BME Module 5

7/25/2019 BME Module 5

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ENGINEERING MATERIALS

METALS

A metal is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and

has good electrical and thermal conductivity. Metals are generally malleable that is, they can be

hammered or pressed permanently out of shape without breaking or cracking as well as fusible

(able to be fused or melted) and ductile (able to be drawn out into a thin wire). About 91 of the

118 elements in the periodic table are metals (some elements appear in both metallic and non-

metallic forms).

ALLOYS

An alloy is as a material that's made up of at least two different chemical elements, one of which

is a metal. The most important metallic component of an alloy (often representing 90 percent or

more of the material) is called the main metal, the parent metal, or the base metal. The other

components of an alloy (which are called alloying agents) can be either metals or nonmetals and

they're present in much smaller quantities (sometimes less than 1 percent of the total).

Most engineering metallic materials are alloys. Metals are alloyed to enhance their properties,

such as strength, hardness or corrosion resistance, and to create new properties, such as shape

memory effect.

ENGINEERING

MATERIALS

METALS PLASTICS CERAMICS COMPOSITES

METALS

FERROUS

METALS

AMORPHOUS

METALS

NON FERROUS

METALS


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FERROUS METALS AND ALLOYS

Ferrous metals are those which contain iron. They can be a mixture of other metals or elements,

but all ferrous materials contain some form of iron which give them a magnetic quality and

makes them prone to corrosion. Ferrous metals include caste iron and steel.

FERROUS

METAL

CAST

IRONSTEEL

CAST IRON

WHITE

CAST IRON

GREY CAST

IRON

MALLEABLE

CAST IRON

NODULAR

CAST IRON

STEEL

MILD STEEEL OR

LOW CARBON

STEEL

MEDIUM

CARBON STEEL

HIGH CARBON

STEEL

HIGH SPEED

STEELSTAINLESS

STEEL


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FERROUS MATERIAL

MATERIAL APPLICATION

Cast ironA strong metal when it is in

compression. It is verybrittle material. It is 93%iron and 1.75% to 4.3%

carbon with other elements.

Car brake discs, car cylinder, metal work vices, machinery bases,

manhole covers.

Mild steel or low carbon

steel0.15% to 0.45% carbon. A

ductile and malleable metal.

Mild steel will rust quicklyif tit is in frequent contact

with water.

Nuts and bolts, car body, building girders, gates etc.

Medium-carbon steel

0.45% to 0.8% carbon.High tensile strength and

ductility, despite its

brittleness when compared

to other forms of steel.

Axle shafts, crank shafts, and gearing plates, railway wheels, rails,

structural beams.

The ductility of the steel allows it to be formed into thin shafts ortoothed plates without losing any of its tensile strength.


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High carbon steel

Contains carbon 0.8% to

1.5%. Very hard and strong

steel that has a high

resistance to abrasion.

Hand tools as screw drivers, hammer, chisels , saws, springs and

garden tools.

High speed steel

HSS is a steel containing

high content of tungsten,vanadium and chromium.

Highly brittle. Highresistance to wear.

Drill bits, lathe cutting tools. It is used where high speed and high

temperature is used.

Stainless steel

It is an alloy of iron with atypical 18% chromium, 8%

nickel and 8% magnesium.

It is very resistant to wear,corrosion and rust.

Kitchen sinks, teapots, cookwares and surgical instruments.


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NON-FERROUS METALS

Non-ferrous metals are the opposite of ferrousthey do not contain any iron. They will not have

a magnetic quality and typically resist corrosion much better than ferrous metals. The category of

non-ferrous metals also includes raw materials pure metals. Aluminum, copper, aluminum

alloys, lead, tin are all considered non-ferrous metals.

MATERIAL APPLICATION

Aluminium-It can be polished to a mirror like

appearance. It is light in weight.

Saucepan, cooking foil, window frames,

ladders, expensive bicycles.

CopperA ductile and malleable metal. It is

red/brown colour. It is a good conductor of

heat and electricity.

Plumbing, electric components, cookware and

roof coverings.
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Zinc Very resistant to corrosion from

moisture. Mainly used for coating steel.

Used as a coating on screws, steel buckets. It is

used to galvanize steel.

Tin Very ductile and malleable metal.

Resistant to corrosion from moisture. It is

bright silver in appearance. Tinplates are steel

with a tin coating.

Coating on beer cans, food cans, tin foil,

whistles and soldering.

Lead soft malleable metal. It is counted as

one of the heavy metals. Lead has a bluish

white colour after being cut fresh, but it soon

tarnishes to a dull grayish colour when exposed

to air.

Roof flashing, used for batteries, for protection

of X ray protection.


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NON FERROUS ALLOYS

Brass copper and 4 to 45% zinc alloy.

Colour of brass varies from dark reddish brown

to light silvery yellow. It is stronger and harder

than copper but not as strong as steel. Easy to

form into shapes, a good conductor of heat and

generally resistant to corrosion from salt water.

