MANUAL MECHANICAL WORKSHOP PRACTICE

JABATAN KEJURUTERAAN MEKANIKAL

MANUAL
MECHANICAL
WORKSHOP
PRACTICE

FITTING
MACHINING
WELDING

NORMAH ISHAK

TABLE OF CONTENTS

1 FITTING
2 MACHINING
3 WELDING

1
FITTING

MANUAL FITTING SHOP

FITTING

1.0 INTRODUCTION

1.1 WHAT IS WORKSHOP PRACTICE

Workshop practice gives the basic working knowledge required for the production
of various engineering products. Its explains the construction, function, use and aplication
of different working tools, equipment, machines as well as the techniqueof manufacturing
a product from its raw material.

1.2 WHAT IS FITTING?

Fitting is a manufacturing process which refers to assembling of parts together and
removing metals to secure necessary fit. Fitting is also the process of assembling various
parts manufactured in the machine shop. This operations include measuring and marking,
sawing, chipping and filing. Tools used in fitting shop is holding tools, cutting tools, striking
tools and marking and measuring tools.

Fitting work includes laying out, various cutting operations, filing, threading, bending
and straightening, lapping, drilling, countersinking, reaming, riveting, and soldering.
Laying out is the planning of the work on the surface of the material that is to be made into the
finished part. It is the scribing of lines which indicates cuts to be made, the centerlines of holes to
be drilled, and other details that guide the worker in completing the job.

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2.0 WHAT ARE SAFETY PRECAUTIONS?

Precautions are most important for safety from accident. Follow safety precautions
should be taken when using hand tool and equipment. Keep proper discipline in the
shop.

1. Do not play with the tools because they are sharp.
2. All files should be fitted with suitable handle at the end of file.
3. When using Hacksaw, check its teeth should be sharp and forward position.
4. When using chisel its direction should be kept away from other working persons.
5. When files are of forward cut, then only apply the force in forward stroke not in

backward and vice versa.
6. When using Hacksaw check its blade which must be fitted in pins properly.
7. When using the micrometer and Vernier caliper, must check its error.
8. Clean up oil and grease or other liquid which spills on the flour otherwise they may

be a cause of accident.
9. Always wear the apron and closed shoes, not loose clothes.
10. Do not wear any necktie, jewelry, rings, watches during in the working in shops

2.1 WORKSHOP SAFETY RULES

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3.0 FITTING TOOL
All types of work require the use of large number of tools involving a number of operations

such as filing, chipping, scraping, sawing, tapping, etc. to finish the work to the desired shape and
size. Different types of tools used in Fitting.
The tools used in fitting shop may be classified into following groups. The Tools used in
Fitting workshop are as follows:
MEASURING TOOLS: Steel Ruler, Inside Caliper, Outside Caliper and Vernier Caliper
and Vernier Height Gauge.
HOLDING TOOLS: All types of vices.
CUTTING TOOLS: Chisel, Hacksaw and Files.
MARKING TOOLS: Scriber, Divider, Center Punch and L Square.
STRIKING TOOLS: All types of hammers.
THREADING: Tap and Dies.
FIXING: Spanner, Wrench, Chuck Keys and Screw drivers.
CHECKING: All Types of Gauges.
FINISHING TOOLS: Filing.
SUPPORTING TOOL: Anvil, surface Plate and V-Block.
SUPPORTING WORK: Bench Work.

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3.1 TYPES OF FITTING TOOLS
1. MEASURING TOOLS
i. Steel ruler
Steel ruler come in rigid and flexible versions. While their primary purpose is
accurate measurement, they can also be used as guides for laying out lines, and
if rigid enough, for cutting.

ii. Inside Caliper
The inside calipers are used to measure the internal size of an object.
inside calipers measure hole diameters and distances between surfaces

iii. Outside Caliper
Outside calipers measure thicknesses and outside diameters of objects.

iv. Vernier Caliper
The Vernier calipers found in the laboratory incorporates a main scale and
a sliding Vernier scale which allows readings to the nearest 0.02 mm. This
instrument may be used to measure outer dimensions of objects (using the
main jaws), inside dimensions (using the smaller jaws at the top), and
depths (using the stem).

