To press or beat into intimate and permanent
union, as two pieces of iron when heated almost to fusion. [1913
Webster] Note: Very few of the metals, besides iron and platinum.
are capable of being welded. Horn and tortoise shell possess this
useful property. [1913 Webster]
Fig.: To unite closely or intimately. [1913
Webster] Two women faster welded in one love. --Tennyson. [1913
Webster]
Word Net
welding n : fastening two pieces of metal together by softening with heat and applying pressureVerb form
welding- present participle of weld
Noun
- A method of manufacture or repair involving joining two pieces of metal or plastic by fusion. Heat is normally used such as an open flame (i.e. acetylene, propane or butane), laser light or electric arc, and the fusion may be autogenous or with the addition of a similar substance to the weld pool
Translations
method involving joining
- Finnish: hitsaaminen, hitsaus
- Greek: οξυγονοκόλληση, ηλεκτροσυγκόλληση
Derived terms
Welding is a fabrication
process
that joins materials, usually metals or thermoplastics, by causing
coalescence.
This is often done by melting the workpieces and
adding a filler material to form a pool of molten material (the
weld puddle) that cools to become a strong joint, with pressure sometimes used in
conjunction with heat, or
by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a
lower-melting-point material between the workpieces to form a bond
between them, without melting the workpieces.
Many different energy
sources can be used for welding, including a gas flame, an electric
arc, a laser, an
electron beam, friction,
and ultrasound. While
often an industrial process, welding can be done in many different
environments, including open air, underwater
and in space. Regardless
of location, however, welding remains dangerous, and precautions
must be taken to avoid burns, electric
shock, eye damage, poisonous fumes, and overexposure to
ultraviolet
light.
Until the end of the 19th century, the only
welding process was forge
welding, which blacksmiths had used for centuries to join
metals by heating and pounding them. Arc welding
and
oxyfuel welding were among the first processes to develop late
in the century, and resistance
welding followed soon after. Welding technology advanced
quickly during the early 20th century as World War I
and World War
II drove the demand for reliable and inexpensive joining
methods. Following the wars, several modern welding techniques were
developed, including manual methods like
shielded metal arc welding, now one of the most popular welding
methods, as well as semi-automatic and automatic processes such as
gas
metal arc welding, submerged
arc welding, flux-cored
arc welding and electroslag
welding. Developments continued with the invention of laser
beam welding and electron
beam welding in the latter half of the century. Today, the
science continues to advance. Robot
welding is becoming more commonplace in industrial settings,
and researchers continue to develop new welding methods and gain
greater understanding of weld quality and properties.
History
The history of joining metals goes back several millennia, with the earliest examples of welding from the Bronze Age and the Iron Age in Europe and the Middle East. Welding was used in the construction of the Iron pillar in Delhi, India, erected about 310 and weighing 5.4 metric tons. The Middle Ages brought advances in forge welding, in which blacksmiths pounded heated metal repeatedly until bonding occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled in the process, and the industry continued to grow during the following centuries. Welding, however, was transformed during the 19th century—in 1800, Sir Humphry Davy discovered the electric arc, and advances in arc welding continued with the inventions of metal electrodes by a Russian, Nikolai Slavyanov, and an American, C. L. Coffin in the late 1800s, even as carbon arc welding, which used a carbon electrode, gained popularity. Around 1900, A. P. Strohmenger released a coated metal electrode in Britain, which gave a more stable arc, and in 1919, alternating current welding was invented by C. J. Holslag, but did not become popular for another decade.Resistance
welding was also developed during the final decades of the 19th
century, with the first patents going to Elihu
Thomson in 1885, who produced further advances over the next 15
years. Thermite welding
was invented in 1893, and around that time, another process,
oxyfuel welding, became well established. Acetylene was
discovered in 1836 by Edmund Davy,
but its use was not practical in welding until about 1900, when a
suitable blowtorch was
developed. At first, oxyfuel welding was one of the more popular
welding methods due to its portability and relatively low cost. As
the 20th century progressed, however, it fell out of favor for
industrial applications. It was largely replaced with arc welding,
as metal coverings (known as flux)
for the electrode that stabilize the arc and shield the base
material from impurities continued to be developed.