Water fittings, screws, radiators, musical

instruments, catridge for firearms.

Bronze copper and 12% tin alloy.Hard and

brittle material. Very high resistance tocorrosion.

Ship propellers, under water fittings, statues

and medals.

Gunmetal

88% Copper, 10% zinc and 2%tin. Hard alloy with high wear resistance. Automobile body parts, gun barrels, pi[pefittings.

Solder Tin and lead alloy. It is fusible metal

alloy used to join meal work pieces.

Electronis, plumbing, jewelry and repair

process where metal parts cannot be effectivelywelded.


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Duralumin- Aluminium, 4% copper, 0.5%

magnesium, 0.5% manganese and 0.5 silicon.It is a light weight material and corrosion

resistant.

Construction & Equipment,Containers

& Packaging, Automotives, Aerospace

AMORPHOUS METALS

Metallic Glasses or Amorphous Metals are inorganic mixtures fused at high temperatures

which solidify on cooling, but do not crystallize. These materials consist of very rapidly cooled

molten alloys which are not given time to crystallize before solidification. The alloys vary

slightly in composition but most contain about 92% iron, 3% boron and 5% silicon by weight.

In an amorphous material, similar to glass, the atoms are not arranged in any ordered structure.

Rather, they have a tightly-packed, yet random arrangement.

Because there are no structured planes of atoms in an amorphous material, the atoms are

gridlocked into the glassy structure, making the movement of groups of atoms very difficult. Oneconsequence of this atomic gridlock is that some amorphous metals are very hard and have very

high stiffness and a very high elastic modulus. The combination of hardness and elasticity of

amorphous material is an important factor in its many applications.


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Application

Using soft magnetic cores made from amorphous metal alloys reduces energy loss in electrical

transformers by up to 85 percent.

tennis racket, razor blades that last much longer, coatings in refineries and oil pipes, armor,phone casings, anti-theft devices, and fine jewelry, such as watches and rings.

BEHAVIOUR

AND

PROPERTIES OF

MATERIALS

STRUCTURE OF

MATERIALS

ATOMIC BONDS

CRYSTALLINE

AMORPHOUS

PARTLY CRYSTALLINE

POLYMER CHAINS

MECHANICAL

PROPERTIES

STRENGTH

STIFFNESS

ELASTICITY

PLASTICITY

DUCTILITY

BRITTLENESS

MALLEABILTY

TOUGHNESS

RESILENCE

CREEP

FATIGUE

HARDNESS

PHYSICAL AND

CHEMICAL PROPERTIES

DENSITY

MELTING POINT

SPECIFIC HEAT

MAGNETIC PROPERTIES

ELECTRICAL

CONDUCTIVITY

THERMAL

CONDUCTIVITY

THERMAL EXPANSION

CORROSSION

PROPERTY

MODIFICATION

HEAT TREATMENT

ALLOYING

COMPOSITES

REINFORCEMENT

LAMINATES

FILLERS


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THE IMPORTANT MECHANICAL PROPERTIES OF METALS

I. Strength.It is the ability of a material to resist the externally applied forces without breaking

or yielding.

2. Stiffness. It is the ability of a material to resist deformation under stress. The modulus of

elasticity is the measure of stiffness.

3. Elasticity.It is the property of a material to regain its original shape after deformation n the

external forces are removed. This property is desirable for materials used in tools and machines.

It may be noted that steel is more elastic than rubber.

4. Plasticity. It is property of a material which retains the deformation produced under load

permanently. This property of material is necessary for forgings, in stamping images on coins,

and in ornamental work.

5. Ductility. It is property of a material enabling it to be drawn into wire with the application i\e

force. The ductile materials commonly used in engineering practice (in order of diminishing

duct1ility) are mild steel, copper, aluminium, nickel, zinc, tin and lead.

6. Brittleness.It is the property of a material opposite to ductility. It is the property of breaking

of a material with little permanent distortion. Cast iron is a brittle material.

7. Malleability.It is a special case of ductility which permits materials to be rolled or hammered

into thin sheets. A malleable material should be plastic but it is not essential to be so strong.

Malleable materials commonly used in engineering practice (in order of diminishingmalleability) lead. soft steel, wrought iron, copper and aluminium.

8. Toughness. It is the property of a material to resist fracture due to high impact loads like

hammer blows. The toughness of a material decreases when it is heated. This property is

desirable in parts subjected to shock and impact loads.

9. Resilience.It is property of a material to absorb energy and to resist shock and impact loads. It

is measured by the amount of energy absorbed per unit volume within elastic limit. This property

is essential for spring materials.

10. Creep.When a part is subjected to a constant stress at high temperature for a long period of

time, it will undergo a slow and permanent deformation called creep. This property is considered

in designing internal combustion engines, boilers and turbines.

