Manufacturing Proecesses

Chapter 3
Manufacturing Processes
A J Bhosale
AISSMS CoE Pune,
Dept of Mechanical Engineering

AISSSMS College of Engineering, Pune
102013 Basic Mechanical Engineering A J Bhosale
Syllabus
• Introduction to Manufacturing Processes and their
Applications (Casting, Forging, Sheet metal working and
Metal joining processes), Description of Casting process:
Sand casting (Cope & Drag). Sheet metal Forming,
(shearing, bending, drawing), Forging (Hot working and
cold working comparison), Electric Arc welding,
Comparison of Welding, Soldering, Brazing

Manufacturing Process
Raw
Material
Machine
Tool
Finished
Product
Manufacturing Process

Manufacturing
Processes
Cutting
Turning
Drilling
Milling
Grinding
Shaping
Boring
Sawing
Facing, Taper
Turning
Gear Cutting
Finishing
Non- Cutting
Casting
Rolling
Forging
Press Work
Extrusion
Drawing
Fabrication
Welding
Brazing
Soldering
Riveting
Screw
Fastening

Casting Process:
It is the process in which molten metal is poured
into a cavity which confirms the shape of the desired
component.
CASTING
Refractory mold  pour liquid metal  solidify, remove  finish

Casting Methods
• Sand Casting
High Temperature Alloy,
Complex Geometry,
Rough Surface Finish
• Investment Casting
Complex Geometry,
Moderately Smooth Surface
Finish
• Die Casting
Moderate Geometry,
Smooth Surface
• VERSATILE: complex geometry, internal cavities, hollow sections
• VERSATILE: small (~10 grams)  very large parts (~1000 Kg)
• ECONOMICAL: little wastage (extra metal is re-used)
• ISOTROPIC: cast parts have same properties along all directions

Types of Casting:
1. Sand Casting.
2. Investment Casting.
3. Die Casting.
4. Centrifugal Casting
Features of casting process:
• Cast Components are brittle.
• Close dimensional controls are not expected .
• No restriction on the size of the component
• No restriction on the type of metal or alloy used.
• Surface finish is un satisfactory, Machining is required.
• Extremely thin sections can not be cast.
• Large variations in section thickness of components are not allowed.
• Economically suitable for both job and mass production.

Casting Terminology
• Pattern
It is replica of component to be
manufactured
• Flask
The box containing the mold
• Cope
The top half of any part of a 2-part mold
• Drag
The bottom half of any part of a 2-part mold
• Core
A shape inserted into the mold to
form internal cavities
• Core Print
A region used to support the core

Casting Terminology
• Mold Cavity
The hollow mold area in which metal solidifies into the part.
• Riser
An extra cavity to store additional metal to prevent shrinkage.
• Gating System
Channels used to deliver metal into the mold cavity
• Pouring Cup
The part of the gating system that receives poured metal
• Sprue
Vertical channel
• Runners
Horizontal channels

`
Sand Casting Process

cope: top half
drag: bottom half
core: for internal
cavities
pattern: positive
funnel  sprue 
 runners  gate 
 cavity 
 {risers, vents}

Advantages of sand casting:
• Intricate shapes component can be produced.
• Highly economical & cost of component is very low.
• Not require high initial investments.
• Not required highly skilled man power.
• Suitable for small job production.

Limitations of sand casting:
• Poor dimensional accuracy.
• It involves melting of metal, high energy consumption process.
• Not suitable for highly complex shapes
• Can not produce extremely thin sections. (less than 6 mm)
• For each casting requires one mould hence this process requires large
man power for mould making
• Large working space, in addition storing raw material, installing
furnace & molding sand
• Large man power.
• Environmental pollution is high.

