What Is Welding?- Definition | Types Of Welding

Most individuals envision welding as a gas torch process or an electric arc welding process. They also envision welding as merely melting together metal. In welding’s prior history, that was indeed the case, but today welding is much more than that.

For instance, welds can be made without an arc or flame as in the induction welding (IW) process; without heat as in the pressure welding (PW) process; or with an explosion as in the explosion welding (EW) process. As a matter of fact, welding today is far more than the basics, it can be a very sophisticated process.

Thinking about starting a career in welding? It can help to know key industry terminology and applications, and more. Start with the types of weldings and build your knowledge from there.

What Is Welding?

Welding is a type of fabrication in which two or more pieces are joined together by heat, pressure or both that forms a joint as the parts are cooled. Welding is usually performed on metals and thermoplastics but could be done on wood as well. The welded joint may be called a weldment.

Some materials have specific processes and processes specific to them, while others are called “unweldable”, which is not a term that is found in a dictionary but is relevant and meaningfully descriptive in the science of engineering.

The parts that are joined together are called base materials. The material added to make the joint is called the filler, or consumable paper to help identify its use.

Depending on the shape of this material, you could refer to it in several ways, as a base plate or tube, consumable electrode (for arc welding), flux-cored wire, etc., but they are usually called consumables.

Consumables are usually chosen to be along the same lines of composition to the base material, therefore generating a homogenous weld, but there are instances where the filler with a response of a very different composition and therefore properties is utilized, like when welding brittle cast irons. These welds are termed heterogeneous.

The welded joint may be referred to as a weldment.

Definition Of Welding

The definition of welding as defined by the American Welding Society (AWS) is very technical and captures differences in the welding processes used today.

A weld is defined by the American Welding Society (AWS) as “a localized coalescence (the fusion or growing together of the grain structure of the materials being welded) of metals or nonmetals produced either by heating to the required welding temperatures, with or without the application of pressure, or by the application of pressure alone, and with or without the use of filler materials”.

Welding is defined as “a joining process that produces coalescence of materials by heating them to the welding temperature, with or without the application of pressure or by the application of pressure alone, and with or without the use of filler metal.”

The term coalescence means the fusion or growing together of the grain structure of the materials being welded. The definition includes the terms metals or nonmetals because there are materials like plastics and ceramics that are not metals and can be welded.

The phrase with or without the application of pressure is important because without the application of considerable pressure, some processes will not work like electric resistance welding (ERW) and friction welding (FW).

In some processes of welding only pressure is used to cause localized coalescence like the PW and EW processes. The last part of the definition is “with or without the use of filler materials”, this means that welded joints can be made using only the base material.

A nontechnical definition of welding would be that welding is the joining together of the surface(s) of material with the application of heat only, pressure only, or heat and pressure together so that the surfaces fuse together. The filler material may or may not be added to the joint.

How Does Welding Work?

Welding is the process of joining together two or more workpieces at high temperatures. The heat from welding creates a weld pool of molten material that later cools and fuses together to form a weld. In some cases, the weld may be much stronger than the base metals.

Almost anything can be welded, but there are many types of welding, and they all involve heat or pressure to melt the metals to produce welded joints. Conventional welding is an application of heat, which can often be produced by electrical energy.

The source of heat or pressure can vary considerably depending on the application and the specific material that is welded.

Welding metals is the most common and probably the simplest way of welding; it is easy to understand the principles of welding metals. Many metals can be welded, and there are many different processes for welding metals.

Plastic welding is also very common; wood welding is also in its infancy. Whenever there is heat and/or pressure, it could be considered an application of welding.

There are many factors that impact welding as well. For example, many welding processes require additional tools and shielding gases along with welding electrodes and filler material.

Let’s examine some common welding methods that are used today, and what differentiates each type from the other.

Development Of Welding Processes

Modern welding procedures stem from discoveries and inventions dating as far back as 2000 B.C. when forge welding was the first means of metal joining.

It was a crude process of joining metal by heating and hammering to cause two objects to fuse together, while forge welding is today only used in limited applications.

In 1836, Edmund Davy discovered acetylene gas, and when mixed with oxygen, acetylene produced a flame that was useful for welding and cutting. The arc welding process was based on using heat from an electric arc made by carbon electrodes.

The process of resistance welding, which also used electricity, was developed in the late 1800’s and first used in the early 1900s.

One of the more notable developments was the introduction of an electrode that is consumed into the weld while providing heat from an arc (the shielded metal arc welding process). The amendment of the coating applied to the consumable electrode afforded a wider range of applications for arc welding.