II. Fatigue.When a material is subjected to repeated stresses, it fails at stresses below yield point

stresses. Such type of failure of a material is known as fatigue. The failure is caused b) means of


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a progressive crack formation which are usually fine and microscopic size. This property

considered in designing shafts, connecting rods, springs, gears etc.

12. Hardness.It is a very important property of the metals and has a wide variety of meanings It

embraces many different properties such as resistance to wear, scratching, deformation and

machine ability etc. It also means the ability of a metal to cut another metal.

PLASTICS

Plastics are materials containing synthetic or semi synthetic organics. They can be molded to

diverse shape when heated and then hardened. They are synthetic and mostly derived from

petrochemicals, but many are partially natural. The first fully synthetic plastic is Bakelite.

THERMOSETTI NG PLASTICS OR THERMOSETS

Plastics which cures irreversibly, That sis they hardened permanently when cooled. They cannot

be reheated and melted to another shape. That is they can be shaped only once.

Epoxy resin, Polyester resin, Phenolic resin.

ApplicationAdhesives, electrical insulation, handles, control knobs, bonding materials.

THERMOSOFTENI NG PLASTICS AND TH ERMOPLASTICS

These are plastics that do not undergo chemical change in their chemical composition when

heated. They are molded above a specific temperature and solidifies on cooling. They can be

molded again and again.

PLASTICS

THERMOSETTING

OR

THERMOSETS

THERMOSOFETENING

OR

THERMOPLASTICSELASTOMERS


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Polyethylene, Propelyne, Poly vinychloride (PVC), Polystyrene

ApplicationWash basins, chairs, toys, bottles, medical equipments, kitchen equipments.

ELASTOMERS

Rubbery material composed of polymers that are capable of recovering their original shape after

being stretched.

Poly isoprene (Natural rubber)gaskets, shoe heels

Poly eurethene - in textile industry for elastic clothing, foams

Poly butadiene - tyres for vehicles because of extraordinary wear resistance.

Neoprene - wet suits, industrial belts

CERAMICS

Nonmetallic substances made by inorganic compounds like oxides, carbides and nitrides. It has;

high refractoriness, poor load carrying capacity, high brittleness and poor machinabilty.

ApplicationPottery, tiles, refractory materials, glass.

COMPOSITE MATERIAL

These are materials produced by combining two or more materials together having superior

properties.

Wood is a natural composite where as concrete and plywood are artificial composites.

Application fiber glass door, automobile parts, semiconductors, electrical and electronic

components.

For BMW M3 model the Al bumper is replaced by a glass/polymide material. A weightreduction from 7 kg to 3.1 kg is realized. The crash performance increased 3 to 4 times than a

metal beam.


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MANUFACTURING PROCESS

Materials are converted into finished products though different manufacturing processes.

Manufacturing processes are classified into shaping [casting], forming, joining, and coating,

dividing, machining and modifying material property.

METHODS OF MANUFACTURING

CASTING:

In casting process the components are manufactured by pouring molten metal such as cast iron,

aluminium, brass etc. into moulds prepared in molding boxes by wooden or metal patterns.

A mould is formed into the geometrical shape of a desired part. Molten metal is poured into the

mold; the mold holds the material in shape it solidifies. A metal casting is created. The mold

contains a delivery system for the molten material to reach the mold cavity.

MOULD:

A mould is defined as the negative print of the part to be cast and is obtained by the pattern in

moulding boxes into which molten metal is poured and allowed to solidify.

TYPES OF MOULDS

1. Temporary moulds

These moulds are destroyed at the removing of casting from them e.g, green sand moulds.


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2. Permanent moulds

These moulds are used in die casting. These moulds are used for long time. E.g, metallic moulds.

PATTERN

Patterns are objects by which the interior cavities of the mold where the molten metal solidifies

are formed by impression. It is a geometrical replica of the metal casting to be produced. Patterns

are formed by wood or metals like aluminium, steel or cast iron.

GATING SYSTEM


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Main parts of Gating System

Pouring basin: It is also known as pouring cup. Molten metal is poured through the

pouring basin.

Sprue: The sprue takes molten metal from the pouring basin to the runner.

Runner: The runner carries molten metal to the gate. Gate: The molten metal entries the mould through the gate.

Riser: Riser is a passage. After the mould is filled up with molten metal rises into the

riser and comes to the top.

TYPES OF SAND MOULDING

GREEN SAND MOULDI NG

Green sand is by far the most diversified molding method used in current metal castingoperations. The green sand process utilizes a mold made of compressed or compacted moist sand

packed around a wood or metal pattern. The term "green" denotes the presence of moisture in the

molding sand, and indicates that the mold is not baked or dried.

STEPS IN GREEN SAND MOLDING

For green sand molding a two piece pattern is used.

One half of the pattern is placed on a molding board.

The drag box is placed around the pattern 20mm layer of facing sand is first

placed around the pattern.


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Then the drag box is filled up with green sand.

Ramming is done by hammer.

