hold safely.

The heat of the arc causes both the core wire and the flux covering at the electrode tip to melt

off as droplets (Figure.b). The molten metal collects in the weld pool and solidifies into the

weld metal. The lighter molten flux, on the other hand, floats on the pool surface and

solidifies into a slag layer at the top of the weld metal.

Computer Integrated Manufacturing

Since the Industrial Revolution, U.S. industry has been undergoing a process of continuous

development. During the nineteenth century, new machines expanded the productivity of

workers; with the beginning of the twentieth century, new automation technology in the form

of mass production through transfer and assembly lines emerged. Factory manufacturing

grew to include more and more new sectors of work and finally became a composite of

different departments, each separate from the others and dedicated to a certain task. Al-

though automation and computerization of these isolated islands of work have been

increasing steadily since the early 1950s, barriers of understanding and methods of working

have also been growing. Although the number of blue-collar workers on the shop floor has

continually decreased, large numbers of white-collar personnel, ranging from managers to

clerks, have been needed to handle paperwork and to transfer information among the different

departments in order to tie them together. It is, therefore, obvious that automating isolated

tasks in the process of product development, although relatively cost-effective, cannot alone

achieve either significant savings in lead time taken to develop a product or gains in

productivity. It is also clear that these goals can be accomplished only by automating the flow

of information in the business organization and by optimizing the process of product

development as a whole through the adoption of a system's approach.

The solution is complete implementation of computer-integrated manufacturing (CIM).

Figure (a) shows how different departments in a corporation can be electronically channeled

so that each department has immediate access to all other departments as well as to the

mainframe database. This arrangement ensures efficient control of the corporation and,

consequently, optimization of the whole system. On the other hand, Figure (b) illustrates how

companies function , with isolated automated work islands and white-collar workers doing

paperwork to pass information from one department to another. A comparison of these

figures will reveal to us the anticipated benefits of CIM.

An interesting definition of computer-integrated manufacturing (CIM) was given by Eugene

Merchant (the father of the theory of metal cutting):

CIM is a closed-loop feedback system whose prime inputs are product requirements and

product concepts and whose prime outputs are finished products. It comprises a combination

of software and hardware: product design, production planning, production control,

production equipment, and production processes.

A truly integrated CAD/CAM or CIM system provides computer assistance to all business

functions from marketing to product shipment. It embraces what historically have been

classified as "business systems" applications, including order entry, bill of material

processing, inventory control, and material-requirements planning; design automation,

including drafting, design, and simulation; manufacturing planning, including process

planning, routing and rating, tool design, and parts programming; and shop floor applications

such as numerical control, assembly automation, testing, and process automation.

Benefits of CIM

Improved product quality :- Improved product quality is a result of the CIM concept of

developing the product within the computer, thus basing the product development process on

rational and profound analysis instead of today's common philosophy of "build and test."

Prototypes will still be built, but not to find out how a product performs. Instead, they will be

used to verify the results of the analysis carried out by the computer. Other factors that

contribute to improving the product quality and consistency include lower probability of

human error and ensured uniformity of product attributes because of the use of on-line

computer-aided inspection and quality control.

Improved labor productivity :- Automating the information flow will result in a decrease

in indirect labor, while at the same time increasing the efficiency of information transfer and

eliminating redundant data collection. Any decrease in indirect labor will lead to a reasonable

decrease in unit cost because the total costs for a typical highly automated production plant

(in the United States today) are composed of to 6 percent for direct labor, 18 to 22 percent for

overhead and indirect labor, and about 75 percent for materials and machines. Also,

increasing the efficiency of information transfer will result in more effective management.

Improved equipment productivity :- Equipment productivity is improved because of the

better utilization of machines when CIM is implemented. Factors like programmability of

equipment and computerized monitoring and control of the entire manufacturing facility will

largely improve the efficiency of machine utilization.

