Ultrasonic welding, diffusion bonding, and explosive welding are solid state joining processes. Ultrasonic welding uses high-frequency vibrations to create heat and join thermoplastics. Diffusion bonding joins metals by applying high pressure and temperature to allow atomic diffusion across the interface. Explosive welding bonds metals through high velocity impact using explosives, creating strong metallurgical bonds between the faying surfaces.

1. ULTRASONIC WELDING
DIFFUSION BONDING
EXPLOSIVE WELDING

2. ULTRASONIC WELDING

3. Definition
Ultrasonic plastic welding is the joining or reforming
of thermoplastics through the use of heat generated
from high-frequency mechanical motion.
It is accomplished by converting high-frequency
electrical energy into high-frequency mechanical
motion.
That mechanical motion, along with applied force,
creates frictional heat at the plastic components
mating surfaces (joint area) so the plastic material will
melt and form a molecular bond between the parts.

5. Ultrasonic Welding Process

6. SystemComponents and Functions
The basic ultrasonic assembly system consists mainly
of four major components:
• Generator (Power supply)
• Transducer (Converter)
• Booster
• Horn (Acoustic tool)

8. o The generator changes standard electrical power
(120 – 240 volts, 50/60 Hz) into electrical energy at
the frequency at which the system is designed to
operate.
o Although several different operating frequencies
are in use throughout the world, the most common
frequencies used in manufacturing production are
15, 20, 30 and 40 kilohertz (kHz).
o The high frequency electrical energy produced by
the generator is sent through a cable to the
transducer, which changes the electrical energy into
vertical, low amplitude mechanical motion, or
vibrations.
o These vibrations are then transmitted to a booster,
which is used to increase or decrease the amplitude
of the vibrations.

9. The ratio of output amplitude to input amplitude of a
booster or horn is called gain.
A 2:1 booster attached to a transducer doubles the
amplitude of the vibrations leaving the workface of the
booster.
A 3:1 booster triples the amplitude of the vibrations.
A 0.5:1 booster decreases the amplitude of the
vibrations by one-half.

10. Ultrasonic Horns
The design of the horn is determined by the amplitude
required, the type of welding process and the material
selected. We design each horn to specific application
requirements.

11. Types of US welding
• Spot Welding
• Line Welding
- Linear Sonotrode
• Continuous Seam Welding
- Roller Sonotrode

12. .
Types of Ultrasonic Welding

13. Sonotrode Tip and Anvil Material
High Speed Tool Steels used to weld
• Soft Materials
• Aluminum
• Copper
• Iron
• Low Carbon Steel
Hardenable Nickel-Base Alloys used to weld
• Hard, High Strength Metals and Alloys

15. Welding Variables
Clamping force should be sufficient merely to provide
intimate contact between the welding tip and the work
piece.
Power requirements are generally higher for harder and
lower for softer in thinner materials.
Time required to weld varies with amount of power,
material properties and thickness of one of the pieces
being welded. A fine wire may be welded ultrasonically
in 0.005 sec, a heavy section may be require 1 sec.

16. Ultrasonic Welding Methods
Longitudinal method:
oThis is the most common ultrasonic
method for welding plastic components.
Generally the entire welding system is
arranged vertically.
oThe vibrations are applied vertically to
the connecting pieces; the welding
pressure is produced by a cylinder that
pushes the entire system along the
welding axis towards the upper
connecting piece.

17. Torsional method:
Here the system is also generally arranged
vertically, but this time the process is entirely
different. This method is a type of high-
frequency friction welding.
The vibrations are applied tangentially:
the horn moves the upper connecting piece
horizontally in relation to the lower
connecting piece. The friction produces a melt
between the two connecting pieces thanks to
the high vibration frequency (20 KHz),
amplitude and pressure.
Because of the tangential motion of the
upper connecting piece, the lower
connecting piece is placed under virtually no
strain by the ultrasound.
This method is therefore particularly suitable
for applications where additional vibrations in
the direct vicinity of the ultrasonic weld are
undesirable due to a risk of damage, e.g.
sensitive parts, foils, fabrics and thin die-cast
components electronics.