After completing the ramming process the excess sand is removed by strike off

bar.

Vent holes are made.

Then the drag box is tilted upside down.

Parting sand is applied on the upper side to prevent two pieces of pattern from

sticking to each other.

Cope box is placed correctly in position on the drag box.

Sprue pin and riser pin are placed in position.

Then the cope box is filled up with molding sand and ramming is done.

Vent holes are made; sprue pin and riser pin are removed.

Cope box and drag box are separated.

The pattern pieces are removed slowly and gate is cut to mould.

Repair works are done in mould if necessary.

Surfaces of the mould are coated with graphite to give smooth surface to the

casting. The two moulds are assembled in correct position.

A pouring weight is placed. Now the mould is ready for pouring.

Advantages

Most ferrous / non-ferrous metals can be used.

Low Pattern & Material costs.

Almost no limit on size, shape or weight of part.

Adaptable to large or small quantities Used best for light, bench molding for medium-sized castings or for use with production

molding machines.

Disadvantages

Low design complexity. Lower dimensional accuracy.

DRY SAND MOLDI NG

The step by step procedure of making dry sand mould is the same as that of green sand molding.

The only difference is that after making the mould it is heated. The heating is done by oxy-

acetylene flame for large moulds. Small moulds are heated in ovens.

Application:


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Dry sand moulds are used for large castings such as engine cylinders, engine blocks.

Advantages:

Dry sand mould is stronger than green sand mould.

Dimensional accuracy of dry sand mould is high as compared with green sand mould. Dry sand moulds are coated with wax therefore surface finish is more.

Disadvantages

This type of molding is much more expensive than green sand molding and is not a high-production process. Correct baking (drying) times are essential.

SHEET METAL OPERATIONS

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used

in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday

objects are constructed of the material. Sheet metal processes can be broken down into two major

classifications and one minor classification

Shearing processes -- processes which apply shearing forces to cut, fracture, or separate

the material.

Forming processes-- processes which cause the metal to undergo desired shape changes

without failure, excessive thinning, or cracking. This includes bending and stretching.

SHEET METAL CUTTING OR SHEARING OPERATION

The cutting or shearing operations are conducted to convert the shape of the sheet to that of the

pattern. The different types of shearing operations are

1. Cutting off: It is the process of cutting a piece from a sheet metal .The cut is made along

a straight line for removing a piece. With each cut a new part is produced.


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2. Parting: Separating a part from the remaining sheet, by punching away the material

between parts. Parting is less efficient than cut as it results in wastage of materials.

3. Blanking: It is the process of cutting out a metal strip of required shape from a work

usually called blank. The metal blanked out through the die is the required product. The

sheet metal left on the die is the scrap. The cut out shape is called blank. Punches are

used for this purpose.

4. Punching:It is a piercing operation. This is the operation of making circular holes on the

sheet. Punches are used for this purpose.


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5. Notching: This is the process of removing metal to the desired shape from the edge of

the sheet. Notching die and punch is used for this purpose.

6. Slitting: This is a process of cutting along a number of parallel lines to form the sheet by

using snips. Slitting is a type of metal cutting process where large rolls, or coils, of sheet

metal stock are cut using extremely sharp rotary blades. In metal slitting, straight lines are

cut lengthwise into the large coil to create strips of metal that are narrower in width.

7. Trimming: This is the operation of cutting away the excess metal from a formed part to

establish shape by snips or chisel.

8. Lancing: Lancing is the operation of cutting an interior section of the sheet metal without

removing the section then bending the cut portion. Lancing leaves an opened metal tab.


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METAL FORMING PROCESSES

Bending

Bending is a non-cutting operation. This operation is carried out in a press. It is a process of

plastically deforming the metal sheet along a line.

Bending should be done perpendicular to the direction of the grains. If bending is done parallel

to the grains, cracks will develop. Bending operation can be performed only in ductile materials.

Air bending is the most common type of3 types of bending used in sheet metal shops today. In

this process the work piece comes in contact with the outside edges of the die, as well as the

punch tip. The punch is then forced past the top of the die into the v-opening without coming

into contact with the bottom of the v. Because the punch tip does not need to be forced past the

surface of the metal much less tonnage is required to bend.
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Seaming involves bending the edges of two parts over on each other. As the bends are locked

together each bend helps resists the deformation of the other bend, providing a well joint

structure.

Stretching

Stretch forming is a metal forming process in which a piece of sheet metal is stretched and bent

simultaneously over a die in order to form large contoured parts. Ductile materials are preferable,the most commonly used being aluminum, steel, and titanium.

Stretch forming is performed on a stretch press, in which a piece of sheet metal is securely

gripped along its edges by gripping jaws. Stretch formed parts are typically large and possess

large radius bends. The shapes that can be produced vary from a simple curved surface to

complex non-uniform cross sections.

Stretch forming is capable of shaping parts with very high accuracy and smooth surfaces.

