Welding is the process of joining two or more pieces of materials, especially metals or thermoplastics, with the help of heat and pressure.
Over the past 20 decades, this resourceful technique has been used by enthusiasts and professionals alike to transform pieces of materials into new products.
Before the 19th century, there existed only one type of welding (The Forge Welding) predominantly used by the blacksmiths.
However, with the advent of new technologies in the welding industry, presently there exist nothing less than 30 different types of welding processes including the Arc, Oxy-Acetylene, Oxy-Hydrogen, and Electron Beam Welding among others.
In this article, we shall be highlighting the three basic types of welding processes and then further explain some of the more advanced types of welding techniques.
Basic Types of Welding
Basically, we have just three types of welding, all other forms of welding fall under these three classes.
1. Liquid State Welding
It is also referred to as fusion welding. In this welding technique, metals are heated at the junction point and are then allowed to solidify after heating in order to fuse together. A filler material is also supplied to the metal during the welding process to make it firm and strong. Gas Welding and ARC welding fall under the Liquid State Welding.
2. Solid State Welding
This is otherwise called Cold Welding. This involves no application of heat; rather an external pressure is applied for the diffusion process. Parts are welded at the junction point without any contamination from atmospheric constituents. Explosive welding, friction welding, and ultrasonic welding are classified under the solid-state welding.
3. liquid-solid welding
Popularly known as the Plastic Welding or pressure welding. This welding technique involves combining together small parts or pieces of metals. Before these small components are joined together, they are first heated to a high temperature to achieve to a plastic state. External pressure is then applied to join these small pieces together.
Different Types of Welding Processes
Gas Welding was developed by two French engineers Edmond Fouche and Charles Picard in 1903.
The Gas welding is also known as oxyacetylene or Oxyfuel welding; this welding technique involves the process of combining pure oxygen and fuel gases such as methane to increase welding torch’s flame temperature up to about 3,500 degrees centigrade to cut and fuse metals pieces.
Though Gas welding is one of those oldest welding techniques, it is however still used in most industries for pipe and tube welding, as well as for other forms of repair work. Gas welding involves two major processes
(a) Welding or fusing
Here Tip of the welding torch is used to fuse metals. The welding torch consists of Fuel gas control valve, oxygen control unit and mixer
(b) Slicing or cutting
In this case, a cutting torch is used to crop the metal. Usually, the oxygen blast lever on the torch is pressed, and the metal components are heated up to ignition point. Heat and Iron oxide is formed after the reaction of metal with oxygen. The amount of heat produced determines the cutting process.
The gas welding process is mostly employed for polishing in Glass companies, jewelry designing and also to produce bright light in theatres.
The different types of welding techniques that fall under the Gas welding include:
1. Oxy-Hydrogen Welding
In this technique, Hydrogen and Oxygen is used for cutting and fusing. The flame produced is typically pale blue and has a temperature of about 2000 degrees Celsius. The metal piece is first heated, then the melt bar fused-in to make in the connection. This welding process usually takes about 2 to 5 minutes, depending on the size of the metal sheet. The technique is mostly used by manufacturing industries for melting expensive metals and also for polishing acrylic glass surfaces. One set back of this process is its expensiveness as compared to other alternative processes.
2. Air Acetylene Welding
In this welding process, heat is produced by combining the mixture of air and acetylene. The temperature produced during this process is about 2700 degree Celsius, the weld point is formed without using a filler metal. This process is less expensive and easy to handle. This welding process is employed to weld leads with small cross-sectional Area and also copper sheets of smaller thickness.
The Arc welding process may be manual or automated. In this process, metals are joined end to end using electrode with the help of a power supply to produce a sufficient amount of heat for the welding purpose. The welded material is then allowed to cool and fuse together. Arc welding is the most popular type of welding as it consists of many of the most common types of welding, such as TIG, MIG, and Stick welding.
There are two types of electrodes used in Arc welding
(a) Consumable electrodes. And (b) Non-consumable electrodes.
What are the different types of welding processes under the Arc Welding technique?
Below listed are some of the major welding processes under Arc Welding.
1. Stick welding or Shielded Metal Arc Welding (SMAW )
This is a manual welding technique that uses a consumable electrode coated in flux to lay the weld. It is referred to as Stick welding because it uses welding rods or sticks made of filler material and flux. The temperature generated is about 7000 degrees Fahrenheit. Although stick welding is quite an old technique, it is still popularly used around the world especially in the third world countries. Some fields in the welding industry (e.g. automotive, refrigeration, plumbing and construction) rely major on Stick welding as the best option.
2. Metal Inert Gas (MIG ) Welding
It is otherwise called Gas Metal Arc Welding (GMAW). This process is not 100 percent manual. It can be fully automatic or semi-automatic. The MIG welding was first employed for welding aluminum and other non ferrous metals but it was later used for welding steel because of its quick welding time. A filler material is supplied during the welding process. The MIG welding process is very easy and simple to learn. The shielding gas used in MIG welding is Carbon dioxide (CO2) or a mixture of CO2 and Argon-carbon dioxide. The MIG welding is also used in automobile and fabrication industry.