Investment Casting or Lost Wax Casting

STEP-1
STEP-2
STEP-3
STEP-4 STEP-5 STEP-6

STEP-7 STEP-8
STEP-9
STEP-10

Die Casting

1. Automobiles:
1. Engine Blocks
2. Cylinder head
3. Pistons.
4. Clutch Housing, etc
2. Aircrafts:
1. Jet engine blades
2. Gear box housing
3. Pulleys.
3. Machine tool:
1. Machine tool beds
2. Frames
3. Gear box housing
4. Gears
5. Machine tool slides and heavy
components, etc
4. Water Pump Casings.
5. Turbine casings.
6. Flywheels.
Applications of casting process.

Application of Casting Process

Sand casting system

1. Solid Pattern 2. Split Pattern
3. Match Plate Pattern 4. Cope and Drag Pattern

Pattern Allowances
•Patterns are always made larger.
•Excess dimensions are Pattern Allowances
•The modification that are made into pattern are
called allowances.
•Types of allowances
1. Shrinkage allowance
2. Draft allowance
3. Machining allowance
4. Distortion allowance
5. Shaking or Rapping allowance

1.Shrinkage allowance
All most all cast metals shrink or contract
volumetrically on cooling.
The metal shrinkage is of two types:
1. Liquid Shrinkage:
2. Solid Shrinkage:

2. Draft or Taper allowance:
 It is given to all surfaces perpendicular to parting
line.
 Draft allowance is given so that the pattern can
be easily removed from the molding material
tightly packed around it with out damaging the
mould cavity.

Fig. taper in design

3. Machining allowance:
A Casting is given an allowance for machining, because:
i. Castings get oxidized in the mold and during
heat treatment; scales etc., thus formed need to
be removed.
ii. It is the intended to remove surface roughness
and other imperfections from the castings.
iii. It is required to achieve exact casting
dimensions.
iv. Surface finish is required on the casting.

4. Distortion allowance:
A casting will distort or wrap if :
i. It is of irregular shape,
ii. All it parts do not shrink uniformly i.e., some
parts shrinks while others are restricted from
during so,
iii. It is u or v-shape

5. Shake allowance:
A pattern is shaken or rapped by striking the
same with a wooden piece from side to side. This
is done so that the pattern a little is loosened in
the mold cavity and can be easily removed.
In turn, therefore, rapping enlarges the mould
cavity which results in a bigger sized casting.
Hence, a –ve allowance is provided on the
pattern i.e., the pattern dimensions are kept
smaller in order to compensate the enlargement
of mould cavity due to rapping.

Molding Materials
Major part of Molding material in sand casting are
1. 70-85% silica sand (SiO2)
2. 10-12% bonding material e.g., clay cereal etc.
3. 3-6% water
Properties of molding sand are:
(a) Refractoriness-ability to remain solid at high temp.
(b) Cohesiveness- Bonding
(c) Strength/Adhesiveness- ability to retain gas forces
(d) Permeability- gas flow through mold
(e) Collapsibility- ability to collapse easily after solidification
(f) Flowability- ability to flow easily into flask
(g) Chemical Inactiveness- It should not react chemically
with hot molding metal.

Molding Sand Composition:
The main ingredients of any molding sand are:
 Base sand,
 Binder, and
 Moisture
 Additives

Sheet Metal Forming Processes
Thanks to Mechanical Engineer for making
cooking easier than it was earlier !!

SHEET METAL WORKING
Sheet metal working:-
It is the process of manufacturing the components
from the sheet metal of thickness ranging from 0.4
mm to about 6 mm.
It is carried out by a machine tool called Press (Press
working).
The applications of sheet metal working can be seen
such as home appliances, Automobile industry,
Airline industry, Railways, Ship building etc

Sheet Metal Working
Sheet Metal Cutting (Shearing) Operations
• Piercing
• Punching
• Blanking
• Perforating
• Notching
• Lancing
• Slitting
Sheet Metal Forming Operations
• Bending
• Deep Drawing
• Embossing
• Coining (Squeezing)

Shearing
A large scissors action, cutting the sheet along a straight line
Main use: to cut large sheet into smaller sizes for making parts.
The Shearing process involves
cutting sheet metal into individual
pieces by subjecting it to shear
stresses in the thickness direction,
typically using a punch and die,
similar to the action of a paper
punch.