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v. Vernier Height Gauge
Vernier height gauges employ the use of a main scale and a Vernier scale
to provide for greater resolution of the measured value. They are generally
available in measuring size ranges from 6 inches to 6 feet. Models can have
imperial (inch) or metric (mm) scales or both on them.

2. HOLDING TOOLS

i. All types of Vices
Vise, also spelled Vice, device consisting of two parallel jaws for holding a
workpiece; one of the jaws is fixed and the other movable by a screw, a
lever, or a cam. When used for holding a workpiece during hand operations,
such as filing, hammering, or sawing, the vise may be permanently bolted
to a bench.

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3. CUTTING TOOLS
i. Chisel

Chisel, cutting tool with a sharpened edge at the end of a metal blade, used often
by driving with a mallet or hammer in dressing, shaping, or working a solid material
such as wood, stone, or metal.

ii. Hacksaw
Hacksaws were originally and principally made for cutting metal, but can also cut
various other materials, such as plastic and wood.

iii. Files
A file is a tool used to remove fine amounts of material from a workpiece. It
is common in woodworking, metalworking, and other similar trade and
hobby tasks.

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4. MARKING TOOLS
i. Scriber

A scriber is a hand tool used in metal work to mark lines on workpieces, prior to
machining. The process of using a scriber is called scribing and is just part of the
process of marking out.

ii. Divider
Divider, instrument for measuring, transferring, or marking off distances,
consisting of two straight adjustable legs hinged together and ending in sharp
points.

iii. Center Punch
A center punch tool is a special type of punch tool that's used to create a shallow
indention in a workpiece for the purpose of drilling. Prior to drilling a hole in a
workpiece, a worker may use a center punch tool to “mark” the area of the
workpiece where the drill bit will enter.

iv. L Square
“L” Square The “L” square is one of the most basic of the pattern making rulers.
This ruler helps to create accurate 90° angles and straight edges. It measures,
rules, and squares simultaneously.

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5. STRIKING TOOLS
i. All types of hammer

A hammer is a tool consisting of a weighted "head" fixed to a long handle that is
swung to deliver an impact to a small area of an object. This can be, for example,
to drive nails into wood, to shape metal (as with a forge), or to crush rock.

6. THREADING
i. Tap and Dies

Taps and dies are tools used to create screw threads, which is called threading.
Many are cutting tools; others are forming tools. A tap is used to cut or form the
female portion of the mating pair (e.g. a nut). A die is used to cut or form the male
portion of the mating pair (e.g. a bolt).

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7. FIXING
i. Spanner

The spanner is a hand-held tool used to provide grip and tighten or loosen
fasteners. It gives a mechanical advantage in applying torque to turn objects. The
tool is used in turning rotary fasteners like nuts and bolts.

ii. Wrench
Wrenches are made in various shapes and sizes and are used for gripping,
fastening, turning, tightening and loosening things like pipes, pipe fittings, nuts and
bolts. There are basically two major kinds of wrenches: Pipe wrenches used in
plumbing for gripping round (cylindrical) things.

iii. Chuck Keys

A chuck key or wrench is a tool that is made for the purpose of tightening or
loosening the jaws of a chuck. A chuck is a type of clamp that is used to hold a
cylinder object. On a lathe, it holds the rotating piece—whereas on a drill or mill, it
holds the rotating tool.

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iv. Screw drivers

Screwdriver, tool, usually hand-operated, for turning screws with slotted heads.
For screws with one straight diametral slot cut across the head,
standard screwdrivers with flat blade tips and in a variety of sizes are used.

8. CHECKING
i. All Types of Gauges

It is used as a reference for the setting of measuring equipment used in machine
shops, such as micrometers, sine bars, calipers, and dial indicators.

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9. FINISHING TOOLS

i. Files
Finishing processes aim to alter the surface of a manufactured part in
order to achieve a particular characteristic. There are two main categories
of finishing processes and they largely depend on how they affect a
workpiece. These processes are either removing/reshaping finishing or
adding/altering finishing.

