What Is Welding?- Definition and Types Of Welding

What Is Welding?

Welding is a fabrication process that uses heat, pressure, or both to fuse two or more parts together, forming a joint as the parts cool. Welding is typically used on metals and thermoplastics, but can also be used on wood. The completed welded joint can be referred to as a weldment.

Some materials require the use of specific processes and techniques. Some are considered “unweldable,” a term not typically found in dictionaries but useful and descriptive in engineering.

The parts that are joined are known as base materials. The material that is added to form the joint is called a filler or consumable. Because of the shape of these materials, they can be referred to as a base plate or tube, flux-cored wire, consumable electrode (for arc welding), etc.

Consumables are usually chosen to be similar in composition to the base material, thus forming a homogenous weld, but there are occasions, such as when welding brittle cast irons, when a filler with a very different composition and, therefore, properties is used. These welds are called heterogeneous.

The completed welded joint may be referred to as a weldment.

Definition Of Welding

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.

How Does Welding Work?

Welding works by joining two materials together without a separate binder material. Unlike brazing and soldering, which use a binder that has a lower melting point, welding joins the two workpieces directly together.

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 a 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 workpieces 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 give 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 a 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.

Types Of Welding

There are four main types of welding. MIG – Gas Metal Arc Welding (GMAW), TIG – Gas Tungsten Arc Welding (GTAW), Stick – Shielded Metal Arc Welding (SMAW), and Flux-cored – Flux-cored Arc Welding (FCAW). We dive deeper into each type of welding here.

#1. MIG Welding Or GMAW.

MIG welding is one of the most common types of welding that beginners need to learn. MIG welding is used in the auto industry to repair vehicle exhaust and in the construction of houses and buildings. This is a type of arc welding that uses a continuous wire called an electrode. You also use a shielding gas that flows through the welding gun and protects against contamination.

MIG welding is two different types of welding. The first use bare wire and the second uses flux core. Bare wire MIG welding can be used to join thin pieces of metal together. Flux core MIG welding can be used outdoors as it does not require a flow meter or gas supply. MIG welding is usually the welding of choice for DIY and amateur welders who don’t have the cash to spend on expensive equipment.

#2. TIG Welding Or GTAW.

Like MIG, TIG welding also uses arcs, but it is also one of the more difficult welding techniques to learn. TIG welding uses a tungsten electrode. Tungsten is one of the hardest metal materials. It does not dissolve or burn off.

Tig welding can be done by a process known as fusion, which may or may not use a filler metal. TIG also uses an external gas supply such as argon or helium.

Two hands are required for TIG welding. One hand guides the rod while the other holds a TIG torch. This torch produces the heat and arc used to weld the most common metals including aluminum, steel, nickel alloys, copper alloys, cobalt, and titanium.

TIG welders can be used to weld steel, stainless steel, Chromoly, aluminum, nickel alloys, magnesium, copper, brass, bronze, and even gold. TIG is a useful welding process for bike frames, lawnmowers, door handles, fenders, and more.

The aerospace and automotive industries use TIG welding as do other industrial markets. This is also a great type of welding for Iowa as it can be very useful for farmers to weld wagon frames, fenders, and other vital equipment.

#3. Stick Welding Or SMAW.

Want to take your welding to go? A major benefit of stick welding is that it is portable. Stick welding is used in construction, maintenance and repair, underwater pipelines, and industrial manufacturing. For this type of welding, use shielded metal arc welding, better known as stick welding.

Stick welding, also known as arc welding, does it the old-fashioned way. Stick welding is a bit more difficult to master than MIG welding, but you can buy stick welding equipment for very little money if you want to try it at home. Stick welding uses a stick electrode welding rod.

They use a consumable and protected electrode or stick. The stick softens and bonds metals by heating with an electric arc between a covered metal electrode and the base metal workpiece. As the stick melts, its protective cover also melts, shielding the welding area from oxygen and other gases that may be in the air.

#4. Flux-Cored Arc Welding (FCAW).