Shearing
Shearing Punch
Sheet Metal

Punching (Piercing): It is a cutting operation by which
various shaped holes are made in sheet metal. Punching is
similar to blanking except that in punching, the hole is the
desired product, the material punched out to form the hole
being waste.
Punching Circular Hole Only,
Piercing Any shape Hole
E.g.- Punching Machine.

• Blanking Piercing Piercing Bending(if
needed)

• Blanking: Blanking is the operation of cutting a
flat shape sheet metal. The article punched out is
called the blank and is the required product of the
operation. The hole and metal left behind is
discarded as waste.
• E.g.- Washers, Coins etc. Blank

Blanking Die

Blanking & Punching example

How Washer is made?
Material flow
direction

• Perforating: This is a process by which multiple
holes which are very small and close together are cut
in flat work material.
• E.g.- Kitchen appliances, filtering devices, Showers,
Bench Plates etc.

• Notching: This is cutting operation by which
metal pieces are cut from the edge of a sheet,
strip or blank.
• E.g.- Razor Blades, Exam Pad.
Notches

• Lancing: This is a cutting operation in which a
hole is partially cut and then one side is bent
down to form a sort of tab. Since no metal is
actually removed, there will be no scrap.
• E.g.- Peelers, Railway windows etc.

• Slitting: Cutting a metal sheet in a straight line
along a length.
• E.g. Razor Blades.
First Slitting then Notching

• Punching a series of
small overlapping
slits or holes along
a path to cut-out a
larger contoured
shape.
Nibbling

Shearing away minimal
material from the edges of
a feature or part, using a
small die clearance. Used
to improve accuracy or
finish. Tolerances of
±0.025 mm are possible.
Shaving

Cutoff - Separating a
part from the remaining
sheet, without
producing any scrap.
The punch will produce
a cut line that may be
straight, angled, or
curved.
Cutoff

• Separating a part
from the remaining
sheet, by punching
away the material
between parts.
Parting

Automobile bodies
Aircraft bodies

Industrial ComponentsMachine Parts

Metal Forming processes
• It is a process in which flat plate metal sheet is converted into
a desired shape without wasting the material.
 Deep drawing
 Bending
 Coining
 Embossing

Bending
• Bending is defined as the straining of metal around a
straight axis. During this process, the metal on the
inside of the neutral axis is compressed, while the
metal on the outside of the neutral axis is stretched.

• In V-bending the sheet metal blank is bent
between a V-shaped punch and die. The figure
below shows a front view and isometric view of a
V-bending setup with the arrows indicating the
direction of the applied force
Types of Bending: V-Bending

Types of Bending :Edge Bending
• Edge or wipe bending involves cantilever loading of the
material. A pressure pad is used to apply a Force to hold
the blank against the die, while the punch forces the
workpiece to yield and bend over the edge of the die. The
figure below clearly illustrates the edge (wipe)-bending
setup with the arrows indicating the direction of the
applied force (on the punch)

Bending Animation

Springback Animation

Channel bending U-bending air-bending
Offset-bending Corrugating Tube forming
Various Bending Operations

Bending Operations
Straight flanging Stretch flanging Shrink flanging
Hemming Seaming Curling

Bending
Body of Olympus E-300 camera
component with multiple bending operations
[image source: dpreview.com]
component with punching,
bending, drawing operations

• Deep drawing is a
metal forming process
in which sheet metal is
stretched into the
desired shape.
• A tool pushes
downward on the
sheet metal, forcing it
into a die cavity in the
shape of the desired
part.
Deep Drawing

Deep Drawing Sequence

• Certain designs are
embossed on the
sheet metal.
• Punch and die are
of the same
contour but in
opposite direction.
Embossing

• Similar to
embossing with
the difference
that similar or
different
impressions are
obtained on both
the sides of the
sheet metal.
Coining

