What is Welding? – Definition, Processes, and Types

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 usually used on metals and thermoplastics but can also be used on wood. The completed welded joint may be referred to as a weldment.

What is Welding?

Welding is a fabrication process that joins two or more pieces of metal or thermoplastics together by heating the material to its melting point and applying pressure to fuse the parts together.

To create a weld, a material known as filler or consumable is added to the parent material to help form the join. The parent material and filler material must be chosen carefully to ensure that they are compatible and will result in a strong, homogenous weld. If the filler material is not similar in composition to the parent material, the result is referred to as a heterogeneous weld.

Different materials may require different welding processes and techniques, and some materials are considered ” non-weldable.”

In welding, a filler material is typically added to the joint in order to create a pool of molten material that will cool and form a joint. The joint created by welding can be stronger than the base metal itself, depending on the configuration of the weld (butt, full penetration, fillet, etc.). Pressure can also be used in conjunction with heat or by itself to produce the weld.

It is important to protect the filler metal or melted metal from contamination or oxidation during the welding process. This is achieved through the use of a form of a shield, which helps to prevent any unwanted reactions from taking place.

Consumables are usually chosen to be similar in composition to the base metal, so they form a homogeneous weld, but there are cases, such as welding of brittle cast iron, where fillers of very different compositions are used and so the properties are very different. These welds are called dissimilar welds.

A completed welded joint is sometimes called a weldment.

How Does Welding Work?

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal (parent metal). There are two main categories of welding: arc welding and torch welding.

Arc welding uses an electrical arc to generate heat, which melts the work materials and filler material to join the parts. In this process, a grounding wire is attached to the welding material or metal surface and an electrode lead are placed on the material to be welded.

When the electrode lead is pulled away from the material, an electric arc is generated, melting the workpieces and filler material.

There are several different methods of arc welding, including Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (MIG), and Gas Tungsten Arc Welding (TIG). Each method has its own advantages and disadvantages, such as ease of use, speed, versatility, and quality of the welds.

Torch welding, on the other hand, uses an oxyacetylene torch to melt the working material and filler material. The welder controls the torch and filler material simultaneously, which gives the welder more control over the weld. Torch welding is not as commonly used in industry, but it is still frequently used for maintenance and repair work and in sculpting.

Types of Welding Processes

Gas Metal Arc Welding (GMAW/MIG).

Gas Metal Arc Welding (GMAW/MIG) is a welding process that uses a shielding gas along with a wire electrode to join two metals. It is a commonly used industrial welding process that can be used to weld plate and large bore pipes.

The GMAW/MIG welding process uses four primary methods of metal transfer:

  • Globular transfer. This method produces a rougher weld bead due to the large size of the metal droplets and the likelihood of spattering. This method is best for welding thick metal plates in horizontal positions.
  • Short-circuiting. This method works by rapidly tapping the welding wire onto the base metal many times per second, resulting in little spattering. This method can be used in any welding position.
  • Spray transfer. This method delivers a steady flow of tiny droplets of molten metal, maintaining a steady-contact arc weld during the process. This method is best used on horizontal, thick, and flat pieces.
  • Pulsed-spray. This method is similar to Spray Transfer but uses a high-low current pulse to allow for micro-cooling periods. This method can be used on a wide variety of metal plate thicknesses and in almost all welding positions.

Gas Tungsten Arc Welding (GTAW/TIG).

Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding, is a welding process that uses a fixed tungsten electrode to produce the weld. This process is commonly used to weld thick sections of stainless steel or non-ferrous metals. It is considered a more precise and controlled method of welding compared to other welding methods such as MIG, Stick, or Flux Cored Arc Welding.

The melting point of non-ferrous metals, such as stainless steel, can vary greatly, so it is important to identify the composition of the base metal before welding. Stainless steel must contain at least 11% chromium to be considered as such, and this presence narrows the temperature range for welding to 2,750 +/- degrees F. Carbon steel, on the other hand, melts in the 2,600 to 2,800-degree F range.

TIG welding aluminum requires a high level of skill, as it requires a steady hand, a trained eye, and an artistic touch to create a smooth, seamless weld. This type of welding is considered a showcase of welding skills and is highly valued in the welding industry.

Shielded Metal Arc Welding (SMAW).

Shielded Metal Arc Welding (SMAW) is a type of manual welding process that uses an electric arc to join two metal parts together. The process involves using a stick electrode (a metal rod coated with a flux material) that is connected to an electric power source.

When the electrode is touched to the metal parts to be joined, an electric arc is formed between the electrode and the metal. This heat generated by the arc melts the metal, fusing the two parts together.

SMAW is commonly used in the construction of steel structures, as well as in industrial fabrication for welding iron, steel, and mild steel pipe. The welder must have a high level of skill, as the process is manual and requires precision to produce a strong and reliable weld. The finished weld must be able to pass a destructive bend test, which checks the strength and reliability of the weld.

SMAW can be used to weld a variety of metal materials, including carbon steel, alloyed steel, stainless steel, cast iron, and ductile iron. It can also be used for some non-ferrous metals such as nickel and copper but is rarely used for welding aluminum due to the difficulty in controlling the heat input and the risk of melting the metal.