World War I
caused a major surge in the use of welding processes, with the
various military powers attempting to determine which of the
several new welding processes would be best. The British primarily
used arc welding, even constructing a ship, the Fulagar, with an
entirely welded hull. The Americans were more hesitant, but began
to recognize the benefits of arc welding when the process allowed
them to repair their ships quickly after German
attacks in the New York
Harbor at the beginning of the war. Arc welding was first
applied to aircraft during the war as well, as some German airplane
fuselages were constructed using the process.. Also noteworthy is
the first welded road bridge in the world built across
the river Słudwia
Maurzyce near Łowicz,
Poland) in 1929, but designed by Stefan
Bryła of the
Warsaw University of Technology in 1927.
During the 1920s, major advances were made in
welding technology, including the introduction of automatic welding
in 1920, in which electrode wire was fed continuously. Shielding
gas became a subject receiving much attention, as scientists
attempted to protect welds from the effects of oxygen and nitrogen
in the atmosphere. Porosity and brittleness were the primary
problems, and the solutions that developed included the use of
hydrogen, argon, and helium as welding atmospheres.
During the following decade, further advances allowed for the
welding of reactive metals like aluminum and
magnesium. This, in
conjunction with developments in automatic welding, alternating
current, and fluxes fed a major expansion of arc welding during the
1930s and then during World War
II.
During the middle of the century, many new
welding methods were invented. 1930 saw the release of stud
welding, which soon became popular in shipbuilding and
construction. Submerged
arc welding was invented the same year, and continues to be
popular today. Gas
tungsten arc welding, after decades of development, was finally
perfected in 1941, and gas
metal arc welding followed in 1948, allowing for fast welding
of non-ferrous materials
but requiring expensive shielding gases.
Shielded metal arc welding was developed during the 1950s,
using a flux coated consumable electrode, and it quickly became the
most popular metal arc welding process. In 1957, the flux-cored
arc welding process debuted, in which the self-shielded wire
electrode could be used with automatic equipment, resulting in
greatly increased welding speeds, and that same year, plasma
arc welding was invented. Electroslag
welding was introduced in 1958, and it was followed by its
cousin, electrogas
welding, in 1961.
Other recent developments in welding include the
1958 breakthrough of electron
beam welding, making deep and narrow welding possible through
the concentrated heat source. Following the invention of the
laser in 1960, laser
beam welding debuted several decades later, and has proved to
be especially useful in high-speed, automated welding. Both of
these processes, however, continue to be quite expensive due the
high cost of the necessary equipment, and this has limited their
applications.
Welding processes
Arc welding
These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.Power supplies
To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.The type of current used in arc welding also
plays an important role in welding. Consumable electrode processes
such as shielded metal arc welding and gas metal arc welding
generally use direct current, but the electrode can be charged
either positively or negatively. In welding, the positively charged
anode will have a greater
heat concentration, and as a result, changing the polarity of the
electrode has an impact on weld properties. If the electrode is
positively charged, the base metal will be hotter, increasing weld
penetration and welding speed. Alternatively, a negatively charged
electrode results in more shallow welds. Nonconsumable electrode
processes, such as gas tungsten arc welding, can use either type of
direct current, as well as alternating current. However, with
direct current, because the electrode only creates the arc and does
not provide filler material, a positively charged electrode causes
shallow welds, while a negatively charged electrode makes deeper
welds. Alternating current rapidly moves between these two,
resulting in medium-penetration welds. One disadvantage of AC, the
fact that the arc must be re-ignited after every zero crossing, has
been addressed with the invention of special power units that
produce a square wave
pattern instead of the normal sine wave,
making rapid zero crossings possible and minimizing the effects of
the problem.
Processes
One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of steel and is covered with a flux that protects the weld area from oxidation and contamination by producing CO2 gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.The process is versatile and can be performed
with relatively inexpensive equipment, making it well suited to
shop jobs and field work. An operator can become reasonably
proficient with a modest amount of training and can achieve mastery
with experience. Weld times are rather slow, since the consumable
electrodes must be frequently replaced and because slag, the
residue from the flux, must be chipped away after welding.
Furthermore, the process is generally limited to welding ferrous
materials, though special electrodes have made possible the welding
of cast
iron, nickel,
aluminium, copper, and other metals.
Inexperienced operators may find it difficult to make good
out-of-position welds with this process.
