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Casting, Forming & Welding
Casting Forming & Welding
(ME31007)
J u au
Jinu Paul
Dept. of Mechanical Engineering
1
Welding ecture
Welding Lecture – 11
11 Oct 2012, Thursday 8.30 am‐9.30 am
Design of Weld
joints
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Design of Weld joints
(Refer class notes)
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Example No: 3
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Example No: 4
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Welding ecture
Welding Lecture ‐ 12
12 October 2012, Friday 11.30 am ‐12.30 pm
Welding Processes‐
Other fusion
Oh f i
welding processes
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Thermite mixture
Metallic fuel + Oxidiser  Energy
Thermite Reaction
Metal oxide + Aluminum 
Metal + Aluminum oxide +
Heat
• Bimolecular reactions and reaction rates are controlled by
diffusion times between reactants.
• Thermite mixtures of nano-sized reactants reduce the critical
diffusion length thus increasing the overall reaction rate
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Thermite Reaction stages
(1/2)Fe3O4 + Al  Fe + (1/2)FeAl2O4
2FeO + Al  (3/2)Fe + (1/2)FeAl2O4
(1/2)FeAl2O4 + (1/3)Al  (1/2)Fe + (2/3)Al2O3
Thermite types
Fuels Oxidisers
Aluminium, Boron(III) oxide,
Magnesium, Silicon(IV) oxide,
Titanium, Chromium(III) oxide,
Zinc, Manganese(IV) oxide,
Silicon, Iron(III) oxide,
Boron Iron(II,III) oxide,
Copper(II) oxide
oxide,
Lead(II,III,IV) oxide,
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Thermite welding (TW)
• Heat for coalescence is produced by
superheated molten metal from the chemical
reaction of Thermite
• Example: 2Al + Fe2O3  2Fe + Al2O3 + heat
• Filler metal is obtained from the liquid metal
• More in common with casting than it does with
welding
• Applications in joining of railroad rails and
repair of cracks in large steel castings and
forgings such as ingot moulds, large diameter
shafts, frames for machinery, and ship
rudders
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Thermit welding (TW)
Fe2O3 + Al  2Fe + Al2O3 + ~850kJ
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High-Energy-Density Beam Welding
Processes
• Electron beam and
Electron-beam
• Laser-beam welding
• Focussed beam of electromagnetic energy
– IR welding
– Imaged arc welding
– Microwave welding
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Comparison of Conventional and
E/Laser-Beam Welding
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Electron-beam welding (EBW)
• Uses kinetic energy of
dense focused electrons
• Electrons emitted by
cathode, accelerated by
ring shaped anode, focused
by electromagnetic field
• High energy density 10
MW/mm2
• Heat focus on few
micrometers
• Vacuum chamber
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Electron speed Vs
Accelerating
voltage
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E-Beam interaction with work piece
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Electron-beam penetration Vs
operating pressure
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EBW or LBW of a butt joint
Melting
Butt joint A key The keyhole
occurs at the The weld
prior t
i to hole and it molten
d its lt
point of forms upon
welding forms envelope
impingement solidification
penetrates
of the E-beam
workpiece
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Laser-beam welding (LBW)
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Laser-beam welding
• Coalescence is achieved by the energy of a highly
concentrated, coherent light beam focused on the
joint to be welded
• LBW is normally performed with shielding gases
(e.g., helium, argon, nitrogen, and carbon dioxide)
to prevent oxidation
• No vacuum chamber is required, no X-rays are
emitted
• Laser beams can be focused and directed by optical
lenses and mirrors.
• LBW does not possess the capability for the deep
welds and high depth-to-width ratios of EBW
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Example‐1
A carbon dioxide laser with a power output of 1 kW operates in
the continuous wave mode. (For CO2 laser, wavelength = 10
micron = 0.01 mm). Focal length f and diameter of the lens
used is 100 mm and 8 mm respectively. The diameter of laser
beam is 6 mm.
The laser-beam welding operation will join two pieces of steel
plate together as shown in figure. The plates are 25 mm thick.
The unit melting energy is 10 J/mm3. The heat transfer factor is
0.70 and the melting factor is 0.55. Find the velocity of the
laser beam movement if the beam penetrates the full thickness
of the plates?
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Laser beam‐ Depth of
penetration
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Focussed IR welding
• Infrared radiation from the sun or an artificial light source can be used
• Radiation is focused into an intense, high-density spot directed onto the work
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Imaging arc welding
• High energy density due to focussing
• Advantage is freedom from the electromotive Lorentz forces
associated with conventional arc welding
Comparison of Electron‐Beam and Laser‐
Beam Welding
EBW LBW
1.