Flux Cored Arc Welding (FCAW).

Flux Cored Arc Welding (FCAW) is a semi-automatic welding method that uses a continuous flux-cored wire as the filler material and an arc welding power source to heat the metal being welded.

Unlike other welding methods, FCAW uses a self-shielding wire, which eliminates the need for shielding gas and provides higher portability and ease of use. This makes it ideal for outdoor or construction projects where access to shielding gas may be limited.

One of the benefits of FCAW is its high welding speed, which allows for faster completion of projects. The speed of the wire feed, voltage levels, polarity used, and operating angles can all be adjusted to match the specific welding project requirements. However, the fast-welding speed also means that the newly joined metal cools quicker, which can result in porosity (small holes) in the welded joint if not handled properly.

It is important to note that FCAW produces a significant amount of smoke and fumes during the welding process. It is recommended to use FCAW in outdoor settings or under industrial ventilation hoods to ensure proper ventilation and reduce exposure to harmful fumes.

Welding Equipment

Welding is a specialized job that requires you to have a variety of essential tools, including (but not restricted to) the following equipment:

  • Welding gun. The welding gun is the handheld tool used to control the flow of the welding electrode, which is the metal rod used to join the metal pieces together.
  • Welding torch. A welding torch is used to heat the metal pieces to the required temperature.
  • Wire brush. A wire brush is used to clean the metal surface prior to welding.
  • Chipping slag hammer. A chipping slag hammer is used to remove any slag (residue) left on the metal after welding.
  • Angle grinder.  An angle grinder is a power tool used for cutting, grinding, and polishing metal.
  • Tape measure. A tape measure is used to measure the length and width of the metal pieces to be welded.
  • Welding magnets. Welding magnets are used to hold the metal pieces in place while welding.
  • Soapstone marker. A soapstone marker is used to mark the metal pieces prior to welding.
  • Pliers. Pliers are used to grip and bend metal.
  • C-clamps. C-clamps are used to hold the metal pieces together while welding.
  • Electrode tip cleaners. Electrode tip cleaners are used to clean the tip of the welding electrode.
  • Flint strikers. Flint strikers are used to ignite the welding torch.
  • Cold chisels. Cold chisels are used to shape the metal pieces prior to welding.
  • Screwdrivers. Screwdrivers are used to tighten screws and bolts on the welding equipment.
  • Charged electrode. A charged electrode is an electrically charged metal rod used to join the metal pieces together.
  • Wire and electrode feed. The wire and electrode feed is the mechanism used to control the flow of the welding electrode to the welding gun.

Advantages and Disadvantages of Welding


Welding has many advantages, including the following:

  • Strong and durable joints. Welding creates a permanent bond between two materials, making it one of the strongest and most durable methods of joining materials.
  • Simple process with a great finish. Welding is a simple process that produces a clean and polished finish. This makes it ideal for applications that require a high-quality appearance.
  • Stronger welds. When used with filler material, welding produces a stronger bond than the base material, making it ideal for applications where strength is a key factor.
  • Flexibility. Welding can be performed anywhere, making it an ideal solution for projects that require on-site fabrication or repair.
  • Affordability. Welding is an economical process that is widely available and accessible to a range of industries.
  • Widely used in various industries. Welding is used in a wide range of industries, including construction, automobile, aerospace, and many others.


Some of the disadvantages of welding include:

  • Health hazards. Welding can expose workers to harmful fumes and radiation, which can cause respiratory problems, eye damage, and skin burns.
  • Cost. Welding is often a relatively expensive process, especially when specialized equipment and materials are required.
  • Equipment maintenance. Welding equipment is often complex and requires frequent maintenance and repairs, which can be time-consuming and costly.
  • Skill and training. Welding requires a high level of skill and training, and the quality of the weld depends on the experience and expertise of the welder.
  • Material limitations. Certain materials cannot be welded, and others may require special techniques or equipment.
  • Quality control. Welds must be regularly checked for quality and strength, and if defects are found, the entire weld may need to be redone.
  • Post-weld cleaning. Welds often require cleaning to remove excess material and ensure that the surface is smooth and clean.
  • Heat distortion. Welding generates heat, which can cause materials to warp or distort, affecting the final product’s quality and appearance.

Application Of Welding

Welding processes are commonly used across a range of industries including aerospace, automotive, energy, and construction amongst others. Used to join metals, thermoplastics, or wood for a variety of applications, it is also used to create artwork by a growing community of artists. Also, welding is widely used in a variety of applications, including:

  • Construction. Welding is commonly used in the construction industry for building and repairing structures, including bridges, buildings, and pipelines.
  • Manufacturing. Welding is an important tool in the manufacturing of various products, including cars, airplanes, boats, and other machines and equipment.
  • Repair and maintenance. Welding is also used to repair broken or damaged parts in various industries, such as automotive, aerospace, and electrical.
  • Art and sculpture. Welding is also used in the creation of artistic and sculptural works, including large-scale public installations, sculptures, and other works of art.

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