• Roll forming is a continuous
bending operation in which a
long strip of sheet metal is
passed through sets of rolls
mounted on consecutive
stands, each set performing
only an incremental part of
the bend, until the desired
cross-section profile is
obtained.
• Roll forming is ideal for
producing constant-profile
parts with long lengths and in
large quantities.
Roll Forming

• Stretch forming is a
metal forming process in
which a piece of sheet
metal is stretched and
bent simultaneously
over a die in order to
form large bent parts.
Stretch Forming

Applications:
▫ Automobile body parts (bike , car , buses etc), aircraft
body parts.
▫ Steel furniture, Utensils
▫ Electronics appliances
Advantages:
•Components produced are light in weight.
•Cheap
•Rate of production is high
•High dimensional accuracy
•Not required skilled man power
Limitations:
•Limitation of thickness of metal sheet
•Components have low strength.
•Not suitable for job production.
•Vibrations are more during operations
•Noisy in operation.
•Dies are costly.

Metal Forming Processes
It is the process in which the component of desired shape
and size is obtained through the plastic deformation of the
metal under the action of extremely applied force.
Can be carried out on metal in hot and cold conditions.
• Types of Metal Forming Process
1. Forging
2. Rolling
3. Extrusion
4. Drawing Rolling
Forging
Extrusion Drawing

What is meant by Hot working?
• Deformation at temperatures above re-crystallisation
temperature
• Re-crystallization temperature = about one-half of melting point
on absolute scale
▫ In practice, hot working usually performed somewhat above
0.5Tm
▫ Metal continues to soften as temperature increases above
0.5Tm, enhancing advantage of hot working above this level.
Hot Working Operations:
• FORGING
• ROLLING
• EXTRUSION
• SPINNING
• HOT PIERCING AND ROLLING

What is meant by Cold Working?
• Performed at room temperature or slightly above
• Many cold forming processes are important mass
production operations
• Minimum or no machining usually required
▫ These operations are near net shape or net shape processes
Cold Working Processes
• COLD ROLLING
• EXTRUSION
• PRESSING
• DEEP DRAWING
• SQUEEZING
• BENDING
• SHEARING

Forging
• Forging is perhaps oldest metal working process and was
known even during prehistoric days when metallic tools
were made by heating and hammering.
• Forging is basically involves plastic deformation of
material between two dies to achieve desired
configuration. Depending upon complexity of the part
forging is carried out as open die forging and closed
die forging.
• In open die forging, the metal is compressed by repeated
blows by a mechanical hammer and shape is manipulated
manually.
• In closed die forging, the desired configuration is
obtained by squeezing the workpiece between two shaped
and closed dies.

Grain Structure: Forging
• Parts have good strength
• Favorable Grain Structure
• High toughness
• Forgings require additional heat treating
• Typical forged products:
▫ Bolts
▫ Rivets
▫ Connecting rods, Camshafts
▫ Gears
Fig : A part made by three different procedures, showing grain flow (a) casting (b) machining (c) forging

Open-Die Forging
• Is the simplest forging process
• Sizes can vary from very small parts to very large parts

Impression-Die & Closed-Die Forging
• The workpiece acquires the shape of the die cavities while
being forged between the two shaped dies

Process details
Closed-die forging
A heated blank is placed between 2 halves of a die

A single compressive stroke squeezes the blank into the
die to form the part. In hammer or drop forging this
happens by dropping the top of the mould from a height.
An alternative is to squeeze the moulds together using
hydraulic pressure.

Once the die halves have separated, the part can
be ejected immediately using an ejector pin.

The waste material, flash, is removed later.