1 Deep penetration in all materials 1.
1 Deep penetration in many materials but
materials,
not in metals that reflect laser light/or of
specific wavelengths
2. Very narrow welds 2. Can be narrow (in keyhole mode)
3. High energy density/low linear 3. Same
4. Best in vacuum, to permit electrons 4. Can operate in air, inert gas, or vacuum
5. Usually requires tight-fitting joints 5. Same
6. Difficult to add filler for deep welds 6. Same
p
7. Equipment is expensive 7. Same
8. Very efficient electrically (99%) 8. Very inefficient electrically (- 12%)
9. Generates x-ray radiation 9. No x-rays generated
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Welding ecture 3
Welding Lecture ‐ 13
17 October 2012 9.30 am ‐10.30 am
Solid state welding
processes
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Solid state/Nonfusion welding
• Accomplish welding by bringing the atoms (or ions or
molecules) to equilibrium spacing  through plastic
molecules) to equilibrium spacing through plastic
deformation  application of pressure at
temperatures below the melting point of the base
material
• Without the addition of any filler
• Chemical bonds are formed and a weld is produced
as a direct result of the continuity obtained, 
di l f h i i b i d
always with the added assistance of solid‐state
diffusion
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Solid state/Nonfusion welding
1. Pressure Welding  By pressure and gross
deformation
2. Friction welding  By friction and
microscopic deformation
3. Diffusion welding  By diffusion, without or
with some deformation
4. Deposition welding  Solid‐state deposition
welding
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Pressure WeldingCold welding
• Pressure is used at room temperature to produce
coalescence of metals with substantial plastic
l f t l ith b t ti l l ti
deformation  No heat
• The faying surfaces must be exceptionally clean
• Cleaning is usually done by degreasing and wire brushing
immediately before joining
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Pressure Welding Cold welding
• At least one of the metals to be joined must be highly
ductile and not exhibit extreme work hardening
and not exhibit extreme work hardening
• FCC metals and alloys are best suited for CW. Example‐ Al,
Cu, and Pb
• To a lesser degree, Ni and soft alloys of these metals such
as brasses, bronzes, babbitt metals (Sn, Cu, Sb, Pb), and
pewter (Sn, Cu, Sb, Bi)
pewter (Sn Cu Sb Bi)
• Precious metals, Au, Ag, Pd, and Pt, are also ideally suited
to cold welding, as they are face‐centered cubic (soft)
and are almost free of oxides
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Pressure Welding  Cold welding
• Ideal for joining of dissimilar metals  no
intermixing of the base metals is required
• Allows inherent chemical incompatibilities that
make fusion welding difficult to be overcome
• E.g.  Cold welding of relatively pure Al to
relatively pure Cu  Electrical connections
• Formation of brittle intermetallics (e.g., AI,Cu) 
either during postweld heat treatment or in
service, (resistance heating in the electrical
connector)
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Micro‐patterning of Organic Electronic
Devices by Cold‐Welding
Calculated normal stress at the interface
(yy) normalized to the applied pressure (P)
as a function of distance (x) normalized to
the stamp half-width (a)
Figure 1 35
Micro‐patterning of Organic Electronic
Devices by Cold‐Welding
• A prepatterned, metal‐coated stamp composed of a rigid material (Si) is
pressed onto an unpatterned film consisting of the organic device layers
coated with the same metal contact layer as that used to coat the stamp.
coated with the same metal contact layer as that used to coat the stamp.
• Organic layer thickness ~ 100 nm, same thickness for the metal cathode
• When a sufficiently high pressure is applied, an intimate metallic junction is
formed between the metal layers on the stamp and the film, leading to a
cold‐welded bond (Fig 1, top).
• To induce selective lift‐off, additional pressure is applied to weaken the
metal film at the edge of the stamp (Fig. 1 , middle).
• This additional pressure leads to substrate deformation, which is expected to
enhance the local weakening of the metal film.
• When the stamp and film are separated, the metal cathode breaks sharply,
forming a well‐defined patterned electrode (Fig. 1, bottom).
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Fabrication of OLEDs
(A) Optical micrograph of an array of 230-mm-diameter Mg-Ag alloy
contacts patterned by cold-welding followed by cathode lift-off. (B) Scanning
electron micrograph (SEM) of the edge of a 12-mm-wide stripe showing a
clearly defined nearly featureless layer pattern.
