UNIT
1
Engineering Materials
Learning Objectives
On completion of this unit a learner will be able to
• Describe ferrous metals , non-ferrous metals and non-metals
• Know the properties and uses of ferrous and non ferrous metals
• Know the safety precautions to be followed in a work shop
1.0 Introduction
Engineering materials are those which are extensively used in various
engineering applications such as used for construction of bridges, machine tools,
automobiles, locomotives, ships, space crafts and many more.Steel is extensively
used in construction of bridges.Iron is used for various machine tools.Aircrafts
have aluminium bodies.Large number of household ,industrial goods,electronics
goods are made using plastics like TV cabinets computer bodies & toys.
Classification of Engineering Materials
Engineering materials are basically classified into two groups namely metals
and non-metals, and their sub classification is given below.
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Engineering Materials
Metals
Ferrous
metals
Wrought iron,
Carbon Steels,
Alloy steels,
Cast Iron.
Non Ferrous
metals
Al, Cu,
Sl, tin,
zn
Non Metals
Ceramics
Polymers
T he rmo
static plastics
Phenol
formal
dehyde
Thermo
plastic
PVC
Polythene,
Acrylic resins
Classification of Engineering Materials
Refractoreis,
Abrasives,
glass, Cement
and concrete
Mechanical Properties of Metals
The mechanical properties that determine the behavior of metals under
applied forces. These properties are most important for the designing point of
view.
1. Strength : Ability of a material to resist loads without failure.
2. Tensile Strength : Ability of a material in tension to withstand stress
without failure.
3. Shear Strength : Ability of a material to withstand transverse loads
without fracture.
4. Elasticity : Property of material which enables it to regain its original
shape after deformation with in the elastic limit.
5. Stiffness : Property of material which enables it to resist deformation.
6. Plasticity : Ability of material to be deformed permanently without
fracture even after removal of force.
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7. Ductility : Ability of a material to deform plastically without rupture
under tensile load.
8. Malleability : Property which enables the metal to withstand
deformation by a compressive load without fracture.
9. Brittleness : Property of the material of sudden fracture without any
appreciable deformation.
10. Hardness : Property of the material which enables it to resist abrasion,
indentation, machining and scratching.
11. Toughness : Ability of material to absorb maximum energy upto fracture
takes place.
12. Fatigue : Failure of material under repeated (cyclic) loads or fluctuating
loads.
13. Weldability : Ability of a material to be joined by welding
14. Castability : Property of a metal which indicates the ease with which
it can be cast into different shapes and sizes from its liquid state.
Ferrous Metals
The metals which contain iron as base are called ferrous metals. Eg. Cast
iron, Alloy steels etc. These are clssified as
1) Pig iron
2) Cast iron
4) Carbon Steel
5) Alloy steel.
3) Wrought iron
The properties and uses of common engineering materials.
1.1 Cast Iron
Pig iron remelted and there by refined together with definite amount of lime
stone,steel scrap and spoiled castings in cupola. It contain 2-4% carbon, a
small percentage of silicon, sulphur, phosphorus and manganese.
Properties of Cast Iron
1. It has good fluidity
2. It can be easily machined
3. It is brittle in nature
4. It is resistance to deformation
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5. It is wear resistant.
Uses of Cast Iron
1. It is used in making pipes
2. It is used for making machine bodies
3. It is used in making automotive industry parts.
1.2 Mild Steel
These are also called low carbon steels having carbon content of 0.15 0.3%.
Properties of Mild Steel
1. It has low fluidity.
2. It has good tensile strength.
3. It is ductile
4. It can be cold worked easily.
Uses
1. It is used for making structures
2. It is used for making nuts and bolts
3. It is used for making machine components.
4. It is used for making boiler plates.
1.3 High Carbon Steels
High carbon steels have more than 0.60% carbon i.e. 0.6 - 0.9% carbon .
It is generally used for making parts requiring strength, hardness and wear
resistance.
Properties of High Carbon Steels
(1) It has good strength
(2) It has high toughness
(3) It has increased wear resistance.
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Uses
1. It is used for making Drop hammers
2. It is used for making Screw drivers
3. It is used for making laminated Springs
4. It is used for making gears.
5. It is used for making piston rings
1.4 Alloy Steels
Steel is a metal alloy consisting mostly of iron, in addition to small amount
of carbon, depending upon the grade and quality of the steel. Alloy steel is any
type of steel to which one or more elements besides carbon have been added to
produce a desired physical properties. The most common alloying elements
added to steel are Chromium, Nickel, manganese, silicon, Vanadium etc. .
Properties of Alloy Steel
(1) High Strength
(2) High corrosion resistance
(3) High wear resistance
(4) Good toughness.
Uses
(1) It is used for making Aeroplane parts
(2) It is used for making automobile parts
(3) It is used for railway track work
(4) It is used for making locomotive parts
1.5 Stainless Steel
It contains 18% chromium, 8% nickle, 0.06% to 0.12% carbon. They are
called stainless because in the presence of oxygen, they develop a thin adherent
film of chromium oxide that protects the metal from corrosion.
Properties of Stainless Steel
1. It has high corrosion resistance.
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2. It has high strength
3. Good toughness
4. It posses non magnetic properties.
5. It can be rolled.
Uses
1. It is used for making surgical instruments.
2. It is used for making utensils
3. It is used for making containers for pharmacautical industries.
4. It is used for making springs.
Non Ferrous Metals
The metal which do not contain iron as base Eg: Al, cu, Lead ,Zn and gold
etc. All the non ferrous metals have common set of properties. The melting
point of these metals are generally lower than ferrous metals.
1.6 Copper
Copper is easily identified from all other metals due to reddish in colour
and is extracted from copper pyrates.
Properties of Copper :
1. It is relatively soft.
2. It is very malleable and ductile
3. It is very good conductor of heat and electricity.
4. It is very flexible.
Uses of Copper
1. It is used for making electrical cables.
2. It is used for making kitchen vessels
3. It is used for making pipes which are used in refrigerators.
4. It is used making for ornaments.
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1.7 Brass
It is basically refers to a yellowish alloy of copper and zinc and it comprises
of 65% copper and 35% zinc. There are various classes of brass, depending on
the proportion of copper and zinc are available for various uses. The melting
point of brass ranges from 800oC - 1000 oC.
Properties of Brass
1. It is non corrosive
2. Air, water and some acids do not affect it.
3. It is poor conductor of electricity.
Uses
1. It is used for making utensils.
2. It is used for manufacturing ornaments.
3. It is used in hydraulic fittings, pump lining, in making bearing and bushes.
4. It is used in making locks.
1.8 Bronze
It is alloy of copper and tin. The composition range is 5-25% tin and 75 to
95% copper. The corrosion resistance of bronzes are superior than brasses.
Properties of Bronze
1. It is comparativley hard
2. It is resistance to surface wear
3. It can be casted into wires and sheets
4. It has high strength.
Uses
1. It is used in hydraulic fittings, pump linings,
2. It is used in making utensils, bearings, bushes, sheets, rods, wire etc.
1.9 Tin
Although it is used in small amounts, tin is an important metal. Tin is used as
protective layer on the sheet metal. It is obtained from tin stone.
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Properties of Tin
1. It is white soft metal
2. Good resistance to acid corrosion
3. Low strength
4. It is malleable and ductile.
5. It does not corrode at both dry and wet climates.
Uses
1. It is used as a coating on steel containers for preservation of food products
2. It is used in making thin foils and as an alloying element in the manufacture
of bearings.
1.10 Zinc
It is fourth most utilized industrially after iron, Aluminium and copper. It is
used for galvanising the steel sheet or wire as it serves as anode to protect from
corrosion attack.
Properties of Zinc
1. It is soluble in copper
2. Low melting point and high fluidity.
3. High corrosion resistance
4. It is ductile and malleable.
Uses
1. It is used for die casting
2. It is used for production of brass
3. It is used in battery cells for making dry batteries
4. It is used as protective coating in iron and steel against rusting
1.11 Gun Metal
Gun metal contains 10%tin, 88% copper and 2% zinc. Zinc is added to
clean the metal and increase fluidity. It is not suitable for being worked in th cold
state.
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Properties of Gun Metal
1. It is highly anti corrosive
2. It has good machinability
3. It has good hardenability.
Uses
1. It is used for casting guns and cannons.
2. It is used for boiler fitting.
3. It is used for making bearings.
4. It is used for making glands in centrifugal pumps
1.12 White Metal
White metal contains copper-tin-antinomy and it contain 88% tin, 8%
antimony and 4 % copper.
Properties
1. It is a soft metal with low coefficient of friction
2. It has little strength
Uses
It is the most common bearing metal used into cast iron boxes when the
bearing are subjected to high pressure and load.
1.13 Aluminium
Aluminium is most abundant metal in the earth crust. It is silvery white in
colour. It makes up about 8% by weight of the earth’s solid surface Aluminium
is remarkable for its low density and ability to resist corrosion
Properties of Aluminium
1. It is a good conductor of heat and electricity.
2. It is very light in weight.
3. In pure state is very weak and soft.
Uses
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Uses
1. It is used for making automobile parts
2. It is used for ornamemtal purpose
3. It is used for making aircraft parts
4. It is used for making bars, tubes&rivets
1.14 Non Metals
1. Wood : Another name given to wood is timber.It is obtained from trees
after full growth and made suitable for engineering building process.
2. Plastics : The word plastic is commen term that is used for many
materials of a synthetic or semi synthetic nature. Now plastic materials are most
widely used for domestic as well as industrial purpose due to its low cost, light
weight and it looks decorative.
3. Rubber : Rubber is a polymer which is a word that is derived from the
greek meaning “many parts”. Natural rubber is formed in the latex which comes
from the rubber trees. It is collected in a cup mounted on each tree. Rubber is
used for making tyres, tubes, shock absorbers, rubber cushions, weather stripping
around car’s windshield and gaskets.
1.15 Safety Precautions
1. Never wear loose clothing, ties and shirts with long sleeves.
2. Keep the shop floor clean and free from oil and greese.
3. Donot use blunt or dull tool, it slips and causes injury.
4. While using chisels, see that cutting is performed in the direction away
from the body.
5. Keep hands away from moving parts.
6. There must be sufficient light and ventilation at work place.
7. Exhaust fans should be provided to remove smokes and fumes.
8. Use proper tools according to the nature of the job.
9. Use of shoes and apron is essential.
10. Never carry tools in pocket.
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11. Observe all the safety codes while working in the workshop.
Summary
1. All engineering materials are mainly clssified into metals and non metals
2. Metals are further classified in to ferrous and non ferrous metals.
3. The metals which contain iron as base are ferrous metals
4. Ferrous metals are classified in to five types i) Pig iron ii) Cast iron
iii) Wrought iron iv) Carbon steels v) Alloys steels.
5. The metals which do not contain iron as base are non-ferrous metals
6. All non ferrous metals have common set of properties
7. Steels are classified in to i)low crbon steels ii)medium carbon steels
iii)high carbon steels
Activity
1. A learner should collect a piece of cast iron and mild steel
2. A learner should collect a piece of copper,silver,aluminium and lead
Short Answer Type Questions
1. Classify Engineering materials
2. Write the properties of copper
3. What is the composition of gunmetal
4. What are uses of aluminium
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UNIT
2
Fitting
Learning Objectives
On completion of this unit a learner will be able to
• Explain various cutting tools used in fitting shop.
• Describe various work holding device used in fitting shop.
• List out various marking and measuring tools used in fitting.
• Explain about radial drilling machine.
2.0 Introduction
Although majority of the work can be finished to fairly good degree of
accuracy through various machining operations, but still needs some hand
operations to obtain desired finish and fit .These operations are usually carried
on bench by fitter. Hence fitting is the process of assembling various parts
manufactured in the machine shop. Also a fitter’s task is unavoidable when
different parts are to be assembled in position.
Hence various tools and equipments are required to perform operations to
finish the work to the desired shape and size in assembling the unit.
Tools used in fitting:
Tools used in fitting is classified into following groups:
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1. Cutting tools
2. Striking tools
3. Holding tools
4. Marking and measuring tools
In addition to the above tools ,the fitter needs other miscellaneous tools
such as screw drivers and spanners etc.
2.1 Cutting Tools
Cutting tools plays a most important role in removing excess metal from the
job to obtain desired finished part. The various cutting tools used in fitting are:
1. Chisels
2. Hacksaws
3. Files
4. Scrapers
5. Drill bits
6. Reamers
7. Taps
8. Dies and sockets
2.1.1 Chisels
Cold chisels are used for cutting thin sheets and to remove excess material
from large surfaces .In this case the surface finish and accuracy are usually poor.
Parts of chisel:It consists of following parts
a) Head
b) Body or shank
c) Point or cutting edge
Head : The head is tapered towards top and made tough to with stand
hammer blows
Body or Shank : The cross section of the shank is made hexagonal or
octagonal to have grip while working.
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Point or Cutting Edge : The cutting edge is hardened and tempered and
made to specified angle. The hardening followed by tempering makes the chisel
to maintain its sharp edge.
HEAD
SHANK
POINT
Fig. 2.1 Parts of Chisel
The shape of cutting edge is required to specify the chisel. The five most
important types of chisels are:
1. Flat chisel
2. Cross cut chisel
3. Half round chisel
4. Diamond point chisel
5. Side chisel
Flat Chisel: It is most common chisel used for chipping large surfaces and
cutting the sheets. It is also used to part off metal after chain drilling. The length
of a flat chisel varies from 100mm to 400mm and the width from 16mm to
32mm.
Fig. 2.2 Flat Chisel
Cross Cut Chisel: The cross cut chisel or cape chisel is used for cutting
grooves and channels and keys ways in shafts and pulleys. Its cutting edge
wider than the supporting metal to provide clearance. The length of chisel varies
from 100mm to 400mm and width varies from 4mm to 12mm.
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Fig. 2.3 Cross cut Chisel
Half Round Chisel : It is particularly useful for cutting oil ways ,cutting
curved grooves in bearings ,bosses and pulleys .They are also used for setting
over pilot holes. When a hole is to be drilled a pilot hole is drilled first.
Fig. 2.4 Half Round Chisel
Diamond Point Chisel.: Its edge is in the form of diamond used for cutting
V- grooves, cleaning corners and squaring small holes.
Fig. 2.5 Diamond Point Chisel
Side Chisel : This is used for chipping and removing the surplus metal in
rectangular slots. The shank of the chisel is bent out a little side way and vertically
down again.
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Fig. 2.6 Side Chisel
2.1.2 Hack Saw : It is a basic hand cutting tool used for cutting unwanted
material. It is used for cutting metals and making recesses priper to filing or
chipping. It is also used for cutting slots and contours.
Parts of Hack saw : It consists of the following parts.
