What Is Welding?- Definition | Types Of Welding

Most people think of welding as either a gas torch or electric arc welding process. They also think of it as just melting metal together. In the earlier history of welding, that was true, but welding is a lot more than that today.

For example, welds can be made without an arc or flame with the induction welding (IW) process; without heat using the pressure welding (PW) process; or with an explosive using the explosion welding (EW) process. In fact, welding today is much more than the basics; it can be a very sophisticated process.

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

What Is Welding?

Welding is a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool. Welding is typically used on metals and thermoplastics, but can also be used on wood. The completed welded joint can be referred to as a weldment.

Some materials require the use of specific processes and techniques. Some are considered “unweldable,” a term not typically found in dictionaries but useful and descriptive in engineering.

The parts that are joined are known as base materials. The material that is added to form the joint is called a filler or consumable. Because of the shape of these materials, they can be referred to as a base plate or tube, flux-cored wire, consumable electrode (for arc welding), etc.

Consumables are usually chosen to be similar in composition to the base material, thus forming a homogenous weld, but there are occasions, such as when welding brittle cast irons, when a filler with a very different composition and, therefore, properties is used. These welds are called heterogeneous.

The completed welded joint may be referred to as a weldment.

Definition Of Welding

The American Welding Society’s (AWS) definition of welding is very technical to reflect the 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 the materials 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 materials such as plastics ceramics, and so forth, are not metals and they can be welded.

The phrase with or without the application of pressure is important because without the application of significant pressure, some of the processes would not work, such as electric resistance welding (ERW) and friction welding (FW).

In some welding processes only, pressure is used to cause localized coalescence such as the PW and EW processes. The last part of the definition says with or without the use of filler materials, meaning welded joints can be made by using only the base material.

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

How Does Welding Work?

Welding works by joining two or more workpieces together at high temperatures. The heat causes a weld pool of molten material which after undergoing cooling, solidifies as one piece, forming a weld. The weld can even be stronger than the parent metals.

There are many different types of welding but all of them involve heat or pressure to melt the metals to create welded joints. The source of heat or pressure may vary depending on the application and the material used.

Metals are known as the most commonly welded materials, given their easy and straightforward welding principles. Plastic welding is also quite widespread but welding wood is just in its nascent phase.

The welding process is influenced by many factors, such as the need for specific additional tools, shielding gases, welding electrodes, and filler material. Let’s have a closer look at some of the most common welding methods used today and find out what makes each of them unique.

Development Of Welding Processes

Modern welding processes evolved from discoveries and inventions dating back to the year 2000 B.C. when forge welding was first used as a means of joining two pieces of metal. It was a crude process of joining metal by heating and hammering until the objects were fused together. Today, forge welding is used only in limited applications.

Acetylene gas was discovered in 1836 by Edmund Davy. When combined with oxygen, acetylene produced a flame suitable for welding and cutting. Applying heat generated from an electric arc between carbon electrodes was the basis for the arc welding process.

Resistance welding, which also uses electricity, was developed in the late 1800s and first used in the early 1900s.

One of the most significant developments at the time was the invention of an electrode that is consumed into the weld while providing heat from an arc (the shielded metal arc welding process). Modifications to the coating applied on the consumable electrode allowed greater applications for arc welding.

Another improvement in the arc welding process was the addition of an inert shielding gas to protect the weld area from atmospheric contamination (the gas tungsten arc welding process). This proved to be an especially important process in welding magnesium and aluminum on World War II fighter planes. The electrode used was made out of tungsten and was not consumed into the weld. Originally, helium was used as a shielding gas but was later replaced by the less expensive argon.

New developments in the field continue to address new requirements and applications in industry. Current welding processes are the product of continued refinements and variations of the welding processes discovered in the 1800s.

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 type of welding process that joins metals by heating them with an electric arc. The arc is struck between a welding electrode and the base metal The welding electrode is a component of the welding circuit that terminates at the arc.

The joint area is shielded from the atmosphere until it is cool enough to prevent the absorption of harmful impurities from the atmosphere.

Arc welding is the most common method of welding metals. Arc welding processes include shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), Flux cored arc welding (FCAW), and submerged arc welding (SAW). and plasma arc welding (PAW).

Shielded Metal Arc Welding

Shielded metal arc welding (SMAW) is a type of arc welding process in which the arc is shielded by the decomposition of the electrode coating. The electrode is consumed into the weld while providing heat from an electric arc.

Variations in the composition of the electrode coating allow different applications of the SMAW process. Common applications of SMAW are in the fabrication of machinery and structural steel for buildings and bridges.

SMAW is considered ideal for making storage and pressure vessels as well as for production-line products using standard commercial metals. SMAW is also used in repair work and in welding large structures.

Gas Tungsten Arc Welding or Tig Welding

Gas tungsten arc welding (GTAW) is a type of arc welding process in which a shielding gas protects the arc between a non-consumable (does not become pan of the weld) tungsten electrode and the weld area. GTAW uses a non-consumable tungsten electrode and a shielding gas, usually helium or argon for welding.

The GTAW process can be used to weld using filler metal, or without Filler metal to form an autogenous weld. GTAW is widely used for joining thin-wall tubing and depositing the root pass in pipe joints. GTAW produces a very high-quality weldment.

Gas Metal Arc Welding or Mig Welding

Gas metal arc welding (GMAW) is an arc welding process that uses an arc between a continuous wire electrode and the weld pool. Argon is used as a shielding gas for non-ferrous metals such as aluminum, and carbon dioxide/carbon dioxide mixtures (such as 75/25, 98/2) with argon are used as a shielding gas for steels.

