This document provides an overview of various joining processes, including fusion welding processes like gas welding, arc welding, TIG welding, MIG welding, plasma arc welding, and electron beam welding. It also discusses solid-state welding processes and resistance welding processes like spot welding and seam welding. Specific details are provided on plasma arc welding and resistance welding, including their principles, advantages, and applications.

1. JOINING PROCESSES
By:- P.Dipak
Lecturer at G H Raisoni Polytechnic,
Jalgaon.(Maharashtra)
M.No - 7058192488

2. Contents
• Gas welding
• carbon arc welding
• shielded metal arc welding
• TIG welding
• MIG welding
• plasma arc welding
• resistance welding –spot &
seam projection.
• Electron beam welding
• laser beam welding
• welding defects.
• soldering and brazing
– Process, fillers, heating
methods & applications

3. Introduction
• Welding is a process in which two or more
parts are joined permanently at their touching
surfaces by a suitable application of heat
and/or pressure. Often a filler material is
added to facilitate coalescence. The
assembled parts that are joined by welding
are called a weldment. Welding is primarily
used in metal parts and their alloys.

4. Welding processes are classified into two major groups:
• 1. Fusion welding: In this process, base metal is
melted by means of heat. Often, in fusion welding
operations, a filler metal is added to the molten pool
to facilitate the process and provide bulk and
strength to the joint. Commonly used fusion welding
processes are: arc welding, resistance welding,
oxyfuel welding, electron beam welding and laser
beam welding.
• 2. Solid-state welding: In this process, joining of parts
takes place by application of pressure alone or a
combination of heat and pressure. No filler metal is
used. Commonly used solid-state welding processes
are: diffusion welding, friction welding, ultrasonic
welding.

18. Arc welding and similar processes
• Arc welding is a method of permanently joining two or more metal
parts. It consists of combination of different welding processes wherein
coalescence is produced by heating with an electric arc, (mostly
without the application of pressure) and with or without the use of
filler metals depending upon the base plate thickness.
• A homogeneous joint is achieved by melting and fusing the adjacent
portions of the separate parts. The final welded joint has unit strength
approximately equal to that of the base material. The arc temperature
is maintained approximately 4400°C.
• A flux material is used to prevent oxidation, which decomposes under
the heat of welding and releases a gas that shields the arc and the hot
metal.The second basic method employs an inert or nearly inert gas to
form a protective envelope around the arc and the weld. Helium,
argon, and carbon dioxide are the most commonly used gases.

43. Plasma arc welding
• This process is similar to TIG. A non-consumable electrode
is used in this process. Arc plasma is a temporary state of
gas.
• The gas gets ionized after the passage of electric current
and becomes a conductor of electricity. The plasma consists
of free electrons, positive ions, and neutral particles.
• Plasma arc welding differs from GTAW welding in the
amount of ionized gas which is greatly increased in plasma
arc welding, and it is this ionized gas that provides the heat
of welding

44. Plasma Arc Welding
• Plasma Arc Welding is the welding process utilizing heat generated by a
constricted arc struck between a tungsten non-consumable electrode and
either the work piece (transferred arc process) or water cooled
constricting nozzle (non-transferred arc process).
Plasma is a gaseous mixture of positive ions, electrons and neutral gas
molecules.
Transferred arc process produces plasma jet of high energy density and
may be used for high speed welding and cutting
of Ceramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel
alloys.
Non-transferred arc process produces plasma of relatively low energy
density. It is used for welding of various metals and for plasma
spraying (coating). 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.

45. Advantages of Plasma Arc Welding (PAW):
• Requires less operator skill due to good tolerance
of arc to misalignments;
• High welding rate;
• High penetrating capability (keyhole effect)
Disadvantages of Plasma Arc Welding (PAW):
• Expensive equipment;
• High distortions and wide welds as a result of
high heat input (in transferred arc process).

