This notes will be sufficient for the welding portion of primary manufacturing processes, ME 403 Mechanical engineering.

1. Notes For ME 403 Part-I
Students are suggested to refer to the class notes in addition to the following.
Q. Classification of welding processes
Welding processes
1. Fusion Welding
 Arc welding
o Shielded Metal Arc Welding (SMAW);
o Flux Cored Arc Welding (FCAW);
o Submerged Arc Welding (SAW);
o Metal Inert Gas Welding (MIG, GMAW);
o Tungsten Inert Gas Arc Welding (TIG, GTAW);
o Electroslag Welding (ESW);
o Plasma Arc Welding (PAW);
 Resistance Welding (RW);
o Spot Welding (RSW);
o Flash Welding (FW);
o Resistance Butt Welding (UW) ;
o Seam Welding (RSEW);
 Gas Welding (GW);
o Oxyacetylene Welding (OAW);
o Oxyhydrogen Welding (OHW);
o Pressure Gas Welding (PGW);
2. Solid State Welding (SSW);
 Forge Welding (FOW);
 Cold Welding (CW);
 Roll Welding (RW);
 Friction Welding (FRW);
 Explosive Welding (EXW);
 Diffusion Welding (DFW);
 Ultrasonic Welding (USW);
3. Special Welding Processes
 Thermit Welding (TW);
 Electron Beam Welding (EBW);
 Laser Welding (LW).
Oxy-fuel Gas Welding
Oxyfuel gas welding refers to a group of welding processes that use the flame produced by the
combustion of a fuel gas and oxygen as the source of heat.
There are three major processes within the OFW group:
1. oxyacetylene welding
2. oxyhydrogen welding,
3. pressure gas welding.

2. There is one process of minor OFW, Oxy Fuel welding industrial significance, known as air acetylene
welding, in which heat is obtained from the combustion of acetylene with air. Welding with
methylacetone-propadiene gas (MAPP gas) is also an oxy fuel procedure
(Oxyfuel gas welding )Acetylene is more widely than other gases. It produces a temperature of about
3250o
C in a two stage reaction.
In the first stage the supplied oxygen and acetylene react to produce carbon monoxide and hydrogen.
This reaction occurs near the tip of the torch and generates intense heat.
C2H2+O2 --------> 2CO +H2+ heat
In the second stage reaction involves the combustion of the CO and H2 and occurs just beyond the first
combustion zone.
2CH+O2 --------> 2CO2 + heat
H2+1/2O2 --------> H2O+ heat
The two stage combustion process produces a flame having two distinct regions. The maximum
temperature occurs near the end of the inner cone, where the first stage of combustion is complete. Most
welding should be performed with the torch positioned so that this point of maximum temperature is just
above the metal being welded. The outer envelope of the flame serves to preheat the metal and, at the
same time, provides shielding from oxidation, since oxygen from the surrounding air is consumed in the
secondary combustion.
Advantages of Oxy-Acetylene Welding :
 It's easy to learn.
 The equipment is cheaper than most other types of welding rigs (MIG/TIG welding)
 The equipment is more portable than most other types of welding rigs (MIG/TIG welding)
 Oxy/Acetylene equipment can also be used to "flame-cut" large pieces of material.
Disadvantages of Oxy-Acetylene Welding :
 Limited power density
 Very low welding speed
 Severe distortion
 Oxy/Acetylene weld lines are much rougher in appearance than other kinds of welds, and require
more finishing if neatness is required.
 Oxy/Acetylene welds have large heat affected zones (areas around the weld line that have had
their mechanical properties adversely affected by the welding process).
Materials Suitable for Oxy/Acetylene Welding:
 Mild Steel
 Brazing can be done on many other materials i.e. aluminum, stainless steel, copper, and brass

