What Is Welding? (Definition + Processes – In-depth Guide)


Welding is a fabrication process that involves joining metallic parts together using heat, pressure, or a combination of both. The technique is widely used in various industries, from construction and manufacturing to automotive and aerospace.

This guide provides an in-depth look at the principles, processes, and techniques involved in welding, as well as their applications in different industries.

That’s what we’ll be talking about in this in-depth guide on welding’s definition and processes.

What Is Welding?

What is welding? In the simplest terms, welding is the act of joining two metal pieces together. Using high heat levels and introducing other metals or gases, the metallic structures of the two parts combine to become one.

In this way, it’s different from brazing and soldering.

I have recently written an article in which I describe what Soldering is in more detail, read this article here

On the other hand, soldering requires heating the metal instead of melting it. At the same time, brazing works by melting the two base metals and flowing another filler metal right into the joint.

What Is Welding? >> Check out the video below:

The Fundamentals of Welding

Welding is far from a simple process, and it requires a high level of skill and practical knowledge in various fields, including physics, chemistry, and metallurgy. Here are some essential principles of welding:

  • Welding primarily involves working with metals, but it can also be used to fuse thermoplastics and wood.
  • A completed joint formed through welding is called a weld joint or weldment.
  • The parts being fused are known as the parent materials, and the material used to help form the weld joint is called the filler material.
  • Welding involves bonding the same type of material (e.g., metal-to-metal or wood-to-wood) using heat welding, pressure welding, or both.
  • Welders often add metal to the welded joint to strengthen the weldment, while a shielding gas like carbon dioxide protects the joint from contamination and atmospheric elements.
  • Different metals react differently, depending on their physical, mechanical, and chemical properties.
  • Heat can alter the strength, ductility, and malleability of metal. Welding can straighten out a warped piece of metal by applying adequate heat.
  • Welding involves heating and cooling of the metal, without any other chemical reaction involved. However, the weld can become weak if oxygen reacts with the molten metal. Protective gases around the weld pool prevent oxygen and other contaminants from damaging the joint.
  • Extreme heat can alter the crystalline structure and weaken any metal.

Benefits of Welding

Welding offers numerous advantages, such as:

  • Creating a permanent weld that is excellent for fusing two materials
  • Ensuring strength and durability by using the right filler metal, resulting in long-lasting weld joints
  • Being cost-effective in terms of materials, fabrication, and equipment
  • Providing versatility and flexibility, as it can be used both indoors and outdoors
  • Producing smooth, polished, and visually appealing welded joints
  • Being one of the fastest fabrication methods in terms of speed

How Welding Works

Welding works by joining two or more workpieces together at high temperatures. This is achieved by using pressure and heat, which causes a weld pool of molten material to form. The resulting weld, once cooled and solidified, can be stronger than the parent materials. Different welding processes are used depending on the material and the desired outcome.

Metal Welding

In most cases, using pressure and heat together over the base material enables quick and efficient metal welding. A shielding gas safeguards the molten metal or weld pool from getting contaminated or oxidized.

Plastic Welding

In plastic welding, the surfaces are first prepared, followed by the application of heat and pressure. After this, the materials are cooled to create a strong bond.

Wood Welding

Wood welding involves subjecting the materials to pressure before using the heat generated by linear friction movement to create a bond. This technique enables wood to be joined without the need for adhesives or nails.

Types of Welding Joints

Welding joints are classified based on their configurations and can include the following:

  • Butt Joint: A connection between the ends or edges of two parts that form an angle of 135-180° inclusive in the region of the joint.
  • T Joint: A connection between the end or edge of one part and the face of the other part, with the parts forming an angle of more than 5 up to and including 90° in the region of the joint.
  • Corner Joint: A connection between the ends or edges of two parts that form an angle of more than 30 but less than 135° in the region of the joint.
  • Edge Joint: A connection between the edges of two parts that form an angle of 0 to 30° inclusive in the region of the joint.
  • Cruciform Joint: A connection in which two flat plates or two bars are welded to another flat plate at right angles and on the same axis.
  • Lap Joint: A connection between two overlapping parts that form an angle of 0-5° inclusive in the region of the weld or welds.

