How Welding Works

The men and women behind these welding masks build much of what you see: skyscrapers, cars, even cruise ships.
The men and women behind these welding masks build much of what you see: skyscrapers, cars, even cruise ships.
Steve Weinrebe/­Getty Images

­Skyscrapers, exotic cars, rocket launches -- certain things simply demand your attentio­n. Welding, in all likelihood, isn't one of them. You may have gone your whole life without ever having thought about the subject. It might surprise you then, that welding affects an estimated 50 percent of the United States gross national product  [source: Hobart]. Without it, none of those amazing skyscrapers, cars or rockets would exist.

Welding is, at its core, simply a way of bonding two pieces of metal. While there are other ways to join metal (riveting, brazing and soldering, for instance), welding has become the method of choice for its strength, efficiency and versatility.


­There are tons of different welding methods, and more are being invented all the time. Some methods use heat  to essentially melt two pieces of metal together, often adding a "filler metal" into the joint to act as a binding agent. Other methods rely on pressure to bind metal together, and still others use a combination of both heat and pressure. Unlike soldering and brazing, where the metal pieces being joined remain unaltered, the process of welding always changes the work pieces.

This may seem like a trivial point, but it's actually critical to understanding why welding produces such strong bonds. In the processes of soldering and brazing, two pieces of metal are joined by introducing a third material (with a lower melting point) into the mix. Melting this third material between the surfaces of the original pieces binds the pieces together. The bond, however, is only as strong as the joining material. Welding, on the other hand, cuts out the middleman and joins the original pieces directly to each other. The result is a strong, cohesive bond that's often as strong as the material itself.

­In this article, we'll take a closer look at exactly how welding works. We'll also examine some of the numerous applications for welding, along with the expertise and equipment necessary to make it all happen. But before we do, let's look at where it all began.

The History of Welding

An underwater welder hands off his welding torch after securing the underwater piers that will carry the I-195 roadway in Providence, R.I., in 2005.
An underwater welder hands off his welding torch after securing the underwater piers that will carry the I-195 roadway in Providence, R.I., in 2005.
­AP Photo/Stew Milne

With all the power and precision machinery involved in production welding, you might think of welding as a relatively new process. In reality, welding has been around for thousands of years. Early examples of welding have been found in locations ranging from Ireland to India, with some dating back to the Bronze Age. Naturally, these civilizations lacked the vast array of tools and machinery that welders have access to now. How did they manage to weld?

The process they used is known as forge welding. To start the process, blacksmiths would heat the metal until it was bright red in color (but still not at its melting point). The blacksmiths would then place the two pieces, slightly overlapping, on an anvil and pound them together. Forge welding has multiple limitations. Only relatively s­oft metals can be forge welded, and the process is very labor intensive. In places without electricity, however, the process is still used.


Forge welding was the only game in town until the 19th century. With the onset of the industrial revolution, however, numerous discoveries pushed welding forward fast. Research on electricity yielded electrodes and electric arcs. Rudimentary torches were developed by mid-century as well. Both discoveries would play heavily into the welding methods of the next century.

­By the late 1800s, many of the pieces were in place to make welding a driving force in manufacturing. Still, the methods of this era weren't perfect. Oxidation (the process of metals bonding to the oxygen particles in the atmosphere) occurred during the welding process and made welds porous and brittle. Such welds posed a grave risk to workers. During the period from 1895 to 1905, for instance, poorly made boilers exploded daily, causing thousands of deaths in the process [source: Sapp]. Clearly there was an urgent need for better welding methods. Over the next few sections, we'll learn more about those new and improved methods, starting with a closer look at the tools of the trade.

Welding Tools of the Trade


­By now, you may have gathered that welding isn't necessarily a complicated process. You can learn the basics of several welding meth­ods in hours. Like chess, however, welding is easy to learn yet hard to master. Professional welders have a mountain of different variables to consider when doing their job. No matter how complicated the job, though, they only need three things to get it done: a welding rig, material to weld and safety equipment.

The most basic welding rigs, for occasional use in a home workshop, can be had for under $100. Typically, these rigs are set up for shielded metal arc welding (SMAW), or stick welding. Many units only have an on/off switch in the way of controls, making them simple to operate. Torch welding rigs are small and easy to work with, which is part of why they're commonly used. These torches use oxyacetylene for the flame, along with a filler rod. But some rigs (like those used in laser-beam welding) are so expensive and complicated that they are only used in industrial applications.


As for materials, some are much easier to weld than others. Steel can be a great choice because of its strength, affordability and weldability. As a rule, the stronger the steel, the harder it is to weld. Accordingly, several steel alloys were developed with welding in mind. Of course, almost any metal can be welded, including cast iron, bronze, aluminum and even titanium, although the latter requires a highly protected atmosphere because the metal is so reactive.

Whatever you're welding, remember: safety first. If you've ever seen welding in person, you can testify to the blinding brightness the process creates. Looking directly at a weld site without protection can produce what's known as arc eye, a painful inflammation of the cornea that feels like getting sand in your eye. No wonder that a good welder's mask is a prerequisite for any welding outfit.

­Welding masks come in many styles. The simplest ones have a darkened panel that the welder looks through while welding. More advanced masks auto-darken as the welding site gets brighter. In addition to dazzling brightness, welding can generate temperatures of up 10,000 degrees F (5,538 degrees Celsius) and showers of sparks, making heavy-duty gloves and a long-sleeve shirt necessary.