10. SUPPORTING TOOL
i. Anvil

The anvil forms a support for blacksmiths work when hammering and it is
also used in workshop to support the work pieces when they are made to
chiseling and punching operations

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ii. Surface Plate

Its specific use is in testing the trueness of a finished surface, testing a try
square, providing adequate bearing surface for V-block and angle plates,
etc., in scribing work.
It is a cast iron plate having a square or rectangular top perfectly planed
true and square with adjacent machined faces. The top is finished true by
means of grinding and scrapping. This plate carries a cast iron base under
it and the bottom surface of the base is also machined true to keep the top
surface of the plate in a perfect horizontal plane.

iii. v’ – block
A ‘V” block serves as a very useful support to the work in marking. It usually
works in conjunction with a U-clamp.

11. MISCELLANEOUS TOOLS
i. Number punch & Letter punches are used to mark the numbers and names on
the work piece for identification purpose. Generally it is made up of hard steel.

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12. SUPPORTING WORK
i. Bench Work
The term 'bench work' refers to the production of components by hand on
the bench, where as fitting deals which the assembly of mating parts, through
removal of metal, to obtain the required fit. Both the bench
work and fitting requires the use of number of simple hand tools and
considerable manual efforts.

4.0 DRILLING TOOL

4.1 Bench Drilling Machine

A drill or drilling machine is a tool primarily used for making round holes or driving
fasteners. It is fitted with a bit, either a drill or driver, depending on application,
secured by a chuck. Some powered drills also include a hammer function. Drills vary
widely in speed, power, and size.

Drilling is a cutting process that uses a drill bit to cut a hole of circular cross-
section in solid materials. ... Instead, the hole is usually made by hammering
a drill bit into the hole with quickly repeated short movements.

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4.2 Twist Drill Bit

A twist bit is the most common type of drill bit for home use. It works for general-
purpose drilling in wood, plastic and light metal.

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4.3 Safety for Drilling

5.0 SAFETY

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PROJECT DIAGRAM

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MACHINING

MANUAL MACHINE SHOP

MACHINING

1.0 INTRODUCTION
1.1 WHAT IS MACHINE SHOP PRACTICE
Machine Shop Practice is principles of machining,tool bits, measurement, tool

grinding, and machine shop safety.

1.2 WHAT IS MACHINING?

Machining is any process in which a cutting tool is used to remove small chips of material
from the workpiece (the workpiece is often called the "work"). ... The shape of the tool and its
penetration into the work surface, combined with these motions, produce the desired shape of
the resulting work surface.

A lathe is a tool that rotates the workpiece on its axis to perform various operations such as
cutting, sanding, knurling, drilling, or deformation, facing, turning, with tools that are applied to the
workpiece to create an object with symmetry about an axis of rotation.

What is a lathe machine used for?
A lathe is a machining tool that is used primarily for shaping metal. It works by rotating
the workpiece around a stationary cutting tool. The main use is to remove unwanted
parts of the material, leaving behind a nicely shaped workpiece

2.0 MACHINE SHOP SAFETY

As always we should be aware of safety requirements and attempt to observe
safety rules in order to eliminate serious injury to ourselves or others. Safety
precautions at machine shop are:

1. Choose proper personal protective equipment (PPE) for the machine shop.
2. Wear safety glasses at all times in the shop. At any time, debris may fly out of a

machine and into your eye.
3. Consider a face shield when you are working up close with grinding and cutting job

tasks.
4. Wear comfortable shoes with a non-slip sole.
5. Consider toe reinforcement if you work with heavy objects.
6. Earplugs protect your hearing in a noisy machining environment.
7. Do not wear rings, watches, bracelets, or other jewelry that could get caught in

moving machinery.
8. Keep the floor always clean.
9. Switch off the machine immediately when supply fail.
10. Do not operate any machine unless authorized
11. Concentrate n the work, avoid unnecessary talks while operating machine.

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3.0 MEASURING INSTRUMENT AND TOOLS.
Measuring instrument have an important role in a mechanical workshop. The

quality of work is based on the accuracy and precision of the instruments used for
inspection. There are different types of measuring instrument used in a workshop.
Some of them are given below:

1. Steel ruler

Used to measure and mark out wood, metal and plastics.

2. Calipers
A caliper is a type of measuring tool that measures the distance between two
opposite sides of an object. Calipers are meant for measuring thicknesses
and internal or external diameters inaccessible to a scale.

3. Vernier Caliper

This instrument used to measure outer dimensions of objects (using the main
jaws), inside dimensions (using the smaller jaws at the top), and depths
(using the stem).