Forging: Squeezing hot metal in dies
Drop Forging. Pneumatic forging hammer
99

• Upsetting:
Upsetting is the process in which the cross
sectional diameter of a hot metal work piece is
increased with a corresponding reduction in its
length.
During this process the hot metal piece is held in
a tong and placed on the anvil in vertical
position and then is stroke with a hammer.
Forging Operations:

Upsetting

• It is also known as drawing down.
• Exactly the reverse of upsetting.
• Contrary to upsetting this process is used to reduce the thickness
/width/diameters or increasing the length of red hot workpiece.
Drawing out:

• It is the operation of reducing the thickness of a
work piece.
• Hot work piece is placed in the grooves of the lower
fuller and then the top fuller is placed over it.
• The hammering operation is carried out until the
piece gets squared thickness.
Fullering:

• This operation is performed to level the job
surface.
• The red hot metal work piece is placed on the
anvil and is stroked hardly using hammer set to
flatten the metal work piece.
Flattening:

• The process of giving the desired angle or curves
to a hot metal work piece is known as bending.
• The process is done on the edge of anvil.
• Circular shaped, eye bolts, hooks or any other
types of bent shape can be prepared with this
operation.
Bending:

Edging
• It is a process in which the metal piece is
displaced to the desired shape by striking
between two dies. Edging is frequently as primary
drop forging operation

Difference between Cold &Hot
Working Forging
Parameters Hot Working Forging Cold Working Forging
Definition It is Defined as the
deformation of the material
into predetermined shape
carried out at a temperature
above its recrystallation
temperature.
It is Defined as the
deformation of the
material into
predetermined shape
carried out at a
temperature below its
recrystallation
temperature.
Force &
Energy
required
Low High
107

108
Parameters Hot Working Forging Cold Working Forging
Dimensional accuracy Poor (due to thermal
contraction during
cooling)
Good
Machine requirement Light Heavier and Powerful
Ductility of
component
Increases Decreases
Type of materials Need not be soft Soft like Aluminum
Strain Hardening
effect
Absent Present

Advantages:
 High dimensional accuracy and good surface finish.
 Forging process reduces the grain size, which improve the strength
and toughness of the forged components.
Thin sections are possible without reducing strength, which results
in light weight components.
 Produces the components without shrinkage cavities, blow holes,
machining scratches, which increases the endurance strength.
 Better withstand the external load.
 Better resistance to shock and vibrations.
Forged component compared with cast and Machined component

Applications:
▫ I C Engine parts like crankshafts, connecting rods, rocker
arms, etc.
▫ Small tools
▫ Gear blanks, Levers.
▫ Automobile and Aircraft components.
110
Limitations:
•Brittle materials can not be used.
•Complex components with intricate shapes can be produced
by casting and not by forging process.
•Forged component cost is more than cast components.
•Cost of forging dies is high.

APPLICATION
Typical Products
 Spanners
 pedal cranks
 gear blanks
 valve bodies
 hand tools
 crankshafts
 Hammers
 Handles

Forging Applications

Forging Tools
Hammers
Tong chisel
Swage Block

Rolling is a bulk deformation process in which the thickness
of the work is reduced by compressive forces exerted by two
opposing rolls. The rolls rotate to pull and simultaneously
squeeze the work between them.
Introduction to Rolling

The basic process shown in the previous figure is “Flat
Rolling”, used to reduce the thickness of a rectangular cross
section. A closely related process is “shape rolling”, in
which a square cross section is formed into a shape such as
an I-beam.
Shape Rolling
Flat Rolling
Shape Rolling

•As any other metal forming process, rolling can be
performed hot (hot rolling) or cold (cold rolling).
•Most rolling is carried out by hot rolling, owing to the
large amount of deformation required.
•Hot-rolled metal is generally free of residual stresses,
and has isotropic properties. On the other hand, it does
not have close dimensional tolerances, and the surface
has a characteristic oxide scale. Moreover, cold rolled
metals are stronger.

Types of Rolling
Based on work piece geometry :
Flat rolling - used to reduce thickness of a rectangular
cross section
Shape rolling - square cross section is formed into a
shape such as an I-beam
Based on work temperature :
Hot Rolling – most common due to the large amount
of deformation required
Cold rolling – produces finished sheet and plate stock

The Rolls
Rotating rolls perform two main functions:
•Pull the work into the gap between them by friction
between work part and rolls.
•Simultaneously squeeze the work to reduce its cross
section.

