Abstract:

The welding processes, in their official groupings. The letter designation assigned to the process can be
used for identification on drawings, tables, etc. Allied and related processes include adhesive bonding,
thermal spraying, and thermal cutting. Capillary attraction distinguishes the welding processes grouped
under "Brazing" and "Soldering" from "Arc Welding", "Gas Welding", "Resistance Welding", "Solid State
Welding", and "Other Processes."

The American Welding Society has made each welding process definition as complete as possible so that
it will suffice without reference to another definition. They define a process as "a distinctive progressive
action or series of actions involved in the course of producing a basic type of result".

The official listing of processes and their grouping is shown by Figure 1., the AWS Master Chart of
Welding and Allied Processes. The welding society formulated process definitions from the operational
instead of the metallurgical point of view. Thus the definitions prescribe the significant elements of
operation instead of the significant metallurgical characteristics.

The AWS definition for a welding process is "a materials joining process which produces
coalescence of materials by heating them to suitable temperatures with or without the application of
pressure or by the application of pressure alone and with or without the use of filler material".

AWS has grouped the processes together according to the "mode of energy transfer" as the primary
consideration. A secondary factor is the "influence of capillary attraction in effecting distribution of
filler metal" in the joint. Capillary attraction distinguishes the welding processes grouped under
"Brazing" and "Soldering" from "Arc Welding", "Gas Welding", "Resistance Welding", "Solid State
Welding", and "Other Processes."

The welding processes, in their official groupings, are shown by Table 1. This table also shows the
letter designation for each process. The letter designation assigned to the process can be used for
identification on drawings, tables, etc. Allied and related processes include adhesive bonding,
thermal spraying, and thermal cutting.

Table 1. Welding processes and letter designation.

Group Welding Process Letter Designation
Arc welding Carbon Arc CAW
Flux Cored Arc FCAW
Gas Metal Arc GMAW
Gas Tungsten Arc GTAW
Plasma Arc PAW
Shielded Metal Arc SMAW
Stud Arc SW
Submerged Arc SAW
Brazing Diffusion Brazing DFB
Dip Brazing DB
Furnace Brazing FB
Induction Brazing IB
 Infrared Brazing IRB
Resistance Brazing RB
Torch Brazing TB
Oxyfuel Gas Welding Oxyacetylene Welding OAW
Oxyhydrogen Welding OHW
Pressure Gas Welding PGW
Resistance Welding Flash Welding FW
High Frequency Resistance HFRW
Percussion Welding PEW
Projection Welding RPW
Resistance-Seam Welding RSEW
Resistance-Spot Welding RSW
Upset Welding UW
Solid State Welding Cold Welding CW
Diffusion Welding DFW
Explosion Welding EXW
Forge Welding FOW
Friction Welding FRW
Hot Pressure Welding HPW
Roll Welding ROW
Ultrasonic Welding USW
Soldering Dip Soldering DS
Furnace Soldering FS
Induction Soldering IS
Infrared Soldering IRS
Iron Soldering INS
Resistance Soldering RS
Torch Soldering TS
Wave Soldering WS
Other Welding Processes Electron Beam EBW
Electroslag ESW
Induction IW
Laser Beam LBW
Thermit TW

Arc Welding

The arc welding group includes eight specific processes, each separate and different from the
others but in many respects similar.
The carbon arc welding (CAW) process is the oldest of all the arc welding processes and is
considered to be the beginning of arc welding. The Welding Society defines carbon arc welding as
"an arc welding process which produces coalescence of metals by heating them with an arc
between a carbon electrode and the work-piece. No shielding is used. Pressure and filler metal may
or may not be used." It has limited applications today, but a variation or twin carbon arc welding is
more popular. Another variation uses compressed air for cutting.

The development of the metal arc welding process soon followed the carbon arc. This developed
into the currently popular shielded metal arc welding (SMAW) process defined as "an arc welding
process which produces coalescence of metals by heating them with an arc between a covered
metal electrode and the work-piece. Shielding is obtained from decomposition of the electrode
covering. Pressure is not used and filler metal is obtained from the electrode."

Automatic welding utilizing bare electrode wires was used in the 1920s, but it was the submerged
arc welding (SAW) process that made automatic welding popular. Submerged arc welding is
defined as "an arc welding process which produces coalescence of metals by heating them with an
arc or arcs between a bare metal electrode or electrodes and the work piece. Pressure is not used
and filler metal is obtained from the electrode and sometimes from a supplementary welding rod." It
is normally limited to the flat or horizontal position.