3. Q. Explain Various Types of flames in Oxy fuel gas welding.
Types of Flames:
1. When oxygen is turned on, flame immediately changes into a long white inner area (Feather)
surrounded by a transparent blue envelope is called Carburizing flame (30000
c)
2. If the ratio is between 1: l and 1.15.1, all reactions are carried to completion and a neutral flame
is produced. This mixture gives a bright whitish cone surrounded by the transparent blue envelope
is called Neutral flame (It has a balance of fuel gas and oxygen) (32000
c).It is used for welding
steels, aluminium, copper and cast iron
3. If more oxygen is added .i.e., higher ratio, such as 1,5:l, the cone becomes darker and more
pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame. Has the
highest temperature about 34000
c. It is used for welding brass and brazing operation

4. Q. Shielded Metal Arc Welding (SMAW)
SMAW is a welding process that uses a flux covered metal electrode to carry an electrical current. The
current forms an arc that jumps a gap from the end of the electrode to the work. The electric arc creates
enough heat to melt both the electrode and the base material(s). Molten metal from the electrode travels
across the arc to the molten pool of base metal where they mix together. As the arc moves away, the
mixture of molten metals solidifies and becomes one piece. The molten pool of metal is surrounded and
protected by a fume cloud and a covering of slag produced as the coating of the electrode burns or
vaporizes. Due to the appearance of the electrodes, SMAW is commonly known as ‘stick’ welding.
SMAW is used primarily because of its low cost, flexibility, portability and versatility. Both the
equipment and electrodes are low in cost and very simple. SMAW is very flexible in terms of the
material thicknesses that can be welded (materials from 1/16” thick to several inches thick can be welded
with the same machine and different settings). It is a very portable process because all that’s required is a

5. portable power supply (i.e. generator). Finally, it’s quite versatile because it can weld many different
types of metals, including cast iron, steel, nickel & aluminum.
Some of the biggest drawbacks to SMAW are (1) that it produces a lot of smoke & sparks, (2) there is a
lot of post-weld cleanup needed if the welded areas are to look presentable, (3) it is a fairly slow welding
process and (4) it requires a lot of operator skill to produce consistent quality welds.
Q. Flux cored arc welding (FCAW)
Flux cored arc welding (FCAW) is an arc welding process in which the heat for welding is produced by
an arc between a continuously fed tubular electrode wire and the work. Shielding is obtained by a flux
contained within the tubular electrode wire or by the flux and an externally supplied shielding gas.
Advantages
Flux cored arc welding has many advantages for a wide variety of applications.
It often competes with shielded metal arc welding, gas metal arc welding, and submerged arc welding
(SAW) for many applications. Some of the advantages of this process are:
1. It has a high deposition rate and faster travel speeds
2. Using small diameter electrode wires, welding can be done in all positions.
3. Some flux -cored wires do not need an external supply of shielding gas, which simplifies the
equipment.
4. The electrode wire is fed continuously so there is very little time spent on changing electrodes
5. Deposits a higher percentage of the filler metal when compared to shielded metal arc welding.
6. Obtains better penetration than shielded metal arc welding
Limitations
1. Melted contact tip – when the contact tip actually contacts the base metal, fusing the two and
melting the hole on the end
2. Irregular wire feed – typically a mechanical problem
3. Porosity – the gases (specifically those from the flux-core) don’t escape the welded area before
the metal hardens, leaving holes in the welded metal
4. More costly filler material/wire as compared to GMAW
5. The equipment is less mobile and more costly as compared to SMAW or GTAW.
6. The amount of smoke generated can far exceed that of SMAW, GMAW, or GTAW.
7. Changing filler metals requires changing an entire spool. This can be slow and difficult as
compared to changing filler metal for SMAW or GTAW.
8. Creates more fumes than SMAW
FCAW is sutable for following aloys:
 Mild and low alloy steels
 Stainless steels
 Some high nickel alloys
 Some wear facing/surfacing alloys

