Lec 11 solid state welding

1. ACE 305- Dr Mohamed Elfarran

2. Solid-State Welding Processes
Solid-State Welding Processes is an important family of
joining processes in which the work pieces do not undergo a
phase change and no filler metal is used; if heat is used, it is not
externally applied, but instead is generated internally-for
example, with friction.
in solid-state welding no liquid or molten phase is present
in the joint. The principle of solid-state welding is demonstrated
best with the following example: If two clean surfaces are
brought into close contact with each other under sufficient
pressure, they form bonds and produce a joint
To form a strong bond, it is essential that the interface be
free of oxide films, residues, metalworking fluids, other
contaminants, and even adsorbed layers of gas.
Solid-state bonding involves one or more of the following phenomena:
1.Diffusion (friction welding) 2. Pressure(roll bonding) 3. Relative
interfacial movements(ultrasonic welding)
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ACE 305- Dr Mohamed Elfarran

3. Schematic illustration of the roll
bonding, or cladding, process.
In cold welding (CW), pressure is applied to the workpieces through
dies or rolls. Because of the plastic deformation involved, it is necessary
that at least one (but preferably both) of the mating parts be ductile.
Cold Welding and Roll Bonding
Cold welding can be used to join small workpieces made of soft, ductile
metals. Applications include wire stock and electrical connections.
Roll Bonding. The pressure
required for welding can be
applied through a pair of rolls ;
this process is called roll
bonding or roll welding (ROW).
Developed in the 1960s, roll
bonding is used for
manufacturing some U.S. coins.
The process can be carried out
at elevated temperatures (hot
roll bonding). Surface
preparation is important for
interfacial strength.
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ACE 305- Dr Mohamed Elfarran

4. (a) Components of an ultrasonic-welding machine for making lap welds. The lateral
vibrations of the tool tip cause plastic deformation and bonding at the interface of the
workpieces. (b) Ultrasonic seam welding using a roller as the sonotrode.
Ultrasonic Welding
In ultrasonic welding (USW), the faying surfaces of the two
components are subjected to a static normal force and oscillating
shearing (tangential) stresses.
The shearing stresses are applied by the tip of a transducer, which is similar
to that used for ultrasonic machining.
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ACE 305- Dr Mohamed Elfarran

5. Ultrasonic Welding
The frequency of oscillation is generally in the range from 10 to 75
kHz, although a lower or higher frequency can be employed.
Proper coupling between the transducer and the tip (called-by
analogy with electrode-a sonotrode, from the word sonic) is
important for efficient operation
The shearing stresses cause plastic deformation at the interface of
the two components, breaking up oxide films and contaminants and
thus allowing good contact and producing a strong solid-state bond.
The temperature generated in the weld zone is usually in the range
from one-third to one-half of the melting point (absolute scale) of the
metals joined. Consequently, neither melting nor fusion takes place.
In certain situations, however, the temperature generated can be
sufficiently high to cause metallurgical changes in the weld zone.
Also, the mechanism responsible for the joining of thermoplastics by
ultrasonic welding is different from that for metals, and melting
does take place at the interface, because plastics have much lower
melting temperatures.
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ACE 305- Dr Mohamed Elfarran

6. Friction Welding
In friction welding (FRW), the heat required for welding is
generated through (as the name implies) friction at the interface of
the two components being joined. You
In friction welding, developed in the 1940s, one of the workpiece
components remains stationary while the other is placed in a chuck
or collets and rotated at a high constant speed.
The two members to be joined are then brought into contact under
an axial force . The surface speed of the rotating parts may be as
high as 900 m/min.
After sufficient contact is established, the rotating member is
brought to a quick stop (so that the weld is not destroyed by
shearing) while the axial force is increased. Oxides and other
contaminants at the interface are removed by the radically
outward movement of the hot metal at the interface.
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ACE 305- Dr Mohamed Elfarran

7. Sequence of operations in the friction-welding process: (1) The part on the left is
rotated at high speed; (2) The part on the right is brought into contact with the part
on the left under an axial force; (3) The axial force is increased, and the part on the
left stops rotating; flash begins to form; (4) After a specified upset length or
distance is achieved, the weld is completed. The upset length is the distance the
two pieces move inward during welding after their initial contact; thus, the total
length after welding is less than the sum of the lengths of the two pieces. The flash
subsequently can be removed by machining or grinding.
Friction Welding
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ACE 305- Dr Mohamed Elfarran

8. Shape of the fusion zones in
friction welding as a function of
the axial force applied and the
rotational speed.
The shape of the welded joint depends
on the rotational speed and on the axial
pressure applied . These factors must be
controlled to obtain a uniform strong joint.
Friction Welding
The radially outward movement of the
hot metal at the interface pushes
oxides and other contaminants out of
the interface.
Solid steel bars up to 100 mm in
diameter and pipes up to 250 mm in
outside diameter have been friction
welded successfully.
The surface speed of the rotating
member may be as high as 15 m/s.
Because of the combined heat and
pressure, the interface in frictional
welding develops a flash by plastic
deformation (upsetting) of the heated
zone. This flash (if objectionable) can
easily be removed by machining or
grinding. 8
ACE 305- Dr Mohamed Elfarran