Typical stretch formed parts are - large curved panels such as door panels in cars or wing panels

on aircraft, window frames and enclosures.


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Deep drawing

Deep drawing is a metal forming process in which sheet metal is stretched into the desired part

shape. A tool pushes downward on the sheet metal, forcing it into a die cavity in the shape of the

desired part. The tensile forces applied to the sheet cause it to plastically deform into a cup-

shaped part. Deep drawn parts are characterized by a depth equal to more than half of the

diameter of the part.

These parts can have a variety of cross sections with straight, tapered, or even curved walls, but

cylindrical or rectangular parts are most common. Deep drawing is most effective with ductile

metals, such as aluminum, brass, copper, and mild steel.

Examples of parts formed with deep drawing include automotive bodies and fuel tanks, cans,

cups, kitchen sinks, and pots and pans.

Spinning or Spin forming

Spinning, sometimes called spin forming, is a metal forming process used to form cylindrical

parts by rotating a piece of sheet metal while forces are applied to one side. A sheet metal disc is

rotated at high speeds while rollers press the sheet against a tool, called a mandrel, to form the

shape of the desired part. Spun metal parts have a rotationally symmetric, hollow shape, such as

a cylinder, cone, or hemisphere.

Examples include cookware, hubcaps, satellite dishes, rocket nose cones, and musical

instruments.


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Spinning is typically performed on a manual or CNC lathe and requires a blank, mandrel, and

roller tool. The blank is the disc-shaped piece of sheet metal that is pre-cut from sheet stock and

will be formed into the part.

Roll forming

Roll forming, sometimes spelled roll forming, is a metal forming process in which sheet metal is

progressively shaped through a series of bending operations. The process is performed on a roll

forming line in which the sheet metal stock is fed through a series of roll stations.

Each station has a roller, referred to as a roller die, positioned on both sides of the sheet. The

shape and size of the roller die may be unique to that station, or several identical roller dies may

be used in different positions. The roller dies may be above and below the sheet, along the sides,

at an angle, etc.

As the sheet is forced through the roller dies in each roll station, it plastically deforms and bends.

Each roll station performs one stage in the complete bending of the sheet to form the desired

part.


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Typical roll formed parts include panels, tracks, shelving, etc. These parts are commonly used in

industrial and commercial buildings for roofing, lighting, storage units, and HVAC applications.

FORGING

Forgingis the process by which metal is heated and is shaped by plastic deformation by suitably

applying compressive force. Usually the compressive force is in the form of hammer blows using

a power hammer or a press.

Forging refines the grain structureand improves physical propertiesof the metal. With proper

design, the grain flow can be oriented in the direction of principal stresses encountered in actual

use. Grain flow is the direction of the pattern that the crystals take during plastic deformation.

Physical properties (such as strength, ductility and toughness) are much better in a forging than

in the base metal, which has, crystals randomly oriented.

The forging process is very important in industrial metal manufacture, particularly in extensive

iron and steel industry.


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FORGING OPERATIONS:

1: Drawing:

This is the operation in which metal gets elongated with a reduction in the cross section area. For

this, a force is to be applied in a direction perpendicular to the length axis.
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2: Up setting:

This is applied to increase the cross sectional area of the stock at the expense of the length. Toachieve the length of upsetting force is applied in a direction parallel to the length axis, For

example forming of a bolt head.

3: Bending:

Bending is very common forging operation. It is an operation to give a turn to metal rod or plate.This is required for those which have bends shapes.

4: Punching:

It is a process of producing holes. The molten plate is placed over the hollow cylindrical die by

pressing the punch over the plate, the hole is made.
http://4.bp.blogspot.com/_2_P6uqc8P3w/TN0esiM_DTI/AAAAAAAAAGg/polq0Cv20DI/s1600/punching.bmphttp://1.bp.blogspot.com/_2_P6uqc8P3w/TN0bixHo8CI/AAAAAAAAAGc/G82Cgc0uMWg/s1600/bending.bmp


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5: Forged welding:

Forge welding is a solid-state welding process that produces a weld by heating the work pieces to

welding temperature and applying blows sufficient to cause permanent deformation at the faying

surface. It is a solid state process whereby the melting temperature is not reached.

Mighty hammer blows cause permanent deformation and assure metallurgical contact between

two elements to be welded together.

6: Cutting:

It is a process in which a metal rod or plate cut out into two pieces, with the help of chisel and

hammer, when the metal is in red hot condition.

7: Swaging:

Swaging is a process that is used to reduce or increase the diameter of tubes and/or rods.

This is done by placing the tube or rod inside a die that applies compressive force by hammering

radially. This can be further expanded by placing a mandrel inside the tube and applying radial

compressive forces on the outer diameter. Thus, the inner diameter can be a different shape, for

example a hexagon, and the outer is still circular.