6. Gas Metal Arc Welding (GMAW)
Gas Metal Arc Welding (GMAW), by definition, is an arc welding process which produces the
coalescence of metals by heating them with an arc between a continuously fed filler metal electrode and
the work. The process uses shielding from an externally supplied gas to protect the molten weld pool.
The alloy material range for GMAW includes: carbon steel, stainless steel, aluminum, magnesium,
copper, nickel, silicon bronze and tubular metal-cored surfacing alloys.
Advantages of GMAW
The GMAW process enjoys widespread use because of its ability to provide high quality welds, for a
wide range of ferrous and non-ferrous alloys, at a low price. GMAW also has the following advantages:
• The ability to join a wide range of material types and thicknesses.
• Simple equipment components are readily available and affordable.
• GMAW has higher electrode efficiencies, usually between 93% and 98%, when compared to other
welding processes.
• Higher welder efficiencies and operator factor, when compared to other open arc welding processes.
• GMAW is easily adapted for high-speed robotic, hard automation and semiautomatic welding
applications.
• All-position welding capability.
• Excellent weld bead appearance.
• Lower hydrogen weld deposit — generally less than 5 mL/100 g of weld metal.
• Lower heat input when compared to other welding processes.
• A minimum of weld spatter and slag makes weld clean up fast and easy.
• Less welding fumes when compared to SMAW (Shielded Metal Arc Welding) and FCAW (Flux-Cored
Arc welding) processes
• Generally, lower cost per length of weld metal deposited when compared to other open arc welding
processes.
• Lower cost electrode.
• Handles poor fit-up with GMAW-S and STT modes.
• Reduced welding fume generation.

7. • Minimal post-weld cleanup.
Limitations of GMAW
• The lower heat input characteristic of the short-circuiting mode of metal transfer restricts its use to thin
materials.
• The higher heat input axial spray transfer generally restricts its use to thicker base materials.
• The higher heat input mode of axial spray is restricted to flat or horizontal welding positions.
• The use of argon based shielding gas for axial spray and pulsed spray transfer modes is more expensive
than 100% carbon dioxide (CO2).
GAS TUNGSTEN ARC WELDING GTAW
An arc is established between the end of a tungsten electrode and the parent metal at the joint line.
The electrode is not melted and the welder keeps the arc gap constant. The current is controlled by the
power-supply unit.
A filler metal, usually available in 1 m lengths of wire, can be added to the leading edge of the pool
as required. The molten pool is shielded by an inert gas which replaces the air in the arc area. Argon
and helium are the most commonly used shielding gases.
ADVANTAGES
 GTAW produces precise and clean, nearly spatter free welds on almost all metals with superior
quality in comparison to the other arc welding processes. It has found use in the aerospace, food
processing, and nuclear industries. It is particularly useful on smaller sectioned parts and on
reactive metals such as titanium.
 It can be used with filler metal or without filler metal (autogenous). This process allows the heat
source and filler metal additions to be controlled independently.
 It is easily automated and can produce welds in all positions, even with intricate geometries.
 Superior quality welds, generally free from spatter, porosity, or other defects

8.  Precise control of arc and fusion characteristics
 Weld almost all metals
 Used with or without filler wire
 Easily automated
 Used in all positions
 Intricate geometries weldable
DISADVANTAGES
 Deposition rates are lower with GTAW than any other arc welding process. In general, the
process is limited to thicknesses of 3/8-inch or less since productivity makes the process cost
prohibitive. Tungsten inclusions or contamination of the weld pool may occur if the electrode
touches the weld pool or proper gas
 Higher operator skill Required
 Sensitive to draft
 shielding is not maintained
 Manual GTAW requires more dexterity and welder coordination than with manual GMAW or
SMAW. As with the other gas shielded processes, drafts can blow away the shielding gas,
which limits the outdoor use of the process.
 Less economical than consumable electrode processes for sections thicker than 3/8 inch
 Lowest deposition rate of all arc processes
 Tungsten inclusions
SUBMERGED ARC WELDING (SAW)
Submerged Arc Welding (SAW) is a common arc welding process. Submerged Arc Welding is so named
because the weld zone and arc are submerged beneath a blanket of flux. When molten, the flux becomes
conductive and provides a current path between the electrode and the work. SAW is normally operated in
the automatic or mechanized mode, however, semi – automatic SAW guns with pressurized or gravity
flux feed delivery are available. Single or multiple electrode wire variations of the process exist. • DC or
AC power can be used, and combination of DC and AC are common on multiple electrode systems. •
Constant voltage welding power supplies are most commonly used. The flux, which is part of the
powder, acts as a thermal insulator, allowing deep penetration of heat into the workpiece. The
consumable electrode is a coil of bare round wire (1.5 − 10 mm diameter) and is fed automatically
through a tube (welding gun). Because the powder is fed by gravity, the SAW process is limited to weld