18. Advantages of Ultrasonic Welding
Dissimilar metals can be joined
Very low deformation of the work pieces
surfaces
High quality weld is obtained
The process may be integrated into
automated production lines
Moderate operator skill level is enough

19. Disadvantages of Ultrasonic Welding
Only small and
thin parts can
be welded
Work pieces
may bond to
the anvil

20. Application of Ultrasonic Welding
 Computer and electrical industries delicate
circuits, Junctions of wire harnesses, flash drives
and computer disks, Semiconductor devices
 Aerospace and automotive industries instrument
panels, door panels, lamps, air ducts, steering
wheels, and engine components
 Medical industry

21. Diffusion bonding

22. oDiffusion bonding is a solid-state welding technique,
wherein coalescence of the faying surfaces is
produced by the application of pressure and
temperature to carefully cleaned and mated metal
surfaces so that they actually grow together by
atomic diffusion.
oThe process does not involve macroscopic
deformation or relative motion of the parts. The
process can join either like or dissimilar metals with
or without the use of another material between.

23. Theory of diffusion Welding
Diffusion welding process involves two steps:
 Any surface to be diffusion welded is never
extremely smooth. It has a number of peak points
and valleys. Moreover, this surface may have,
(i) An oxidized layer,
(ii) Oil, grease, dirt etc.,
(iii) Absorbed gas, moisture.

24. The first stage is to achieve intimate metal to metal
contact between the two pieces to be diffusion welded.
This is done by the application of pressure that
deforms the substrate roughness and disrupts and
disperses the above mentioned surface layers and
contaminants.
The pressure applied in diffusion welded ranges from
350 to 700 kg/cm2.
The second stage involves diffusion and grain growth
to complete the weld and ultimately eliminate the
interface formed in the previous stage. The second
stage induces complete metallic bonding across the
area of contact.
In order to increase diffusion rate, moderate heating
temperatures are used.

25. Schematic representation of diffusion bonding using
electrical resistance for heating

26. Diffusion Bonding Process
a
b
c
d
e
a) Initial 'point' contact
b) Yielding and creep leading to
reduced voids
c) Final yielding and creep (some
voids left)
d) Continued vacancy diffusion,
leaving few small voids
e) Bonding is complete

27. Diffusion Bonded Methods
1. Gas pressure boding
2. Vacuum fusion bonding
3. Eutectic bonding
Gas pressure boding:
Parts to be joined are placed together in intimate
contact and then heated to around 815 0C. During
heating, an inert gas pressure is built up over all the
surfaces of the parts to be welded.
Non ferrous metals are joined with the help of gas
pressure bonding method.

28. Vacuum fusion bonding:
Parts to be joined are pressed together
mechanically or hydraulically. A hydraulic press used
for diffusion welding resembles that employed in
forging and is equipped to pressurize from three
directions.
Heating is carried out the same way as in gas
pressure bonding.
Process is carried out in vacuum chamber.
Since, pressure higher than those in gas pressure
bonding can be applied in this process, vacuum
fusion boding is used for steel and its alloys.
For diffusion bonding of steel, the temperature and
pressure required are approximately 1150 0C and 700
kg/cm2 respectively.

29. Eutectic fusion bonding:
It is a low temperature diffusion welding process.
A thin plate of some other material is kept between
the pieces to be joined.
As the pieces are heated to a elevated temperature,
the filler material diffuses and forms an eutectic
compound with the parent metals.

31. Diffusion bonding parameters
Main diffusion bonding parameters are
1. Pressure
2. Temperature
3. Time
Others parameters are
4. Surface preparation
5. Metallurgical factors
6. Use of interlayer

32. Pressure:
•It assures consistency of bond formation.
•The initial deformation phase of bond formation is
directly affected by the intensity of pressure applied.
•For any given time temperature value, increased
pressure invariably results in better joints.
•However, increased pressures require costlier
equipment.

33. Temperature:
oIt serves the important function of increasing the surface
energy.
oTemperature affects
(i) Plasticity
(ii) Diffusivity
(iii) Oxide solubility
(iv) Allotropic transformation
(v) Recrystallization
oTemperature must be controlled to promote or avoid these
factors as desired.
oGenerally, increasing temperature shortens diffusion
welding cycle and improves the economics of the process.
oDiffusion welding temperature usually ranges from 0.55 to
0.8 Tm.