1. Metal frame
2. Blade
3. Handle.
4. Wing nut
5. Screw
The frame is made to hold the blade tightly. They are made in two types.
a) The solid frame hack saw in which the length cannot be changed. b) The
adjustable frame in which the frame can be adjusted to hold the blades of different
lengths.
Adjustable Frame
Solid Frame
Wing
Nut
Handle
Pin
Stand
Blade
(b) Adjustable Frame Hacksaw
Fig. 2.7 Hack Saws
Hacksaw Blade : It is thin, narrow steel strip made of high carbon steel
or low alloy steel or high speed steel. The balde has two pin holes at the ends
which fits over two pins which project from the stand that slides in and out of the
frame end. Tightening the wing nut at the front end tensions the blade sufficiently
to prevent it from flexing when cutting. The blade must be fitted such that teeth
pionts away from the handle so that cut takes on the forward stroke.
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Blade Length
Pin Hole
Pin Hole
250 to 200 mm
Width
Direction of Cut
Fig. 2.8 Hack Saw Blade
2.1.3 FILES : File is a cutting tool with multiple teeth like cutting edges
used for producing smooth surface. The accuracy that can be acheived from
0.2 to 0.05 mm.
Point or Tip
Edge
Teeth
Face
Heel
Shoulder Feerule
Length of File
Tang
Face
Handle
Heel
Tip
Edge
Shoulder
Ferrule
Fig. 2.9 Parts of File
Parts of the File
1. Tang
2. Tip or point
3. Face or side
4. Edge
5. Heel
6. Shoulder
7. Handle
Wooden
handle
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1. Tang : It is the pionted part which fits in to the wooden handle.
2. Tip or point : It is the opposite end of the tang.
3. Face or side : This is the broad part of a file with teeth cut on it.
4. Edge : It is the safe edge of file which has no teeth.
5) Heel : The heel is next to handle of the file with or without teeth.
6) Shoulder : The curved part of the file separating the tang from the body.
7) Handle : The part which is fitted to the handle made of wood.
.
The files of different cross section or types are needed to suit the various
job operations. The most commonly used files are (a) Flat file (b) Hand File (c)
Square file (d) Round file (e) Half round file (f) Triangular file (g) Knife edge file
(h) Pillar file.
(a) Flat File : This is tapered in both width and thickness used for heavy
filing. This file is parallel to about two third of length, then tapers in both width
and thickness.
Fig. 2.10 Flat file
(b) Hand File : This is used where flat file is not suitable for filing flat
surfaces and has rectangular cross section with parallel edges throughout, but
thinkness is tapered towards point.
Fig. 2.11 Hand file
(c) Square file : This is in square cross section used for filing square and
rectangular holes and for finishing the bottom narrow slots.
Fig. 2.12 Square file
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(d) Round File : They are round in cross-section and usually tapered.
They are used for filing circular holes, curved surfaces and finishing fillets.
Fig. 2.13 Round File
(e) Half Round File : This file is tapered double-cut and its cross-section
is not a half circle but only one third of a circle. This file is used for round cuts
and filing curved surfaces.
Fig. 2.14 Half Round File
(f) Triangular File : The cross section of file is like equilateral triangle
used for filing grooves, slots , holes and sharp corners.
Fig. 2.15 Triangular File
(g) Knife Edged File : Its shape is like a knife used to file narrow slots,
grooves and sharp corners. Its width and thickness are tapered towards point in
the form of knife.
Fig. 2.16 Knife Edge File
2.1.4 Scrapers : These are used to shaving off thin slices of metal to make a
fine and smooth surface which is not possible with a file or chisel. This is made
of good quality forged steel and its cutting edge is usually made thin, made from
old files.
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Parts of Scrapers
1. Cutting edge with rounded corners. 2. Blade 3. Tang
4. Wooden handle.
Fig. 2.17 Parts of Scrapper
1. Cutting edge with rounded corners : The cutting edge is hardened
without tempered to make hard.
2. Blade : The broad part of a scraper
3. Tang : The narrow part which fits into wooden handle.
4. Wooden handle : That fits into tang to have grip while scrapping
According cross section, the scrapers are classified into three types. They are
(a) Flat Scraper (b) Triangular Scraper (c) Half round scraper.
(a) Flat Scraper
Fig. 2.18 Flat Scrapper
This type of scraper is used for scapping plane surfaces or slots and the
cutting edge at the ends of the balde is curved. The corners are rounded to
prevent deep scratches on finished surface. It also helps to scrap the metal
exactly at the desired spot.
(b) Triangular Scraper
Fig. 2.19 Triangular Scrapper
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It has three cutting edges and is made from old triangular files used to scrap
round or curved surfaces and to remove sharp corners.
(c) Half round Scraper :
It is used for finishing curved surfaces and chamfering holes and removing
burrs.
2.1.5 Drill Bits
A drill is a cutting tool for making through hole in a metal piece and usually
it has two cutting edges set an angle with axis. It does not produce accurate
hole. There are three types of drills.
(a) Flat Drill (b) Straight Fluted Drill (c) Twist Drill
(a) Flat Drill : It is a simple drill used for producing holdes in softer materials
like wood and plastic. This is made of high carbon steel and has two cutting
edges.
Fig. 2.20 Flat Drill
(b) Straight Fluted Drill : It has two cutting edges and two straight flutes
used for drilling brass and non-ferrous metals.
Fig. 2.21 Straight Fluted Drill
(c) Twist Drill : This is most commonly used cutting tool in workshop. It
has two cutting edges and two helical grooves which admits coolant and allows
the chips to escape during the drilling. These are made of high speed steel.
Neck
Shank
Cutting
Edge
Body
Flute
Fig. 2.22 Twist Drill
Land
Body Clearance
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2.1.6 Reamers : A drill does not produce accurate hole and it must be
finished by finishing tool called reamer. When an accurate hole with a smoother
finish a required a reamer is used. Hence the reamer can only follow the drilled
hole and removes very small amount of metal to make it smooth
There are two types of reamers
(a) Hand Reamers
(b) Machine Reamers
(a) Hand Reamer : This reamer is turned by hand called hand reamer.The
shank has a square tang so that a tap wrench can be used to turn the reamer in
to work. These are available with straight or helical flutes.
Fig. 2.23 Hand Reamer
(b) Machine Reamers : These are used to turn by the machine called
machine reamers. Its shank is tapered which fits directly in the internal taper of
the machine spindle. These are also available with straight shanks which are
held and driven by drill chuck.
Fig. 2.24 Machine Reamer
2.1.7 Taps : A tap is a screw like tool which has threads like a bolt and
three or four flutes cut across the threads which is used to produce internal
threads. The edge of the thread formed by the flutes are the cutting edges. The
lower part of the tap is some what tapered so that it can well attack the walls of
the drill hole.
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Hand taps are usually made in sets of three (1) Taper tap (2) Second tap
(3) Bottom tap.
(1) Taper Tap : In this tap about six threads are tapered and is used to
start the thread, so that the threads are formed gradually as the tap is turned into
the hole.
Fig. 2.25 Taper Tap
(2) Second tap : It is tapered back from the edge about three or four
threads used after taper tap.It has been used to cut the threads as far as possible
Fig. 2.26 Second Tap
(3) Bottom Tap : It has full threads for the whole of its length. This is used
to finish the work prepared by the other two taps.
Fig. 2.27 Bottom Tap
2.1.8 Dies
It is a circular disc of harderned tool steel used to make external threads on
a round rod or bolts with a die and stock. Die has a hole containing threads and
flutes which form cutting edges. These are mainly two types
1. Solid Die 2. Adjustable Die.
1. Solid Die : It is one which has fixed dimension and cannot be adjusted
for smaller or large diameter. It is used for recutting damaged threads and may
be driven by suitable wrench.
2. Adjustable Die : It can be set to cut larger and smaller diameters. It
has a split through one side and a slight adjustment is possible with the help of
set screw.
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Fig. 2.28 Two - Plate Die
2.1.9 Sockets
It is used for the drills whose taper is larger than spindle hole taper. It is
much larger than sleeve. Its taper shunk conforms to the spindle hole taper and
fits in to it.
2.2 Striking Tools --- Hammers
Hand hammers are also called striking tools used to strike the job. They
are made of forged steel of various sizes and shapres to suit various purposes
like punching, chipping, marking, bending and riverting.
2.2.1 Parts of Hammer
Face
Fig. 2.29 Parts of Hand Hammer
A hammer consists of four parts namely Face, Peen, Cheek and eye hole.
Face : It is the striking portion polished well and is given slight convexity to
avoid spoilage of the surface of the metal to be hammered.
Peen : It is the other end of the head and is made into different shapes to
suit various operations.
Cheek : Middle portion of the hammer head.
Eye-Hole : It is made oval or elliptical in shape to accommodate the handle..
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Depending upon the shape of the peen, hand hammers are classified as 1)
Ball peen hammer 2) Cross peen hammer 3) Straight peen hammer.
1. Ball Peen Hammer : It has a flat striking face and ball shaped peen
which is hardened and polished. This hammer is chiefly used for chipping and
riverting.
Fig. 2.30 BallPen Hammer
2. Cross - Peen Hammer : It has wedged shape peen across the eye. It
is used for bending, stretching, hammering into shoulders.
Fig. 2.31 Cross-Pen Hammer
3. Straight Peen Hammer : This is similar to cross peen hammer except
that the peen in this case is parallel to eye. It is used for stretching and peening
the metal.
Fig. 2.32 Straight Peen Hammer
4. Soft Hammer or Mallet : These are soft hammers used give light
blows where the work surface must not be damaged . They are made of either
rubber, plastic or wood.
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Fig. 2.33 Soft Hammer
2.3 Holding Devices or Vices
In most of the metal cutting operations quite a large number of forces will
be involved. So it is necessary that the work must be secured highly so that it
does not move when subjected to the cutting forces. Therefore, holding the job
is an important aspect of all metal cutting operations. A vice is a work holding
device used to grip the job tightly. Different types of vices are used for various
purposes. They include
a. Bench vice
b. Pipe vice
c. Hand vice
d. Pin vice
e. Tool maker’s vice
2.3.1 Bench vice
This is most commonly used tool for
holding the work. It has two jaws one of
which is fixed to the bench and other slides
with the aid of square screw and a box nut
arrangement.The outer end of screw carries
a handle, and a collar prevents the screw from
coming out of the unit while rotating.The
sliding jaw moves close to the fixed jaw to
hold the work and the tightening force is
exerted by further rotation of handle.The
working faces of jaws are serrated to give
additional grip.
Sliding Jaw
Face
Body
Handle
Fig.2.34 Bench Wise
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2.3.2 Pipe Vice
It is generally used for holding round sections ,tubes and pipes etc.It has
two serrated jaws,one is fixed and the is moved by rotation of handle.It is used
in lumbing work and it grips the circular objects at four points on its surfaces.
Fig. 2.35 Pipe Vice
2.3.3 Hand vice
It is used for gripping small objects like screw, rivets, keys when they are
inconvenient to hold by the bench vice. It has two legs made of Mild steel which
holds two jaws at the top and are hinged together at the bottom .A spring is
provided between these legs to keep them away. The work is held between the
serrated jaws by means of a wing nut and screw.
Fig. 2.36 Hand Vice
2.3.4 Pin vice
It is used for holding small parts such as wires ,nails and pins. It consists of
three jaw self centering chuck which is operated by turning the handle to hold
work.
Fig. 2.37 Pin Vice
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2.3.4 Tool makers vice
It is a small vice made of mild steel used for holding small jobs which
requires fitting or drilling.It is used by tool and die makers and silver smiths to
hold small jobs.
Handle
Fixed Jaw Movable Jaw
Screw
Body
Fig. 2.38 Tool Maker’s Vice
2.4 Marking Tools
1. Surface Plate
2. V - Block
3. Scribers
4. Angle plate
5. Punches
6. Try - Square
2.4.1 Surface Plate
Surface plate is made of grey cast iron of solid design. It is used for testing
the flatness of work and also used for marking-out the work. A surface plate has
a surface of proved flatness. When used for testing flatness,the top of the plate
should be coated with their layer of red lead in oil. The surface to be tested must
be cleaned, then place in contact with the plate and moved about. If it is reasonably
flat, subsequent examination will show spot of blue or red all over the surface.
Fig. 2.39 Surface Plate
2.4.2 V - Block : It is made of hardened steel with V-shaped grooves on
the top and botton,and rectangular slots on two sides for the location of clamps.
Roundly shaped workpieces which are to be marked or drilled are placed on
V-supports. In this way, they are firmly supported in a horizontal position and
cannot rotate easily.
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Fig. 2.40 Surface Plate
2.4.3 Scribers : It is made of tool steel with hardened and tampered
points and knurled on the body to provide grip. Scriber is used for making
straight lines on metal surface with the aid of steel rule, try square and templates.
The bent end is used to scratch line in places where the straight end cannot
reach. The ends are sharpened on an oil stone when necessary.
Fig. 2.41 Single point Scriber
Fig. 2.42 Double point Scriber
2.4.4 Angle plate : This is used in conjunction with the surface plate for
supporting work in the perpendicular position. It is madeof grey cast iron has
two plane surfaces at right angles to each other. It has various slots in it to enable
the work to be held firmly by bolts and clamps.
Fig. 2.43 Angle Plate
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2.4.5 Punches : Punches are used in a bench work for marking out work,
locating centres, etc in permanent manner. It is made of tool steel, hardened
and tempered . The shank is knurled to provide grip.
Punches are two types
1. Prick punch 2. Centre punches.
Prick punch is sharply pointed tool used for marking small dots along the
layout lines in order to make them last longer. Centre punch has an angle more
than abtuse and used to mark the centres of holes to be drilled.
Fig. 2.44 Prick Punch
Fig. 2.45 Centre Punch
2.4.6 Try Square : It is made of steel and consist of a blade and a stock
made in one piece set at right angle to each other. It is used to test trueness of
mutually perpendicular surfaces and for making straight lines at right angle to
each other.
BLADE
STOCK
Fig. 2.46 Try Square
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2.5 Miscelleneous Tools
In addition to the above tools, the following tools are widely used in fitting.
1) File Card
2) Screw driver
3) Spanner
4) Pliers
1. File Card
It is the short wire brush used to remove small chips called pins, and to
clean the file. While filing these chips are deposited between the teeth of file
which reduces cutting ability and casuing scratches on work piece.
Fig. 2.47 File Card
2. Screw Driver
Screw driver is used for tightening and loosening the screws. It is made in
variety of shapes to suit various job operations.
Fig. 2.48 Screw Driver
3. Spanners
These are also called wrenches, are used for tightening or loosening nuts
and bolts. The following types of spanners are widely used in fitting.
a. Single end Spanner
b. Double end Spanner
c. Adjustable Spanner
d. Box Spanner
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Automobile Engineering Technician
Fig. 2.49 Spanner
4. Pliers
These are used for holding small jobs which are difficult to held by hand.