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Cold welding of ultrathin gold nanowires
Singlecrystalline gold nanowires with diameters between 3 and 10 nm
can be cold-welded together within seconds by mechanical contact alone
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Head‐to‐head welding of two Au‐ nano rods
a,b, One nanorod (right)
is caused to approach
another (left) until their
front surfaces come into
contact.
contact
c–e, The welding
process is completed
within 1.5 s (c,d)
followed by structure
relaxation (d,e).
f–i, After withdrawal of
the STM probe (f–i), the
as-welded nanowire is
left in the free-standing
state
(Triangles indicate the front edges of the two nanorods. Arrows indicate the
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withdrawing direction of the STM probe. Scale bars, 5 nm)
Pressure WeldingHot Pressure
Welding
HEAT + PRESSURE
Vacuum or shielding
MACROSCOPIC DEFORMATION
Examples:
COALESCENCE
1) Pressure gas welding
2) Forge welding
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Pressure Welding Forge welding (FOW)
• Earliest form of welding 
still used today by
blacksmiths
• Produces the weld by heating
work pieces to hot working
temperatures and applying
blows sufficient to cause
deformation at the faying
deformation at the faying
surfaces
• Low‐carbon steels (most
commonly forge‐welded
metal), high‐carbon steel
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Pressure Welding Forge welding
Schematic of
typical joint
designs for (a)
manual and (b)
automated forge
welding
ldi
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Pressure WeldingRoll Welding
• Pressure applied by rollers  Performed hot or cold
li d b ll f dh ld
• Applications  cladding stainless steel to mild or low alloy steel
for corrosion resistance
• Making bimetallic strips
• Producing ‘‘sandwich’’ coins for the U.S. mint
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Pressure WeldingExplosion welding
• Coalescence of two metallic surfaces is caused by the
energy of a detonated explosive
energy of a detonated explosive
• Commonly used to bond two dissimilar metals
• E.g.  To clad one metal on top of a base metal over
large areas
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Pressure WeldingExplosion welding:
Applications
• Applications include production of corrosion‐
resistant sheet and making processing equipment
it t h t d ki i i t
in the chemical and petroleum industries
• E.g. Commercially pure titanium clad to mild steel
• Often performed under water to enhance the
shock wave to move and deform material
shock wave to move and deform material
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Compatible
materials for
Explosion
welding
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2.1 Friction welding (FRW)
• Solid state welding  Coalescence is achieved by
frictional heat combined with pressure
frictional heat combined with pressure
• Friction is induced by mechanical rubbing
between two surfaces  usually by rotation of
one part relative to the other  raises the
temperature at the joint interface to the hot
working range  Parts are driven toward each
working range  Parts are driven toward each
other with sufficient force to form a metallurgical
bond
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2.1 Friction welding (FRW)
Mechanical Rubbing FRICTION HEAT
+ MICROSCOPIC
DEFORMATION
PRESSURE
No melting occurs at the faying surfaces COALESCENCE
No filler metal, flux, or shielding gases
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2.1 Friction welding (FRW)
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Drive parameter characteristics in FRW
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2.2 Friction stir welding (FSW),
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FSW Tool
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2.2 Friction stir welding (FSW),
• A rotating tool is fed along the joint
p
line between two work pieces 
Generates friction heat
• Mechanically stirring of the metal to
form the weld seam
• The process derives its name from
this stirring or mixing action
• FSW is distinguished from
FSW is distinguished from
conventional FRW  Friction heat is
generated by a separate wear‐
resistant tool rather than by the
parts themselves
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2.2 Friction stir welding (FSW),
• The rotating tool is stepped,
consisting of a cylindrical shoulder
consisting of a cylindrical shoulder
and a smaller probe projecting
beneath it
• The probe has a geometry
designed to facilitate the mixing
action
• Th h ld
The shoulder serves to constrain
i
the plasticized metal flowing
around the probe
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2.2 Friction stir welding (FSW),
• During welding, the shoulder rubs
against the top surfaces of the two
parts, developing much of the friction
heat
• While the probe generates additional
heat by mechanically mixing the metal
along the butt surfaces
• The heat produced by the combination
of friction and mixing does not melt the
metal but softens it to a highly plastic
condition
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Heat generated in FSW
(Refer Class notes)
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2.2 Friction stir welding (FSW),
• Typical applications  butt joints on large aluminium parts
• Other metals, include steel, copper, and titanium, as well as
polymers and composites
l d i
• Advantages of FSW
– Good mechanical properties of the weld joint,
– Avoidance of toxic fumes, warping, shielding issues, and other
problems associated with arc welding,
– Little distortion or shrinkage
– Good weld appearance
• Disadvantages include
– An exit hole is produced when the tool is withdrawn from the work,
and
– Heavy‐duty clamping of the parts is required
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Key benefits of friction stir welding
Metallurgical benefits Environmental Energy benefits
benefits
1. Solid phase process 1. No shielding gas 1. Improved materials
2. Low di t ti of work
2 L distortion f k required use (e g joining
(e.g.,
piece 2. No surface cleaning different thickness)
3. Good dimensional required allows reduction in
stability and 3. Eliminate grinding weight
repeatability wastes 2. Only 2.5% of the
4. No loss of alloying 4. Eliminate solvents energy needed for a
elements required for laser weld
5.