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4. Vernier height gauge

These measuring tools are used in metalworking or metrology to either set or
measure vertical distances; the pointer is sharpened to allow it to act as a scriber
and assist in marking out work pieces.

5. Micrometer

A micrometer is a tool used for the precise measurement of very small
objects. A micrometer can measure the depth, length and thickness of
whatever object fits between its anvil and spindle. It is commonly used in
mechanical engineering and machining applications.

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6. Dial test indicator

The dial indicator is used to indicate the run-out (the misalignment between
the workpiece's axis of rotational symmetry and the axis of rotation of the
spindle) of the workpiece, with the ultimate aim of reducing it to a suitably
small range using small chuck jaw adjustments.

7. Screw thread pitch gauge

Used to measure the pitch or lead of a screw thread. Thread pitch
gauges are used as a reference tool in determining the pitch of a thread that
is on a screw or in a tapped hole.

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8. Screw cutting gauge

Screw Cutting Gauge. 55 AND 60 DEG. A must tool for the lathe Made from
hardened and polished stainless steel and is used for checking tool angles
while machining threads in metal turning lathes.

9. Rubber mallet

Used to bend sheet metal without damaging the metal. Can also be used to
separate any gently knock wood joints into place.

10. Machine vice

Used to hold your work securely when drilling The vice can be bolted to the
drill table.

11. Wrench 5
A double ended tool with one end being like an open end wrench or open
ended spanner and the other end being like a box end wrench or ring
spanner. Both ends generally fit the same size of bolt

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4.0 CUTTING TOOL TERMINOLOGY
There are many different tools that can be used for turning, facing, and parting

operations on the lathe. Each tool is usually composed of carbide as a base material,
but can include other compounds. This section covers the different appearances and
uses of lathe cutting tools.

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4.1 SINGLE POINT CUTTING TOOLS
What is a single point cutting tool?
Single-point tools are used in turning, shaping, planning and similar operations,
and remove material by means of one cutting edge. ... It is a body having teeth or
cutting edges on it. Grinding tools are also multipoint tools.

4.2 TO SETUP A CUTTING TOOL FOR MACHINING
1. Move the tool post to the left-hand side of the compound rest.
2. Mount a toolholder in the tool post so that the set screw in the toolholder is
about 1 inch beyond the tool post.
3. Insert the proper cutting tool into the toolholder, having the tool extend
beyond the toolholder.
4. Set the cutting tool point to center height. Check it with straight rule or
tailstock.
5. Tighten the tool post securely to prevent it from moving during a cut

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4.3 INSTALLING A CUTTING TOOL

• Tool holders are used to hold lathe cutting tools.
• To install, clean the holder and tighten the bolts.
• The lathe’s tool holder is attached to the tool post using a quick release

lever.
• The tool post is attached to the machine with a T-bolt.

4.4 HOW TO CENTRE THE CUTTING TOOL
Before any turning takes place it is common practice to check that the

point of the lathe tool is centred. This means that the lathe tool point should
be the same height as the tip of the tailstock centre. If this is not done and the
tool point is either above or below the centre point - usually the finish to the
steel will be poor. Also, a significant amount of vibration could take place
during turning.

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5.0 LATHE MACHINE
A lathe is a machine tool which is used to rotate a workpiece to perform various
operations such as turning, facing, knurling, grooving etc., with the help of tools
that are applied to the workpiece.

5.1 Parts of lathe machine

1. Headstock
It is present on the left-hand side of the lathe. It holds the gear train, main
spindle, chuck, gear speed control levers, and feed controllers. It is aligned with
the tailstock. The headstock is made up of cast iron.

2. Tailstock.
It is present at the right-hand side of the lathe. It is used to provide supports to
the workpiece. It supports the workpiece from one end i.e. right end.

3. Bed
It is the main part of the lathe. All the parts of the lathe are bolted on the bed. It
comprises of headstock, tailstock, carriage guideways and other parts. It is made
of cast iron.

4. Carriage
The carriage is present in between the headstock and tailstock. It carries apron,
saddle, compound rest, cross slide and tool post.

5. Quick Change Gearbox 9
A cluster of gears on a machine tool, the arrangement of which allows for the
rapid change of gear ratios.