They are used for bending and cutting the wires. The following types of pliers
are most common.
1. Cutting pliers
Fig. 2.50 Cutting Plier
2. Nose Pliers
Fig. 2.51 Nose plier
2.6 Checking and Measuring Instruments
Measuring Instruments :
a) Steel rule
b) Calipers
c) Depth gauge
d) Vernier Calipers
e) Micrometer
f) Gauge block
a) Steel Rule
It is used for direct measurement of length which do not require great
accuracy and also used to transfer the measurements from steel rule to calipers.
These are available in 150 mm or 300 mm in length.
Fig. 2.52 Steel Rule
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b. Calipers
These are used for measuring and transferring the inside or outside
dimensions for components. These are also used for comparing the sizes with
existing standards. The following types of calipers are most widely used in
workshops
1. Outside Calipers
2. Inside Calipers
1. Outside Calipers
It is used for measuring outside dimensions of cylindrical shapes and the
thickness of metal pieces. It has two steel legs bent inwards.
Fig. 2.53 Outside Calipers
2. Inside Calipers
It is used to measure the diameter of holes and width of key ways or
recesses. Its legs are bent outwards.
Fig. 2.54 Inside Calipers
3) Depth Gauge
It is used to measure the bling holes, slots, recesses and height of projections.
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Fig. 2.55 Depth Guage
4. Vernier Calipers
These are widely used for precision measurement of length, thickness, depth
and inside and outside diameters. With vernier caliper we can achieve accuracy
upto 0.02 mm.
Fig. 2.56 Vernier Calipers
5. Micrometer
Micrometer is a precision tool used to measure external or internal dimensions
such as diameters and thickness, with an accuracy upto 0.01 mm.
Fig. 2.57 Screw Thread Micrometer
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Barrel
Spindle
(Ext-Rod)
Thimble
Distance
Measured
Handle
Fig. 2.58 Inside Micrometer
6. Gauge Block
They are used to check the accuracy of gauges to set comparators, sine
bars and to make machine tool setups.
Vernier Slide
Work
Fine Adjustment
Beam
Vernier Scale Lock Screws
Fig. 2.59 Guage Block
7. Dividers
These are used for transferring dimensions and scrubing circles and arcs on
work surface. These are also used for dividing straight and curved lines.
2.7 Drilling Machines
Drilling is a process of making holes in a work piece and is carried out by
driving a rotating tool called “drill” into a rigidly held work peice. To accomplish
the drilling two things are required i.e. drilling macine and drilling tools. A drilling
machine is used for drilling holes. However it can perform operations other than
drilling such as reaming, boring, lapping etc.
Types of Drilling Machine
1) Portable drilling machine
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2) Sensitive drilling machine
3) Radial drilling machine
4) Upright drilling machine
5) Gang drilling machine
2.7.1 Sensitive Drilling Machine
It isa small drilling machine is mounted on a bench in which feed is hand
operated, and the cutting force applied is determined by sense of feel of the
operator. The parts of sensitive drilling machine as shown below. It consists of a
vertical column, a work table, head supporting the motor and driving mechanism,
and a vertical spindle for driving and rotating the drill.
The work is mounted on the work table which may be raised or lowered
by the clamp to accomodate work pieces of different sizes. The driving mehanism
consists of V-belt drive from machine spindle to drill spindle. Three or four
speed stepped cone pulley is provided to give various speed ranges. The spindle
is designed and mounted in a sleeve such that the spindle rotates and
simultaneously moves up and down to provide feed for drill. This is achieved by
a rack and pinion mechanism.
Fig. 2.60 Sensitive Drilling Machine
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2.7.2 Radial Drilling Machine
Radial drilling machines are used for drilling heavy work pieces, where it is
easier to move the drill rather than work and specially for the jobs where high
degree of accuracy is required. It consists of base, column, radial arm, drill head
and driving mechanism. The arm of radial drilling machine can be swing around
the column to any position and angle. A wide range of spindle speeds, together
with automatic feed of the spindle, makes the radial drilling machine suitable for
drilling large castings. For lowering or raising the radial arm, a separate motor is
provided. The work can be firmly champed on the table having T-slots. The
table is fixed to the base. The radial arm and the spindle can be adjusted without
disturbing the work setting.
Fig. 2.61 Radial Drilling Machine
2.8 Drill Fittings
The following devices are used for holding the drills.
a. Drill Chuck : It is designed to hold straight shank drills of different sizes.
The jaws of the chuck are tightened around the drill by means of drill chuck key.
. These drill chucks have standard taper shanks.
b. Machine spindle : These have morse taper holes. Standard taper drills
are directly fitted in the spindle. The drill may be removed by driving the drift..
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Automobile Engineering Technician
Fig. 2.62 Drill Chuck
Fig. 2.63 Machine Spindle
c. Sleeve : It is used to hold the taper shank drills whose taper is less than
taper hole of the spindle.
Taper Shank
Taper hole
Fig. 2.64 Sleeve Fig. 2.65 Socket
d. Socket : It is used for the drilling whose taper is larger than spindle hole
taper. It is much longer than sleeve. Its taper shank confirms to the spindle hole
taper and fits into it.
2.9 Drilling Operations
The following operations are generally performed on drilling machine.
a) Drilling
b) Reaming
c) Boring
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d) Counter boring e) Counter sinking
f) Tapping
a) Drilling : It is the process of making cylindrical hole by rotation of
cutting tool.
b) Reaming : It is the process of making a hole smoothly and accurately
by the tool called reamer.
c) Boring : It is the operation of enlarging a drilled hole to bring it to
required size by using single point cutting tool.
d) Counter boring : This operation is used for enlarging only to a certain
depth of already drilled hole in order to maintain alignment and true concentricity
of the counter bored hole with the previously drilled hole and the tool is provided
with a pilot at its bottom.
e) Counter Sinking : It is the operation of enlarging the end of a drilled
hole to give a conical shape for a short distance. This is done for providing a
seat to the counter sunk heads of screws.
f) Tapping : It is the operation of cutting internal threads by using a cutting
tool called tap. In order to tap the hole, a special tapping chuck must be used.
Drilling
Counter Sinking
Reaming
Tapping
Fig. 2.66 Drilling Machine Operations
Boring
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Summary
1. Fitting is the process of assembling various parts manufactured in the
machine shop.
2. In fitting the hand tools are classified as cutting tools, marking tools,
striking tools,holding tools, measuring and checking instruments.
3. Chisels are used to cut thin sheets and to remove excess material in the
form of layers
4. Hacksaw is abasic hand cutting tool used to remove excess metal from
the job
5. Files are used to remove excess metal from the job in the form of powder to make it smooth
6. Scrapers are used to remove excess metal in form of thin layers at selected spots to make it truly flat surface
7. Drilling is the process of making circular holes on the metal piece by
rotating the tool against work piece
8. Reamer is a tool used to finish the already drilled hole on cylindrical
holes
9.Tap is acutting tool used to cut internal threads and dies are used to cut
external threads on the cylindrical rods and pipes
10. Striking tools are hammers used to strike the work or tool
11. Holding devices are used to hold work tightly to prevent slipping during
cutting operations.
Activity
1. A learner should collect L-shape M S flat.
2. A learner should collect T-shape MS flat.
Short Answer Type Questions
1. What is the use of a file.
2. What is the purpose of chisel.
3. Define scrappers.
4. Differentiate tap and die.
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5. What are srtiking tools.
6. Define drilling and reaming.
7. What is the importance of holding devices.
8. Name different types of drilling machines.
Long Answer Type Questions
1. Define file and explain about any four files with sketch.
2. Explain about bench vice with naet sketch.
3. Define chisel and Explain about any two.
OJT Type Question
1. Prepare U,V,L& T Shapes from a given MS Flat
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Automobile Engineering Technician
UNIT
3
Sheet Metal Work
Learning Objectives
On completion of this unit, a learner will be able to
• List out metals used for sheet metal work.
• List and explain various tools used in sheet metal work.
• Explain various sheet metal operations.
• List and explain various sheet metal joints commonly used.
• Explain various fastening methods.
3.0 Introduction
Sheet metal work is generally regarded as the working of metal from 16
SWG down to 30 SWG with hand tools and simple machines into various
forms by cutting ,forming into shapes and joining. Each guage designates a definite
thickness.Higher the gauge number and lesser the thickness. The common
examples of sheet metal work are pipes, boxes, funnels, photoframes, buckets,
and cans etc. In sheet metal work the knowledge of geometry, mensuration and
properties of metal are most important for preparation of specific object.
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3.1 Metals used in Sheet Metal Work
The following metals are used in sheet metal work.
1. Black iron
2. Galvanised iron
3. Copper
4. Aluminium
5. Tin
6. Stainless Steel
1. Black Iron :It has a bluish black appearance. It is cheapest metal and
rusts rapidly . Its use is limited to fabrication of articles for general use and are
to be painted with enamel for protecting them from rust. It is used for making
tanks, stoves, pipes etc.
2. Galvanised Iron : Zinc coated iron is called galvanised iron. This is soft
sheet is popularly known as G.I. sheet. The zinc coating resists rust, improves
the appearance of the metal and permits it to be soldered with ease. It is used
for making buckets, pans, cabinets, gutters etc.
3. Copper : Copper resist rust and have better appearance, but the cost is
very high. It is used for ornamental work and making kitchen wear.
4. Aluminium : It is not used in pure form as it is very soft, but it is used
with a small amount of copper, silicon, manganese etc. It is anti corrosive and
has good appearance, relatively cheap and light in weight. It is used in making a
number of articles like household appliances, refrigerator trays, light fixtures,
windows, in the construction of aero plane parts etc.,
5. Tin : Steel sheets are coated with pure tin and have bright silvery
appearance. This is used for nearly all solder work as it is easiest metal to join
by soldering. The thickness of the tin plates are denoted by special marks not by
gauge numbers. It is used for making buckets, pans, cans, etc.
6. Stainless Steel : Resists rust and has pleasing appearance. But the cost
is high. This is alloy of steel with nickle, chromium and traces of other elements.
It is used in canneries, food processing plants and chemical plants, kitchen
wares etc.
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3.1.1 Sheet Metal Hand Tools
A large number of hand tools used by sheet metal workers. Some of the
important tools used are given below.
1. Measuring tools
(a) Steel rule
(b) Folding rule
(c) Circumference rule
(d) Vernier Calipers
(e) Micrometer
(f) Sheet metal guage
2. Straight edge
3. Scriber
4. Divider
5. Trammel point
6. Chisel
7. Punches
8. Hammers
9. Snips or Shears
10. Pliers
11. Stakes
12. Groovers
13. Rivetsets
14. Soldering Iron
3.1.2. Measuring Tools
(a) Steel Rule : It is used for measuring and layouting small works with an
accuracy upto 0.5 mm.
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Fig. 3.1 Steel rule
(b) Folding Rule : It is used for measuring and laying out larger work
pieces accuracy upto 0.5 mm
Fig. 3.2 Folding rule
(c) Circumference Rule : It is used to find out directly the circumference
of a cylinder. One of the edge is marked with diameters and the values of
circumference corresponding to each diameter is marked in the other edge.
Fig. 3.3 Circumference Rule
(d) Vernier Caliper : It is used for measuring dimensions upto 0.02 mm.
Fig. 3.4 Vernier Caliper
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Automobile Engineering Technician
(e) Micro Meter : This is used to measure the thickness of the metal
sheet accurately upto 0.01 mm.
Fig. 3.5 Micrometer
(f) Sheet Metal Guage : This is used to measure the thickness of the
sheet.
Fig. 3.6 Sheet Metal Guage
(2) Straight Edge : It is a steel bar has one long edge is bevelled and
comes in variety of lengths. It is used for drawing long straight lines.
Straight Edge
Work
Scriber
Fig. 3.7 Straight Edge
(3) Scriber : It is a steel wire and its one end is sharply pointed and
hardened to mark layout lines on the sheet metal.
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Fig. 3.8 Single point Scriber
Fig. 3.9 Double point Scriber
(4) Divider : Dividers are used to draw circle or arcs on sheet metal and to
divide the lines into two equal parts.
Fig. 3.10 Divider
(5) Trammel Point : These are used to describe large circles and arcs
beyond the limits of dividers.
Fig. 3.11 Trammel point
(6) Chisels : These are used to cut sheets, rivets, bolts and for chipping
operations.
Fig. 3.12 Chisels
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(7) Punches : There are various types of punches used for making small
indentation for locating centres in a more permanent manner. There are two
most common types of punches are used 1) Prick punch, used for making small
dots 2) Centre punch, used for making location of points and centre of holes to
be drilled.
Fig 3.13 Punches
(8) Hammers : Hammers are used for forming shapes by hollowing,
stretching or throwing off. The commonly used hammers are given below.
(a) Ball peen Hammer : It is a general purpose hammer
(b) Rivet Hammer : This is used for spreading rivets .
Fig 3.14 River Hammer
(c) Setting Hammer : A flat face is used for flattering seams without
damage to the sheet metal.
Fig 3.15 Setting Hammer
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(d) Raising Hammer : This hammer is used for denting the metal down
to shape.
Fig. 3.16 Raising hammer
(e) Mallet : Mallets are used where ever light blows are required. These
may be made of either fiber, plastic, wood or rubber.
Fig. 3.17 Mallet
(9) Snips or Shears : These are heavy scissors used for making straight
or circular cuts. It is used only to cut 20 guage or thinner metals. The most
common types of snips are a) Straight snips, used for straight cuts, b) Bent
snips, used to make curved cuts.
Fig. 3.18 Straight Snips
(10 ) Pliers : There are two pliers which are used in sheet metal work.
They are flat nose plier and round nose plier. Flat nose pliers are used for
forming and holding work while round nose pliers are used for holding and
forming in to various shapes.
Fig. 3.19 Pliers
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(11) Stakes : These are sheet metal worker’s anvil used for bending
seaming, forming using hammer or a mallet. They are actually work supporting
tools while working. They are made in different shapes and sizes to suit the
requirements of the work. The double seaming stake is used to make double
seam. The break horn state is used for riveting, forming round and square
surfaces, bending straight edges and making corners. The bevel edged stake is
used to form corners and edges. Hatched stake is used to make straight and
sharp bends .
Honk
Head
Shanks
Fig. 3.20 Stakes
(12) Groovers : These are used for grooving and flattening a seam. These
are available in many shapes.
Fig. 3.21 Groovers
13) Rivet Set : Rivetset has a deep hole in the bottom to draw a rivet
through metal and a cup shaped hole to form the finished head of a rivet.
Outlet on side
Burrs Outlet
Deep hole
Shallow concav
Fig.3.22 Sections of Rivet Sets
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(14) Soldering Iron : It is used to join two pieces of sheet metal by soft
soldering (al alloy of tin and lead). Soft solder is transferred to the joint by
means of soldering iron.
