Welding
Process
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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.
Figure
1.
AWS master chart of welding and allied
processes.
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 to a suitable temperature and by
using a filler metal, having a liquidus above 450oC
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 to a suitable
temperature and by using a filler metal having a liquidus not
exceeding 450 oC (840 oF) 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.
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