This type of welding is like MIG welding. MIG welders can often double duty as FCAW welders as well. Just like MIG welding, a wire that serves as the electrode and filler metal is passed through your rod. This is where things start to differ. For FCAW, the wire has a flux core that forms a gas shield around the weld. This eliminates the need for an external gas supply.

FCAW is better suited for thicker, heavier metals as it is a high-temperature type of weld. Because of this, it is often used for repairs on heavy equipment. It’s an efficient process that doesn’t generate a lot of waste. Since no external gas is required, it is also cost-effective. There will be some slag left over, however, and it needs a bit of cleaning up to make a nicely finished weld.

#5. Plasma Arc Welding.

Plasma arc welding is a precision technique and is commonly used in aerospace applications where the metal thickness is 0.015 inches. An example of such an application would be an engine blade or air seal. Plasma arc welding is technically very similar to TIG welding, but the electrode is recessed and the ionizing gases in the arc are used to generate heat.

The usual gas combination is argon as the plasma gas, with argon plus 2 to 5% hydrogen as the shielding gas. Helium can be used for a plasma gas, but as it is hotter this reduces the amperage of the nozzle.

Want to know more about Plasma Welding? Check out this article.

#6. Laser Beam Welding.

Laser Beam welding is a type of welding that can be used on metals or thermoplastics. As the name suggests, a laser is used as a heat source to create the welds. It can be used on carbon steels, stainless steels, HSLA steels, titanium, and aluminum. It can be easily automated with robotics and is therefore widely used in manufacturing, for example in the automotive industry.

#7. Electron-Beam Welding.

This is a type of welding in which a high-speed electron beam uses kinetic energy to generate heat and weld two materials together. This is a very demanding form of welding that is carried out mechanically, mostly in a vacuum.

#8. Gas Welding.

Gas welding is only rarely used and has been largely superseded by TIG welding. Gas welders require oxygen and acetylene and are very portable. They are still sometimes used to weld parts of car exhaust back together.

#9. Atomic Hydrogen Welding.

Atomic hydrogen welding is a form of extremely high-heat welding formerly known as Atomic Arc Welding. In this type of welding, two tungsten electrodes are shielded with hydrogen gas.

It can reach temperatures more than that of an acetylene torch and can be conducted with or without filler metal. This is an older form of welding that has been replaced by MIG welding in recent years.

#10. Electroslag.

This is an advanced welding process used to join the thin edge of two metal plates together vertically. Instead of the welding being made on the outside of a joint, it takes place between the edges of the two panels.

A copper electrode wire is passed through a consumable metal guide tube that serves as the filler metal. When current is applied, the arc is created and a weld begins at the bottom of the seam and is slowly moved up, creating the weld instead of the seam as it progresses. This is an automated process and is done by machine.

Types Of Welds

#1. Fillet Welds.

Fillet welding refers to the process of joining two pieces of metal vertically or at an angle. These welds are commonly called tee joints, two pieces of metal perpendicular to each other, or lap joints, two pieces of metal that are overlap and welded on their edges.

The weld is triangular in shape and depending on the skill of the welder, it can be concave, flat or convex. Welders use fillet welds when connecting flanges to pipes and substructure welding sections and when bolts are not strong enough and wear easily.

A fillet weld joins two surfaces perpendicularly and creates a nearly right angle between them. This style of welding can be classified into the following subgroups:

• Full Fillet filling. For full fillet welds, the weld size is equal to the thickness of the thin wall parts being joined.
• Staggered intermittent fillet weld. An obscure alternating fin weld is characterized by the formation of two offset alternating weld lines on either side of the joint.
• Chain alternating fillet welding. Interrupted fillet welds form a chain of two interrupted fillet weld lines approximately opposite each other on either side of the T joint.

The versatility and low cost of fillet welds make them one of the most widely used joints in the welding industry. Typical applications include:

• Connecting flanges to pipes
• Bracing connections
• Shear tabs
• Cover plates
• Column bases
• Seam and stitch welds

#2. Groove Welds.