(a) Straight Iron
(b) Hatchet Iron
Fig. 3.23 Types of Soldering Irons
3.2 Sheet Metal Operations
The major types of sheet metal operations are given below.
(1) Shearing
(2) Bending
(3) Drawing
(4) Squeezing
(1) Shearing
Shearing is the process of cutting across a sheet or strip. The various shearing
operations include
(a) Cutting off
(b) Parting
(c) Blanking
(d) Punching
(e) Piercing
(e) Slitting
(g) Trimming
a. Cutting Off : It is the operation of shearing the piece from sheet metal
with a cut along a single line.
b. Parting : This means that the strip is removed between the two pieces to
part them.
c. Blanking : It is the operation of cutting the flat sheet to the required
shape and size using punch and die.
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Automobile Engineering Technician
d. Punching : It is the operation of making only circular holes in a sheet
metal.
e. Piercing : It is the operation of making a hole of any shape in a sheet
metal by punch and die.
f. Slitting : It is the operation of cutting the sheet metal in a line along the
length.
g. Trimming : It is the operation of finishing the edges of a part by removing
excess metal around it.
2. Bending : It is the folding operation by using suitable tools. It may be
done over stakes. The common forms of bending the sheet metal is single bend
and double bend etc.
3. Drawing :It is the process of producing thin walled hallow or vessel
shaped parts from the sheet metal. Again this process can be divided into two
types. a) Deep drawing and shallow drawing..In deep drawing, the height of the
component is greater than the diameter or width. In shallow drawing the height
of the component is less than the diameter or width.
Fig. 3.24
(4) Squeezing : It is the quick and widely used method. The operation
involves severe cold deformation and it requires a greater amount of pressure
to deform the metal at cold state.
The most commonly used squeezing operation are sizing, coining, hobbing,
riveting.
(a) Sizing : This operation is used for surfacing or flattening. A special die
is needed for every job.
(b) Coining : This is a process of making impressions or raising of images
by a plastic flow by using a punch and die.
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(c) Hobbing : It is the process of producing cavities into surface of material
by pressing with a special punch called hub.
(d) Riveting : It is the process of fastening the two metal sheets by inserting
metal pin in to the sheets and spreading out by hammering to form the rivet
head.
3.3 Sheet Metal Joints
3.3.1 Hem and Seam Joints
(1) Hem Joint : Hem is an edge or border made by folding. It strengthens
the edges and eliminate the sharp edges. Hems are three types a) Single hem b)
Double hem c) Wired edged hem
(a) Single Hem : It is made by single folding of the edge of sheet metal.
Fig. 3.25 Single Hem
(b) Double Hem : It is made by folding the edge over twice to make it
smooth. It provides much greater strength than single hem.
Fig. 3.26 Single Hem
c) Wired Edged Hem : It consists of holding a piece of sheet metal around
a wire of given diameter.
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Automobile Engineering Technician
Sheet
Hammer
Wire
Fig. 3.27 Wired Hem
(2)Seam Joint : It is the joint formed by two edges of sheet metal. The
process of joining the edges are called seaming. Different kinds of seams are
given below. a) Lap seam b) Groove seam c) Single seam d) Double seam e)
Dovetail seam f) Flanged Seam
a) Lap Seam : It is a simple type of seam which consists of lapping the
edgeof one sheet over the other and the joint is made by soldering or riveting.
Fig. 3.28 Lap Seam
(b) Grooved Seam : It is made by hooking two single hems together
Fig. 3.29 Grooved Seam
(c) Single Seam : Single seam is used to join a bottom to vertical bodies
of various shapes.
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Fig. 3.30 Single Seam
(d) Double Seam : It is similar to single seam with the difference that its
formed edges bent upwards against the body.
Fig. 3.31 Double Seam
(e) Flanged Seam : It is used to join the bottom of a container to its body.
Fig. 3.32 Flanged Seam
(f) Dovetail Seam : It is used to join sections such as one pipe to another
pipe or a sheet to pipe It consists of narrow strips of metal which are formed by
slitting the end of pipe.
Fig. 3.33 Dovetail Seam
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3.3.2 Fastening Methods
The following fastening methods are widely adopted in sheet metal work.
(a) Riveting
(b) Soldering
(c) Brazing
(d) Welding.
(a) Riveting : It is a permanent fastening method by using rivet. Rivet
consists of head, shank and tail are generally made of same metal as the parts
that are being joined. The required holes must be either punched or drilled before
riveting.
Hammer Blow
Hammer Blow
a) Drawing Rivet Set
b) Shaping Rivet Set
c) Forming Rivet
Fig. 3.34 Rivet Sets
(b) Soldering : It is the process of joining two or more metal pieces by
means of an alloy. This alloy is called solder made of lead and tin. The melting
point of solder is less than the metal to be joined. For soldering, the base metal
is heated by soldering iron which also melts solders and flux. the flux (zinc chloride
paste) is used to dissolve the oxide film on the surface and also prevents oxidation
during soldering. The molten solder fills the space between mating surfaces. It
solidifies and forms a strong joint.
Solder
Solder Iron
Fig. 3.35 Solder
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c) Brazing : It is similar to soldering, but it gives much stronger joint. The
major difference is that use of a harder filler material called spelter and its melting
point is higher than solder., but lower than the metal being joined. In brazing
operation the two metal pieces are to be joined must be cleaned. Flux (Borax)
is applied on the joint and heated to a temperature just above the melting point
of the spelter. The liquid spelter is distributed between the surfaces by capillary
action. After solidification it forms strong joint.
d) Sport Welding : The spot welding is used for joining the sheets by
application of heat and pressure at specific locations called spots. In this, the
sheets to be joined together are held between two electrodes at required located
sports. Normally a high amperage current and low voltage is passed through
electrodes causing local heating at that spots. The pressure applied on the
electrodes squeezes the sheet metal at various locations thus joining the two
sheets together to form a joint.
1,2 Electrodes
3. Movable Arm
4. Fixed Arm
5. Frame
Spot Weld
Tra nsformer
Fig. 3.36 Sport Welding
Summary
1. Sheet metal work is the process of making useful articles for household
as well as industrial.
2. Commonly used sheet metals are black iron, galvonised iron, copper,
aluminium, stainless steel etc.
3. Tools used in sheet metals are measuring tools and operational tools.
4. Most common sheet metal operations are shearing, bending, drawing,
squeezing etc.
5. Important fastening methods in sheet metal are riveting, soldering, brazing
and spot welding.
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Automobile Engineering Technician
Activity
1. A learner should collect funnel madeof sheet metal.
2. A learner should collect a square tray
3. A learner should collect riveted joint sheet metal piece.
4. A learner should collect soldered joint sheet metal piece.
Short Answer Type Questions
1. Name different tools used in sheet metal work.
2. Define Seam in sheet metal work.
3. What is the purpose of mallet ?
Long Answer Type Questions
1. Explain about any four important sheet metal operations.
2. Explain different sheet metal joints with sketches.
3. Explain brazing and soldering.
OJT / Related Questions
1. Prepare a rectangular tray from a given G.I . sheet
2. Prepare a funnel of given dimensions from G.I. Sheet metals.
3. Join the given two sheet metal pieces by soldering.
4. Join the given sheet metal pieces by riveting.
UNIT
4
Carpentary
Learning Objectives
On completion of this unit a learner will be able to
• Explain various hand tools used in carpentry
• Know the importance of holding devices
• Explain about various carpentry joints
• Know the different carpentry processes
4.0 Introduction
Carpentry deals with the processing of wood to obtain desired shapes
and sizes. Strictly speaking carpentry deals with all works of a carpentry such
as roofs, floors, partitions etc of a buildings. While joining deals with the making
of doors, windows, cupboards, dressers stairs and all interior fitments for a
building.
Timber is the basic material used for any type of wood work. It is available
in a wide choice of weights, strengths, colours and textures. Wood having good
machining characteristics.
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4.1 Markings and Measuring Tools
Marking is one of the most important features of wood work and the job
accuracy depends upon marking and measuring. These tools are used in wood
work for marking, measuring and checking the work at various stages.
Measuring Tools
The following tools are commonly used in wood work.
1. Steel rule
2. Wooden folding rule
3. Steel tape
(1) Steel Rule : It is simplest and direct measuring instrument. Various
sizes and designs are available for measuring and setting out dimensions. This is
graduated on both sides as millimeter and centimeter.
(2) Wooden Folding Rule : This is graduated both in centimeters and
inches. The most commonly used wooden rule is form fold wood rule. It is
made of pieces of each 150mm length.
(3) Steel Tape : This is used to measure longer dimensions. They are
available in different lengths ranging from 0.6 m to 2.5 m.
(a) Steel Rule
(b) Four-Fold Rule
(c) Steel Tape
Fig. 4.1 Measuring Tools
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Marking Tools
The following tools are used for marking in wood working.
(1) Straight Edge
(2) Try square
(3) Marking guage
(4) Divider
(5) Marking knife
(1) Straight Edge : The straight edge is a machined flat piece having truely
straight and parallel edges. One of the longitudinal edge is generally made
bevelled. It is used for testing trueness of surface and straightness of edges.
Straight Edge
Work
Scriber
Bevelled Edge
Fig. 4.2 Straight Edge
(2) Try Square : This is used for marking and testing angles of 90o. It
consists of a steel blade, rivetted to a hard woodstock which has a protective
brass plate on the working surface.
Fig. 4.3 Try square
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(3) Mitre Square : It is used for marking and testing 45o. It consists of a
steel blade fitted in a wooden or metal stock at an inclination of 45o with
horizontal.
Fig. 4.4 Mitre Square
(4) Marking Knife : All the dimensional lines marked with pencil are cut
with marking knife. It has a chisel edge at one end and sharp point at other end.
It is made of steel.
Fig. 4.5 Marking Knife
(5) Marking Guage : It is commonly used when absolute accuracy is
required. It has a stem with a sharp point pin at one end. It is used to cut line
along the grains and parallel to an edge. The distance can be adjusted by sliding
the stock.
Fig. 4.6 Marking Guage
(6) Divider : It has two pointed legs and hardened to prevent wear. It is
used for transferring dimensions and scribing curves or circles.
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Fig. 4.7 Divider
4.2 Cutting Tools
Cutting tools are used to cut the wood to approximate size. The following
cutting tools are used in carpentry.
(a) Saw or Hand Saw : The saw is most commonly used cutting tool in
wood working section. All saws used in wood work essentially consists of two
main parts - the blade which carries the cutting teeth and the handle used for
holding during the cutting operations to apply pressure. The classification of
saws is according to their teeth and the direction of grains of the wood to be cut.
Fig. 4.8 Hand Saw
The following types of saws are used in wood working.
(b) Rip Saw : Rip saw is used to cut the wood along the grains. The cutting
action starts from near the tip and gradually the whole length.
Fig. 4.9 Rip Saw
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(b) Crosscut Saws : It is used for cutting the wood across the grains. The
action of the teeth is that of a series of knives which sever the fibre and force out
the waste wood in the form of saw dust.
Fig. 4.10 Cross-cut saw
(c) Panel Saw : It has a fixer blade and is used for fine work, mostly on the
bench. This is often used for ripping as well as cross cutting. The teeth have
slightly more hook than those of a cross cut saw.
(d) Tenon Saw : This saw is mostly used for cross-cutting when a fine and
more accurate finishing is required. The blade is very thin and reinforce with a
rigid steel back.
Fig. 4.11 Panel Saw
(e) Dovetail Saw : It is a smaller version of tenon saw, this saw is used
where the greatest accuracy is needed and fine shallow cuts are to be needed.
Fig. 4.12 Dovetail Saw
(f) Bow-Saw : It has a narrow blade which is held in tension by twisting the
string with a small wooden lever. These saws are used for cutting quick curves
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and the handles can revolve in their sockets. The blades can be adjusted to any
desired position when in use.
Fig. 4.13 Bow Saw
(g) Key Hole Saw : It is smallest saw. It has a tapered blade fixed into the
handle by screws. It is used for cutting key holes and is very useful for internal
and intricate work.
Fig. 4.14 Key hole Saw
Chisels : A fairly large number of chisels are used in wood work for cutting
in different manners to produce desired shapes and cavities. The chisel consists
of these parts irrespective of their size and use. The common types of chisels are
used in carpentry work are the following.
Handle
Brass
Tang
Shoulder
Neck
Blade
Cutting Edge
Fig. 4.15 Chisel
Handle
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(i) Firmer Chisel : This chisel is capable of doing heavy work and is used
for joining and shaping the wood with or without mallet. The blade is made of
rectangular section with bevel edge.
(ii) Paring Chisel : These chisel have a long blades used to cut the deep
corners with hand pressure. These are mostly used for pattern making.
(iii) Mortise Chisel : It is used for taking heavy and deep cuts resulting in
more stock removal as in case of making mortises.
(iv) Socket Chisel : It is provided with socket instead of tang. The wooden
handle is inserted into this socket. This prevents splitting of handle while removing
heavy stock.
(i) Firmer Chisel
(ii) Pairing Chisel
(iii) Mortise Chisel
Blade
Socket
Handle
(iv) Socket Chisel
Fig. 4.16 Types of Chisels
Planes
Planes are used in producing flat and smooth surfaces by cutting thin layers
of wood. The plane consists of these parts - Body, cutting blade, handle, knob
and other controls. The common types of planes used in carpentry are
(a) Jack Plane : It consists of a wooden body or stock in which blade or
cutter is fastened at an angle 45o to the sole. The plane iron and cap iron are
assembled and inserted in a mouth of plane along with the wedge. The back iron
supports the cutting edge and also breaks the shavings so that curl away from
the blade. The blade can be set for taking deeper or shallower cuts.
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Fig. 4.17 Wooden Jack Plane
(b) Trying Plane : These are used to make a true flat surfaces which are
formed by jack plane. It is longer than jack plane.
Fig. 4.18 Trying Plane
(c) Smoothing Plane : It is nothing but a smaller wooden jack plane without
handle. In operation its stock itself is held in both hands. It is used for better
finish and smoothness to the surface already plane by a jack plane.
Fig. 4.19 Smoothing Plane
(d) Rebate Plane : It is small in size and is used to cut the recess along the
edge of a work piece. In rebate plane the edges of cutting iron is in line with the
side of plane.
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Fig. 4.20 Rebate Plane
(e) Plough Plane : It is used for making deep grooves of standard size. A
deep guage is fixed on the body, and is operated by thumb screw. It allows the
plane to make a groove of constant depth.
Fig. 4.21 Plough Plane
(f) Router Plane : These planes are used for finishing the grooves to a
constant depth which are formed by chisel or saw.
