UNIT- III METAL FORMINGuafulucknow.ac.in/wp-content/uploads/2020/03/... · 2020. 3. 31. · worked...

Lecture Notes on Manufacturing Process (TME-101/201)

Er. Arshad Abbas, Deptt. of Civil Engg., KMCL University, Lucknow

UNIT- III

METAL FORMING

Large group of manufacturing processes in which plastic deformation is used to change the shape

of metal work pieces

The tool, usually called a die, applies stresses that exceed yield strength of metal

The metal takes a shape determined by the geometry of the die.

Forming is defined as a process in which desired shape and size are obtained through the plastic

deformation of material under the action of external force. At elevated temperature plastic

deformation takes place in the material and the new grains are formed at location of internal

stresses by slip or twin deformation. This process of formation of new grain is called

recrytalization and temperature at which new grain are formed is called recrytalization

temperature

Cold working It is defined as the process in which working temperature is lower than recrytalization

temperature of the material. Cold working is performed at low temperature due to which

oxidation and scaling of work material does not take place and then is less reduction of material.

Cold working improves

1. Hardness

2. Yield strength

3. Ultimate strength

4. Fatigue

Advantage of cold working: 1. Good surface finish is obtained

2. Strength, fatigue, and wear properties are improve through strain hardening

3. Directional properties can be achieved

4. High dimensional control is achieved

5. Problem regarding contamination is less

6. Suitable for mass production

Disadvantage of cold working; 1. Heavy and powerful equipment are required

2. High force is required to deform a metal plastically

3. Undesirable and residual stresses are produce

4. Annealing is required to compensate for the loss of ductility

5. Decrease in ductility and creep resistance of metal

6. Distortion in grain structure in metal



Hot working It is defined as a process which working temperature is higher than recrytalization temperature

of the material. Hot working refine the grain structure and improve the mechanical properties

such as elongation, reduction in area, impact strength.

Advantage of hot working:

1. Growth of grain takes place in range of working temperature so proper control of

grain size is possible

2. Due to absence of strain hardening sufficient amount of working can be imparted

3. Elevated temperature reduces the strength and work load so large products and

material of high strength and can be worked under hot condition by using low

tonnage equipments.

4. Due to high ductility of material at high temperature brittle material can be worked

under hot working condition

Disadvantage of hot working

1. Hot working is not used when very accurate dimensional control is required because

of shrinkage and scaling

2. There are some metals which are more brittle at high temperature so cannot be hot

worked

3. At high temperature scaling of surface occurs and poor surface finish obtained

4. Dimensional tolerance are greater than that in cold work metals

5. Structure and properties of metal are not uniform over the entire cross-section

Ex. Hot rolling, Forging, Extrusion etc

Material Properties in Metal Forming

Desirable material properties:

– Low yield strength and high ductility

These properties are affected by temperature:

– Ductility increases and yield strength decreases when work temperature is raised

Other factors:

– Strain rate and friction



Figure- Classification of metal forming process

Rolling Rolling operation

It is a process in which the thickness or cross sectional area of a work piece is reduced by the

action of compressive force. When they are subjected to pass through a set of rolls. As the cross

sectional area of the work piece is reduced, its length is increased in order to compensate the

change in cross sectional area.

Rolling is the most rapid method of forming metal into a desired shape it normally belongs to the

class of Hot working process unless specifically mentioned as cold working. In the hot rolling

processes metal in a hot plastic state is passed between two rolls revolving at the same speed but

in opposite direction (see figure). As the metal passes through the rolls, it is reduced in thickness

and increased in length.

Rolling

Foward Ext

Forging Hot

E on xTrusi Back Ext

Metal Forming

Extrusion

Cold Extrusion

Wire Drawing

Tube Drawing

Impact Ext

Hydraulic

Ext

Drawing



Figure - Rolling process

Figure -Rolling Process showing changes in grain structure

Types of rolling

Two high non-reversing rolling mills/stand

Two high reversing rolling mills/stand

Three high rolling mills/stand

Four high rolling mills/stand

Cluster mills



1. Two high non-reversing rolling mills/stand: - It has rolls positioned with one roll directly

above the other. The rolls are supported in bearings and always move in one direction only.

The upper roll may be raised or lower to adjust the distance between the rolls.

(a) (b)

Figure (a) Two High Non-reversing rolling mills (b) Two High Reversing Rolling Mills

2. Two high reversing rolling mills/stand: - In this rolling stand, direction of rotation of rolls

can be reversed. This arrangement reduces the handling of hot metal in between the rolling

passes, but consumes more power as compared to non-reversing rolling.

3. Three high rolling mills/stand: Three high rolling stands are used to eliminate the need of

reversing the rolls. In this arrangement work piece is feed in between upper and middle rolls

in a direction opposite to the direction of feeding of work piece between lower and middle

rolls, resulting in high rate of production

Figure: Three High reversible Rolling mill.



4. Four high rolling mills/stand: In four high rolling stand backup rolls provides the rigidity

to smaller rolls and prevent their deflection. It is used for hot and cold rolling of wide plates

and sheets.

Figure: Four High rolling mills

Cluster mills:

It consists of two work rolls of smaller diameter and four more backup rolls. Backup rolls

support the smaller work rolls. Foils are always rolled on cluster mills.

Figure: Cluster mill



Cold Rolling:

Cold rolling is generally employed for providing a smooth and bright surface finish to the

previously hot rolled steel. It is also used to finish the hot rolled component to close tolerances

and improve their toughness and hardness. The items generally subjected to cold rolling for this

purpose are bars, rods, sheet, plates, strips, and wires etc. Before being put to cold rolling the hot

rolled articles are cleaned through pickling and other operations. The same types of rolling mills,

describe earlier in connection with hot rolling, are used in cold rolling. In order to obtain a

smooth surface finish the roll surfaces are polished and scratches, if any, removed. The part

being rolled is usually annealed and pickled before the final pass is made, so as to bring it

accurate size and obtain a perfectly clean surface.

Rolling defects

• Undesirable

– Degraded surface appearance adversely affect the strength

• Sheet metal defects include:

– Scale, Rust, Scratches, Gouges, Pits, & Cracks which may be caused by

impurities and inclusions

• Wavy edges are the result of roll bending

• Alligatoring – This usually occurs in rolling of slabs especially of aluminum and

molybdenum alloys where the work piece splits along a horizontal plane at the exit. The

top and bottom parts follow the rotation of their respective rolls

Figure: Rolling Defects



Example of Rolling

Schematic illustration of ring rolling operation. Thickness reduction result in an increase in the part diameter. Another illustration of sheet of foil rolling



FORGING

Forging is manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings.

• Heated metal to be shaped is placed on a mold. Pressure is applied to the metal with the help of a press or hammer and due to this impact the malleable metal conforms

to the

Die cavity shape.

• Extreme pressure is produced when the die halves are closed. The seam of the die

as well as punch acts as a relief valve. Once the metal object is shaped, flashing is

removed

Use of a proper lubricant during the process helps to prevent sticking of the work piece with

the die. It also acts as a thermal insulator and helps the wear and tear on the die

Types of forging process

1. Open Die Forgings or Hand forgings

In this process the forgings are made with the help of repeated blows in an open die. Here the

operator manipulates the work piece in the die during the „blow‟ process, similar to the

traditional manufacturing process used by a blacksmith.