46. Resistance welding
Principle- Resistance welding is conducted as
follows:
• Apply force and current through electrodes
contacted metal parts to be welded.
• Resistance heat is generated at the interface of
metal parts and makes a nugget, resulting in melt
joint.
• Though a large current flows, there is no danger
of an electric shock because only low voltage is
impressed

47. Features of resistance welding
• No flux such as solder is necessary, so welded parts can be easily recycled. Spatter and
ultraviolet ray are most unlikely to be generated; consequently, clean and neat worksite
is realized.
• Easy operation as only pressing buttons facilitates process automation and does not
require trained skills unlike arc welding and gas welding.
• As this welding is performed efficiently in a short period of time, it is suited for a high-
volumes production of low-cost products.
• Since welding is done in short time duration, it gives less heat-affected area on work
pieces, resulting in beautiful appearance with less indentation.
• Electric facility is required in some cases due to use of large current. Optimum welding
parameters must be figured out before actual welding since those parameters depend
on material and thickness of parts to be welded. welding condition setting must be
prepared.
• Visual inspection is difficult because welded portion cannot be checked from the
outside.

48. • Resistance Welding is a welding process, in which
work pieces are welded due to a combination of a
pressure applied to them and a localized heat
generated by a high electric current flowing through
the contact area of the weld.
Heat produced by the current is sufficient for local
melting of the work piece at the contact point and
formation of small weld pool (”nugget”). The molten
metal is then solidifies under a pressure and joins the
pieces. Time of the process and values of the
pressure and flowing current, required for formation
of reliable joint, are determined by dimensions of
the electrodes and the work piece metal type.

49. AC electric current (up to 100 000 A) is supplied through copper
electrodes connected to the secondary coil of a welding
transformer.
• The following metals may be welded by
Resistance Welding:
• Low carbon steels - the widest application of
Resistance Welding
• Aluminum alloys
• Medium carbon steels, high carbon
steels and Alloy steels (may be welded, but
the weld is brittle)

50. Advantages of Resistance Welding:
• High welding rates;
• Low fumes;
• Cost effectiveness;
• Easy automation;
• No filler materials are required;
• Low distortions.
Disadvantages of Resistance Welding:
• High equipment cost;
• Low strength of discontinuous welds;
• Thickness of welded sheets is limited - up to 1/4” (6 mm)
• Resistance Welding (RW) is used for joining vehicle body
parts, fuel tanks, domestic radiators, pipes of gas oil and
water pipelines, wire ends, turbine blades, railway tracks.

51. Resistance Welding Types
• The most popular methods of Resistance
Welding are:
• Spot Welding (RSW)
• Flash Welding (FW)
• Resistance Butt Welding (UW)
• Seam Welding (RSEW)

53. Spot Welding (RSW)
Spot Welding is a Resistance Welding
(RW) process, in which two or more
overlapped metal sheets are joined by spot
welds.
The method uses pointed copper
electrodes providing passage of electric
current. The electrodes also transmitt
pressure required for formation of strong
weld.
Diameter of the weld spot is in the range
1/8” - 1/2” (3 - 12 mm).
Spot welding is widely used in automotive
industry for joining vehicle body parts.

55. Seam Welding (RSEW)
Seam Welding is a Resistance Welding
(RW) process of continuous joining of
overlapping sheets by passing them
between two rotating electrode
wheels. Heat generated by the electric
current flowing through the contact
area and pressure provided by the
wheels are sufficient to produce a
leak-tight weld.
Seam Welding is high speed and clean
process, which is used when
continuous tight weld is required (fuel
tanks, drums, domestic radiators).

57. Flash Welding (FW)
Flash Welding is a Resistance Welding
(RW) process, in which ends of rods
(tubes, sheets) are heated and fused by
an arc struck between them and
then forged (brought into a contact under
a pressure) producing a weld.
The welded parts are held in electrode
clamps, one of which is stationary and the
second is movable.
Flash Welding method permitts fast (about
1 min.) joining of large and complex parts.
Welded part are often annealed for
improvement of Toughnesstoughness of
the weld.
Steels, Aluminum alloys, Copper
alloys, Magnesium alloys, Copper
alloys and Nickel alloys may be welded by
Flash Welding.
Thick pipes, ends of band saws, frames,
aircraft landing gears are produced by
Flash Welding.