Fig. 4.22 Plough Plane
Boring Tools
Boring tools are necessary to make holes in wood. The various types of
boring tools used are as follows
(1) Bradawl : It is used for boring small holes for inserting the screws and
nails. It has chisel like point and it is operated by hand.
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(a) Bradawl
(b) Gimlet
Fig. 4.23
(2) Gimlet : It is hand operated tool used for making small holes for screws.
It has a spiral flutes with screw like point.
(3) Brace : It is a boring tool used for making holes. It holds and rotates
various types of bits for producing holes and is operated by hand.The most
commonly used braces are ratchet brace and wheel brace. These are used for
making larger holes of different sizes.
Head
Crank
Sweep
Handle
Cam Ring
Ratchet
Chuck
Jaws
Fig. 4.24 Ratchet Braces
(4) Auger bit : It is used for producing long deep holes of diameter ranging
from 6 to 40 m. It is steel bar , an eye at top to which the handle is fitted. The
bottom end is provided with a screw point.
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Fig. 4.25 Auger
Striking Tools
Striking tools are called hammers used to drive in nails and to operate
chisels. The most common striking tools used in carpentry are hammers and
mallets.
(a) Warrington hammer:It is used for bench work and light work. It is
made of cast steel with tempered face and peen. The wooden handle fits in the
eye and steel widge is driven in to form a rigid joint.
(b) Claw Hammer: It is dual purpose hammer and face is used to drive in
nails, and claw at the other end for pulling out nails.
(c) Mallet : It is used for operating the chisel and gauges. it is made of
hard wood and is provided with handle.
(a) Warrington Hammer
(b) Claw hammer
(c) Mallet
Fig. 4.26 Striking Tools
4.3 Holding Devices
To enable the wood worker to cut the wood accurately, it must be held
steady. There are number of devices to hold the job
(a) Bench vice : it is made of steel. It has the jaws, one is fixed to the side
of the table while the other is kept movable by means of a screw and handle.
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The job tab is held between the two jaws. The faces of jaws are lined with hard
wood to prevent damage of work surface.
Fig. 4.27 Bench Vice
(b) Bench Stop : It is simply a block of wood projecting above the top
surface of the bench. This is used to prevent the wood from moving forward
when being planed.
(c) Bench hold Fast : It consists of a cast iron pillar, steel arm and screw
with a handle. It is used for securing the work to the bench. The pillar drops into
a hole bored in the bench and the screw operates the arm to hold work on the
table.
Fig. 4.28 Bench Hook
Fig. 4.29 Bench Holdfast
(d) Bench hook : It is used to support work while planning or cutting. It is
made of wood and can be placed conveniently on the work table.
(e) Sash Cramp : This is used for holding wide work such as frames or
tops. It consists of a steel bar fitted with two jaws one of which is movable by a
screw and other is fixed into one of the spaced holes by a fastening pin.
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Fig. 4.30 Sash Cramp
(g) G-Clamp : It is used to hold small works and it consists of frame with
a fixed jaw at one end and movable jaw is operated by a screw and a thumb nut
at the other end. It is also used to hold small parts for gluing.
Fig. 4.31 G-Clamp
4.4 Miscellaneous Tools
(1) Rasp or File : It is used for finishing the wood surface. It has sharp
cutting teeth and it is used for finishing small curved surfaces.
(b) File
(a) Rasp
Fig. 4.32 Rasp and File
(2) Scraper : It has a fine edge which cuts fine shavings and removes plane
marks.
(3) Glass paper : Where a surface is having very small imperfections that
the no other cutting tool will do, then glass paper is used. It consists of small
particles of glass struck tosheet of paper. Its sharp edges cuts the wood.
(4) Ratchet Screw Driver : It is very useful for turning screws through a
few degrees in.
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(a) Cabinet Screw Driver
(b) Ratchet Screw Driver
Fig. 4.42 Types of Screw Driver
(5) Screw Driver : These are used for screwing or unscrewing for the
screws used in wood work.
4.5 Carpentary Processes
1. Marking : It is one of the most important operation of wood work and
the success of completing a job depends on accurate and orderly marking.
These dimensions can be measured from an existing model and can be set out
from the drawing prepared for the purpose. The dimensions are marked with
respect to the finished edge or finished face of a work.
2. Sawing : Sawing is one of the basic cutting operation carried out in a
carpentry shop. To start the cut, the thumb of left hand is placed against the
blade. This steadies the blade and enabling it to start in the right place. One or
two short movements are given first, taking care that the saw works in the right
direction. And then full, easy strokes are applied to cut the wood in a forward
direction only. A point to note in all sawing work that the cut is made on one side
of the line already marked and that is on waste side
Fig. 4.33 Sawing
3. Planing : It is the operation of tuning up a piece of wood by a planner.
The work for planning is supported by the bench stop in the vice. The pressure
is applied during forward stroke and released on the returned stroke. It is
important to move plane in straight line to avoid rounding at the ends and to
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obtain smooth surface. Planing is done along the grains. The surface planed are
tested for flatness in all directions using a try square.
(a) Surface Planning
(b) Edge Planning
Fig. 4.34 Planning
4. Chiselling : It is the process of cutting excess wood with chisel to obtain
desired shape. In chiselling hard pressure is applied to remove thin layers. Mallet
is used when cuts are made across the grains.
(a) Horizontal Paring
(b) Vertical Paring
Fig. 4.35 Chiselling
5. Boring : It is the process of making holes in wood. The work is secured
to suitable vice and the hole position is marked with punch. The hole is provided
by turning and feeding the bit into work.
6. Rebating : It is the process of cutting a recess along the edge of wood
by a rebate plane. While rebating, the plane must be kept pressed into the side
of the wood.
7. Polishing : It is the process of producing a smooth reflecting surface
with only the minimum removal of material. To obtain such a finish it is necessary
to incorporate a suitable abrasive within the polishing composition.
4.6 Carpentary Joints
Terms joinery involves connecting of different wooden parts together by
means of properly made joints. In order to achieve good results, the joint made
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in wood work are usually secured firmly by means of suitable fastners such as
glues, dwels, screws, bolts and buts etc.
1. Halving Joint : The purpose of this joint is to reuse the corners and
inter sections of the framing and at the same time keep all the face flush that in
the same plane. These joints are used in construction of frames. Marking and
cutting of any joint must be accurate, so that it can shed together with the final
extreme surface level.
(a)Dovetail
Halving joint
(b)T- Joint
Fig. 4.36 ‘T’ Halving Joint
2. Mortise and Tenon Joint : It is strongest joint and is used for the
construction of doors windows and frames. The tenon (tongue) fits into a mortise
(mouth).
3. Mitre Joint : It is formed by cutting the ends at an angle. The two ends
are joined by nails or screws. This joint is used in photo frames.
Fig. 4.37 Mortise & Tenon Joint
4. Dovetail Joint :This is strongest joint used for construction of boxes
and cup boards.
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Fig. 4.38 Mitre Joint
Fig. 4.39 Dovetail Joint
5. Butt Joint : The fastening of boards edges to edges is frequently
necessary to give a wider board. eg. Drawing board. In butt joint two true
edges are joined with glue. If it is properly done this joint is very strong.
Fig. 4.40 Butt Joint
4.7 Wood Working Machines
Wood working machine plays a vital role in the modern wood work
particularly where large scale production of wooden articles is carried out.
Modern development in wood working machinery with regard to the greater
safety for the operator, easy operation and greater accuracy. These developments
led to higher output.
The commonly used wood working machines are as follows.
1. Wood Turning Lathe : It is one of the important and oldest machine
used in carpentry shop. This is employed primarily for turning jobs in making
cylindrical parts. It resembles the engine lathe most frequently used in the machine
shop and consists of a cast iron bed, head stock, tail stock, tool rest, live and
dead centres and speed control device.
In practice the work piece is either clamped between two centres or on the
face plate. Long jobs are held between the centres and turned with the help of
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goauge, chisel, parting tools. Generally the lathe is supplied together with a number
of accessories for making it useful for a variety of jobs.
Fig. 4.41 Wood Turning Lathe
2. Circular Saw : It can be used for ripping, cross cutting, bevelling and
grooving. This saw has flat table upon a which the work rests while being cut, a
circular cutting blade, cut-off guide and a ripping fence that acts as a guide while
sawing along the grain of the wood. The circular saw usually has provisions for
tilting the table upto 45o to enable the machine to cut at different angles required
during mitering and levelling.
Fig. 4.42 Circular Saw and Its Use
3. Band Saw : It means that an endless metal saw band that travels over
the rims of two or more rotating wheels. Other parts of band saw are frame,
table ,saw guide, saw tensioning arrangement. It is most useful for making curved
or irregular cuts in wood. The band saw is available in two models vertical and
horizontal. In horizontal band saw, two wheels are arranged side by side and the
table is mounted underneath. In the vertical band saw the wheels are arranged
one over the above in a vertical plane below the table, angular cuts are obtained
by tilting the saw table.
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Fig. 4.43 Band Saw
4. Wood Planner : It is used for planning large work pieces and capable
of producing true surface with enough accuracy at a faster rate. It consist of
table over which the work is fed against a revolving cylindrical cutter head carrying
2-3 knifes. The cutter is mounted on a over head raft and the table can raised or
lowered to attain desired thickness.
Fig. 4.44 Principle of Wood Planer
5. Sanding Machine : The sanding machine are used for producing smooth
surface after planning the wood. It seems a surface suitable for painting. The
action of sanding machine is some as the sand paper producing the smooth
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surface. In sanding an abrasive is rubbed over the surface of wood to wear
down hills by friction and thus present a smooth, uniform surface.
Work Piece
Stop
Guard
Table
Wheel
Tool or workres
Belt
Fig. 4.55 Belt Sander
Fig. 4.56
Summary
1. Carpentry is the processing of wood to obtain desired shape and size
2. In carpentry hand tools are classified in to five types ie marking tools ,
cutting tools ,boring tools ,striking tools and holding devices.
3. The wood working operations includes marking, sawing, planing,
chiseling, boring and rebating.
4. The successful construction of wood depends on satisfactory joining.The
most common carpentry joints are halving joint,mortise joint tenon
joint,mitre joint,dovetail joint,and butt joint.
5. Wood working machines are primarily intended to increase the
productivity with higher accuracy which includes wood turning lathe,band
saw,circular saw, sanding machine.
Activity
1. A learner should collect T-halving joint.
2. A learner should collect plain tenon joint.
3. A learner should collect dovetailbridge and bridge cornerjoint.
Short Answer Type Questions
1. Name different cutting tools used in carpentry.
2. What is the use of pincer.
3. Name different types of planes.
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4. Listout carpentry joints.
Long Answer Type Questions
1. Explain about any four carpentry processes.
2. Explain about wood turning lathe with neat sketch.
OJT Questions
1. Make saw practicing.
2. Make Plane practicing.
3. Make boring practice.
4. Prepare a corner , T , butt joints etc., from a given wooden piece.
UNIT
5
Forging and Welding
Learning Objectives
On completion of this unit, a learner will be able to
• Know different types of hand tools, and their usage.
• Describe important smithy operations.
• Explain various machine forging operations.
• Know the safety precautions to be followed while doing welding.
• Get the knowledge about arc welding and gas welding procedure and
proper handling of equipment used for the purpose
5.0 Introduction
Forging is the process of deforming the metal into different shapes by heating
up to plastic state and by hammering or pressing at red hot condition. The process
is usually carried out above re-crystalization temperature. Therefore this process
is called hot working process. The term usually preferred to the production of
heavy parts and in large scale.
5.1 Hand Tools used in Forging
The following hand tools are used in forging.
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1) Anvil
2) Swage block
3) Tongs
4) Hammer
5) Chisel
6) Hardie Tools
7) Swages
8) Fullers
9) Flatters
10) Set Hammers 11) Punches
12) Drifts
1. Anvil : The anvil forms a good support for black smith’s work when
hammering. Its body is made of mild steel. These are made in different forms to
provide the means for other forging operations. The usual form of anvil has a
round hole called pitchel hole for bending rods and a square hole called hardie
hole for holding square shanks of various tools such as swages, fullers, hardies,
chisels.
Round Hole
Hardie Hole
Working Face
Step
Cutting Face
Body
Horn
Beak
Fig. 5.1 Anvil
2) Swage Block : It has different sizes and shapes of slots like half round,
square and rectangular along its four sides. It is made of cast iron. This is used
as a support in punching holes and forming different shapes.
Fig. 5.2 Swage Block
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3. Tongs : Blacksmith requires tongs to handle the job while forging. These
are used to hold the job in position and turning over during forging. The commonly
used tongs are
(a) Closed mouth
(b) Open mouth
(c) Round hollow tong
(d) Square tong
(a) Closed Mouth : This is used for holding thin sections.
(b) Open Mouth : This is suitable for holding heavier stock,
(c) Round Hollow Tong : This is used for holding round, hexagonal, and
octagonal shapes.
(d) Square Tong : This is used for holding square work.
(a) Open Mouth
(b) Closed Mouth
(c) Round Hollow
Tong
(d) Square
Fig. 5.3 Types of Tongs
4. Hammers : These are two kinds. a) The Sledge hammers are used by
smith’s helper used for heavy blows weighs from 4 kg to 10 kg. b) Hand
hammer are used by smith himself used for light blows
Fig. 5.4 Sledge Hammers
Fig. 5.5 Hand Hammers
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5. Chisels : These are used for cutting metals and for necking prior to
breaking. They may be hot or cold depending on whether the metal to be cut is
hot or cold. The hot chisel is used for cutting the metal when hot and its edge is
at an angle of 30o. The cold chisel is used to cut cold materials.
(a) Hot Chisel
(b) Cold Chisel
Fig. 5.6 Types of Chisels
6. Hardie Tools : It is a cutting tool with square shank to fit in the square
hole of the anvil. It is used in combination with hot or cold chisel.
Fig. 5.7 Hardie Tools
7. Swages : Swages are used for reducing and finishing the round, square,
and hexagonal shapes. A set of swages are designed for round shapes and
square shapes
Fig. 5.8 Swages
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8. Fullers : These are used in pair for necking down a piece of work. The
bottom fuller has square shank to fit in the hardie hole and top one is provided
with handle.
Fig. 5.9 Fullers and Their Use
9. Flatters : These are used to obtain smooth and finished flat surfaces
which have already been shaped by fullers and swages.
Fig. 5.10 Flatter
10. Set Hammers : It is really a form of flatter. A set hammer is used for
finishing corners in shouldered work where the flatter would be inconvenient to
use
Fig. 5.11 Set Hammer and Its Use
11. Punches : A punch is used for making holes in metal parts when it is at
forging heat.
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Fig. 5.12 Punch and Its use
12. Drifts : It is a tool for enlarging the hole made by punch. They are
driven right through the punched hole.
