My presentation-welding

Advanced metallic Materials, Summer Semester 2015 1
Welding
Presented By: Niranjan Ramakrishnegowda

History of Welding
 The first metal to be shaped in welding history is thought to be copper
since it can be hammered and bent.
B.C. Welding History
4000 B.C: Welding history is thought to begin in Egypt in the starting of
4000 B.C. In general, civilizations started with copper and then progressed
to bronze, silver, gold and iron.
1000 B.C: Gold boxes found in Ireland that were fabricated by hammering
lapped joints (form of pressure welding).
589 B.C: The Chinese during the Sui Dynasty developed the ability to turn
wrought iron into steel in 589 A.D. The Japanese manufactured steel
through a welding and forging process to produce Samurai swords.
A.D. Welding History
310 A.D: The Iron Pillar of Delhi is fabricated using iron billets. Blacksmiths
forge welded the structure that is approximately 25 feet high and weighs 6
tons.

History of Welding
1375 A.D: The Middle Ages (5th to 15th century) brought a
phase in welding history where forge welding was front and
center. Blacksmiths pounded hot metal until it bonded.
19th
Century
1800: Sir Humphrey Davy invented the electric arc. The arc
was created between 2 carbon electrodes that were powered
by a battery.
1838: Patent issued to Eugene Desbassayrs de Richemont
for fusion welding.
1903: Thermite welding is invented, another process,
oxyfuel welding, also became well established as a
commercial process.
1943: Gas Metal Arc Welding was invented.
1950: Shielded Metal Arc Welding.
Modern Welding
Friction stir welding, Magnetic Pulse welding
Iron Pillar of Delhi, India.
Welding For Ships Was Not
Reliable due to Cracking Until
World War I.

Introduction
Definition: Welding is a technique of joining similar
and dissimilar metals and plastics by adopting ways
which do not include adhesives and fasteners.
From Wikipedia:
Fabrication or sculptural process to join materials
(Usually metals or thermoplastics).
High temperature metal joining technique (Heated till
the fusion point).
Filler material is often used addition to melting of the
base metal.
Permanent joints are produced.
Localized coalescence in the weld pool caused by
suitable combination of temperature, pressure and
metallurgical conditions.

Basics
Distinction Between Welding, Soldering and Brazing:
Soldering: Soldering differs from welding in that soldering does not involve melting
the work pieces.
Brazing: Brazing differs from welding in that it does not involve melting the work
pieces and from soldering in using higher temperatures for a similar process, while also
requiring much more closely fitted parts than when soldering.
https://www.youtube.com/watch?v=c3mnk_rqGMc

Heat Sources
Variation of heat input to the work piece with power
density of the heat source.

Weld Design
Joint Type: 5 Basic Joint Types
Welds are made at the junction of all the
pieces that make up the weldment
(assembled part).
Butt Joint: A joint between two members
aligned approximately in the same plane.
Corner Joint: A joint between two
members located approximately at right
angles to each other in the form of an L.
Lap Joint: Between two overlapping
members located in parallel.
T Joint: A joint between two members
located approximately at right angles to each
other in a form of a T.
Edge Joint: Between the edges of two or
more parallel or nearly parallel members

Weld Design
Weld Type:
•Fillet weld: On the Joint.
•Groove weld: In the Joint.
•Back weld: Made on the backside of
the joint.
•Slot weld: Used with prepared holes.
•Spot weld: Weld at the interface of
the members.
•Seam weld: Without prepared holes.
•Stud weld: Welding a metal stud.
•Surface weld: Weld beads deposited
on the base metal or broken surface.

Weld Design- Fillet Weld
Fillet weld on corner joint Fillet weld on lap joint Fillet weld on T-joint
• Triangular shaped weld having concave,
convex or flat surface.
Example: Connecting flanges to pipes.
http://www.lincolnelectric.com/en-us/support/process-and-
theory/Pages/weld-fusion-weld-penetration.aspx

Weld Design- Groove Weld
• There are seven basic groove welds: square, V, bevel, U, J, flare V and flare
bevel.

Classification
Various welding process differ in a manner in which temperature and pressure
are combined and achieved, classification can also be done on the source of energy.