58. Resistance Butt Welding (UW)
Resistance Butt Welding is a Resistance
Welding (RW) process, in which ends of
wires or rods are held under a pressure
and heated by an electric current passing
through the contact area and producing a
weld.
The process is similar to Flash Welding,
however in Butt Welding pressure and
electric current are applied
simultaneously in contrast to Flash
Welding where electric current is followed
by forging pressure application.
Butt welding is used for welding small
parts. The process is highly productive
and clean. In contrast to Flash Welding,
Butt Welding provides joining with no loss
of the welded materials

59. Electron beam welding
• Electron beam welding is defined as a fusion welding
process wherein coalescence is produced by the heat
obtained from a concentrated beam of high velocity
electron.
• When high velocity electrons strike the work piece, kinetic
energy is transformed into thermal energy causing
localized heating and melting of the weld metal.
• The electron beam generation takes place in a vacuum,
and the process works best when the entire operation and
the work piece are also in a high vacuum of 10-4torr or
lower.
• However, radiations namely ray, infrared and ultraviolet
radiation generates and the welding operator must be
protected

60. Electron beam welding

62. • Electron Beam Welding is a welding process utilizing a heat generated
by a beam of high energy electrons. The electrons strike the work piece
and their kinetic energy converts into thermal energy heating the metal
so that the edges of work piece are fused and joined together forming a
weld after Solidification.
The process is carried out in a vacuum chamber at a pressure of about
2*10-7 to 2*10-6 psi (0.00013 to 0.0013 Pa). Such high vacuum is
required in order to prevent loss of the electrons energy in collisions
with air molecules.
The electrons are emitted by a cathode (electron gun). Due to a high
voltage (about 150 kV) applied between the cathode and the anode the
electrons are accelerated up to 30% - 60% of the speed of light. Kinetic
energy of the electrons becomes sufficient for melting the targeted
weld. Some of the electrons energy transforms into X-ray irradiation.
•
Electrons accelerated by electric field are then focused into a thin beam
in the focusing coil. Deflection coil moves the electron beam along the
weld.

63. Electron Beam is capable to weld work pieces with thickness from 0.0004”
(0.01 mm) up to 6” (150 mm) of steel and up to 20” (500 mm)
of aluminum. Electron Beam Welding may be used for joining any metals
including metals, which are hardly weldable by other welding methods:
refractory metals (tungsten, molybdenum, niobium) and chemically active
metals (titanium, zirconium, beryllium). Electron Beam Welding is also able
to join dissimilar metals.
Advantages of Electron Beam Welding (EBW):
• Tight continuous weld;
• Low distortion;
• Narrow weld and narrow heat affected zone;
• Filler metal is not required.
Disadvantages of Electron Beam Welding (EBW):
• Expensive equipment;
• High production expenses;
• X-ray irradiation.

66. LASER BEAM WELDING
• The term laser is an acronym for Light
Amplification by Stimulated Emission of
Radiation.
• A laser beam is a powerful, narrow,
monochromatic and directional beam of
electromagnetic radiation.
• Often, these beams are within the visible
spectrum of light.
• A laser device excites the atoms in a losing
medium. The electrons of these atoms move to a
higher orbit, then release photons, creating a
laser beam.

67. Properties of Laser Beam
• A LASER beam is highly intense in nature.
• LASER beam is having strictly monochromatic.
• LASER light is highly powerful and capable of
propagating over long distance & are not
easily absorbed by water.
• LASER beam is also said to be highly
directional.
• This beam is coherent with the wave train in
phase with each other.

68. Types of laser Beam
Types of lasers include gas, liquid and solid.
1. Gas lasers excite the electrons in gases, such as
helium, neon, cadmium, carbon dioxide and
nitrogen.
2. Liquid lasers include the dye laser, which uses
organic dye molecules in liquid form to produce a
wavelength of radiation that can be tuned.
3. Solid lasers include the ruby laser, which uses a
precious stone to produce a beam of red light.

69. • In general cases heat is required to fuse the
metals for any types of welding, in laser beam
welding process the heat is obtained from the
application of a concentrated coherent light
beam which striking upon the weld metal and
melt the metal, such this weld joint is
obtained, this welding process is called laser
welding.