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Blanking

Blanking is a metal fabricating process, during which a metal work piece is removed from the

primary metal strip or sheet when it is punched. The material that is removed is the new metal

work piece or blank.
http://www.advantagefabricatedmetals.com/blanking.htmlhttp://www.advantagefabricatedmetals.com/blanking.html


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ROLLING PROCESS

In rolling operation the work piece material is deformed plastically by compressive forces

between two constantly spinning rolls. These forces act to reduce the thickness of the metal and

affect its grain structure. In addition to reducing the thickness of the work, the rolls also act to

feed the material as they rolls in opposite directions to each other. Friction is therefore an

important part of the rolling operation.

TYPES OF ROLLING

Hot rolling:

Hot rolling is the process of rolling a metal above its recrystallization temperature. The rolling

mills are driven by an electric motor of up to 20 MW capacities.

Cold rolling

Cold rolling is a process of rolling metals and alloys below their recrystallization temperature.

Generally they are worked at room temperatures. Cold rolling does not reduce the thickness of a

work piece as much as hot rolling.

Comparison between cold and hot rolling

Sl. No Hot rolling Cold rolling

1Metal is heated above the

recrystallization temperature.

Metal is heated below the recrystallization

temperature.

2Higher coefficient of friction between

the rollers and work.

Less coefficient of friction between the

rollers and work piece.

3Heavy reduction in area can be

obtained.

Heavy reduction in area cannot be obtained.

4Mechanical properties are improved. Hardness increases, brittleness increases,

ductility decreases.


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5 Roller radius is larger. Smaller rollers are used.

6Surface finish is not good. Good surface finish and dimensional

tolerance.

7 Higher machines are used. Heavy machines are used.

TYPES OF ROLLING MILLS

1. Two high roll mill:

In two high rolling mills two equal sized rollers are used. These two rollers rotate in opposite

direction. The space between the rolls can be adjusted by raising or lowering the upper roll. A

series of reduction can be made by the same set of rolls, by passing the work back and forth.

2. Three high roll mill

This type of rolling mill consists of three equal sized rollers. The upper and lower rollers are

driven by electric motor and the middle roller rotates by friction. The direction of rotation of

upper and lower rollers is the same.


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3. Four high roll mill

The four high rolling mill consists of two working rollers and two backing rollers. The function

of the working rollers is to apply pressure on the work piece. The backup rollers are used to

prevent the deflection of the small rollers. This extremely rigid set up is usually used for cold

rolling high strength material to very thin width.

4. Cluster roll mill

The working rollers are driven by electric power. The backup rollers support the work piece.It is

a special type of four high rolling mill in which each of the two working rolls is backup by two

or more of the larger backup rolls for rolling hard in materials. It may be necessary to employ

work rolls of a very small diameter but of considerable length. In such cases adequate of the

working rolls can be obtained by using a cluster mill.


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POWDER METALLURGY

1.

Powder production

a. Atomising Process


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In this process the molten metal is forced through an orifice into a stream of high velocity air,

steam or inert gas. This causes rapid cooling and disintegration into very fine powder particles

and the use of this process is limited to metals with relatively low melting point.

b.

Gaseous Reduction

This process consists of grinding the metallic oxides to a fine state and subsequently, reducing it

by hydrogen or carbon monoxide. This method is employed for metals such as iron, tungsten,

copper, etc.

c. Electrolysis Pr ocess

In this process the conditions of electrode position are controlled in such a way that a soft spongy

deposit is formed, which is subsequently pulverized to form the metallic powder. The particle

size can be varied over a wide range by varying the electrolyte compositions and the electrical

parameters..

For example, for the production of copper powder, copper sulphate solution is the electrolyte.

Copper plate forms the anode and aluminum plate is used as cathode. When current is passed

copper deposited on the aluminum cathode plate. After a definite time the cathode plate is

scraped.

d. Mechanical Al loying

In this method, powders of two or more pure metals are mixed in a ball mill. Under the impact ofthe hard balls, the powders are repeatedly fractured and welded together by forming alloy under

diffusion.


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2. Mixi ng of powders (Blending)

This can often involve the introduction of alloying additions in elemental powder form or the

incorporation of a pressing lubricant.

a. Blending imparts uniformity in the shapes of the powder particles,

b. Blending facilitates mixing of different powder particles to impart wide ranging physical and

mechanical properties,

c. Lubricants can be added during the blending process to improve the flow characteristics of the

powder particles reducing friction between particles and dies.

d. Binders can be added to the mixture of the powder particles to enhance the green strength

during the powder compaction process.

3.

Forming of the mixed powder in to a compact

Compaction is carried out by pouring a measured amount of metallic powder into the die cavity

and applying pressure by means of one or more plungers. To improve uniformity of pressure and

reduce porosity in the compacted part, compressive forces from both the top and the bottom sides

are necessary.

The compaction exercise imparts the following effects.

a. Reduces voids between the power particles and enhance the density of the consolidated

powder,

b. Produces adhesion and bonding of the powder particles to improve green strength in the

consolidated powder particles,

c. Facilitates plastic deformation of the powder particles to conform to the final desired shape of

the part,

4.