Arc Welding
 Gas metal arc welding (GMAW) :
• Also called Metal inert-Gas welding.
• Weld area is shielded by an inert gas like argon, helium or carbon dioxide.
• Consumable bare wire with de-oxidizers are fed automatically into weld area by
wire feed drive motor.
• Suitable only for thin sheets and sections less than 6mm. (Otherwise Incomplete
fusion, spatter losses are more)
(1) Torch handle, (2) Molded phenolic
dielectric (shown in white) and threaded
metal nut insert (yellow), (3) Shielding gas
diffuser, (4) Contact tip, (5) Nozzle output
face

Arc Welding
 Gas tungsten arc welding (GTAW):
• Also called Tungsten Inert Gas welding
(TIG).
• Non-Consumable tungsten electrode.
• Filler metal normally used.
• Weld area is protected by Shielding gases
like Argon or Helium.
• Not safe- protective clothing needed.
• Difficult of all the welding techniques
known since a short arc length has to be maintained.
• A high frequency generator is used to strike electric spark, this arc is the
conductive path for the welding current through the shielding gas while the
electrode and the work piece are separated (1.5-3mm).
• Filler rod is always withdrawn every time the electrode advances but never taken
out of the weld pool in order to avoid the oxidation.

Arc Welding
 Shielded Metal Arc Welding (SMAW):
• Electrode and the work piece melts forming the weld pool that cools to
form a joint.
• The flux coating disintegrates giving raise to the vapor which serve as a
shielding gas and forming a layer of slag later which acts as a shield for the
atmospheric contamination.

Electron Beam welding-Major Breakthrough
• Beam focus and beam deflection are a part of todays weld schedule and can be
programmably varied.
• Small Heat affected Zone.

Electron Beam welding
• Formation of a Key Hole in
EBW, the high energy density
instantly vaporizes the material
forming a key hole as shown in
figure.
Possibilities:
•Depth-to-width ration of 40:1 have been achieved in production for many years.
•Conduction mode welding produces a wide and shallow welds, this can be done
by lowering the beam power and either defocusing the e-beam or widening the
beam by using deflection pattern.

Electron Beam welding
Weld with root porosity. Pattern generator-A unique e-beam
welding parameter.
Manual Transmission gear component.

Solid State Welding-Major Breakthrough
 Friction Stir Welding (FSW):
• A non consumable rotating tool with a pin and a shoulder is inserted into the
abutting edges of the plates.
• The tool heats up (by friction) the work piece and moves the material to produce
joint.
• It is a ‘‘green’’ technique, due to its energy efficiency, environment friendliness,
and versatility.

Defects in Weldments
A welding defect is any flaw that compromises the usefulness of a weldment.
There is a great variety of welding defects.
Misalignment
Geometric Imperfections
Undercutting
Convex and Concave welds
Porosity

Weld Metallurgy
Presentation of the various constituent parts of a welded
joint.
• Welding metallurgy can be considered a special branch, since reaction times are in the
order of minutes, seconds, fraction of seconds, whereas in the other branches reactions
are in hours and minutes.
• Welding metallurgy deals with the interaction of different metals and interaction of
metals with gases and chemicals of all types.

Weldability of Steels
• Iron-carbon equilibrium diagram provides an insight of the behavior of steels in connection
with welding thermal cycles and heat treatment. This diagram represents the alloy of iron with
carbon, ranging from 0% to 5% carbon.

• 0% carbon, pure iron,
above 1540ºC, in liquid state, no crystalline structure
• 1540 ºC, solidification starts, BCC structure, Delta iron
• 1400 ºC, transformation occurs, FCC structure, Gamma iron
• 910 ºC, iron back to BCC, alpha iron until room temp
• Iron and carbon form a compound known as iron carbide (Fe3C) or cementite.
• When iron carbide or cementite is heated above 1115 ºC, it decomposes into liquid
iron saturated with graphite, which is a crystalline form of carbon.
Martensite Formation:
• At fast cooling rates, the austenite might not have sufficient time to transform
completely to ferrite and pearlite and will provide a different microstructure. In this
case, some of the untransformed austenite will be retained and the carbon is held at
supersaturated state. This new structure is called ‘martensite’.
• If the cooling rate is sufficiently fast, the austenite might transform completely into
martensite. It is harder than pearlite or ferrite-pearlite structure and it has lower
ductility.

Hardenability:
Hardness mainly depends on the carbon content but cooling rate also
influences the microstructure and causes higher hardness. This is because the
crystal lattice is changed or distorted and this hardens the material.
By adding different alloys to the steel, the tendency of austenite to transform
into martensite upon cooling increases, which is the basis of hardening steels.
Carbon, manganese, chromium, molybdenum etc.
The amount of alloys and their power to create this microstructure
transformation are known as hardenability.
Grain size and microstructure relate directly to hardness and strength. Fine
grain size promotes both increase in strength and hardness.
This is an advantage for heat treatment but it can be detrimental to welding
since high hardness is not desired in welds of softer materials.