9. in a flat or horizontal position. Circular welds can be made on pipes, provided that they are rotated during
welding. The unfused powder can be recovered, treated, and refused.
ADVANTAGES:
 High deposition rates.
 Great intensities of heat can be generated and kept concentrated to weld thicker sections with
deep penetrations.
 The submerged process can be used for welding in exposed areas with relatively high winds.
 High heat concentration supports considerably higher welding speeds.
 Welding is carried out without sparks, smoke, flash or spatter.
 Practically no edge preparation is necessary.
 Low distortion
 Welds produced are sound, uniform, ductile, corrosion resistant, and have good impact value.
 Very neat appearance and smooth weld shapes can be obtained.
 50% to 90% of the flux is recoverable.
LIMITATIONS
 Limited to ferrous and some nickel based alloys.
 Normally limited to long straight seams or rotated pipes or vessels.
 Flux and slag residue can present a health and safety concern.
 Requires inter-pass and post weld slag removal.

10.  The flux needs replacing of the same on the joint which is not always possible.
 Flux is subjected to contamination that may cause weld porosity.
 Weld metal chemistry is difficult to control. A change in welding variables especially when
using alloyed fluxes may affect weld metal composition adversely.
 Cast iron, Aluminium alloys, Magnesium alloys, Lead and Zinc cannot be welded by this
process.
PLASMA ARC WELDING (PAW)
Plasma arc welding a type of arc welding process that produces coalescence of metals by heating them
with a constricted arc between an electrode and the work piece (transferred arc) or between the electrode
and the water-cooled constricting nozzle (non transferred arc). Plasma is a gaseous mixture of positive
ions, electrons and neutral gas molecules.
Process of heat production:
Gas is heated to an extremely high temperature and ionized so that it becomes electrically conductive.
PAW process uses this plasma to transfer an electric arc to the work piece. The metal to be welded is
melted by the intense heat of the arc and fuses together.
There are two methods in PAW
1. Transferred arc mode:
 Arc is struck between the electrode(-) and the work piece(+)
 Used for high speed welding and
 Used to weld Ceramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel
alloys.
2. Non-transferred mode:
 Arc is struck between the electrode(-) and the nozzle(+), thus eliminating the necessity to have
the work as a part of the electrical system.
 Arc process produces plasma of relatively low energy density.
 Since the work piece in non-transferred plasma arc welding is not a part of electric circuit, the
plasma arc torch may move from one work piece to other without extinguishing the arc.
ADVANTAGES:
 Permits faster metal deposition rate and high arc travel speed as compared to TIG