I have recently written an article in which I describe welding joints in more detail, read this article here (5 Types of Welding Joints and Their Use – Complete Guide)

Welds Based on Configuration, Penetration, and Accessibility

Welding can also be categorized based on their configuration, penetration, and accessibility.

Slot Weld

A joint between two overlapping components made by depositing a fillet weld around the periphery of a hole in one component to join it to the surface of the other component exposed through the hole. A slot weld can also be made by filling a hole in one component with filler metal to join it to the surface of an overlapping component exposed through the hole.

Full Penetration Weld

A welded joint where the weld metal fully penetrates the joint with complete root fusion. In the US, the preferred term is complete joint penetration weld (CJP).

Partial Penetration Weld

A weld in which the fusion penetration is intentionally less than full penetration. In the US, the preferred term is partial joint penetration weld (PJP).

Features of Completed Welds

Some common features of completed welds include the parent metal, filler metal, weld metal, fusion line, weld zone, weld face, weld root, and weld toe. These terms are essential for understanding the anatomy of a weld and assessing the quality of the resulting joint.

Welding Processes and Techniques

The welding process depends on the material being used and the desired outcome. Some of the most popular types of welding processes include:

1. Arc Welding

Arc welding includes several manual, semi-automatic, and automatic processes, such as metal inert gas (MIG) welding, stick welding, tungsten inert gas (TIG) welding, gas welding, metal active gas (MAG) welding, flux-cored arc welding (FCAW), gas metal arc welding (GMAW), submerged arc welding (SAW), shielded metal arc welding (SMAW), and plasma arc welding.

These techniques usually use a filler material and are primarily used for joining metals like stainless steel, aluminum, nickel, copper alloys, cobalt, and titanium. Arc welding processes are widely used across various industries, including oil and gas, power, aerospace, automotive, and more.

2. Friction Welding

Friction welding techniques join materials using mechanical friction, which can be performed in various ways on different welding materials, such as steel, aluminum, or wood. The mechanical friction generates heat, which softens the materials, allowing them to mix and create a bond as they cool.

Friction welding does not require filler metals, flux, or shielding gas. It is often used in aerospace applications, as it is ideal for joining otherwise ‘non-weldable’ lightweight aluminum alloys. Friction processes are also being explored as a method for bonding wood without adhesives or nails.

3. Electron Beam Welding

Electron beam welding is a fusion joining process that uses a beam of high-velocity electrons to join materials. The kinetic energy of the electrons transforms into heat upon impact with the workpieces, causing the materials to melt together.

Electron beam welding is performed in a vacuum (using a vacuum chamber) to prevent the beam from dissipating. This method is versatile and can be applied across various industries, including aerospace, nuclear power, automotive, and rail.

4. Laser Welding

Laser welding is used to join thermoplastics or pieces of metal using a laser to provide concentrated heat, ideal for narrow, deep welds and high joining rates. This process is easily automated and is perfect for high-volume applications, such as in the automotive industry. Laser beam welding can be performed in air rather than in a vacuum, unlike electron beam joining.

5. Resistance Welding

Resistance welding is a fast process commonly used in the automotive industry. This process can be divided into two types: resistance spot welding and resistance seam welding.

Spot welding uses heat delivered between two electrodes applied to a small area as the workpieces are clamped together. Seam welding is similar to spot welding, but it replaces the electrodes with rotating wheels to deliver a continuous, leak-free weld.

Welding Equipment and Safety

Welding is a specialized job that requires various essential tools and equipment, including welding guns, torches, wire brushes, chipping slag hammers, angle grinders, tape measures, welding magnets, soapstone markers, pliers, C-clamps, electrode tip cleaners, flint strikers, cold chisels, and screwdrivers.

Welding can be a high-risk job if you don’t use protective gear. Welders must use the following safety equipment at the job site:

  • Safety glasses
  • Welding helmet
  • Welding gloves
  • Heat-resistant jacket
  • Leatherwork shoes
  • Earplugs

What Gases Are Used in Welding?

When the air gets into the arc or the weld pool while the welder is working, it can lead to the formation of gas bubbles that might ruin the weld.