70. Principle of LBW
• A laser beam is produced inside of the Ruby Crystal.
The Ruby Crystal is made of aluminium oxide with
chromium dispersed throughout it. Which is forming
about 1/2000 of crystal, this less than natural ruby.
Silver coated mirrors are fitted internally in the both
side of crystal. The one side of mirror has a tiny hole, a
beam is come out through this hole.
• A flash tube is placed around the Ruby Crystal, which is
filled with xenon inert gas. The flash is specially
designed such as which is made flash rate about
thousands flashes per seconds.

72. LBWAdvantages:
• precise working with exact placing of the energy spot
• welding of complicated joint geometry
• low heat application, therefore minor changes in microstructure
• low thermal distortion
• cavity-free welds
• low post weld operation times
• large working distance is possible ( welding up to 500 mm distance and also to
inaccessible parts).
Disadvantages:
• The welding plants are expensive, depending upon the equipment.
• If filler material is necessary they are, because of the limited amount produced,
relatively expensive. This disadvantage is counteracted by the low amount used
compared to the welding time and also that there are few post welding operations.
Applications
• Laser beam welding of high-strength aluminium alloys for aerospace applications
• Laser beam welding of high strength aluminium alloys for automotive applications

73. SOLDERING AND BRAZING
• Soldering and brazing provide permanent joint to
bond metal pieces.
• Soldering and brazing process lie some where in
between fusion welding and solid state welding.
These processes have some advantages over
welding process.
• These can join the metal having poor walkability,
dissimilar metals, very less amount of heating is
needed.
• The major disadvantage is joint made by soldering
and brazing has low strength as compared to
welded joint.

74. Objectives
After studying this unit, you should be able to
• introduction to allied welding processes,
• welding soldering and brazing comparative study.
• different methods of soldering and brazing and
machine tool, and
• defects and applications of soldering and brazing.

75. PRINCIPLE OF BRAZING
• In case of brazing joining of metal pieces is done
with the help of filler metal. Filler metal is melted
and distributed by capillary action between the
faying surfaces of the metallic parts being joined.
• In this case only filler metal melts. There is no
melting of workpiece metal. The filler metal
(brazing metal) should have the melting point
more than 450oC. Its melting point should be
lesser than the melting point of work piece metal.
• The metallurgical bonding between work and filler
metal and geometric constrictions imposed on the
joint by the work piece metal make the joint
stronger than the filler metal out of which the joint
has been formed.

76. PRINCIPLE OF SOLDERING
• Soldering is very much similar to brazing and it
principle is same as that of brazing. The major
difference lies with the filler metal.
• The filler metal used in case of soldering should have
the melting temperature lower than 450oC.
• The surfaces to be soldered must be pre-cleaned so
that these are faces of oxides, oils, etc. An
appropriate flux must be applied to the faying
surfaces and then surfaces are heated.
• Filler metal called solder is added to the joint, which
distributes between the closely fitted surfaces.
• Strength of soldered joint is much lesser than
welded joint and les than a brazed joint.

77. DIFFERENT TYPES OF SOLDERS
• Most of the solder metals are the alloy of tin and
lead. These alloys exhibit a wide range of melting
point so different type of soldering metal can be
used for variety of applications.
• Percentage of lead is kept least due to its toxic
properties. Tin becomes chemically active at
soldering temperature and promotes the wetting
action required for making the joint.
• Copper, silver and antimony are also used in
soldering metal as per the strength requirements
of the joint.
• Different solder their melting point and
applications are given in the Table 6.1.

79. TYPES OF SOLDERING FLUXES
Soldering fluxes can be classified as :
(a) Organic, and
(b) Inorganic fluxes.
• Organic Fluxes- Organic fluxes are either rosin or water
soluble materials. Rosin used for fluxes are wood gum, and
other rosin which are not water soluble. Organic fluxes are
mostly used for electrical and electronic circuit making. These
are chemically unstable at elevated temperature but non-
corrosive at room temperature.
• Inorganic Fluxes- Inorganic fluxes are consists of inorganic
acids; mixture of metal chlorides (zinc and ammonium
chlorides). These are used to achieve rapid and active fluxing
where formation of oxide films are problems.