11.  Uniform penetration with high welding rate is possible
 Stability of arc and Excellent weld quality
 Can produce radiographic quality weld at high speed
 Can weld steel pieces up to about half inch thick, square butt joint
 Useful for semi automatic and automatic processes.
 Process is very fast and clean
 Requires less operator skill due to good tolerance of arc to misalignments;
 High penetrating capability (keyhole effect);
LIMITATIONS:
 Special protection is required as Infrared and UV Radiations is produced
 Consumption of Inert Gas is high
 Needs high power electrical equipment.
 Gives out ultraviolet and infrared radiation.
 Operation produces a high noise of the order of 100dB.
 Expensive equipment;
 Can weld only upto 25mm thickness.
 High distortions and wide welds as a result of high heat input (in transferred arc process).
 More chances of Electrical hazards.
RESISTANCE WELDING
Resistance welding is a thermo-electric process in which heat is generated at the interface of the parts to
be joined by passing an electrical current through the parts for a precisely controlled time and under a
controlled pressure (also called force). The name “resistance” welding derives from the fact that the
resistance of the workpieces and electrodes are used in Combination or contrast to generate the heat at
their interface. This is the same principle used in the operation of heating coils. In addition to the bulk
resistances, the contact resistances also play a major role. The contact resistances are influenced by the
surface condition (surface roughness,
cleanliness, oxidation, and platings). The general heat generation formula for resistance welding is:
Heat = I2
x R x t x K
Where
I = the weld current through the workpieces,
R= the electrical resistance (in ohms) of the workpieces,
T= the weld time (in hertz, milliseconds or microseconds), and
K= a thermal constant.
The weld current (I) and the duration of current (t) are controlled by the resistance welding power supply.
The resistance of the workpieces (R) is a function of the weld force and the materials used.
The thermal constant “K” can be affected by part geometry, fixturing and weld force.
The bulk and contact resistance values of the workpieces, electrodes, and their interfaces both cause and
affect the amount of heat generated
ADVANTAGES:
• Very short process time

12. • No consumables, such as brazing materials, solder, or welding rods
• Operator safety because of low voltage
• Clean and environmentally friendly
• A reliable electro-mechanical joint is formed
A. Resistance Spot Welding
(Method and principle are same as Resistance welding, refer to previous section)

13. (The picture is only for the purpose of better understanding, not necessarily important for wbut)
Applications of resistance spot welding
 Automobile industry
 Dental Prosthesis
 Batteries
 Nuts and Bolts
[ Explanation:
Spot welding is typically used when welding particular types of sheet metal, welded wire mesh or wire
mesh. Thicker stock is more difficult to spot weld because the heat flows into the surrounding metal more
easily. Spot welding can be easily identified on many sheet metal goods, such as metal buckets.
Aluminum alloys can be spot welded, but their much higher thermal conductivity and electrical
conductivity requires higher welding currents. This requires larger, more powerful, and more expensive
welding transformers.
The most common application of spot welding is in the automobile manufacturing industry, where it is
used almost universally to weld the sheet metal to form a car. Spot welders can also be completely
automated, and many of the industrial robots found on assembly lines are spot welders (the other major
use for robots being painting).
Spot welding is also used in the orthodontist's clinic, where small-scale spot welding equipment is used
when resizing metal "molar bands" used in orthodontics.
Another application is spot welding straps to nickel–cadmium or nickel–metal hydride cells to make
batteries. The cells are joined by spot welding thin nickel straps to the battery terminals. Spot welding
can keep the battery from getting too hot, as might happen if conventional soldering were done.

14. Good design practice must always allow for adequate accessibility. Connecting surfaces should be free of
contaminants such as scale, oil, and dirt, to ensure quality welds. Metal thickness is generally not a factor
in determining good welds.]
Advantages of resistance spot welding
 Quick and Easy
 No need of Flux and Filler metals
 Multiple sheets joined together at the same time
 No dangerous open flames
 Saves production cost
 Dimensional Accuracy
Limitations of resistance spot welding
 Difficulty for maintenance or repair
 Generally have higher cost than most arc welding equipment
 Low tensile and fatigue strength
 The full strength of the sheet cannot prevail across a spot welded joint
Resistance Seam Welding
RSEW is modification of spot welding wherein the electrodes are replaced by rotating wheels or
rollers. The electrically conducting rollers produce a spot weld. RSEW can produce a continuous
seam & joint that is liquid and air tight
Description and Operation: The two workpieces to be joined are cleaned to remove dirt, grease and
other oxides either chemically or mechanically to obtain a sound weld. The workpieces are
overlapped and placed firmly between two wheel shaped copper alloy electrodes, which in turn are
connected to a secondary circuit of a step-down transformer. The electrode wheels are driven
mechanically in opposite directions with the workpieces passing between them, while at the same
time the pressure on the joint is maintained. Welding current is passed in series of pulses at proper
intervals through the bearing of the roller electrode wheels • As the current passes through the
electrodes, to the workpiece, heat is generated in the air gap at the point of contact (spot) of the two
workpieces. This heat melts the workpieces locally at the contact point to form a spot weld. Pressure
is applied by air, spring or hydraulically. Under the pressure of continuously rotating electrodes and
the current flowing through them, a series of overlapping spot welds are made progressively along the
joint as shown in the figure. • The weld area is flooded with water to keep the electrode wheels cool
during welding.