Figure- Open die drop hammer

forging



2. Impression Die Forgings or Precision Forgings

In impression die forging, two dies are brought together, squeezing the metal causing it to fill

the die impression. Depending on the design, metal can be allowed to flow outside of the dies

or can be allotted no escape. The impression die forging process usually requires one hit

through a die cavity for the metal. The impression die forging process relies heavily on the

work of the dies and less on the work of the operator.

Figure- Impression die forging

These forgings are the refined form of blocker forgings. The finished metal part much more

identical to the die impression.



3. Close Die Forging/Flashless forging

Close die or close impression die forging overcomes the limitation of open die forging.

Figure shows typical set of dies. Here the closed impression rather than open face dies are

used. In this process there is a drastic flow of metal in the dies due to repeated hammer blows

on the metal. For products of complicated shapes a preliminary shaping operation using more

than one set of dies may be required. Close die forging also overcomes the problem of flash

formation in impression die forging.

4. Upset Forgings

These forgings increase the cross-section by reducing the length of the metal. The process is

used to make heads on valves, bolts and fasteners, and other similar parts.

Length of the stock to be upset should not be more than two to three times its diameter

otherwise bending of stock occurs. Forging machine can produce 400 to 600 parts/hr.



(a) (b)

5. Roll forging

Figure (a) Upset forging (b) Roll forging

In roll forging thickness of round or flat bar stock is reduced and length is increased. Forging

machine have two cylindrical or semi cylindrical rolls containing one or more grooves to

impart a desired shape to the work piece. Main application of roll forging is to found in leaf

spring, axles, lever, etc.

6. Swaging

It is used to reduce the diameter of the rod or tube to impart a desired shape to the piece. In

swaging die itself act as a hammer and metal is hammered from various angles due to which

metal flows inward and take the shape of die



FORGING OPERATION

1. Drawing out: The operation in which cross-section area reduces and length of

stock increases is known as drawing out operation. In this operation force is to

applied in a direction perpendicular to the length axis

2. Upsetting: The operation in which cross-section area increase and length of

stock reduces is known as upsetting operation. To perform the operation force

applied in a direction parallel to the length axis

3. Heading: heading operation is done at one end of the stock to produce large

cross- section. Head of bolts, nails and screw are formed by heading operation.

4. Fullering: It is the operation of displacing the metal away from centre to

reduce thickness in middle and increase the length

(a) (b) (c)

Figure (a) Fullering, (b) edging and (c) bending operation.

5. Edging: It is the operation in which material is displaced from edge to inside i.e.

between two cup shaped die to create bulge in middle.

6. Bending: In bending operation die are shaped to produce directional change in the

work piece rather than changing the size of section.



FORGING DEFECTS

Main cause due to which defects occurs in forging are improper heating, incorrect die design,

uneven cooling of stock, defect in original metal, improper forging operation, incorrect forging

condition etc. Some common defects found in forging are

1. Cold shut: Cold shut are short cracks. They are caused due to folding of metal

surface against itself during forging. It can be avoided by rounding the sharp corner.

2. Pitting: pitting is caused by scales which is not completely removed from the die

cavities and is worked into the surface of forging. Scale produces shallow depression

on the surface of forging. It can be avoided by cleaning of dies and proper control of

forging.

3. Incomplete penetration of dies: Due to incomplete filling of closed

compression die cavity these defects occurs. It occurs due to many reason such as

poor forging design, poor heating, insufficient no of blows during forging etc.

4. Die shift: Die shift is caused due to upper and lower die misalignment. This defect

is caused due to lose wedges. So wedges should be rigidly fixed.

5. Fins and rags: Fin and rags are small projection or piece of loose metal driven into

the surface of forging. To control this defect proper die design is required.

6. Cracks: Both transverse and longitudinal cracks occur on forging surface. It occurs

due to improper heating of forging, bad quality ingot and improper cooling of alloy

steel.

7. Flakes: Flakes are internal breaks and ruptures caused due to rapid cooling of forging.

8. Hair line cracks: hair line cracks are very fine cracks on the surface of the forging

caused due to rapid cooling of forging and defective metal piece



EXTRUSION Method of forming substances by forcing them through a perforated plate or die to Produce

tubes, rods, or other desired shapes (like squeezing toothpaste out of a tube)

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is

pushed or drawn through a die of the desired cross-section. The two main advantages of this

process over other manufacturing processes are its ability to create very complex cross-

sections and work materials that are brittle, because the material only encounters compressive

and shear stresses. It also forms finished parts with an excellent surface finish.

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-

continuous (producing many pieces). The extrusion process can be done with the material hot

or cold.

Figure-Extrusion Process

What types of materials can be extruded? Metals (aluminum, copper, steel, etc.) plastics (polyethylene, polystyrene, nylon) Foods (typically high starch content)

Examples of products formed by extrusion?

Metals: Automobiles, Food or beverage cans, appliances

Plastics: Pipes, milk cartons, packing peanuts, toys



Extrusion

Hot extrusion Cold Extrusion

Forward/Direct Extrusion

Backward/indirect Extrusion

Impact Extrusion Hydraulic Extrusion

TYPES OF EXTRUSION

Figure-Types of extrusion

Hot Extrusion

Generally done at fairly high temperatures, approximately at 50 to 75 % of the melting point of

the metal. The pressures range from 35-700 MPa (5076 - 101,525 psi). To cool down the high

temperatures and pressures and its adverse effect on the die life as well as other components, good

lubrication is a must. Oil graphite and glass powder is preferred as lubricants.

Application of Hot Extrusion: Aluminum, copper with their alloys is successfully used to manufacture products using hot

extrusion process. Electrical wires, bars and tubes are some of the items produced.

Cold Extrusion Cold extrusion takes place at room temperature or slightly elevated temperatures. This process is

useful for withstanding the stresses created by extrusion.



The advantages of cold extrusion are:

No oxidation process.

Good mechanical properties provided the temperatures created are below the re-

crystallization temperature. Good surface finish

Application of Cold Extrusion: Examples of the metals that can be extruded are copper, lead, tin, aluminum alloys, titanium,

molybdenum, and vanadium, steel. Which are used to make parts like collapsible tubes, gear

blanks, aluminum cans, cylinders etc.

In automobile sector they have found wide applications in Injection technology; Engine control;

Fuel supply; Automatic transmissions Seat technology; Safety systems (restraint systems).

Direct extrusion Direct extrusion is also called forward extrusion and it is the most general extrusion process. Its

work operation includes the placement of the billet in a container, which is heavily walled. Ram or

screw is used to push the billet through the die. In between the billet and ram, there is a dummy

block, which is reusable and is used for keeping them separated.