Gas
metal arc welding (GMAW), also known as metal inert gas or MIG
welding, is a semi-automatic or automatic process that uses a
continuous wire feed as an electrode and an inert or semi-inert gas
mixture to protect the weld from contamination. As with SMAW,
reasonable operator proficiency can be achieved with modest
training. Since the electrode is continuous, welding speeds are
greater for GMAW than for SMAW. Also, the smaller arc size compared
to the
shielded metal arc welding process makes it easier to make
out-of-position welds (e.g., overhead joints, as would be welded
underneath a structure).
The equipment required to perform the GMAW
process is more complex and expensive than that required for SMAW,
and requires a more complex setup procedure. Therefore, GMAW is
less portable and versatile, and due to the use of a separate
shielding gas, is not particularly suitable for outdoor work.
However, owing to the higher average rate at which welds can be
completed, GMAW is well suited to production welding. The process
can be applied to a wide variety of metals, both ferrous and
non-ferrous.
A related process, flux-cored
arc welding (FCAW), uses similar equipment but uses wire
consisting of a steel electrode surrounding a powder fill material.
This cored wire is more expensive than the standard solid wire and
can generate fumes and/or slag, but it permits even higher welding
speed and greater metal penetration.
Gas
tungsten arc welding (GTAW), or tungsten inert gas (TIG)
welding (also sometimes erroneously referred to as heliarc welding), is a manual
welding process that uses a nonconsumable tungsten electrode, an inert or
semi-inert gas mixture, and a separate filler material. Especially
useful for welding thin materials, this method is characterized by
a stable arc and high quality welds, but it requires significant
operator skill and can only be accomplished at relatively low
speeds.
GTAW can be used on nearly all weldable metals,
though it is most often applied to stainless
steel and light metals. It is often used when quality welds are
extremely important, such as in bicycle, aircraft and naval
applications. A related process, plasma
arc welding, also uses a tungsten electrode but uses plasma gas
to make the arc. The arc is more concentrated than the GTAW arc,
making transverse control more critical and thus generally
restricting the technique to a mechanized process. Because of its
stable current, the method can be used on a wider range of material
thicknesses than can the GTAW process, and furthermore, it is much
faster. It can be applied to all of the same materials as GTAW
except magnesium, and
automated welding of stainless steel is one important application
of the process. A variation of the process is plasma
cutting, an efficient steel cutting process.
Submerged
arc welding (SAW) is a high-productivity welding method in
which the arc is struck beneath a covering layer of flux. This
increases arc quality, since contaminants in the atmosphere are
blocked by the flux. The slag that forms on the weld generally
comes off by itself, and combined with the use of a continuous wire
feed, the weld deposition rate is high. Working conditions are much
improved over other arc welding processes, since the flux hides the
arc and almost no smoke is produced. The process is commonly used
in industry, especially for large products and in the manufacture
of welded pressure vessels. Other arc welding processes include
atomic
hydrogen welding, carbon
arc welding, electroslag
welding, electrogas
welding, and stud arc
welding.
Gas welding
The most common gas welding process is
oxyfuel welding, also known as oxyacetylene welding. It is one
of the oldest and most versatile welding processes, but in recent
years it has become less popular in industrial applications. It is
still widely used for welding pipes and tubes, as well as repair
work. It is also frequently well-suited, and favored, for
fabricating some types of metal-based artwork. Oxyfuel equipment is
versatile, lending itself not only to some sorts of iron or steel
welding but also to brazing, braze-welding, metal heating (for
bending and forming), and also oxyfuel cutting.
The equipment is relatively inexpensive and
simple, generally employing the combustion of acetylene in oxygen to produce a welding flame
temperature of about 3100 °C. The flame, since it is less
concentrated than an electric arc, causes slower weld cooling,
which can lead to greater residual stresses and weld distortion,
though it eases the welding of high alloy steels. A similar
process, generally called oxyfuel cutting, is used to cut metals.
Other gas welding methods, such as air
acetylene welding, oxygen
hydrogen welding, and pressure
gas welding are quite similar, generally differing only in the
type of gases used. A water torch is
sometimes used for precision welding of small items such as
jewelry. Gas welding is also used in plastic
welding, though the heated substance is air, and the
temperatures are much lower.