Fig. 5.13 Use of Drift
5.2 Heating Devices
The stocks are heated to the correct forging temperature in a smith’s hearth
or in a furnace. Gas oil of electric resistance furnaces are induction heating
classified as open or closed hearths. Gas and oil are economical, easily controlled
and mostly used as fuels. A common form of smith;s hearth is made of thick steel
sheets. It is lined with fire bricks. It holds the coke and provides with tuyere and
a tank containing water. Air is supplied through a fan or blower to hearth. The
air is admitted into the hearth may be regulated by a suitable valve arrangement.
The hood at the top collects the fumes from the fire. Smoke and gas are finally
removed into atmosphere. After firing the hearth the work piece is kept under
the fire. When it becomes sufficiently hot it is removed from the hearth for
shaping.
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5.3 Smithy Operations
For giving desired shape to the metal, number of operations are performred
in a smithy shop.They are listed here under.
a) Upsetting
b) Drawing down
c) Setting down
d) Bending
e) Fullering
f) Swaging
g) Flattering
a. Upsetting : It is the process of increasing cross-sectional area at the
expense of its length. It is achieved by heating the bar at the middle and striking
the end with hammer as shown in diagram.
Fig. 5.14 Upsetting
b. Drawing Down : It is the process of decreasing the cross section area
with a corresponding increase in length of a bar. The operation is carried by
using the edge or horn of the anvil or fullers. The bar is finally finished by flatters.
(a) Edge and Straight Peen Hammer(b) Set of
(c) Horn and Hand
(d) Finishing by Flatters
Fig. 5.15 Drawing Down
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c. Setting Down : It is the process of decreasing thickness rather than
general reduction of area. It is initiated with fullers and finished with flatters.
Blow
Blow
Blow
Flatter
Fuller
Set Hammer
Fig. 5.16 Setting down
d. Bending : This can be performed to produce different types of bent
shapes such as angles, ovals and circles etc. for making a bend at that particular
part of job.
a. Bending of Horn
b. Angular bending in a vice
c. Bending in a fixture for mass production
Fig. 5.17 Bending
e. Fullering : It is the process of increasing the length by necking the bar
between two fullers.
f. Swaging : It is an operation through which desired shapes are obtained
on the job by placing it an similar shape slot on the swage bock and then
applying top swage on the other side of the job.
g. Flattering : It is an operation through which the surface of job shaped
by fulters and swages are usually finished.
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Fig. 5.18 Swaging
5.4 Machine Forging
Heavy and medium forging are made in machine forging where as in hand
forging only a limited quantities of light forgings are produced. In machine forging
sledge hammer is replaced by power driven forging hammers or presses. Because
sledge hammers are unable to produce required degree of deformation of metal
during forging.
5.5 Forging Hammers
The forge hammers are classified as
(1) Mechanical
(2) Drop Hammers
(1) Mechanical Hammers are classified as
Mechanical hammers are classified as
a) Spring hammer
b) Pneumatic Hammer
(a) Spring Hammer : It is a light weight power hammer and is adopted for
small forgings. It has a heavy rigid frame carrying a vertical projection at its top.
This projection acts as housing for the bearing in which the laminated spring
oscillates. The rear end of this spring is pinned to small end of connecting rod
and its front end is connected to a vertical top to which the die is fixed. The
bottom end of the connecting rod is attached to an eccentric sheave. This in turn
connected to the crank wheel that is driven by an electric motor. The bottom die
is keyed to the anvil block.
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To operate this, the treadle is to be pressed down. This causes the eccentric
sheave to rotate through the crank wheel and thus the laminated springs start
oscillating in the bearing. This oscillation of the spring causes tip to move up and
down and thus the required blows are delivered on the job which is placed
between die and hammer.
Fig. 5.19 Spring Hammer
(b) Pneumatic Hammer : A common form of pneumatic hammer carries
compressor cylinder. A piston works inside this cylinder is connected to the
main motor shaft by means of a crank and connecting rod mechanism. A hand
lever operates an air valve provide air passage from the compressor cylinder to
Ram cylinder. Ram piston carrying the tip at its bottom works inside the ram
cylinder. The tip is made to slide inside fixed guide.
Ram
Cylinder
Rotary Valve
Compressor Cylinder
Piston
Ram
Top Die
Bottom Die
Crank
Anvil
Fig. 5.20 Pneumatic Hammer
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Air is compressed on both upward and downward strokes of the piston in
compressor cylinder. This air enters into the ram cylinder through a control value.
Hammer falls by imparting blow to work piece due to its own weight when
the air pressure exerted above the piston. The upward stroke of the hammer is
obtained by exhausting the air above the piston and admitting in beneath the
piston.
(2) Drop Hammer
The drop hammer is suitable for production of large number of identical
forging components also. High quality components are by made this process.
There are two types a) Steam or Air drop hammer b) Board Drop or Gravity
drop hammer
(a) Steam or Air Drop Hammer : These hammers are run by steam or
compressed air. These are similar to pneumatic hammer except that they do not
have a built in compressor. The generation of compressed air or steam takes
place separately and not within the hammer. There are two types of steam
hammers in common use i) Single acting and ii) Double acting
In single acting steam (or air) hammer, the steam (or air) is admitted through
bottom part which lifts the ram upwards and then the ram is allowed to fall down
under gravity to provide required blow.
Safety Cover
Cylinder
Valves
Frame
Controls
Ram
Dies
Anvil
Fig. 5.21 Steam Hammer
(b) Board Drop (Gravity drop Hammer) : In this case the energy blow
is entirely depends upon the weight of the hammer. The ram is attached to the
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board which passes between two rockers which are in continuous motion. The
ram moves up with the help of routers and is held at desired height by clamps
until they are released by the operator. At a preset height the board is rebased
so that it strikes the die which is fixed to the anvil. The work is deformed by the
force of blow. If the weight of the ram and the height from which it falls is
greater, the impact of blow will be more.
Fig. 5.22 Board drop Hammer
5.6 FORGING PRESSES
In press forging, the metal is shaped by squeezing it into the die cavities by
pressing. Presses of 500 to 6000 tonnes capacities are in common use. Normally
two types of presses are used a) Hydraulic presses are used for heavywork b)
Mechanical presses are used for light work.
Mechanical presses operate at faster speed than hydraulic presses, but
hydraulic presses provide greater squeezing force than mechanical presses.
Welding
Introduction
Welding is the process of joining two or more metals by application of heat
with or without application of pressure and addition of filler rod. Now the basic
purpose of welding is to provide a means to join pieces by raising their temperature
to the fusion point so that they forms a pool of molten metal at the ends to be
joined and if needed supplement their pool with a filler metal which is normally
same metal as the metal pieces to be joined.
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Types of Welding
The modern methods of welding may be classified under two broad headings.
a) Plastic welding b) Fusion Welding
In plastic welding or pressure welding, the pieces of metal to be joined are
heated to a plastic state and then forced together by external pressure.eg forging
In fusion welding or non pressure welding, the material at the joint is heated
to a molten state and allowed to solidify. eg.Gas welding and arc welding etc.
1. Gas Welding : It is a fusion welding or non pressure welding method in
which a strong gas flame is used to raise the temperature of the ends of the
pieces to be joined to a heat sufficient to melt them. The metal thus melted starts
flowing along the ends to be joined and forms a strong weld joint after solidifies.
So many different combination of gases may be used, but the most common of
these are oxygen and Acetylene, O2 & H2. Oxygen and hydrogen gas welding is
used for metal for low melting point like non ferrous metal.
5.6.1 Oxygen - Acetylene Welding
This welding can be used for welding almost all metals and alloys used in
engineering practice. The highest temperature that can be produced by a flame
of oxygen and acetylene is nearly 3200OC. The correct adjustment of the flame
is important for reliable works. When oxygen and acetylene are supplied to
torch in nearly equal volumes, a neutral frame is produced having a maximum
temperature of 3200oC.
This neutral flame is widely used for welding steel, Stainless steel, Cast
iron, copper, Aluminium etc. An oxydising flame in which there is an excess of
oxygen used for welding brass. A carburising flame is one in which there is an
excess of acetylene compared to oxygen used for welding cast iron
Gas Welding Equipment
The most commonly used tools and equipment for oxy acetylene welding
consists of following.
a) Welding torch
b) Pressure Regulator
c) Welding tip
d) Hose and Hose fittings
e) Goggles, gloves and spark lighter f) Gas cylinders
a) Welding Torch : This is a tool for mixing oxygen and acetylene in
required proportions and burning the mixture at the end of its tip.
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(b) Welding Tip : It is that portion of the welding apparatus through which
the gases pass just prior to their ignition and burning. These tips of different
shapes and sizes are governed by the diamter of opening. The diameter of the
tip opening used depends upon the types of metal to be welded.
(c) Pressure Regulator : The function of a pressure regulator is to reduce
the cylinder pressure to required working pressure and also to produce a steady
flow of gas regardless of the pressure variation at the source.
(d) Hose and Hose Fittings : The hose for welding torches should be
strong, durable, nonporous and light. The most common method of piping both
oxygen and acetylene gas is the reinforced rubber hose. The colour of oxygen
pipes is black and acetylene is red.
(e) Goggles, Gloves and Spark Lighter : Goggles are fitted with coloured
lenses are provided to protect the eyes from harmful heat , ultraviolet and infrared
rays.
Gloves : These are used to protect the hands from any burnings or injury.
Spark Lighter : Provides a convenient and instant means for lighting the
welding torch.
Gas Cylinders : Oxygen cylinders are usually charged with about 40 litres
of oxygen at a pressure of 154 kgs/ cm2 at 21oC. A full cylinder has a weight of
about 80 kgs. Oxygen cylinder is painted with black. A safety valve is provided
to release the oxygen before there is any danger of excess pressure.
Acetylene Cylinder : These cylinder carry a porous mass inside soaked
in acetone which has a capacity to dissolve 25 times its own volume of acetylene
for every atmosphere of pressure applied. These cylinders are usually filled to a
pressure of 16 kgs to 21 kg/ cm2. It is painted with maroon colour
Gas Welding Procedure :
1. Arrange the two cylinders (O2 & C2 H2) in proper position (upright).
2. Blow out both cylinder valves before fitting the regulators so that all dirt
may be cleaned out and this operation should be done quickly.
3. The regulator and valve fitting should be thoroughly checked that there is
no oil or grease.
4. Fix the oxygen and acetylene regulator and pressure gauges to cylinders.
5. Connect or check hose fittings of O2 and C2 H2.
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6. Open the cylinder valves gradually to avoid abrupt strain.
7. Check out for leakages at all joints before starting the work.
8. To start the work turn on the acetylene first and allow it to pass through
the nozzle. Then turn on the oxygen slightly and allow the mixture to flow through
hoses and blow pipes are full and cleared off air.
9. Adjust the required pressure of the two gases and light the mixture.
10. Adjust the flames by regulating the supply of the gasses in correct
proportions.
11. After the work is completed the oxygen valve should be closed first
followed by the acetylene valve.
12. Care should be taken always that oil and grease do not present at any
fittings may lead to an explosion.
5.6.2 Arc Welding
Arc welding is the most extensively employed method of joining metal parts.
Here the source of heat is an electric arc. It is a fusion welding process in which
no mechanical pressure is applied for joining the metal. In this, the metal pieces
to be joined are heated locally to the melting temperature by creating an electric
arc and then allowed to solidify to form the welded joint.
Arc Welding Equipment
1. AC or DC welding machine 2. Electrode
3. Electrode holder
4. Cable, Cable connectors
5. Cable lugs.
6. Chipping hammer
7. Earth Clamps
8. Wire brush
9. Helmet
10. Safety goggles
11. Hand gloves 12. Appron and sleeves.
1. Welding Machine : Both AC and D.C’s are used for arc welding.
When welding is employed the current is generated by a D.C generator. This
generator can be driven by means of an electric motor or by means of petrol or
diesel engine. With the result D.C arc welding processes can be employed
irrespective of whether main A.C supply is available or not.
For A.C arc welding a step down transformer is used which receives current
from the supply mains at 200-440 volts and transforms it to the required voltage
for welding i.e 40-100 volts. Arc welding machine consists of a steel tank mounted
on three tyred wheels and the front wheel is steerable by means of a draw bar.
An oil cooled, double wound step down transformer reduces the supply mains
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voltage to a welding voltage of 80 volts. All windings are totally enclosed in the
steel tank. The output of transformer can be varied by rotating a hand wheel
which alters the air gap in the core of the choke resulting in stepless regulation of
the current between 50-400 amps. The welding setting can be directly read at
the window on the top cover.
(2) Electrode : Both non consumable and consumable electrodes are used
for arc welding. Non consumable electrode, may be made of carbon, graphite
or tungsten which donot consume during the welding operation. Consumable
electrode may be made of various metals depending upon their purpose and the
chemical composition of the metal to be welded. These consumable electrodes
may be bare or coated. Bare electrodes are cheaper but the weld produced
through these are poor quality and it needs high degree of skill on part of welder,
if satisfactory results are expected. Therefore bare electrodes are rarely used in
modern welding practice, where as more popularly used in metal arc welding
are the coated electrodes which carry a core of bare metallic wire, provided
with a coating on the outside surface. Main advantage in using coating electrode
is to protect the molten metal from the oxidisation and nitrogen , to the
establishment and maintenance of the arc. Mild steel is the most commonly
used material for the core wire. Some of the other metals and alloy are also used
as core wire material. The electrode covering the flux coating perform many
functions that reducing atmosphere to prevent oxidation, forming stage with metal
impurities, establishing arc, providing necessary alloying elements to the weld
metal. The common ingredients of a flux are asbestos, mica, silica, flour spar,
stealite, mg carbonate etc.
Arc Welding Procedure
Before starting the welding, the joint should be prepared well and thoroughly
cleared to remove dirt, grease, oil, oxide etc. from the work surface. Edges of
thickened section should be bevelled . The work pieces should be firmly held.
Make sure that connection are given properly to main supply as well as electrode
rod and work piece to be welded. The arc column is generated between anode
which is positive pole of power supply and the cathode (-ve pole). When these
two conductors of an electric circuit are brought together and separated for a
small distance i.e. 2-4 mm such that an electric arc is formed. Heat is generated
as the ions strike the cathode. The temperature of an electric arc, depends upon
the type of electrode between which it struck. The heat of the arc raises the
temperature of the parent metal which is melted forming a pool of molten metal.
The electrode rod is also melted and transferred between metal pieces to be
welded.Two thirds of heat is generated near the positive pole and one third is
developed near the negative pole. As a result an electrode that is connected to
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the positive pole will burn away approximately 50% faster than when connected
to the negative pole. The electrode of suitable size should be held at an angle of
60-80o with work piece. Then the welding may be proceeded by maintaining a
gap 2-4 mm between the electrodes. After desired length has been welded the
electrode holder should be lifted quickly to break the arc.