(a) (b)

Figure (a) Direct extrusion (b) Indirect extrusion

Indirect Extrusion

Indirect extrusion is also called backwards extrusion and in this process, the die is constant whereas

the billet & container move together. To keep the die stationary, a “stem” is used which must be

longer than the length of container. The final and maximum extrusion length is decided



by the stem's column strength. As the billet movement is along with the container, all the

frictional forces are easily eliminated. This results in following advantages:

25 to 30% reduction of friction, allowing extrusion of larger billets, enhanced speed,

and an increased ability to extrude smaller cross-sections

Less tendency for extrusions to crack as no heat formation takes place from friction

Container liner lasts longer, due to less wear

More uniform use of billet ensures that extrusion defects & coarse grained

peripherals zones are less likely

Hydrostatic Extrusion Hydrostatic extrusion is a process in which the billet is completely circumscribed by a pressurized

liquid in all the cases, with the exception being the case where billet is in the contact with die. This

process can be carried out in many ways including warm, cold or hot but due to the stability of

the used fluid, the temperature is limited. Hydrostatic extrusion has to be carried out in a

completely sealed cylinder for containing the hydrostatic medium. The fluid may be pressurized in

following two ways:

1. Constant-Rate Extrusion: A ram or plunger is used for pressurizing the fluid in the

container

2. Constant-Pressure Extrusion: A pump with a pressure intensifier is used for

pressurizing the fluid, which is then pumped into the container

(a) (b)

Figure (a) Hydrostatic Extrusion (b) Impact Extrusion



Impact Extrusion

Impact extrusion is another important way to produce extruded profiles using metals.

Contrary to conventional extrusion, that can only be operational at high temperatures for

softening the material, Impact extrusion typically uses cold metal billets. These billets are

extruded at high pressure. A typical Impact extrusion process works like this. A properly

lubricated slug is put in a die cavity and then struck with a single stroke by a punch. This

forces the metal to flow back around the punch, via an opening between the die and the

punch. The impact extrusion best suits materials that are a bit softer like lead, aluminum or

tin. An impact extrusion process is shown in the image above:



WIRE AND TUBE DRAWING

Drawing is an operation in which the cross-section of solid rod, wire or tubing is reduced

or changed in shape by pulling it through a die.

The principle of this procedure consists of reducing the thickness of a pointed, tapered wire

by drawing it through a conical opening in a tool made of a hard material. The wire will

take shape of the hole. Drawing improves strength and hardness when these properties are

to be developed by cold work and not by subsequent heat treatment.

This process is widely used for the production of thicker walled seamless tubes and

cylinders therefore; shafts, spindles, and small pistons and as the raw material for fasteners

such as rivets, bolts, screws. Drawing is classified as

1. Wire drawing

2. Tube drawing

Wire Drawing:-

Wire drawing is a metal-reducing process in which a wire rod is pulled or drawn through a

single die or a series of continuous dies, thereby reducing its diameter. Because the volume

of the wire remains the same, the length of the wire changes according to its new diameter.

Various wire tempers can be produced by a series of drawing and annealing operations.

(Temper refers to toughness.)

(a)Wire drawing sectional view



(b) Wire Drawing Set Up (c) Enlarge View of Wire Reduction

Process Characteristics

Pulls a wire rod through a die, reducing its diameter

Increases the length of the wire as its diameter decreases

May use several dies in succession (tandem) for obtaining small diameter wires.

Improves material properties due to cold working

Wire temper can be controlled by swaging, drawing, and annealing treatments

Tube Drawing

When a hollow tube is drawn through a die, generally a mandrel or plug is used to support

the inside diameter of the tube, this process is called tube drawing. The function of the plug

is to effect wall reduction and to control the size of the hole. However, the mandrel may be

omitted if it is not necessary to make a reduction in the wall thickness, or if the dimensions

and surface of the inside are not important. The process to draw a pipe without any

mandrel is known as tube sinking.

In drawing tubes over a stationary mandrel, the maximum practical sectional area

reduction does not exceed 40 per cent per pass due to the increased friction from the

mandrel. If a carefully matched mandrel floats in the throat of the die, it is possible to

achieve a reduction in area of 45 percent, and for the same reduction the drawing loads are

lower than for drawing with a fixed plug. This style is called the drawing with floating

plug. It is worth mentioning here that in this style, the tool design and lubrication can be

very critical. Problems with friction in tube drawing



are minimized in drawing with a long mandrel. The mandrel consists of a long hard rod or

wire that extends over the entire length of the tube and is drawn through the die with the

tube. In this design, the area reduction can be 50 per cent. However, after drawing, the

mandrel must be removed from the tube by rolling (reeling), which increases the tube

diameter slightly and disturbs the dimensional tolerances. The drawing process discussed

above has been illustrated in the figure.

Tube drawing processes.

(a) Sinking; (b) fixed plug; (c) floating plug; (d) moving mandrel

Defects in drawing process:

Figure (a) Wrinkling in the flange or (b) in the wall (c) tearing, (d) Earing, (e) surface

scratches

Basic press working Operation

Sheet metal working is also a metal forming operation where the material being worked is

in the form of sheets the working is usually at room temperature. The process is called the

press working of sheet metal. For sheet metal working a set of die and punch assembly is

normally used to obtain various components from a sheet metal.



Die and Punch assembly

A simple die and punch assembly also called die-set is shown in figure. The parts of the die

and punch system are labeled. This assembly is mounted on press.

Figure-Die and Punch Assembly

The press supports a ram (slide) that holds a punch and a bed that holds the die in a die

holder connected to the bolster plate. In sheet metal working operation, the sheet thickness

remains almost constant. The process has the following advantage:

1. The part fabricated are light in weight

2. High labour productivity

3. High efficiency of the process

4. Gives close tolerance

The important characteristic of the sheet material is its formability i.e. its ability to stretch

uniformly (resistance to thinning). Various tests are available to assess the formability of

sheet. Some problem arise out of sheet used being thin, such as spring back. Buckling, and

wrinkling. A proper die design and minimizing the unsupported length during processing

may solve the problem.



Cutting Process (Sheet Metal Working/ Press Working)

A brief introduction of some important sheet- metal working operation is given below:

1. Blanking and Punching: In these processes a finite shape of sheet metal is

removed by shearing the entire contour using a die and a punch. If the portion

removed is the required product, the operation is called Blanking and the product is

called blank. On the contrary, if the pierced sheet is final product, the operation is

termed as punching. A simple blanking die and blanking operation is shown in

figure. It is important to note that the punch and die corners are sharp and not

provided with any radius as the process need to cause a rupture of the material. A

clearance c is provided on die in punching operation and the punch is to the

required size. Hence die diameter Dd =Dp+2c where Dp and Dd are the die and

punch diameter.

(a) Blanking and (b) punching

2. Shaving: The rough edges of a blanked part are removed by cutting (shearing) thin

strip of metal along the edges on the periphery.

3. Trimming: trimming is the operation of cutting and removing unwanted excess

material (flash, etc) from the periphery of previously formed/forged/cast

component.



(a) shaving and (b) trimming

4. Notching: Notching is a cutting operation in which metal sheet, stripsor blank are

cut (sheared) at the edge as shown in figure. Ting

5. Perforating: perforating is a process used to make multiple holes which are small

in diameter and close together, in flat work material.

6. Slitting: Slitting refers to the operation of making incomplete holes from s slit (an

opening) in the sheet metal as shown in figure.

7. Lancing: Lancing is a operation of cutting on one side and bending on other side to

form a sort of tab or louver.

(a) Notching, (b) Slitting, (c) Lancing (d) Nibbling

8. Parting: parting is a operation of shearing a sheet into two or more pieces.

9. Nibbling: Nibbling is the operation used to punch overlapping small holes along a

contour to cut out contoured parts from sheet metal. This operation is generally a



substitute for blanking if the number of pieces required is small. The part is usually

guided by hand continuously.