Related: What Gases Do MIG Welders Use? >> Welding Shielding Gas | Complete Guide

Besides, anything like air or debris might contaminant the weld pool. That’s why welders require a shielding gas to protect the weld from atmospheric air to prevent porosity and excessive spatter.

Here are the most commonly used gases in welding.


Argon is commonly used as a shielding gas in welding since it’s an inert gas that doesn’t react with other substances.

However, they recently discovered that it changes form at very high temperatures, which limited its uses. Yet, it’s still the most commonly used shielding gas to keep contaminants away from the weld pool.


Carbon dioxide is extracted from nature and pressured into cylinders to be used as a shielding gas too. It’s an alternative to argon. It’s a cheaper alternative and one of less quality as well.

Due to its less than perfect performance and the spatter it produces, it’s mostly used in mixtures, along with other gases. Flux core welding and plasma cutting require using CO2 in its pure form, though.


Helium is used as a shielding gas, as well. It provides deeper penetration, but it doesn’t excel when it comes to arc consistency. When it comes to TIG welding, the perfect shielding gas is a mix of helium and argon.


Oxygen is added in small amounts to shielding gases to introduce some fluidity to the mix. The goal is to add fluidity to the weld pool to speed up the welding process.

Known for its combustion properties, oxygen is used to amplify heat for gas welding.

Related reading: Is Welding Oxygen The Same as Medical Oxygen?

Testing in Welding – How Do They Ensure Quality?

Being a highly specialized discipline, the welding process doesn’t stop at producing the final product.

It goes further to test the fabricated weld under conditions that are similar to -sometimes harder- than those at the welded piece site to ensure satisfactory performance of the welded structure.

I have recently written an article in which I describe weld Testing in more detail, read this article here (Physical Weld Testing: Destructive and Non-Destructive)

Here’s a glimpse of the most common welding tests. Some of them require destroying the piece to inspect it, while others are non-destructive.

Nick Break Test

This is probably the most known type of welding tests. In the nick break test, the welding joint is intentionally broken to examine the fractured pieces closely.

Examining these pieces will detect defects like porosity, slag inclusions, and gas pockets.

The pressure is applied to the piece and then with a strong press or a hammer blow, it’s broken into pieces, and the inspection starts.

Bend Test

A bend test is one of the most straightforward welding tests. Plus, it’s easy to perform. It relies on the premise that each metal piece that’s welded at the top should withstand a certain amount of bending before it breaks.

It’s often used in quality control of butt joints because it’s inexpensive. There are various ways to perform this test, through jigs, a wrap-around guided bend test, or a side bend test.

Acid Etch Test

This is the cleanest and most clever test of them. You cut a cross-section of the weld and immerse it in an etching solution like nitric acid.

This way, the acid will react with the welded material and show the boundary between the metal surface and the weld, revealing the imperfect of the welds.

Visual Inspection

The friendliest non-destructive test is a visual inspection. In this test, a qualified, trained observer watches over the welder while he’s working. He inspects everything!

Typically, he’s looking for inclusions, gas pockets, or undercutting. He spots these mistakes.

When the welding process is over, the detected piece is terminated, and the welder is required to remake the weld.

Ultrasonic Inspection

This method uses an ultrasonic wave probe to go into the metal. The results are displayed on a monitor screen, and when the waves encounter a discontinuity, they bounce back to the probe, indicating a flaw.

Moreover, ultrasonic inspection enables us to know the exact size of the defect from the wavelength of the detected wave. The rule is that the defect is half the size of the wavelength.

Welding Safety – Is It That Dangerous?

It’s crystal clear that welding isn’t the safest job out there. A big part of being a professional welder is knowing all the possible safety hazards and working your way to avoid them.

Welding Safety Hazards

Here, we’ll take a look at the four common welding hazards and their safety precautions.

Physical Hazards

Physical Hazards are the ones that might cause burns, eye injury, cuts, or even crushed fingers. To protect yourself from these, you need to wear complete personal protective equipment from head to toe.

Fumes & Gas Exposure

Frequent exposure to fumes and gas makes welders prone to plenty of diseases like respiratory illness and impaired speech.

Fire & Explosions

The number one cause of fires and explosions in welding work sites are flammable material lying around the workplace unattended. That’s why keeping a clean, well-organized area is a must.