Two High Rolling Mill.
Roll configurations in rolling mills

Three High Rolling Mill.

Four High Rolling Mill.

Multiple backing rolls allow even smaller roll
diameters
Cluster Rolling Mill.

A series of rolling stands in sequence
Tandem Rolling Mill.

Production steps in Rolling

Steps in the shape rolling of an I-beam part. Various other structural
sections, such as channels and rails, also are rolled by this kind of
process.

Change in grains structure in Rolling

Introduction: Extrusion
Extrusion – It is a process where a billet is forced
through a die.
• Parts have constant cross-section
• Typical Products of Extrusion – Sliding Doors,
tubing having various cross-sections, structural
and architectural shapes and door and window
frames.

Extrusions
Fig : Extrusions and
examples of
products made
by sectioning
off extrusions.

The Extrusion Process
Types of Extrusion :
Direct Extrusion (or) Forward Extrusion – Billet is placed
in a chamber and forced through a die opening by a hydraulically-
driven ram or pressing stem.
Indirect Extrusion – Die moves towards the billet.
Hydrostatic Extrusion – The billet is smaller in diameter that
the chamber, which is filled with a fluid, and the pressure is
transmitted to the billet by a ram.
Extrusion Ratio = Ao/Af
Ao – cross-sectional area of the billet
Af - cross-sectional area of extruded product

Welding
Application of
pressure
(Optional)
Filler material
(Optional)
Heat
(Essential)
131
Welding is a process of joining two metallic parts together by heating
them to a plastic or semi molten state with or without application of
pressure and with or without a filler material.
Lets Join the world Together!!!

• Pressure Welding (Plastic Welding):-
▫ In this process, metal pieces to be welded are heated
to a temp. so as to make them plastic and then forced
together by external pressure.
▫ This process does not require additional metal for
completing the weld.
• Fusion Welding (Non-Pressure Welding):-
• In this process, metal pieces to be welded are
heated to molten (fusion) state & allowed to solidify.
• No pressure is required in this process.
• Additional metal is generally supplied by filler rod
(welding rod) to complete the joint.
132

Electric Arc Welding
▫ It is a fusion welding process, in which welding heat is
obtained from an electric arc between electrode &
work.
▫ The electrode is first allowed to touch the work to form
an electric circuit and then separated by a small
distance ( 4 to 6 mm), so that current continuous to
flow through the gaseous medium.
▫ The temp. produced by an electric arc is about 5500°C.
▫ The base metal is melted by the temp. of the arc,
forming a pool of molten metal which is forced out of
the pool by blast from the arc.
▫ Metal of the electrode also gets melted & deposited at
the weld.
▫ Either A.C. or D.C. is used for arc welding.
133

Electric Arc Welding

Common Electric Arc Welding Processes
1. SMAW
2. GMAW
3. FCAW
4. GTAW
135
Shielded Metal Arc Welding
Gas metal arc welding
Flux core arc welding
Gas tungsten arc welding

Arc Welding Requirements
136
Parameters
Electric arc Inert gas-flux Consumable
electrode
Electric arc Inert gas Consumable
wire
Electric arc Inert gas-
cylinder
Consumable
wire
Electric arc Inert gas-
cylinder
Manual rod
Heat Shielding
Filler
Material
SMAW
GMAW
GTAW
How do these arc welding processes meet the three requirements
of arc welding?
FCAW

Arc Welding Processes
a.) NON CONSUMABLE ELECTRODE
- The electrode is a tungsten electrode type.
- Need externally supplied shielding gas because of the high
temperature involved in order to prevent oxidation of the weld
zone.
- DC is used and the polarity is important.
- For straight polarity which is also known as direct-current
electrode negative (DCEN); the workpiece is positve (anode) ,
while the electrode is negative (cathode).