10. Deep Drawing: This is also known as cup or radial drawing as it produces cup

shaped objects. Depth produced in deep drawing is more than the diameter. Shallow

parts can also be produced by this method. Typical products made by this process

include domestic pots, pans, food container, automobile fuel tanks, etc. In deep

drawing a flat sheet metal blank kept under a blank holder is forced into a die cavity

by means of a punch. Force on blank holder should be sufficient to prevent

wrinkling of sheet but should allow the blank to slide into the die cavity as it is

drawn in.

Figure- Deep drawing

11. Bending: In bending operation the metal is stressed in both tension and

compression at values below the ultimate strength of the material without

appreciable change in its thickness. In designing a rectangular section for bending,

the material allowed for the bend must be determined, since the outer fiber are

elongated and the inner ones shortened, the neutral axis of the section moves in

towards the compression side which throws more of the fibers in tension. The total

thickness is slightly decreased and width increased on the tension side and

narrowed on the other. The bent part retains some of its elasticity which is

recovered after the punch is removed as shown in figure. This is known as spring

back. Spring back may be corrected by over bending by an amount that brings the

part to return to the correct shape.



Bending Operation

Application of sheet- metal working:

Sheet metal is widely used for numerous industrial and non-industrial applications including:

Aircraft: Fuselages, wings, body panels, trim parts, etc.

Automotive: body panels, bumpers, doors, chassis, trim parts, brackets etc.

Construction: roofing, home building and structural applications.

Other applications: appliances, food and beverage containers, boilers, kitchen equipment, office equipment etc.


Er. Arshad Abbas, Deptt. of Civil Engg., KMCL University, Lucknow Page 1

UNIT-IV

MACHINING PROCESSES AND THEIR APPLICATIONS

Introduction of machining

Machining is the most commonly used technological process used in manufacturing. Generally, in the

field of manufacturing, the term machining means removal of material from raw material by cutting small

chip, in order to obtain the desired shape and dimensions for final part. The machining is strictly

necessary when finished part has to have very tight tolerance of dimension or when the roughness of

surfaces needs to be very smooth.

Basic Principle of lathe machine

A lathe is a machine tool which rotates the work piece on its axis to perform various operations such as

cutting, knurling, drilling, or deformation with tools that are applied to the work piece to create an object

which has symmetry about the axis of rotation.

Lathes are used in woodturning, metalworking, metal spinning, glass and plastic working.

Lathe Machine

Parts of a lathe machine: Main parts of the lathe machine as follows

1. Bed 5. Feed mechanism

2. Head stock 6. leg

3. Tail stock 4. Carriage



1. Bed

The bed of the lathe provides the foundation for the whole machine and holds the headstock, tailstock and

carriage in alignment. The surfaces of the bed that are finely machined and upon which the carriage and

tailstock slide are known as "ways".

Some beds have a gap near the headstock to allow extra-large diameters to be turned. Sometimes the gap

is formed by the machined ways stopping short of the headstock, sometimes by a piece of bed that can be

unbolted, removed-and lost.

2. Tailstock

Tailstock is a movable casting which can be moved along the way to accommodate different length of

work piece. Upper part of the tailstock accommodates a hollow barrel whose one end is provided with a

Morse taper to hold dead centre or to support and feed tools to perform various operation like drilling,

reaming etc.

3. Head stock

(a) Tailstock (b) Carriage assembly

It is situated at the left hand of the bed and is fixed. It house:

1. Driving mechanism

2. Transmission mechanism(Gear box)

3. Head stock spindle etc.

Head stock spindle is hollow throughout its length and is supported on two bearing. Outer surface of

spindle nose is generally threaded to mount the chuck or face plate. Head stock also contains some sub

parts like



1. High speed /low speed lever

2. Tumbler lever

4. Leadscrew

This is a long threaded rod normally found running along the front of the bed or, on some early examples

running between the bed ways down the bed's centre line. By using a train of gears to connect the lathe

spindle to the leadscrew and the leadscrew to the lathe carriage - the latter, together with its cutting

tool, could be forced to move a set distance for every revolution of the spindle.

5. Carriage The whole assembly of Saddle, Apron, Top and Cross Slide is known as the "Carriage". Carriage is

movable part located between headstock and tailstock. It is used for holding and feeding the tool against

the job and has following main parts.

1. Tool post

2. Compound rest

3. Cross slide

4. Saddle

5. Apron

1. Saddle: It is ‘H’ shape component that slides along the bed ways. It contains cross-slide,

compound rest and tool post.

2. Cross Slide: It is mounted on the top of saddle to provide transverse tool movement and

can be operated manually with a hand wheel or by power feed.

3. Compound rest: it is mounted on cross slide and has a circular base graduated in

degrees. It can be swiveled about a vertical axis in various angular positions. It is

essential in most of the taper turning operations.

4. Tool post: It is mounted on the compound rest and is the top most part of carriage. It is

used for holding various tools and tool holder.

5. Apron: It is fastened to the saddle and in front of the carriage. It consists of a split nut,

gears and clutches to transmit motion from the feed rod to the carriage in thread cutting.

6. Feed mechanism: Feed mechanism is used to transmit power to the carriage. Initially

power is transmitted by a gear train to quick change gear box, which in turn regulates the

tool movement per revolution of spindle.

7. Leg: Legs are used to support the entire load of machine and are firmly fixed to the floor by

foundation bolts. It is made up of cast iron



OPERATIONS PERFORMED ON A LATHE MACHINE

1. Turning: Turning is an operation of removing excess material from the outer surface of

the work piece to obtain finished surface. Turning are basically two types:

a) Plain turning: In plain turning operation first of all the cutting tool is adjusted

for required depth of cut with the help of cross-slide. Then the tool is moved

slowly parallel to axis of spindle to remove the excess material and generate a

cylindrical surface

Plain Turning operation

(b) Taper Turning: The taper turning is an operation of producing a conical

surface by gradual reduction in the diameter of a cylindrical work piece.

Taper Turning



(c) Step Turning: Step turning produces various steps of different diameters

Step Turning

Apart from these operation some more operations can be performed on a lathe like

Drilling, Boring, Reaming, Milling, Knurling, Grooving or Necking, Parting or Cutting

off and grinding.

2. Facing: Facing is an operation for generating flat surfaces in lathes. The feed is in this

case given in a direction perpendicular to the axis of revolution. The tool used should thus

have an approach angle suitable so that it would not interfere with the workpiece during the

tool feeding.



3. Knurling: Knurling is a metal working operation done in a lathe machine. In this, a

knurling tool having the requisite serrations is forced on to the workpiece materials, thus

deforming the top layer. This force as top surface to be rough and provides a proper

gripping surface

.

Knurling Operation



4. Parting and Grooving: Parting and grooving are similar operations. In this, a flat

nosed tool would plunge cut the workpiece with a feed in the direction perpendicular to the

axis of revolution. This operation is carried out for cutting off the part from the parent

material.

Parting Operation

Parting Operations



Basic Description of other machine tool

Shaper

A shaper is a machine with a reciprocating tool that takes a straight line cut. By successive movement of

the work across the path of this tool, a plane surface is generated. Power is supplied to the machine by a

motor, either through gears or belt or by the employment of a hydraulic system. As shown in figure 3.61 a

horizontal shaper consisting of a base and a frame that support a horizontal rams. The ram that carries the

tool is given a reciprocating motion equal to the length of the stroke desired. The quick-return mechanism

driving the ram is designed so that the return stroke of the shaper is faster than the cutting stroke. A

clapper box tool holder attached to the ram by means of a pivot at the upper end.