The GMAW process uses a continuously fed consumable wire, eliminating the need to stop and change electrodes. This has increased the popularity of GMAW in manufacturing.

Flux Cored Arc Welding.

Flux-cored arc welding (FCAW) is an arc welding process that uses a tubular electrode with flux in its core. FCA W produces fast, clean welds with excellent appearance and high deposition rates, and the process can be automated.

Like GMAW, the primary benefit of FCAW over SMAW is the higher productivity rate possible with the continuous-feed system, which also results in lower production costs.

FCAW is commonly used to weld carbon, low-alloy, stainless steel, and cast iron. Typical applications include field and shop fabrications.

Submerged Arc Welding.

Submerged arc welding (SAW) is a type of arc welding process that uses an arc between a bare metal electrode and the weld pool. The electrode, arc. and weld pool are submerged in a granular flux poured on the base metal.

SAW is limited to flat or low curvature base metals. SAW produces high-quality weld metal with fast deposition rates. The weld surface is smooth with no spatter. SAW is automated and most often used to join thick metals requiring deep penetration, such as in heavy steel plate fabrication.

Plasma Arc Welding.

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

Transferred arc PAW produces a deep, narrow, uniform weld zone and is suitable for almost any metal. Transferred arc PAW is used for welding high-strength, thin metal. Non-transferred arc PAW is typically used for thermal spraying.

Oxyfuel Welding/ Oxyacetylene Welding

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

The heat is obtained from the combustion of a combustible gas and oxygen. OFW welding processes are used with or without filler metal, if filler metal is not used in the joint, the weld is autogenous. An autogenous weld is a fusion weld made without filler metal.

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

Because of its flexibility and mobility. oxyacetylene welding is used in all metalworking industries but is most commonly used for maintenance and repair work.

Resistance Welding

Resistance welding (RW) is a type of welding process in which welding occurs from the heat obtained by resistance to the flow of current through the metals joined. A resistance welding machine fuses metals together by heat and pressure.

RW is used to make localized (spot) or continuous (seam) joints. An advantage of resistance welding is its adaptability to rapid fusion of seams.

RW uses special fixtures and automatic handling equipment for the mass production of automobile bodies, electrical equipment, hardware, or other domestic goods. RW can be used for joining almost all steel, including stainless steel, and aluminum alloys. and some dissimilar metals.

How To Select Welding Process?

The selection of the joining process for a particular job depends on many factors. No one specific rule controls the welding process to be selected for a certain job. The following are a few of the factors that must be considered when choosing a joining process.

• Availability of equipment—The types, capacity, and condition of the equipment that can be used to make the welds.
• Repetitiveness of the operation—How many of the welds will be required to complete the job, and are they all the same?
• Quality requirements—Is this weld going to be used on a piece of furniture, to repair a piece of equipment, or to join a pipeline?
• Location of work—Will the weld be 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 the finished product—Will this be a weldment that is needed only to test an idea, or will it be a permanent structure?
• Size of the parts to be joined—Are the parts small, large, or different sizes, and can they be moved, or must they be welded in place?
• Time available for work—Is this a rush job needing a fast repair, or is there time to allow for pre-weld and post-weld cleanup?
• Skill or experience of workers—Do the welders have the ability to do the job?
• Cost of materials—Will the weldment be worth the expense of special equipment materials or finishing time?
• Code or specification requirements—Often the selection of the process is dictated by the governing agency, codes, or standards.

The welding engineer and/or the welder not only must decide on the welding process but also must select the method of applying it.

The following methods, manual operation, semiautomatic operation, machine operation, automatic operation, and automated operation, are used to perform welding, cutting, or brazing operations.

• Manual—The welder is required to manipulate the entire process.
• Semiautomatic—Filler metal is added automatically, and all other manipulation is done manually by the welder.
• Machine—Operations are done mechanically under the observation and correction of a welding operator.
• Automatic—Operations are performed repeatedly by a machine that has been programmed to do an entire operation without interaction of the operator.
• Automated—Operations are performed repeatedly by a robot or other machine that is programmed flexibly to do a variety of processes.

Advantages Of Welding

• As no hole is required for welding, hence no reduction of area. So structural members are more effective in taking the load.
• In welding filler plates, gusseted plates, connecting angles etc, are not used, which leads to reduced overall weight of the structure.
• Welded joints are more economical as less labor and less material is required.
• The efficiency of the welded joint is more than that of the riveted joint.
• The welded joints look better than the bulky riveted/butted joints.
• The speed of fabrication is faster in comparison with the riveted joints.
• Complete rigid joints can be provided with the welding process.

Disadvantages Of Welding

• Welded joints are more brittle and therefore their fatigue strength is less than the members joined.
• Due to uneven heating & cooling of the members during the welding, the members may distort resulting in additional stresses.
• Skilled labor and electricity are required for welding.
• No provision for expansion and contraction is kept in welded connection & therefore, there is a possibility of racks.
• The inspection of welding work is more difficult and costlier than the riveting work.

Application Of Welding

Modern welding techniques are used in the construction of numerous products. Ships, buildings, bridges, and recreational rides are examples of welded fabrications,

The exploration of space would not be possible without modern welding techniques. From the very beginning of early rockets to today’s aerospace industry, welding has played an important role. Many aerospace welding advancements have helped improve our daily lives.

Many experiments aboard the Space Station have involved welding and metal joining. The International Space Station was constructed using many advanced welding techniques. Someday, welders will be required to build even larger structures in the vacuum of space.

Welding is used extensively in the manufacture of automobiles, farm equipment, home appliances, computer components, mining equipment, and construction equipment. Railway equipment, furnaces, boilers, air-conditioning units, and hundreds of other products we use in our daily lives are also joined together by some type of welding process.

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