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5.2 Working Principle of Lathe Machine
The function of a lathe is to remove metal from a piece of work to give it a
desired shape and size. In a lathe machine, the workpiece rotates against the
tool. The tool is used to remove material from the workpiece. The direction of the
motion of the tool is called a feed.

5.3 Lathe Machine Operations
The various operations that we perform on the lathe are:

i. Facing
It is the first operation that is done on the workpiece. It is a machining
operation that is done to produce flat surfaces at the ends of the workpiece.
This operation is performed by feeding the tool perpendicular to the axis of
rotation of the chuck.

ii. Turning
In turning operation, the excess material is removed from the surface of the
workpiece to produce a cylindrical surface of desired shape and size. During
the turning operation, the feed is moved along the axis of rotation of the
chuck. It reduces the diameter of the cylindrical workpiece.

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iii. Boring
The process of removing material from hole of the workpiece is called
boring. Holes are bored with the help of single point cutting tool.

iv. Drilling
It is the process of making holes in the workpiece by the use of drills. The
drill is held in the tailstock and the drilling operation is done by advancing
the drill in the workpiece by rotating the handle of the tailstock.

v. Reaming
The process of enlarging the holes to accurate sizes is called reaming.
Reaming is always performed after drilling operation. It is similar to the
drilling process. The reamer is held in the tailstock to carry out reaming
operation.

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vi. Counter Boring
The process of boring a hole to more than one diameter on the same axis is
called counterboring. This operation is performed by boring tool.

vii. Knurling
It is the process of making indentations (recess or sharp depression) on
the border of a workpiece. The knurling operation is done to provide a
better grip to the job. It is performed by the knurling tool. The knurling tool
is pressed against the job to perform the knurling operation.

viii. Chamfering
Chamfering is the process of beveling the extreme ends of a workpiece. It
is done in order to remove the burrs, to protect the end of the workpiece
from being damaged and to have a better look.

ix. Parting Off
It is the process of cutting a workpiece after it has been machined to the
required shape and size.

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x. Grooving

The process of creating a narrow slot on the workpiece is called grooving.
It is also known as recessing or necking

xi. Forming
It is process in which a convex, concave or any irregular surface is formed
on the workpiece with the help of a forming tool. Forming tool having the
required shape is used to perform forming operation.

xii. Taper Turning
It is the process in which a conical shape is produced on the workpiece.
During taper turning the feed is set at an angle to the workpiece.

xiii. Threading
The process of making threads on a cylindrical job is called threading.

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5.4 LATHE SPECIFICATIONS
Specification of a Lathe:
i. Swing- the largest work diameter that can be swung for the lathe bed.
ii. The distance between the headstock and tailstock center.
iii. Length of the bed in a meter.
iv. The pitch of the lead screw.

5.5 Work Holding Devices
A chuck is one of the most important device for holding and rotation a work
piece in a lathe. The various types of chuck as follow:
i. Three jaws chuck
ii. Four jaws chuck
iii. Drill or collet chuck
iv. Magnetic chuck

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5.6 TOOL HOLDER

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5.7 COOLANTS

Coolants are an instrumental part of machining, including grinding, milling, and
turning. They help extend tool life and provide an improved surface finish of the
parts being machined.

Understanding the role and types of coolant help you select a coolant that is
the right fit for your machine and operation. By properly maintaining the
concentration levels of your coolant, you extend not only the life of the coolant
but also your tools and machine.

The critical functions of coolant in the machining process include:
1. Reducing and removing the heat build-up in the cutting zone and workpiece.
2. Provides lubrication to reduce friction between the tool and removal of the

chips.
3. Flushes away chips and small abrasive particles from the work area.
4. Protects against corrosion.

Types of Coolants

i. Soluble Oils: The most common of all water-soluble cutting fluids
and a great option for general purpose machining. The drawback is
that they are prone to microbiological growth of fungus and bacteria
if the coolant sump is not correctly maintained.

ii. Synthetic Fluids: These types of fluids tend to be the cleanest of all
cutting fluids because they contain no mineral oil and reject tramp
oil. However, they provide the least lubrication.

iii. Semi-synthetic Fluids: Considered to be the best of both worlds,
they have less oil than emulsion-based fluids, a less stinky smell, and
retain much of the same lubricating attributes. This makes them
usable for a broader range of machining.

iv. Straight Oils: These are not water-miscible and have a composition
of a mineral or petroleum oil base and contain lubricants like
vegetable oils, fats, and esters. They provide the best lubrication but
have the poorest cooling characteristics.