Resistance welding
Resistance welding involves the generation of heat by passing current through the resistance caused by the contact between two or more metal surfaces. Small pools of molten metal are formed at the weld area as high current (1000–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the equipment cost can be high.Spot welding
is a popular resistance welding method used to join overlapping
metal sheets of up to 3 mm thick. Two electrodes are simultaneously
used to clamp the metal sheets together and to pass current through
the sheets. The advantages of the method include efficient energy
use, limited workpiece deformation, high production rates, easy
automation, and no required filler materials. Weld strength is
significantly lower than with other welding methods, making the
process suitable for only certain applications. It is used
extensively in the automotive industry—ordinary cars can
have several thousand spot welds made by industrial
robots. A specialized process, called shot
welding, can be used to spot weld stainless
steel.
Like spot welding, seam welding
relies on two electrodes to apply pressure and current to join
metal sheets. However, instead of pointed electrodes, wheel-shaped
electrodes roll along and often feed the workpiece, making it
possible to make long continuous welds. In the past, this process
was used in the manufacture of beverage cans, but now its uses are
more limited. Other resistance welding methods include flash
welding, projection
welding, and upset
welding.
Energy beam welding
Energy beam welding methods, namely laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are quite similar, differing most notably in their source of power. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easily automated, making them highly productive. The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking. Developments in this area include laser-hybrid welding, which uses principles from both laser beam welding and arc welding for even better weld properties.Solid-state welding
Like the first welding process, forge welding, some modern welding methods do not involve the melting of the materials being joined. One of the most popular, ultrasonic welding, is used to connect thin sheets or wires made of metal or thermoplastic by vibrating them at high frequency and under high pressure. The equipment and methods involved are similar to that of resistance welding, but instead of electric current, vibration provides energy input. Welding metals with this process does not involve melting the materials; instead, the weld is formed by introducing mechanical vibrations horizontally under pressure. When welding plastics, the materials should have similar melting temperatures, and the vibrations are introduced vertically. Ultrasonic welding is commonly used for making electrical connections out of aluminum or copper, and it is also a very common polymer welding process.Another common process, explosion
welding, involves the joining of materials by pushing them
together under extremely high pressure. The energy from the impact
plasticizes the materials, forming a weld, even though only a
limited amount of heat is generated. The process is commonly used
for welding dissimilar materials, such as the welding of aluminum
with steel in ship hulls or compound plates. Other solid-state
welding processes include co-extrusion
welding, cold
welding, diffusion
welding, friction
welding (including friction
stir welding), high
frequency welding, hot
pressure welding, induction
welding, and roll
welding.
Geometry
Welds can be geometrically prepared in many
different ways. The five basic types of weld joints are the butt
joint, lap joint, corner joint, edge joint, and T-joint. Other
variations exist as well—for example, double-V
preparation joints are characterized by the two pieces of material
each tapering to a single center point at one-half their height.
Single-U and double-U preparation joints are also fairly
common—instead of having straight edges like the single-V
and double-V preparation joints, they are curved, forming the shape
of a U. Lap joints are also commonly more than two pieces
thick—depending on the process used and the thickness of
the material, many pieces can be welded together in a lap joint
geometry.
Often, particular joint designs are used
exclusively or almost exclusively by certain welding processes. For
example, resistance spot welding, laser beam welding, and electron
beam welding are most frequently performed on lap joints. However,
some welding methods, like shielded metal arc welding, are
extremely versatile and can weld virtually any type of joint.
Additionally, some processes can be used to make multipass welds,
in which one weld is allowed to cool, and then another weld is
performed on top of it. This allows for the welding of thick
sections arranged in a single-V preparation joint, for
example.
After welding, a number of distinct regions can
be identified in the weld area. The weld itself is called the
fusion zone—more specifically, it is where the filler
metal was laid during the welding process. The properties of the
fusion zone depend primarily on the filler metal used, and its
compatibility with the base materials. It is surrounded by the
heat-affected
zone, the area that had its microstructure and properties
altered by the weld. These properties depend on the base material's
behavior when subjected to heat. The metal in this area is often
weaker than both the base material and the fusion zone, and is also
where residual stresses are found.