Sintering of the compact to enhance in tegri ty and strength

This process step involves heating of the material, usually in a protective atmosphere, to a

temperature that is below the melting point of the major constituent. Sintering facilitates thebonding action between the individual powder particles and increase in the strength of the final

part.


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5. Secondary operations

The application of finishing processes to the sintered part. In the Powder Metallurgy industry,

such processes are often referred to as secondary operations.

Advantages

Efficient material utilization

Enables close dimensional tolerancesnear net shape possible

Good surface finish

Manufacture of complex shapes possible

Hard materials used to make components that are difficult to machine can be

readily madetungsten wires for incandescent lamps

Parts with controlled porosity can be made

No material is wasted as scrap

Bimetallic products can be produced

Limitations

High cost of powder material & tooling


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Less strong parts than wrought ones

Less well known process

Powder metallurgy is not economical for small scale production

The density is not uniform throughout the products

The size of the products is limited , large components require heavy press

Application

Parts like self-lubricating bearings, filters, oil pump gears etc.

Brake linings and motor brushes

Nozzles used in rocket and missiles can be produced.

SOLDERING

Solderingis defined as the process of joining two pieces of metals using a filler metal, known as

solder, having a low melting point below the melting point of the work piece.

It is often confused with welding but the difference between them is, in soldering the work piece

is not melted, they are joined using a filler metal, but in welding work piece is joined by

melting. Soldering is accomplished with temperature under 400C

To achieve a sound soldered joint, the following should be considered:

Pre-cleaning: The surfaces must be thoroughly cleaned to allow the solder to wet the basemetal.

Fluxing: A flux must be provided to remove traces of surface film or oxides and to

prevent formation of oxides during the soldering operation.

Proper fixtures or alignment of parts must be maintained to insure a sound soldered joint.

Heating of the base metals should be uniform or even on base metals, to insure good

penetration of the filler alloy into the joint.


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The filler metal used is known as solder. It is an alloy of Tin and Lead (60% 40%).

The purpose of the flux is to clean the surface. Soldering flux removes the film of oxides from

the metal and makes the solder and metal more able to dissolve in each other.

BRAZING

Brazingis also a metal-joining process. Brazingis when a filler metal or alloy is heated to its

melting temperature above 450C.

It is then distributed in liquid form between two or more close-fitting parts by capillary action.

The filler metal is then brought slightly above its melting temperature. It then interacts with a

thin layer of the base metal (known as wetting) and is then cooled quickly. This forms a sealed

joint.

Brazed joints are generally stronger than the individual filler metals that have been used to make

them.

Basic steps in brazing

1. Ensure fit and clearance

2. Clean metal

3. Flux prior to brazing

4. Fixturing of parts

5. Brazing the assembly

6.

Cleaning the new joint

The flux applied is generally borax. The filler metal used is an alloy of cu and zn, known as

speltor.
http://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Celsius


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Advantages

It's easy to learn.

You can join virtually any dissimilar metals.

The bond line can be very neat in appearance.

Joint strength is strong enough for most non-heavy-duty use applications

The essential difference between brazing and soldering is the:

a. Types of filler materials

c. Melting temperature of the filler metals

d. Melting temperature of the fluxes

WELDING

Welding is a process of joining metallic components with or without application of heat, with orwithout pressure and with or without filler metal.

Types of welding:

Welding processes can be broadly classified into (i) fusion welding, and (ii) solid state welding

Fusion welding:

In fusion-welding processes, heat is applied to melt the base metals. In many fusion welding

processes, a filler metal is added to the molten pool during welding to facilitate the process and

provide strength to the welded joint.

When no filler metal is used, that fusion welding operation is referred to as autogenous weld.

Types: Arc welding, Resistance welding, Oxyfuel gas welding, electron beam welding, laser

welding.

1.

Arc welding:

It is a fusion welding process in which the melting and joining of metals is done by the heat

energy generated by the arc between the work and electrode.

An electric arc is generated when the electrode contacts the work and then quickly separated to

maintain the gap. A temperature of 5500C is generated by this arc.

This temperature is sufficient to melt most of the metals. The molten metal, consisting of base

metal and filler, solidifies in the weld region. In order to have seam weld, the power source

moves along the weld line.


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Two types of electrodes are used:

Consumable and non-consumable electrodes.

The consumable electrode is consumed by the arc during the welding process and added to the

weld joint as filler metal whereas non consumable electrodes are not consumed during weld.

Filler metal must be supplied by means of a separate wire that is fed into the weld pool.

Arc shielding:

Shielding gas:

This covers the arc, electrode tip and weld pool from external atmosphere. The metals being

joined are chemically reactive to oxygen, nitrogen, and hydrogen in the atmosphere.

So the shielding is done with a blanket of gas or flux, or both, which inhibit exposure of the

weld metal to air.