Non Consumable Electrode
i) GAS TUNGSTEN-WELDING (GTAW)
- Also known as TIG (Tungsten Inert Gas) welding.
- Tungsten is used as electrode.
- Suitable for thin metals.
- This process is expensive because of the cost of inert gas
- Provides welds with very high quality and surface finish
- Filler metal is supplied from a filler wire
- The shielding gas is usually argon or helium

- In this filler metals are similar to the metal that need to be welded,
and flux is not used.
- In this operation, tungsten electrode is not consumed, therefore a
constant and stable arc gap is maintained at a constant current level.
- Power supply either 200A DC or 500A AC; depending on the
metals to be welded.
- Generally, AC is suitable for aluminum and magnesium.
- Thorium or zirconium may be used in the tungsten electrodes to
improve the electron emission characteristics.
Non Consumable Electrode

Gas Tungsten-Arc Welding

i) SHIELDED METAL-ARC WELDING (SMAW)
- Old method , simplest, held manually.
- Most of all industries and maintenance welding currently
performed with this process.
- The electric arc is generated by touching the tip of a coated
electrode against the workpiece.
- Need to have a sufficient distance and movement to maintain
the arc.
Consumable Electrode

• - The heat generated, melts a portion of the electrode tip, its
coating, and the base metal in the intermediate arc area.
• - The molten metal consists of a mixture of the base metal (work
piece), the electrode metal, and substance from the coating on the
electrode; thus this mixture forms the weld when it solidifies.
• - The electrode coating deoxidizes the weld area and provides a
shielding gas to protect it from oxygen in the environment.
• - The equipment consists of a power supply, cables and electrode
holder.
• - Power supply: can be either DCor AC, ranges between 50 to 300A.
• - For sheet metal welding, DC is preferred because of the steady arc
produces.

• The functions of coating on covered electrodes:
1. Shielding of the Weld Metal - The most important function of a
coating is to shield the weld metal from the oxygen and nitrogen of
the air as it is being transferred across the arc, and while it is in the
molten state. This shielding is necessary to ensure the weld metal
will be sound, free of gas pockets, and have the right strength and
ductility.
2. Stabilization of the Arc - A stabilized arc is one that starts easily,
burns smoothly even at low amperages, and can be maintained
using either a long or a short arc length
3. Alloying Additions to Weld Metal - A variety of elements such
as chromium, nickel, molybdenum, vanadium and copper can be
added to the weld metal by including them in the coating
composition. It is often necessary to add alloys to the coating to
balance the expected loss of alloys of the core wire during the
welding operation.

Shielded Metal-Arc Welding

ii) SUBMERGED-ARC WELDING (SAW)
- The weld arc is shielded by a granular flux consisting of lime, silica,
manganese oxide, calcium fluoride.
- The flux is fed into the weld zone from a hopper by gravity flow
through a nozzle.
- The thick layer of flux completely covers the molten metal and it
prevents from spatter and sparks.
- The flux also acts as a thermal insulator by promoting deep
penetration of heat into the workpiece.

- The consumable electrode is a coil of bare round wire 1.5 to 10 mm
in diameter; and fed automatically through a tube which is called
welding gun.
- Electric current: range between 300 to 2000 A.
- Power supply: single or three phase power point; rating up to 440V.
- Due to flux is a gravity fed type; therefore this welding process
is limited largely to welds into flat or horizontal position.
- Circular weld can be made on pipes or cylinders provided that they
are rotated during welding process.
-Suitable for carbon and alloy steel and stainless steel sheet or plates.
- Welding speeds: as high as 5 m/min.

Submerged-Arc Welding

iii) GAS METAL-ARC WELDING (GMAW)
- Also known as Metal Inert-Gas (MIG).
- The weld area is shielded by an effectively inert atmosphere of argon,
helium, carbon dioxide, or other various gas mixtures.
- The temperatures generated are relatively low.
- Suitable only for thin sheets which is less than 6mm.
-The consumable bare wire is fed automatically through a nozzle into
the weld area controlled by wire-feed drive motor.