Weldability of Aluminium alloy
Parameters Controlling Microstructure and Hardness during Friction-
Stir Welding of Precipitation-Hardenable Aluminum Alloy 6063.
Relationship between the welding rotation speed and
the maximum temperature of the welding thermal
cycle.
Cross sections perpendicular to the welding direction of the
welds of Al alloys 6063-T5 and T4.

Optical microstructures in the stir zones in the
welds of Al alloys 6063-T5 and T4.
OIM images in the stir zones in the welds of Al alloy
6063-T5.

Relationship between the grain size and the
maximum temperature of the welding thermal cycle.
Horizontal hardness profiles of the welds of Al alloy
6063-T5 (a) in the as-welded condition and (b) in the
postweld-aged condition.

Applications
Aircraft industry Ship building
Automotive industry

References
 Gourd, L.M., Principles of welding technology, 3rd edition, 1995, Edward
Arnold, ISBN 0 340 61399 8.
 Parameters Controlling Microstructure and Hardness during Friction-Stir
Welding of Precipitation-Hardenable Aluminum Alloy 6063 by YUTAKA
S. SATO, MITSUNORI URATA, and HIROYUKI KOKAWA.
 Microstructural investigation of friction stir welded 7050- T651 aluminium
by J.-Q. Su a, T.W. Nelson a, , R. Mishra b, M. Mahoney.∗
 www.Wikipedia.com
 Cary, H.B., Modern welding technology, 4th edition, 1998, Prentice Hall,
ISBN 0-13-241803-7.
 Welding metallurgy by American Welding Society.

Questions?

Smart Mater. Ex. WS 2012, Name, Title 31

 Fume extraction arm

Defects in Weldments
Weld Damage
Spatter

Welding Safety
 Mention about the lung damage caused by fumes.
 Mention about use of welding helmet (cost online lol)

Solid State Welding-Major Breakthrough
 Magnetic Pulse Welding (MPW) and Explosion Welding:
MPW and Explosion welding are alike but not the same.
MPW System Explosion Welding

Weld Metallurgy
Grains
The size of the crystals and grains depends on the rate of growth of the crystal. The rate of
crystal growth depends on the rate of cooling of the molten solidifying metal.
When the rate of cooling is high, the solidification process occurs more rapidly and the crystal
size and grain size tend to be smaller and vice versa.
Microstructures
The overall arrangement of grains, grain boundaries, phases present in an alloy is called its
microstructure. It is largely responsible for the properties of the metal.
The microstructure is affected by the composition or alloy content and by other factors such
as hot or cold working, straining, heat treating etc.
The microstructure of weld metal and adjacent metal is greatly influenced by the welding
process, which influence the properties of the weld.
Microstructure of a weld used in stainless steel Microstructure of base metal of the same stainless steel.

39
Weld Metallurgy-Crystal Structures
• The structure of metal is complex. When metal is
in a liquid state, usually hot, it has no distinct
structure or orderly arrangement of atoms. So that
atoms move freely since they have high degrees
of mobility due to the heat energy involved
during melting process.
• As the metal cools, atoms loose their energy
and their mobility. When temperature is
further reduced, the atoms are no longer able
to move and attracted together into definite
patterns.
• These patterns consist of three-dimensional
lattices, which are made of imaginary lines
connecting atoms in symmetrical arrangements.
• Metals in a solid state possess this uniform
arrangements, which is called crystals. All metals
are crystalline solids made of atoms arranged in a
specific uniform manner.

40
Weld Metallurgy-Phase Transformation
 Some metals change their crystallographic arrangement with changes in
temp. Iron has a BCC lattice structure from room temp. up to 910ºC, and
from this point to 1388 ºC it is FCC. Above this point to melting point,
1538 ºC it is again BCC. This change is called as phase transformation
or allotropic transformation. Like, titanium, zirconium and cobalt.
 Transformation occurs when metal melts or solidifies;

In melting, arrangement of atoms disappears and atoms move
randomly.

In solidifying, crystalline arrangement reestablish itself.
 Pure metals melts or solidify at a single temperature, while alloys solidify
or melt over a range of temperature with a few exceptions.
 Phase changes can be related to alloy compositions and temp when they
are in equilibrium, and shown on a diagram (known as phase diagrams,
alloy equilibrium diagrams or constitution diagrams).

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