Working Principle of shaper

Shaper is intended to produce horizontal vertical or inclined flat surface by means of a reciprocating

single point cutting tool. Tool is given reciprocating motion by converting the circular motion into

reciprocating motion with the help of a mechanism known as quick return mechanism.

Shaper Machine



Shaper Machine

Working of shaper machine

The shaper can be driven by a mechanical quick-return mechanism. It consists of a rotating crank driven

at a uniform speed connected to an oscillating arm by a sliding block that works in the center of the rather

massive oscillating arm. The crank is contained in the large gear and its arm length can be varied by a

screw mechanism. The stroke length is varied by changing the length of the crank. The ratio of return to

cutting speed is about 3:2

Types of surface commonly machined by shaping and planning



Parts of a shaper

• Base • Column

• Table • Ram

• cross Tail • Tool Head

Shaper operation

1. Horizontal Cutting

2. Vertical Cutting

3. Angular Cutting

4. Irregular Cutting: Irregular cutting generally performed by using a form tool or by combination of vertical feed and horizontal cross-feed to generate required contour in surface

(a) (b) (c)

Planer

(a) Horizontal cutting (b) Vertical cutting (c) Angular cutting

Planers also used preliminary to produced horizontal, vertical or inclined flat surfaces, but on work

pieces that are too large to be accommodate on shapers. In the majority of planers the action is opposite

to that of shapers in that the work is moved past one or more stationary, single-point cutting tools.

The figure shows the basic components and motions of a planer. Because a large and heavy work piece

and table must necessarily be reciprocated at relatively low speeds, several tool heads are provided, often

with multiple tools in each head, In addition many players are provided with tool heads arranged so that

cuts occur on both direction of the table movement. However, because only single-point cutting tools are



1. It is relatively lighter machine

2. Tool reciprocates against the fixed work

piece.

3. It can only do small work. 4. Large depth of cut and coarse feed is

not possible.

5. Usually accommodate only one tool

6. Feed is given to the work during idle

stroke of ram

used and the cutting speeds are quite low, planer are quite low in productivity as compared with some

other types machine tools. As a result, they have, to a large degree, been replaced by planer type milling

machines.

Planer Machine

Comparison between Shaper and Planer

Shaper Planer

1. It is comparatively heavy and robust in construction.

2. Work piece reciprocate against the fixed tool.

3. It is meant for heavy work

4. Large depth of cut and coarse feed can

be taken.

5. It can accommodate multiple tool.

6. Feed is given to tool during idle stroke.



Milling machine

Milling machines cut metal using a rotating cutting tool called a milling cutter. These machines cut flat

surfaces, angles, slots, grooves, shoulders, inclined surfaces, etc

Types of milling machines

Milling machines are of two major types depending upon the orientation of the axis of rotation

of the spindle. Another feature is its knee and column construction. These are general purpose

machines. This we have two classes of machines:

1. Horizontal knee and column type milling machine

2. Vertical knee and column type milling machine

Main parts of column and knee type milling machine are: Base, column, knee, saddle, table,

over hanging arm, arbor, and feed mechanism. These parts can be seen in figure 3.11

(a) (b)

Figure (a) Horizontal knee and column type milling machine (b) Vertical knee and column type milling

machine



Milling processes- The various milling process are shown below:

1. Peripheral milling 4. Straddle milling 7. Slitting

2. Face milling

3. End milling

5. Form milling

6. Slotting

Figure -slab milling, face milling, end milling, straddle milling, form milling, slotting and slitting

The peripheral or slab milling can be further subdivided into

1. Up milling (Figure (a))

2. Down milling (Figure (b))

Up Milling: It is known as conventional milling. In this work piece is fed in direction opposite to cutter.

It requires rigid clamping due to tendency of lifting the job. Chip thickness is minimum at the beginning

and maximum at end.

(a) (b)

Figure (a) Up milling (b) down Milling

Down Milling: It is also known as climb milling. In this work piece is fed in the direction of cutter.

Clamping is not so crucial. Chip thickness is maximum at beginning and minimum at the end.



Difference between up milling and down milling

Up milling Down milling

1. Job is fed against the motion of cutter. Job is fed in same direction as that of cutter rotation.

2.

Cutting force in directed upward.

Cutting force is directed downward

3. Chips thickness varies from minimum to maximum Chips thickness varies from maximum to minimum

4. Generally thick jobs are machined Generally thin jobs are machined

5. Chips removal problem exists Chips removal is easy

6. Jobs must be clamped to counteract upward cutting force

Cutting helps in pressing the job to the table. Less

clamping force are required.

7. Coolant application is difficult.

Coolant application is easy.

8. Cutting force is zero at beginning Cutting force is maximum at the beginning and it

reduces to minimum at the end of cutting by tooth.

Grinding

Grinding is a metal cutting process in which the material is removed from the work piece by the abrasive

action of rotating cutting tool known as a grinding wheel which rotates at a high speed (v= 10-80 m/s)

while the work is fed past the wheel at a rate of 0.2 m/s to 0.6 m/s. It has some similarity with up milling

operation except that the cutting points are irregularly shaped and randomly distributed

Abrasive and Bonds;

Abrasives used are in the form of grits (particle with sharp cutting points) which are bonded together by

means of an organic binder. Cutting forces cause the bond to fracture and fail to expose a new sharp grits

to participate in cutting while the dull used grit is removed. The strength of bonding is normally termed

the Grade of the wheel. Cutting action is like chip removed in milling. Here the chips are very fine about

one tenth of the thickness of human hair.

Grinding operation is performed to:

1. Machine hard surface

2. Impart better surface finish

3. Sharpen the cutting tool

4. Finish the work piece within the close tolerance.



Elements Of Grinding Wheel

Classification of grinding machines

1. Rough grinders: These grinders are used for removal of a large material rather than for accuracy

2. Precision grinders: These grinders are used to finish the work piece within close tolerances obtaining

desired dimension accurately.

Drilling Operation

Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called a

drill. The machine used for drilling is called drilling machine

Drilling Machine

1. It is the simplest and accurate machine used in production shops

2. The work piece is held stationary i.e. clamped in position and the drill rotates to make a hole.



Figure - Drill machine

Operations performed on drilling machine

1. Drilling:- Drilling produces holes in an object by forcing a rotating drill tool against

work(drill press) or forcing a stationary drill against a rotating work(as in lathe machine)

2. Boring: - This is the operation of enlarging a hole already drilled or cast. It produces

more accurate (true) holes than drilling. It is internal turning operation producing

different types of internal surfaces of revolution.

3. Reaming: - A reamer enters the workpiece axially and enlarges an existing hole to the

diameter of the tool. Reaming removes a minimal amount of material and is often

performed after drilling to obtain both a more accurate diameter and a smoother internal

finish.

4. Threading: - Threading is an operation of making helical grooves in a workpiece. It is

usually done using a tool on a lathe machine.