9. The principle of the friction-stir-welding process.
Aluminum-alloy plates up to 75 mm (3 in.) thick
have been welded by this process.
Friction Stir Welding.
In conventional friction welding, heating of an interface is achieved
through friction by rubbing two contacting surfaces. In the friction
stir-welding (FSW) process, developed in 1991, a third body is rubbed
against the two surfaces to be joined.
A rotating non consumable probe, typically 5 to 6 mm in diameter and 5 mm
high, is plunged into the joint
The contact pressure
causes frictional
heating, raising the
temperature to
between 2300 and
260°C.
The probe at
the tip of the
rotating tool
forces mixing
(or stirring) of
the material in
the joint.
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ACE 305- Dr Mohamed Elfarran

10. Friction Stir Welding
Materials such as aluminum, copper, steel, and titanium have been
welded successfully, and developments are taking place to extend
FSW applications to polymers and composite materials. The process
is now being applied to aerospace, automotive, shipbuilding, and
military vehicles, using sheet or plates.
The thickness of the welded material can be as little as 1 mm and
as much as 50 mm welded in a single pass. Welds produced by
friction stir welding have high quality, minimal pores, and a uniform
material structure.
The welds are produced with low heat input and therefore low
distortion and little microstructural changes. No shielding gas or
surface cleaning is required.
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ACE 305- Dr Mohamed Elfarran

11. Resistance Welding
The category of resistance welding (RW) covers a number of
processes in which the heat required for welding is produced by
means of electrical resistance across the two components to be
joined.
These processes have major advantages, such as not requiring
consumable electrodes, shielding gases, or flux.
The heat generated in resistance welding is given by the general
expression
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ACE 305- Dr Mohamed Elfarran

12. Equation is often modified so that it represents the actual heat
energy available in the weld by including a factor K, which denotes
the energy losses through conduction and radiation. The equation
then becomes
Resistance Welding
The total resistance is the sum of the following properties
The actual temperature rise at the joint depends on the specific heat
and the thermal conductivity of the metals to be joined.
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ACE 305- Dr Mohamed Elfarran

13. Similar or dissimilar metals can be joined by resistance welding. The
magnitude of the current in resistance-welding operations may be as
high as 100,000 A, but the voltage is typically only 0.5 to 10 V.
Resistance Welding
The strength of the bond depends on surface roughness and on the
cleanliness of the mating surfaces. Oil films, paint, and thick oxide
layers should therefore be removed before welding. The presence of
uniform, thin layers of oxide and of other contaminants is not as
critical.
Resistance Spot Welding
In resistance spot welding (RSW), the tips of two opposing solid,
cylindrical electrodes touch a lap joint of two sheet metals, and
resistance heating produces a spot weld
In order to obtain a strong bond in the weld nugget, pressure is
applied until the current is turned off and the weld has solidified.
Accurate control and timing of the alternating electric current and of the
pressure are essential in resistance welding.
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ACE 305- Dr Mohamed Elfarran

14. (a) Sequence of events in resistance spot welding. (b) Cross section of a
spot weld, showing the weld nugget and the indentation of the electrode on
the sheet surfaces. This is one of the most commonly used processes in
sheet-metal fabrication and in automotive body assembly.
Resistance Spot Welding
The weld nugget is
generally 6 to 10 mm
in diameter. The
surface of the spot
weld has a slightly
discolored
indentation. Currents
range from 3000 to
40,000 A.
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ACE 305- Dr Mohamed Elfarran

15. Two electrode designs for easy access
to the components to be welded.
The current level depends on the materials
being welded and on their thicknesses. For
example, the current is typically 10,000 A for
steels and 13,000 A for aluminum. Electrodes
generally are made of copper alloys and must
have sufficient electrical conductivity and hot
strength to maintain their shape.
Resistance Spot Welding
Spot welding is the simplest and most
commonly used resistance-welding
process.
Welding may be performed by means of
single (most common) or multiple pairs of
electrodes (as many as a hundred or more),
and the required pressure is supplied through
mechanical or pneumatic means.
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ACE 305- Dr Mohamed Elfarran

16. Spot-welded (a) cookware and (b) muffler. (c) An
automated spot-welding machine. The welding tip can
move in three principal directions. Sheets as large as
2.2  0.55 m (88  22 in.) can be accommodated in this
machine with proper workpiece supports. Source:
Courtesy of Taylor–Winfield Corporation.
Spot welding is used
widely for fabricating sheet-
metal parts. Examples
range from attaching
handles to stainless-steel
cookware to spot-welding
mufflers and large sheet-
metal structures and large
sheet-metal structures
Modern spot-welding
equipment is computer
controlled for optimum
timing of current and
pressure; its spot-
welding guns are
manipulated by
programmable robots
Automobile bodies
can have as many
as 10,000 spot
welds 16
ACE 305- Dr Mohamed Elfarran

17. Test methods for spot welds: (a) tension-
shear test, (b) cross-tension test, (c) twist test,
(d) peel test
Testing Spot Welds
Spot-welded joints may be tested for weld-nugget strength by
means of the following techniques
Because they are easy to
perform and are inexpensive,
tension-shear tests are
commonly used in fabricating
facilities. The cross-tension and
twist tests are capable of
revealing flaws, cracks, and
porosity in the weld area. The
peel test is commonly used for
thin sheets. After the joint has
been bent and peeled, the shape
and size of the torn-out weld
nugget are evaluated.
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ACE 305- Dr Mohamed Elfarran

18. The Monosteel® piston. (a) Cutaway view of the piston, showing the oil
gallery and friction-welded sections; (b) detail of the friction welds before
the external flash is removed by machining; note that this photo is a
reverse of the one on the left.
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ACE 305- Dr Mohamed Elfarran

19. The heat required to melt 1 g of steel is about 1400 J
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ACE 305- Dr Mohamed Elfarran

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ACE 305- Dr Mohamed Elfarran