34. Time:
Time is a dependent process parameter.
An increase in temperature shortens the time
required to complete the diffusion welding.
Time required for diffusion welding varies from a few
minutes to several hours.

35. Surface preparation:
Better prepared and cleaned surfaces lower the
minute the minimum diffusion welding temperature or
pressure.
Surface to be diffusion bonded are
(i) Machined, ground or abraded so that they are
sufficiently smooth to ensure that the interfaces
can be passed to proper contact without
excessive deformation.
(ii) Cleaned of chemically combined films, oxides
etc.
(iii) Cleaned of gaseous, aqueous or organic
surface films.

36. Metallurgical factors:
1. Allotropic transformation:
Hardenable steels undergo allotropic
transformation and involve volume change during
diffusion welding. This may affect dimensional
stability of the welded component.
2. Recrystallization:
Many cold worked metals tend to recrystallize
during diffusion welding. This may be good for
certain materials but undesirable for others, e.g.,
refractory metals.
3. Surface oxides:
Beryllium, aluminium, chromium, etc., form
tenacious surface oxides. They and alloys
containing them are, therefore, more difficult to
weld than those which form less stable oxide films
such as copper, nickel etc.

37. Use of interlayers:
An interlayer is a lower strength intermediate or one
containing a diffusive element. An interlayer solves
alloying compatibility problems when joining
dissimilar metals. Also, it being soft, confines
deformation to itself and thus minimizes distortion of
work pieces when pressed to contact.
Interlayers may, however, give rise to decreased
strength or stability.
The most common interlayer materials used at this
time are titanium, nickel and silver.

38. Materials diffusion bonded
Many similar and dissimilar metals have been joined
by diffusion welding, but most applications of this
process have been with
Titanium alloys,
Zirconium Alloys and
Nickel base alloys.

39. Advantages of diffusion bonding
a) Welded having essentially the same physical,
chemical and mechanical properties as the base
metal can be produced.
b) Heat treating operations can be incorporated
during the bonding cycle.
c) Continuous, leak tight welds can be formed.
d) The process is well suited for welding dissimilar
metals and ceramics.
e) Numerous welds can be made simultaneously.
f) Weldability is largely independent of material
thickness.

40. Limitations of diffusion bonding
i. A major difficulty is the removal of oxide and the
contaminating layers present on practically all
metals exposed to natural or industrial
environment.
ii. Opposing surfaces must be mated in size to within
a few angstroms of each other in order to achieve
a satisfactory metal bond.
iii. Diffusion welding requires a relatively long, time
consuming thermal cycle.
iv. With dissimilar materials, difficulties due to time /
temperature / pressure requirements are
frequently encountered.
v. Diffusion welding is not classified as a mass
production process.

41. Application of Diffusion bonding
1. Fabrication of reactor components in atomic
energy industries.
2. Fabrication of honeycomb, rocket engines,
helicopter rotor hub, turbine components, etc., in
aerospace missile and rocketry industries.
3. Two controversial aerospace vehicles have brought
diffusion bonding into the light e.g., B-1 bomber
and space shuttle.
4. Fabrication of composite materials.

42. Explosive Welding

43. Explosive welding
Definition:
In this process a piece of metal is made to strike
another piece under a heavy impact force and a weld
between them is achieved.

44. Principle of concept
 Cladder metal can be placed parallel or inclined to the
base plate.
 Explosive material is distributed over top of cladder
metal.
 Upon detonation, cladder plate collides with base plate
to form weld.
 Waves are generated so due to mechanical bonding
joining takes place.
 A single detonation cap can be used to ignite the
explosive.