Summary
1. Forging of a heated metal by hammering or pressing.
2. Different tools used in forging are classified as
a) Heating Devices
b) Supporting tools
c) Holding tools
d) Cutting Tools etc.
3. Most of the forging work is done with hot metal and heating of metal is
carried out in a hearth or furnace are two types a) Open hearth
b) Closed hearth.
4. Supporting tools are used to support the work while hammering.
5. Most important forging operations are upsetting, drawing
down, setting down, bending, fullering, swaging and flattering.
6. Machine forging is suitable to produce large number of identical forgings
and is carried out by forcing the metal into die cavities by repeated
hammer blows.
Activity
1. A learner should collect a round bar made from square rod.
2. A learner should collect S-hook
3. Collect a crane hook
4. Collect T-bolts
5. Collect arc welded, T-Joint, Lap joint, Butt joint.
6. Collect gas welded, T-joint, lap joint, and butt joint.
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Short Answer Type Questions
1. Define forging.
2. What is meant by upsetting ?
3. What are Tongs ?
4. Write about supporting device in forging
Long Answer Type Questions
1. Explain about any four smithy operations ?
2. Name different types of machine forging hammers and explain about any
one them
OJT Questions
1. Make the practice of usage of forging tools.
2. Prepare a round bar from a square bar.
3. Make a crane hook, S-hook.
4. Make a butt joint by arc welding process.
5. Make a lap joint by Gas welding process.
UNIT
6
Foundry
Learning Objectives
On completion of this unit a learner will be able to
• Describe various hand moulding tools used in foundry.
• Explain about pattern making and different type of patterns used
• Classify moulding sands and their properties.
• Know the purpose of core and core making.
• Explain about various casting methods.
• Know about various defects in casting.
Introduction
Manufacturing is the art of transforming the raw material into finished
product. This chapter deals with manufacture of products from molten metal
and the products obtained are called Casting. Casting are produced when the
molten metal is poured into the mould cavity and left to solidify. This is cheapest
method of producing parts to a given shape.
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6.1 Advantages and Linitation of Casting
Advantages of Casting
1. Size is not a limitation
2. There are several metals which can be cast.
3. Intricate components with cavities can be casted with accuracy and
good surface finish.
4. Casting, in general resists creep under high temperature.
5. Metal casting can be adopted for job work as well as for mass production.
Disadvantages
1. The process is not suitable for the metals having high melting point and
low fluidity.
2. Casting do not exhibit directionality of properties . The strength and
toughness of castings are usually inferior to forgings.
6.2 Foundry Equipment and Hand Mould Tools
Foundry tools and equipment may be classified into three groups namely
hand tools, flasks and mechanical tools.
Hand Tools in Moulding
(1) Shovel : It is used for mixing and tempering the moulding sand and
loading the sand into flask.
Fig. 6.1 Shovel
(2) Riddle : It is a wire mesh fitted in to a wooden frame used for screening
the sand and to scatter the fine moulding sand over pattern.
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Fig. 6.2 Riddle
(3) Rammer : These are used for packing the sand around the pattern in a
flask. This is made of hard wood with one end flat and other wedge.
Fig. 6.3 Rammer
(4) Trowels : These are used for cleaning, smoothing and patching the flat
surface of the mould.
Fig. 6.4 Types of Trowels
(5) Slick : It has a flat on one end and spoon on the other end. It is used for
patching and smoothing the mould after the pattern has been drawn.
Fig. 6.5 Slick
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(6) Lifter : It is used for removing the sand particles from the mould.
(7) Strike of bar : This is used to cutting off extra sand after ramming and
bringing it to level with the surface.
Fig. 6.7 Strike of Bar
(8) Bellow : These are used to blow excess parting material form the
pattern and also to blow loose sand particles from the mould.
Fig. 6.6 Bellow
(9) Sprue Pin : Pin used to make riser hole called riser pin.
(10) Swab : It is soft brush used for moistening the sand around the pattern.
(11) Gate Cutter : It is a piece of steel sheet bent in the form used to cut
gates.
Fig. 6.7 Sprue Pin
Fig. 6.8 Gate Cutter
Fig. 6.9 SWAB
(12) Mallet : It is used to loosen the pattern to withdraw it from the
mould and for stripping the core box from the cores.
(13) Vent rod : It is used to make series of small holes to permit gasses to
escape while molten metal in being poured.
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Fig. 6.10 Vent Rods
(14) Draw Spike or Screen : It is used to rap and draw patterns from the
sand.
(15) Water Sprinkle : It is a device used for wetting and tempering the
mould sand.
Fig. 6.11 Water Sprinkle
(16) Spirit Level : It is used for aligning flasks and adjusting the straight
edges in pit moulding.
Moulding Boxes : Sand moulds are prepared in specially constructed
boxes called flasks. The purpose of flask is to impart the necessary strength to
the sand in moulding. Moulding flask is generally made into two parts. The
Cope (Top section) and the drag (bottom section). These two are held in position
by dwel pins. The common types of moulding boxes are
Fig. 6.12 Moulding Boxes
(a) Snap flask : It is a small flask with open form. It is made with hinge on
one corner and a lock on the opposite corner. It can be removed from the
mould before it is poured.
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(b) Box Flask : It is suitable for small and medium size castings, it is removed
from the mould only after solidification of casting.
(c) Wooden moulding boxes : Wooden boxes are often used for making
relatively large castings.
Mechanical Tools: These tools in the foundry include the many types of
moulding machines that will ram the mould, roll it over, and draw the pattern.
Besides there are power operated riddles sand mixtures and sand conveyers
etc.
6.2 Types of Sands and Properties
The common sources of collecting foundry sands are from rivers, lakes,
sea and deserts. The principal ingredients of moulding sands are silica sand
grains, clay, moisture and miscellaneous materials. Moulding sand is classified
as under
(1) Natural sand
(2) Synthetic sand
Natural Sand : Natural sand containing required proportion of clay (520%) is referred as green sand. It requires only to mix water. The clay develops
the strengths and plasticity for moulding. They are less refractory than synthetic
sand.
Synthetic: These are obtained by crushing and mixing soft yellow sand
stone, carbon ferrous rocks. This sand essentially high silica grains containing
no clay in natural form. They are mixed with clay (3-5%) and water 3-4% to
develop required moulding properties.
Properties of Moulding Sand
Proper moulding sand must posses six important properties.
(1) Porosity : The sand should have sufficiently porous to provide a passage
for steam and gases other wise the gases penetrate into metal which leads to the
formation of gas cavities in casting.
(2) Plasticity : It is the ability of a sand to acquire shape from the pattern
that is moulded and retain it during casting.
(3) Flowability : It is the ability to flow under externally applied forces in to
deeper sections of pattern and uniformly fill the flask.
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(4) Collapsability : It is the property of sand that permits it to collapse
easily during its knockout from the casting.
(5) Adhesivness : It is the ability of sand to stick to the surfaces of moulding
boxes. This enables the mould to retain in a box during handling.
(6) Cohesiveness : It is the ability of sand particles to stick each other. It
refers to the strength of moulding sand to hold the grains together.
(7) Refractiveness : It is the ability of sand to withstand the heat of molten
metal without fusion.
6.3 Pattern : Classification and Making
The type of pattern used depends upon the design of casting, complexity of
shape, the number of castings to be produced. The following types of patterns
are in common use.
(1) Solid Piece
(2) Split pattern
(3) Match plate pattern
(4) Gated pattern
(5) Sweep pattern
(6) Cope and drag pattern etc.
(1) Solid Pattern : It is made in single piece and is best suited for limited
production.
Fig. 6.13 Solid Pattern
(2) Split Pattern : It is used for intricate casting of unusual shapes. split
pattern may be two or three piece.
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(3) Match plate Pattern : These patterns are mostly used in machine
moulding as well as for producing large number of small castings by hand
moulding.
(4) Gated Pattern : These patterns include gates and risers for producing
casting. The use of gated pattern eliminates the time required to cut the gating
system by hand.
(5) Sweep Pattern : The template made of wood or metal revolving around
a fixed axis in the mould shapes the sand to the desired contour. It is suitable for
production of symmetrical castings.
Fig. 6.13 Sweep Pattern
Fig. 6.14 Gated Pattern
(6) Cope and Drag Pattern : This pattern is made of two halves which
are mounted on different plates. In this case, cope and drag parts of the mould
are made separately..
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Pattern Making
A pattern may be defined as a replica or facsimile model of the desired
casting which, when packed in a suitable moulding material, produces a cavity
called mould. This cavity when filled with molten metal produces desired casting.
A pattern size is slightly larger than the finished casting by an amount called
allowance. 1) Shrinkages allowance : The pattern must be made over size to
compensate for contraction of liquid metal on cooling. 2) Machining allowance
: It necessary to produce the finished surface of casting by machining. The excess
in the dimensions of the casting over the finished casting called machining
allowoance. 3) Draft Allowance : When a pattern is removed from a mould, the
tendency to tear away the edges of the mould is greatly reduced if the vertical
surfaces of the pattern are tapered inwards. 4) Distorsion Allowance : This
allowance is applied to the castings of irregular shapes that are distorted in
cooling because of metal shrinkages. The material selected for a pattern should
be easily workable,durable and should maintain dimensional accuracy. The
common material used for making pattern are wood, metal, plastic and wax.
The pattern maker, before making pattern should study the blue print.
Reproductions of the blue print laid out to full size scale on a flat smooth wooden
board. Select a working face and place a working edge straight, smooth and
square with the face of the board. Start the layout of a symmetrical pattern from
centre line. Select the proper contraction rule for making layout measurements.
Mark straight line with knife edge and circles with divider. colour the layout
marks and preserve the layout until the pattern has been constructed.
After preparing the layout proceed for pattern construction. Study the layout
and decide the location of parting lines. As per the layout, try to visualize the
shape of the pattern and determine the number of separate pieces to be made.
Start the construction of pattern from main part of its body. Cut and shape
different parts providing adequate draft on them. Check all the prepared parts
finally by placing them over the prepared layout. Assemble different parts in
position by glueing or by means of dowels pin. Finally check the whole of the
completed pattern for accuracy.
6.4 Core and Core Making
Cores are separate shapes of sand that are generally required to form the
hollow interior of the casting or a hole through the casting. These are placed in
the mould cavity before pouring to form the interior surface of the casting and
are removed from finished part during shakeout and further processing.
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Core Making
Core making consists of the following operations 1) Core Sand
preparation 2) Core moulding 3) Baking 4) Core finishing
(1) Core Sand Preparation : The first consideration in making a core is
to mix and prepare the sand properly. The mixing must be homogenous so that
the core will be of uniform strength throught out.
(2) Core Moulding : Core is then made manually or with machines.
Normally a core box is required for the preparation of cores.
(3) Core Baking : After the cores are prepared and placed on metal plate
or core carriers, they are backed to remove the moisture and to develeop the
strength of the binder in core ovens at temperatures from 150oC - 400oC
depending upon the types of the binder used, the size of the cores and the length
of baking time.
(4) Core Finishing : All rough places and unwanted fins are removed by
filing some cores are made in two or more pieces which must be assembled
usually by pressing together with dextrin. The last operation in making of a core
is to apply a fine refractory coating to the surfacing.
6.5 Green Sand Moulding
These moulds are prepared with natural moulding sands or with mixture
of silica sand, bonding clay, and water. These materials are thoroughly mixed in
proportions which will give desired properties for the class of work being done.
The clay has been added to withstand the forces as the molten metal poured
into the mould. These are widely used for small and medium castings. In this
case no dry process of mould is necessary and the molten metal is poured as
soon as mould is prepared. The term green refers to the moisture and not the
colour of the sand. To prevent the sand from burning on the face of the mould,
a layer of facing sand is given to surrounding pattern.
6.5.1 Dry Sand Moulding
These sand moulds are prepared in similar way as in green sand moulds
except that the mould is dried before pouring molten metal. Drying is usually
carried out in oven at about 240oC. The time of backing is depending on the
binders used in the sand mixture and the amount of mould surface to be dried.
The removal moisture makes the mould stronger, improves erosion resistance
and surface condition. Dry sand moulds are used in preference to green sand
moulds for making medium to large size castings of cast iron and steel.
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6.6 SHELL MOULDING
It is basically a sand moulding in which the clay is replaced by resin bonding
agent. it consists of the following steps.
(a) Preparation of thin shell made of a mixture of sand and thermo setting
resin around a heated metal pattern.
(b) Separating the shell from the metal pattern
(c) Clamping two halves of the shell to form the mould.
(a) Preparation of Thin shell : Silica sand is thoroughly mixed with
about 5% thermo setting resin binder such as phenolformaldehyde and placed
in a container. The metal pattern plate is heated to about 250oC in a oven and is
clamped to the top of the box. The dump box is inverted so that the sand resin
mixture covers the pattern. After 30 seconds, the resin curves causing the bonding
of sand grains to form a shell around the pattern.
(b) Separating Shell : The dump plate is returned to its original position
and the surplus sand mixture falls back into the box. The pattern plate is removed
and the shell is released by the ejector pins. The shells are light and thin usually
5-10 mm thick.
(c) Mould Formation : Shell is hardened by final curing for a few minutes
at about 320oC. The two halves of shell are joined together by adhesives to
form the mould. This is placed in suitable box and is supported by coarse sand
or steel shots held in a box . The mould is ready.
Pattern Plate
Ejector Pins
Sand with
Pattern
Dump box
(a) Preparation of Shell
(b) Separation of Shell
(c) Clamping of Shells to form a
Fig. 6.15 Shell Moulding Process
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6.7 Ceramic Moulding
This techniques employs a metal pattern and the pattern is kept in a flask. A
thick slurry of refractory material is applied to expose pattern surfaces. The
coating becomes tacky almost on contact and is ready to receive backing material.
This coarse slurry is poured over the facing coat until the flask is filled. It sets in
about 3-5 minutes. The pattern is then withdrawn and the ceramic mass removed
from the flask is treated with catalyst to stabilise it chemically. The mould is then
heated at about 980oC in a furnace to expel the liquid binders completely. The
molten metal is then poured and the moulds are allowed to cool down slowly.
6.8 Special Casting Methods
Most of the moulds are destroyed after solidification of castings and hence
cannot be reused. This is not suitable for mass production. Now these special
castings are used for large scale production of castings with close dimensional
tolerances and has a smooth surface finish. The principle of special casting
methods such as die casting and centrifugal castings.
Die Casting : This is nothing but permanent metal moulds or dies. This die
is made in two pieces are closed to form cavity. The die castings are two types
1) Pressure die casting 2) Gravity die Casting
1) Pressure Die Casting : It involves the forcing of molten metal into die
cavity under pressure and maintain this pressure until it solidifies.