3. Tungsten Inert Gas (TIG) Welding
The Tungsten Inert Gas is also referred to as Gas Tungsten Arc Welding (GTAW). This type of welding uses a Non-consumable tungsten electrode and inert gas (usually Argon) to weld pieces of metal together. In TIG, heat is produced by running electric current through a tungsten electrode creating an arc used to melt metal wire to create a weld pool. Shielding gases and a filler gas is used for protection. During the welding process, it is very important to keep a short arc length in order to prevent contact between the workpiece and electrode. TIG welding is a very popular technique in most manufacturing industries because it offers a high degree of purity, high-quality weld and can be used for various industrial, commercial and residential applications. TIG welding is commonly used to weld stainless steel, mild steel and copper. TIG can also be used to weld Magnesium, aluminum and Nickel as well.
4. Flux-Cored Arc Welding (FCAW)
This is quite similar to GMAW, except that it uses a special tubular wire filled with flux and also the shielding gas is not always necessary, depending on the type of the filler. We have two different types of FCAW. One uses a shielding gas, whereas the other doesn’t. The one with no shielding gas uses a tabular consumable electrode containing flux-core. It’s very portable and has a high penetrating power into metals. Flux-Cored Arc Welding is widely used across the world; it’s cheap and easy to learn. It’s used in quick automotive machines, for welding stainless steel, nickel alloys, copper and aluminum. However, there are some limitations to its applications.
5. Submerged Arc Welding (SAW)
The Submerged Arc Welding involves welding beneath a blanket of granular fusible flux, which contains silica, lime, manganese oxide, and calcium fluoride. As the heat builds up, the molten conductive flux provides a path between the electrode and the workpiece. SAW is mostly employed on ferrous steel and nickel-based alloys. SAW is safer than most welding processes as it emits a reduced amount of welding fumes and arc lights. SAW achieves deep weld penetration, it requires minimal preparation, hence making it very quick and efficient.
6. Plasma Arc welding (PAW)
Plasma arc welding has the same processes as TIG welding. Their main differences are that: in PAW, the position of the electrode is right on the torch. In addition, plasma arc is also separated from shielding gas protection. In PAW, Argon is generally preferred over helium for shielding purpose.
Plasma processes include: plasma arc cutting, plasma arc spraying and plasma arc spacing.
7. Carbon Arc Welding
This welding technique was developed by Benardos and Stanislaw Olszewski in 1881. It was the first Arc welding invented but is rarely used nowadays as it has been replaced by more advanced welding processes such as TCAW. In CAW, metals are welded together using a non consumable carbon electrode, the heat produced during the welding process ranges from 2500 to 3000 degrees Celsius. Within this temperature range, metals form bonds and hence became welded.
There are two subtypes of CAW.
- Twin Carbon Arc Welding (TCAW)-In TCAW, Arc is placed between two carbon electrode.
- Gas Carbon Arc Welding (CAW-G )-In CAW-G, usually, a filler metal is used to make the bondage in workpieces.
8. Atomic Hydrogen Welding (AHW)
This is rather an older form of Arc welding process that is gradually replaced by GMAW. In AHW, arc is applied between 2 Tungsten electrodes in a hydrogen atmosphere. A filler material may or may not be used in this process. This welding process was invented by Langmuir after his discovery of atomic hydrogen. The heat generated during the welding process is above 3000 degrees C.
9. Electroslag welding (ESW )
The ESW is generally used for welding thick, nonferrous metals and requires a very high level of skill. The welding process involves hitting an electric arc at the weld position along with flux until the slag extinguishes the arc. This welding process is employed to weld steal sections that are very thick. It requires a voltage of about 40-60 V and current of about 600 A. ESW is very popular in the aerospace industry and also for maritime applications.
10. Electrogas Welding (EGW)
The EGW was invented in 1961; this form of Arc welding is closely similar to the Electroslag welding. The only difference between them is that in EGW arc is not quenched (i.e. the metal is stuck with a consumable electrode). It is worth noting that no shielding gas is required during the welding process and also no pressure is supplied. The EGW is majorly employed for the construction of storage tanks and in the shipbuilding industries.
This is the welding process mostly employed in production sites to join metal sheets together. It involves direct application of force to the adjacent surfaces of the metal sheets, then the weld is made by passing electrical current near and upon the surfaces in order to generate intense heat to melt and weld the metals. There are certain factors affecting the welding temperatures, this includes the size of the electrode, amount of current, geometry and the interval of welding time.
The subtypes of welding process under resistance welding are:
1. Seem welding
This is an automated type of welding technique that produces an efficient and durable weld. It is used to connect the surfaces of two similar metals. Two rotating disc-shaped copper electrodes are used during the welding process. This form of welding is commonly used for the construction of beverage cans.