Quality
Most often, the major metric used for judging the quality of a weld is its strength and the strength of the material around it. Many distinct factors influence this, including the welding method, the amount and concentration of energy input, the base material, the filler material, the flux material, the design of the joint, and the interactions between all these factors. To test the quality of a weld, either destructive or nondestructive testing methods are commonly used to verify that welds are defect-free, have acceptable levels of residual stresses and distortion, and have acceptable heat-affected zone (HAZ) properties. Welding codes and specifications exist to guide welders in proper welding technique and in how to judge the quality of welds.Heat-affected zone
The effects of welding on the material surrounding the weld can be detrimental—depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity of the base material plays a large role—if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input. To calculate the heat input for arc welding procedures, the following formula can be used:- Q = \left(\frac \right) \times
where Q = heat input (kJ/mm), V = voltage (V), I = current
(A), and S =
welding speed (mm/min). The efficiency is dependent on the welding
process used, with shielded metal arc welding having a value of
0.75, gas metal arc welding and submerged arc welding, 0.9, and gas
tungsten arc welding, 0.8.
Distortion and cracking
Welding methods that involve the melting of metal
at the site of the joint necessarily are prone to shrinkage
as the heated metal cools. Shrinkage, in turn, can introduce
residual stresses and both longitudinal and rotational distortion.
Distortion can pose a major problem, since the final product is not
the desired shape. To alleviate rotational distortion, the
workpieces can be offset, so that the welding results in a
correctly shaped piece. Other methods of limiting distortion, such
as clamping the workpieces in place, cause the buildup of residual
stress in the heat-affected zone of the base material. These
stresses can reduce the strength of the base material, and can lead
to catastrophic failure through cold
cracking, as in the case of several of the Liberty
ships. Cold cracking is limited to steels, and is associated
with the formation of martensite as the weld cools.
The cracking occurs in the heat-affected zone of the base material.
To reduce the amount of distortion and residual stresses, the
amount of heat input should be limited, and the welding sequence
used should not be from one end directly to the other, but rather
in segments. The other type of cracking, hot cracking
or solidification cracking, can occur with all metals, and happens
in the fusion zone of a weld. To diminish the probability of this
type of cracking, excess material restraint should be avoided, and
a proper filler material should be utilized.
Weldability
The quality of a weld is also dependent on the
combination of materials used for the base material and the filler
material. Not all metals are suitable for welding, and not all
filler metals work well with acceptable base materials.
Steels
The weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the probability of forming martensite during welding or heat treatment. The hardenability of steel depends on its chemical composition, with greater quantities of carbon and other alloying elements resulting in a higher hardenability and thus a lower weldability. In order to be able to judge alloys made up of many distinct materials, a measure known as the equivalent carbon content is used to compare the relative weldabilities of different alloys by comparing their properties to a plain carbon steel. The effect on weldability of elements like chromium and vanadium, while not as great as carbon, is more significant than that of copper and nickel, for example. As the equivalent carbon content rises, the weldability of the alloy decreases. The disadvantage to using plain carbon and low-alloy steels is their lower strength—there is a trade-off between material strength and weldability. High strength, low-alloy steels were developed especially for welding applications during the 1970s, and these generally easy to weld materials have good strength, making them ideal for many welding applications.Stainless
steels, because of their high chromium content, tend to behave
differently with respect to weldability than other steels.
Austenitic grades of stainless steels tend to be the most weldable,
but they are especially susceptible to distortion due to their high
coefficient of thermal expansion. Some alloys of this type are
prone to cracking and reduced corrosion resistance as well. Hot
cracking is possible if the amount of ferrite in
the weld is not controlled—to alleviate the problem, an
electrode is used that deposits a weld metal containing a small
amount of ferrite. Other types of stainless steels, such as
ferritic and martensitic stainless steels, are not as easily
welded, and must often be preheated and welded with special
electrodes.
Aluminum
The weldability of aluminum alloys varies significantly, depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.Unusual conditions
While many welding applications are done in
controlled environments such as factories and repair shops, some
welding processes are commonly used in a wide variety of
conditions, such as open air, underwater, and vacuums (such as space). In
open-air applications, such as construction and outdoors repair,
shielded metal arc welding is the most common process. Processes
that employ inert gases to protect the weld cannot be readily used
in such situations, because unpredictable atmospheric movements can
result in a faulty weld. Shielded metal arc welding is also often
used in underwater
welding in the construction and repair of ships, offshore
platforms, and pipelines, but others, such as flux cored arc
welding and gas tungsten arc welding, are also common. Welding in
space is also possible—it was first attempted in 1969 by
Russian
cosmonauts, when they performed experiments to test shielded metal
arc welding, plasma arc welding, and electron beam welding in a
depressurized environment. Further testing of these methods was
done in the following decades, and today researchers continue to
develop methods for using other welding processes in space, such as
laser beam welding, resistance welding, and friction
welding. Advances in these areas could prove indispensable for
projects like the construction of the
International Space Station, which will likely rely heavily on
welding for joining in space the parts that were manufactured on
Earth.