5 Excellent metallurgical degreasing 3. Decreased fuel
properties in the joint 5. Consumable consumption in light
area materials saving, weight aircraft,
such as rugs, wire automotive and ship
6. Fine microstructure applications
7. Absence of cracking or any other gases
8. Replace multiple parts
joined by fasteners
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2.3 Ultrasonic welding (USW)
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2.3 Ultrasonic welding (USW)
• Two components are held together under
modest clamping force
d t l i f
• Oscillatory shear stresses of ultrasonic
frequency are applied to the interface to
cause coalescence
• Oscillatory motion between the two parts
Oscillatory motion between the two parts
breaks down any surface films  allows
intimate contact and strong metallurgical
bonding between the surfaces
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2.3 Ultrasonic welding (USW)
• Although heating of the contacting surfaces occurs due to
interfacial rubbing and plastic deformation, the resulting
temperatures are well below the melting point
temperatures are well below the melting point
• No filler metals, fluxes, or shielding gases are required in
USW.
• The oscillatory motion is transmitted to the upper work
part by means of a sonotrode, which is coupled to an
ultrasonic transducer. This device converts electrical power
ultrasonic transducer. This device converts electrical power
into high‐frequency vibratory motion. Typical frequencies
used in USW are 15 to 75 kHz, with amplitudes of 0.018 to
0.13mm
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2.3 Ultrasonic welding (USW)
• Clamping pressures are well below those used in
cold welding and produce no significant plastic
ld ldi d d i ifi t l ti
deformation between the surfaces.
• Welding times under these conditions are less
than 1 sec.
• USW operations are generally limited to lap joints
USW operations are generally limited to lap joints
on soft materials such as aluminum and copper.
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3. Diffusion welding (DFW)
• Welding process results from the application of heat and
p
pressure, usually in a controlled atmosphere, with
y p
sufficient time allowed for diffusion and coalescence to
occur
• Temperatures are well below the melting points of the
metals (about 0.5 Tm)
• Plastic deformation at the surfaces is minimal
• The primary mechanism of coalescence is solid state
diffusion, which involves migration of atoms across the
interface between contacting surfaces
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3. Diffusion welding (DFW)
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3. Diffusion welding (DFW)
• Applications of DFW include the joining of high‐strength
and refractory metals in the aerospace and nuclear
industries.
industries
• The process is used to join both similar and dissimilar
metals, and in the latter case a filler layer of a different
metal is often sandwiched between the two base metals
to promote diffusion.
• The time for diffusion to occur between the faying
The time for diffusion to occur between the faying
surfaces can be significant, requiring more than an hour
in some applications
• Key parameters of the process‐ temperature, time, and
pressure 65
3. Diffusion welding (DFW)
• Diffusion occurs by an Arrhenius relationship, that is, exponentially
with temperature:
• Where,
– D is diffusion coefficient (of the diffusing species) at temperature T,
– Do is a constant of proportionality (dependent on the particular diffusing species and
host),
– Q is the activation energy for diffusion to occur,
– k is Boltzmann’s constant, and
– T is the temperature on an absolute scale
T is the temperature on an absolute scale
• In general, diffusion welding begins to take place at a reasonable
rate when the temperature exceeds half the absolute melting point
of the base or host material(s), and, as a rule‐of‐thumb, the rate of
diffusion doubles every time the temperature is raised
approximately 30°C 66
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3. Diffusion welding (DFW)
• Time is important because diffusion takes time to
occur, since for atoms to jump from site to site takes
occur, since for atoms to jump from site to site takes
time. Thus, the distance over which diffusion occurs
depends on time:
• Where
– x is the diffusion distance
x is the diffusion distance,
– D is the diffusion coefficient (as above),
– t is time, and C is a constant for the system.
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3. Diffusion welding (DFW)‐
Features
1. Metals as well as ceramics can be joined directly to form a
completely solid state weld
2. Filler can be used to permit increased micro deformation to
ll b f
provide more contact for bond formation and/or promote more
rapid diffusion by providing a faster diffusing species
3. Dissimilar materials either by class or type, including metal‐to‐
ceramic joints, can be joined directly or with the aid of a
compatible filler or intermediate
4. Large areas can be bonded or welded, provided uniform
intimate contact can be obtained and sustained
5. No heat‐affected zone as such, since the entire assembly in
which the diffusion weld is being made is virtually always heated
to the same temperature.
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