A groove weld is defined as an opening between two joint members that provides space for the insertion of metal. After fillet welds, groove welds are the most widely used welds. The second most common method of welding is groove welding.

Groove welding is the placement of a nut in the groove between two parts to be joined. The type of weld used determines how the seams, joints or surfaces are prepared.

Groove welding allows parts to be joined on the same plate by placing a weld bead in a groove between the parts. The main types of groove welds are:

• Flare-bevel weld
• Flare-V weld
• Single-bevel groove weld
• Single-J groove weld
• Single-U groove weld
• Single-V groove weld
• Square groove weld

The groove welding process is generally slow and difficult compared to other forms of welding and usually requires special chamfers on one or both sides to join.

However, it produces a strong weld that is easily inspected and provides excellent strain control. Common applications for groove welding include:

• Moment connections
• Column splices
• Hollow structural steel (HSS) connections

#3. Surfacing Weld.

These are welds consisting of one or more strings or weave beads deposited that are joined to an unbroken surface to obtain desired properties or dimensions.

Surfacing is a welding process used to apply a hard, wear-resistant metal layer to the surface or edge of worn parts. One of the most economical ways to increase and maintain the life of construction machinery, tools and equipment.

A surfacing weld is composed of one or more stringer or weave beads. Surface treatments, also called hardfacing or wear, are often used to repair worn shafts, gears, or cutting edges.

The most common types of surfacing welds include:

• Flux-cored arc welding (FCAW) surfacing
• Furnace fusing
• Gas metal arc welding (GMAW) surfacing
• Gas tungsten arc welding (GTAW) surfacing
• Oxy-acetylene surface welding
• Plasma arc surfacing
• Submerged arc welding (SAW) surfacing
• Submerged metal arc welding (SMAW) surfacing

Surface welding is commonly used to add a wear-resistant metal layer to an object to strengthen its surface or restore worn areas. In this case, welding is done using a metal with higher wear resistance than the base material.

This technology is one of the most cost-effective ways to protect and extend the life of equipment and tools used in aggressive and high-wear applications. Surface welding can also be used in combination with butt joints to improve the quality of the final weld.

#4. Plug Weld.

Plug welding, also called rosette welding, is when two metals are joined together by a weld that is placed in a small circular hole. This process usually involves overlapping two metals, with the upper metal having a hole for the weld deposit.

Plug welding is an alternative to spot welding used by car manufacturers with poor access to a spot welder. Commonly used in DIY auto restoration to replace spot welds on panel flanges that were originally spot welded.

Plug welds, when done correctly, are stronger than original spot welds. Rally car manufacturers often use this technique and it is acceptable in UK MOT tests as an alternative to spot welding used to repair older cars.

Other applications include:

• Welding rods inside a pipe
• Joining metals that differ in thickness
• Auto body manufacturing and repair

#5. Slot Weld.

A slot weld joins the surface of one material to another through an elongated hole. The hole can be open at one end and partially or completely filled with welding material.

It is a weld that joins a slotted hole in one member of a lap or tee joint to the surface of another member exposed through the hole. This hole may be open on one side and may be partially or completely filled with welded metal.

A slot weld joins one surface to another through a slotted hole. The difference between plug and slot welds is that the shape of plug welds is determined by diameter while the shape of slot welds is determined by diameter and length.

Depending on the part specification, the hole may be open at one end or the hole may be partially or completely filled with weld material.

Slot welds are useful when the part design requires overlap between two surfaces. The special applications of slot welding are:

• Transmitting shear force in lap joints
• Preventing buckling in overlapped parts

#6. Flash Weld.

Flash welding is a resistance welding method that does not require filler metal. During the flash welding process, an electric current is applied to create resistance between the two surfaces to be joined. When two surfaces come into contact with a small contact, an electric current flow and the material melts.

The molten material is ejected from the joint as a spray of molten particles, creating a unique flushing action. Oxides and other contaminants are removed from the interface and form a thermally softened region at the edge of the two surfaces.