Safety issues
Welding, without the proper precautions, can be a dangerous and unhealthy practice. However, with the use of new technology and proper protection, risks of injury and death associated with welding can be greatly reduced. Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant. To prevent them, welders wear personal protective equipment in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat and flames. Additionally, the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Goggles and welding helmets with dark face plates are worn to prevent this exposure, and in recent years, new helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light. To protect bystanders, translucent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.Welders are also often exposed to dangerous gases
and particulate
matter. Processes like flux-cored arc welding and shielded metal
arc welding produce smoke
containing particles of various types of oxides, which in some cases can
lead to medical conditions like metal fume
fever. The size of the particles in question tends to influence
the toxicity of the
fumes, with smaller particles presenting a greater danger.
Additionally, many processes produce fumes and various gases, most
commonly carbon
dioxide, ozone and
heavy
metals, that can prove dangerous without proper ventilation and
training. Furthermore, because the use of compressed gases and
flames in many welding processes poses an explosion and fire risk,
some common precautions include limiting the amount of oxygen in the air and keeping
combustible materials away from the workplace. Welding fume
extractors are often used to remove the fume from the source and
filter the fumes through a HEPA filter.
Costs and trends
As an industrial process, the cost of welding
plays a crucial role in manufacturing decisions. Many different
variables affect the total cost, including equipment cost, labor
cost, material cost, and energy
cost. Depending on the process, equipment cost can vary, from
inexpensive for methods like shielded metal arc welding and oxyfuel
welding, to extremely expensive for methods like laser beam welding
and electron beam welding. Because of their high cost, they are
only used in high production operations. Similarly, because
automation and robots increase equipment costs, they are only
implemented when high production is necessary. Labor cost depends
on the deposition rate (the rate of welding), the hourly wage, and
the total operation time, including both time welding and handling
the part. The cost of materials includes the cost of the base and
filler material, and the cost of shielding gases. Finally, energy
cost depends on arc time and welding power demand.
For manual welding methods, labor costs generally
make up the vast majority of the total cost. As a result, many
cost-savings measures are focused on minimizing the operation time.
To do this, welding procedures with high deposition rates can be
selected, and weld parameters can be fine-tuned to increase welding
speed. Mechanization and automatization are often implemented to
reduce labor costs, but this frequently increases the cost of
equipment and creates additional setup time. Material costs tend to
increase when special properties are necessary, and energy costs
normally do not amount to more than several percent of the total
welding cost.
In recent years, in order to minimize labor costs
in high production manufacturing, industrial welding has become
increasingly more automated, most notably with the use of robots in
resistance spot welding (especially in the automotive industry) and
in arc welding. In robot
welding, mechanized devices both hold the material and perform
the weld, and at first, spot welding was its most common
application. But robotic arc welding has been increasing in
popularity as technology has advanced. Other key areas of research
and development include the welding of dissimilar materials (such
as steel and aluminum, for example) and new welding processes, such
as friction
stir, magnetic
pulse,
conductive heat seam, and laser-hybrid
welding. Furthermore, progress is desired in making more
specialized methods like laser beam welding practical for more
applications, such as in the aerospace and automotive industries.
Researchers also hope to better understand the often unpredictable
properties of welds, especially microstructure, residual
stresses, and a weld's tendency to crack or deform.
References
- ASM International (2003). Trends in Welding Research. Materials Park, Ohio: ASM International. ISBN 0-87170-780-2
- Blunt, Jane and Nigel C. Balchin (2002). Health and Safety in Welding and Allied Processes. Cambridge: Woodhead. ISBN 1-85573-538-5.
- Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
- Hicks, John (1999). Welded Joint Design. New York: Industrial Press. ISBN 0-8311-3130-6.
- Kalpakjian, Serope and Steven R. Schmid (2001). Manufacturing Engineering and Technology. Prentice Hall. ISBN 0-201-36131-0.
- Lincoln Electric (1994). The Procedure Handbook of Arc Welding. Cleveland: Lincoln Electric. ISBN 99949-25-82-2.
- Weman, Klas (2003). Welding processes handbook. New York: CRC Press LLC. ISBN 0-8493-1773-8.
Notes
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