Welding
is a fabrication or sculptural 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 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.
Arc welding and
oxyfuel welding were among the first processes to develop late in the
century, and electric resistance welding followed soon after.
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 , electron beam welding, electromagnetic pulse welding and friction stir welding in the latter half of the century.
Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.
ContentsThese 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.
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.
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.
One of the most common types of arc welding is shielded metal arc welding ; it is also known as manual metal arc welding or stick welding.
Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of filler material and is covered with a flux that protects the weld area from oxidation and contamination by producing carbon dioxide gas during the welding process.
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 , aluminum, copper , and other metals.
Gas metal arc welding , 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.
A related process, flux-cored arc welding , 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 , or tungsten inert gas 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.
Submerged arc welding 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.
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.
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.
Developments in this area include laser-hybrid welding , which uses principles from both laser beam welding and arc welding for even better weld properties, laser cladding and X-ray welding .
Solid-state Like the first welding process, forge welding, some modern welding methods do not involve the melting of the materials being joined.
Other
solid-state welding processes include friction welding ,
electromagnetic pulse welding , co-extrusion welding , cold welding ,
diffusion bonding , exothermic welding , high frequency welding , hot
pressure welding , induction welding , and roll welding .
Many welding processes require the use of a particular joint design; for example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed on lap joints.
Other welding methods, like shielded metal arc welding, are extremely versatile and can weld virtually any type of joint.
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 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.
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.
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, designed by Stefan Bryła of the Warsaw University of Technology in 1927, and built across the river Słudwia Maurzyce near Łowicz, Poland in 1929.
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.
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.
Other recent developments in welding include the 1958 breakthrough of electron beam welding, making deep and narrow welding possible through the concentrated heat source.
To do this, welding procedures with high deposition rates can be selected, and weld parameters can be fine-tuned to increase welding speed.
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 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 increases in popularity as technology advances.
Other key areas of research and development include the welding of dissimilar materials 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.
Without proper fusion to the base materials provided by sufficient arc time on the weld, a project inspector cannot ensure the effective diameter of the puddle weld therefore he or she cannot guarantee the published load capacities unless they witness the actual installation. This method of puddle welding is common in the United States and Canada for attaching steel sheets to bar joist and structural steel members.
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 , electron beam welding, electromagnetic pulse welding and friction stir welding in the latter half of the century.
Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.
ContentsThese 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.
Processes
Arc
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.
Power
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.
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.
One of the most common types of arc welding is shielded metal arc welding ; it is also known as manual metal arc welding or stick welding.
Processes
Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of filler material and is covered with a flux that protects the weld area from oxidation and contamination by producing carbon dioxide gas during the welding process.
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 , aluminum, copper , and other metals.
Gas metal arc welding , 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.
A related process, flux-cored arc welding , 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 , or tungsten inert gas 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.
Submerged arc welding 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.
Gas welding
It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. 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.
Resistance
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.
Energy beam
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.
Developments in this area include laser-hybrid welding , which uses principles from both laser beam welding and arc welding for even better weld properties, laser cladding and X-ray welding .
Solid-state Like the first welding process, forge welding, some modern welding methods do not involve the melting of the materials being joined.
Many welding processes require the use of a particular joint design; for example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed on lap joints.
Other welding methods, like shielded metal arc welding, are extremely versatile and can weld virtually any type of joint.
Quality
Many distinct factors influence the strength of welds and the material around them, including the welding method, the amount and concentration of energy input, the weldability of the base material, filler material, and flux material, the design of the joint, and the interactions between all these factors.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 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.
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.
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.
History
In 1881–82 a Russian inventor Nikolai Benardos created the first electric arc welding method known as carbon arc welding , using carbon electrodes.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, designed by Stefan Bryła of the Warsaw University of Technology in 1927, and built across the river Słudwia Maurzyce near Łowicz, Poland in 1929.
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.
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.
Other recent developments in welding include the 1958 breakthrough of electron beam welding, making deep and narrow welding possible through the concentrated heat source.
Trends
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.To do this, welding procedures with high deposition rates can be selected, and weld parameters can be fine-tuned to increase welding speed.
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 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 increases in popularity as technology advances.
Other key areas of research and development include the welding of dissimilar materials 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.
Without proper fusion to the base materials provided by sufficient arc time on the weld, a project inspector cannot ensure the effective diameter of the puddle weld therefore he or she cannot guarantee the published load capacities unless they witness the actual installation. This method of puddle welding is common in the United States and Canada for attaching steel sheets to bar joist and structural steel members.
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