2. Spot Welding
Just like the seem welding process, also in spot welding 2 copper electrodes are used to fuse two or more metal sheets as current is passed through these metal sheets. A high amount of heat is generated when current is passed to the metal sheets through the electrodes. Due to high electrical resistance at the contact point of the metal sheets and the electrodes, the temperature continues to rise, the workpieces achieved a molten state and hence became welded. The process is fully automated, no filler material is required. Most cars manufacturing industries uses Pot welding to prepare metal sheets.
3. Flash welding
Flash welding does not involve the use of any filler material. During the welding process, a specific distance is maintained between the workpiece (metals to be welded). Once the current is applied to the metals, a resistance force is created between the spaces, hence generating the required amount of heat for the welding purpose. The flash welding technique is mostly used by railroad construction industry. It can also be used to fuse copper, steel and aluminum in various conductors.
4. Resistance Butt Welding
In resistance butt welding, metals are joined when an adequate amount of heat and pressure is applied in a localized area to be welded. This technique is used to make Butt joints in wires and rods up to 16mm diameter. Current is passed through dies which cause resistance heating of the welding spot. The process is very fast and clean and it can be used to weld small metal components.
5. Projection welding
This is also one of the subtypes of resistance welding technique. In this case, the weld is fixed to a specified position with the help of projections on the metal pieces to be joined. High amount of heat is generated during this process. However, the workpieces may suffer internal cracks and wears.
This is a collection of welding techniques that welds materials below their melting points. Below is the broad explanation of the various welding processes under solid state welding.
1. Cold welding
This welding method uses high pressure at ambient temperature to weld metal components. Generally, this technique is employed to join two different ductile metals such as copper and aluminum.
2. Diffusion Welding
This form of solid state welding can be used to join two similar or different metal types. Most times, the process needs to be carried out in a vacuum or the presence of inert gas conditions if the metal contains strong oxide layers. Metals like Zirconium and titanium can be melted using this method. This welding technique is best appreciated in electronics and nuclear industries.
3. Forge Welding
Formerly referred to as hammer welding, this process involves the application of sufficient pressure, which results in coalescing the metals. Although the forge welding process is rarely used today, its however still employed in the production of shotgun barrels, swords, and cookware.
4. Explosive welding (EXW)
The EXW was first used during world war II; it’s a process is based on metallurgical bonding. The EXW method is used to manufacture plates and tube sheets. The process is fast, clean and efficient. It can be used to weld two metals that are difficult to weld by other alternatives.
5. Friction Welding (FRW)
In Friction Welding heat is generated due frictional force between the workpieces. Friction surfacing is the procedure involved in Friction Welding method (a case where a substrate is protected with coating substance). FRW is used to join two or more thermoplastics. The process is clean and efficient. It’s mostly preferred to join dissimilar materials like steels and aluminum in aerospace industry.
6. Hot Pressure Welding
This is a form of solid state welding where welds are produced between two or more connecting metals. No filler material is required in this method. Pressure of about 50-60 MPa is supplied during the welding process; at the same time, heat is generated with the help of eddy currents.
7. Ultrasonic Welding (USM)
This is regarded as the most advanced welding method ever. In USM, high-frequency ultrasonic vibrations are applied to workpieces to form welds. It’s mostly used for coalescing plastics or other dissimilar materials. This welding technique is employed in the production of capacitors, transformers, and in microcircuits.
8. Roll Welding
In this process, 2 or more metals are pass between 2 rollers. The high amount of pressure applied on the rollers reduced the metal thickness and hence coalescing the metals. This technique is said to be the best option for cladding metal sheets. In order to improve the strength and quality of the weld, the process needs to be carried out in quite warm conditions.
Radiant Energy Welding (REW)
In REW, radiant energy produced while welding two metal pieces together is used. The two subtypes of welding processes under the REW technique are:
1. Electron Beam Welding (EBW )
This is also an advanced type of welding technique which uses high-velocity electrons to weld workpieces. It involves firing a beam of highly energetic electrons towards the material to be welded. The kinetic energy of these energetic electrons is then converted into heat energy. As a result of that, the workpieces melt, coalesce and fuse together.
EBW is commonly used in aircraft engine manufacturing industries and automotive part production companies. This welding technique can be used to join dissimilar metals that have different melting points and thermal conductivities.
2. Laser Beam Welding (LBW)
This is the process of joining metal components using a laser beam. Welding is achieved as a result of the light beam falling on the metal to be welded. The monochromatic light in the laser beam is highly energetic due to its coherency and single frequency. This welding technique is highly efficient for welding small metal components.
Though welding processes have experienced tremendous development over the past years, it is very necessary we understand the differences between all the existing types of welding techniques. This will help us to make the right decision in terms of picking the best technique for a job as well as hire the right professionals whenever we need to.