Welding: processes, equipment, safety, history and applications

Welding joins metals (and some non‑metals) by melting or pressure. Overview of common processes, equipment and materials, safety practices, brief history, uses and distinctions from soldering or brazing.

Author: Leandro Alegsa Creation date: November 13, 2022 Last updated: May 22, 2026

Overview

Welding is a family of fabrication processes that join pieces of metal or thermoplastics by causing coalescence through melting, pressure, or both. Heat can be supplied by electricity (an arc or resistance) or by a flame, among other energy sources. Some methods add filler material to strengthen the joint; others rely on the parent materials alone.

Main processes

The practice of welding includes a number of distinct processes, each suited to particular materials and applications. Common categories are:

Arc welding — an electric arc melts the workpieces and usually a filler; examples include shielded metal arc welding (SMAW), gas metal arc welding (GMAW or MIG), and gas tungsten arc welding (GTAW or TIG). Arc welding is widely used in industry.
Resistance welding — heat is generated by passing current through contacting surfaces; spot and seam welding are typical forms. Resistance welding is common in automotive assembly.
Oxy‑fuel (gas) welding — a flame from burning oxygen and a fuel gas melts the metal; useful for repair, cutting, and when portable heat is needed.
Solid‑state and specialty processes — methods such as friction stir welding, laser welding, and electron‑beam welding join materials without full melting, offering advantages for certain alloys and precision work.

Equipment and materials

Basic welding setups include a power source, an electrode or filler, grounding clamps, and, for some processes, shielding gas to protect the molten metal from the atmosphere. Consumables vary by process: rods or wires for filler metal, flux to stabilize the arc or remove oxides, and specialized electrodes. Joints are prepared in specific geometries (butt, lap, T, corner) and can be executed in multiple positions, each requiring different technique and equipment settings.

Safety and personal protection

Welding involves intense light, hot spatter, fumes, and ultraviolet radiation. Observers and operators must use appropriate personal protective equipment: a welding helmet with a properly rated filter to protect eyes and face, and safety goggles when needed. Additional PPE includes flame‑resistant gloves and clothing, hearing protection, and respirators or local exhaust to manage fumes. Sparks and hot metal create fire risks, so workspace housekeeping and ventilation are essential.

History and applications

Joining metals by heating has ancient roots in brazing and forge welding, but modern electric and gas welding developed in the late 19th and early 20th centuries as reliable power sources and consumables became available. Today welding is fundamental in construction, shipbuilding, pipelines, automotive and aerospace manufacturing, heavy equipment, and artistic metalwork. Automated and robotic welding increasingly handle high‑volume, repetitive tasks with consistent quality.

Distinctions and notable facts

Welding differs from soldering and brazing in temperature and metallurgical bonding; soldering uses a low‑melting filler without melting the base metal, while brazing uses higher temperatures but still below the base‑metal melting point. Some advanced processes create joints without melting (solid‑state), reducing distortion and retaining material properties. Qualifications and codes govern many structural welding tasks, and training plus inspection are critical for reliable, safe joints.

For further reading on specific processes, equipment standards, or safety guidance, consult technical manuals and recognized industry sources or training programs. Links to introductory resources and standards are often provided by educational institutions and professional organizations.

Joining two tubes by oxyacetylene welding with filler wire, 1942

History of welding

→ Main article: History of welding

See also: History of production engineering

Outline of the welding processes

The welding processes can be classified according to

Type of energy acting on the workpiece

thermal energy, for example during fusion welding

thermal energy with simultaneous or subsequent pressing together of the workpieces, for example in many resistance welding processes

mechanical energy, for example in cold pressure welding

mechanical energy that is converted into thermal energy, for example in friction welding

Type of base material

Metals
Thermoplastics
other materials and combinations of materials, such as glass

Purpose of welding

Joint welding is used to join workpieces together
Deposition welding is used to coat a workpiece; if the base material and the deposit material are different, a further distinction is made between the deposition welding of

Armour
Plating
Buffer layers

physical process of welding

Fusion welding is welding with localized melt flow, without application of force with or without filler metal of the same type (ISO 857-1). In contrast to brazing, the liquidus temperature of the base materials is exceeded. In principle, all materials that can be transferred to the molten phase can be joined by fusion welding. In many processes, additional material is added, for example in the form of a welding wire.
Pressure welding brings the materials to be joined to the required welding temperature using different forms of energy, whereupon the joint is produced under the action of a force. Pressure welding does not require any additional material such as welding wire.

Degree of mechanization

Manual welding

than purely manual welding
as partially mechanised welding, in which the filler metal and the auxiliary materials (shielding gases) are supplied mechanised, but the torch is moved manually,

all-mechanical welding
(fully) automated welding

Classification of the metal welding processes according to DIN 1910-100 with order numbers according to DIN EN ISO 4063

Questions and Answers

Q: What is welding?

A: Welding is a process of heating pieces of metal using electricity or a flame in order to melt and join them together.

Q: How many different types of welding are there?

A: There are several different types of welding, including arc welding, resistance welding, gas welding, and Oxy-fuel welding.

Q: Which type of welding is the most common?

A: The most common type of welding is arc welding.

Q: Why is it important to wear special eye protection when near arc welding?

A: The arc produced during welding is very bright and looking at it without visual protection can cause permanent eye damage.

Q: Can welding cause burns?

A: Yes, hot sparks from welding can cause burns to any exposed skin.

Q: What is Oxy-fuel welding?

A: Oxy-fuel welding is a type of welding that uses a flame to heat up the metal instead of an electric arc.

Q: Are there any other types of welding that do not use an arc?

A: Yes, there are other types of welding that do not use an arc besides Oxy-fuel welding.

Author

Creation date: November 13, 2022

Last updated: May 22, 2026