80. Fluxes should be removed after soldering either by
washing with water or by chemical solvents. The main
functions performed by fluxes are :
• (a) remove oxide films and tarnish from base part
surfaces,
• (b) prevent oxidation during heating, and
• (c) promote wetting of the faying surfaces.
The fluxes should
• (a) be molten at soldering temperature,
• (b) be readily displaced by the molten solder during
the process, and
• (c) leave a residue that is non-corrosive and non-
conductive.

81. SOLDERING METHODS
• There is a lot of similarity between soldering and
brazing processes. The major difference between
them is less heat and lower temperature is required
in case of soldering.
• The different processes (methods) used in soldering
are touch soldering, furnace soldering, resistance
soldering, dip soldering and infrared soldering. All
the above methods are common to both soldering
and brazing processes.
• There are some more methods used in case of
soldering only, these are hand soldering; wave
soldering and reflow soldering. These methods are
described below.

83. SOLDERING PROCEDURE
• Work Preparation- Workpieces which are to be joined together should be
perfectly clean. There should not be any dirt, dust, rust, paint or grease. This is
so that the solder or spelter can stick to the joint with proper strength. Cleaning
is done with the help of a file or sandpaper. In case of joining of conducting
wires, insulation of portion to be joined should be perfectly removed.
Sometimes chemicals are used to clean the workpieces. De-scaling (removal of
scaling) is done by dipping the workpieces into dilute HCl.
• Preparation of Joint-After cleaning workpieces should be kept together in
correct position to make the
• final joint. Workpieces should be clamped to avoid any relative movement
between them that may disturb the joint making. At the joint smaller grooves
are made on the workpieces to facilitate better flow of molten solder and so
good strength of the joint. There may be the two objectives of joint :
to bear load, and
to make electrical contact.
• In case of load bearing joints lap joint or butt joints are preferred. It is important
to note down that strength of a soldered joint can not be compared with welded
joint. If electrical contact is to be made the solder should be so selected that
resistance of joint should match with the resistance of the conductor.

84. • Fluxing-Fluxing includes selection of appropriate flux and its
application to the joint. Selection of flux depends on the
material of workpiece keeping its purpose inview. It is applied
to the joint with the help of a brush before soldering. It avoids
oxidation of molten metal, helps in flow of molten solder into
the joint and so maintains strength of the joint.
• Tinning- In this step of soldering procedure, the bit of solder
iron is cleaned, application of flux is done over it. It is brought in
contact of solder wire so the bit carries sufficient amount of
molten solder over it.
• After that it is used to make tags of solder at various process
through out the joint. If soldering is done to make electrical
contacts of conductivity wires the complete joint is made by
tagging few times. In case of long joint, after tagging the molten
solder is filled to the joint by bringing hot bit of solder iron and
solder wire together in contact with the joint. Filling the joint
with molten solder and allowing to solidify is the last step of the
procedure called soldering.

86. SOLDERING DEFECTS AND THEIR
REMEDIES
• Granular formation at the surface of the joint of solder
is one of the common soldering defects.
• Formation of spheroids at the surface of soldering joint
is also similar defect. This happen due to under heating
or over heating of solder iron, insufficient use of flux.
Formation of spheroids make the joint ugly and week
in strength.
• Improper or uneven application of flux may make the
joint of weaker strength.
• Proper coordination between flux application and
soldering makes the joint of good quality.

87. SAFETY PRECAUTIONS IN SOLDERING
• Keep solder iron always on its stand.
• All electrically operated instruments/equipment should have
proper earthing.
• Sometimes emission of (smoke) soldering operation may be
poisonous due to a particular type of flux. Operator should
have protection from the same.
• Flux should be applied gradually while soldering.
• While diluting HCl, water should not be added to HCl but HCl
should be mixed into the water drop by drop, to avoid
accident.
• Work place should have enough ventilation and smoking
should be strictly
• prohibited during the operation. Work place should have the
facility of first aid.
• It should be noted down good quality surface preparation
always contributes to good quality joint.