45. Welding Equipment
 Base component
• Joined to cladder
• Remains stationary
• Supported by anvil
 Cladding metal
• Thin plate in direct contact with explosives
• Can be shielded by flyer plate

46.  Flyer plate
• Sacrificial plate placed between explosive material
and cladder plate
• Used to protect cladder metal
 Interlayer
• Thin metal layer
• Enhances joining of cladder to base plate
 Anvil
• Surface of which the backer rests during explosion

47.  Standoff Distance
• Distance between cladder and base plate before
explosion
 Bond Window
• A range of variable in process such as velocity,
dynamic bend and standoff distance that result in
successful weld
 Bonding Operation
• Detonation of explosives that result in a weld

48. Placement of Cladder metal - parallel

49. Cladder placement - Angled
Where
VC = Collision velocity
VD = Detonation velocity
VP = Plate Collision velocity
α = Angle of incidence
β = Dynamic bend angle
γ = Collision angle
Vc
VD
Vp

50. Salient Features
 The high velocities are promoted by carefully detonated
explosives.
 The process can be done in vacuum to reduce sound &
blast.
 Typical impact pressure are millions of psi.
 Well suited to metals that are prone to brittle joints
when heat welded such as,
• Al on steel
• Ti on steel

51.  This process does not work well for,
• Brittle metals with < 5% tensile elongation
• Charpy V - notch value < 10 ft.lb
 Important factors are critical Velocity, stand off
distance & critical angle.
 If two materials can be brought close enough together,
they will bond at a molecular level.
 High velocity explosives require smaller gaps between
plates and buffers such as rubber and Plexiglas are
used.

52. Explosive material
 High velocity (4572 - 7620 m/s)
• Trinitrotoluene (TNT)
• Cyclotrimethylenetrinitramine (RDX)
• Pentaerythritol Tetra nitrate (PETN)
• Datasheet
• Primacord
 Mid - low velocity (1524 - 4572 m/s)
• Ammonium nitrate
• Ammonium per chlorate
• Amatol
• Nitroguonidine
• Dynamites
• Diluted PETN

53. Assuring a good weld
Three types of detonation wave welds
 If sonic velocity of the explosive is greater than 120%
of the material with higher sonic velocity, a shock
wave develops (type 1)
 Detached shock wave results when detonation
velocity is between 100% and 120% of material sonic
velocity (type 2)
 No shock wave is produced if detonation velocity is
less than material sonic velocity (type 3)

54. Type 1
 Material behind shock wave is
compressed to peak pressure and
density.
 Creates significant plastic deformation
locally and results in considerable
hardening known as ‘shock hardening’.
Type 2 & 3
 Pressure is generated ahead of collision
point of metals.
 When subject to large pressures, metal
ahead of collision point flows into spaces
between plates and takes form of high -
velocity jet.
 Effaces material and removes unwanted
oxides and other unwanted surface films.
 No bulk diffusion and only localized
melting.

55. Sonic velocity of cladding material can calculated
using:
Where:
K = Adiabatic bulk modulus
ρ = Cladding material density
E = Young’s Modulus of cladding material
‫ע‬ = Poisson’s ratio of cladding material

56. Advantages of Explosion Welding
• Very large work pieces can be welded.
• (Al + Steel) materials can be welded.
• Can bond many dissimilar, normally unweldable
metals.
• Material melting temperatures and coefficients of
thermal expansion differences do not affect the final
product.
• Process is compact, portable and easy to maintain.

57. • Welding can be achieved quickly over large areas.
• No need for surface penetration.
• Backer plate has no size limits.
• The strength of the weld joint is equal to or greater than
the strength of the weaker of two metals joined.
• No heat - affected zone (HAZ).

58. Disadvantages of Explosion Welding
Brittle materials (low ductility and
low impact toughness) cannot be
processed.
Thickness of flyer plate is limited
Safety and security aspects of storage and
using explosives.

59. Application of Explosion Welding
oA number of dissimilar metal combinations have
been joined successfully with the help of explosive
welding.
e.g.
Aluminium to steel
Tungsten to steel
Copper to stainless steel
oStrong metallurgical bonds can now be produced
between metal combinations which cannot be welded
by other processes.

60. Pipes and tubes up to 1.5 meter length have been clad
with this process.
Major areas of use of explosively clad products are
heat exchanger tube sheets and pressure vessels.
Explosive cladding is finding use in the die casting
industry for nozzles, die cast biscuits and other
components.
Explosive welding has been used for plugging of
nuclear heat exchanger.
Metal / metal wire composite materials have been
fabricated using explosives.
Chemical process vessels, transition joints, electrical
industry, ship building industry, cryogenic applications.

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