Lastly, proper ventilation is crucial, depending on the welding method. Welders may be exposed to harmful substances such as lead, mercury and carbon monoxide. Vent hoods can prevent fumes from accumulating in the workspace.

The Process of Welding


We're all ­­suited up and ready to start welding. Mo­st welding done today falls into one of two categories: arc welding­ and torch welding.


­Arc welding use­s an electrical arc to melt the work materials as well as filler material (sometimes called the welding rod) for welding joints. Arc welding involves attaching a grounding wire to the welding material or other metal surface. Another wire known as an electrode lead is placed on the material to be welded. Once that lead is pulled away from the material, an electric arc is generated. It's a little like the sparks you see when pulling jumper cables off a car battery. The arc then melts the work pieces along with the filler material that helps to join the pieces.

Feeding the filler into the welding joint takes steady hands and an eye for detail. As the rod melts, the welder must continuously feed the filler into the joint using small, steady, back-and-forth motions. These motions are what gives welds their distinctive appearance. Going too fast or slow, or holding the arc too close or far away from the material can create poor welds.

Shielded metal arc welding (SMAW or stick welding), gas metal arc welding (more commonly known as metal inert gas, or MIG, welding) and gas tungsten arc welding (frequently called tungsten inert gas, or TIG, welding) all exemplify arc welding.

These three common methods each offer unique advantages and drawbacks. Stick welding, for instance, is inexpensive and easy to learn. It's also slower and less versatile than some other methods. Oppositely, TIG welding is difficult to learn and requires an elaborate welding rig. TIG welding produces high-quality welds, however, and can weld materials that other methods can't.

Torch welding represents another popular welding method. This process typically uses an oxyacetylene torch to melt the working material and welding rod. The welder controls the torch and rod simultaneously, giving him or her a lot of control over the weld. While torch welding has become less common industrially, it's still frequently used for maintenance and repair work, as well as in sculptures (more on that later).

A Good Weld Is Hard to Find

You may remember from our look at the history of welding that brittle, porous welds posed serious safety concerns in industrial applications. Much of the problem with those early welds stemmed from oxidation. As the science of welding advanced, methods of shielding the welding site from oxygen were developed. In stick welding, for instance, the welding rod is coated in flux. Flux serves several different purposes, one of which is to create a gas shield for the welding site as the flux is burned. MIG and TIG welding go so far as to use gas canisters that constantly envelop the welding site in inert gases. Preventing welding sites from oxidizing is crucial to forming a strong weld.

­The process of joint preparation is perhaps equally important to producing strong welds. Ensuring that work materials are free of grease, dirt and dust is only the first step in properly preparing a welding joint. Edge joints, lap joints, t-joints, butt joints -- there are almost as many ways to prepare a welding joint as there are ways to weld the pieces together. Selecting the right type of joint for the job at hand is critical to producing a quality weld.


­Once a weld is in place, you can check its quality in several ways. Visual inspection can reveal evidence of welding performed at the wrong speed or of current, cracks or inclusions in the weld and other problems. Welders may also inspect their work using magnetic particle testing, liquid penetration inspection, ultrasonic testing, X-ray inspection, pressure testing or other methods. Destructive testing, while destroying the weld under examination, is also frequently used to determine the quality of a weld. No m­atter what test is used, ensuring welds are strong and durable is an important step in the process.

Welding in Industry (and Art!)

You can see why Chicagoans affectionately call this metallic masterpiece of welding the bean.
You can see why Chicagoans affectionately call this metallic masterpiece of welding the bean.
Justin Lightley/Getty Images

­N­early half a million welders are employed in the United States [source: U.S. Department of Labor]. Although the U.S. Department of Labor expects the welding profession to grow slowly, the agency foresees tremendous opportunities for good welders due to a short supply. In addition, many welding processes can't be automated; even those that can still require a welder's expertise for setting up and inspecting the process.

­Most welding jobs are related to manufacturing in many different industries. Automakers, ship builders, commercial construction, bridge building -- the list of welding applications goes on and on. Welders can get certified at institutions like the American Welding Society, although some companies devise their own certification methods.


Like any profession, welding offers a wide variety of pay. While welders make around $15 an hour on average, those with specialties and experience can make much more. Underwater welders, for instance, can make upwards of $100,000 annually [source: University of Phoenix]. Though most welders are men, thousands of women make their living as welders, too. Women welders played key roles in shipbuilding during ­World War II, for instance.

One of the more interesting uses of welding comes from the art community. So­me of the first examples of welding ever discovered were pieces of art, like the Iron Pillar of Delhi in India and golden bowls and goblets dating back more than 1,000 years. Structures like St. Louis' Gateway arch (630 feet, or 192 meters, tall and made to last 1,000 years) and Brussels' Atomium (a 334-foot, or 102-meter, high tribute to the atom) illustrate how far the art of welding has come.

­The tradition of artistic welding remains strong as welding makes creating massive sculptures weighing several tons a possibility, even for individual artists. Though artists make up only a small segment of the welding industry, they can display welding's potential for millions to see.

Keep reading for more links on welding and cool tools you might like.

Lots More Information

Related HowStuffWorks Articles

More Great Links

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