2) Gravity Die Casting : In gravity die casting in which molten metal is
poured to the cavity by gravity. There fore it is known as gravity die casting.
Here the moulds are coated with refracting materials and are closed.
Mould
Cavity
Moving
Platen
Fixed
Platen
Liquid
Metal
Injection
Piston
Fig. 6.15 Pressure Die Casting
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Centrifugal Casting
It is the variety method of producing castings in a rotating mould. The molten
metal is poured in to the mould which is rotating at a speed of 1500 rpm and the
centrigufal force spreads the molten metal uniformly along the entire length of
the mould and holds it there until solidification is completed.
Gate
Sprue
Clamp
Vertical Parting
Line
Metal Core
Casting
Fig. 6.15 Permanent Mould Casting
6.9 Defects in Casting
The various defects which are commonly occur in castings.
(1) Blow holes : These are appear as cavities in a casting. When they are
visible on the upper surface of the casting, they are called open blow holes.
When they are concealed in the casting are called blow holes. These are formed
due to the trapped bubbles of gases in the metal and are exposed only after
machining.
(2) Porosity : This defects occur in the casting in the form of pin holes.
These are caused by the gases absorbed by the molten metal. The gases
commonly observed are O2, H2, and N2. The later two forms oxides and nitride
respectively.
(3) Shrinkage Allowance : It is a void or depression in the casting caused
mainly due to uncontrolled solidification of the metal.
(4) Hot Tears : They are internal or external cracks having ragged edges
occuring immediateley after metal has solidification. These are produced due to
poor design and sudden sectional changes.
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(5) Shift : This is an external defect in a casting caused due to core
misplacement or mismathing of top and bottom parts.
(6) Shell : It is an enlargement of the mould cavity by metal pressure resulting
in localised or overall enlargement of casting.
(7) Scabs : These are lumps of excess metal on the casting as a result of
erosion of mould by the stream of molten metal.
Summary
1. Foundry is the process of forming unfinished metal product by melting
the raw material and pouring it in to mould cavity
2. Foundry tools are classified in to three groups namely hand tools ,flasks
and mechanical tools
3. Moulding sand in foundry is classified in to natural and synthetic
4. Proper moulding sand must posses six important properties such as
porosity, flowability, collapsability, adhesiveness, cohesiveness and
refractiveness
5. Pattern is the full size model of the desired casting
6. Core is the body of the sand design to form holes and cavities in the
castings.These cores are two types, green sand cores and dry sand
cores.
7. Common defects occur in castings are blow holes ,cold struts and misruns
,hot tears,mismatch,shrikages cavities and swells ect,.
Short Answer Type Questions
1.Define Pattern.
2.What is the purpose of Core.
3. Name different types of hand moulding tools used in foundry.
4. Give names of different moulding Sands.
5. What is Mould.
Long Answer Type Questions
1. Explain Dry Sand Moulding.
2. Explain about different hand moulding tools with sketch.
3. Write about common Casting Defects.
UNIT
7
Mechanical Working of Metals
Learning Objectives
On completion of this unit a learner will be able to
• Explain about hot working process
• Explain about cold working process
7.0 Introduction
Mechanical working of a metal is the plastic deformation performed to
change dimensions, properties, and surface condition by means of mechanical
pressure. Mechanical working may be either hot working or cold working.
Cold working is done below recrystalization temperature where no
transformation of grain structure takes place. Hot working often allows more
extensive deformation which is done above the recrystalisation temperature.
7.1 Hot Working Process
The plastic deformation of metals above the recrystalisation temparature is
called hot working. However this temperature should not be too high because
that gives rise to grain growth. In addition to more change of shape, hot working
has profound effects on metal characteristics or properties.
The main hot working processes are
(1) Rolling
(2) Piercing
(4) Spinning
(5) Extrusion
(3) Drawing
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(1) Rolling : It is the most efficient method of reducing the cross sectional
area of large sections. The plastic deformation of metal takes place as its passes
through a pair of rollers rotating in opposite direction. The hot rolling is used to
produce bars, plates, sheets, rails and other structural sections.
Fig. 7.1 Principle of Hot Rolling
(2) Piercing : Hot piercing is used to produce seamless tubes which is the
natural form from which is made any thin- walled round objects. A small hole is
made at the end of heated billet. It is pressed between two piercing rolls rotating
in the same direction.
Fig. 7.2 Piercing Process
(3) Drawing or Cupping : It is the process of making cup shaped articles
from flat circular blanks. The heated blank is placed over the die. The punch
forces the metal through a die to form a cup shaped article.
Fig. 7.3 Hot Drawing or Cupping
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(4) Spinning : Spinning is a highly specialized art for producing lamp
reflectors, cooking utensils, funnels and containers used in chemical plants. The
blank is held between former and the adopter. The blanks rotates with the former.
A specially shaped tool is then pressed against the blank and slowly move to
cover the former. This process is suitable for ductile materials.
Fig. 7.4 Spinning Process
(5) Extrusion : Hot extrusion is used to produce long lengths with desired
cross section which is very difficult by any other process. Basically the extrusion
process is like squeezing tooth paste of a tube.
Fig. 7.5 Direct Extrusion
7.2 Cold Working Process
The plastic deformation of metals below the recrystalization temperature is
called cold working. Cold working processes are usually carries at room
temperature. During cold working operation the metal hardens, becomes stronger
and its ductility is reduced. The principal methods of cold working are as follows.
1) Rolling
2) Bending
3) Drawing
4) Spinning
5) Extrusion
6) Squeezing
7) Riveting
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(1) Rolling : Cold rolling is performed at room temperature. In cold rolling,,
metal is deformed into long lengths between heavy rollers. It is also used to
improve surface quality and dimensional accuracy.
(2) Bending : Cold Bending is the process by which a straight length is
transformed into a curved length. It is one of the most widely used forming
process for changing plates into drums and curved channels.
(3) Drawing : Long components of uniform cross section can be produced
by drawing. Drawing operation involves the forcing of metal through a die by
means of a tensile force to the exit side of the die. Cold drawing require high
ductility in the metal. It is used in the production of rod of various cross sections,
wires and fuses.
Fig. 7.6 Wire drawing
(4) Spinning : It is the process of forming thin metal by pressing against a
form which is in rotation. It is similar to hot working except that the process
takes place at room temperature. This process is suitable for soft metals.
(5) Extrusion : The process of cold extrusion is similar to that of hot
extrusion except that the process takes place at room temperature. The metal
which is to be extruded must posses the necessary ductility even at room
temperature. The most popular method of cold extrusion is impact extrusion. In
impact extrusion cold metal billet is placed in the die and ram drives the punch
into die cavity as a result extruded part is formed.
Fig. 7.7 Cold Extrusion
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(6) Squeezing Operation : Squeezing operation involves the severe cold
deformation. It requires greater amount of pressure to attain the desired shape
which is confined to cavity of die and punch. The following squeezing operations
are commonly used in metal working.
(a) Cold Heading (b) Cold reeding
(a) Cold heading : Basically it is a cold forging process for manufacture
of headed components from ductile material. These components include bolts,
screws, rivets and similar items.
Fig. 7.8 Process of Cold Heading
(7) Reeding : It is process of indenting large quantities of steel shorts into
the surface of metal. This is done by air blast or same mechanism means. Due to
this indentation favorable compressive stresses are developed at outer layer.
This increases fatigue strength of metal and at the same time its surface is slightly
hardened and strengthened.
7.3 Advantages of Hot Working
(1) Internal residual stress are not developed in the metal.
(2) Mechanical properties are improved.
(3) Maximum deformation is possible because of increased plasticity.
(4) Power requirement for the process is less.
Disadvantages
(1) Surface finish is poor
(2) Close dimensional tolerance can be minimized.
(3) Tooling cost is high.
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Advantages of Cold Working
(1) No oxidation and scaling results.
(2) Smooth finish is possible.
(3) Closer dimensional tolerances can be maintained.
(4) Strength and hardness are increased.
Disadvantages
(1) Internal stresses are relieved in the metal.
(2) There is possibility of crack formation.
(3) It requires high power
(4) Only suitable for ductile materials.
Summary
1.Large number of parts are manufactured by metals forming techniques
which involves the severe plastic deformation under the action of applied
forces.
2. Hot working is done above recrystallasition temperature
3. Cold Working is done below recrystallasition temperature are usually at
room temperature.
4. Important hot working processes are hot rolling,Extrusion,hot piercing
etc.,
5. The coldworking processes are rolling,drawing,bending,squeezing ,
shearing
Short Answer Type Questions
1. Define hot and cold working
2. Define cold spinning
3. Explain hot extrusion
Long Answer Type Questions
1. Explain about any four hot working processes.
2. What are advantages and disadvantages of hot working over cold
working ?
UNIT
8
Lathe
Learning Objectives
On completion of this unit a learner will be able to
•
Know the working principle of lathe
• Draw the lathe diagram and identify its parts,and various operations
• State working principle of grinding
• Explain the application of grinding
8.1 Introduction
A lathe is one of the old and most important machine tools used in
production. It operates on the principle of excess metal removal by using a
cutting tool which is fed in to rotating work piece and can be given linear motion
in the desired direction. The undesired excess material from the job is removed
in the form of chips to obtain required shape and size.
Types of Lathe
(1) Speed lathe
(2) Engine Lathe
(4) Capston and turret lathe
(6) Automatic lathe
(3) Bench Lathe
(5) Tool room lathe
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8.1 Lathe Main Parts
The main parts of lathe are a) Bed b) Head stock c) Tail stock
d) Carriage e) Tool post
f) Lead Screw
g) Feed rod.
Fig. 8.1 Lathe Machine
(a) Bed
It forms the base of the machine and gives support to all the mountings of
lathe and provides ways to facilitate movement of carriage and the tail stock. It
has V-ways and flats surfaces are accurately machined to the give true alignment
to the head stock, tail stock and carriage throughout length of the bed.
(b) Head Stock
Head stock is located permanently at the left side of the lathe bed. It contains
lathe spindle, cone pulley, speed change gears, back gear and spindle driving
mechanism.
(c) Tail Stock
The tail stock is located at the right hand end of the bed and consists of a
body fastened to the base and the base is mounted on bed guide ways. The
base can slide to facilitate the holding of work pieces of different lengths.
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(d) Carriage
The carriage consists of a saddle and apron. The saddle slides on the
guide ways and support the cross slide and compound rest. The apron is the
part of the carriage facing the operator. It contains gears and feed clutches that
transmits motion from the lead screw to carriage and cross slide.Compound
rest is mounted on the cross slide and can be swiveled to required angle to
produce taper.
(e) Tool Post
Tool post is located on the compound rest to hold the cutting tool.
(f) Lead Screw
The lead screw is used for thread cutting operation and it will be in the front
side of the machine passing through carriage.
(g) Feed Rod
It is used for employing automatic feed.
8.2 Lathe Operations
The following operations are most common on lathe machines.
a) Turning
b) Facing
c) Reaming
d) Drilling
e) Knurling
f) Tapertuning.
(a) Turning
Turning in a lathe is to remove excess material from the work piece to
produce a cone shaped or a cylindrical surface. The various types of turning
made in lathe work are 1) Straight turning 2) Shoulder turning 3) Step turning.
Fig. 8.2 Turning
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(b) Facing
Facing is the operation of producing flat end surfaces that is normal to the
axis of rotation. The movement of tool is perpendicular to the axis of work
piece.
Fig. 8.3 Facing
(c) Reaming
It is the operation of finishing and sizing a drilled or bored hole. The reamer
is held in a tail stock spindle is fed slowly into the work which is revolving at very
low speed.
(d) Drilling
It is the process of making holes on work pieces. The drill is held in tail
stock spindle and fed slowly in to the work piece which is revolving in a chuck
of the head stock
(e) Knurling
It is the process of indenting the various forms on cylindrical work surfaces
by using a knurling tool which is pressed against the rotating work and the design
of the knurl rolls over the work and will be reproduced on the work
Fig. 8.4 Knurling
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(f) Taper Tuning
A taper may be defined as an uniform increase or decrease in the cross
section of a work piece measured along its length. A conical surface produced
on lathe. In taper turning tool moves at an angle to the axis of rotation.
Fig. 8.5 Taper Torning
8.3 Grinding Machines
Working Principle
Grinding is a metal cutting operation performed by means of a rotating
abrasive wheel that acts as a cutting tool. This is used to finish work piece which
shows a high surface quality, accuracy of shape and dimension.
8.4 Grinding Wheel Materials
A grinding wheel is a multitooth cutter made up of many hard particles
known as abrasives. The abrasive grains are mixed with a suitable bond, which
acts as a holder when the wheel is in use. Abrasives may be classified in two
principal groups a) Natural b) Artificial or manufactured.
(a)Natural : The natural abrasives include sand stone or solid quartz,
emery, corundum and diamond.Sandstone or solid quartz is one of the natural
abrasive stones from which grind stones are shaped .The quartz or cutting
agent is relatively soft so that materials harder than quartz cannot be abraded
rapdily.
(b)Emery : It is a natural aluminium oxide. It contains 55 to 65% of alumina,
the remaining consists of iron oxide and other impurities.
Corundum : It is a natural aluminium oxide. It contain from 75 to 95%
aluminium oxide.Both emery and corundum have agreater hardness and better
abrasive action than quartz.
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Diamonds : Diamonds of less than gcm quality are crushed to produce
abrasive grains for making grinding wheels.
Artificial :
a) Silicon Carbide
b) Aluminium Oxide
(a) Silicon Carbide : It is manufactured from 56 parts of silica sand, 34
parts of powdered coke,2 parts of salt and 12 parts of saw dust in a along.
(b) Aluminium oxide : It is manufactured by heating mineral bauxite, a
hydrated aluminium oxide clay containing silica, iron oxide, titanium oxide mixed
with ground coke iron borings
8.5 Applications of Grinding
Applications of grinding include the grinding of external and internal
cylindrical grinding , tapered and formed surfaces, gear teeth, threads and other
using appropriate wheels.
Summary
1. Lathe operates on the principle that the excess metal is removed by
using a cutting tool which is fed in to a rotating work piece.
2. According to design and construction the lathes are classified as i)Speed
lathe ii)engine lathe iii) Tool room lathe iv)capston and turret lathe
3. Operations which are performed on the lathe are turning, facing
,taper turning ,drilling,boring and knurling
4. Grinding machine is used to finish the work piece to much higher accuracy
and is performed by means of a rotating abrasive wheel that acts as a
cutting tool.
5. Grinding wheel materials are two types ie natural and synthetic
Short Answer Type Questions
1. Explain the working principle of lathe
2. Name different lathe operations
3. Define knurling
4. Explain the principle of grinding
5. Name grinding wheel materials
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Long Answer Type Questions
1. Draw a neat sketch of lathe and name the parts
2. Explain about any four lathe operations
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