Another improvement of the arc welding process was inert shielding gas added to protect the weld area from the atmosphere (the gas tungsten arc welding process) which proved to be a very important process for welding magnesium and aluminum on fighter planes in World War II.

The electrode for this process was made of tungsten and not consumed in the weld. Helium served as the shielding gas at the beginning, but this was later replaced with cheaper argon.

Developments in the field of welding are still ongoing as new requirements and applications continue to arise in industry. Contemporary welding processes represent the product of refinements and variations of welding processes discovered in the 1800’s.

Types of Welding Process

There are a variety of different welding process types with their own techniques and applications for industry, these include:

Arc Welding

Arc welding is a welding methodology where metals are joined together by heating them using an electric arc. The arc is established by the welding electrode and base metal. The electrode is an element of the welding circuit and the end point of the arc.

The weld area is shielded from the atmosphere until the electrodes cool enough to not draw harmful impurities from the atmosphere.

Arc welding is the most widely used way to weld metals. Arc welding processes are shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux cored arc welding (FCAW), submerged arc welding (SAW), and plasma arc welding (PAW).

Shielded Metal Arc Welding

Shielded metal arc welding (SMAW) is an arc welding process where the arc is protect through the mechanism of the decomposing electrode coating.

During the SMAW process, the electrode is consumed into the weld deposit and the electric arc is used to supply the heat needed to melt the parent materials during welding.

Differences in the coating compositions in the electrode allows for different variations of electrodes to be used for varying uses of SMAW. The most common uses of SMAW is in the fabrication of machinery and structural steel for buildings and bridges.

SMAW, is regarded as the best welding process for production-line products with standard commercial metals, and for making storage and pressure vessels, is as well as for repair work in addition to welding on large fabrications.

Gas Tungsten Arc Welding or Tig Welding

Gas tungsten arc welding (GTAW) is an arc welding process where the arc between the tungsten electrode and weld area are protected by a shielding gas.

GTAW uses a non-consumable tungsten electrode and a shielding gas, which is usually helium or argon for welding.

The GTAW process can be used to create an autogenous weld by welding without filler metal, or welding with filler metal. GTAW is often used to weld thin-wall tubing and deposit the root pass in pipe joints. GTAW also provides a very high quality weldment.

Gas Metal Arc Welding or Mig Welding

Gas metal arc welding (GMAW) is an arc (or gas metal arc) welding process that accomplishes welding with an arc between a continuously fed, consumable wire electrode, and the weld puddle.

Argon is used as a shielding gas for non-ferrous metals (aluminum), while carbon dioxide/carbon dioxide mixtures (75/25, 98/2) with argon are used as shielding gas for steels.

Because the GMAW process uses a continuously fed, consumable wire, it eliminates the need to stop and replace electrodes. The GMAW process has become more popular in manufacturing because of this reason.

Flux Cored Arc Welding.

Flux-cored arc welding (FCAW) is a distinct arc welding process that uses a tubular electrode with flux in the core. FCAW produces fast, clean welds with superior appearance, and has high deposition rates. In addition, FCAW can be automated in situations where arc welding is required.

Again, the major advantage of FCAW over SMAW is the tube or continuous-feed of electrode and higher productivity rates that lead to lower production costs.

FCAW is typically used to weld carbon, low-alloy, stainless steel and cast iron materials. Applications include field and shop fabrications.

Submerged Arc Welding.

Submerged arc welding (SAW) is a type of arc welding process in which an arc forms between a bare metal electrode and the weld pool. In this process, the electrode, arc, and weld pool are submerged under granular flux poured over the base metal.

SAW is limited to flat or low curvature base metals. It is well suited to producing high quality weld metal with high deposition rates. The surface of the weld is smooth, with no spatter.

SAW is an automated process that is most frequently adopted in heavy steel plate fabrication, as the process is suitable for joining thick metals requiring deep penetration welding.

Plasma Arc Welding.

Plasma arc welding (PAW) is an arc welding process which utilizes a constricted arc between a non-consumable tungsten electrode and the weld pool (transferred arc) or constricting nozzle (non-transferred arc).

Transferred arc PAW creates a deep, narrow and uniform weld zone; it is also capable of being used with almost all metals. Transferred arc PAW is used to weld high-strength thin metal. Non-transferred arc PAW is normally used for thermal spraying.

Oxyfuel Welding/ Oxyacetylene Welding

Oxyfuel welding (OFW) is a welding process that uses heat from the combustion of a mixture of oxygen and fuel, such as acetylene, methylacetylene-propadiene stabilized (MAPP) gas, propane, natural gas, hydrogen, or propylene .