Once the material has melted enough, a force is applied to bond the surfaces together. This facilitates the creation of butt welds without molten material at the joint.

The flash welding process is fast, cost-effective and can fuse dissimilar metals with different melting points. Flash welding is often used:

• Joining sections of mainline rail in railway construction
• Connecting thick workpieces such as chains or pipes
• Merging metal sheets, rods, and bars

#7. Seam Weld.

Seam welding is the process of joining two similar or dissimilar materials in a joint using electric current and pressure. Seam welding is possible due to the contact resistance created between the two metals. When current passes between metals, heat is generated in small gaps.

This process is mainly used for metals because they easily conduct electricity and can withstand relatively high pressures. When current passes between metals, heat is generated in small gaps. Electrodes maintain and control the flow of electricity.

This type of weld can be created in two ways:

• Resistance seam welding. Resistance seam welding is an adaptation of spot welding that uses a motor wheel instead of a fixed rod on the welding electrode. Common applications include sheet metal processing and the manufacture of automotive parts such as fuel tanks, radiators and steel drums.
• Friction seam welding. Friction seam welding uses friction instead of an electrode to generate heat. This allows the surfaces to merge into the solid phase, thus eliminating the occurrence of interdiffusion. Friction seam welding is often preferred for materials that are inherently difficult to weld using conventional arc welding methods.

Benefits of seam welding include:

• Provides sturdy, durable welds
• Relatively easy to perform
• Ideal for manufacturing liquid- and gas-tight vessels

#8. Spot Weld.

Spot welding (also called resistance spot welding) is a resistance welding process. This welding process is primarily used to weld two or more metal sheets by applying pressure and heat from an electric current to the weld area.

This is done by placing a copper alloy electrode on the surface of the sheet, where pressure and current are applied, and heat is generated as the current flows through a resistant material such as low-carbon steel.

Spot welding is relatively easy and inexpensive, making it a popular welding choice in several major industries, including:

• Automotive
• Aerospace
• Construction
• Electronics
• Metal furniture building
• Railway

#9. Upset Weld.

Upset welding (UW)/resistance butt welding is a welding technique that produces coalescence simultaneously over the entire area of abutting surfaces or progressively along a joint, by the heat obtained from resistance to electric current through the area where those surfaces are in contact.

Apply pressure before starting heating and maintain pressure during heating. The equipment used for flux welding is very similar to flash welding equipment. Available only if the parts to be welded have equal cross-sections.

Adjacent surfaces must be carefully prepared to provide adequate heating. The difference in flash welding is that the parts are clamped with a welding machine and force is applied to them for a tight connection.

A high amperage current then passes through the junction and heats the junction surface. When they are heated to the proper forging temperature, a disturbing force is applied and the current is interrupted. Fusion occurs due to the high temperature and pressure of work on joint surfaces. After cooling, the power is released and welding is completed.

The intrusion welding process has several distinct advantages, including:

• High-quality welds with fewer fusion defects
• Compatibility with a wide variety of standard and difficult-to-weld materials
• Welding equipment that is easy to control, operate, and maintain

Advantages Of Welding

• Welded joints are strong and may be stronger than base metal.
• Can weld different materials.
• Welding can be done anywhere and does not require a long distance.
• Offers a sleek look and simplicity of design.
• They can be done in any shape, any direction.
• Can be automatic.
• Provides a perfectly rigid joint.
• Easy addition and modification of existing structures.

Disadvantages Of Welding

• Members may be distorted during welding due to uneven heating and cooling.
• They are permanent joints, so welds must be cut to separate them.
• High initial investment.

Application Of Welding

Welding is commonly used in pressure vessels, bridges, buildings, aircraft and spacecraft, rail vehicle and shipbuilding, automotive, electrical, electronics, and defense industries, pipelines and railways, and nuclear power plants.

• Installation.
• Fabrication of sheet metal.
• Automotive and aerospace industries.
• Connecting ferrous and non-ferrous metals.
• Joining of thin metals.

FAQs.