5. Counter boring: - A counter bore tool enters the workpiece axially and enlarges the top

portion of an existing hole to the diameter of the tool. Counter boring is often performed

after drilling to provide space for the head of a fastener, such as a bolt, to sit below the

surface of a part. The counter boring tool has a pilot on the end to guide it straight into

the existing hole.

6. Countersinking: - A countersink tool enters the workpiece axially and enlarges the top

portion of an existing hole to a cone-shaped opening. Countersinking is often performed

after drilling to provide space for the head of a fastener, such as a screw, to sit flush with



the workpiece surface. Common included angles for a countersink include 60, 82, 90,

100, 118, and 120 degrees.

7. Tapping: - A tap enters the workpiece axially and cuts internal threads into an existing

hole. The existing hole is typically drilled by the required tap drill size that will

accommodate the desired tap. Threads may be cut to a specified depth inside the hole

(bottom tap) or the complete depth of a through hole (through tap).

Various Drilling Operations



UNIT- V

FABRICATION PROCESSES

Importance and Basic Concept of Welding

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by

causing coalescence. This is often done by melting the work pieces and adding a filler

material to form a pool of molten material (the weld pool) that cools to become a

strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce

the weld.

Welding is used in every industry large or small, as a principle means of fabrication and

repairing metal product. The process is efficient, economical and dependable. This is the only

process which has been tried in the space and finds applications for fabricating products in

air, underwater and in space

Classification of welding process

There are many ways in which the welding processes can be classified. A simple and logical

way is to satisfy the welding processes according to the sources of energy used for achieving

coalescence. The welding processes can thus be broadly classified as;

(a) Fusion welding

(b) Pressure welding

(c) Thermo chemical welding

(a) Fusion welding

1. Gas flame welding

Oxy-acetylene welding

Oxy-hydrogen welding

2. Electric arc welding

Carbon arc welding

Shielded metal arc welding

Submerged arc welding

Tungsten arc welding

Metal inert gas (MIG) welding

Plasma arc welding

Atomic hydrogen welding

3. Radiant energy welding

Electron beam welding

Laser beam welding

4. Electric resistance welding

Spot welding



Seam welding

Projection welding

Resistance butt welding

Flash welding

Percussion welding

Electroslag welding

The following processes fall under solid state (cold) welding

(a) Pressure welding Friction welding

Ultrasonic welding

Explosive welding

Forge and diffusive welding

(c) Thermo chemical welding Thermit welding

Atomic hydrogen welding

Out of the above welding processes carbon arc and atomic hydrogen welding are not

commonly used in industries these days.

Fusion welding;

Fusion welding is a group of processes that bond metals together by heating a portion of

each piece above the melting point and causing them to flow and fuse together. Usually filler

materials are used to insure the joint is filled. All fusion welding processes have four

requirements for obtaining satisfactory welds.

1. A source of energy to create union (e.g. gas flame, electric arc, electric resistance etc.)

2. Removing surface contaminants (e.g. organic and oxide films etc.)

3. Protecting metal from atmospheric contamination ( shielding gas atmosphere like argon,

helium, carbon dioxide, smoke of burning flux coating)

4. Control of weld metallurgy (e.g. preheat, post welding heat treatment)

Gas Welding

It is fusion welding process that joins the metal by using heat of combustion of a strong gas

flame. The intense heat raises the temperature of ends, melts and fuses together the edges of

the plate to be welded. Filler metal may be added the plate to flowing molten to fill the cavity

between the plates. Different oxy-acetylene combinations are used to produce different types

heating flames i.e. O2 and C2H2, O2 and H2 with coal gas etc. Oxy –acetylene welding is the

most commonly used gas welding process. This process is explained in detail in the following

paragraphs.



OXY-ACETYLENE WELDING (O2, C2H2)- Oxyacetylene welding is a gas welding process. In this process coalescence (or bond) is

produced by heating with the gas flame obtained from the combustion of acetylene with

oxygen. A welding torch is used to mix the gases in the proper proportions and to direct the

flame against the parts to be welded. The molten edges of the parts then literally fuse together

and after cooling form a strong joint. Usually, it is necessary to add extra material to the joint.

The correct material in the rod form of a rod is dipped in a flux powder and is fused with the

puddle of and fuses with the puddle of molten metal obtained from the parent metal parts.

Acetylene is widely used as the combustible gas because of its high flame temperature when

mixed with oxygen. The temperature, which ranges from approximately21000- 3500

0, is far

above the melting point of all commercial metals thus it provides a means for the rapid,

localized melting essential in welding. The oxyacetylene flame is also used in cutting ferrous

metals. The oxyacetylene welding and cutting methods are widely used by all types of

maintenance activities because the flame is easy to regulate, the gases may be produced

inexpensively, and the equipment can be transported easily and safely.

Combustion of gas and heat liberated

First stage-

C2H2 + O2 → 2 CO + H2 + 448 Kj/mol

Second stage 2 CO + H2 + 3O → 2 CO2 + H2O + 812

Kj/mol Total heat liberated by combustion= 448+812= 1260 Kj/mol of acetylene.

Gas welding equipments

1. Oxygen gas cylinder

2. Acetylene gas cylinder

3. Welding torch

4. Pressure regulator

5. Hose pipe

6. Stop valve

7. Pressure gauge



Types of flame

Figure -Oxy acetylene equipments

To achieve successful and efficient welding, proper mixing of gas in appropriate proportion is

necessary. According to the volume of O2 and C2H2 flame can be classified as

Figure - Gas welding flame

1. Neutral flame- Neutral Flame is produced when equal volume of O2 and C2H2 are mixed.

It has well defined inner cone, which has light blue color. Neutral Flame doesn’t create any

change in the molten metal and doesn’t oxidize or carburize the metal. This flame is used for

welding of mild steel, cast iron, aluminum and stainless steel. Temperature of neutral flame is

32320 C.



2. Oxidizing flame- oxidizing flame is obtained by increasing the supply of oxygen in

mixture. It has small white cone which is shorter and more pointed than that of neutral flame.

It creates high temperature of 3482̊ C. It is normally not used except in the case of brass.

3. Reducing flame- it is produced when supply of C2H2 is higher than supply of oxygen

and can create an approximate temperature of 31500 C its outer envelope is longer than that of

neutral flame. It is used for the welding of lead.

In these flames the temperature is maximum at the tip of the inner cone. Feather or

brush exists next to the cone and occurs in carburizing flame only.

Figure -Types of gas welding flame



Electric arc Welding

1. In electric arc welding metal pieces to be joined are heated to melting point by

creating an electric arc between them to form a pool of molten metal and then

allowing it solidify to form welded joint. Sometimes additional material is added to

form the weld by melting the wire known as filler metal. Electric arc welding is

classified as

1. Carbon arc welding (Obsolete)

2. Metal arc welding

Metal arc welding- In metal arc welding arc is maintained between electrode and work piece and work piece

which form the two terminals. In this welding electrode used may be bare or coated. Bare

electrode has same composition as that of parent metal whereas coated electrode have some

material or flux that prevents the oxidation of surface.

To obtain the required heat arc is struck by making light contact of electrode with work piece

and then electrode is withdrawn to a proper distance. This current arc produces large amount

of heat and melts the electrode end and the work piece. Due to melting of electrode material

droplets are transferred to the work piece through the arc and deposited along the joint.