The heat is produced from burning a combustible gas and oxygen. OFW welding processes use filling metal or do not use filler metal, if nothing is used in the joint it is autogenous. An autogenous weld is a fusion weld without filler metal.

Oxyacetylene welding is the most common oxyfuel welding process. Oxyacetylene welding (OAW) is an oxyfuel welding process that uses acetylene as a fuel gas.

Oxyacetylene welding is used in all metalworking sectors mainly because of its versatility and mobility, but the process is more used in maintenance and repair work.

Resistance Welding

Resistance welding (RW) is a category of welding process whereby welding is achieved from the heat generated from the resistance of the flow of current through the metals being joined. A resistance welding machine is capable of fusing metals together through heat and pressure.

RW is employed to make localized (spot) joints or continuous (seam) joints with the potential for rapid welding of seams being a useful feature of RW.

RW employs special fixtures and automatic handling equipment for mass producing automobile bodies, electrical equipment, hardware, or other household goods. RW is suitable for joining nearly all steels, including stainless steel, aluminum alloys, and some dissimilar metals.

How To Select Welding Process?

The choice of joining process for a particular job is controlled by several factors. There is no one rule that governs which welding process will be selected for a particular job. Here are some factors that must be examined when selecting a joining process.

• Availability of equipment: The kinds, capacity, and condition of equipment that can be used to make the welds.
• Repetition of the operation: How many of the welds will be part of completing the job, if all are they the same?
• Quality requirements: Is this going to be used on a piece of furniture, to repair a piece of equipment or join a pipeline?
• Location of work: Is the weld in a shop or on a remote job site?
• Materials to be joined: Are the parts made out of a standard metal or some exotic alloy?
• Appearance of finished product: Is this going to be a weldment that is needed only to test an idea, or will this be a permanent structure?
• Size of parts to be welded: Are the parts small, large or different sizes, and will they be able to moved or must the weld be completed in place?
• Time available for work: is this a rush job needing fast repair, or is there time to pre-weld or clean after welding?
• Skill or experience of workers: Do the welders have the ability to do the job?
• Cost of materials: Will the weldment justify the cost of special equipment and/or materials, or finishing time?
• Code or specification requirements: Often determining the process is dictated by governing agency, codes, or standards.

The establishment and/or welder must not only create the selection of the welding procedure but also consider the method to apply it.

The methods of manual operation, semiautomatic operation, machine operation, automatic operation, and automated operation will all generate welds, cuts or braze.

• Manual: The welder manipulates the whole process.
• Semiautomatic: The filler metal is fed in automatically, and all other manipulation is performed again manually by the welder.
• Machine: The operation is performed mechanically under observation and correct of a welding operator.
• Automatic: The operation is performed repeatedly with a programmed machine that can do the entire operation without operator involvement.
• Automated: The operation is performed repeatedly by a robot or other machine that is programed to flexibly to do a variety of processes.

Advantages Of Welding

• Because no hole is required for welding, there is no area reduction. Thus structural members spend much less time taking the load.
• Welding filler plates, gusseted plates, connecting angles, etc. are not needed using welding, results in a lower overall weight of the structure to fabricate.
• The overall economy of downsizing is better with welding, because of less labor/material, and weight.
• The efficiency of the welded joint is better than the riveted joint.
• Welded joints look better than the bulky riveted/butted joints.
• The speed of fabrication is faster than riveted joints.
• Solid rigid joints can be provided by using the welding process.

Disadvantages Of Welding

• The fatigue strength is less than that of the members joined because welded joints are brittle.
• Matters such as uneven heating & cooling of the members during the welding can lead to distortion of the members which results in additional stress.
• Welding involves skilled labor and also requires electricity.
• Welded connections do not have any provision for expansion and contraction and therefore there is the possibility of racks.
• The inspection of welding work is more difficult and is more costly than riveted work.

Application Of Welding

Manufacturers use modern welding processes to make a multitude of items. Although not noticed, some examples of welded fabrications are buses, ships, buildings, bridges, and amusement park rides.

Welding has made possible the exploration of space and has been important from the first design of rockets to what we have today as the aerospace market. Many of the advancements in aerospace welding have helped improve the quality of life for everyone.

Many of the experiments conducted aboard the Space Station have used welding and metal joining for advances in technology. Many advanced welding processes were used to build the International Space Station. One day, welders will help build even larger structures in the vacuum of space.

Welding is used in the manufacture of cars, farm equipment, everyday appliances, computer components, mining machines, and construction machines. Even today, railway engines, subways, furnaces, boilers, air conditions, and hundreds of everyday items are manufactured through welding.

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