What is Welding? Definition, Types & How Processes Work
May 24, 2025
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What is Welding? Definition, Types & How Processes Work

Welding is a process used in metal fabrication, construction, manufacturing, and much more.

From repairing machinery to constructing vehicles, welding plays a crucial role in multiple UK industries. In this guide, we’ll cover what welding is, how it works, common processes and joints, and what it’s used for.

Whether you’re an apprentice or just want to find out more, our guide is a great place to start.

What is welding?

Welding is the process of joining materials - usually metals - using heat, pressure, or both. There are various types of welding, such as MIG/MAG, TIG or stick, each with its own advantages and ideal uses.

Dictionary Definition

  • to unite (metallic parts) by heating and allowing the metals to flow together or by hammering or compressing with or without previous heating
  • to unite (plastics) in a similar manner by heating
  • to repair (something) by this method
  • to produce or create as if by such a process

If you’re a welder, you can use these techniques for a wide range of fabrication or repair tasks.

How does welding work?

Joining Materials Together

Welding fuses two or more materials to form a strong joint. The materials being joined are known as the parent materials. Sometimes, a filler metal or consumable is used to strengthen the bond.

Welds can be classified into:

  • Homogeneous welds – The filler metal is the same as the parent material
  • Heterogeneous welds – The filler metal is different from the parent material
  • Autogenous welds – No filler metal is used, only the parent materials are fused

Using Heat or Pressure

Fusion welding (like MIG, TIG or stick welding) uses heat to melt the parent and filler materials together.

Pressure welding joins materials through friction or force, sometimes with heat applied alongside.

The welding process produces a molten material, known as the weld pool, which solidifies to create a bond. In some welds, shielding gas is used to protect the bond from defects or contaminants in the environment.

Types of Welding Process

Here are some of the most common welding techniques, each suited to different materials or situations.

Arc welding

What is arc welding?

In this guide, we’ll focus on arc welding. MIG/MAG, TIG and stick welding are all subtypes of arc welding.

Arc welding is a common welding process that uses an electric arc to create heat, which melts the parent materials and filler metal to form a strong bond. It can be used to join a wide variety of metals together.

This type of welding is often used for heavy-duty construction, as the high heat can warp thin materials.

A welder using MIG technique at a table, creating sparks as they work on a metal piece.

MIG/MAG welding

MIG welding uses a continuous feed of wire electrode that melts as the electric arc heats the base materials.

It stands for Metal Inert Gas Welding and is one of two subtypes of Gas Metal Arc Welding (GMAW). The other is Metal Active Gas (MAG), which uses active gases like helium rather than inert gases like argon.

How does MIG/MAG welding work?

In both types, the process works with a welding torch, or ‘gun’. When the torch trigger is pressed:

  1. The torch starts to feed welding wire from a spooled wire feed unit.
  2. An electrical arc is created between the welding wire and workpiece.
  3. This heats the workpiece, melts the wire and fuses it to the joint area.
  4. The torch releases a shielding gas flow to shield the junction and wire.

The process uses shielding gas (inert for MIG, active for MAG) to protect the weld from contamination.

What is MIG welding used for?

Because of its speed, versatility, and ease of automation, MIG/MAG welding is one of the most widely used welding processes in industrial settings. However, it can be tricky to do outside as gas can blow away.

Common uses include:

  • Automotive & Manufacturing – Used for car frames, exhaust systems, and machinery
  • Construction & Structural Fabrication – Ideal for steel beams, pipes, and sheet metal
  • Shipbuilding & Aerospace – Ensures strong, clean and precise welds in large structures

You can find out more about MIG welding here, in our beginner’s guide to the technique and its uses.

A welder in a welding helmet and gloves, focused on TIG welding, sparks flying around the work station.

TIG welding

Although sharing some similarities, there are some key differences between TIG and MIG/MAG welding.

How does TIG welding work?

TIG (Tungsten Inert Gas) welding uses a tungsten electrode to generate an arc that melts the base metal, creating a molten weld pool. Unlike MIG/MAG welding, the tungsten electrode does not melt.

Instead, a separate filler rod is manually fed into the pool if needed. Shielding gas is used to protect the weld.

What is TIG welding used for?

TIG welding is a slower welding process than MIG, but results in a stronger and better-looking weld when it’s completed by a skilled welder. You have to carefully manipulate the weld pool and feed in the filler wire.

Common uses include:

  • Welding a wide variety of metals – Such as low alloy steels, stainless steels and aluminium
  • Welds that need to be strong and look good – TIG welding offers more control over the process
  • Welds that need a clean process – No sparks, spatter, or slag is generated with TIG welding

TIG welding can be done from a variety of positions, where precision and quality is more important than speed. It’s especially useful for aerospace, food equipment, high-purity processing, and motorsports.

You can find out more about TIG welding here, in our one-stop guide to this type of welding process.

how to select an ESAB tig welder decision tree

Stick Welding

Stick welding is also known as Manual Metal Arc or MMA welding. It is one of the oldest types of welding.

How does stick welding work?

Instead of shielding gas, stick welding uses a consumable electrode coated in flux to create an arc and weld the metal. During stick welding, the flux coating burns off the electrode, creating a protective slag layer.

After the molten weld pool has cooled, the slag layer must be chipped away to expose the clean weld.


What is stick welding used for?