Gas Metal-Arc Welding

Soldering
The accepted definition of soldering is:-
• The joining of metals using a filler material of a lower melting
point than that of the parent metals to be joined.
• It is a process in which two or more metal items are joined
together by melting and flowing a filler metal into the joint.
(below 450oC) tin-lead alloy.
Note that some metals are easier to solder than others:-
• Tin, Copper and Brass are far easier to solder
than Steel or Aluminium

Solders
Traditional Solder is an amalgam of Tin and Lead. The percentage
of each of these materials defines the use for the solder
%Tin %Lead Use
60 40 Good for all electrical and mechanical work
45 55 Very liquid used in plumbing
50 32 Low melt solder for white-metal casings
Plumbers solder is not suitable for electrical work
Modern Lead Free solders need higher temperatures
and greater care is needed

What is Flux?
Flux is a chemical compound that is applied and shields the joint
surface from air and prevents oxide formation. Although flux will
dissolve and absorb oxides, the metals that are being joined
should be properly cleaned prior to brazing.

Applications
 Soldering is used in plumbing in electronics and in jewelry
metalwork.
 Jewelry components, machine tools and some refrigeration and
plumbing components are often assembled and repaired by the
higher temperature silver soldering process
 It can also be used as a semi-permanent patch for a leak in a
container or cooking vessel.
 Electronic soldering connects electrical wiring and electronic
components to printed circuit boards (PCBs)

Advantages of soldering
• Low power is required;
• Low process temperature;
• No thermal distortions and residual stresses in the joint parts;
• Microstructure is not affected by heat;
• Easily automated process;
• Dissimilar materials may be joined;
• High variety of materials may be joined;
• Thin wall parts may be joined;
• Moderate skill of the operator is required.

Disadvantages of soldering
• Careful removal of the flux residuals is required in order to
prevent corrosion;
• Large sections cannot be joined;
• Fluxes may contain toxic components;
• Soldering joints can not be used in high temperature
applications;
• Low strength of joints.

• Brazing is a metal joining process whereby a filler metal
is heated above (450oC) and distributed between two or
more close fitting parts by capillary action.
• Brazing is when a filler metal or alloy is heated to its
melting temperature above 450°C. It is then distributed in
liquid form between two or more close-fitting parts by
capillary action.
• The filler metal is then brought slightly above its melting
temperature.
• It then interacts with a thin layer of the base metal
(known as wetting) and is then cooled quickly.
• This forms a sealed joint.
• Brazed joints are generally stronger than the individual
filler metals that have been used to make them.
• This is because of the geometry of the joint and the
metallurgical bonding that occurs.
Brazing

Filler Material: Brazing
• Some of the more common types of filler metals
used are
• Aluminium-silicon
• Copper
• Copper-silver
• Copper-zinc (brass)
• Gold-silver
• Nickel alloy
• Silver

Comparison b/w Brazing and Soldering
Parameters Brazing Soldering
Heating Temperature Above 450oC Below 450oC
Filler Material Alloys of copper, silver
or Nickel
Tin- Lead alloy Zinc-
Aluminum
Surface Finish Good Not good
Strength of Joint Lower than welded
joint but relatively
good
Very Low
159

Advantages of Welding:
• Gives light weight construction.
• High strength joint.
• High rate of production.
• Ability to produce complicated shapes.
• Used effectively for repairing broken parts.
• Low cost process.
• Ability to produce fluid tight joints.
160
Limitations of Welding:
• Not possible t disassemble the parts.
• Joints weak against vibrations.
• Quality and strength of joint is operator dependant.
• Gives harmful radiations.

161
Applications :
• Fabrications of Bridges, Electric and Transmission Towers.
• Manufacturing of Automobile bodies.
• Building of Ships and Aircrafts.
• Manufacturing of Boiler, Pressure Vessels, Storage Tanks, Pipelines
• Manufacturing of Steel Furniture, Window and Door Frames,
Window Grills. etc

Manufacturing Proecesses

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