15. Resistance Projection Welding RPW
One of the limitations of spot welding is difficulty in maintaining the geometry of the electrode
surface during large scale production. Due to repeated use, the tip of the electrodes erode and need
constant replacing.
Projection welding is a modification of spot welding. In this process, the weld is localized by means
of raised sections, or projections, on one or both of the workpieces to be joined. Heat is concentrated
at the projections, which permits the welding of heavier sections or the closer spacing of welds. The
projections can also serve as a means of positioning the workpieces. Projection welding is often used
to weld studs, nuts, and other screw machine parts to metal plate. It is also frequently used to join
crossed wires and bars. This is another high-production process, and multiple projection welds can be
arranged by suitable designing and jigging.
Advantages of Projection Welding:

16.  More than one spot weld can be made in a single operation, so the operation is very fast.
 Welding current and pressure required is less
 It helps in obtaining a satisfactory heat balance in welding of difficult to weld combinations of
metals and thickness.
 Closer spacing of welds is possible
 Electrodes can be shaped to act as assembly fixtures for mass welding of parts
 Uniform welds with good finish are produced.
 Suitable for automation
 Filler metals are not used. Hence clean weld joints are obtained
Disadvantages of projection welding:
 Projections cannot be made in thin work pieces.
 Thin work pieces cannot withstand the electrode pressure
 Additional operation is required after the welding process is over.
 Equipment is costlier
(more examples)
SOLID STATE WELDING (SSW)

17. Forge Welding FOW
Forge welding is a welding process in which components to be joined are heated to hot working
temperature range and then forged together by hammering or similar means. It has a historic
significance in development of manufacturing technology.This process dates from about 1000 B.C.,
when blacksmiths learned to weld two pieces of metal. At present date, it is of minor commercial
importance today except for its variants.
Cold Welding CW
Cold Welding is SSW process done by applying high pressure between clean contacting surfaces at
room temperature.
• Cleaning usually done by degreasing and wire brushing immediately before joining
• No heat is applied, but deformation raises work temperature
• At least one of the metals, preferably both, must be very ductile
• Soft aluminum and copper suited to CW
Applications: making electrical connections
Roll Welding ROW
Roll Welding is SSW process in which pressure sufficient to cause coalescence is applied by means
of rolls, either with or without external heat.
• Variation of either forge welding or cold welding, depending on whether heating of workparts is
done prior to process
• If no external heat, it is called cold roll welding
• If heat is supplied, it is called hot roll welding
Applications of Roll Welding
• Cladding stainless steel to mild or low alloy steel for corrosion resistance
• Bimetallic strips for measuring temperature
• "Sandwich" coins for U.S mint
Diffusion Welding DFW
DFW is a SSW process uses heat and pressure, usually in a controlled atmosphere, with sufficient
time for diffusion and coalescence to occur
• Temperatures  0.5 Tm
• Plastic deformation at surfaces is minimal