Lower costs of products :- Higher labor and equipment productivity will certainly result in

lower product cost. This is added to the advantages of designing the product with the required

manufacturing processes in mind (i.e., design for manufacturing), which can easily be

achieved through the integration of CAD and CAM. The use of design for manufacturing

(DFM) will ensure the production of a part through the easiest and cheapest methods, thus

reducing its cost. In fact, it has been found that designs that take into account only the

product and its functions generally create the need for special manufacturing equipment,

leading to a noticeable increase in the production cost.

Increased market share and more profit :- By its very nature, CIM increases the flexibility

of the manufacturing facility, thus enabling it to react quickly to fast-changing market

demands. The reason is that much less lead time is taken to develop a product in a

corporation where CIM is implemented (lead time is the time from the moment at which

design work begins until the moment the product is shipped out of the factory).Also, less lead

time means lower manufacturing cost of the products, which translates into greater

manufacturing flexibility.

A Brief History of Lean Manufacturing

The history of manufacturing is centuries old. Evolutions in manufacturing systems gradually

took place during the last three centuries, which can be broadly classified into three distinct

phases :

Craft production

Mass production

TPS – Lean production

Craft production : During the 19th

and early 20th

centuries , manufacturing was mainly

based on ‗ craft production ‘ in which the products were made by individual artisans or

mechanics. Quality and productivity was totally dependent on the skill and attitude of

individual craftsmen. There was no consistency in quality, costs were high, and delivery

schedules were practically not predictable. Due to these limitations, demand was always

higher than supply. Manufacturers were not able to meet the customer requirements in time.

That compelled industry to evolve into a high volume production system.

Mass production : The first person to revolutionize the production system was Henry Ford

who introduced the assembly line concept in 1913 in the Ford car plant at Highland Park ,

Miami USA. In this plant instead of people, the ‗object under production‘ was moving on a

conveyor and mechanics were stationed at their fixed work station to fix the specific

component in predetermined sequence. This concept was called ‗flow production‘, which

resulted in dramatic improvement in productivity , consistency in quality and reduction of

cost. It worked well until the 1950s, but after world war II , as the buying power of people

increased especially in the developed countries, they wanted varieties according to their

personalized taste. The problem of the Ford system was not the productivity or flow, but lack

of variety and huge inventories.

Toyota Production System : Two great visionaries from Japan ,Kiichiro Toyoda , and

Taiichi Ohno , along with other members of the Toyota Motors Corporation team observed

the limitations of the Ford system. They made innovati,ve improvements in the mass

production system by introducing a large variety of products along with continuity of process

flow in the assembly line. The new TPS in essence shifted the focus of manufacturing from

individual machines and their utilization, to the flow of the product through the total process.

Toyota modified the size of machines and assembly line to produce smaller volumes of

automobiles , but in larger variety. This could be made possible by making machines self-

monitoring to ensure quality and introducing quick changeover system so that each machine

could make small volumes of many components without changeover delays.

Lean production: TPS explained through a unique set of five principles and was named as

Lean by a research team of MIT (Massachusetts Institute of Technology) under the

leadership of Prof. James P. Womack and Prof. Daniel T Jones. It was labeled as ‗lean‘,

because it uses less of everything compared with mass production – half of the human effort

in the factory, half the manufacturing space , half the investment in tools , half the

engineering hours to develop a new product.

Lean manufacturing is a performance-based strategy for maximizing customer value by

elimination of waste , while improving profit for the company.

Mass production versus Lean production

In mass production production planning is based on ―push production‖ developed from

hypothetical sales forecast and companies tend to build inventories in the case they were

needed.

Whereas lean manufacturing works on ―pull production‖ based on the concept that

production can and should be driven by real customer order. Instead of producing what you

hope to sell : lean manufacturing can produce what your customer wants…. with shorter lead

times. Instead of pushing product to market , it is pulled by the customer through a lean

management system.

Benefits of lean Manufacturing

Reduces cost by eliminating wasteful use of resources.

Improves delivery speed by eliminating unnecessary time consuming activities.

Improves quality by eliminating root-causes of defects.

Reduces space requirement by reducing inventory and reengineering layout.