Metal electrode is coated with a flux which burns and produces a gas shield around the arc to protect it from atmospheric contamination of molten weld metal

Figure-Electric arc welding



Arc welding Power source- In arc welding both A.C and D.C. power sources could be

used. In D.C. welding

Polarity in arc welding- When A.C is used polarity is not fixed at any terminal and it

interchanges in every cycle thus the heat generated at each pole is same. But in D.C welding polarity is fixed. Job acts as one terminal and electrode acts as another terminal. Heat

developed at +ve terminal is 2/3 rd and at –ve terminal is 1/3 rd of the total heat. In D.C welding polarity is of two types.

Straight polarity-

In straight polarity electrode forms the –ve terminal and work piece forms the +ve terminal.

This polarity is used in welding of thick materials due to large requirement of heat on the

plate

Reverse polarity-

In Reverse polarity electrode forms the +ve terminal and work piece form the -ve terminal. This polarity is used in welding of thin materials due to less requirement of heat in welding

zone.

(a) (b)

Figure (a) D C Straight polarity (b) D C Reverse polarity

Types of electrodes 1. Consumable electrodes

a. Bare Electrodes

b. Coated Electrodes

2. Non- consumable electrodes

Resistance Welding

It is the process of joining two metal pieces by application of mechanical pressure and heat.

The heat is generated due the resistance offered by the two pieces to the flow of current. In

resistance welding two metal pieces to be joined are held together and high electric current is

passed



through it. Due to flow of current across the resistance the temperature at the junction reaches the fusion point. At this time slight mechanical pressure is applied to complete the weld.

The magnitude of current in resistance welding varies from 3000 to 100,000 ampere for a fraction of a second with voltage of 1 to 25 volts.

Heat generated in resistance welding is given by

H=I2 RT

Where H= Heat generated in

Joules I= Current in ampere

T= Time of current flow in second

Resistance welding can be further classified as

Spot welding

Seam welding

Projection welding

Butt welding

Flash welding

Percussion welding

Resistance spot welding-

Spot welding is a resistance welding process in which overlapping metal plates are held

between two copper electrodes, which concentrate welding current to melt the interface over

a spot and apply pressure to complete the weld.

In this welding Current is order of 3000- 10000 ampere

Temperature of weld zone is 8150 C-930

0C

Electrode- Copper base alloy

Weld nugget- 6-10 mm in diameter

Advantage;-

High welding rates;

Low fumes;

Cost effectiveness;

Easy automation;

No filler materials are required;

Low distortions.



Disadvantages

High equipment cost;

Low strength of discontinuous welds;

Thickness of welded sheets is limited - up to 1/4” (6 mm);

Resistance Seam welding- Seam welding is similar to spot welding except that continuous circular rotating electrodes are used in place of tip electrode. The weld produced is continuous air tight seam. It can also be defined as continuous series of spot welds.

(b)

Figure (a) Spot welding and (b) Seam welding

Resistance projection welding-Projection welding is a development of resistance spot

welding. In spot welding, the size and position of the welds are determined by the size of the

electrode tip and the contact point on the work pieces, whereas in projection welding the size

and position of the weld or welds are determined by the design of the component to be

welded. The force and current are concentrated in a small contact area which occurs

naturally, as in cross wire welding or is deliberately introduced by machining or forming

(a) (b) (c)



Figure 5.7 Example of projection welding configurations: a) embossed projection; b) stud to plate; c) annular projection

Advantage

The advantages of projection welding include its versatility, the speed and ability to

automate, the ability to make a number of welds simultaneously and minimization of

marking on one side of joints in sheet materials. Capacitor discharge supplies used with

machined annular projections can compete with power beam welding, as the weld is

completed in a single shot within milliseconds.

Disadvantage

There are some limitations on material weldability but attention to correct setting up and

good process control can solve most production problems. The main safety factors are

trapping hazards and splash metal. Little fume is produced but may need attention when

welding coated steels or when oils or organic materials are present.

Flash Welding (FW) Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets)

are heated and fused by an arc struck between them and then forged (brought into a contact

under a pressure) producing a weld.

The welded parts are held in electrode clamps, one of which is stationary and the second is

movable. Flash Welding method permits fast (about 1 min.) joining of large and complex

parts. Welded parts are often annealed for improvement of Toughness of the weld. Steels,

Aluminum alloys, Copper alloys, Magnesium alloys, Copper alloys and Nickel alloys may be

welded by Flash. Thick pipes, ends of band saws, frames, and aircraft landing gears are

produced by Flash Welding.

(a) (b)

Figure (a) Flash Welding and (b) Butt welding

Resistance Butt Welding

Resistance Butt Welding is a Resistance Welding (RW) process, in which ends of wires or

rods are held under a pressure and heated by an electric current passing through the contact

area and producing a weld.

Butt welding is used for welding small parts. The process is highly productive and clean. In



contrast to Flash Welding, Butt Welding provides joining with no loss of the welded materials.

Percussion Welding - It is a resistance welding process wherein coalescence is produced

simultaneously over the entire area of abutting surfaces by heat obtained from an arc

produced by a rapid discharge of electrical energy, with pressure percussively (rapidly)

applied during or immediately following the electrical discharge.

Soldering and Brazing

Soldering Soldering involves the heating a joint to a suitable temperature and using filler metal (solder)

which melts below 4500 C. solder gets distributed between the properly fitted surfaces of the

joint by capillary attraction. Heat is required to melt the solder, promotes fluxing action on

metal surface which permits the molten solder to wet and flow into the joint. Successful

soldering requires:

2. Proper fit-up (close together)

3. Cleaning the surfaces to be joined

4. Applying flux, assembling parts, and applying heat and solder.

5. Remove flux residues after joint is cooled

Soldering Methods

1. Dip soldering 5. Induction soldering

2. Iron soldering 6. Furnace soldering

3. Resistance soldering 7. Infrared soldering

4. Torch soldering 8. Ultrasonic soldering

Solders can be classified as:

6. Soft Solder- is an alloy of lead and tin with the following composition

a) Tin 50%, Lead 50%

b) Tin 67%, Lead 33%

c) Tin 33%, Lead 67%

Soft solder melts at temperature below 350̊ C and operation is known as soft

soldering.

7. Hard Solder- is an alloy of Copper and Zinc that melts above 600 C the operation is

performed with hand solder is called hand soldering.

To prevent the oxidation of joint surfaces, fluxes are used. Flux should be light

in weight so it could be displaced by molten metal

Example of flux- Zinc chloride, rosin and rosin plus alcohol based flux, mixture of zinc

chloride and ammonium chloride



Skill is needed for manual soldering operation especially for critical electronic

equipment/components. Automated soldering requires less operator skill as the process

variable are set before the soldering operation, machine setting, process control and

inspection determine joint quality. Lap joint is most commonly used while special types of

joints are used to solder electronic component.

(a) (b)

Figure (a) Soldering operation (b) 30 watt Solder

iron

Application

1. Process is used to join a wide range of metal thickness from thin film to quite heavy

components like bus bars and piping.

2. Expensive automated equipment produces many high quality joints at a time, thus

reducing the cost per joint.

3. Manual soldering is although slow, but still economical when production needs are low

or joint design is complex.

Brazing

Brazing is a group of welding processes in which the parts are heated to suitable temperature

and the filler metal used has a melting temperature above 4500 C and below the solidus of the

base metal. The filler metal flows between the closely fitted joints by capillary attraction.