The need to weld nonferrous metals, particularly magnesium and aluminum, challenged the
industry. A solution was found called gas tungsten arc welding (GTAW) [also known as tungsten
inert gas (TIG) welding] and was defined as "an arc welding process which produces coalescence of
metals by heating them with an arc between a tungsten (non-consumable) electrode and the work
piece. Shielding is obtained from a gas or gas mixture."

Plasma arc welding (PAW) is defined as "an arc welding process which produces a coalescence of
metals by heating them with a constricted arc between an electrode and the work piece (transferred
arc) or the electrode and the constricting nozzle (non-transferred arc). Shielding is obtained from the
hot ionized gas issuing from the orifice which may be supplemented by an auxiliary source of
shielding gas." Shielding gas may be an inert gas or a mixture of gases. Plasma welding has been
used for joining some of the thinner materials.

Another welding process also related to gas tungsten arc welding is known as gas metal arc
welding (GMAW). It was developed in the late 1940s for welding aluminum and has become
extremely popular. It is defined as "an arc welding process which produces coalescence of metals
by heating them with an arc between a continuous filler metal (consumable) electrode and the work
piece. Shielding is obtained entirely from an externally supplied gas or gas mixture." The electrode
wire for GMAW is continuously fed into the arc and deposited as weld metal. This process has many
variations depending on the type of shielding gas, the type of metal transfer, and the type of metal
welded.

A variation of gas metal arc welding has become a distinct welding process and is known as flux-
cored arc welding (FCAW). It is defined as "an arc welding process which produces coalescence of
metals by heating them with an arc between a continuous filler metal (consumable) electrode and
the work piece. Shielding is provided by a flux contained within the tubular electrode." Additional
shielding may or may not be obtained from an externally supplied gas or gas mixture.

The final process within the arc welding group of processes is known as stud arc welding (SW).
This process is defined as "an arc welding process which produces coalescence of metals by
heating them with an arc between a metal stud or similar part and the work piece". When the
surfaces to be joined are properly heated they are brought together under pressure. Partial shielding
may be obtained by the use of ceramic ferrule surrounding the stud.
Brazing (B)

Brazing is "a group of welding processes which produces coalescence of materials by heating them
o
to a suitable temperature and by using a filler metal, having a liquidus above 450 C and below the
solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the
joint by capillary attraction."

A braze is a very special form of weld, the base metal is theoretically not melted. There are seven
popular different processes within the brazing group. The source of heat differs among the
processes. Braze welding relates to welding processes using brass or bronze filler metal, where the
filler metal is not distributed by capillary action.

Oxy Fuel Gas Welding (OFW)

Oxy fuel gas welding is "a group of welding processes which produces coalescence by heating
materials with an oxy fuel gas flame or flames with or without the application of pressure and with or
without the use of filler metal."

There are four distinct processes within this group and in the case of two of them, oxyacetylene
welding and oxyhydrogen welding, the classification is based on the fuel gas used. The heat of
the flame is created by the chemical reaction or the burning of the gases. In the third process, air
acetylene welding, air is used instead of oxygen, and in the fourth category, pressure gas
welding, pressure is applied in addition to the heat from the burning of the gases. This welding
process normally utilizes acetylene as the fuel gas. The oxygen thermal cutting processes have
much in common with this welding processes.

Resistance Welding (RW)

Resistance welding is "a group of welding processes which produces coalescence of metals with the
heat obtained from resistance of the work to electric current in a circuit of which the work is a part,
and by the application of pressure". In general, the difference among the resistance welding
processes has to do with the design of the weld and the type of machine necessary to produce the
weld. In almost all cases the processes are applied automatically since the welding machines
incorporate both electrical and mechanical functions.

Other Welding Processes

This group of processes includes those, which are not best defined under the other groupings. It
consists of the following processes: electron beam welding, laser beam welding, thermit
welding, and other miscellaneous welding processes in addition to electroslag welding which
was mentioned previously.

Soldering (S)

Soldering is "a group of joining processes which produces coalescence of materials by heating them
o o
to a suitable temperature and by using a filler metal having a liquidus not exceeding 450 C (840 F)
and below the solidus of the base materials. The filler metal is distributed between the closely fitted
surfaces of the joint by capillary attraction." There are a number of different soldering processes and
methods.

Solid State Welding (SSW)

Solid state welding is "a group of welding processes which produces coalescence at temperatures
essentially below the melting point of the base materials being joined without the addition of a
brazing filler metal. Pressure may or may not be used."

The oldest of all welding processes forge welding belongs to this group. Others include cold
welding, diffusion welding, explosion welding, friction welding, hot pressure welding, and
ultrasonic welding. These processes are all different and utilize different forms of energy for
making welds.