Common shielding gas: Argon, Helium

Flux

is used mainly to protect the weld region from formation of oxides and other unwanted

contaminants, or to dissolve them and facilitate removal.

During welding, the flux melts and covers the weld region giving protection and it should be

removed by brushing as it is hardened.

Additional function, other than giving protection: stabilize the arc, and reduce spattering


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2. Resistance welding:

In this operation, electric resistance is generated to the flow of current that generates heat energy

between two contacting surfaces that are held in pressure.

3. Gas welding:

Oxyfuel gas welding is a welding operation in which heat is generated by a hot flame generated

mixture gas of oxygen and acetylene. This heat is used to melt base material and filler material,

if used.

4. Electron beam welding:

In this process, welding is carried out by highly focused, high intensity electron beam

bombarding against the work piece.

Generally carried out in vacuum, otherwise there will be disruption of electron beam by air

molecules.

5. Laser beam welding (LBW)

LBW is a fusion welding process in which joining/coalescence is attained by the heat energy of a

highly concentrated, coherent light beam focused on the joint to be welded.LB welds are of

high quality, deep penetrated.

6. Thermite (thermit):

A mixture of aluminum powder and iron oxide that produces an exothermic reaction when

ignited.

In thermit welding, the heat for coalescence/joining is produced by superheated molten metal

formed from the chemical reaction of thermit.

The following chemical reaction is seen when a thermit mixture is ignited at 1300C. The

temperature of the reaction is 2500C.

8Al + 3Fe3O4= 9Fe + 4Al2O3+ heat

At this temperature, superheated molten iron plus aluminum oxide is made that floats on the top

as a slag and protects the iron from the atmosphere.

Solid State Welding:

In this method, joining is done by coalescence resulting from application of pressure only or a

combination of heat and pressure. In solid state welding, joining of materials are performed with

the help of heat and pressure or pressure alone.


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A metallurgical bond is created with little or no melting of the base metals. To metallurgically

bond two similar or dissimilar metals, the two metals must be brought into intimate contact so

that their atomic forces attract each other.

Even if heat is used, the temperature in the process is less than the melting point of the metals

being welded (unlike in fusion welding). No filler metal is utilized.

The two surfaces must be cleaned and free of oils, dirt, chemical films, gases etc. to permit

atomic bonding.

1.

Dif fusion welding:

Two part surfaces are held together under pressure at elevated temperature and the parts join by

solid state diffusion.

2. Fri ction welding/Stir welding:

The heating is accomplished by friction between the tool and the work piece and plastic

deformation of work piece. The localized heating softens the material.

3. Ul trasonic welding:

Moderate pressure is applied between the two parts and an oscillating motion at ultrasonic

frequencies is used in a direction parallel to the contacting surfaces.

No Advantages of welding Disadvantages of welding

1 A good weld is as strong as base metal Welding gives harmful radiations, fumes

and spatter.

2 General welding equipment is not costly Welding results in residual stresses and

distortion of work pieces.

3 Portable welding equipments are available Edge preparation of the work pieces isgenerally required before welding.

4 Welding permits considerable freedom indesign

A skilled welder is a must to produce agood welding.

5 A large number of metals/alloys both similar

and dissimilar can be joined by welding

Welding heat produces metallurgical

changes. The structure of the weldedjoint is not the same as that of the parent

metal.


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COMPARISON OF WELDING, SOLDERING AND BRAZING

Sl

No

WELDING SOLDERING BRAZING

1 Welding joints are strongest

joints used to bear the load.Strength of the welded portion of

joint is usually more than the

strength of base metal

Soldering joints are weakest

joints out of three. Not meant tobear the load. Use to make

electrical contacts generally.

Brazing joints are weaker

than welding joints butstronger than soldering

joints. This can be used to

bear the load up to someextent

2 Temperature required is 3800degree Centigrade in Welding

joints

Temperature requirement is upto 450 degree Centigrade in

Soldering joints.

Temperature may go to600 degree Centigrade in

Brazing joints.

3 Work piece to be joined need to

be heated till their melting point.

Heating of the work pieces is

not required

Work pieces are heated

but below their melting

point.

4 Mechanical properties of basemetal may change at the jointdue to heating and cooling. -

between-welding-soldering-and-

brazing

No change in mechanicalproperties after joining. May change in mechanicalproperties of joint but it isalmost negligible.

5 Heat cost is involved and high

skill level is required. -

Cost involved and skill

requirements are very low.

Cost involved and sill

required are in between

others two

6 Heat treatment is generallyrequired to eliminate undesirable

effects of welding.

No heat treatment is required. No heat treatment isrequired after brazing.

7 No preheating of work piece isrequired before welding as it is

carried out at high temperature.

Preheating of work piecesbefore soldering is good for

making good quality joint.

Preheating is desirable tomake strong joint as

brazing is carried out atrelatively low temperature

Documents

BME Module 5