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6.0 SAFETY

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3
WELDING

MANUAL WELDING

ARC WELDING

1.0 INTRODUCTION
Arc welding is a type of welding process using an electric arc to create heat to melt
and join metals. A power supply creates an electric arc between a consumable or
non-consumable electrode and the base material using either direct (DC) or
alternating (AC) currents.

Welding is done by creating an arc between the base metal (the metal being welded)
and the filler metal. The arc melts the base metal and filler metal, combining them into
one material to join the base metals. The filler metal is consumed in the process.

Comparison of AC and DC arc welding

Alternating Current (From Transformer) Direct Current (From Generator)
1. More efficiency Less efficiency
2. Power consumption less Power consumption more
3. Cost of equipment is less Cost of equipment is more
4. Higher voltage – hence not safe Low voltage – safer operation
5. Not suitable for welding nonferrous metal Suitable for both ferrous and nonferrous
metal
6. Not preferred for welding thin sections Preferred for welding thin sections
7. Any terminal can be connected to the work or Positive terminal connected to the work

electrode. Negative terminal connected to the
electrode

Principle of arc welding
Arc welding is welding using the heat of an arc as a heat source. In arc welding,
positive voltage is applied to the electrode (welding rod/wire) and negative voltage is
applied to the base material. This makes an arc occur from the base material to the
electrode.

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2.0 ARC WELDING EQUIPMENT
It is a type of welding that uses a welding power supply to create an
electric arc between a metal stick ("electrode") and the base material to melt the
metals at the point of contact. Arc welders can use either direct (DC) or alternating
(AC) current, and consumable or non-consumable electrodes.

Arc Welding Setup

What are the welding equipment?

Other Tools. Most welders also use an angle grinder to help smooth out joints, wire
brushes, to clean metal surfaces or abrade them before welding, a chipping slag
hammer, C-clamps, ball peen hammer, electrode tip cleaners, flint strikers, needle
nose and linesmen cutting pliers.

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3. 0 ELECTRODE

What is electrode in welding?
In arc welding, an electrode is used to conduct current through a workpiece to
fuse two pieces together. Depending upon the process, the electrode is either
consumable, in the case of gas metal arc welding or shielded metal arc welding,
or non-consumable, such as in gas tungsten arc welding.

Electrode is a consumable. It gets melted during the welding process. Is
composed of two parts:

i. Core rod (Metal filler)
- Carries welding current
- Becomes part of the weld

ii. Flux coating
- Produces a shielding gas
- Can provide additional filler
- Forms a slag

There are several factors to consider in welding rod selection:
1. Base metal properties.
2. Tensile strength.
3. Welding current.
4. Base metal thickness, shape and joint fit-up.
5. Welding position.
6. Specification and service conditions.
7. Environmental job conditions.

What is consumable electrode?

Consumable electrodes are the ones that would have significant changes in their
structure when they are used. This is to say that these electrodes would be consumed
in their use. Non consumable electrodes are the ones that are not consumed during
the process of welding.

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What is consumable electrode process?
Electrodes are used in all-electric arc welding processes. Consumable
electrodes become part of the weld bond itself. The electrode serves as the filler
metal and melts along with the metals to be welded together.

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OXY ACETYLENE WELDING

1.0 INTRODUCTION

Oxyacetylene gas welding is commonly used to permanently join mild
steel. A mixture of oxygen and acetylene, burns as an intense / focussed flame,
at approximately 3,500 degrees centigrade. When the flame comes in contact
with steel, it melts the surface forming a molten pool, allowing welding to take
place. Oxyacetylene can also be used for brazing, bronze welding, forging /
shaping metal and cutting.

1.1 Gas Welding Principle

Gas welding is a most important type of welding process. It is done by
burning of fuel gases with the help of oxygen which forms a concentrated
flame of high temperature. This flame directly strikes the weld area and melts
the weld surface and filler material. The melted part of welding plates diffused
in one another and create a weld joint after cooling. This welding method can
be used to join most of common metals used in daily life.