Enhances production capacity of the plant without investment

Concept of value and waste

In any activity of a business process, at any moment of time people are doing only two

things:

Either adding value to product or service through useful activities

Or

Generating waste by doing non-value added activities

Waste is defined as ― any business activity that adds no value but absorb resources‖

As per TPS wastes are classified in seven main categories:

Over production

Excess inventory

Defects

Waiting

Inappropriate processing

Unnecessary motion

Transportation

Untapped human potential ( later o an eighth category was added)

The goal of lean manufacturing is ―to eliminate waste and non-value added steps at all

points in the manufacturing process‖

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 three 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.

Agile manufacturing emerged after lean production yet shares many aspects. Agile

manufacturing can he defined as (1) an enterprise level manufacturing strategy of introducing

new products into rapidly changing markets and (2) an organizational ability to thrive in a

competitive environment characterized by continuous and sometimes unforeseen change.

A study was conducted on 1991 at Lehigh University and identified four principles of agility.

Manufacturing companies that are agile competitors tend to exhibit these principles or

characteristics. The four principles are:

1. Organize to Master Change - An agile company is organized in a way that allows it to

thrive on change and uncertainty. In a company that is agile, the human and physical

resources can be rapidly reconfigured to adapt to changing environment and market

opportunities.

2. Leverage the Impact of People and Information - In an agile company, knowledge is

valued, innovation is rewarded, authority is distributed to the appropriate level of the

organization. Management provides the resources that personnel need. The organization is

entrepreneurial in spirit. There is a "climate of mutual responsibility for joint success'"

3. Cooperate to Enhance Competitiveness-"Cooperation-internally and with other

companies-is an agile competitor's operational strategy of first choice." The objective is to

bring products to market as rapidly as possible. The required resources and competencies (Ire

found and use wherever they exist. This may involve partnering with other companies,

possibly even competing companies.

4. Enrich the Customer--"An agile company is perceived by its customers as enriching them

in a significant way not only itself.'" The products of an agile company are perceived as

solutions to customers' problems. Pricing of the product can be based on the value of the

solution to the customer rather than on manufacturing cost.

As our definition and the list of four agility principles indicate, agile manufacturing involves

more than just manufacturing. It involves the firm's organizational structure, it involves the

way the firm treats its people. It involves partnerships with other organizations, and it

involves relationships with customers. Instead of "agile manufacturing," it might be more

appropriate to just call this new system of doing business "agility:

Environmental Conscious Design and Manufacturing

All over the world, so many millions of passenger cars and tyres are discarded each

year; And so much of are reused in various Ways. Billions of kilograms of plastic

products are discarded each year. Every month industries and consumers discard

enough aluminium to rebuild the country‘s commercial air fleet.

Lubricants and coolants are often used in most manufacturing operations.

Various fluids and solvents are used in cleaning manufactured products; Some of

these fluids pollute the air and Water during their use.

Many by-products from manufacturing plants have been discarded for years (i.e., sand

containing additives used in metal-casting processes; water, oil and other fluids from

heat-treating facilities and from planting operations; slag from foundries and from

Welding operations.)

A variety of metallic and non-metallic scrap, produced in operations such as sheet

forming, casting and molding are discarded.

The effects of these activities, their damage to out environment and to the earth‘s

ecosystem, and, ultimately, their effect on the quality of human life are well

recognized.

The above are the major causes for water and air pollution, acid rain ozone depletion,

the greenhouse effect, hazardous wastes, landfill seepage and global warming.

Many laws have been set in place to help reduce the pollution.

The following environmentally conscious design and manufacturing methods will help to

reduce the ill effects of above

By reducing waste of materials, by refinements in product design and reducing the

amount of materials used

By reducing the use of hazardous materials in products and processes.

By conducting research and development into environmentally safe products and into

manufacturing technologies. ,

By ensuring proper handling and disposal of all waste.

By making improvements in recycling waste treatment and reuse of materials.