18. • Primary coalescence mechanism is solid state diffusion
Limitation: time required for diffusion can range from seconds to hours
Applications of DFW
• Joining of high-strength and refractory metals in aerospace and nuclear industries
• Can be used to join either similar and dissimilar metals
• For joining dissimilar metals, a filler layer of different metal is often sandwiched between base
metals to promote diffusion
Explosive Welding EXW
ESW is a SSW process in which rapid coalescence of two metallic surfaces is caused by the energy of
a detonated explosive. It is commonly used to bond two dissimilar metals, in particular to clad one
metal on top of a base metal over large areas.
• No filler metal used
• No external heat applied
• No diffusion occurs - time is too short
• Bonding is metallurgical, combined with mechanical interlocking that results from a rippled or
wavy interface between the metals
FRICTION WELDING FRW
FRW is a SSW process in which coalescence is achieved by frictional heat combined with pressure
• When properly carried out, no melting occurs at faying surfaces
• No filler metal, flux, or shielding gases normally used
• Process yields a narrow HAZ
• Can be used to join dissimilar metals
• Widely used commercial process, amenable to automation and mass production
Procedural Steps
(1) Rotating part, no contact;
(2) parts brought into contact to generate friction heat;
(3) rotation stopped and axial pressure applied; and
(4) weld created

19. Applications:
• Shafts and tubular parts
• Industries: automotive, aircraft, farm equipment, petroleum and natural gas
Limitations:
• At least one of the parts must be rotational
• Flash must usually be removed (extra operation)
• Upsetting reduces the part lengths (which must be taken into consideration in product design)
FRICTION STIR WELDING (FSW)
FSW a cylindrical, shouldered tool with a profiled probe is rotated and slowly plunged into the joint
line between two pieces butted together. Frictional heat is generated between the wear resistant
welding tool and the material of the work pieces. The plasticized material is transferred the front edge
of the tool to back edge of the tool probe and it’s forged by the intimate contact of the tool shoulder
and pin profile. • This heat is without reaching the melting point and allows traversing of the tool
along the weld line.
Advantages
 Good mechanical properties as in weld condition
 Improved saftey due to absence of toxic fumes
 No consumables
 Easily automated on simple milling machines
 Can operate on all positions (vertical,horizontal) etc
 Low environment impact
 High superior weld strength
Limitations
 Work pieces must be rigidly clamped

20.  Exit hole left when tool is withdrawn.
 Large down forces required with heavy-duty clamping necessary to hold the plates together.
 Less flexible than manual and arc processes (difficulties with thickness variations and non-linear
welds).
 Often slower traverse rate than some fusion welding techniques, although this may be offset if fewer
welding passes are required
Suitable materials:
 Copper and its alloys
 Lead
 Titanium and its alloys
 Magnesium alloys
 Zinc
 Plastics
 Mild steel
 Stainless steel
 Nickel alloys
Applications
 Shipbuilding and offshore
 Aerospace
 Automotive
 Railways
 Fabrication
 Robotics
 Personal computers
ULTRASONIC WELDING (USW)
Ultrasonic welding uses high-frequency ultrasonic acoustic vibrations which are applied to materials that
are being held together under pressure to create a solid-state weld. The vibration that results is at a
frequency that is appreciably above the range of human hearing, hence the name ultrasonic.
Working procedure:
The ultrasonic machine places pressure on on the component being welded. The ultrasonic horn is
activated and vibrates the two pieces together at a rate of 20,000 or 40,000 hertz. Weld cycle times are
usually less than 1 second.

21. Advantages of Ultrasonic Welding
• The ability to weld metals of significantly dissimilar melting points that normally form brittle
alloys when joined.
• Welds can be in close proximity to heat sensitive components, such as electronics or
• plastic components (some electronics may be too sensitive for ultrasonic).
• Ultrasonic welds are made without consumables such as glue, solder or filler.
• Use far less energy usage than traditional joining techniques.
• Does not produce exorbitant amount of fumes
• No caustic chemicals
Limitations:
• Large joints (>250 x 300 mm) cannot be welded in a single operation.
• Specifically designed joints are required.
• Ultrasonic vibrations can damage electric components.
• Tooling costs for fixtures are high.
Applications :
Applications for ultrasonic welding that includes metals such as wire, connectors, plastic parts with
relatively similar melting points (when two melting points are too different for ultrasonics, look at the
Trinetics infrared non-contact welder), inserting or staking of metal into plastic, bag making, sealing
containers and packaging, food sealing, medical devices and tools, toys, and many other devices