2.0 GAS WELDING EQUIPMENT

1. Gas Cylinders
2. Regulators
3. Pressure Gauges
4. Hoses
5. Welding Torch
6. Check Valve
7. Non Return Valve

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i. Gas Cylinder
a. Oxygen Cylinder:
For proper burning of fuel, appropriate amount of oxygen required.
This oxygen supplied by a oxygen cylinder. A black line is used to
indicate oxygen cylinder.

b. Fuel Gas Cylinder:
Gas cylinder is filled either by oxy acetylene gas, hydrogen gas,
natural gas or other flammable gas. The fuel gas selection is
depends on the welding material. Mostly oxy acetylene gas is used
for all general purpose of welding. Normally these cylinders have
Maroon line to indicate it. The fuel gases passes through it.

ii. Regulator
The main job of the welding pressure regulator is to control the pressure
of the gases used in oxyfuel welding. For example, the pressure
acetylene gas is under in the cylinder is typically more than seven times
greater than the pressure of the gas in the torch.

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iii. Pressure regulator
Both oxygen and fuel gases are filled in cylinder at high pressure.
These gases cannot use at this high pressure for welding work so a
pressure regulator is used between flow. It supplies oxygen at pressure
about 70 – 130 KN / M2 and gas at 7 – 103 KN / M2 to the welding
torch.

iv. Hoses
Hoses are manufactured in three common colors: black, green, and
red. The use of these colors is not standardized. However, the red hose
is usually used for carrying acetylene or other fuel gases. Either the
green or the black hose is used to carry the oxygen.

v. Welding Torch:
Welding torches are most important part of gas welding. Both the fuel gas

and oxygen at suitable pressure fed through hoses to the welding torch. There
are valves for each gas witch control the flow of gases inside the torch. Both
gases mixed there and form a flammable mixture. These gases ignite to burn
at the nozzle. The fire flame flow through nozzle and strikes at welding plates.
The nozzle thickness depends on the size of the welding plates and material
to be welded.

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vi. Check Valve
Check valves are generally installed in pipelines to prevent backflow.
A check valve is basically a one-way valve, in which the flow can run
freely one way, but if the flow turns the valve will close to protect the
piping, other valves, pumps etc.

vii. Non Return Valve
A non-return valve allows a medium to flow in only one direction and
is fitted to ensure that the medium flows through a pipe in the right
direction, where pressure conditions may otherwise cause reversed
flow.

3.0 PREPARING THE CYLINDERS FOR WELDING
Slowly open the main valve of the acetylene tank and adjust the acetylene
pressure regulator to 5PSI (pounds to square inch).

Open the needle valve on the torch and adjust the pressure on the
acetylene regulators to show 5PSI. Close the needle valve.

Go through the same procedure for the oxygen cylinder.

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a. IGNITING THE ACETYLENE / OXYGEN MIXTURE

1. TURNING ON:
Acetylene slowly turned on (quarter/half turn of the needle valve) and
ignited, producing a small flame. At this stage, a small amount of
soot/smoke is given off the end of the flame.

Acetylene increased and oxygen turned on slowly.

Acetylene increased slowly and oxygen more rapidly, to produce an
intense, local flame, capable of precise welding.

2. TURNING OFF:
Turn off the oxygen first, followed by the acetylene.

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4.0 FLAME

5.0 APPLICATION:

▪ It is used to join thin metal plates.
▪ It can used to join both ferrous and non-ferrous metals.
▪ Gas welding mostly used in fabrication of sheet metal.
▪ It is widely used in automobile and aircraft industries.

Advantages and Disadvantages

i. Advantages:

▪ It is easy to operate and dose not required high skill operator.
▪ Equipment cost is low compare to other welding processes

like MIG, TIG etc.
▪ It can be used at site.
▪ Equipment’s are more portable than other type of welding.
▪ It can also be used as gas cutting.

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ii. Disadvantages:

▪ It provides low surface finish. This process needs a finishing
operation after welding.

▪ Gas welding have large heat affected zone which can cause
change in mechanical properties of parent material.

▪ Higher safety issue due to naked flame of high temperature.
▪ It is Suitable only for soft and thin sheets.
▪ Slow metal joining rate.
▪ No shielding area which causes more welding defects.

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