In Braze welding, the filler metal is deposited in a groove exactly at the point where it is to be

used capillary action is not a factor. Brazing differ from soldering by the filler metal melting

temperature being below 4500 C.

The basic elements to be considered for brazing are: 1. Joint design

2. Filler metal

3. Uniform heat

4. Protective (or reactive) cover



Processes used for brazing are classified on the basis of methods of heating.

1. Torch brazing (oxy-fuel gas torch: for welding thin section 0.25 mm to 6 mm) making

lap joint

2. Furnace brazing (flux and braze filler is preplaced.

3. Induction brazing (3 mm normal up 25 mm)

4. Resistance brazing (0.1-12.00 mm sheets)

5. Dip brazing (molten salt or molten metal bath)

6. Infrared brazing

7. Diffusion brazing



INTRODUCTION TO NEWER MACHINING PROCESS

ELECTRICAL DISCHARGE MACHINING (EDM)

Electrical discharge machining is a machining process in which metals are cut to a

precise shapes using electricity.

PRINCIPLE OF ELECTRICAL DISCHARGE MACHINING PROCESS

Electrical Discharge Machining (EDM) is a controlled metal-removal process that is

used to remove metal by means of electric spark erosion. In this process an electric

spark is used as the cutting tool to cut (erode) the work piece to produce the finished

part to the desired shape. The metal-removal process is performed by applying a

pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to

the work piece. This removes (erodes) very tiny pieces of metal from the work piece at a

controlled rate.

Fig. Electrical Discharge Machining

FUNCTIONING OF EDM PROCESS

EDM spark erosion is the same as having an electrical short that burns a small hole in a

piece of metal it contacts. With the EDM process both the workpiece material and the

electrode material must be conductors of electricity. The EDM process can be used in

two different ways:

1. A preshaped or formed electrode (tool), usually made from graphite or copper, is

shaped to the form of the cavity it is to reproduce. The formed electrode is fed

vertically down and the reverse shape of the electrode is eroded (burned) into the

solid work piece.

2. A continuous-travelling vertical-wire electrode, the diameter of a small needle or



less, is controlled by the computer to follow a programmed path to erode or cut a

narrow slot through the work piece to produce the required shape.

ELECTRO CHEMICAL MACHINING (ECM)

Electrochemical machining (ECM) is a metal-removal process based on the principle of

reverse electroplating. In this process, particles travel from the anodic material (work

piece) toward the cathodic material (machining tool). A current of electrolyte fluid

carries away the deplated material before it has a chance to reach the machining tool.

The cavity produced is the female mating image of the tool shape

Fig.: Electrochemical Machining Process (ECM)

ADVANTAGES OF ECM

The components are not subject to either thermal or mechanical stress.

No tool wears during ECM process.

Fragile parts can be machined easily as there is no stress involved.

ECM deburring can debur difficult to access areas of parts.

High surface finish can be achieved by ECM process.

Complex geometrical shapes in high strength materials particularly in the

aerospace industry for the mass production of turbine blades, jet engine parts and

nozzles can be repeatedly and accurately.

Deep holes can be made by this process.



LIMITATIONS OF ECM

ECM is not suitable to produce sharp square corners or flat bottoms because of

the tendency for the electrolyte to erode away sharp profiles.

ECM can be applied to most metals but, due to the high equipments costs, is

usually used primarily for highly specialized applications.

ULTRASONIC MACHINING (USM)

USM is mechanical material removal process or an abrasive process used to erode holes

or cavities on hard or brittle work piece by using shaped tools, high frequency

mechanical motion and an abrasive slurry. USM offers a solution to the expanding need

for machining brittle materials such as single crystals, glasses and polycrystalline

ceramics, and increasing complex operations to provide intricate shapes and work piece

profiles. It is therefore used extensively in machining hard and brittle materials that are

difficult to machine by traditional manufacturing processes. The hard particles in slurry

are accelerated toward the surface of the work piece by a tool oscillating at a frequency

up to 100 KHz - through repeated abrasions, the tool machines a cavity of a cross

section identical to its own.

Fig.: Ustrasonic Machining (USM)

ADVANTAGES OF USM

Any materials can be machined regardless of their electrical conductivity.

Especially suitable for machining of brittle materials.

Machined parts by USM possess better surface finish and higher structural

integrity.

USM does not produce thermal, electrical and chemical abnormal surface.



DISADVANTAGES OF USM

USM has higher power consumption and lower materials removal rates than

traditional fabrication process.

Tool wears fast in USM.

Machining area and depth in restraint in USM.

LASER BEAM MACHINING (LBM)

Laser Beam Machining or more broadly laser material processing deals with machining

and material processing like heat treatment, alloying, cladding, sheet metal bending etc.

Such processing is carried out utilizing the energy of coherent photons or laser beam,

which is mostly converted into thermal energy upon interaction with most of the

materials. Nowadays, laser is also finding application in regenerative machining or rapid

prototyping as in processes like stereo-lithography, selective laser sintering etc.

LASER BEAM MACHINING PROCESS

Lasing process describes the basic operation of laser, i.e. generation of coherent (both

temporal and spatial) beam of light by “light amplification” using “stimulated

emission”. In the model of atom, negatively charged electrons rotate around the

positively charged nucleus in some specified orbital paths. The geometry and radii of

such orbital paths depend on a variety of parameters like number of electrons, presence

of neighboring atoms and their electron structure, presence of electromagnetic field etc.

Each of the orbital electrons is associated with unique energy levels. At absolute zero

temperature an atom is considered to be at ground level, when all the electrons occupy

their respective lowest potential energy. The electrons at ground state can be excited to

higher state of energy by absorbing energy form external sources like increase in

electronic vibration at elevated temperature, through chemical reaction as well as via

absorbing energy of the photon.

On reaching the higher energy level, the electron reaches an unstable energy band and it

comes back to its ground state within a very small time by releasing a photon. This is

called spontaneous emission. The spontaneously emitted photon would have the same

frequency as that of the “exciting” photon.



Fig.: Laser Beam Machining

COMPUTER AIDED DESIGNING (CAD) / COMPUTER AIDED

MANUFACTURING (CAM)

The use of computers to aid design and manufacturing process:

It is concerned with the application of computers to the manufacture of

engineering components from the drawing phase to the production phase ( to the

machining and assembly shops) to the quality control department and to the

warehouses.

The technology of CAD/CAM represents an efficient, accurate and consistent

method to design and manufacture high quality products.

The role of computers in manufacturing:

It is classified into two groups:

1. Computer monitoring and control of the manufacturing process.

2. Manufacturing support applications which deals with the preparations for the

actual manufacturing and post manufacturing process.

3. In the first category computer is directly interfaced with the manufacturing

process for manufacturing operators.

E.g.: CAD – Use of computers to develop the geometric model of the product in

3D form.

CAE (Engg.) – To support basic errors, checking, analysis, optimization,

manufacturing.



CAM – Use of computers to generate software to develop the computer

numerical control part programs for machining and other processing applications.

CATD (Tool design) – Computer assistance to be used for developing the tools

for manufacture of jigs, fixture, dies and moulds.

CAQ (Quality assurance) – The use of computers and computer controlled

equipments for accessing the inspection methods.

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