Unlike MIG/MAG and TIG welding, stick welding doesn’t need bottled gas. This makes it a good welding process for harsh or outdoor environments. It works well for thick materials that don’t have to look perfect.

Common uses include:

  • Construction & Heavy-Duty Welds - Used for structural steel, bridges, and pipelines
  • Repair & Maintenance - For example fixing farm equipment, machinery, or industrial parts
  • Outdoor & Remote Welding - May work better than MIG/TIG in damp, windy conditions

Keep in mind that stick welding requires additional time for chipping away the slag layer. While not as precise as TIG welding, or as fast as MIG welding, stick welding is affordable, portable, and ideal for dirty metals.

Want to know more about how stick welding works? Check out our guide to stick welding basics.

Other Types of Arc Welding

MIG/MAG, TIG and stick are types of welding our industry-leading welding equipment can help you with. However, there are many other types of arc welding (and other welding processes), including the below:

  • Flux-cored arc welding (FCAW) is similar to MIG welding but uses a flux-filled wire that creates its own shielding. This makes it ideal for outdoor or heavy-duty welding without the need for bottled gas.
  • Submerged arc welding (SAW) is where the arc is submerged beneath a layer of granular flux, preventing spatter and contamination. It’s ideal for high-quality welds on thick materials.
  • Plasma arc welding (PAW) is similar to TIG welding, but uses a constricted arc for high precision and deep penetration. It’s ideal for high-tech industries requiring ultra-clean, high-quality welds.

Now we’ve explained welding’s definition and some common processes, let’s look at how weld joints work.

Types of Welding Joints

A key part of welding is choosing how to join materials together. Joints affect the strength, appearance, and durability of the weld. Here are five common types of joints, how they work, and what they’re used for.

Weld Joint

How it Works

Common Uses

Butt

Two workpieces are placed in the same plane and the side of each workpiece is joined by welding along their edges

Pipelines and structures

Lap

The surfaces of the two workpieces overlap each other, and the weld is formed where the two surfaces intersect

Sheet metals, joining different thickness

Edge

Workpieces are aligned parallel to each other and welded along their edges (not suitable for load-bearing welds)

Where workpieces are not subject to stress

Tee

One workpiece is welded perpendicular to another, forming a T-shape, offering high mechanical strength and durability

Structural steel, machinery, supports

Corner

Two workpieces form a 90° angle and are welded at the corner (easy to assemble and requires little preparation)

Box frames, cabinets, metal furniture

Read our dedicated blog post about basic types of weld joints and useful tips for getting a high-quality result. As well as these popular joints, different weld types can be used to create strong, lasting connections.

For example, groove welds are made in a prepared groove between two pieces, often used for full penetration in structural welding, pipelines or pressure vessels. Fillet welds, which form a triangular shape, are common in Tee and corner joints, providing cost-effective strength with less filler material than butt.

Others include plug welds, which fill circular holes to fuse overlapping materials, and slot welds, which use elongated holes to distribute stress evenly. These may replace rivets in auto and structural applications. 

Choosing the right welding process for the job is important, but what are some practical applications?

What welding is used for:

Welding plays a crucial role in multiple UK industries, from building vehicles to green energy equipment.

Vehicles & Machinery

In the manufacture, repair and maintenance of vehicles and machinery, strength and speed are essential.

  • MIG/MAG welding is popular for vehicle bodywork, due to its fast production time and relatively clean finish. However, you may use TIG welding for cleaner, high-precision welds on thinner metals.
  • Where welding is needed on a mass scale, robotic welding or welding automation is an option.

Construction

Welding plays a significant role in construction, including in buildings, bridges, and pipelines. In construction, weld joints need to be designed to handle heavy loads and withstand extreme weather conditions.

  • Stick welding (SMAW) is common for structural steelwork, especially when welding outdoors or in damp conditions. Flux-cored arc welding (FCAW) also doesn’t need an external gas supply, making it suitable for heavy-duty welds on thick materials on construction sites in all types of weather.
  • Appearance is less important in some construction applications, but the strength and durability of the welds are paramount. Stick and flux-cored arc welding produce slag, but are fast and strong.

Repairs & Maintenance

Welding is often used for repairs and maintenance, for example fixing a broken part or worn-down machinery.

  • TIG welding is typically used for repairs, due to its strength, precision, and suitability for a wide range of metals. It produces clean and good-looking welds but requires time and skill to do well.
  • For sheer speed, MIG/MAG welding is another option for large-scale repairs, especially if control or appearance isn’t a big consideration. It can also be easier to weld thicker metals using MIG.

Specialised fields like aerospace also use welding, requiring the highest quality welds on unusual materials. 

In submarine construction, stick and submerged arc welding are used for strong, durable welds on thick materials that must withstand high pressure. Hobbyists, craftspeople, and sculptors also use welding.

Our guide should have given you an overview of what welding is and how different welding processes work.

Start Welding with ESAB

If you want to become a pro welder, or just do some weekend metalwork, start your journey with ESAB.

No matter the project, we offer a wide range of welding equipment, welding accessories, and PPE for your needs. Our portfolio of high-performance yet user-friendly MIG welders, TIG welders and stick welders offer:

  • a complete line of fabrication solutions for virtually every application and UK industry
  • rugged industrial machine design with impact-resistant housing and multiple lift points
  • superior arc characteristics and technology to deliver consistent, high-quality welds

Or, browse our ESAB University section for the latest welding articles, expert videos, and courses.