Organization for Manufacture

Manufacturing organisation must organize themselves to accomplish the four functions

described in Fig. This figure illustrates the cycle of information-processing activities that

typically occur in a manufacturing firm which produces discrete parts and assembles them

into final products for sale to its customers. The factory operations are pictured in the center

of the figure. The information-processing cycle, represented by the outer ring can be

described as consisting of four functions:

1. Business functions

2. Product design

3. Manufacturing planning

4. Manufacturing control

Business functions

The business functions are the principal means of communicating with the customer. They

are the beginning and the end of the information-processing cycle. Sales and marketing, sales

forecasting, order entry, cost accounting, customer billing and others are included in this

category.

An order to produce a product will typically originate from the sales and marketing

department of the firm. The production order will be one of the following forms:

1, an order to manufacture an item to the customer‘s specifications,

2. a customer order to buy one or more of the manufacturer‘s proprietary products, or

3. an order based on a forecast of future demand for a proprietary product.

Product design

If the product is to be manufactured to customer specifications, the design will be provided

by the customer not by the manufacturer‘s product design department.

If the product is proprietary, the manufacturing firm is responsible for its development and

design. The product design is documented by means of component drawings, specifications,

and a bill of materials that defines how many of each component is required.

Manufacturing planning

The information and documentation that constitute the design of the product flow into the

manufacturing planning function. The departments in the organization that perform

manufacturing Planning include manufacturing engineering, industrial engineering and

production planning and control.

As shown in figure , the information-processing activities in manufacturing planning include

process planning, master scheduling, requirements planning and capacity planning.

Process planning consists of determining the sequence of the individual processing and

assembly operations needed to produce the part. The document used to specify the process

sequence is called a route sheet. The route sheet lists the production operations and

associated machine tools for each component (and subassembly) of the product.

The manufacturing engineering and industrial engineering departments are responsible for

planning the processes and related manufacturing details. The authorization to produce the

product must be translated into the master schedule or master production schedule.

The master schedule is a listing of the products to be made, when they are to be delivered,

and in what quantities. Units of months are generally used to specify the deliveries on the

master schedule.

Based on this schedule, the individual components and subassemblies that make up each

product must be planned. Raw materials must be requisitioned, purchased parts must be

ordered from suppliers, and all of these items must be planned so that they are available when

needed. This whole task is called requirements planning or material requirements planning.

In addition, the master schedule must not list more quantities of products than the factory is

capable of producing with its given number of machines and workers each month. The

production quantity that the factory is capable of producing is referred to as the plant

capacity. Capacity planning is concerned with planning the manpower and machine

resources of the firm.

Manufacturing Control

Manufacturing control is concerned with managing and controlling the physical operations

in the factory to implement the manufacturing plans.

Shop floor control is concerned with the problem of monitoring the progress of the product

as it is being processed, assembled, moved, and inspected in the factory.

The sections of a traditional production planning and control department that are involved in

shop floor control include scheduling, dispatching, and expediting.

Production scheduling is concerned with assigning start dates and due dates to the various

parts (and products) that are to be made in the factory. This requires that he parts be

scheduled one by one through the various production machines listed on the route sheet for

each part.

Based on the production schedule, dispatching involves issuing the individual work orders to

the machine operators to accomplish the processing of the parts.

Even with the best plans and schedules, things sometimes go wrong (e.g., machine

breakdowns, improper tooling, parts delayed at the vendor). The expediter compares the

actual progress of a production order against the schedule. For orders that fall behind, the

expediter attempts to take the necessary corrective action to complete the order on time.

Inventory control attempts to strike a proper balance between the danger of too little

inventory (with possible stock-outs of materials) and the expense of having too much

Inventory.

Shop floor control is also concerned with the materials being processed in the factory (called

work-in-process).

The mission of quality control is to assure that the quality of the product and its components

meet the standards specified by the product designer. To accomplish its mission quality

control depends on the inspection activities performed in the factory at various times

throughout the manufacture of the product. Also raw materials and components from outside

sources must be inspected when they are received. Final inspection and testing of the finished

product is performed to ensure functional quality and appearance.