Labeling materials clearly is also essential, in addition to marking emergency exits and having fire extinguishers.

Electric Shock

What makes electrocution probably the worst hazard is that it’s immediate. Once the electric discharge reaches the human body, it’ll suffer from injury or death. That’s why inspecting welding equipment and electrodes shall be taken seriously.

Personal Protection Equipment – PPE

Here’s how welders protect their bodies while they’re at the worksite.

Eyes & Face

You need something to protect your eyes and face against spatter, hot slag, and debris, as these can lead to serious burns. On top of that, you need protection against radiation and intense light.

For these reasons, you undoubtedly need a face shield, preferably with eye protection. Eye goggles are a must in most welding types. Hand shields come in handy, as well.

Head & Ears

A welding cap is a necessity when you’re working. People with long hair must tie it up and tuck it inside the cap. This is essential for protection against flying spatter.

It depends on your shield, if it doesn’t cover your head and ears, then you need a helmet. There is some head covering that welders wear under their helmets that’s fire-resistant, this definitely helps with the protection.

Add to these ear muffs or plugs, especially when you’re working in an odd position, like overhead welding. They’ll be an asset if you’re in a loud workplace too.


The fumes and gases produced from welding are greater than the normal lungs’ capacity. That’s why it’s vital to wear a filer mask with a respirator, especially for those who work for long hours.

Hands & Feet

You need something to protect your hands and feet against the heat. The goal is to provide protection against burns, fires, and electric shocks.

For this purpose, welders wear dry insulated gloves. Ideally, they should be flame resistant to get the job done. Mostly, they’ll be made of thick leather, especially when it comes to SMAW and FCAW.

As for boots, welders need to make sure that their boots comply with ASTM F2412 and ASTM F2413 requirements. Leather boots with metal toes are the best for welders. Flame resistant boots are definitely a plus.

One well-known tip is not to tuck your pants into your welder’s boots so as not to catch a spark if any.


Any part of exposed skin other than your hands and head needs to be covered. These body parts are still prone to burns, excessive heat, and fire.

You need to wear overall protective gear that’s made of heavy material. The heavier the material, the better.

Long shirts are favored over short sleeves. Long pants with no cuffs are preferable too. The clothes should be clean, dry, and oil-free. Also, try to cover any pockets or cuffs as they might catch fire.

Depending on the welding technique you use, it’ll always be better to wear a leather apron for an extra layer of protection. Well, regular clothes do not offer protection anyhow. You can add leather sleeves or leggings if you want.

Finally, never wear synthetic material in there, they catch fire easily.

Is Welding a Good Career?

In short, yes. Welding is a good career with good pay, and welders are in demand nowadays. According to the American Welding Society, the average age of a welder is 55 years. This number is among a rough estimate of 450,000 welders in the U.S.

Two takeaways here, there are not enough welders to cover demand, and you can pursue welding at any age!

Welding will be in demand as long as there’s metal in industry, which doesn’t seem to be ending soon. Skillful welders are an integral part of several industries, construction, aerospace, automobiles, maintenance, etc.

Even Hollywood knows how integral welders are to every industry!

Welding in Popular Culture >> Check out the video below:

Average Salary of a Welder

The average salary of a welder is around $40,000 – $45,000 annually. Other highly skilled welders might take off to take welding jobs in the military or underwater welding, where they can earn as much as $150,000 per year.

The skill level is the main determinant of the salary here, so there are always opportunities to climb up this career ladder.

Related reading: Do Welders Make Good Money? Highest Paying Welding Jobs


Welding is a critical process in various industries, and understanding its principles, processes, and techniques is essential for professionals in the field.

With advancements in technology, welding methods continue to evolve, offering more efficient and precise ways to join materials.

By staying up-to-date with the latest developments and ensuring proper safety measures, welders can create strong, durable, and high-quality joints for a wide range of applications.

Recommended Reading

David Harper

David is the Co-Founder and Senior Editor at weldingtroop.com. David's an experienced fitter and tuner/welder who's passionate about helping others develop in life through new skills and opportunities.

Recent Posts

error: Content is protected !!